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Chapter 28 The Reproductive Systems Lecture Outline Principles of Human Anatomy and Physiology, 11e 1 INTRODUCTION • Sexual reproduction is a process in which organisms produce offspring by means of germ cells called gametes. • The organs of reproduction are grouped as gonads (produce gametes and secrete hormones), ducts (transport, receive, and store gametes), and accessory sex glands (produce materials that support gametes). • Gynecology is the specialized branch of medicine concerned with the diagnosis and treatment of diseases of the female reproductive system. Urology is the study of the urinary system but also includes diagnosis and treatment of diseases and disorders of the male reproductive system. Principles of Human Anatomy and Physiology, 11e 2 Chapter 28 The Reproductive Systems • Sexual reproduction produces new individuals – germ cells called gametes (sperm & 2nd oocyte) – fertilization produces one cell with one set of chromosomes from each parent • Gonads produce gametes & secrete sex hormones • Reproductive systems – gonads, ducts, glands & supporting structures – Gynecology is study of female reproductive system – Urology is study of urinary system & male reproductive system Principles of Human Anatomy and Physiology, 11e 3 MALE REPRODUCTIVE SYSTEM • The male structures of reproduction include the testes, a system of ducts (ductus epididymis, ductus deferens, ejaculatory duct, urethra), accessory sex glands (seminal vesicles, prostate gland, bulbourethral glands), and several supporting structures, including the penis (Figure 28.1). Principles of Human Anatomy and Physiology, 11e 4 Male Reproductive System • Gonads, ducts, sex glands & supporting structures • Semen contains sperm plus glandular secretions Principles of Human Anatomy and Physiology, 11e 5 Scrotum • The scrotum is a cutaneous outpouching of the abdomen that supports the testes; internally, a vertical septum divides it into two sacs, each containing a single testis (Figures 28.2). • Skin contains dartos muscle causes wrinkling • Temperature regulation of testes – sperm survival requires 3 degrees lower temperature than core body temperature – cremaster muscle in spermatic cord • elevates testes on exposure to cold & during arousal • warmth reverses the process Principles of Human Anatomy and Physiology, 11e 6 Scrotal Sacs, Dartos & Cremaster Mm Principles of Human Anatomy and Physiology, 11e 7 Testes • The testes, or testicles, are paired oval-shaped glands (gonads) in the scrotum (Figure 28.3). • The testes contain seminiferous tubules (in which sperm cells are made) (figure 28.5). • Embedded among the spermatogenic cells in the tubules are large Sertoli cells or sustentacular cells (Figure 28.4). – The tight junctions of these cells form the blood-testis barrier that prevents an immune response against the surface antigens on the spermatogenic cells. Principles of Human Anatomy and Physiology, 11e 8 Testes • Paired oval glands measuring 2 in. by 1in. • Surrounded by dense white capsule called tunica albuginea – septa form 200 - 300 compartments called lobules • Each is filled with 2 or 3 seminiferous tubules where sperm are formed Principles of Human Anatomy and Physiology, 11e 9 Tunica Vaginalis Tunica vaginalis • Piece of peritoneum that descended with testes into scrotal sac. • Facilitates movement of testes within scrotum Principles of Human Anatomy and Physiology, 11e 10 Descent of Testes • Develop near kidney on posterior abdominal wall • Descends into scrotum by passing through inguinal canal – during 7th month of fetal development • Failure of the testes to descend is called cryptorchidism; it may involve one or both testes. Principles of Human Anatomy and Physiology, 11e 11 Cryptorchidism • Testes do not descend into the scrotum • 3% of full-term & 30% of premature infants • Untreated bilateral cryptorchidism results in sterility & a greater risk of testicular cancer • Descend spontaneously 80% of time during the first year of life – surgical treatment necessary before 18 months Principles of Human Anatomy and Physiology, 11e 12 Testes - cells • The sustentacular cells – nourish spermatocytes, spermatids, and spermatozoa – mediate the effects of testosterone and follicle stimulating hormone on spermatogenesis – phagocytose excess spermatids cytoplasm as development proceeds – control movements of spermatogenic cells and the release of spermatozoa into the lumen of the seminiferous tubule – secrete fluid for sperm transport and the hormone inhibin. • The Leydig cells or interstitial endocrinocytes found in the spaces between adjacent seminiferous tubules secrete testosterone (Figure 28.4). Principles of Human Anatomy and Physiology, 11e 13 Spermatogenesis - Introduction • Spermatogenesis is the process by which the seminiferous tubules of the testes produce haploid sperm. (Review the discussion of reproductive cell division in Chapter 3. Take special note of Figures 3.33 and 3.34) • It begins in the diploid spermatogia (stem cells). They undergo mitosis to reserve future stem cells and to develop cells (2n primary spermatocytes) for sperm production. Principles of Human Anatomy and Physiology, 11e 14 Formation of Sperm Spermatogenesis is formation of sperm cells from spermatogonia. Principles of Human Anatomy and Physiology, 11e 15 Spermatogenesis - Introduction • The diploid primary spermatocytes undergo meiosis I forming haploid secondary spermatocytes. • Meiosis II haploid spermatids. – The spermatids are connected by cytoplasmic bridges. • The final stage of spermatogenesis is spermiogenesis which is the maturation of the spermatids into sperm. • The release of a sperm from its connection to a Sertoli cell is known as spermiation. Principles of Human Anatomy and Physiology, 11e 16 Review • Review of Meiosis Principles of Human Anatomy and Physiology, 11e 17 Chromosomes in Somatic Cells & Gametes • Somatic cells (diploid cells) – 23 pairs of chromosomes for a total of 46 • each pair is homologous since contain similar genes in same order • one member of each pair is from each parent – 22 autosomes & 1 pair of sex chromosomes • sex chromosomes are either X or Y • females have two X chromosomes • males have an X and a smaller Y chromosome • Gametes (haploid cells) – single set of chromosomes for a total of 23 – produced by special type of division: meiosis Principles of Human Anatomy and Physiology, 11e 18 Meiosis I -- Prophase I tetrad • Chromosomes become visible, mitotic spindle appears, nuclear membrane & nucleoli disappear • Events not seen in prophase of Metaphase or Meiosis II – synapsis • all copies of homologous chromosomes pair off forming a tetrad – crossing-over • portions of chromatids are exchanged between any members of the tetrad • parts of maternal chromosomes may be exchanged with paternal ones – genetic recombination produces gametes unlike either parent Principles of Human Anatomy and Physiology, 11e 19 Exchange of Genetic Material • Chromosomes are exchanged between chromatids on homologous chromosomes Principles of Human Anatomy and Physiology, 11e 20 Meiosis I -- Metaphase I, Anaphase I & Telophase I • In metaphase I, homologous pairs of chromosomes line up along metaphase plate with attached microtubules • In anaphase I, each set of homologous chromatids held together by a centromere are pulled to opposite ends of the dividing cell • Telophase I and cytokinesis are similar to mitotic division • Result is 2 cells with haploid number of chromosomes Principles of Human Anatomy and Physiology, 11e 21 Meiosis II • Consists of 4 phases : prophase II, metaphase II, anaphase II and telophase II • Similar steps in this cellular process as in mitosis – centromeres split – sister chromatids separate and move toward opposite poles of the cell • Each of the daughter cells produced by meiosis I divides during meiosis II and the net result is 4 genetically unique haploid cells or gametes. Principles of Human Anatomy and Physiology, 11e 22 Spermatagonium Principles of Human Anatomy and Physiology, 11e 23 Location of Stages of Sperm Formation • Seminiferous tubules contain – all stages of sperm development: spermatogonia, primary spermatocyte, secondary spermatocyte, spermatid, spermatozoa – supporting cells called sertoli cells • Leydig cells in between tubules secrete testosterone Principles of Human Anatomy and Physiology, 11e 24 Supporting Cells of Sperm Formation (N) • Sertoli cells -- extend from basement membrane to lumen – form blood-testis barrier – support developing sperm cells – produce fluid & control release of sperm into lumen – secrete inhibin which slows sperm production by inhibiting FSH Principles of Human Anatomy and Physiology, 11e 25 Spermatogenesis • Spermatogonium (stem cells) give rise to 2 daughter cells by mitosis • One daughter cell kept in reserve -- other becomes primary spermatocyte • Primary spermatocyte goes through meiosis I – DNA replication – tetrad formation – crossing over Principles of Human Anatomy and Physiology, 11e 26 Spermatogenesis • Secondary spermatocytes are formed – 23 chromosomes of which each is 2 chromatids joined by centromere – goes through meiosis II • 4 spermatids are formed – each is haploid & unique – all 4 remain in contact with cytoplasmic bridge – accounts for synchronized release of sperm that are 50% X chromosome & 50% Y chromosome Principles of Human Anatomy and Physiology, 11e 27 Spermiogenesis & Spermiation • Spermiogenesis = maturation of spermatids into sperm cells • Spermiation = release of a sperm cell from a sertoli (sustentacular) cell Principles of Human Anatomy and Physiology, 11e 28 Sperm Morphology (Figure 28.8) • Adapted for reaching & penetrating a secondary oocyte • Head contains DNA & acrosome (hyaluronidase and proteinase enzymes) • Midpiece contains mitochondria to form ATP • Tail is flagellum used for locomotion • They are produced at the rate of about 300 million per day and, once ejaculated, have a life expectancy of 48 hours within the female reproductive tract. Principles of Human Anatomy and Physiology, 11e 29 Hormonal Control of the Testes • GnRH (gonadotropin releasing hormone) stimulates anterior pituitary secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). – LH assists spermatogenesis and stimulates production of testosterone. – FSH initiates spermatogenesis • Figure 28.7 summarizes the hormonal relationships of the hypothalamus, pituitary gland, and testes. Principles of Human Anatomy and Physiology, 11e 30 Hormonal Control of Spermatogenesis • Puberty – hypothalamus increases its stimulation of anterior pituitary with releasing hormones (GnRH) – anterior pituitary increases secretion LH & FSH • LH stimulates Leydig cells to secrete testosterone – an enzyme in prostate & seminal vesicles converts testosterone into dihydrotestosterone (DHT is more potent.) • FSH stimulates spermatogenesis – with testosterone, stimulates sertoli cells to secrete androgen-binding protein (keeps hormones levels high) – testosterone stimulates final steps spermatogenesis Principles of Human Anatomy and Physiology, 11e 31 Hormonal Control of Spermatogenesis • Testosterone – controls the growth, development, functioning, and maintenance of sex organs – stimulates bone growth, protein anabolism, and sperm maturation – stimulates development of male secondary sex characteristics. – Negative feedback systems regulate testosterone production (Figure 28.8). • Inhibin is produced by sustentacular (Sertoli) cells. Inhibition of FSH by inhibin helps to regulate the rate of spermatogenesis. Principles of Human Anatomy and Physiology, 11e 32 Hormonal Effects of Testosterone • Testosterone & DHT bind to receptors in cell nucleus & change genetic activity • Prenatal effects male genitalia • At puberty, final development of 2nd sexual characteristics and adult reproductive system – sexual behavior & libido – male metabolism (bone & muscle mass heavier) – deepening of the voice Principles of Human Anatomy and Physiology, 11e 33 Control of Testosterone Production • Negative feedback system controls blood levels of testosterone • Receptors in hypothalamus detect increase in blood level • Secretion of GnRH slowed • Anterior pituitary (FSH & LH hormones) slowed • Leydig cells of testes slowed • Blood level returns normal Principles of Human Anatomy and Physiology, 11e 34 Effect of Inhibin Hormone • Sperm production is sufficient – sertoli cells release inhibin – inhibits FSH secretion by the anterior pituitary – decreases sperm production • Sperm production is proceeding too slowly – less inhibin is released by the sertoli cells – more FSH will be secreted – sperm production will be increased Principles of Human Anatomy and Physiology, 11e 35 Reproductive System Ducts in Testes • The duct system of the testes includes the seminiferous tubules, straight tubules, rete testis, efferent ducts, and ductus epididymis. Principles of Human Anatomy and Physiology, 11e 36 Pathway of Sperm Flow through the Ducts of the Testis • • • • • • Principles of Human Anatomy and Physiology, 11e Seminiferous tubules Straight tubules Rete testis Efferent ducts Ductus epididymis Ductus (vas) deferens 37 Epididymis • The epididymis is a comma-shaped organ that lies along the posterior border of the testis (Figures 28.3a). • Sperm are transported out of the testes through the efferent ducts in the epididymis which empty into a single tube called the ductus epididymis. • The ductus epididymis is lined by stereocilia and is the site of sperm maturation and storage; sperm may remain in storage here for at least a month, after which they are either expelled or degenerated and reabsorbed. Principles of Human Anatomy and Physiology, 11e 38 Epididymis • 1.5in long along posterior border of each testis – Head, body and tail region – Multiple efferent ducts become a single ductus epididymis in the head region • 20 foot tube if uncoiled – Tail region continues as ductus deferens Principles of Human Anatomy and Physiology, 11e 39 Histology of the Epididymis • Ductus epididymis – lined with pseudostratified ciliated columnar epithelium – layer of smooth muscle • Site of sperm maturation – motility increases over 2 week period • Storage for 1-2 months • Propels sperm onward Principles of Human Anatomy and Physiology, 11e 40 Anatomy • The ductus (vas) deferens, or seminal duct, stores sperm and propels them toward the urethra during ejaculation (Figures 28.3a). • The spermatic cord is a supporting structure of the male reproductive system, consisting – ductus deferens – testicular artery – autonomic nerves – veins and lymphatic vessels – cremaster muscle (Figure 28.2). Principles of Human Anatomy and Physiology, 11e 41 Spermatic Cord • All structures passing to and from the testes – testicular artery – pampiniform plexus of veins – autonomic nerves – lymphatic vessels – ductus (vas) deferens – cremaster muscle Principles of Human Anatomy and Physiology, 11e 42 Anatomy • The ejaculatory ducts are formed by the union of the ducts from the seminal vesicles and ducti deferens; their function is to eject spermatozoa into the prostatic urethra (Figure 28.9). • The male urethra is the shared terminal duct of the reproductive and urinary systems which serves as a passageway for semen and urine. The male urethra is subdivided into three portions: prostatic, membranous, and spongy (cavernous) (Figures 28.1 and 26.22). Principles of Human Anatomy and Physiology, 11e 43 Ejaculatory Ducts Posterior View • Formed from duct of seminal vesicle & ampulla of vas deferens • About 1 inch long • Adds fluid to prostatic urethra just before ejaculation Principles of Human Anatomy and Physiology, 11e 44 Ductus (Vas) Deferens • Pathway of 18 inch muscular tube – ascends along posterior border of epididymis – passes up through spermatic cord and inguinal ligament – reaches posterior surface of urinary bladder – empties into prostatic urethra with seminal vesicle • Lined with pseudostratified columnar epithelium & covered with heavy coating of muscle – convey sperm along through peristaltic contractions – stored sperm remain viable for several months Principles of Human Anatomy and Physiology, 11e 45 • 8 inch long passageway for urine & semen Urethra – Prostatic urethra (1 inch long) – Membranous urethra (passes through UG diaphragm ) – Penile (spongy) urethra (through corpus spongiosum) Principles of Human Anatomy and Physiology, 11e 46 Vasectomy • • • • • • Male sterilization Vas deferens cut & tied off Sperm production continues Sperm degenerate 100% effective 40% reversible Principles of Human Anatomy and Physiology, 11e 47 Inguinal Canal & Inguinal Hernias The inguinal canal is 2 inch long tunnel through (i.e., weak spot in) the 3 muscles of the anterior abdominal wall • originates at deep inguinal ring and ends at superficial ring • Hernia: a rupture or separation of a portion of the abdominal wall resulting in the protrusion of a part of an organ (most commonly the small or large intestine). – Indirect hernia -- loop of intestine protruding through deep ring – Direct hernia -- loop of intestine pushes through posterior wall of inguinal canal Principles of Human Anatomy and Physiology, 11e 48 Accessory Sex Glands • The seminal vesicles secrete an alkaline, viscous fluid that contains fructose, prostaglandins, and clotting proteins (Figure 28.9). • The alkaline nature of the fluid helps to neutralize acid in the male urethra and female reproductive tract. • The fructose is for ATP production by sperm. • Prostaglandins contribute to sperm motility and viability. • Semenogelin is the main protein that causes coagulation of semen after ejaculation. Principles of Human Anatomy and Physiology, 11e 49 Accessory Sex Glands Principles of Human Anatomy and Physiology, 11e 50 Seminal Vesicles • Pair of pouchlike organs found posterior to the base of bladder • Alkaline, viscous fluid – neutralizes vaginal acid & male urethra – fructose – prostaglandins – coagulation proteins Posterior View Principles of Human Anatomy and Physiology, 11e 51 The prostate gland (Figure 28.9) • Is a donut shaped gland about the size of a golf ball which is inferior to the urinary bladder and surrounds the prostatic urethra. • It secretes a milky, slightly acidic fluid that contains: – citric acid, which can be used by sperm for ATP production – acid phosphatase – several proteolytic enzymes, including: • prostate-specific antigen (PSA), pepsinogen, lysozyme, amylase, and hyaluronidase which liquefy coagulated semen. • Prostatitis is a common group of disorders which may be characterized by symptoms such as difficult urination, urinary frequency, and pain; or which may be asymptomatic. Principles of Human Anatomy and Physiology, 11e 52 Prostate Gland • Single organ – size of chestnut – inferior to bladder – pH 6.5 fluid – citric acid – enzymes for seminal liquefaction • Many duct openings • Enlarges with age Posterior View Principles of Human Anatomy and Physiology, 11e 53 Bulbourethral or Cowper’s Glands • The bulbourethral (Cowper’s) glands – mucus for lubrication and an alkaline substance that neutralizes acid (Figure 28.9). Principles of Human Anatomy and Physiology, 11e 54 Bulbourethral or Cowper’s Glands • Paired, pea-sized gland within the urogenital diaphragm • alkaline mucous • connects to spongy urethra Posterior View Principles of Human Anatomy and Physiology, 11e 55 Secretions - Summary Semen (seminal fluid) is a mixture • spermatozoa and accessory sex gland secretions that provides the fluid in which spermatozoa are transported, provides nutrients, and neutralizes the acidity of the male urethra and female vagina • antibiotic, seminal plasmin, and prostatic enzymes that coagulate and then liquefy semen to aid in its movement through the uterine cervix. Once ejaculated, liquid semen coagulates within 5 minutes due to the presence of clotting proteins from the seminal vesicles. After about 10-20 minutes, semen re-liquifies because PSA and other proteolytic enzymes produced by the prostate gland break down the clot. Principles of Human Anatomy and Physiology, 11e 56 Semen Statistics • Mixture of sperm & seminal fluid – slightly alkaline, milky appearance, sticky • Typical ejaculate is 2.5 to 5 ml in volume • Normal sperm count is 50 to 150 million/ml • Coagulates within 5 minutes • Reliquifies in 15 minutes • Semen fertility analysis----bad news if sperm show lack of forward motility, low count or abnormal shapes. Principles of Human Anatomy and Physiology, 11e 57 Penis • The penis contains the urethra and is a passageway for the ejaculation of semen • Body composed of three erectile tissue masses – filled with blood sinuses – lined by endothelial cells – surrounded by smooth muscle and elastic connective tissue. – paired corpora cavernosa penis – unpaired corpus spongiosum penis • Four anatomical parts – root = bulb + crura – body – glans penis Principles of Human Anatomy and Physiology, 11e 58 Anatomy of the Penis (Figure 28.10) • Passageway for semen & urine • Body composed of three erectile tissue masses filled with blood sinuses • Composed of bulb, crura, body & glans penis Principles of Human Anatomy and Physiology, 11e 59 Cross-Section of Penis • Corpora cavernosa – upper paired, erectile tissue masses – begins as crura of the penis attached to the ischial & pubic rami and covered by ischiocavernosus muscle • Corpus spongiosum – lower erectile tissue mass – surrounds urethra – begins as bulb of penis covered by bulbospongiosus muscle – ends as glans penis • All surrounded by the tunica albuginea Principles of Human Anatomy and Physiology, 11e 60 Glans Penis • Enlarged distal end of corpus spongiosum • The distal end of the unpaired corpus spongiosum is the glans penis. • External urethral orifice is spiral small slit • The prepuce, or foreskin, covers the uncircumcised glans penis. Principles of Human Anatomy and Physiology, 11e 61 Circumcision • Removal of prepuce • 3 - 4 days after birth • Possibly lowers UTIs, cancer & sexually transmitted disease Principles of Human Anatomy and Physiology, 11e 62 Root of Penis & Muscles of Ejaculation • Bulb of penis or base of corpus spongiosum enclosed by bulbospongiosus muscle • Crura of penis or ends of corpora cavernosa enclosed by ischiocavernosus muscle Principles of Human Anatomy and Physiology, 11e 63 Erection & Ejaculation • Erection – parasympathetic reflex causes erection – sexual stimulation dilation of arteries supplying the penis • nitric oxide mediates local vasodilation – veins become compress, and blood is trapped • Ejaculation – sympathetic reflex – muscle contractions close sphincter at base of bladder – peristaltic contractions in the ductus deferens, seminal vesicles, ejaculatory ducts and prostate propel semen into the penile portion of the spongy urethra – ischiocavernous & bulbospongiosus promote emission Principles of Human Anatomy and Physiology, 11e 64 FEMALE REPRODUCTION SYSTEM • The female organs of reproduction include the ovaries (gonads), uterine (Fallopian) tubes, uterus, vagina, vulva, and mammary glands (Figure 28.11). Principles of Human Anatomy and Physiology, 11e 65 Female Reproductive System • • • • • Ovaries produce 2nd oocytes & hormones Uterine tubes transport fertilized ova Uterus where fetal development occurs Vagina & external genitalia constitute the vulva Mammary glands produce milk Principles of Human Anatomy and Physiology, 11e 66 Female Reproductive System • • • • • Ovaries produce 2nd oocytes & hormones Uterine tubes transport fertilized ova Uterus where fetal development occurs Vagina & external genitalia constitute the vulva Mammary glands produce milk Principles of Human Anatomy and Physiology, 11e 67 Ovaries • The ovaries are paired glands – Ovaries and testes are developmentally homologous. • The ovaries are located in the upper pelvic cavity, on either side of the uterus. They are maintained in position by a series of ligaments (Figure 28.11b and 28.12). • The histology of the ovary is illustrated in Figure 28.13. Principles of Human Anatomy and Physiology, 11e 68 Reproductive Ligaments • • • • • Broad ligament suspends uterus from side wall of pelvis Mesovarium attaches ovaries to broad ligament Ovarian ligament anchors ovary to uterus Suspensory ligament covers blood vessels to ovaries Round ligament attaches ovaries to inguinal canal Principles of Human Anatomy and Physiology, 11e 69 Ovaries: Overview • The germinal epithelium covers the surface of the ovary but does not give rise to ova. It is followed by the tunica albuginea, ovarian cortex (contains ovarian follicles), and ovarian medulla (containing blood vessels, lymphatics, and nerves). • Ovarian follicles lie in the cortex and consist of oocytes in various stages of development. – A mature (Graafian) follicle expels a secondary oocyte by a process called ovulation. • A corpus luteum contains the remnants of an ovulated follicle and produces progesterone, estrogens, relaxin, and inhibin until it degenerates into a corpus albicans. Principles of Human Anatomy and Physiology, 11e 70 The Ovary: Anatomy • Pair of organs, size of unshelled almonds found in upper pelvic region • Regional histology – tunica albuginea is capsule of dense connective tissue – cortex is region just deep to tunica, containing follicles – medulla is deeper region composed of connective tissue, blood vessels & lymphatics – germinal epithelium is simple epithelial covering over the ovary Principles of Human Anatomy and Physiology, 11e 71 Oogenesis and Follicular Development • Oogenesis occurs in the ovaries. It results in the formation of a single haploid secondary oocyte. • The oogenesis sequence includes reduction division (meiosis I), equatorial division (meiosis II), and maturation (Figure 28.15). • While oogenesis is occurring, the follicle cells surrounding the oocyte are also undergoing developmental changes (Figures 28.13 and 28.14). The sequence of follicular cell changes is: primordial, primary, secondary, and mature (Graffian) follicles, and corpus luteum and corpus albicans. • Table 28.1 summarizes the events of oogenesis and follicular development. Principles of Human Anatomy and Physiology, 11e 72 Follicular Stages • • • • • primordial primary secondary graafian ovulation • Corpus luteum is an ovulation wound – fills in with hormone-secreting cells • Corpus albicans is a white scar left after corpus luteum degenerates (when it is not needed.) • An ovarian cyst is a fluid filled sac in or on an ovary. Most require no treatment, but the larger ones may require surgery. Principles of Human Anatomy and Physiology, 11e 73 Histology of a Graafian Follicle • Zona pellucida – clear area between oocyte & granulosa cells • Corona radiata – granulosa cells attached to zona pellucida--still attached to oocyte at ovulation • Antrum – formed by granulosa cells secreting fluid • By this time, the oocyte has reached the metaphase of meiosis II stage and stopped developing -- the first polar body has been discarded Principles of Human Anatomy and Physiology, 11e 74 Early Life History of Oogonia • Germ cells from yolk sac migrate to ovary & become oogonia – In the female fetus, oogonia divide to produce millions by mitosis but most degenerate (atresia) – Some develop into primary oocytes & stop in prophase stage of meiosis I • 200,000 to 2 million are present at birth • 40,000 remain at puberty, but only 400 mature during a woman’s life • Each month, hormones cause meiosis I to resume in several follicles so that meiosis II is reached by ovulation • Penetration by the sperm causes the final stages of meiosis to occur. Principles of Human Anatomy and Physiology, 11e 75 Review of Oogenesis Principles of Human Anatomy and Physiology, 11e 76 Follicular Development Principles of Human Anatomy and Physiology, 11e 77 Uterine or Fallopian Tubes • Narrow, 4-inch tube extends from ovary to uterus – infundibulum is open, funnel-shaped portion near the ovary • fimbriae are moving finger-like processes – ampulla is central region of tube – isthmus is narrowest portion joins uterus Principles of Human Anatomy and Physiology, 11e 78 Uterine Tube • Histology: three layers – the internal mucosa, the middle muscularis, and the outer serosa (Figure 28.17 a-c). – Ciliated cells and peristaltic contractions help move a secondary oocyte toward the uterus. Principles of Human Anatomy and Physiology, 11e 79 Histology & Function of Uterine Tube • The uterine (Fallopian) tubes transport ova from the ovaries to the uterus and are the normal sites of fertilization (Figure 28.16). Histology = 3 Layers • mucosa = ciliated columnar epithelium with secretory cells provide nutrients • muscularis = circular & longitudinal smooth muscle – peristalsis helps move ovum down to the uterus • serosa = outer serous membrane Function -- events occurring in the uterine tube – fimbriae sweep oocyte into tube – cilia & peristalsis move it along – sperm reaches oocyte in ampulla, fertilization occurs within 24 hours after ovulation – zygote reaches uterus about 7 days after ovulation Principles of Human Anatomy and Physiology, 11e 80 Lining of the Uterine Tubes Principles of Human Anatomy and Physiology, 11e 81 Uterus • The uterus (womb) is an organ the size and shape of an inverted pear that functions in the transport of spermatozoa, menstruation, implantation of a fertilized ovum, development of a fetus during pregnancy, and labor (Figure 28.18). • Anatomical subdivisions – fundus – body – isthmus – cervix Principles of Human Anatomy and Physiology, 11e 82 3 inches long by 2 in. wide and 1 in. thick • subdivided – fundus – body – isthmus – cervix • interior contains uterine cavity accessed by cervical canal (internal & external os) Principles of Human Anatomy and Physiology, 11e Anatomy of the Uterus 83 Uterus – Clinical Application • The uterus normally projects anterior and superior to the urinary bladder in a position called anteflexion (Figure 28.11). • The uterus is normally held in position by a series of ligaments (Figure 28.12). • Uterine prolapse is a downward displacement of the uterus. It has many causes and may be characterized as first degree (mild), second degree (marked), or third degree (complete). Treatment depends on the degree of prolapse. Principles of Human Anatomy and Physiology, 11e 84 Position of Uterus • Anteflexion -- normally projects anteriorly and superiorly over the urinary bladder • Retroflexion -- posterior tilting of the uterus Principles of Human Anatomy and Physiology, 11e 85 Histology • Histology (Figure 28.18) – outer perimetrium – middle myometrium • The myometrium consists of three muscle layers. – inner endometrium, divided into • stratum functionalis (shed during menstruation) • stratum basalis (gives rise to a new stratum functionalis after each menstruation) Principles of Human Anatomy and Physiology, 11e 86 • Endometrium – simple columnar epithelium – stroma of connective tissue and endometrial glands • stratum functionalis – shed during menstruation • stratum basalis – replaces stratum functionalis each month • Myometrium – 3 layers of smooth muscle • Perimetrium – visceral peritoneum Principles of Human Anatomy and Physiology, 11e Histology of the Uterus 87 Blood Supply • Blood is supplied to the uterus by the uterine arteries and their numerous branches and is drained by the uterine veins (Figure 28.19). Principles of Human Anatomy and Physiology, 11e 88 Blood Supply to the Uterus • Uterine arteries branch as arcuate arteries and radial arteries that supply the myometrium • Straight & spiral branches penetrate to the endometrium – spiral arteries supply the stratum functionalis – their constriction due to hormonal changes starts menstrual cycle Principles of Human Anatomy and Physiology, 11e 89 Hysterectomy • Surgical removal of the uterus • Indications for surgery – endometriosis, ovarian cysts, excessive bleeding, cancer of cervix, uterus or ovaries • Complete hysterectomy removes cervix • Radical hysterectomy removes uterus, tubes, ovaries, part of vagina, pelvic lymph nodes and supporting ligaments • Hysterectomy is the most common gynecological operation Principles of Human Anatomy and Physiology, 11e 90 Secretions and Functions • Secretory cells of the mucosa of the cervix produce a cervical mucus (a mixture of water, glycoprotein, serum-type proteins, lipids, enzymes, and inorganic salts) – when thin, is more receptive to sperm – when thick, forms a cervical plug that physically impedes sperm penetration – mucus supplements the energy needs of the sperm. • Both the cervix and the mucus serve as a sperm reservoir, protect sperm from the hostile environment of the vagina, and protect sperm from phagocytes. • The cervix and the mucus also play a role in capacitation. Principles of Human Anatomy and Physiology, 11e 91 Vagina (Figures 28.11, 28.16) • The vagina functions as a passageway for spermatozoa and the menstrual flow, the receptacle of the penis during sexual intercourse, and the lower portion of the birth canal • 4 inch long fibromuscular organ ending at cervix – mucosal layer • stratified squamous epithelium & areolar connective tissue • large stores of glycogen breakdown to produce acidic pH – muscularis layer is smooth muscle allows considerable stretch – adventitia is loose connective tissue that binds it to other organs • lies between urinary bladder and rectum Principles of Human Anatomy and Physiology, 11e 92 Vagina - Anatomy • The vaginal orifice is often partially covered by a thin fold of vascularized mucous membrane called the hymen. If the orifice is completely covered, this imperforate hymen must be surgically opened to permit menstrual flow (Figure 28.20). • A small amount of vaginal discharge is normal and varies during the menstrual cycle. • Abnormal discharge is heavier and thicker than usual, abnormal in color and odor, and accompanied by stinging, itching, or burning. It may be caused by infection or chemical irritation. • Abnormal bleeding is any bleeding other than normal menstrual discharge. It has numerous causes. Principles of Human Anatomy and Physiology, 11e 93 Vagina - Histology • The mucosa of the vagina is continuous with that of the uterus and lies in a series of transverse folds called rugae. • Mucosa dendritic cells are APCs (antigen-presenting cells) that participate in the transmission of viruses, such as HIV, to a female during intercourse with an infected male. • The mucosa contains large stores of glycogen which decompose into organic acids which set up a hostile acid environment for sperm. • Alkaline components of semen neutralize the acidity and increase sperm viability. Principles of Human Anatomy and Physiology, 11e 94 Vulva • The term vulva, or pudendum, refers to the external genitalia of the female (Figure 28.20). • It consists of the mons pubs, labia majora, labia minora, clitoris, vestibule, vaginal and urethral orifices, hymen, bulb of the vestibule, and the paraurethral (Skene’s), greater vestibular (Bartholin’s), and lesser vestibular glands (Figure 28.21). • Table 28.2 summarizes the homologous structures of the male and female reproductive systems. Principles of Human Anatomy and Physiology, 11e 95 Vulva (pudendum) • Mons pubis -- fatty pad over the pubic symphysis • Labia majora & minora -- folds of skin encircling vestibule where find urethral and vaginal openings • Clitoris -- small mass of erectile tissue • Bulb of vestibule -- masses of erectile tissue just deep to the labia on either side of the vaginal orifice Principles of Human Anatomy and Physiology, 11e 96 Perineum • The perineum is the diamond-shaped area between the thighs and buttocks of both males and females that contains the external genitals and anus (Figure 28.21). • During childbirth the emerging fetus may cause excessive stretching and tearing of the perineum. A physician may make a surgical incision (episiotomy) in this region to prevent excessive, jagged tears. Principles of Human Anatomy and Physiology, 11e 97 Perineum • Diamond-shaped area between the thighs in both sexes – bounded by pubic symphysis and coccyx – urogenital triangle contains external genitals – anal triangle contains anus Principles of Human Anatomy and Physiology, 11e 98 Mammary Glands • The mammary glands are modified sudoriferous (sweat) glands that lie over the pectoralis major and serratus anterior muscles (Figure 28.22). – Milk-secreting cells, referred to as alveoli, are clustered in small compartments (lobules) within the breasts. • The essential functions of the mammary glands are synthesis of milk, secretion and ejection of milk, which constitute lactation. Principles of Human Anatomy and Physiology, 11e 99 Mammary Glands • Modified sweat glands that produce milk (lactation) – amount of adipose determines size of breast – milk-secreting glands open by lactiferous ducts at the nipple – areola is pigmented area around nipple – suspensory ligaments suspend breast from deep fascia of pectoral muscles (aging & Cooper’s droop) Principles of Human Anatomy and Physiology, 11e 100 Fibrocystic Disease of the Breasts • Fibrocystic disease is the most common cause of a breast lump • one or more cysts (fluid-filled sacs) • thickening of alveoli (clusters of milk-secreting cells) develop • Cause – hormonal imbalance • excess of estrogen or deficiency of progesterone in the postovulatory phase – result is lumpy, swollen & tender breast a week before menstruation begins Principles of Human Anatomy and Physiology, 11e 101 Female Reproductive Cycle - Introduction • The general term female reproductive cycle encompasses the ovarian and uterine cycles, the hormonal changes that regulate them, and cyclical changes in the breasts and the cervix – Controlled by monthly hormone cycle of anterior pituitary, hypothalamus & ovary • Ovarian cycle – changes in ovary during & after maturation of oocyte • The uterine (menstrual) cycle – involves changes in the endometrium – preparation of uterus to receive fertilized ovum – if implantation does not occur, the stratum functionalis is shed during menstruation Principles of Human Anatomy and Physiology, 11e 102 Hormonal Regulation of Reproductive Cycle • GnRH secreted by the hypothalamus controls the female reproductive cycle stimulates the release of FSH and LH by the anterior pituitary gland (Figure 28.23). – FSH initiates growth of follicles that secrete estrogen • estrogen maintains reproductive organs – LH stimulates ovulation & promotes formation of the corpus luteum which secretes estrogens, progesterone, relaxin & inhibin • progesterone prepares uterus for implantation and the mammary glands for milk secretion • relaxin facilitates implantation in the relaxed uterus • inhibin inhibits the secretion of FSH • At least six different estrogens have been isolated from the plasma of human females, with three in significant quantities: beta-estradiol, estrone, and estriol. Principles of Human Anatomy and Physiology, 11e 103 Overview of Hormonal Regulation Principles of Human Anatomy and Physiology, 11e 104 Overview of Female Reproductive Cycle Principles of Human Anatomy and Physiology, 11e 105 Estrogens have several important functions: • Promotion of the development and maintenance of female reproductive structures, secondary sex characteristics, and the breasts. • Increase protein anabolism and build strong bones. • Lower blood cholesterol. • Moderate levels of estrogens in the blood inhibit the release of GnRH by the hypothalamus and secretion of LH and FSH by the anterior pituitary gland. • Progesterone works with estrogens to prepare the endometrium for implantation and the mammary glands for milk synthesis. Principles of Human Anatomy and Physiology, 11e 106 Other Hormones • A small quantity of relaxin is produced monthly to relax the uterus by inhibiting contractions (making it easier for a fertilized ovum to implant in the uterus). During pregnancy, relaxin relaxes the pubic symphysis and helps dilate the uterine cervix to facilitate delivery. • Inhibin inhibits secretion of FHS and GnRH and, to a lesser extent, LH. It might be important in decreasing secretion of FHS and LH toward the end of the uterine cycle. Principles of Human Anatomy and Physiology, 11e 107 Hormonal Changes Principles of Human Anatomy and Physiology, 11e 108 Phases of the Female Reproductive Cycle • The female reproductive cycle may be divided into four phases (Figure 28.24). – The menstrual cycle (menstruation) lasts for approximately the first 5 days of the cycle. • During this phase, small secondary follicles in each ovary begin to develop. • the stratum functionalis layer of the endometrium is shed, discharging blood, tissue fluid, mucus, and epithelial cells. Principles of Human Anatomy and Physiology, 11e 109 Menstrual Phase - 5 days • First day is considered beginning of the 28 day cycle • In ovary – 20 follicles that began to develop 6 days before are now beginning to secrete estrogen – fluid is filling the antrum from granulosa cells • In uterus – declining levels of progesterone caused spiral arteries to constrict -- glandular tissue dies – stratum functionalis layer is sloughed off along with 50 to 150 ml of blood (average.) Principles of Human Anatomy and Physiology, 11e 110 Preovulatory Phase - days 6-13 • In the uterus (proliferative phase) – the time between menstruation and ovulation. This phase is more variable in length that the other phases. – endometrial repair occurs Principles of Human Anatomy and Physiology, 11e 111 Preovulatory Phase - days 6-13 • In the ovary (follicular phase) – primary follicle develop into secondary follicle (occasionally more than one) – The dominant follicle continues to increase its estrogen production under the influence of an increasing level of LH (Figure 28.24). – develops into a vesicular ovarian (Graafian) follicle, or mature follicle. – by day 14, graafian follicle has enlarged & bulges at surface of the ovary (Figure 28.13). – follicular secretion of estrogen & inhibin has slowed the secretion of FSH – increasing estrogen levels trigger the secretion of LH • In the uterus (proliferative phase) – increasing estrogen levels have repaired & thickened the stratum functionalis to 4-10 mm in thickness Principles of Human Anatomy and Physiology, 11e 112 Ovulation • Ovulation is the rupture of the vesicular ovarian (Graafian) follicle with release of the secondary oocyte into the pelvic cavity, usually occurring on day 14 in a 28-day cycle. – high levels of estrogen during the last part of the preovulatory phase exert positive feedback on both LH and GnRH to cause ovulation (Figure 28.25). – GnRH promotes release of FSH and more LH by the anterior pituitary gland. – The LH surge brings about the ovulation. Principles of Human Anatomy and Physiology, 11e 113 Ovulation • Rupture of follicle & release of 2nd oocyte on day 14 • Cause – increasing levels of estrogen stimulate release of GnRH which stimulates anterior pituitary to release more LH • Corpus hemorrhagicum results Principles of Human Anatomy and Physiology, 11e 114 Signs of Ovulation • • • • Increase in basal body temperature Changes in cervical mucus Cervix softens Mittelschmerz---pain Principles of Human Anatomy and Physiology, 11e 115 Ovulation • Following ovulation, the vesicular ovarian follicle collapses (and blood within it forms a clot) to become the corpus hemorrhagicum (Figure 28.13). • The clot is eventually absorbed by the remaining follicle cells. • In time, the follicular cells enlarge, change character, and form the corpus luteum, or yellow body, under the influence of LH. • Stimulated by LH, the corpus luteum secretes estrogens and progesterone. Principles of Human Anatomy and Physiology, 11e 116 Phases - Postovulatory - days 15-28 • Time between ovulation and onset of the next menstrual period. (Figure 28.26): most constant timeline = lasts 14 days • In the ovary (luteal phase) – both estrogen and progesterone are secreted in large quantities by the corpus luteum. – if fertilization does not occur, then the corpus albicans is formed • as hormone levels drop, secretion of GnRH, FSH & LH rise – if fertilization does occur, then the developing embryo secretes human chorionic gonadotropin (hCG) which maintains health of corpus luteum & its hormone secretions Principles of Human Anatomy and Physiology, 11e 117 Phases - Postovulatory - days 15-28 • Time between ovulation and onset of the next menstrual period. (Figure 28.26): most constant timeline = lasts 14 days • In the uterus (secretory phase) – hormones from corpus luteum promote thickening of endometrium to 12-18 mm • formation of more endometrial glands & vascularization – if no fertilization occurs, menstrual phase will begin Principles of Human Anatomy and Physiology, 11e 118 Negative Feedback on GnRH Principles of Human Anatomy and Physiology, 11e 119 Fertilization • If fertilization and implantation do occur, the corpus luteum is maintained – The placenta will take over its hormone-producing function. – During this time, the corpus luteum, maintained by human chorionic gonadotropin (hCG) from the developing placenta, secretes estrogens and progesterone to support pregnancy and breast development for lactation. – Once the placenta begins its secretion, the role of the corpus luteum becomes minor. • With reference to the uterus, this phase is also called the secretory phase because of the secretory activity of the endometrial glands as the endometrium thickens in anticipation of implantation. Principles of Human Anatomy and Physiology, 11e 120 Menstrual Abnormalities • Amenorrhea = absence of menstruation – hormone imbalance, extreme weight loss or low body fat as with rigorous athletic training • Dysmenorrhea = pain associated with menstruation – severe enough to prevent normal functioning – uterine tumors, ovarian cysts, endometriosis or intrauterine device • Abnormal uterine bleeding = excessive amount or duration or intermenstrual – fibroid tumors or hormonal imbalance Principles of Human Anatomy and Physiology, 11e 121 Review • Figure 28.26 summarizes the hormonal interactions during the ovarian and uterine cycles. • Women athletes who train intensively may develop three conditions which disrupt their reproductive cycle. This is known as female athlete triad and consists of amenorrhea, disordered eating, and premature osteoporosis. Principles of Human Anatomy and Physiology, 11e 122 BIRTH CONTROL METHODS • Several methods of birth control are available, each with advantages and disadvantages. • Only total abstinence is 100% reliable is. • Methods of birth control discussed in the text include surgical sterilization (vasectomy, tubal ligation), hormonal methods (oral contraception, the Norplant implant, DepoProvera injection, the vaginal ring), intrauterine devices (IUDs), spermacides, barrier methods (condom, vaginal pouch, diaphragm, cervical cap), periodic abstinence (rhythm method, sympto-thermal method), coitus interruptus (withdrawal), and induced abortion (including the drug RU 486, or mifepristone). • A summary of methods of birth control and their failure rates is presented in Table 28.3. Principles of Human Anatomy and Physiology, 11e 123 Surgical Sterilization • Male (vasectomy) – removal of a portion of the vas deferens • incision in posterior scrotal sac • out patient & local anesthesia – sperm can no longer reach the exterior • degenerate and removed by phagocytosis – sexual desire not effected since testosterone levels unchanged • Female (tubal ligation) – uterine tubes are tied closed and cut – sperm can not reach oocyte Principles of Human Anatomy and Physiology, 11e 124 Hormonal Birth Control • Oral contraceptive --- “the pill” – progesterone & estrogen combination pill • negative feedback on the anterior pituitary & hypothalamus to prevent secretion of FSH & LH – no follicular development or ovulation – no possible pregnancy – other benefits of the pill • regulate menstrual cycle & reduce endometriosis • Risks increased for smokers – increased chances of blood clot formation • Not recommended for people with liver disease, hypertension, heart disease, migraines Principles of Human Anatomy and Physiology, 11e 125 Other Hormonal Methods • Norplant – surgically implanted capsules releasing progestin & inhibiting ovulation for 5 years • Depo-provera – intramuscular injection of progesterone every 3 months that changes uterine lining & ovum maturation • Vaginal ring – worn internally releasing progestin or combination of progestin & estrogen Principles of Human Anatomy and Physiology, 11e 126 Intrauterine Devices • Small object made of plastic, copper or steel left in cavity of uterus – changes uterine lining so is unfavorable for embryo implantation – approved for 10 year usage • May cause excessive bleeding or discomfort Principles of Human Anatomy and Physiology, 11e 127 Spermatocides • Chemical substances in foam, cream, jelly, douche or suppository that kill sperm upon contact • Available without prescription • Normally used in conjunction with a barrier device • May inactivate HIV virus & decrease incidence of gonorrhea Principles of Human Anatomy and Physiology, 11e 128 Mechanical Barriers • Male & female condoms (vaginal pouch) • covers penis or lines vagina • Diaphragm = dome-shaped cap over cervix • prevents entry of sperm into uterus • does not protect against AIDS or STD • may cause recurrent UTIs • All of the above may offer some protection against sexually transmitted disease Principles of Human Anatomy and Physiology, 11e 129 Physiological Methods of Birth Control • Rhythm method (periodic abstinence) – abstaining from intercourse when secondary oocyte is likely to be viable (3 to 7 days of cycle) • 3 days before ovulation, ovulation & 3 days after • few women absolutely regular cycles • will not know it was an irregular cycle until too late • Sympto-thermal method – observe body for signs of ovulation & abstain form intercourse accordingly • increased basal body temperature & mucus changes • problem is sperm is viable for 48 hours • Coitus interruptus (withdrawal before ejaculation) Principles of Human Anatomy and Physiology, 11e 130 Induced Abortion • Miscarriage is a spontaneous loss of the fetus • Induced abortions – vacuum aspiration (suction) – infusion of saline solution to kill embryo – surgical evacuation (scraping) • `RU 486 is called a nonsurgical abortion – antiprogestin drug that causes uterine lining to collapse & embryo is lost (menstruation occurs) – can be taken up to 5 weeks after conception Principles of Human Anatomy and Physiology, 11e 131 DEVELOPMENT OF THE REPRODUCTIVE SYSTEMS • The gonads develop from intermediate mesoderm(Figure 28.29). • Indeterminate gonads appear during the fifth week of development • Also, both mesonephric (Wolffian) ducts and paramesonephric (Mullerian ducts) are present and empty into the urogenital sinus. Principles of Human Anatomy and Physiology, 11e 132 DEVELOPMENT OF THE REPRODUCTIVE SYSTEMS • If a SRY gene on the Y chromosome is expressed, the Sertoli cells begin to secrete Mullerian-inhibiting substance (MIS) which causes apoptosis of cells of the paramesonephric (Mullerian) ducts. • The primitive gonadal tissue begins to secrete testosterone which cause the mesonephric duct to develop into the epididymis, ductur deferens, ejaculatory duct, and seminal vesicle. • The testes connect to the mesonephric duct through a series of tubules that eventually become the seminiferous tublule. Principles of Human Anatomy and Physiology, 11e 133 DEVELOPMENT OF THE REPRODUCTIVE SYSTEMS • In the female, SRY is absent. The gonads develop into ovaries, The paramesonephric ducts fuse to form the uterus and vaginal and the unfused portions become the fallopian tubes. • The external genitalia develop from the genital tubercle (Figure 28.28). • In male embryos, some testosterone is converted to dihydrotestosterone (DHT). This causes the genital tubercle to develop into the urethra, prostate, and external genitals. • In the absence of DHT the genital tubercle develops into the clitoris, labia minora, labia majora, and vestible. Principles of Human Anatomy and Physiology, 11e 134 Early Developmental Anatomy Male Duct Development Female Duct Development In 6 week old embryo, paramesonephric & mesonephric ducts are found near the gonadal bulge Principles of Human Anatomy and Physiology, 11e 135 Early Anatomy -- Male • Depends upon SRY gene on Y chromosome Pattern – sertoli cells secrete Mullerian inhibiting substance – leydig cells secrete testosterone causing mesonephric duct to develop into male tubes • seminiferous tubules, epididymis & vas deferens & seminal vesicles • prostate & cowper’s glands are outgrowths of urethra – testosterone secretion stops at birth when hCG from the placenta stops stimulating leydig cells Principles of Human Anatomy and Physiology, 11e 136 • Females have 2 X chromosomes so SRY gene is absent • Gonads develop into ovaries – no mullerian-inhibiting substance is produced so female pattern of duct development occurs – paramesonephric duct develops into vagina, uterus & uterine tubes – mesonephric ducts degenerate • Female pattern depends on the absence of testosterone Principles of Human Anatomy and Physiology, 11e Early Anatomy -Female Pattern 137 Development of External Genitalia • External genitals similar at 8 weeks (genital tubercle) • DHT causes external male structures to develop before birth – Labioscrotal swelling • scrotum or labia majora – Urethral folds • spongy penile urethra or labia minora – Glans area • glans penis or clitoris • Absence of DHT results in development of female Principles of Human Anatomy and Physiology, 11e 138 Deficiency of 5 Alpha-Reductase • Rare genetic defect producing a deficiency of 5 alphareductase – enzyme that converts testosterone into dihydrotestosterone (DHT) • At birth, baby looks externally female due to lack of DHT during development • At puberty, testosterone levels rise – masculine characteristics appear – breasts fail to develop – an internal exam reveals testes & other structures Principles of Human Anatomy and Physiology, 11e 139 AGING AND THE REPRODUCTIVE SYSTEMS • Puberty refers to the period of time when secondary sexual characteristics begin to develop and the potential for sexual reproduction is reached. • In males, declining reproduction function is more subtle, with males often retaining reproductive capacity into their 80s or 90s. • In males, decreasing levels of testosterone decrease muscle strength, sexual desire, and viable sperm. • Prostate disorders are increasingly common with age, particularly benign hypertrophy. Principles of Human Anatomy and Physiology, 11e 140 AGING AND THE REPRODUCTIVE SYSTEMS • In females, the reproductive cycle normally occurs once each month from menarche, the first menses, to menopause, the last menses. • Between the ages of 40 and 50 the ovaries become less responsive to the stimulation of gonadotropic hormones from the anterior pituitary. As a result, estrogen and progesterone production decline, and follicles do not undergo normal development. • In addition to the symptoms of menopause, such as hot flashes, copious sweating, headache, vaginal dryness, depression, weight gain, and emotional fluctuations, with age females also experience increased incidence of osteoporosis, uterine cancer, and breast cancer. Principles of Human Anatomy and Physiology, 11e 141 Aging Male Reproductive System • Decline in reproductive function is more subtle (capacity may remain into 90’s) • Decline in testosterone at 55 – reduced muscle synthesis – fewer viable sperm – reduced sexual desire • Enlargement of prostate (benign hyperplasia) – 1/3 of males over 60 – frequent urination, decreased force of stream, bedwetting & sensation of incomplete emptying Principles of Human Anatomy and Physiology, 11e 142 DISORDERS: HOMEOSTATIC IMBALANCES Principles of Human Anatomy and Physiology, 11e 143 Reproductive System Disorders in Males • Prostate Disorders – In acute prostatitis, the prostate gland becomes swollen and tender. – In chronic prostatitis, one of the most common chronic infections in men of the middle and later years, the gland feels enlarged, soft, and very tender with an irregular surface outline. Principles of Human Anatomy and Physiology, 11e 144 Testicular Cancer • Most common cancer in age group 20-35 – one of the most curable • Begins as problem with spermatogenic cells within the seminiferous tubules • Sign is mass within the testis • Regular self-examination is important Principles of Human Anatomy and Physiology, 11e 145 Prostate Cancer • Leading male cancer death – treatment is surgery, radiation, hormonal and chemotherapy • Blood test for prostate-specific antigen (PSA) – enzyme of epithelial cells – amount increases with enlargement (indication of infection, benign enlargement or cancer) • Treatment for prostate cancer may involve surgery, radiation, hormonal therapy, or chemotherapy. • Over 40 yearly rectal exam of prostate gland • Acute or chronic prostatitis is an infection of prostate causing swelling, tenderness & blockage of urine flow – treat with antibiotics Principles of Human Anatomy and Physiology, 11e 146 Reproductive System Disorders in Males Premature ejaculation is ejaculation that occurs too early. It is usually caused by anxiety or other psychological causes, or an unusually sensitive foreskin or glans penis. Principles of Human Anatomy and Physiology, 11e 147 Erectile Dysfunction (Impotence) • Consistent inability of adult male to hold an erection long enough for sexual intercourse • Causes – psychological or emotional factors – physical factors • diabetes mellitus, vascular disturbances, neurological disturbances, testosterone deficiency, drugs (alcohol, nicotine, antidepressants, tranquilizers,etc) • Viagra causes vasodilation of penile arteries and brings on an erection Principles of Human Anatomy and Physiology, 11e 148 Reproductive System Disorders in Females • Premenstrual syndrome (PMS) refers to severe physical and emotional distress that occurs during the postovulatory (luteal) phase of the female reproductive cycle. • Endometriosis is characterized by the growth of endometrial tissue outside the uterus. – The tissue enters the pelvic cavity via the open uterine tubes and may be found in any of several sites - on ovaries, rectouterine pouch, surface of the uterus, sigmoid colon, pelvic and abdominal lymph nodes, cervix, abdominal wall, kidneys, and/or urinary bladder. – Symptoms include premenstrual pain or unusual menstrual pain. Principles of Human Anatomy and Physiology, 11e 149 Endometriosis • Growth of endometrial tissue outside of the uterus – tissue discharged from open-end of uterine tubes during menstruation – can cover ovaries, outer surface of uterus, colon, kidneys and bladder • Problem is tissue responds to hormonal changes by proliferating then breaking down & bleeding – causes pain, scarring & infertility Principles of Human Anatomy and Physiology, 11e 150 Reproductive System Disorders in Females • Breast cancer is the second-leading cause of death from cancer in United States women. – It is seldom seen before age 30, but its occurrence rises rapidly after menopause. – Two genes increase susceptibility to breast cancer: BRCA1 (breast cancer 1) and BRCA2. Mutation of BRCA1 also confers high risk for ovarian cancer. – Early detection - especially by breast self-examination and mammography - is still the most promising method to increase the survival rate for breast cancer. Principles of Human Anatomy and Physiology, 11e 151 Reproductive System Disorders in Females • Breast cancer is the second-leading cause of death from cancer in United States women. – The factors that increase the risk of breast cancer development include family history of breast cancer, especially in a mother or sister; never having a child or having a first child after age 35; previous cancer in one breast; exposure to ionizing radiation, such as x-rays; excessive alcohol intake; and cigarette smoking. – Treatment for breast cancer may involve hormone therapy, chemotherapy, radiation therapy, lumpectomy (removal of just the tumor and immediate surrounding tissue), a modified or radical mastectomy (removal of part or all of the affected breast, along with underlying pectoral muscles and the axillary lymph nodes in the latter case), or a combination of these. Radiation treatment and chemotherapy may follow the surgery. Principles of Human Anatomy and Physiology, 11e 152 Breast Cancer - Summary • Second-leading cause of cancer death in the U.S. – 1 in 8 women affected – rarely before 30, but more common after menopause • 5% of cases are younger women (genetic mutation) • Detection by self-examination & mammography – ultrasound determines if lump is benign, fluid-filled cyst or solid & possibly malignant • Risk factors – family history, no children, radiation, alcohol & smoking • Treatment – lumpectomy, radical mastectomy, radiation therapy or chemotherapy Principles of Human Anatomy and Physiology, 11e 153 Reproductive System Disorders in Females • Ovarian cancer is the sixth most common form of cancer in females. – Most common cause of gynecological deaths excluding breast cancer – It is difficult to detect before it metastasizes beyond the ovaries. – Risk factors include age (usually over age 50); race (white are at greatest risk); family history of ovarian cancer; never having children or first pregnancy after age 30; high-fat, low-fiber, vitamin A-deficient diet; and prolonged exposure to asbestos or talc. – Early ovarian cancer has no symptoms or only mild ones associated with other common problems. – Later-stage signs and symptoms include an enlarged abdomen, abdominal and/or pelvic pain, persistent gastrointestinal disturbances, urinary complications, menstrual irregularities, and heavy menstrual bleeding. Principles of Human Anatomy and Physiology, 11e 154 Reproductive System Disorders in Females • Cervical cancer starts with cervical dysplasia (change in shape, growth & number of cells) and can be diagnosed in its earliest stages with a Pap smear. – There is some evidence linking cervical cancer to the virus that produces genital warts (papilloma virus). – Other risk factors are increased incidence associated with an increased number of sexual partners, young age at first intercourse, and cigarette smoking. Principles of Human Anatomy and Physiology, 11e 155 Yeast Infection • Vulvovaginal candidiasis is the most common form of vaginitis and is caused by the yeast like fungus Candida albicans. • Candida albicans grows on mucous membranes • Causes vulvovaginal candidiasis or vaginitis – inflammation of the vagina – severe itching and pain – yellow cheesy discharge with odor • The disorder, experienced at least once by about 75% of females, is usually a result of proliferation of the fungus following antibiotic therapy for another condition Principles of Human Anatomy and Physiology, 11e 156 Sexually Transmitted Disease • On the increase in the United States • Chlamydia -- bacteria; asymptomatic, leads to sterility from scar tissue formation • Gonorrhea -- bacteria, discharge common, blindness if newborn is infected during delivery • Syphilis -- bacteria, painless sores (chancre), 2nd stage all organs involved, 3rd stage organ degeneration is apparent (neurosyphilis) • Genital Herpes -- virus, incurable, painful blisters • AIDS & hepatitis B --viruses (chapters 22 & 24) Principles of Human Anatomy and Physiology, 11e 157 Sexually transmitted diseases (STDs) • Chlaymdia is a STD caused by the bacterium Chlamydia trachomatis. At present chlamydia is the most prevalent and one of the most damaging of the STDs. – In most cases, the initial infection is asymptomatic and difficult to recognize clinically. – In males, urethritis is the principal result. – In females, urethritis may spread through the reproductive tract and develop into inflammation of the uterine tubes, which increases the risk of ectopic pregnancy and sterility. Principles of Human Anatomy and Physiology, 11e 158 Sexually transmitted diseases (STDs) • Gonorrhea (“clap”) is an infectious STD that affects primarily the mucous membrane of the urogenital tract, the rectum, and occasionally the eyes. The disease is caused by the bacterium Neisseria gonorrhoreae. – Males usually suffer inflammation of the urethra with pus and painful urination. – In females, infection may occur in the urethra, vagina, and cervix, and their may be a discharge of pus. However, infected females often harbor the disease without any symptoms until it has progressed to a more advanced stage. If the uterine tubes become involved, pelvic inflammation may follow, often causing sterility and occasionally causing peritonitis. – If the bacteria are transmitted to the eyes of a newborn in the birth canal, blindness can result. Administration of a 1% silver nitrate solution or penicillin or erythromycin in the neonate’s eyes prevents infection. Principles of Human Anatomy and Physiology, 11e 159 Sexually transmitted diseases • Syphilis is an STD caused by the bacterium Treponema pallidum. – It is acquired through sexual contact, exchange of blood, or transmitted through the placenta to a fetus. – The disease progresses through several stages: primary, secondary, latent, and tertiary. – During the primary stage, the chief symptom is a painless open sore, called a chanker. – A skin rash, fever, and aches in the joints usher in the secondary stage: a systemic infection. – The tertiary stage occurs when signs of organ degeneration appear. Principles of Human Anatomy and Physiology, 11e 160 Sexually transmitted diseases • Genital herpes is an incurable STD caused by the type II herpes simplex virus (HSV-2). – HSV-2 causes genital infections such as painful blisters on the prepuce, glans penis, and penile shaft in males and on the vulva or sometimes high up in the vagina in females. – The blisters disappear and reappear in most patients, but the virus itself remains in the body. Principles of Human Anatomy and Physiology, 11e 161 end Principles of Human Anatomy and Physiology, 11e 162 Chapter 29 Development and Inheritance Lecture Outline Principles of Human Anatomy and Physiology, 11e 163 Development and Inheritance • From fertilization to birth – fertilization – implantation – placental development – fetal development – gestation – labor – parturition (birth) Principles of Human Anatomy and Physiology, 11e 164 INTRODUCTION • The first two months following fertilization is the period of embryonic development and the developing human is an embryo. • From week nine until birth is the fetal development period and the individual is a fetus. • Prenatal development is the time from fertilization until birth. It is divided into three trimesters. Principles of Human Anatomy and Physiology, 11e 165 Terminology of Development Summary • Gestation period – fertilization to birth (38 weeks) • Prenatal period (before birth) – embryological development • first 2 months after fertilization (embryo) • all principal adult organs are present – fetal development • from 9 weeks until birth (fetus) • placenta is functioning by end of 3rd month • Neonatal period – first 42 days after birth Principles of Human Anatomy and Physiology, 11e 166 INTRODUCTION • Developmental anatomy is the study of the sequence of events from the fertilization of a secondary oocyte to the formation of an adult organism. • Embryology is the study of development from fertilization to the fetal period. • Obstetrics is the branch of medicine that deals with the management of pregnancy, labor, and the neonatal period (the first 42 days after birth). Principles of Human Anatomy and Physiology, 11e 167 EMBRYONIC PERIOD Principles of Human Anatomy and Physiology, 11e 168 From Fertilization to Implantation Principles of Human Anatomy and Physiology, 11e 169 First Week of Development • Fertilization – During fertilization, the genetic material from a haploid sperm cell (spermatozoon) and a haploid secondary oocyte merges into a single diploid nucleus. – Fertilization normally occurs in the uterine (Fallopian) tube when the oocyte is about one-third of the way down the tube to the uterus, usually within 12 to 24 hours after ovulation. (Oocyte usually dies in 24 hours) • The process leading to fertilization begins as peristaltic contractions and the actions of cilia transport the oocyte through the uterine tube. – Sperm swim up the uterus and into the uterine tube by the whip like movements of their tails (flagella) and muscular contractions of the uterus. Principles of Human Anatomy and Physiology, 11e 170 Fertilization • The functional changes that sperm undergo in the female reproductive tract that allow them to fertilize a secondary oocyte are referred to as capacitation. • To fertilize an oocyte, a sperm must penetrate the corona radiata and zona pellucida around the oocyte (Figure 29.1a). • A glycoprotein in the zona pellucida (ZP3) acts as a sperm receptor, binds to specific membrane proteins in the sperm head and triggers the acrosomal reaction, the release of the contents of the acrosome. • The acrosomal enzymes digest a path through the zona pellucida allowing only one sperm to make its way through the barrier and reach the oocyte’s plasma membrane. Principles of Human Anatomy and Physiology, 11e 171 Events Before Fertilization • transport the oocyte towards the uterus – peristalsis of uterine tube – movement of cilia – oocyte releases chemical attractants • sperm swim towards oocyte – flagella – prostaglandins (within the semen) stimulate uterine contractions that help propel sperm • capacitation (final maturation of the sperm) occurs within female – acrosomal membrane becomes fragile Principles of Human Anatomy and Physiology, 11e 172 Fertilization • Fusion of a sperm with a secondary oocyte is called syngamy. • Polyspermy is prevented by chemical changes that prevent a second sperm from entering the oocyte. Principles of Human Anatomy and Physiology, 11e 173 Sperm Contact during Fertilization • Sperm penetrates the granulosa cells around the oocyte (corona radiata) • Sperm digests its way through the zona pellucida – ZP3 glycoprotein binds to sperm head, triggering the acrosomal reaction (enzyme release) • Once a sperm enters a secondary oocyte, the oocyte completes meiosis, and the male pronucleus and female pronucleus fuse forming the fertilized ovum or zygote (Figure 29.1c). Principles of Human Anatomy and Physiology, 11e 174 Sperm Contact during Fertilization • First sperm to fuse with oocyte membrane triggers the slow & the fast block to polyspermy – 1-3 seconds after contact, oocyte membrane depolarizes & other cells can not fuse with it = fast block to polyspermy – depolarization triggers the intracellular release of Ca+2 causing the exocytosis of molecules hardening the entire zona pellucida = slow block to polyspermy Principles of Human Anatomy and Physiology, 11e 175 Twins • Fraternal twins (dizygotic) – independent release of 2 oocytes fertilized by 2 separate sperm – genetically as different as any 2 siblings • Identical twins (monozygotic) – 2 individuals that develop from a single fertilized ovum – genetically identical & always the same sex – if ovum does not completely separate, conjoined twins (share some body structures) Principles of Human Anatomy and Physiology, 11e 176 Cleavage of the Zygote • Early rapid mitotic cell division of a zygote is called cleavage (Figure 29.2). • The cells produced by cleavage are called blastomeres. • Successive cleavages produce a solid mass of cells, called the morula (Figure 29.2). Principles of Human Anatomy and Physiology, 11e 177 Events Within the Egg • Sperm entry, triggers oocyte to complete meiosis II and dump second polar body • Once inside the oocyte, the sperm loses its tail & becomes a male pronucleus • Fusion of male & female haploid pronuclei is the true moment of fertilization • Fertilized ovum (2n) is called a zygote – zona pellucida still surrounds it Principles of Human Anatomy and Physiology, 11e 178 Formation of the Morula • Rapid mitotic cell division of embryo is called cleavage • 1st cleavage in 30 hours produces 2 blastomeres • 2nd cleavage on 2nd day • By 3rd day has 16 cells • By day 4 has formed a solid ball of cells called a morula Principles of Human Anatomy and Physiology, 11e 179 Blastocyst Formation • As the number of cells in the morula increases, it moves from the site of fertilization down through the ciliated uterine tube toward the uterus and enters the uterine cavity. • The morula develops into a blastocyst, a hollow ball of cells that is differentiated into – a trophoblast (which will form the future embryonic membranes) – an inner cell mass or embryoblast (the future embryo) – an internal fluid-filled cavity called the blastocele (Figure 29.2e). Principles of Human Anatomy and Physiology, 11e 180 Development of the Blastocyst • A blastocyst is a hollow ball of cells – enters the uterine cavity by day 5 – outer covering is the trophoblast – inner cell mass – fluid-filled cavity is the blastocele • Trophoblast & part of inner cell mass will develop into the fetal portion of placenta • Most of the inner cell mass will become embryo. Principles of Human Anatomy and Physiology, 11e 181 Stem cell research and therapeutic cloning • Stem cells are unspecialized cells that have the ability to divide for indefinite periods and to give rise to specialized cells. • Pluripotent cells such as those of the inner cell mass can give rise to many different types of cells. – Scientists hope to remove pluripotent cells and use them to grow tissues to treat particular diseases. • Scientists are also studying adult stem cells. – Studies have suggested that stem cells in human adult bone marrow are pluripotent and therefore have potential clinical significance. Principles of Human Anatomy and Physiology, 11e 182 Implantation • The blastocyst remains free with the cavity of the uterus for two to four days before it actually attaches to the uterine wall. • The attachment of a blastocyst to the endometrium occurs seven to eight days after fertilization and is called implantation (Figure 29.3). • Trophoblast develops 2 distinct layers: – syncytiotrophoblast secretes enzymes that digest the endometrial cells – cytotrophoblast is distinct layer of cells that defines the original shape of the embryo • Trophoblast secretes human chorionic gonadotropin (hCG) that helps the corpus luteum maintain the uterine lining Principles of Human Anatomy and Physiology, 11e 183 Implantation Principles of Human Anatomy and Physiology, 11e 184 8 days - 9 days Notice: distinct syncytiotrophoblast and cytotrophoblast layers. Principles of Human Anatomy and Physiology, 11e 185 Implantation • Following implantation the endometrium is known as the decidua and consists of three regions: the decidua basalis, decidua capuslaris, and decidua parietalis. • The decidua basalis lies between the chorion and the stratum basalis of the uterus. It becomes the maternal part of the placenta. • The decidua capsularis covers the embryo and is located between the embryo and the uterine cavity. • The decidua parietalis lines the noninvolved areas of the entire pregnant uterus. • The major events associated with the first week of development are summarized in Figure 29.5. Principles of Human Anatomy and Physiology, 11e 186 Clinical Application • Ectopic pregnancy refers to the development of an embryo or fetus outside the uterine cavity. • Most occur in the uterine tube – usually in the ampullar or infundibular portions – some occur in the ovaries, abdomen, uterine cervix, or broad ligaments. • Common causes are blockages of uterine tube such as tumors or scars from pelvic inflammatory disease • symptoms are missed menstrual cycles, bleeding & acute pain • Twice as common in smokers because nicotine paralyzes the cilia • Depending on the location of the ectopic pregnancy, the condition can become life threatening to the mother. Principles of Human Anatomy and Physiology, 11e 187 Development of the Trophoblast • trophoblast syncytiotrophoblast and cytotrophoblast (Figure 29.6a) part of the chorion as they undergo further growth (Figure 29.11 inset). • The cells of the inner cell mass differentiate into two layers that form a flattened disc referred to as the bilaminar embryonic disc (Figure 29.6a). • hypoblast (primitive endoderm) • epiblast (primitive ectoderm) Principles of Human Anatomy and Physiology, 11e 188 Beginnings of Organ Systems(Gastrulation) • Day 8 – cytotrophoblast forms amnion & amnionic cavity • cells of inner cell mass on amnionic cavity form ectoderm • cells bordering on blastocele form endoderm – ectoderm & endoderm together form embryonic (bilaminar) disk • Day 12 – endodermal cells divide to form a hollow sphere (yolk sac) – cytotrophoblast cells divide to fill the spaces surrounding the yolk sac with extraembryonic mesoderm • spaces develop in that layer to form future ventral body cavity Principles of Human Anatomy and Physiology, 11e 189 Primary Germ Layers • Day 14 --cells of embryonic disc produce 3 distinct layers • endoderm epithelial lining of GI & respiratory • mesoderm muscle, bone & other connective tissues • ectoderm epidermis of skin & nervous system Principles of Human Anatomy and Physiology, 11e 190 Development of the Amnion • Amniotic fluid protects the developing fetus and can be examined in a procedure known as amniocentesis. Principles of Human Anatomy and Physiology, 11e 191 Formation of Embryonic Membranes • Yolk sac – site of early blood formation – gives rise to gonadal stem cells (spermatogonia & oogonia) • Amnion – develops from the epiblast – thin, protective membrane called the amnion – Initially the amnion overlies only the bilaminar embryonic disc; as the embryo grows it eventually surrounds the entire embryo creating the amniotic cavity (Figure 29.11a inset). – surrounds embryo with fluid: shock absorber, regulates body temperature & prevents adhesions – fluid is filtrate of mother’s blood + fetal urine – May be examined for embryonic cells (amniocentesis) Principles of Human Anatomy and Physiology, 11e 192 Amnion, Yolk sac, Chorion, allantois Principles of Human Anatomy and Physiology, 11e 193 • Chorion – becomes the embryonic contribution to the placenta – derived from trophoblast & mesoderm lining it – gives rise to human chorionic gonadotropin (hCG) • Allantois – outpocketing off yolk sac that becomes umbilical cord Principles of Human Anatomy and Physiology, 11e 194 Development of the Yolk sac • The hypoblast cells migrate and become the exocoelomic membrane. • The hypoblast and the exocoelomic membrane form the yolk sac. (Figure 29.6b) • The yolk sac has several important functions. – transfers nutrients to the embryo – early source of blood cells – produces primitive germ cells, which will become spermatogonia and oogonia. Principles of Human Anatomy and Physiology, 11e 195 Amnion, Yolk sac, Chorion, Allantois Principles of Human Anatomy and Physiology, 11e 196 Amnion, Yolk sac, Chorion, Allantois Principles of Human Anatomy and Physiology, 11e 197 Development of Sinusoids • ninth day – blastocyst is completely embedded in the endometrium – syncytiotrophoblast expands and small spaces called lacunae develop within it (Figure 29.6b). • twelfth day – lacunae fuse to form lacunar networks (Figure 29.6c). – Endometrial capillaries around the developing embryo become dilated and are referred to as sinusoids. • The synctiotrophoblast erodes the sinusoids and endometrial glands permitting maternal blood to enter the lacunar networks. • After the extraembryonic mesoderm develops, several large cavities develop in the extraembryonic mesoderm. These cavities fuse to form the extraembryonic coelom (Figure 29.6c) Principles of Human Anatomy and Physiology, 11e 198 21 Days Principles of Human Anatomy and Physiology, 11e 199 Development of the Chorion • The chorion develops from extraembryonic mesoderm and the two layers of the trophoblast (Figure 29.6c). • The chorion becomes the principal embryonic part of the placenta. • The chorion secretes hCG, an important hormone of pregnancy (Figure 29.16). Principles of Human Anatomy and Physiology, 11e 200 Parts of Endometrial Lining • Decidua = all of endometrium lost as placenta – equals all of the endometrium, except stratum basalis • Decidua basalis---portion of endometrium deep to chorion • Decidua capsularis---part of endometrial wall that covers implanted embryo • Decidua parietalis---part of endometrial wall not modified by embryo until embryo bumps into it as it enlarges • Decidua capsularis fuses with decidua parietalis Principles of Human Anatomy and Physiology, 11e 201 Decidua Principles of Human Anatomy and Physiology, 11e 202 Umbilical Cord • Contents – 2 arteries that carry blood to the placenta – 1 umbilical vein that carries oxygenated blood to the fetus – primitive connective tissue • Stub drops off in 2 weeks leaving scar (umbilicus) Principles of Human Anatomy and Physiology, 11e 203 Placenta Previa • Placenta is implanted near or covering os of cervix – occurs in 1 to 250 live births • May lead to spontaneous abortion, premature birth or increased maternal mortality • Major symptom is sudden, painless bright red vaginal bleeding in the 3rd trimester • Cesarean section is preferred delivery method Principles of Human Anatomy and Physiology, 11e 204 Fetal Ultrasonography • Transducer emits high-frequency sound waves – reflected sound waves converted to on-screen image called sonogram – patient needs full bladder • Used to determine fetal age, viability, growth, position, twins and maternal abnormalities Principles of Human Anatomy and Physiology, 11e 205 Third Week of Development Principles of Human Anatomy and Physiology, 11e 206 22-28 days Principles of Human Anatomy and Physiology, 11e 207 28 days Principles of Human Anatomy and Physiology, 11e 208 Placenta & Umbilical Cord • Placenta forms during 3rd month – chorion of embryo & stratum functionalis layer of uterus • Chorionic villi extend into maternal blood filled intervillous spaces --- maternal & fetal blood vessels do not join & blood does not mix – diffusion of O2, nutrients, wastes – stores nutrients & produces hormones – barrier to microorganisms, except some viruses • AIDS, measles, chickenpox, poliomyelitis, encephalitis – not a barrier to drugs such as alcohol • Placenta detaches from the uterus (afterbirth) Principles of Human Anatomy and Physiology, 11e 209 Principles of Human Anatomy and Physiology, 11e 210 Gastrulation • During gastrulation the two-dimensional bilaminar embryonic disc transforms into a two-dimensional trilaminar embryonic disc consisting the three primary germ layers – ectoderm – mesoderm – endoderm • Gastrulation begins with the development of the primitive streak (Figure 29.7c). • Cells of the epiblast move inward below the primitive streak and detach from the epiblast (Figure 29.7b). Principles of Human Anatomy and Physiology, 11e 211 Gastrulation • The primary germ layers form all tissues and organs of the developing organism (Table 29.1) • A solid cylinder of cells the notochord also develops (Figure 29.8). It plays an important role in the process of induction. • The oropharyngeal membrane that will eventually connect the mouth cavity to the pharynx and the remainder of the gastrointestinal tract appears (Figure 29.8 a, b). • The cloacal membrane that will form the openings of the anus and urinary and reproductive tracts also appears. • The allantois, a vascularized out pouching of the yolk sac extends into the connecting body stalk (Figure 29.8b). It is not a prominent structure in humans (Figure 29.11a inset). Principles of Human Anatomy and Physiology, 11e 212 Neurulation • The notochord induces the ectodermal cells over it to form the neural plate (Figure 29.9a) – neural plate the neural folds and neural groove that will fuse to form the neural tube (Figure 29.9d). – Ectodermal cells migrate neural crest (Figure 14.26) which give rise spinal and cranial nerves and their ganglia, autonomic nervous system ganglia, the meninges of the brain and spinal cord, the adrenal medullae, and several skeletal and muscular components of the head. Principles of Human Anatomy and Physiology, 11e 213 Neurulation • The head of the neural tube three primary vesicles – prosencephalon – mesencephalon – rhombencephalon (Figure 14.26) • Later the secondary vesicles will develop. – telencephalon – diencephalon – metencephalon – myelencephalon. • Neural tube defects (NTDs) are caused by arrest of the normal development and closure of the neural tube. These include anencephaly and spina bifida (Clinical Application). Principles of Human Anatomy and Physiology, 11e 214 Development of somites • The somites, a series of paired, cube-shaped structures, develop from the mesoderm. • Eventually 42-44 pairs of somites will develop. • Each somite has three regions (Figure 10.20b). – Myotome – Dermatome – Sclerotome Principles of Human Anatomy and Physiology, 11e 215 Development of the intraembryonic coelom • Small spaces in the lateral plate mesoderm fuse to form a larger cavity, the intraembryonic coelom. • This cavity splits the lateral plate mesoderm into two parts called the splanchnic mesoderm and the somatic mesoderm (Figure 29.9d). – The intraembryonic mesoderm divides into the pericardial, pleural, and peritoneal cavities. – Splanchnic mesoderm forms portions of the heart, respiratory and digestive systems. – Somatic mesoderm gives rise to bones, ligaments, and dermis of the limbs and the parietal layer of the serous membranes. Principles of Human Anatomy and Physiology, 11e 216 Development of the cardiovascular system • Angiogenesis, the formation of blood vessels, begins in the extraembryonic mesoderm in the yolk sac, connecting stalk, and chorion. – initiated when angioblasts aggregate to form isolated masses of cells referred to a blood islands (Figure 21.32). – Angioblasts form the walls of the blood vessels – Spaces in the blood islands from the lumen of blood vessels. • The heart forms in the cardiogenic area of the splanchnic mesoderm. • The mesodermal cells form a pair of endocardial tubes (Figure 20.18). – The tubes fuse to form a single primitive heart. Principles of Human Anatomy and Physiology, 11e 217 Development of the chorionic villi and placenta • Chorionic villi develop as projections of the cytotrophoblast that eventually contain blood filled capillaries (Figure 29.10b). • Blood vessels in the chorionic villi connect to the embryonic heart by way of umbilical arteries and veins (Figure 29.10c). • The placenta has a fetal portion formed by the chorionic villi of the chorion and a maternal portion formed by the decidua basalis of the endometrium (Figure 29.11a) Principles of Human Anatomy and Physiology, 11e 218 Development of the chorionic villi and placenta • Functionally the placenta allows oxygen and nutrients to diffuse from maternal blood to fetal blood that carbon dioxide and wastes diffuse from fetal blood into maternal blood. – also serves as a protective barrier – stores nutrients – secretes several important hormones • The connection between the placenta and the embryo is the umbilical cord (Figure 29.11a). • After the birth of the baby, the placenta detaches from the uterus and is therefore termed the afterbirth. Principles of Human Anatomy and Physiology, 11e 219 Clinical Application • Placenta previa is a condition in which part or the entire placenta becomes implanted in the lower portion of the uterus, near or over the internal os of the cervix. If detected during pregnancy (either by ultrasound or as a result of sudden painless bright red vaginal bleeding during the third trimester), cesarean section is the preferred method of delivery. Principles of Human Anatomy and Physiology, 11e 220 Fourth week of Development • Embryonic folding converts the embryo from a flat, twodimensional trilaminar embryonic disc to a threedimensional cylinder. • Development of the somites and the neural tube occurs during the fourth week. • Several pharyngeal (branchial) arches develop on each side of the future head and neck regions (Figure 29.13). With the pharyngeal clefts and pouches they will form structures of the head and neck. Principles of Human Anatomy and Physiology, 11e 221 Fourth week of Development • The otic placode is the first sign of a developing ear (Figure 29.13a). • The lens placode is the first sign of a developing eye (Figure 29.13a). • The upper limb buds appear (Figure 6.13a) in the middle of the fourth week and the lower limb buds appear at the end of the fourth week. Principles of Human Anatomy and Physiology, 11e 222 Fifth Through Eight Weeks of Development • During the fifth week there is rapid brain development and considerable head growth. • During the sixth week the head grows even larger in relation to the trunk, there is substantial limb growth, the neck and truck begin to straighten, and the heart is now fourchambered. • During the seventh week the various regions of the limbs become distinct and the beginnings of the digits appear. • By the end of the eighth week all regions of the limbs are apparent, the digits are distinct, the eyelids come together, the tail disappears, and the external genitals begin to differentiate. Principles of Human Anatomy and Physiology, 11e 223 FETAL PERIOD • During the fetal period, tissue and organs that developed during the embryonic period grow and differentiate. The rate of body growth is remarkable. • A summary of the major developmental events of the embryonic and fetal period is presented in Table 29.2 and Figure 29.14. Principles of Human Anatomy and Physiology, 11e 224 PRENATAL DIAGNOSTIC TESTS Principles of Human Anatomy and Physiology, 11e 225 PRENATAL DIAGNOSTIC TESTS • The first noninvasive prenatal test was maternal alphafetoprotein (AFP) test. This test analyzes the maternal blood for the presence of AFP. • A high level of AFP after 16 weeks indicates that the fetus has a neural tube defect. This test is used to screen for Down syndrome, trisomy 18, and neural tube defects. It also helps predict delivery date and may reveal the presence of twins. Principles of Human Anatomy and Physiology, 11e 226 Fetal Ultrasonography • In fetal ultrasonography, an image of the fetus, called a sonogram, is displayed on a screen. It is used most often to determine true fetal age when the date of conception is uncertain. It is also used to evaluate fetal viability and growth, determine fetal position, ascertain multiple pregnancies, identify fetal-maternal abnormalities, and serve as an adjunct to special procedures such as amniocentesis and chorionic villus sampling. • Transducer emits high-frequency sound waves – reflected sound waves converted to on-screen image called sonogram – patient needs full bladder Principles of Human Anatomy and Physiology, 11e 227 Amniocentesis • usually done at 14-16 weeks gestation to detect suspected genetic abnormalities. • Fetal cells from 10 ml sample of amniotic fluid are examined for genetic defects • Needle through abdominal wall & uterus – Chance of spontaneous abortion is 0.5% • To asses fetal maturity, it is usually done after the 35th week of gestation (Figure 29.15a). Principles of Human Anatomy and Physiology, 11e 228 Chorionic Villi Sampling • Chorionic villi sampling (CVS) involves withdrawal of chorionic villi for chromosomal analysis. – can be done earlier than amniocentesis (at 8-10 weeks gestation), – results are available more quickly. • 30 mg of placenta removed by suction through cervix (“transvaginal”) or with needle through abdomen (Figure 29.15b). • Chance of spontaneous abortion is 1-2% • Chromosomal analysis reveals same results as amniocentesis Principles of Human Anatomy and Physiology, 11e 229 MATERNAL CHANGES DURING PREGNANCY Principles of Human Anatomy and Physiology, 11e 230 Hormones of Pregnancy • Chorion – from day 8 until 4 months secretes hCG – keeps corpus luteum active – corpus luteum produces progesterone & estrogen to maintain lining of uterus • Human chorionic gonadotropin (hCG) – mimics LH; its primary role is to stimulate continued production by the corpus luteum of estrogens and progesterone - an activity necessary for the continued attachment of the embryo and fetus to the lining of the uterus (Figure 29.16). • Placenta – by 4th month produces enough progesterone & estrogen that corpus luteum is no longer important – relaxin – human chorionic somatomammotropoin (hCS) or human placental lactogen (hPL) – corticotropin-releasing hormone (CRH) Principles of Human Anatomy and Physiology, 11e 231 Placental Hormones • Relaxin – produced by the ovaries, testes, and placenta – inhibits secretion of FSH and might regulate secretion of hGH. • Human chorionic somatomammotropin (hCS) (also known as human placental lactogen, or hPL) – maximum amount by 32 weeks – produced by the chorion – role in breast development for lactation, protein anabolism, and catabolism of glucose and fatty acids. • Corticotropin-releasing hormone (CRH) – increases secretion of fetal cortisol (lung maturation) – thought to be the “clock” that establishes the timing of birth. Principles of Human Anatomy and Physiology, 11e 232 Hormone Blood Levels • Human chorionic gonadotropin (hCG) produced by the chorion is less important after 4 months, because the placenta takes over the hormonal secretion of the corpus luteum. Principles of Human Anatomy and Physiology, 11e 233 Hormonal Secretion by the Placenta Principles of Human Anatomy and Physiology, 11e 234 Clinical Application: Hormones of Pregnancy • Early pregnancy tests detect the tiny amounts of hCG in the urine that begin to show up about 8 days after fertilization. – color change – reaction between urine & antibodies in kit • False-negatives & false-positives do occur – excess protein or blood in urine – rare type of uterine cancer – steroid, diuretics, hormones and thyroid drugs alter test results Principles of Human Anatomy and Physiology, 11e 235 Developmental Changes • Read Table 29.2 to get a full description of the timing of fetal events during development Principles of Human Anatomy and Physiology, 11e 236 Anatomical and Physiological Changes During Pregnancy • During gestation, several anatomical and physiological changes occur. • The uterus continuously enlarges, filling first the pelvic and then the abdominal cavity, displacing and compressing a number of structures (Figure 29.17). Principles of Human Anatomy and Physiology, 11e 237 Anatomical and Physiological Changes During Pregnancy • weight gain; increased protein, fat, and mineral storage; marked breast enlargement; and lower back pain. • increase in stroke volume by approximately 30%, rise in cardiac output by approximately 20-30% • increase in heart rate by 1015%, and increase in blood volume up to 30-50% (mostly during the latter half of pregnancy) Principles of Human Anatomy and Physiology, 11e 238 Anatomical and Physiological Changes During Pregnancy • Pulmonary function alternations include increased tidal volume (30-40%) • decreased expiratory reserve volume (by up to 40%) • increased minute volume of respiration (by up to 40%), decreased airway resistance in the bronchial tree (by up to 36%) • increase in total body oxygen consumption (by 10-20%). Principles of Human Anatomy and Physiology, 11e 239 Maternal Changes During Pregnancy • GI tract compressed causing heartburn & constipation – increase in appetite – decreased motility can result in constipation and delayed gastric emptying. Nausea, vomiting, and heartburn also occur. • Pressure on bladder causing changes in frequency & urgency • Glomerular filtration rate rises up to 40%. • Compression of vena cava causing varicose veins & edema in the legs • Compression of renal vessels causing renal hypertension • skin may display increased pigmentation Principles of Human Anatomy and Physiology, 11e 240 Pregnancy-Induced Hypertension • Approximately 10-15% of all pregnant women in the United States experience pregnancy-induced hypertension • Major cause is preeclampsia – typically occurs after the 20th week of gestation – sudden hypertension – large amounts of protein in the urine – generalized edema, blurred vision & headaches • Autoimmune or allergic reaction to presence of fetus • When associated with convulsions and coma, the condition is termed eclampsia (Clinical Application) Principles of Human Anatomy and Physiology, 11e 241 Exercise and Pregnancy • Exercise may need to be modified during pregnancy to accommodate the changes in the female’s body. • In early pregnancy – avoid excessive exercise & heat buildup – linked to neural tube defects • Moderate physical activity does not appear to endanger the fetuses of healthy females who have a normal pregnancy and is beneficial in many aspects. Principles of Human Anatomy and Physiology, 11e 242 Labor and Parturition • Parturition means giving birth; labor is the process of expelling the fetus • Labor begins when progesterone’s inhibition is overcome by an increase in the levels of estrogen – progesterone inhibits uterine contraction – placenta stimulates fetal anterior pituitary which causes fetal adrenal gland to secrete DHEA – placenta converts DHEA to estrogen – estrogen overcomes progesterone and labor begins • A decrease in progesterone levels and elevated levels of estrogens, prostaglandins, oxytocin, and relaxin are all probably involved in the initiation and progression of labor. Principles of Human Anatomy and Physiology, 11e 243 Positive Feedback during Labor • Uterine contraction forces fetal head into cervix (stretch) • Nerve impulses reach hypothalamus causing release of oxytocin • Oxytocin causes more contractions producing more stretch of cervix & more nerve impulses Principles of Human Anatomy and Physiology, 11e 244 True Versus False Labor • True labor begins when uterine contractions occur at regular intervals, usually producing pain. – Other signs of true labor may be localization of pain in the back, which in intensified by walking – dilation of the cervix – “show” (discharge of blood-containing mucus from the cervical canal) • False labor produces pain at irregular intervals but there is no cervical dilation Principles of Human Anatomy and Physiology, 11e 245 Stages of Labor • Dilation – 6 to 12 hours – regular contractions of the uterus – rupture of amniotic sac & dilation of cervix (10cm) • Expulsion – 10 minutes to several hours – baby moves through birth canal • Placental – 30 minutes – afterbirth is expelled by uterine contractions – constrict blood vessels that were torn – reduce the possibility of hemorrhage Principles of Human Anatomy and Physiology, 11e 246
