Human Reproductive System Flashcards
What are the important endocrine glands in the human reproductive system?
- Hypothalamus
- Pituitary (Anterior and posterior)
- Gonads
What is the function of the gonads in the reproductive system?
Produce gametes and reproductive hormones
What are the water soluble hormones important in the reproductive system?
Peptides and proteins, including:
- GnRH
- FSH
- LH
- Oxytocin
Where is GnRH produced?
Hypothalamus
Where does GnRH act?
The anterior pituitary and the gonads
Where are FSH and LH produced, and what releases them?
The anterior pituitary, where they are released by GnRH
Where is oxytocin produced?
The posterior Pituitary
What are the lipid soluble hormones involved in the reproductive system?
Androgens
Oestrogens
Progestagens
Where are androgens produced?
Testes
Where are oestrogens and progestagens produced?
The ovary
What are the principal androgens, and how do they differ?
Testosterone
5- alpha dihydrotestosterone
Both are made from cholesterols, although they have different side-groups
5 alpha is much stronger than regular testosterone
What are the principal oestrogens and what are they for?
Oestradiol- main oestrogen
Oestrone- weaker, more important for menopause
Oestriol- softens the cervix for childbirth
What hormones released from the hypothalamus are responsible for reproduction, and how are they regulated?
There is only one hormone- GnRH. There is no equivalent inhibiting hormone.
It relies on negative feedback for regulation (apart from ovulation, which uses positive feedback).
How are reproductive hormones released from the hypothalamus?
They are pulsatile- a burst is released every 1-2 hours.
Why is it beneficial that GnRH travels from the hypothalamus to the ant. pituitary via a specific portal system?
It means that the hormones are not lost in general blood circulation.
Why is it important to have a hypothalamus- ant. pituitary - gonadal axis?
It allows the signals to be amplified.
What are the 5 different classes of hormone produced by the hypothalamus?
Somatotrophs Thyrotrophs Lactotrophs Corticotrophs Gonadotrophs
How does the posterior pituitary function, what hormones is it responsible for and what are their functions?
Secretory hormones are synthesized in the hypothalamus, travelling bound to carrier proteins down the axon and into the posterior pituitary, to terminals where they are stored in secretory vesicles.
When an AP arrives, they are released into the bloodstream.
Hormones are oxytocin and ADH.
ADH retains water, while oxytocin affects smooth muscle contraction, causing milk ejection and uterine contractions. It also has a role in pair bonding.
How does the anterior pituitary function, and what does it release?
The hypothalamus produces inhibiting and releasing hormones, and nerve impulses causes their release into the primary plexus and down to the anterior pituitary. These act on specific secretory cels, which secrete their products into the efferent veins.
What is the hypophyseal portal system?
A vascular arrangement in which blood flows from one capillary bed to another without going through the heart. It prevents signal dilution.
What is pulsatile release?
Secretions are released in discrete bursts, and separated by periods of little or no secretion
Why is pulsatile release important?
It prevents desensitization and down-regulation of receptors.
What are the hormones regulating gonadal activity?
FSH and LH
What do FSH and LH do in the female?
FSH: Promotes growth/development of ovarian follicles
LH: Secretion of female sex hormones and the trigger for ovulation
What do FSH and LH do in the male?
FSH: Growth of spermatozoon
LH: Production of testosterone
What is testosterone?
An androgen, the main secretory product of the testis, associated with development and maintenance of male characteristics and fertility.
What does testosterone do?
Male sex development Spermatogenesis Sexual behaviour Muscle development - However, excessive amounts reduce fertility
What are oestrogens?
Main role is the development and maintenance of the female characteristics and fertility
Mainly produced by granulosa cells of growing follicules
What do oestrogens do?
Female sex development
Growth of endometrium
Regulation of menstrual cycle
Bone growth (poor bone growth and osteoporosis is a sign of an oestrogen deficiency)
What are progestagens?
Major steroidal hormones of corpus luteum and placenta.
Associated with prep and maintenance of pregnancy.
What is the vagina?
An elastic muscular tube, extending from the cervix to the exterior of the body, having 3 main functions:
- Passageway for elimination of menstrual fluids
- Receives penis during sexual intercourse, and holds the spermatozoa before their passage to the uterus
- Lower portion of the birth canal through which the fetus passes
What can cause infertility?
STIs
Smoking (inhibits every step of reproduction)
Obesity (every step in female damaged)
Age at childbearing
What are the numbers of follicles and the statistics associated with them?
Born with 7 mil follicles
400 ovulated
2 result in a live birth
0 after menopause
What are the numbers of sperm and statistics associated with them?
1500 sperm produced per second per testicle: 300 million per day from puberty to 90yo
Sperm swim 15km to reach an egg.
What is the uterus?
Small, pear-shaped organ (30-40g).
Forms the pathway for sperm transport
Provides protection, nutrition and waste removal for embryo and fetus.
Contractions of myometrium result in fetal ejection
Source of menstrual flow
What is the structure of the endometrium?
Inner functional zone (stratum functionalis) containing uterine glands, and outer basilar zone, attaching the endometrium to the myometrium.
What does the stratum functionalis do?
Grows during each menstrual cycle, produces secretions for aiding embryonic survival. It is released during menstruation
What are the uterine tubes?
Oocytes are released onto the fimbriae of the uterine tube (fingerlike projections), and transported into the ampulla, where fertilization tends to occur.
The tubes contain lipids and glycogen, for spermatozoa, oocytes and embryos.
Lined with ciliated and nonciliated secretory columnar cells
Surrounded by layers of smooth muscle
Contraction of muscle via peristalsis and ciliar beating moves oocyte from ovary to uterus
What are the ovaries?
Oval organs, 5-10g. Comprised of outer ovarian cortex (containing follicles), central ovarian medulla (ovarian stroma, steroid producing cells), and inner hilum (point of entry for nerves/blood vessels
What is an ectopic pregnancy?
Embryo implants in the uterine tube
How can you tell weeks of pregnancy by size?
No. of cm above pubic bone = no of weeks pregnant
What are the stages of development of a follicle to an embryo?
Primordial Follicle Primary Follicle Secondary Follicle Mature Follicle Ovulation Corpus Luteum Fertilisation
What is the structure of a primordial follicle?
Single layer of flat follicular cells (squamous) surrounding the oocyte become granulosa cells.
This takes place within the ovarian cortex
How does the primordial follicle become a primary follicle?
The follicle grows, but still consists of only one layer of granulosa cells
Some cells respond to FSH and grow even larger, forming many layers of granulosa cells
The oocyte secretes glycoproteins, which form an acellular layer, the zona pellucida
Stromal cells around the follicle condense to form the thecal layer
How does a primary follicle become a secondary follicle?
Granulosa cells proliferate, producing a thick fluid, which comes together to form a single ‘antrum’. The theca interna and externa develops. The theca interna is highly vascular, and secretes oestrogen. The theca externa forms the outer protective layer of the follicle, and is fibrous.
The innermost granulosa becomes firmly attached to the zona pellucida
Loosely arranged granulosa cells surrounding this becomes the cumulus oophorous
How does a secondary follicle become a mature follicle?
Antrum grows, with the oocyte becoming suspended in fluid, attached by a stalk.
How does the mature follicle get ovulated?
The follicle increases even more in size, and moves to the edge of the cortex, causing a bulge. Eventually, the follicle ruptures, causing the oocyte and its surrounding cumulus to the uterine tube
How does the corpus luteum get formed?
The antrum breaks down, the basement membrane between the theca and granulosa breaks down, and blood vessels invade. Granulosa cells form lutein cells, which produce a yellow pigment (referred to as luteinisation).
This is associated with an increased secretion of progesterones, to allow pregnancy to occur.
If fertilization doesn’t occur, the corpus luteum disintegrates within 14 days. Whitish scar tissue remaining (corpus albicans) is reabsorbed into the stromal tissue of the ovary over weeks/months
What happens if the oocyte is fertilized?
The oocyte begins to divide, and the corpus luteum persists past its normal 2 week lifespan. hCG is produced by the embryo, which preserves it.
What are the two phases in the ovarian cycle, and how long do they stretch?
Follicular phase and luteal phase: Follicular is from day 1 to ovulation, while luteal is from ovulation to menstruation
What are the 3 phases of the endomentrial cycle?
Menstrual, proliferative and secretory.
What causes the proliferative phase?
Estrogens (Esp. oestrodiol) released by the theca externa
What causes the secretory phase?
Progesterone and estrogens secreted by the corpus luteum
How long is the luteal phase?
Always 14 days (it is the follicular phase that varies)