Gametogenesis: Spermatogenesis

Where does spermatogenesis take place?

in seminiferous epithelium

Initiation of spermatogenesis

Primordial germ cells undergo lots of mitosis to produce spermatogonial stem cells which are very immature and don’t do much until puberty.

• Spermatogonia stem cell divides by mitosis under hormonal influence

Soermatogenesis during puberty

Testosterone has major influence on the seminferous epithelium and cells will undergo lots of mitosis.

• Spermatogonial stem cell undergoes mitosis creating 1 identical cell (2n Type A spermatogonia) and 1 Type B spermatogonia (2n)

• Type B spermatogonia undergoes mitosis within the seminiferous epithelium to produce a primary spermatocyte (2n)

• Primary spermatocyte enters Meiosis I producing 2 haploid secondary spermatocytes

• Each secondary spermatocyte undergo Meiosis II producing 4 identical haploid spermatids

What is meiosis supported by

somatic cells of the testis:

• sertoli cells

• leydig cells

• peritubular cells

Spermiogenesis

• At the end of meiosis, 4 spermatids are formed from each spermatogonia

• These are round cells with lots of cytoplasm

• These cells undergo spermiogenesis, or differentiation, which change the structure of the cells with no further divisions

Which changes occur during spermiogenesis?

• Acrosome forms over nucleus

• Nucleus condenses and changes shape to form head

• Tail forms

• Mitochondria concentrate in the midpiece to help power movement

• Excess cytoplasm is removed (phagocytosed by sertoli cells)

Acrosome

contains enzymes needed to penetrate the egg during fertilisation.

Oogenesis vs Spermatogenesis: Location

• Oogenesis in ovary

• Spermatogenesis in testis

Oogenesis vs Spermatogenesis: number of gametes per germ cell

• oogenesis 1

• spermatogenesis 4

Oogenesis vs Spermatogenesis: number of gametes produced during life

• oogenesis: ~400 mature oocytes in total

• spermatogenesis: millions

Oogenesis vs Spermatogenesis: beginning of process

• oogenesis: foetal development

• spermatogenesis: puberty

Oogenesis vs Spermatogenesis: timing of gamete production

• oogenesis: once a month

• spermatogenesis: continuous production

Oogenesis vs Spermatogenesis: end of process

• oogenesis: menopause

• spermatogenesis: lifelong but reduces with age

Oogenesis vs Spermatogenesis: meiotic divisions

• oogenesis: arrested twice (prophase I and metaphase II)

• spermatogenesis: continuous

Oogenesis vs Spermatogenesis: motility

• oogenesis: immotile oocytes

• spermatogenesis: highly motile sperm