Kharkov National Medical University Department of Histology Female Reproductive System Part II (placenta, mammary glands)

Kharkov National Medical Kharkov National Medical UniversityUniversity

Department of HistologyDepartment of Histology

Female Reproductive SystemFemale Reproductive System

Part IIPart II(placenta, (placenta,

mammary glands)mammary glands)

PlacentaPlacenta

IImplantationmplantation

•By that time By that time embryo is a embryo is a blastocystblastocyst consisting of consisting of embryoblastembryoblast and and trophoblasttrophoblast..

IImplantation. mplantation.

• In the trophoblast In the trophoblast two distinct layers two distinct layers are formed. are formed.

• The outer layer is The outer layer is called called syncytiotrophoblassyncytiotrophoblastt, the inner one – , the inner one – cytotrophoblastcytotrophoblast..

Blastocyst Cavity

Cytotrophoblast

Inner CellMass

Syncytiotrophoblast

VilliVilli•The syncytiotrophoblast The syncytiotrophoblast

grows rapidly and forms grows rapidly and forms villivilli..

•Villi, consisting of Villi, consisting of cytotrophoblast and cytotrophoblast and syncytiotrophoblast, are called syncytiotrophoblast, are called primaryprimary villi. villi.

•Later the extraembryonic Later the extraembryonic mesoderm lines the inside of the mesoderm lines the inside of the trophoblast, which now is called trophoblast, which now is called chorionchorion. .

•The chorionic mesoderm grows into The chorionic mesoderm grows into the the primary villiprimary villi, forming a central , forming a central core of loose connective tissue. core of loose connective tissue. Such villus is called a Such villus is called a secondary secondary villusvillus. .

•When When blood vessels appearblood vessels appear in the in the mesoderm core of each villus, which mesoderm core of each villus, which now called a now called a tertiarytertiary villus villus..

implanted gastrula

• If fertilization and implantation occur -- a If fertilization and implantation occur -- a gravidgravid phasephase ( (pregnancy) replaces the pregnancy) replaces the menstrual phase.menstrual phase.

After the implantation of the After the implantation of the embryo, the endometrium is embryo, the endometrium is called called the the deciduadecidua (= (= sloughingsloughing).).

• The portion of the decidua that underlies the The portion of the decidua that underlies the implantation site is called implantation site is called the decidua the decidua basalisbasalis. .

• The portion that separates the embryo from The portion that separates the embryo from the uterine lumen is called the uterine lumen is called the the decidua decidua capsulariscapsularis..

• The portion lining the rest of the uterine The portion lining the rest of the uterine cavity is called cavity is called the the decidua parietalis.decidua parietalis.

• Villi related to the Villi related to the decidua capsularisdecidua capsularis begin to degenerate. This chorionic begin to degenerate. This chorionic surface is called the surface is called the chorion laevechorion laeve. .

• The villi that grow into the The villi that grow into the decidua decidua basalisbasalis undergo considerable undergo considerable development due to presence of development due to presence of blood supply. This chorionic surface blood supply. This chorionic surface is called is called chorion frondosumchorion frondosum. .

•The decidua basalis with chorion frondosum The decidua basalis with chorion frondosum forms a disc-shaped mass called forms a disc-shaped mass called placentaplacenta..

After the birth of the child the placenta is shed After the birth of the child the placenta is shed off along with deciduaoff along with decidua..

•Placenta consists of fetal portion and maternal portion:

maternal portion maternal portion includes includes

•10) basal plate 10) basal plate (decidua (decidua basalis), basalis),

•8) septa, 8) septa,

•6) lacuna filled 6) lacuna filled by maternal by maternal blood. blood.

•fetal portion fetal portion includesincludes

• 7) chorionic 7) chorionic plate and plate and

•4) tertiary villi 4) tertiary villi with their with their structural structural elements. 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 In the placenta maternal and fetal maternal and fetal blood blood do not mixdo not mix with each other. with each other.

They are separated They are separated by a membrane or by a membrane or placental barrierplacental barrier

placental barrier placental barrier consists of :consists of :

• Endothelium of the Endothelium of the fetal blood vessels fetal blood vessels and its basement and its basement membrane.membrane.

• Connective tissue Connective tissue surrounding these surrounding these vessels.vessels.

• Cytotrophoblast Cytotrophoblast with its basement with its basement membrane.membrane.

• SyncytiotrophoblasSyncytiotrophoblast.t.

Mammary glandsMammary glands

Mammary gland are modified Mammary gland are modified glands of the skin glands of the skin

• They are They are compound compound branched alveolar branched alveolar glands,glands,

• which consist of 15-which consist of 15-25 lobes 25 lobes

• separated by dense separated by dense interlobar interlobar connective tissue connective tissue and fat. and fat.

Mammary glandMammary gland• The excretory duct of The excretory duct of

each lobe, also called each lobe, also called lactiferous ductlactiferous duct, has , has its own opening on its own opening on the nipple. the nipple.

• Beneath the nipple, Beneath the nipple, the dilated lactiferous the dilated lactiferous duct forms a duct forms a lactiferous sinuslactiferous sinus , , which functions as a which functions as a reservoir for the milk. reservoir for the milk.

• The lactiferous duct The lactiferous duct has a two layered has a two layered epithelium - epithelium - basalbasal cells are cells are cuboidalcuboidal whereas the whereas the superficial cells are superficial cells are columnar. columnar.

Mammary glandMammary gland

• The secretory units The secretory units are alveoli are are alveoli are lined by a lined by a cuboidal cuboidal or columnaror columnar epithelium. epithelium.

• A layer of A layer of myoepithelial cellsmyoepithelial cells is always present is always present between the between the epithelium and the epithelium and the basement basement membrane. membrane.

• Pregnancy induces a considerable Pregnancy induces a considerable growth of the epithelial parenchyma growth of the epithelial parenchyma leading to the formation of new leading to the formation of new terminal branches of ducts and of terminal branches of ducts and of alveoli in the alveoli in the firstfirst half of pregnancy. half of pregnancy.

• Growth is initiated by the elevated Growth is initiated by the elevated levels of estrogen and progesterone levels of estrogen and progesterone produced in the ovaries and placenta. produced in the ovaries and placenta.

Inactive mammary gland: duct system

The continued growth of the mammary The continued growth of the mammary glands during the glands during the secondsecond half of half of pregnancy is due to increases in the pregnancy is due to increases in the height of epithelial cells and an height of epithelial cells and an expansion of the lumen of the alveoli. expansion of the lumen of the alveoli.

• They contain a protein-rich (large They contain a protein-rich (large amounts of immunoglobulins) amounts of immunoglobulins) eosinophilic secretion - the colostrum or eosinophilic secretion - the colostrum or foremilk).foremilk).

Active mammary gland: duct & secretory cells

Mammary glandMammary gland

• Secretion of milk proteins proceeds Secretion of milk proteins proceeds by exocytosis (merocrine secretion), by exocytosis (merocrine secretion), whereas lipids are secreted by whereas lipids are secreted by apocrine secretion. apocrine secretion.

• Secretion is stimulated by prolactin. Secretion is stimulated by prolactin.

Passive diffusion (H2O/ions); protein (merocrine) lipid (apocrine)

Lactating glandLactating gland

• Prolactin secretion in turn is stimulated Prolactin secretion in turn is stimulated by sensory stimulation of the nipple, by sensory stimulation of the nipple, which also initiates the so-called which also initiates the so-called milk milk ejection reflexejection reflex via the secretion of via the secretion of oxytocin from the neurohypophysis. oxytocin from the neurohypophysis.

• Milk is ejected from the glandular Milk is ejected from the glandular tissue into the lactiferous sinuses - now tissue into the lactiferous sinuses - now it's up to the baby to get things out.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.

Ovogenesis

• 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

• ! 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.