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Kharkov National Medical University Department of Histology Female Reproductive System Part II (placenta, mammary glands) Placenta Implantation • By that time embryo is a blastocyst consisting of embryoblast and trophoblast. • In the trophoblast Implantation. • Blastocyst Cavity Syncytiotrophoblast Cytotrophoblast two distinct layers are formed. The outer layer is called syncytiotrophoblast, the inner one – cytotrophoblast. Inner Cell Mass Villi • The syncytiotrophoblast grows rapidly and forms villi. • Villi, consisting of cytotrophoblast and syncytiotrophoblast, are called primary villi. • Later the extraembryonic mesoderm lines the inside of the trophoblast, which now is called chorion. • The chorionic mesoderm grows into the primary villi, forming a central core of loose connective tissue. Such villus is called a secondary villus. • When blood vessels appear in the mesoderm core of each villus, which now called a tertiary villus. implanted gastrula • If fertilization and implantation occur -- a gravid phase (pregnancy) replaces the menstrual phase. After the implantation of the embryo, the endometrium is called the decidua (= sloughing). • The portion of the decidua that underlies the implantation site is called the decidua basalis. • The portion that separates the embryo from the uterine lumen is called the decidua capsularis. • The portion lining the rest of the uterine cavity is called the decidua parietalis. • Villi related to the decidua capsularis begin to degenerate. This chorionic surface is called the chorion laeve. • The villi that grow into the decidua basalis undergo considerable development due to presence of blood supply. This chorionic surface is called chorion frondosum. • The decidua basalis with chorion frondosum forms a disc-shaped mass called placenta. After the birth of the child the placenta is shed off along with decidua. • Placenta consists of fetal portion and maternal portion: maternal portion includes • 10) basal plate (decidua basalis), • 8) septa, • 6) lacuna filled by maternal blood. • fetal portion includes • 7) chorionic plate and • 4) tertiary villi with their structural elements. Placenta is subdivided by connective tissue septa into a number of lobes, called cotyledons. Some villi are attached to the endometrium - anchoring villi. In the placenta maternal and fetal blood do not mix with each other. They are separated by a membrane or placental barrier placental barrier consists of : • Endothelium of the fetal blood vessels and its basement membrane. • Connective tissue surrounding these vessels. • Cytotrophoblast with its basement membrane. • Syncytiotrophoblast. Mammary glands Mammary gland are modified glands of the skin • They are compound • • branched alveolar glands, which consist of 1525 lobes separated by dense interlobar connective tissue and fat. Mammary gland • The excretory duct of • each lobe, also called lactiferous duct, has its own opening on the nipple. Beneath the nipple, the dilated lactiferous duct forms a lactiferous sinus , which functions as a reservoir for the milk. • The lactiferous duct has a two layered epithelium - basal cells are cuboidal whereas the superficial cells are columnar. Mammary gland • The secretory units • are alveoli are lined by a cuboidal or columnar epithelium. A layer of myoepithelial cells is always present between the epithelium and the basement membrane. • Pregnancy induces a considerable growth of the epithelial parenchyma leading to the formation of new terminal branches of ducts and of alveoli in the first half of pregnancy. • Growth is initiated by the elevated levels of estrogen and progesterone produced in the ovaries and placenta. Inactive mammary gland: duct system The continued growth of the mammary glands during the second half of pregnancy is due to increases in the height of epithelial cells and an expansion of the lumen of the alveoli. • They contain a protein-rich (large amounts of immunoglobulins) eosinophilic secretion - the colostrum or foremilk). Active mammary gland: duct & secretory cells Mammary gland • Secretion of milk proteins proceeds by exocytosis (merocrine secretion), whereas lipids are secreted by apocrine secretion. • Secretion is stimulated by prolactin. Passive diffusion (H2O/ions); protein (merocrine) lipid (apocrine) Lactating gland • Prolactin secretion in turn is stimulated by sensory stimulation of the nipple, which also initiates the so-called milk ejection reflex via the secretion of oxytocin from the neurohypophysis. • Milk is ejected from the glandular tissue into the lactiferous sinuses - now it's up to the baby to get things out. Ovogenesis consists of three stages • First stage - stage of division - occurs early in embryogenesis, when primordial germ cells migrate from the yolk sac endoderm to the genital ridge in developing ovary where they take up residence and are called oogonia. Ovogenesis • Diploid oogonia • undergo several mitotic divisions prior to or shortly after parturition. When oogonia begin the first meiotic division, they are called primary oocytes. • Second stage - stage of growth. • Primary oocytes are arrested in • • • • prophase of Meiosis I (exactly diplotene) until the female reaches sexual maturity. They grow in size during this arrested phase, but do not divide. During Menstrual Cycle a small number of primary oocytes are stimulated by FSH to continue through Meiosis I: the number of chromosomes is reduced from the diploid number (2N) to the haploid number (1N). After a primary oocyte completes the first meiotic division, it is called a secondary oocyte (with 1N of chromosomes number, but 2 chromatids). Ovogenesis Ovogenesis • ! NOTE: chromosomes are divided equally, • but most of the cytoplasm stays with the one cell secondary oocyte. • The smaller first polar body contains half the chromosomes but only a small amount of cytoplasm and will eventually degenerate. • !! NOTE: Meiosis I is completed just before ovulation (release of the ovum from the ovary). Ovogenesis • The secondary oocyte immediately begins the second meiotic division that is arrested at the methaphase and completed only if secondary oocyte is penetrated by a spermatozoon. • The secondary oocyte remains viable for 24 hours. If a secondary oocyte is not penetrated by a sperm, it will degenerate. Ovogenesis Ovogenesis • If fertilization occurs the • secondary oocyte is stimulated to continue through Meiosis II, forming a second polar body and a mature ovum (1N). Again, the polar body contains half of the chromosome material, but little cytoplasm, and it eventually degenerates. The stage of formation is absent in the oogenesis.