2 Ovarian events and structures Fig. 11
Primordial follicle with primordial germ calls migrated from the yolk
| . sac
| .
Primary follicle of . At any time during development
oocyte surrounded by ........ a follicle can degenerate, and
follicular cells . most do, becoming an
| . |
| . |
develops under stimulus of . Atresic follicle
FSH of anterior pituitary . |
| . |
Graafian follicle . |
large, fluid-filled, cyst-like . followed by invasion by
| . vessels and CT; if a theca
| . interna was present, it
grows, extends to the surface of forms a temporary glandular
ovary, and bursts at mid-cycle tissue - the
/ | |
/ | Interstitial gland
shedding ovum Empty cavity collapses more obvious in rodents
to be caught Surrounding cells grow than woman; other names are
by the nearby large and glandular, corpus atreticum &
/ forming, under the influence pseudolutein body
/ of pituitary LH, a
Fallopian tube |
|
Corpus luteum
/ \
/ \
grows considerably grows for 12 days
under the influence of only, if the oocyte
placental hCG, if the is not fertilised
oocyte is fertilised |
| |
| |
| |
Corpus luteum Corpus luteum
of pregnancy of menstruation
\ /
\ /
\ /
Glandular cells degenerate, and
fibroblasts form a pale scar-like
\ /
\ /
\ /
Corpus albicans
formed while the cycle starts again
3 Hormonal background
l Dealing with changing structures, either developing or degenerating; with
marked changes in events and appearances at the menarche, when ovarian
cycles begin, and the menopause, when they end.
2 The constant physiological change makes difficult recognizing pathological
changes, e.g., uterine bleeding. Female reproduction is a considerable burden
in its energy demands, e.g., for fat storage and lactation, which can only
be met on an intermittent, i.e., cyclic, basis.
2 FSH and LH/ICSH are pituitary gonadotrophins - hormones with the
gonads as their target organ.
3 Corpus luteum is also influenced by hormones produced by the placenta,
if fertilization has occurred - chorionic gonadotrophins.
4 Distinguish between hormones acting on the gonads, and those produced
by the gonads and acting on other organs, e.g., uterus.
4 Ovarian/menstrual cycle (with details not included in Fig. 11)
l Maturation of oöcyte
2 Development of follicular/granulosa cells and follicle
3 Changes in stroma around maturing follicle
4 Ovulation
5 Corpus luteum: formation, function and fate
2 Myometrium of interwoven smooth muscle, capable of a great hypertrophy during pregnancy, with many blood vessels in the middle stratum vasculare.
3 Mucosa/endometrium with:
l simple, columnar, epithelial lining (some cells ciliated);
2 simple, tubular mucous glands;
3 loose vascular stroma of special fibroblasts, reticular fibres and
much ground substance; some stromal cells can become decidual
around the implantation site;
4 helicine/coiled spiral arteries, a capillary bed, and veins.
4 Mucosa of the sexually mature woman experiences cyclic menstrual
changes, involving all elements and considerable changes in mucosal thickness,
and driven hormonally by the ovary:
l Oestrogens, e.g., oestradiol, from the growing follicle cause cell
proliferation, and an increase in endometrial height.
2 Progesterone, formed by the corpus luteum, then increases cell
secretion and glycogen accumulation, and the stroma dilates with
fluid. The glands coil and sacculate. Spiral arteries continue to
grow up towards the surface.
3 Helicine arteries rhythmically constrict, then dilate, inducing
menstruation or breakdown of the endometrium, altered in the last few days of
the secretory phase by a reduction in progesterone level, and by cytokine
signals for cellular apoptosis. This sloughing of the functional layer
of the endometrium is unaccompanied by blood clotting.
4 Regeneration (physiological) takes place from the basal layer
of the endometrium, where the epithelium survives at the bottom of the glands.
5 The mucosa may experience these cyclic changes minimally, even though no
oocyte was shed from the Graafian follicle - an anovulatory cycle.
5 Uterine cervix differs from the corpus thus:
4 In each lobe are:
2 Nipple
l Cornified stratified squamous epithelium covers a stroma of elastic
fibres, smooth muscle, and collagen, through which pass the lactiferous
ducts.
2 Epithelium is continuous with the somewhat pigmented, glabrous (hairless)
epidermis of the surrounded areola, with its sebaceous glands and
high dermal papillae.
3 The many autonomic nerve fibres to the nipple's smooth muscle
control its rigidity for suckling, and the relaxation of the milk sinuses.
4 Numerous sensory receptors and nerve fibres are present.
3 Histophysiology
l Prepubertal period
.. (a) Nipple remains small and weakly pigmented.
.. (b) Glands stay rudimentary as multiple, branched, tubular units in a CT stroma.
2 Puberty
.. (a) Oestrogen promotes ductal growth, and the formation of stromal
adipose tissue.
.. (b) Increasing levels of progesterone cause some alveoli to bud out
from the duct ends.
3 Early pregnancy
Progesterone and oestrogen cause a marked epithelial proliferation, with
increased branching of ducts, which bud out and form many alveoli; these form
at the expense of stromal tissue.
4 Late pregnancy and post-parturition
6 Post-lactational regression and post-menopausal involution
l Fertilization and blastocyst formation Images - Visembryo
l Oocyte, when penetrated by a spermatozoon (by enzymatic action),
completes its second meiotic/maturation division, with the formation of
another polar body.
2 After one entry, the zona pellucida reacts, becoming impenetrable by other sperm.
3 The condensed sperm head turns itself into the male pronucleus, with reconstitution
of the nuclear membrane and lamina, and of the chromatin.
4 After DNA replication in male and female pronuclei, these fuse, and male
and female chromosomes pair up to give the diploid 46.
5 Over roughly four days, the zygote passes down the uterine tube, dividing to
form a solid mass of cells - the morula.
6 Fluid accumulates amongst the cells resulting in a blastocyst.
7 Blastocyst remains free in the uterine lumen for another two or so days.
8 Blastocyst has an:
.. (a) outer shell of trophoblastic cells;
.. (b) inner cell mass to become the embryo;
.. (c) outermost zona pellucida.
9 Blastocyst sloughs off the zona pellucida, and implants in the
glandular uterine mucosa.
10 Occasional ectopic sites of implantation are the Fallopian tube,
peritoneal cavity, and ovary.
2 Implantation/nidation
l Trophoblastic cells, coming into contact with the uterine epithelium,
attach, proliferate, and invade into the stroma.
2 The blastocystic structure sinks in deeper to become covered by mucosa
(uterine mucosa is henceforth termed decidua).
Mucosa under the
blastocyst is decidua basalis; overlying it is decidua capsularis;
opposite, across the uterine lumen, is the decidua parietalis/vera.
3 Trophoblast encircles the embryonic germ disc, with its amniotic cavity,
yolk sac, and exocoelom.
4 Trophoblast has an inner layer of distinct cells - cytotrophoblast -
and an outer layer of fused cells - syncytiotrophoblast.
5 Syncytiotrophoblast extends out, interrupting maternal blood vessels,
thereby spilling blood into lacunar spaces within its own mass.
3 Formation of the placenta
l Trophoblastic layer proliferates, and takes on an additional
innermost mesenchymal layer, to constitute the chorion.
2 From the chorion, cords of trophoblasts extend out as primary chorionic
villi.
3 Mesenchyme of the extraembryonic mesoblast grows down inside these,
converting them to secondary villi.
4 The villi extend into spaces (intervillous) filled with maternal blood,
replenished via the uterine arteries and veins.
5 Peripherally, the distal tips of anchoring villi, composed of
cytotrophoblasts, unite to form a layer - trophoblastic shell -
covering the uterine decidua cells (except at the openings of maternal blood
vessels).
6 Fetal blood vessels then appear in the cores of the villi, making them
tertiary, or definitive, placental villi.
7 These fetal vessels connect with the body stalk that will form the
umbilical cord to the embryonic vascular system.
8 Later, the villi that have grown all over the chorion: (a) grow and branch
basally to form the chorion frondosum, and eventually the discoidal
placenta;
(b) over the rest of the surface towards the uterine cavity, villi shrink and
disappear (followed by the decidua capsularis) leaving the smooth chorion
laeve.
9 Think of the placenta as two frisbies - chorionic plate and basal plate -
set against each other, face-to-face, creating a space for the maternal blood
and foetal villi.
On slides, the chorionic plate resembles umbilical cord, but on the uterine
side the thin basal plate has separated from the myometrium.
4 Placental villi
l Free villi branch out extensively from each stem villus. The whole
branching unit constitutes one of the fetal cotyledons.
2 Each tertiary villus has an:
5 Maternal-fetal junction
l Trophoblastic shell becomes the foetal part of the basal plate, in
contact with the maternal decidua basalis.
2 Plate subdivides into units - maternal cotyledons - separated by
septa, with perforations allowing some lateral passage of blood.
3 Blood spurts up out of the basal plate from spiral arteries into
the intervillous space, and drops down into venous outlets.
4 The chorionic plate faces the basal plate as the other boundary to
the space for maternal blood. Just below the chorionic plate, where the septa
do not reach, is the open space of the subchorial lake.
5 Cytotrophoblasts persist in the basal plate, as cell islands, and in
the septa, and are often embedded in an eosinophilic, non-fibrous, intercellular
material - fibrinoid.
Basal fibrinoid provides a cleavage plane for separation of the
placenta at term.
6 Maternal decidua cells are large, with lipid and glycogen, lie in a
rich ground substance with reticular fibres, and perform steroid conversions.
7 Granulated endometrial-gland cells (K/Körnchenzellen) are an endometrial
kind of leucocyte, with acidophil granules. Present in the late secretory
phase, their numbers increase in the first-trimester decidua, so they may
somehow assist implantation.
6 Umbilical cord
l Enveloped in amnion and covered by simple, cuboidal, amniotic
epithelium, it consists of mucous CT - Wharton's jelly: a
gelatinous ground substance, with sparse collagen bundles and stellate
fibroblasts.
2 Located in the jelly are three umbilical blood vessels:
.. (a) One vein, with much muscle, but without valves and vasa vasorum.
.. (b) Two arteries, with thick, inner, longitudinal, and outer
circular muscle coats, no internal elastic lamina, and an insignificant
adventitia.
3 The jelly, the thick vessel walls, and their spiral course prevent kinking
and occlusion of the vessels.
4 Remnants of the (a) allantoic endoderm, and (b) yolk sac's stalk, with
vitelline vessels, may persist until quite late in pregnancy.