Transcript placenta, mammary glands

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.