Reproduction Flashcards
Describe the location, structure and function(s) of the components of the male reproductive system.
a) Testes
b) scrotum
c) scrotum
d) epididymis
e) ductus (vas) deferens
f) ejaculatory duct
g) urethra
h) seminal vesicles
i) prostate gland
j) bulbourethral (Cowper’s) gland
k) penis
Describe the location, structure and function(s) of the components of the female reproductive system.
a) Ovaries
b) fallopian tube
c) uterus
d) cervix
e) vagina
f) greater vestibular (Bartholin’s) glands
g) lesser vestibular (Skene’s) glands
h) clitoris
Describe the roles of FSH, LH, and testosterone or estrogens in the male and female reproductive systems.
LH stimulates the Leydig cells in the testes to produce testosterone. FSH indirectly stimulates the spermatogenic cells in the testes to initiate sperm production.
The ovarian cycle is regulated by a hormone from the hypothalamus, GnRH, two hormones from the anterior pituitary gland, FSH and LH, and two hormones from the ovary, oestrogen and progesterone.
Describe the mechanism, stages, and anatomical pathway of sperm release and ovum release.
Sperm are stored in the ampulla of the vas deferens and released by ejaculation. The process of ejaculation involves two stages:
a) Emission: Involves peristaltic contraction of the vas deferens, seminal vesicles, prostate and ejaculatory duct. In the ejaculatory duct, sperm are mixed with seminal and prostatic fluid to form semen which enters the urethra.
b) Expulsion: Involves the powerful contraction of the urethral and penile musculature which forces semen out through the external urethral orifice.
The entire ejaculatory event is called ‘climax’ or ‘orgasm’ and is followed by ‘resolution’, a period of muscular and psychological relaxation.
Describe the ovarian cycle as well as the role of the hypothalamus and anterior pituitary gland in this cycle.
The approximately 28-day cycle of development in the ovary during and after the maturation and release of an oocyte is known as the ovarian cycle
Hormones produced by the ovary during the ovarian cycle regulate the uterine (menstrual) cycle, which is the development and eventual shedding of the uterine lining (menstruation).
On day 1 of the regular 28-day ovarian cycle, the hypothalamus secretes GnRH, which stimulates the anterior pituitary to secrete FSH. FSH causes a few primary follicles to begin development. On day 4 or 5 (i.e. towards the end of the menstrual phase of the uterine (menstrual) cycle), all primary follicles except one degenerates and usually there is one secondary follicle left.
Between days 6 and 13, the amount of fluid in the follicle increases, and the oocyte is pushed to one side. The follicle produces oestrogen. Moderate levels of oestrogen inhibit GnRH secretion, thereby inhibiting FSH and LH secretion.
Towards the end of the follicular phase (near day 14), high oestrogen levels stimulate GnRH secretion, which results in stimulation of FSH and LH secretion. LH is effective at this time.
On day 14, the high level of LH hormone results in ovulation. The mature (Graafian) follicle bursts and an oocyte is shed from the ovary. The ruptured follicle becomes the corpus luteum (yellow body). The corpus luteum produces high levels of progesterone and moderate levels of oestrogen.
Describe the uterine (menstrual) cycle as well as the names and sources of any hormones involved.
a) The menstrual phase is about 5 days long. It is associated with low levels of oestrogen and progesterone in the blood.
b) The proliferation phase occurs from day 6 to 13. During the development of the follicle, oestrogen is produced. The functionalis layer of the endometrium is being reformed as a result of the presence of oestrogen in the blood.
c) Ovulation, which is part of the ovarian cycle (not the uterine (menstrual) cycle), then occurs on day 14. Following ovulation, the corpus luteum produces moderate levels of oestrogen and high levels of progesterone
Correlate the ovarian and uterine (menstrual) cycles and explain their integrated hormonal regulation.
The five main hormones involved in the uterine (menstrual) and ovarian cycles are progesterone, oestrogen, GnRH, FSH and LH. High oestrogen levels stimulate FSH production and stimulate LH production. High progesterone and moderate oestrogen levels produced by the corpus luteum inhibits GnRH, which results in no LH or FSH production. When the corpus luteum degenerates (if no implantation occurs), the low oestrogen and progesterone levels stimulate GnRH production.
Describe the roles of the corpus luteum and placenta if pregnancy occurs.
If fertilisation of an oocyte has taken place and the blastocyst becomes implanted, the corpus luteum does not degenerate. Upon implantation, the developing placenta produces human chorionic gonadotrophic (hCG) hormone, which serves to maintain the corpus luteum which then continues producing progesterone and oestrogen. This maintains the uterus in its receptive state and prevents menstruation.
After about four months, the placenta is well developed, produces oestrogen and progesterone and stops producing hCG. The corpus luteum then begins to degenerate, due to the cessation of hCG production. However, the placenta produces oestrogen and progesterone, so the corpus luteum is no longer necessary.
Distinguish between morula and blastocyst.
a) Morula
The first event is the formation of the morula, a solid ball of cells. It is formed by
cleavage. A single-celled zygote divides, or cleaves, into 2 cells, then 4 cells, then 8 cells, etc., until it becomes a solid ball. Each small cell in the morula is called a blastomere.
b) Blastocyst
About 4 or 5 days after fertilisation, it enters the uterine cavity and the once solid morula is now a hollow ball of cells, called a blastocyst. It has an outer covering of cells consisting of a single layer of cells (the trophoblast) and an inner cell mass. The internal fluid-filled cavity of the blastocyst is called the blastocoel.
Implantation
Implantation is the next stage, in which the blastocyst attaches to the endometrium (inner lining of the uterus). This usually occurs 7 to 8 days after fertilisation. During implantation, the trophoblast produces an enzyme which enables the blastocyst to penetrate the uterine lining and become buried in the endometrium, and eventually develop into an embryo.
Identify the three primary germ layers and which body parts they develop into.
There are two layers of cells between the two cavities, which form the embryonic disc. The upper layer of cells in the embryonic disc is the ectoderm; the lower layer is the endoderm. Certain cells start migrating into the embryonic disc between the two layers, forming the mesoderm.
The primary germ layers are the ectoderm, the endoderm and the mesoderm. The ectoderm develops into the skin and the entire nervous system (e.g. brain, spinal cord).
The endoderm develops into the epithelium lining of the intestinal tract, and the epithelium of the organs that develop from the intestinal tract (e.g. trachea, lungs, gallbladder).
The mesoderm develops into muscles, bones and all other connective tissues (e.g. blood and vessels).
Describe the formation and functions of each of the four extra-embryonic membranes.
The chorion is the outer-most membrane. It develops from the trophoblast and functions to absorb nourishment from the endometrium by means of villi (little projections). After about two weeks of development, the chorion begins to form part of the placenta.
The amnion membrane produces a fluid which acts as an insulator against temperature changes and as a shock absorber. This fluid is known as the amniotic fluid.
The yolk sac develops from an inner cell mass, and forms the lower cavity. It has very little importance in humans, as a human embryo and foetus primarily obtain the required nutrients from the maternal blood supply. However, in animals that lay eggs, the yolk sac is the only source of nutrients for the embryo and foetus. Later on in development, the yolk sac becomes part of the umbilical cord.
The allantois develops into the stalk of the embryo, and functions in the formation of blood cells and umbilical arteries and veins. The allantois eventually becomes part of the umbilical cord.
Describe the formation, structure, and functions of the placenta and umbilical cord.
The placenta
The placenta is a reddish brown vascular structure shaped like a disc. It has two origins: (1) an embryonic component which is the chorion, and (2) a maternal component, the endometrium
In part of the chorion, chorionic villi erode the endometrium to form sinuses (pockets), which get filled with maternal blood. The combined chorion and endometrium where this erosion occurs is the placenta. The allantois in the umbilical cord grows into the placenta, bringing in the arteries and veins which are joined by a capillary network.
The placenta has two important functions. First, it allows for easy diffusion of foods, wastes and gases between child and mother. Second, it is an endocrine, or hormone- producing organ (e.g. it produces hCG hormone).
The umbilical cord is the connection between the embryo and the placenta. It is composed of the allantois and the yolk sac, surrounded by the amnion The umbilical cord has two umbilical arteries and a single umbilical vein. The vein carries oxygen-rich blood from the placenta into the liver of the embryo. The arteries carry oxygen-poor blood from the embryo to the placenta.
Explain the mechanisms underlying the production of fraternal twins and identical twins.
Sometimes two ovarian follicles release their oocytes simultaneously at ovulation. If both are fertilised, the resulting zygotes can develop into fraternal (non-identical) twins.
Identical twins (or monozygotic twins) develop when a single fertilised oocyte splits and develops. This can happen if two inner cell masses form within a blastocyst and each produces an embryo. Twins of this type usually share a single placenta and they are genetically identical. Consequently, they are always the same sex and very similar in appearance.
Name the three stages of labor and describe the events that occur during each stage.
a) In the dilation stage, the foetus moves down the cervix because of the regular contractions of the uterus, and the cervix dilates to a diameter of about 10 cm, until it permits the passage of the head. The amnion is stretched, bursts and releases amniotic fluid through the birth canal.
b) The expulsion stage extends from the time of complete cervical dilation until the delivery. The uterine contractions become more frequent and severe, propelling the foetus through the birth canal.
c) The placental stage actually occurs after the delivery of the foetus. In this stage, the uterus resumes its contractions and expels the placenta. This stage is sometimes referred to as afterbirth. The contractions during this stage serve another role in that they constrict the uterine blood vessels, thereby preventing haemorrhage.
Describe fetal circulation and the changes that occur in fetal circulation following delivery.
