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Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. Chapter 28 The Reproductive System: Embryology and Human Development Introduction Development involves: Differentiation of cells Reorganization of cells Development can be characterized by different periods of time Prenatal development Embryology Postnatal development An Overview of Development Development can be characterized by different periods of time Prenatal development Conception to delivery Involves embryology (development during the prenatal period) Postnatal development Development from birth to maturity Fertilization Fertilization is the joining of two haploid cells to create a diploid cell Function of the haploid cells Spermatozoon Delivers the paternal chromosomes to the ovum Ovum Provides the maternal chromosomes Provides nourishment for embryonic development Fertilization Fertilization occurs in the ampulla of the uterine tube 200 million sperm cells enter the vaginal canal Only about 10,000 make it to the uterine tubes Less than 100 actually contact the egg Only one will fertilize the egg Fertilization Fertilization details When the egg is ovulated, it is surrounded by the corona radiata, which protects the egg as it is being ovulated Numerous sperm cells release hyaluronidase, from their acrosomal cap, in an effort to decompose the corona radiata Prenatal Development Prenatal development is gestation period (9 months) © 2012 Pearson Education, Inc. Page 1 of 12 840941469 Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. Prenatal development is divided into trimesters First trimester (rudiments of all organs appear) Second trimester (fetus looks like a human) Third trimester (organs become functional, rapid growth) Prenatal Development The First Trimester 1 to 12 weeks Four events within the first trimester Cleavage (sequence of cell reproduction) Implantation (implantation into endometrial lining) Placentation (formation of the placenta) Embryogenesis (development of the embryo) Prenatal Development Cleavage and Blastocyst Formation Cell division results in the formation of blastomeres A solid ball of cells eventually develops – this is a morula Some cells migrate to one “edge” of the morula creating a mass of cells and a hollow cavity called the blastocoele The ball of cells is now called the blastocyst The outer layer of the blastocyst consists of cells called the trophoblast Prenatal Development Cleavage and Blastocyst Formation (continued) Trophoblast cells provide nutrients to the developing embryo The inner cell mass consists of stem cells that will develop into all the cells of the body Prenatal Development Implantation Upon contact with the endometrial lining, the trophoblast cells divide rapidly The trophoblast cells “fuse” with the endometrial lining forming a syncytial trophoblast This layer of cells releases hyaluronidase to erode away more of the endometrial lining so the mass can implant Prenatal Development Implantation (continued) Upon implantation, the inner cell mass separates from the trophoblast area When the inner cell mass separates from the trophoblast, two cavities form: Amnionic cavity Blastocoele cavity Prenatal Development Formation of the Blastodisc © 2012 Pearson Education, Inc. Page 2 of 12 840941469 Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. A layer of cells forms between the amnionic cavity and the blastocoele cavity The layers are called Epiblast Hypoblast Prenatal Development Gastrulation and Germ Layer Formation Eventually some cells of the epiblast move toward the center of the blastodisc creating a primitive streak This movement is called gastrulation As the cells move toward the primitive streak area, they begin to migrate between the epiblast and hypoblast layers This creates three distinct layers of cells Prenatal Development Gastrulation and Germ Layer Formation The three layers of cells are: Ectoderm (derived from the epiblast layer) Mesoderm (new layer between the epiblast and hypoblast) Endoderm (derived from the hypoblast layer) Prenatal Development The ectoderm, mesoderm, and endoderm are collectively known as the germ layers Each layer will form specific tissues and organs of the body Germ layers will also form structures involved in embryonic survival called extraembryonic membranes Prenatal Development Formation of Extraembryonic Membranes There are four major extraembryonic membranes Yolk sac Amnion Allantois Chorion Prenatal Development Formation of Extraembryonic Membranes Yolk sac This is a pouch that extends from the hypoblast cells into the blastocoele It is the early site for blood cell formation Amnion Amnionic fluid fills the amnion cavity, which surrounds and cushions the embryo and fetus Prenatal Development Formation of Extraembryonic Membranes (continued) Allantois Eventually gives rise to the urinary bladder Chorion The mesoderm and trophoblast layers form together to form the chorion The chorion will eventually develop extensions into the endometrium © 2012 Pearson Education, Inc. Page 3 of 12 840941469 Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. Prenatal Development Placentation The placenta begins to form when the chorion produces villi (chorionic villi) that extend into the endometrial lining The body stalk connects the embryo to the chorion As the fetus develops and moves farther into the uterus, it obtains its nutrients via the umbilical cord Prenatal Development Embryogenesis Shortly after gastrulation, embryogenesis begins By week 4, a head fold and tail fold develop The embryo is separated from the blastodisc area Prenatal Development Embryogenesis At about 12 weeks, organs begin to form This is called organogenesis Prenatal Development Second Trimester Fetus is covered by the amnion sac Fetus grows faster than the placenta Third Trimester All fetal organs become functional Prenatal Development Changes in the uterus during gestation Uterus will increase in length from 7.5 cm to 30 cm Contains almost 5 L of fluid The uterus and contents weigh about 22 pounds Abdominal organs are pushed out of their normal positions Labor and Delivery The goal of labor is parturition (expulsion of the fetus) There are three stages of labor Dilation stage Expulsion stage Placental stage Labor and Delivery The dilation stage The fetus begins to move down the cervical canal The cervix dilates The amnion sac breaks The expulsion stage The birth of the child The placental stage Ejection of the placenta © 2012 Pearson Education, Inc. Page 4 of 12 840941469 Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. The Neonatal Period This is the period from birth to one month Events that occur from birth to one month are: Lungs fill with air Blood circulation changes with the closing of the ductus arteriosus and the foramen ovale of the heart Heart rate drops from 120–140 beats per minute to about 70 Breathing rate drops from 30 per minute to the normal rate The Neonatal Period Events that occur from birth to one month are (continued): Kidneys filter the infant’s own blood Digestive system becomes active Metabolic rate is increased to maintain warmth for a few days after birth Embryology Summary Overview of Embryology The development of the: Integumentary System Skull Vertebral Column Appendicular Skeleton Muscles Nervous System Spinal Cord Brain Special Sense Organs Embryology Summary The Development of the Integumentary System 1 month: epithelium overlies mesenchyme 3 months: epithelium multiplies to form layers; mesenchyme develops into connective tissue thus forming the dermis 4 months: epidermis begins to grow into the dermis thus forming columns of cells; hair follicles, sweat glands, and sebaceous glands develop from these columns Embryology Summary The Development of the Integumentary System (continued) Skin: at 3 months, the epithelium continues to thicken Melanocytes migrate into the stratum basale layer Nails: develop from the thickening of the epidermis © 2012 Pearson Education, Inc. Page 5 of 12 840941469 Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. Embryology Summary The Development of the Skull 5 weeks Cartilage begins to appear Cartilage within the brain area enlarges to form the chondrocranium Skull walls and floor are beginning but no roof 9 weeks Endochondral ossification appears; frontal and parietal structures appear Embryology Summary The Development of the Skull (continued) 10 weeks Mandibular arch fuses with the chondrocranium Hyoid arch begins to form 12 weeks Ossification is well under way Birth Cranial roof remains incomplete The anterior and posterior fontanels are present Embryology Summary The Development of the Vertebral Column 4 weeks On either side of the developing spinal cord are blocks of mesenchymal tissue called somites The medial side of the somites produces the vertebral column 8 weeks Vertebral cartilage forms around the spinal cord The sacrum and coccyx are fused together Embryology Summary The Development of the Vertebral Column (continued) 12 weeks Ribs and sternum undergo ossification The tips of the longer ribs do not ossify; they remain as cartilage thus forming the costal cartilages Embryology Summary The Development of the Appendicular Skeleton 4 weeks Ridges appear along the length of the embryo An accumulation of ridges at the superior end and the inferior end form pairs of limb buds 5 weeks Limb buds develop a core of cartilaginous tissue Cartilaginous models develop between 5 and 8 weeks 10 weeks © 2012 Pearson Education, Inc. Page 6 of 12 840941469 Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. Ossification occurs Embryology Summary The Development of Muscles 4 weeks Mesoderm on either side of the notochord forms somites The medial portion of each somite forms skeletal muscles; this region is called the myotome 6 weeks Myotome area develops into posterior muscles called epaxial muscles and anterior muscles called hypaxial muscles Embryology Summary The Development of Muscles (continued) 7 weeks: muscles of the face, back, and abdomen develop 8 weeks: limbs enlarge and muscles continue to develop Embryology Summary The Development of the Nervous System 2 weeks Somites appear on either side of the notochord A neural plate is formed A crease develops along the length of the neural plate The edges of the crease are the neural folds The neural folds “fold” to form a tube (neural tube) 3 weeks The neural tube becomes the CNS Axons extending from the neural tube become the PNS Embryology Summary The Development of the Spinal Cord 22 days The neural tube is closed thus producing three layers: Ependymal layer Mantle layer Marginal layer Neurons develop in the mantle layer Axons grow from the mantle layer to the marginal layer Embryology Summary The Development of the Spinal Cord (continued) 23 days Axons form bundles and tracts in the spinal cord © 2012 Pearson Education, Inc. Page 7 of 12 840941469 Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. 7 weeks Ventral roots and dorsal roots develop Glial cells develop Spinal and cranial meninges develop Spinal nerves develop Embryology Summary The Development of the Brain 23 days The cephalic extension forms three brain vesicles Prosencephalon Mesencephalon Rhombencephalon Embryology Summary The Development of the Brain (continued) 4 weeks The rhombencephalon subdivides to form: Metencephalon Myelencephalon The prosencephalon subdivides to form: Telencephalon Diencephalon Embryology Summary The Development of the Brain (continued) 5 weeks Mesencephalon develops Cranial nerves begin to develop 8 weeks Choroid plexus develops Cerebral hemispheres expand 11 weeks Cerebellum develops Embryology Summary The Development of Special Sense Organs 4 weeks Optic bulges appear in the lateral walls of the prosencephalon The bulges indent forming the optic cup The epidermis covering the optic cup forms the lens 5 weeks A pair of thickened areas in the front of the prosencephalon form the olfactory receptors When nerves innervate the tongue, the epithelial cells differentiate to form gustatory cells Embryology Summary The Development of Special Sense Organs (continued) © 2012 Pearson Education, Inc. Page 8 of 12 840941469 Biology 218 – Human Anatomy Lecture Outline Session: FALL Section: 52999 Days / Time: Instructor: MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. 3 weeks Otic regions begin to appear on the lateral sides of the rhombencephalon 4 weeks Deep pockets form in the otic regions, creating otic vesicles 6 weeks The vesicles form the bony labyrinth This process continues until the end of the third month Embryology Summary The Development of the Endocrine System Week 5 Five pharyngeal pouches are formed The pouches form the thymus gland, parathyroid gland, and thyroid gland The pituitary gland forms as a pocket in the pharyngeal area; this ectodermal pocket breaks away from the pharyngeal area and develops just superior to the thyroid gland area Embryology Summary The Development of the Endocrine System Week 5 (continued) After the formation of the neural tube, some neural cells migrate away from the CNS and form an aggregate of cells that become the suprarenal glands Embryology Summary The Development of the Heart Week 2 The heart begins as a pair of tubes in the pharynx area Week 3 The heart begins to pump The tubes fuse forming a one-chambered heart Two large veins bring blood to the heart One large artery carries blood away from the heart; the artery is called the truncus arteriosus Embryology Summary The Development of the Heart (continued) Week 5 The interatrial and interventricular septa begin to form, ultimately forming the four chambers of the heart The foramen ovale and ductus arteriosum form 1 year The foramen ovale and ductus arteriosum have closed (at birth) The remnant of the foramen ovale is the fossa ovalis The remnant of the ductus arteriosum is the ductus ligamentum Embryology Summary © 2012 Pearson Education, Inc. Page 9 of 12 840941469 Biology 218 – Human Anatomy Lecture Outline Session: FALL Section: 52999 MW 5:00 PM – 9:20 PM Days / Time: Instructor: RIDDELL Adapted from Martini Human Anatomy 7th ed. The Development of the Cardiovascular System Week 4 Several aortic arches form and fuse together to form the dorsal aorta Some of the aortic arches disintegrate leaving ultimately just one aortic arch Embryology Summary The Development of the Cardiovascular System Week 4 (continued) Venous circulation begins with the following vessels draining the tissues: Anterior cardinal veins Posterior cardinal veins Subcardinal veins These veins are paired and each pair fuses to form: Superior vena cava Inferior vena cava Embryology Summary The Development of the Cardiovascular System Week 4 (continued) Umbilical arteries carry blood to the placenta Umbilical veins carry blood to the liver Week 12 Right umbilical vein disintegrates Ductus venosus allows some blood to bypass the liver Veins draining the digestive tract fuse to form the hepatic portal vein Embryology Summary The Development of the Lymphoid System Week 7 The thymus gland forms from a pharyngeal pouch The cells lose their attachment and form just inferior to the thyroid gland area Week 8 Numerous lymphatic sacs form throughout the body Embryology Summary The Development of the Respiratory System Week 3 A pulmonary groove forms in the pharynx area Week 4 This groove forms deeper and then forms two blind pouches at the end of the groove The groove forms a tube, which becomes the trachea, and the two blind pouches become the lungs Week 9 The diaphragm forms Embryology Summary © 2012 Pearson Education, Inc. Page 10 of 12 840941469 Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. The Development of the Respiratory System (continued) 3 Months The lung buds continue to branch numerous times 6 Months There are a million branches All the bronchioles are formed 6–9 Months Alveoli begin to form Embryology Summary The Development of the Digestive System Week 3 Yolk sac is formed The layer between the yolk sac and the amniotic sac develops a hindgut and a foregut The hindgut and the foregut form the digestive tube Week 4 Lateral to the digestive tube are cavities called the coelomic cavities The digestive tube is held in position within the midline of the coelomic cavities by the dorsal mesentery and ventral mesentery Embryology Summary The Development of the Digestive System Week 4 (continued) The pancreas is formed within the dorsal mesentery area The liver is formed within the ventral mesentery area Part of the ventral mesentery becomes the falciform ligament of the liver The remaining mesenteric tissue becomes the greater omentum and lesser omentum Embryology Summary The Development of the Digestive System (continued) Week 6 The intestines elongate and coil The yolk sac and the body stalk fuse to form the umbilical cord Embryology Summary The Development of the Urinary System Week 3.5 The kidneys begin as seven pairs of tubules called pronephric tubes Week 6 Branches of the aorta extend toward the pronephric tubes Week 8 The allantois becomes the urinary bladder Week 12 Kidneys begin producing filtrate even though there aren’t any waste products in it © 2012 Pearson Education, Inc. Page 11 of 12 840941469 Biology 218 – Human Anatomy Session: FALL Section: 52999 Days / Time: Instructor: Lecture Outline MW 5:00 PM – 9:20 PM RIDDELL Adapted from Martini Human Anatomy 7th ed. Embryology Summary The Development of the Reproductive System Weeks 3–6 Endodermal cells of the yolk sac migrate to the genital ridges in the abdominal cavity Each ridge consists of columns of cells called primary sex cords; these will further develop into gonads Embryology Summary The Development of the Reproductive System Weeks 3–6 (continued) If the gonad-developing cells are exposed to androgens, a male will develop, regardless of the genetic sex of the embryo If they are not exposed to androgens, a female will develop, regardless of the genetic sex of the embryo The male embryo will begin producing testosterone after week 6, which then directs the development of the external genitalia Embryology Summary Development of the Male Reproductive System Week 7 The primary sex cords proliferate and eventually form the seminiferous tubules within the developing testes Week 10 The urethral folds begin to fuse to form the spongy urethra of the penis This line of fusion can be seen in the adult as the raphe 7 Months The testes descend into the scrotum Embryology Summary Development of the Female Reproductive System Weeks 7–12 Primary sex cords degenerate Primordial germ cells migrate to the genital ridge The urethral folds do not fuse; they become the labia minora Week 10 The ovaries and uterus develop © 2012 Pearson Education, Inc. 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