• Begins at puberty
  • Continuous production
  • Declines with age

image

2 functional units needed for spermatogenesis

  • Seminiferous tubules
    • spermatogenesis
      • in the germinal epithelium
  • Interstitial cells/Leydig cells
    • secrete androgens

image

Blood-testes barrier

  • barrier between basal & apical compartments of seminiferous tubules
    • prevent large substances from blood & ISF from reaching
    • steroids can pass through (because fat soluble?)
  • formed by tight junctions (cytoplasmic bridges)
    • between sertoli cells

Sertoli cells function

  • blood-testes barrier
  • nurse cells/physical support & nourishment for developing germ cells
  • mediate action of testosterone & TSH
    • stimulate spermatogenesis
  • Secrete testicular fluid
  • Phagocytosis
  • Secretion of androgen binding protein (ABP)
    • maintain high local concentrations of androgens
      • stimulates spermatogenesis
  • Secretion of hormones
    • mullerian inhibiting substance (MIS)
      • regression of female duct (mullerian)
      • facilitates descent of testes
    • Inhibins
      • -ve feedback regulation of spermatogenesis by inhibiting FSH
    • Oestrogens
      • -ve feedback regulation of spermatogenesis by inhibiting FSH

_____________________________________________________________________

Spermatogenesis

image

Stage 1 (spermatocytogenesis)
Mitosis

  • Spermatogonia
  • Intermediate spermatogonium
  • Spermatogonium

Stage 2 (Meiosis)

  • Primary Spermatocyte (Diploid)
    • meiosis 1
  • Secondary Spermatocyte (Haploid)
    • meosis 2

Stage 3 (Spermiogenesis)

  • Spermatids
    • spermiogenesis/differentiation
  • Spermatozoa
    • cell remodeling & elongation
    • sheds superfluous cytoplasmic component
    • transported to seminiferous tubule

**for better understanding, read up foundation 1 notes

Structure of a sperm

image

Acrosome

  • lysosome-like organelle
  • contains enzymes (hyaluronidase)
    • for penetration of ovum

Nucleus

  • male complement of chromosome

Centriole

  • for cell division after fusion of nuclei

Mitochondria

  • generation of energy for tail movements

_____________________________________________________________________

Regulation of testicular functions

image

Hypothalamus secretes GnRH stimulating the anterior pituitary to release gonadotrophines (LH, FSH). LH stimulates the Leydig cells to produce angrogens. FSH stimulates the seminiferous tubules to undergo spermatogenesis.

Factors affecting spermatogensis

  • Temperature
    • scrotal cooling mechanism
      • abundant sweat glands
      • thin epidermis
      • absence of fat in superficial fascia
      • air circulation
      • scrotal reflex (dartos muscle)
      • countercurrent exchange of heat between arteries & veins
  • FSH
    • Stimulates sertoli cell activity
  • Androgens
    • stimulates maturation of spermatids (thru sertoli cells)
  • LH
  • Large doses of testosterone
    • decreases spermatogenesis
  • Stress
    • decrease GnRH
  • Ischaemia
  • Radiation
  • Antimitotic drugs (anticancer therapy)
  • Inflammation
    • mumps orchitis
  • Toxins
    • pesticides

_____________________________________________________________________

Semen (Seminal fluid)

Contains

  • spermatozoa
  • seminal plasma
    • seminal vesicle (60%)
    • Prostate gland (20%)
    • Bulbourethral glands (20%)

Buffers:  Phosphate bicarbonate

Prostate specific antigen: hydrolyzes the sperm motility inhibitor

Mucus: lubrication

Spermine: Odour

Flavins?

Semen analysis

  • collect semen after 3 days of abstinence
  • sperm count decreases with repeated ejaculation
  • Data
    • volume: 2-4ml per ejaculation
    • white, opalescent
    • ph 7.4
    • Immediately coagulates
      • why?
    • Liquefaction within 15-30 minutes
      • why?
    • actively motile (60-70%)
    • 50-200million sperms/ml
    • normal structure

Azoospermia

  • absence of sperm in the ejaculation
    • Klinefelter’s Syndrome (XXY)

Oligospermia

  • less than 20 million sperm/ml

Aspermia

  • absence of ejaculation

LEAVE A REPLY

Please enter your comment!
Please enter your name here