Human Reproduction- 2 Flashcards
describe the ovaries
Ovaries are the primary female sex organs that produce the female
gamete (ovum) and several steroid hormones (ovarian hormones).
The ovaries are located one on each side of the lower abdomen
(Figure 2.3b). Each ovary is about 2 to 4 cm in length and is connected to
the pelvic wall and uterus by ligaments. Each ovary is covered by a thin
epithelium which encloses the ovarian stroma. The stroma is divided into
two zones – a peripheral cortex and an inner medulla.
what are the accessory ducts?
describe fallopian tube/ oviduct
The oviducts (fallopian tubes), uterus and vagina constitute the female
accessory ducts. Each fallopian tube is about 10-12 cm long and extends
from the periphery of each ovary to the uterus (Figure 2.3b), the part closer
to the ovary is the funnel-shaped infundibulum. The edges of the
infundibulum possess finger-like projections called fimbriae, which help in
collection of the ovum after ovulation. The infundibulum leads to a wider part of the oviduct called ampulla. The last part of the oviduct, isthmus has
a narrow lumen and it joins the uterus
describe the uterus
The uterus is single and it is also called womb. The shape of the uterus
is like an inverted pear. It is supported by ligaments attached to the pelvic
wall. The uterus opens into vagina through a narrow cervix. The cavity of
the cervix is called cervical canal (Figure 2.3b) which alongwith vagina
forms the birth canal. The wall of the uterus has three layers of tissue. The
external thin membranous perimetrium, middle thick layer of smooth
muscle, myometrium and inner glandular layer called endometrium that
lines the uterine cavity. The endometrium undergoes cyclical changes during
menstrual cycle while the myometrium exhibits strong contraction during
delivery of the baby.
describe the external female genitalia
The female external genitalia include mons pubis, labia majora, labia
minora, hymen and clitoris (Figure 2.3a). Mons pubis is a cushion of fatty
tissue covered by skin and pubic hair. The labia majora are fleshy folds of
tissue, which extend down from the mons pubis and surround the vaginal
opening. The labia minora are paired folds of tissue under the labia majora.
The opening of the vagina is often covered partially by a membrane called
hymen. The clitoris is a tiny finger-like structure which lies at the upper
junction of the two labia minora above the urethral opening. T
describe the hymen
The hymen is
often torn during the first coitus (intercourse). However, it can also be broken
by a sudden fall or jolt, insertion of a vaginal tampon, active participation
in some sports like horseback riding, cycling, etc. In some women the hymen
persists even after coitus. In fact, the presence or absence of hymen is not
a reliable indicator of virginity or sexual experience.
describe the mammary glands
A functional mammary gland is characteristic of all female mammals.
The mammary glands are paired structures (breasts) that contain
glandular tissue and variable amount of fat. The glandular tissue of each
breast is divided into 15-20 mammary lobes containing clusters of cells
called alveoli (Figure 2.4). The cells of alveoli secrete milk, which is stored
in the cavities (lumens) of alveoli. The alveoli open into mammary tubules.
The tubules of each lobe join to form a mammary duct. Several mammary
ducts join to form a wider mammary ampulla which is connected to
lactiferous duct through which milk is sucked out.
what are oogonia? when are they formed? explain when the oogenesis starts?
The process of formation of a mature female gamete is called oogenesis
which is markedly different from spermatogenesis. Oogenesis is initiated
during the embryonic development stage when a couple of million gamete
mother cells (oogonia) are formed within each fetal ovary; no more oogonia
are formed and added after birth. These cells start division and enter into
prophase-I of the meiotic division and get temporarily arrested at that stage,
called primary oocytes. Each primary oocyte then gets surrounded by a
layer of granulosa cells and is called the primary follicle
explain the state of oocyte during puberty
A
large number of these follicles degenerate during the phase from birth to
puberty. Therefore, at puberty only 60,000-80,000 primary follicles are
left in each ovary. The primary follicles get surrounded by more layers of
granulosa cells and a new theca and are called secondary follicles.
describe the tertiary follicle and first meiotic division
i) The secondary follicle soon transforms into a tertiary follicle which is
characterised by a fluid filled cavity called antrum.
ii)The theca layer is
organised into an inner theca interna and an outer theca externa.
iii) it is at this stage that the primary
oocyte within the tertiary follicle grows in size and completes its first meiotic
division.
iv)It is an unequal division resulting in the formation of a large
haploid secondary oocyte and a tiny first polar body. The secondary oocyte retains bulk of the
nutrient rich cytoplasm of the primary
oocyte. The first polar body may divide further or degenerate.
describe the graafian follicle
The tertiary
follicle further changes into the mature
follicle or Graafian follicle (Figure 2.7).
The secondary oocyte forms a new
membrane called zona pellucida
surrounding it. The Graafian follicle now
ruptures to release the secondary oocyte
(ovum) from the ovary by the
process called ovulation
define menstrual cycle
The reproductive cycle in the female primates (e.g. monkeys, apes and
human beings) is called menstrual cycle. The first menstruation begins
at puberty and is called menarche. In human females, menstruation
is repeated at an average interval of about 28/29 days, and the cycle of
events starting from one menstruation till the next one is called the
menstrual cycle.
One ovum is released during each menstrual cycle
describe the menstrual phase
The cycle starts with the menstrual phase, when
menstrual flow occurs and it lasts for 3-5 days. The menstrual flow
results due to breakdown of endometrial lining of the uterus and its
blood vessels which forms liquid that comes out through vagina.
Menstruation only occurs if the released ovum is not fertilised. Lack of
menstruation may be indicative of pregnancy. However, it may also be
caused due to some other underlying causes like stress, poor health etc.
describe the follicular phase
The menstrual phase is followed by the follicular phase. During
this phase, the primary follicles in the ovary grow to become a
fully mature Graafian follicle and simultaneously the endometrium
of uterus regenerates through proliferation. These changes in the
ovary and the uterus are induced by changes in the levels of
pituitary and ovarian hormones
describe hormonal control of menstrual cycle
The secretion of gonadotropins (LH and FSH) increases gradually during the follicular
phase, and stimulates follicular development as well as secretion of
estrogens by the growing follicles. Both LH and FSH attain a peak level
in the middle of cycle (about 14th day). Rapid secretion of LH leading to
its maximum level during the mid-cycle called LH surge induces rupture
of Graafian follicle and thereby the release of ovum (ovulation).
describe the luteal phase
The
ovulation (ovulatory phase) is followed by the luteal phase( secretory phase) during which
the remaining parts of the Graafian follicle transform as the corpus
luteum (Figure 2.9). The corpus luteum secretes large amounts of
progesterone which is essential for maintenance of the endometrium.
Such an endometrium is necessary for implantation of the fertilised
ovum and other events of pregnancy. During pregnancy all events of
the menstrual cycle stop and there is no menstruation. In the absence
of fertilisation, the corpus luteum degenerates. This causes disintegration
of the endometrium leading to menstruation, marking a new cycle.
