Physiology of Male Reproductive System

• Testis

  • spermatogenesis begins in the seminiferous tubules
  • the process starts during puberty, with males producing roughly 200 million sperm (spermatozoa) each day
  • the blood-testis barrier (formed from Sertoli cells) prevents immune cells from recognising the sperm as foreign
• Spermatocytogenesis

  • spermatogonia are diploid cells (46 chromosomes) that exist within the seminiferous tubules
  • they undergo mitosis to produce two identical diploid cells. One of these (type A spermatogonia) will replenish the pool of spermatogonia while the other (type B spermatogonia) becomes known as a primary spermatocyte
  • the primary spermatocytes then undergo meiosis I to produce two haploid (23 chromosomes) cells known as secondary spermatocytes
• Spermatidogenesis

  • these secondary spermatocytes then undergo meiosis II to produce four haploid (23 chromosomes) cells known as spermatids
• Transverse section of seminiferous tubule

  A) spermatogonium

  B) sertoli cell

  C) leydig cells

  D) myoid cell

  E) basal lamina

  F) lumen

  
• Peripheral effects of testosterone:

  • maintain libido
  • muscle/bone growth
  • secondary sex characteristics
  • accessory gland maintenance
• • Spermatids are released from the surrounding Sertoli cells, into the lumen of the seminiferous tubules in a process known as spermiation
  • They then mature within the tubules in a process known as spermiogenesis to produce fully formed spermatozoa
• Spermiogenesis consists of 4 phases:

  • Golgi phase
  • Golgi body enzymes form the acrosome
  • Acrosomal phase
  • Acrosome condenses around the nucleus
  • Tail phase
  • Centriole elongates to form the tail
  • Maturation phase
  • Loss of excess cytoplasm
• • Spermatozoa are initially non-motile. They move to the epididymis, in testicular fluid secreted by Sertoli cells, via peristaltic contraction
  • They become fully motile within the epididymis but their transport through the male reproductive system occurs via peristalsis and muscular contraction
  • spermatozoa are stored within the vas deferens prior to ejaculation
• • Ejaculation occurs due to contractions of the bulbospongiosus and pubococcygeus muscles
  • Spermatozoa travel along the vas deferens to the ejaculatory duct. It then mixes with fluid from the seminal vesicles, prostate and bulbourethral gland to form semen, which then progresses along the urethra.
• • secretions from the seminal vesicle contain fructose (the main energy source for sperm cells) and prostaglandins (which help to suppress the female immune response)
  • secretions from the prostate include enzymes which help to activate the sperm
  • secretions from the bulbourethral glands include mucus to aid sperm motility
  • basic amines are also secreted from these accessory glands, which counteract the acidic environment in the vagina
• • capacitation is the process that occurs within the female reproductive tract, to allow the sperm cell to penetrate the oocyte
  • this involves secretions of the uterine wall, resulting in the removal of cholesterol, proteins and carbohydrates attached to the membrane that covers the sperm cell's cap
  • these proteins and carbohydrates usually bind when the spermatozoa are mixed with the seminal fluid, in order to prevent the sperm from activating prior to coming into contact with the oocyte
• • Spermatozoa are guided to ampulla of fallopian tube by progesterone - where fertilisation will take place
  • when the sperm cell reaches the zona pellucida ZP3 glycoprotein on zona pellucida binds to receptor on cell surface of sperm head
  • this triggers acrosome to burst, releasing enzymes that break down the zona pellucida, allowing the sperm head to fuse with the oocyte
  • after fusion, cortical granules inside oocyte fuse with plasma membrane, releasing enzymes to cause cross-linking of glycoproteins in zona pellucida. Makes matrix hard and impermeable to further sperm cells.
• What term refers specifically to the meiotic division that secondary spermatocytes undergo?

  Spermatidogenesis
• Where are the majority of spermatozoa stored prior to ejaculation?

  Vas deferens
• Which sugar acts as the main energy source for sperm cells?

  Fructose
• Which chemoattractant guides sperm cells towards the oocyte?

  Progesterone
• 1 in 7 couples in the UK are affected by infertility

  80% of couples trying to conceive will do so within 1 year
• Causes of infertility - 40% of affected couples have both male and female infertility factors

  • male factor infertility 40%
  • ovulatory causes for infertility 25%
  • tubal causes of infertility 20%
  • uterine/peritoneal causes for infertility 10%
• History taking for infertility

  • sexual history, STIs
  • libido
  • erectile dysfunction
  • diabetes
  • medications that may affect erection (e.g. antihypertensives, antidepressants)
  • medications that may affect sperm production (e.g. sulfasalazine, anabolic steroids, chemotherapy, cannabis, cocaine)
  • smoking, alcohol history
  • systems review
• Examination for infertility

  • penis
  • size
  • STD symptoms
  • hypospadias
  • testicle
  • size
  • firmness
  • compare sizes
  • epididymis
  • inflammation
  • scar tissue
  • vas deferens
  • presence (absent in CF)
  • spermatic cord
  • blockages
• Investigations

  • blood
  • FSH
  • LH
  • Testosterone
  • Prolactin
  • Semen
  • volume
  • pH
  • sperm
  • concentration
  • total number
  • total motility
  • vitality
  • morphology
• • hypogonadism is diminished functional activity of the gonads (testes/ovaries) that may result in diminished production of sex hormones. This may be due to a disease process affecting the hypothalamus, pituitary or testes/ovaries
• hypertrophic hypogonadism (primary hypogonadism) = disease process of the testes/ovaries
• hypogonadotrophic hypogonadism (secondary hypogonadism) = disease process of the hypothalamus or pituitary
• Hypertrophic hypogonadism

  • causes include testicular trauma, infection, cystic fibrosis, testicular failure
  • FSH and LH are elevated due to negative feedback from the reduced levels of circulating testosterone
  • As it takes time for testosterone levels to fall, a low-normal result does not exclude primary hypogonadism
• Hypotrophic hypogonadism

  • causes include congenital (Kallmann syndrome), idiopathic, drugs, alcohol abuse, infectious lesions
  • FSH and LH are not produced and therefore do not stimulate Leydig cells to secrete testosterone
• Prolactinoma

  • type of pituitary tumour
  • may be classified depending on size (microadenoma or macroadenoma) and whether they secrete prolactin (functional or non-functional)
  • symptoms in men include impotence, loss of libido, galactorrhoea, headache, visual disturbances (bitemporal hemianopia) and hypopituitarism
  • Prolactin causes inhibition of GnRH therefore reducing levels of FSH/LH and testosterone
  • Diagnosis requires and MRI
  • Most patients receive dopamine agonists (cabergoline, bromocriptine) which inhibit prolactin release. If this fails, trans-sphenoidal resection of tumour is considered