Reproduction 1 - Reproductive Physiology Flashcards
1
Q
List the regulatory hormones of the male reproductive system
A
- Gonadotrophin releasing hormone (GnRH - hypothalamus)
- Luteinising hormone (Anterior pituitary)
- FSH (anterior pituitary)
- Testosterone (testes)
2
Q
Describe male reproductive function
A
- Starts at puberty
- Functions continually
- Normally continues throughout the rest of life
- Sperm quantity and quality generally decreases with increasing age
- LH stimulates testosterone production
- FSH and testosterone sustain Sertoli cell function
- Sertoli cells support spermatogenesis
- Sperm production is a very rapid process, and therefore imperfect
3
Q
Describe female reproductive function
A
- Starts at puberty
- Functions cyclically
- Normally operates until around 45 years of age
- Egg quality generally decreases with increasing age
- FSH stimulates (some) development of ovarian follicles and 17b-estradiol synthesis
- LH stimulates progesterone production
- FSH and LH cooperate to form uterine endothelium
- The steroids regulate uterine endometrium
4
Q
Describe the female hypothalamopituitary axis
A
- Hypothalamus produces LHRH (same as GNRH)
- LHRH stimulates release of LH and FSH from the pituitary gland
- LH and FSH stimulate production of oestrogen and progesterone from the ovaries
- Oestrogen and progesterone negatively feedback to the pituitary and hypothalamus
5
Q
List changes in the female HPO axis
A
- Follicular phase oestrogen performs negative feedback to the hypothalamus and anterior pituitary
- Midcycle oestrogen causes positive feedback and large amounts of hypothalamus and anterior pituitary function - increased FSH and LH therefore increased oestrogen
- Luteal phase hypothalamus progesterone is the main hormone, negatively feeding back to the anterior pituitary and thalamus
6
Q
Describe the process of oogenesis
A
- Primordial germ cell (oogonium)
- Oogonium to primary oocyte (mitotic division - diploid)
- Primary to secondary oocyte, producing the first polar body (meiosis I)
- Secondary oocyte to ovum producing the second polar body. Second meiotic division pauses in metaphase (meiosis II)
- Primordial follicle forms antral follicle (secondary oocyte)
7
Q
Briefly describe ovulation
A
- Release of mature oocyte from the ovary
- At this stage, the oocyte is in 2n (metaphase 2) in meiotic arrest.
- Enters the fallopian tube
- If not fertilised within 24 hours, the egg will degenerate
8
Q
What is the function of the male reproductive system?
A
- The provision of androgens (primarily testosterone) to initiate and sustain the necessary male phenotype
- The production of mature sperm.
9
Q
Describe the structure of the testes
A
- Contains seminiferous tubules (which produce sperm) and Leydig (interstitial) cells which produce testosterone (and some other androgens).
- Testosterone is released into the circulation, from where it can affect the whole body.
10
Q
Describe the structure and function of the epididymus
A
- One within each scrotal sac.
- Sperm are released from the testis and stored here prior to ejaculation.
- At ejaculation sperm pass through the two Vas Deferens (which are contractile), and are mixed with fluid from the seminal vesicles.
- The fluid then leaves the ejaculatory duct, and passes into the urethra where it mixes with secretions from the prostate gland.
11
Q
Describe the male HPG axis
A
- GnRH produced from hypothalamus, causing FSH and LH release
- LH causes leydig cells to produce testosterone, which stimulates spermatogenesis and inhibits the hypothalamus and the pituitary
- FSH stimulates spermatogenesis via sertoli cells. Sertoli cells produce androgen binding protein (which enhances sperm production by binding to testosterone) and inhibin to inhibit FSH and LH production
12
Q
Describe the process of spermatogenesis
A
- Primordial germ cell (spermatogonium - diploid) via mitotic division to primary spermatocyte
- Meiotic division 1 produces secondary spermatocyte (haploid)
- Meiotic division II produces spermatids which develop to form mature sperm (spermatozoa, released into lumen of seminiferous tubule)
13
Q
List the main parts of the female reproductive system and their functions
A
- The ovary Parallel functions to the testes, in that they produces the gametes (oocytes) and the steroids needed for female reproductive function (progesterone and estrogens).
- The Fallopian tube (oviduct) through which the oocyte reaches the uterus. Provides an appropriate environment to sustain either an oocyte or a conceptus (fertilised oocyte).
- The uterus, in which the conceptus normally implants and is supported throughout pregnancy.
14
Q
Which cells produce oestrogen and progesterone?
A
- Thecal cells produce oestrogens
- Graulosa-luteal cells produce oestrogens and progesterone during the second half of the ovarian cycle
15
Q
Describe the endometrial cycle
A
- Day 1 - blood shedded and endometrial lining. Remaining basal endothelium is thin. Lasts 5 days.
- Repair and proliferative phase lasts 9 days, stimulation of endothelial cell production by oestrogen, increase in thickness number and length of glands and arteries (from 2-4mm thickness to 7-16mm thickness)
- Secretory phase lasts 13 days, production of nutrients and other factors (stimulated by progesterone and oestrogen), epithelial glands widen, endometrium thickens and there is increased coiling of the arteries (stimulated by progesterone)
- Menstruation is stimulated by a decline in progesterone
16
Q
Describe the ovarian cycle
A
- Follicular phase lasts 14 days. FSH and LH stimulate growth of ovarian follicle, thecal and granulosa cells produce oestradiol which stimulates proliferative phase
- Follicles grow, producing more and more oestrogen until negative feedback becomes positive triggering the LH surge and ovulation
- Luteal phase lasts 14 days, the corpus luteum produces progesterone and oestrogen
17
Q
How long does folliculogenesis take?
A
- Takes more than two complete cycles before the egg enters ovulation
- This is starting from the pause in meiosis
18
Q
Describe the pauses in oogenesis
A
- Meiosis I starts during embryonic development, but halts at the diplotene stage of prophase I (primary follicle); this persists until puberty when meiosis resumes as secondary follicles develop.
- Only a sub-population of follicles become secondary follicles, and these undergo another pause in meiosis at the metaphase stage of Meiosis II.
- Only fertilisation can cause the completion of meiosis in a human oocyte.
19
Q
Describe selection of the follicle for ovulation
A
- Only the dominant follicle is ovulated
- Must first grow over around 3 cycles
20
Q
Describe the process of fertilisation
A
- Deposition of sperm near cervix within female system following sexual intercourse.
- Cervical mucus is normally hostile to sperm (filters out abnormal sperm)
- Cervical mucus changes at mid-cycle, which permits sperm to enter uterus
- Passage of sperm through uterus
- Passage of sperm into Fallopian tube
- Swim from there to Fallopian tube ampulla
- ~30 µm/sec average speed; 2 mm/min; 12 cm/hour
- Survival of the fittest (a few days)
- Capacitation – takes time within uterus
- Capacitation is essential preparation before the sperm meet the oocyte
- Meeting of egg with sperm
- Fusion of egg and one sperm (within 24 hours post ovulation)
- Acrosome reaction: penetration of Zona Pellucida (& Coronal cells)
- Calcium flux
- Resumption of meiosis, release of 2nd polar body
- Alignment of maternal and paternal chromosomes to generate zygote.
- Change in Zona Pellucida to prevent additional sperm fusing with zygote.
Initiation of mitotic (cleavage) divisions in embryo.
21
Q
Describe chromosomes during fertilisation
A
- Meosis of maternal chromosomes continues, forming a female pronucleus and second polar body
- Sperm chromosomes decondense to form male pronucleus
- Chromatids in both haploid pronuclei are duplicated
- They are aligned (mixed) on the mitotic spindle and are separated into 2 identical daughter cells
- Each cell should receive one paternal copy and one maternal copy of each chromosome
- There is no fusion of the female and male pronucleus
22
Q
Describe the female erectile tissue
A
- The female equivalent of the penis is the clitoris
- The clitoris, like the penis, increases in size as a result of an increased blood flow into the tissue
- The mechanism is the same (i.e. release of NO)
23
Q
Describe nervous control of erection
A
- Initiated by: increased parasympathetic activity to smooth muscle of pudendal artery
- Increases the activity of Nitric Oxide Synthase (NOS), and hence nitric oxide (NO)
- NO increases production of cyclic GMP which induces dilatation of arterial smooth muscle.
- Counteracts sympathetic-maintained myogenic tone
- Increases blood flow in corpus cavernosum
which compresses the dorsal vein, restricting the outflow of blood - The urethra is protected from increased pressure by surrounding corpus spongiosum (less turgid)
24
Q
How does viagra work?
A
- Cyclic GMP is normally de-activated by a phosphodiesterase enzyme, and this will reverse the changes leading to penile erection.
- Viagra inhibits the phosphodiesterase, thus potentiating the effects of cyclic GMP.
25
Q
List important pathways in the brain relating to sex
A
- Mesolimbic dopaminergic system (pleasure and reward)
- Nigostriatal tract (control of movements)
- Neuroendocrine pathways reguating fertility
26
Q
Define sexual reproduction
A
Produces offspring that differ genetically from both parents.
27
Q
Why is sexual intercourse important?
A
- Required for sexual reproduction
- Sexual activity
- Sexual pleasure
- Human bonding
28
Q
What is biological sex?
A
- Identifies gender
- Result of chromosomes
- Production of gametes
