Ovarian cycle Ovarian cycle Menstrual cycleMenstrual cycle

PlacentationPlacentation

Department of the Histology, Cytology and EmbryologyDepartment of the Histology, Cytology and Embryology

Tatiana GlobaTatiana Globa

State University of Medicine and Pharmacy “Nicolae Testemitanu”State University of Medicine and Pharmacy “Nicolae Testemitanu”

Ovarian cycle has 2 phasesOvarian cycle has 2 phases

• FOLLICULAR PHASEFOLLICULAR PHASE – consists of the development of a primordial follicle into a mature or Graafian follicle

• LUTEAL PHASELUTEAL PHASE – consists of the formation of the corpus luteum, a major-secreting gland

• At the middle of the ovarian cycle the OVULATIONOVULATION takes place

Follicular Phase Luteal Phase

Endocrine Controlof Follicular Development &Ovulation

GnRH

(12 hrs. after LH peak)

-

Inhibin

Fate of Corpus Luteum (CL)without fertilization

• FSH and LH release is inhibited by the progesterone and estradiol released by the CL

• Without LH, the CL lasts for ~14 days before it degenerates

GnRH

LH maintains thecorpus luteum

Progesterone &estrogen from CLinhibits GnRH, slowing the release of FSH and LH

Without LH, the CL degenerates

Junqueira et al. 8th ed. Appleton and Lange

X X

Fate of Corpus Luteum Fate of Corpus Luteum withwith fertilization & implantationfertilization & implantation

• Chorionic gonadotropinChorionic gonadotropin (hCG) produced by the placenta will support the CL for ~ 6 months

• also estrogen, IGF-I and II (from ovary), LH, prolactin (from ant. pituitary) and insulin contribute to formation and maintenance

• CL grows to a diameter of 5 cm

• Continues to secrete progesterone

• Decreases in size during last 3 months

• Begins to secrete relaxin in preparation for birth

Menstrual cycle Menstrual cycle The endometrium is directly controlled by

OVARIAN hormones (estrogen, progesterone), not by pituitary hormones

Menstrual cycle has 3 phases:

• Proliferative phaseProliferative phase is regulated by estrogens

• Secretory phaseSecretory phase is under the control of progesterone

• Menstrual phaseMenstrual phase results from a decline in the ovarian secretion of progesterone & estrogens

StratumFunctionalis

Stratum Basalis

Myometrium

Endometrium

(glands present;dependent on ovarian hormones for appearance &maintenance)

Uterine lumen

ArcuateArteries(myometrium)

Uterine artery

Spiral arteries(in endometrium – dependent onovarian hormones for growth &maintenance)

Vascular Supply of Myometrium & EndometriumVascular Supply of Myometrium & Endometrium

Spiral arteries: dependentupon estradiol for growth,progesterone formaintenance

Capillary bed with dilated portions of capillary wall (lacunae)

PROLIFERATIVE

PHASE

(days 4 – 14 of cycle)

MENSTRUAL CYCLE

4

Proliferative phase

- under control of estradiol (follicular phase of ovarian cycle)

- glands in s. basalis under go mitosis

- stroma, glands, spiral arteries grow toward lumen

s. basalis

Proliferative phase: day 4 – day 14 of menstrual cycle

Hormonal control of endometrial changes during the menstrual

cycle:

SECRETORY PHASESECRETORY PHASE

(days 14 – 28 of cycle)

Secretory phase

- under control of progesterone (luteal phase of ovarian cycle

- uterine glands coiled, larger lumens

- secrete glycogen, mucin

Secretory phase: day 14 – 28 of menstrual cycle

Gestational hyperplasiaProliferative: day 9 Secretory: day 15 Secretory: day19

Pregnancy

Hormonal control of endometrial changes during

the menstrual cycle:

MENSTRUAL PHASEMENSTRUAL PHASE

(days 1 – 4 of cycle)

Menstruation

At end of luteal phase of ovarian cycle,Progesterone Spiral arteries to constrict

Menstrual phaseMenstrual phase

- the involution of the corpus luteum results from a decrease in blood levels of steroid hormones, leading to an ischemic phase.

- a reduction in the normal blood supply-causing intermittent ischemia-and the consequent hypoxia determine the necrosis of the functional layer of the endometrium, which sloughs off during the menstrual phase.

Blastocyst

Blastocyst = inner cell mass (embryo) +

outer shell (trophoblast)

Fertilization1

2

3

4

56

7

8

9

Morula

Placenta

Implanted in the wall of the uterus

Composed of fetal portion (chorion) and maternal portion (decidua)

Exchange of gases, nutrients waste products without any mixing of maternal & fetal blood

Functions of placenta

Act as • respiratory organ• excretory organ• nutritive organ• protective organ• endocrine organ (progesterone, estrogens,

human chorionic gonatotropin, melanin spreading factor, other hormones also manufactured by the hypothalamus & pituitary.

This is a circumvallate placenta in which the membranes double back for a short distance over the fetal surface when the chorionic plate is too small. There may be increased fetal loss with this condition.

                         

             

The maternal surface of a normal term placenta is seen here. Note that the cotyledons that form the placenta are reddish brown and indistinct.

                         

             

Placenta • The morpho-functional unit is cotyledon. Placenta

has about 15-25 cotyledons.

• Proliferation of the trophoblast, growth of chorionic mesoderm & blood vessel development give rise to:

- primary chorionic villi – a mass of cells

- secondary villi – composed of a core of mesenchyme surrounded by an inner layer of cytotrophoblast & an outer layer of syncytiotrophoblast

- tertiary villi – blood vessels have developed in the cores

Inner cell mass(embryo)

Uterine lumen

Syncytiotrophoblast secretes proteolytic enzymes

Maternal decidua

9 days

Maternal capillary

Uterine lumen

Maternal decidua

Maternal blood enters lacunae

Uterine gland

Syncytiotrophoblast

Uterine lumen

Extraembryonic mesoderm

Cytotrophoblast

Maternal decidua

Blastocyst is now completely embedded Blastocyst is now completely embedded within the endometriumwithin the endometrium

Cytotrophoblast grows into syncytiotrophoblast:

(Maternal decidua)

Extraembryonic mesoderm invades primary villi:

Maternal decidua

(Intervillous spaces)

Fetal vessels grow into secondary villi:

Outer cytotrophoblast shell

Maternal decidua

21 daysMaternal decidua

Human Embryology, Larsen, 1993 Churchill Livingstone

Fetal

Maternal

Small tertiary villi will sprout from larger ones to increase surface area for exchange

Placenta – low magnification = Intervillous space (maternal blood)

Villus from early pregnancy (during 3rd month)

Cytotrophoblast Syncytiotrophoblast

Mesenchyme (embryonic CT)

Fetal capillaries

Villi from late pregnancy – 7th monthBy 4th month, cytotrophoblast begins to thin out and is no longer obvious

syncytial knot

Placental barrier

• Syncytiotrophoblast

• Cytotrophoblast

• Basement membrane of trophoblast

• Connective tissue of the chorionic villus

• Basement membrane of endothelium

• Cytoplasm of endothelial cell

Placental Barrier

Intervillous space(maternal blood)

O2, H2O,electrolytes,carbohydrates,lipids, proteins,antibodies

CO2, H2O, hormones,metabolic wasteproducts

Placental structure and vascular dynamics

Fetal side

Maternal side

Placental HormonesSyncytiotrophoblast secretes:1. Human chorionic gonadotropin (HCG)

- detected 6 days after ovulation (pregnancy test)- keeps CL alive

2. Placental lactogen – lactogenic and growth stimulating properties for mammary gland (a.k.a. hCS: human chorionic somatomammotropin)

3. Estradiol (made in cooperation with fetal adrenal cortex)4. Progesterone

Cytotrophoblast also secretes:

IGF I and II; various other growth factors that stimulatecytotrophoblast growth, plus hCG, estradiol, progesterone

Fetal portion ofthe placenta = CHORION

1. chorionic plate2. chorion frondosum (villi)3. chorion laeve (villi that were here earlier have degenerated)

Chorionic plate

Ham and Cormack, 8th ed. J.B.Lippencott

Maternal portion ofthe Placenta = DECIDUA

1. Decidua basalis2. Decidua capsularis3. Decidua parietalis

Ham and Cormack, 8th ed. J.B.Lippencott

Decidual cells – glycogen, lipid for early embryonic nourishment; later, produce decidual prolactin (trophic effects on CL), prostaglandins

(prevent immunologic rejection of fetus)of fetus), relaxin (dilates cervix and softens pubic symphysis)

upper portion of decidua (near fetus)

Giant cells: multinucleated, trophoblast derivativesthat migrate into the decidua. Establish cleavage plane for separation of placenta from endometrium after birth.

Fusion by 5th month

(form cotyledons(form cotyledons

Placental septae