CH 27C: Meiosis and Spermatogenesis

Meiosis

Process of cell division that starts with diploid cells, but ends with haploid cells

• Same idea & phases as mitosis but there’s TWO ROUNDS OF DIVISION

Diploid Cells

Have 2 copies of each chromosome

• Humans have 46 diploid cells

Haploids

Gametes are haploids, only have 23 chromosome.

• ONE of each chromosome

Spermatogenesis Step 1

Spermatogonia divide via mitosis to form primary spermatocyte

Spermatogenesis Step 2

Primary spermatocyte initiates Meiosis 1, dividing into two secondary spermatocytes

Spermatogenesis Step 3

Secondary spermatocyte undergo meiosis 2, resulting in 4 haploid spermatids

Spermatogenesis Step 4

Spermatids undergo spermiogenesis (physical maturation)

Spermiogenesis

1. Appearance of acrosomal vesicle & flagellum in spermatid

2. Growth of acrosome & flagella

3. Shedding of excess cytoplasm

4. Mature sperm

Sperm production

Occurs in seminiferous tubules starting at around age 14 & continues throughout life

• Roughly 400M sperm produced daily

• Process takes 60-75 days

• Immature sperm are moved to epididymis to mature and store until ejaculation

Male accessory glands

Produce bulk of the semen

• Seminal Vesicles

• Prostate Gland

• Bulbouurethral Gland

Seminal Vesicle (70%)

• Paired glands on posterior bladder

• Contains fructose (energy), coagulating enzymes (clotting), & prostaglandins

• Florescent under UV light

Prostate Gland (30%)

• Singular gland inferior to bladder

• Secretions help activate sperm & contain clot-busting enzymes

Bulbourethral glands

• Tiny pea-sized, paired glands found in urogenital diaphragm

• Secretions neutralize residual urine & lubricate head of penis

Semen

Mixture of sperm, testicular fluid, & accessory gland secretion

• pH 7.2-8.0

• Normal ejaculation is only 2-5mL & contains 20-150M sperm/mL

Semen Contains

• Prostaglandins which reduce viscosity of cervical mucus & induce reverse peristalsis in female tract

• Relaxin & enzymes that activate sperm

• Fructose for energy

• Immune suppressing chemicals

• Antibiotic chemicals

• Clotting factors & clot-busting enzymes