Spermatogenesis vid3-5

Spermatogenesis

Formation of spermatozoa

3 Primary steps of Spermatogenesis

Proliferation phase → mitosis, “spermatocytogenesis”

Meiotic phase → meiosis

Differentiation phase → no cell division, morphological change from round spermatids to spermatozoa (“spermiogenesis”)

Stages of sperm development

Spermatogonia

primary spermatocyte

Secondary spermatocyte

Round spermatids (transitional phase w/ multiple shapes, round to elongated)

Spermatozoa

Two types of spermatogonia

Type A → stem cell keeps undergoing mitosis

Type B → last mitosis, now committed to meiosis (moves from proliferation phase to meiotic phase)

Mitotic divisions

species dependent → between 2-6 divisions (4-64 daughter cells produced)

Cytoplasmic bridges form between daughter cells

Apoptosis of germ cells

Season

Disease

Trauma or heat (testes)

Hormone levels (ex; abnormal T, FSH, or LH)

This is a normal part of spermatogenesis

Stem cell Renewal

To keep spermatogenesis going indefinitely

Related to spermatogonia staying behind

Replenish testis in case of injury trauma or high heat

Spermiogenesis

After meiotic chase, during differentiation phase

round spermatid to an elongated spermatid to a spermatozoa

4 Phases of Spermiogenesis

Golgi phase

Cap phase

Acrosomal phase

Maturation phase

Golgi Phase

Golgi apparatus to one end of nucleus

Centrioles migrate to opposite end of nucleus (where tail will eventually form)

Produces proacrosomic granules

Cap Phase

Acrosome forms a distinct cap over nucleus

Golgi migrates way from nucleus

formation of primary flagellum

Acrosomal Phase

Acrosome continues to spread around nucleus

continued growth of the tail

Manchettes forms → series of microtubules, pulls and elongates nucleus

Maturation phase

manchette migrates towards tail and disappears

mitochondria migrates and clusters around mid piece

Formation of outer fibrous sheath → spermatid now call spermatozoa

Spermiation

occurs at the end of spermiogenesis

release of sperm cell into lumen of the seminiferous tube → release from Sertoli cell

Temporal relation of spermatogenesis

2-4 weeks delay before a “deleterious event” will be observed in ejaculated sperm

Deleterious event → fever, trauma, heat stress, exposure to toxins

6-12 weeks before restoration of normal sperm (after initial 2-4 weeks)

Stages

Specific cellular associations within a small segment of a seminiferous tubule

Not all sections of same tubule at the same stage at the same time

Stagers are not same length of time

Cycle

Progression through sequence of all stages

4.5 cycles to form spermatozoa (some species variation here)

1 of these = 8 stages

Coordination of stages form waves

Some portion of seminiferous tubules is always releasing sperm

Spermatogenic waves