SPERMATOGENESIS

SPERMATOGENESIS

• Process of spermatozoa formation (sperm) from primitive germ cells (spermatogonia).

• Result of stimulation by testosterone

– Secreted from Leydig cells under LH influence.

STEPS:

• Initial essential steps are completed in testis.

• Remaining, formation of mature sperms is completed only in female genital tract

Initial phase: 

• Spermatogonia → 1° spermatocytes → 2° spermatocytes

Maturation phase:

• Spermatids → spermatozoa (sperms)

• Release of sperms – Spermiation

Hormonal influence:

• Testosterone diffuses into tubules & increase its concentration.

• Binds to Androgen Binding Protein (ABP)

– Secreted from Sertoli cells under FSH influence.

• Except for “Maturation phase” all other phases are testosterone independent 

Step 1:

• Seminiferous tubules in testis – Starting point of process.

• Spermatogonia (primitive germ cells) divide & migrate centrally in seminiferous tubules

Step 2 – Maturation – Spermiogenesis:

• Maturation of spermatids to spermatozoa depends on testosterone

• Occurs in epididymis

– Exact location – Deep cytoplasmic folds of Sertoli cells

• Spermatids undergo morphological changes to form Sperm

• Motility develops at this stage.

• Sertoli cells provide nourishment to mature spermatozoa

Step 3 – Spermiation

• Process of release of mature spermatids from Sertoli cells after maturation

Hormonal influence:

• FSH – Produce cytoskeletal organization of protein necessary for sperm release. 

• Testosterone – Ectoplasmic specialization formation.

• Human sperm remains fertile for 24-72 hrs in female genital tract after ejaculation.

TEMPERATURE & SPERMATOGENESIS:

• Spermatogenesis requires temperature considerably lower than core body temperature.

• Location Testes/Scrotum important to produce viable sperm

• Specifically 1°-8 °C lower than normal body temperature of 37 °C (98.6 °F

Maintenance of temperature by:

• Circulating air in scrotum.

• Countercurrent heat exchange between spermatic arteries & veins.

Applied physiology:

• Cryptorchidism – Failure of testicular descent

• Exposes testis to higher temperature (intra-abodimal) 

• Resulting in defective spermatogenesis & infertility.

HORMONES INVOLVED IN SPERMATOGENESIS:

• FSH, LH, testosterone, estrogen, growth hormones, inhibin & activin.

Individual action:

1. FSH – 

• Responsible for initiation of spermatogenesis. 

– Binds with sertoli cells & spermatogonia

– Induces proliferation of spermatogonia. 

• Stimulates sertoli cells 

– Secrete androgen binding protein, inhibin, mullerian inhibing substance & estrogen.

2. LH –

• Stimulates Leydig cells to secrete testosterone.

3. Testosterone –

• Principle hormone – Directly stimulates and maintains spermatogenesis. 

• Responsible for sequencing remaining stages of spermatogenesis (after initiation by FSH). 

4. Estrogen –

• Formed from testosterone (by aromatase) in Sertoli cells. 

• Essential for spermiogenesis. 

5. Growth hormone – 

• Promotes early division of spermatogonia.

6. Inhibin –

• Important role in regulation of spermatogenesis

• By feedback inhibition of FSH secretion.

7. Activin –

• Stimulates FSH secretion & stimulates spermatogenesis.

Important metrics in spermatogenesis:

• Begins at an average age of 13 years.

• Healthy human adult form up to 120 million sperm each day from both of testis together.

• 1 primary spermatocyte gives rise to 4 spermatids.

• 1 Spermatogonium gives rise to 512 spermatids. 

• Formation of mature sperm from primitive germ cells require average of 74 days 

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