Reproduction Week 2 Flashcards
Draw a schematic diagram of the male reproductive tract, showing correct positions of all tubes and glands:
(See PBL revision week 6 p1)
Describe the anatomy of the testes:
BLOOD:
- testicular artery from aorta
- pampiniform plexus forms from testicular veins which drain into IVC on RHS and renal vein on LHS
- innervated by testicular plexus from the coeliac plexus formed by T10 nerve roots
- lumbar plexus from L1/2 gives sensory innervation to the tunica vaginalis of the testes
- DRAINAGE: scrotum by inguinal nodes and testes by para-aortic nodes
- each contains 200-300 lobules separated by fibrous connective tissue
- each lobule contains a coiled seminiferous tubule (250m long)
- straight ends of seminiferous tubules -> retes testes -> efferent ductules -> epididymis -> ductus deferens
What type of epithelium lines the epididymis?
Pseudostratified ciliated columnar - reabsorbs 90% of fluid as the sperm become motile
Describe the histology of the testes:
- 2 regions in the testes: tubule and interstitium
- tubule lined by barrier of peritubular myoid cells (a flattened cell layer surrounding the sertoli cells)
Sertoli cells surround the tubules and extend from the BM to the lumen
- they are joined by tight junctions that form blood-testes barrier, preventing chemicals entering or leaving the lumen so a constant environment is maintained for germ cells to develop
- provide nutritional support to developing germ cells
- secrete ABP (attracts testosterone from interstitium into the tubule)
- most mature sperm found near lumen of tubule where they are released and make their way to the epididymis
Leydig cells are in the interstitium and produce testosterone
Describe the anatomy of the penis:
BLOOD
- supplied by branches of pudendal artery (from internal iliac artery) called the DEEP/DORSAL PENIS ARTERIES and BULBOURETHRAL ARTERIES
- drained by superficial and deep dorsal veins
INNERVATION is S2-4
- sympathetic supply and sensory supply from pudendal nerve
- parasympathetic supply from prostatic nerve plexus
- has glans, body and root
- ROOT: attached to body by two ligaments
- > fundiform ligament = sling attaching penis to pubic symphysis
- > suspensory ligament = connects erectile tissue to pubic symphysis
- BODY: made of three bundles of erectile tissue, each surrounded by tunica albuginea (2 corpus cavernosum and 1 corpus spongiosum)
- GLANS: formed by extension of the corpus spongiosum
Describe the anatomy of the ductus deferens:
- a continuation of the epididymis
- each joins with a seminal vesicle forming two ejaculatory ducts
- the ejaculatory ducts join with the ureter in the prostate forming the urethra
- 35-40cm long
What are the parts of the male urethra and their lengths?
- prostatic 3cm
- membranous 1-2cm
- spongy/penile 15-16cm
Describe the anatomy of the prostate and the contents of its secretions:
- single, donut shaped, chestnut sized gland
- produces secretions which are released into the urethra through 100’s openings called PROSTATIC DUCTS
- secretion contents:
- > alkaline (neutralisation)
- > citrate (for ATP production)
- > proteolytic enzymes and acid phosphatase (for liquefying coagulated sperm)
Describe the anatomy of the bulbourethral glands and the contents of its secretions:
- 2 pea sized glands under the prostate that secrete into the spongy urethra
- add MUCOUS to semen during ejaculation
Describe the anatomy of the seminal vesicles and the contents of its secretions:
- 2 glands which develop as out-pouchings of the ductus deferens
- secretion contents:
- > alkaline (neutralisation of female acidic vaginal environment)
- > fructose (ATP for sperm)
- > prostaglandins (aid sperm motility)
Describe the anatomy of the scrotum and its layers:
- sac supporting the testes
- > skin and dartos muscle (gives wrinkles appearance)
- > external spermatic fascia
- > cremasteric muscle
- > internal spermatic fascia
- > tunica vaginalis (parietal and visceral layers between which a hydrocoele may form - fluid collection)
Describe the physiology of erection:
- inhibition of sympathetic nerve supply (which normally releases NA) to the small arteries of the penis, causing them to dilate and fill with blood (normally they are constricted)
- erect penis formed as 3 vascular tissue bundles fill with high pressure blood
- mechanoreceptors in penis stimulate this REFLEX PATHWAY
- can also be triggered by sight, smell, odour
- higher brain pathways can cause NO (nitric oxide) release from autonomic neurons causing relaxation of the smooth muscle of arterioles and an erection
What prevents retrograde ejaculation or urination in ejaculation?
The sphincter at the base of the urinary bladder closes before ejaculation
Describe the physiology of ejaculation:
- stimulation of sympathetic nerves to the smooth muscle of the duct system
- TWO PHASES:
- > smooth muscle of epididymis, DD, prostatic ducts and seminal vesicles contracts and the sperm and secretions are emptied into the urethra
- > 3ml of secretion with 300 million sperm is expelled from the urethra by contraction of urethral smooth muscle and penile skeletal muscle
- is a reflex pathway also controlled by mechanoreceptors
- rhythmic muscular contractions occur (orgasm) and BP and HR increase
- there is a latent stage after ejaculation where a second erection is not possible
Describe the anatomy of the sperm:
- head = contains nucleus and is covered by acrosome which is a protein filled vesicle containing several enzymes
- midpiece = under the head and contains mitochondria providing the sperm with energy for movement
- tail and end-piece = group of contractile axial filaments that produce whip-like movements and propel the sperm forwards at a rate of 1-4mm/min
Describe spermatogenesis in the male:
- sperm are haploid and join with haploid egg forming full-complement embryo
- spermatogenesis begins at puberty and continues until death
- 100 million sperm are produced per day
- formation of one sperm takes ~64 days
- spermatogonia are the diploid germ cells that spermatozoa form from, and there are various types
- spermatogonis divide into one new spermatogonia and a primary spermatocyte by mitosis (this is why supply of spermatogonia and sperm production never decreases)
- primary spermatocytes become secondary spermatocytes by meiosis 1
- secondary spermatocytes become spermatids by meiosis 2
- spermatids undergo differentiation to form spermatozoa
Describe the types of spermatogonia and what they change into:
- pale A -> mature into B spermatocytes
- dark A -> divide into one dark A and one pale A
- B spermatocytes -> mature into primary spermatocytes
Describe the number of chromosomes and number of chromatids in each of the developing sperm:
spermatogonia = 46 chromosomes and 2 chromatids
1 spermatocytes = 46 chromosomes and 2 chromatids
2 spermatocytes = 23 chromosomes and 2 chromatids
spermatids = 23 chromosomes and 1 chromatid
spermatozoa = 23 chromosomes and 1 chromatid
What happens in capacitation?
The ejaculated sperm cannot penetrate the oocyte until they undergo capacitation and the following changes occur in the uterine tubes:
- > removal of glycoproteins covering the acrosome
- > acrosomal enzymes activated and released
- > plasma membrane of sperm altered to allow fusion with egg (membrane phospholipids reorganised)
- > tail movements change from wave-like to whip-like giving the sperm stronger propulsion (due to influx of calcium)
What is the acrosome reaction?
- is triggered when sperm head binds to the ZP of the egg
1) PM of acrosome changes and acrosomal enzymes are exposed to the ZP
2) acrosomal enzymes digest through the ZP and sperm progress using tail
3) the first sperm to penetrate the ZP completely fuses with the egg’s PM
4) the sperm then slowly enters the cytoplasm of the egg and the tail and outer coating of the sperm disintegrates
What are the sequence of steps in fertilisation?
- egg released onto ovary surface
- fimbriae on infundibulum of uterine tubes contract and egg is swept in
- egg moves along uterine tube as cilia beat in direction towards the uterus (takes about 4 days)
- semen deposited into vagina
- cervical mucous becomes clear and stretchy to aid sperm movement up into the uterus
- sperm take 1-2 days to reach uterus
- only 100-200 sperm make it into the uterine tubes
- sperm undergo capacitation
- sperm moves between granulosa cells of oocyte and binds to ZP which has receptors for acrosomal proteins (this triggers acrosome reaction)
- fertilisation is complete and oocyte completes meiosis 2
How is polyspermy prevented?
1 - membrane potential of egg changes after one sperm has bound
2 - cortical granules containing enzymes fuse with the PM after fertilisation and release their contents onto the ZP
3 - the ZP glycoproteins X-link and make a hard layer which is impermeable to sperm
Describe IUI and when it is used:
- intrauterine insemination
- for women with cervical defects, males with low sperm counts, erectile dysfunction, physical disability where intercourse is not possible, same sex couples etc.
- sperm implanted into uterus using long tube
- may be used in conjunction with female medications to stimulate ovulation
How does sperm donation work and when is it used?
- for people with genetic, reduced sperm number or low sperm quality
- IUI used to implant the sperm
- if woman has normal ovulation, they are offered 6 cycles of donor insemination per year
What is the function of the “UK Guidelines for Medical Laboratory of Screening”?
To screen all donated eggs and sperm for infectious/genetic diseases
When is egg donation used?
Turner’s syndrome, premature menopause, ovarian failure, after chemo/radio therapy, to prevent transmission of genetic disease
When is cryptopreservation used?
used to preserve eggs/sperm before person has radio/chemotherapy which could make them infertile, or before they have a sex change
Describe the process of IVF and when it is used:
- egg and sperm incubated together in lab to produce an embryo
- used for infertile couples after 12 failed artificial insemination rounds
1) stimulation of egg maturation - woman takes FSH agonist to stimulate this and transvaginal ultrasound used to monitor egg development
2) hCG stimulates ovulation
3) egg retrieval - needle (guided with US) inserted through the vagina wall to the ovaries to suck eggs into the needle
4) fertilisation - carried out in lab if sperm are healthy, if not ICSI used.
5) embryo transfer - fertilised egg then placed back into the uterus 1-6 days later, embryo injected into the uterus and self-implants
What are the IVF success rates?
<35yrs = 32% 40-42yrs = 13% 44+yrs = 2%
What is ICSI?
- intracytoplasmic sperm injection
- manually insert sperm into cytoplasm of egg, used in conjunction with IVF
What is surrogacy and what are the different types?
- when a woman carried a baby for a couple who cannot conceive or carry child themselves e.g. same sex couple, IVF failure, premature menopause, hysterectomy, recurring miscarriage
- Type 1 = traditional/straight: artificial insemination using surrogates own eggs, can be carried out in clinic or at home with insemination kit
- Type 2 = host/gestational: IVF carried out with intended mothers eggs and then implanted into surrogate, always carried out in clinic
- it is legal in the UK but there must be no 3rd party involved in a commercial basis
- surrogate can only receive £ to cover the costs incurred with the process e.g. medications, time off work
