Reproductive System- Spermatogenesis

Anatomy and Physiology

Mitosis

Part of somatic cell division. Produce two diploid daughter cells, which have identical numbers of chromosomes. Each pair are homologous chromosomes.

Meiosis

Special form of cell division. Production of gametes. Sperm in males & oocytes in females.

Crossing over-Meiosis

The exchange of maternal and paternal genetic material increases genetic variation among offspring.

• Produce 4 haploid daughter cells-gametes.

• Fuse male and female gametes-zygote with 46 chromosomes.

• Meiosis 1 and 2 cycles

Spermatogenesis

Process of sperm production. Starts at puberty and continues past age 70. Takes up to 64 days to complete the process.

Spermatogonia or stem cells

Divided by mitosis which produces two daughter cells. One remains a spermatogonium and the other differentiates into primary spermatocyte. (16 days)

Spermiogenesis

The spermatid undergoes physical maturation into the sperm. Loses contact with the seminiferous tubule and enters fluid into the lumen which is spermiation. (24 days)

Nurse cells or Sertoli cells

Play a critical role in spermatogenesis.

• Maintain blood-testis barrier.

• Clean up & provide nutrients.

• Stimulated by FSH & Testosterone.

• Secrete inhibin & Androgen-binding protein or ABP

What does mature sperm lack?

The endoplasmic reticulum, Golgi apparatus, Lysosomes, Peroxisomes, and Inclusions.

Loss of organelles reduces the size & mass.

What hormone is released from the Hypothalamus that the Anterior pituitary gland releases?

Gonadotropin-releasing hormone or GnRH release from Hypothalamus.

FSH and LH release from Anterior pituitary gland.

Ejaculation

Occurs with powerful, rhythmic contractions in the ischiocavernosus and bulbospongiosus muscles. Stiffens penis and push semen to the urethral opening.

What hormones are released during ejaculation?

Oxytocin is released, feelings of trust & bonding.

Dopamine is released, reward neurotransmitter.

Testosterone suppresses OXT response.

What is detumescence?

Process of losing erection, blood exits.

Erectile dysfunction or ED

Also called impotence, inability to achieve or maintain an erection.

What are the three steps involved in Spermatogenesis?

1. Mitosis

2. Meiosis

3. Spermiogenesis

During sperm maturation, the sperm leaves the epididymis, the sperm is mature but immobile what must the sperm undergo to become motile?

Capacitation

What are two steps in Capacitation?

1. Sperm become motile when mixed with secretions of the seminal glands.

2. Sperm becomes capable of fertilization when exposed to female reproductive tract.

Anatomy of Sperm- **Head**

Flattened ellipse that contains nucleus with chromosomes.

Anatomy of Sperm- **Acrosome**

Membranous compartment at tip of head and has enzymes essential to fertilization.

Anatomy of Sperm- **Middle Piece**

Attached to head by short neck and has mitochondria.

Anatomy of Sperm- **Tail**

Moves cells from one place to another. Has complex corkscrew motion.

Emission

Occurs under sympathetic stimulation.

Dihydrotestosterone or DHT

Target tissues respond to this instead of testosterone. Makes up 10% of circulating testosterone levels.

Estradiol

Found in small amounts in plasma of adult males. 70% is formed from circulating testosterone by aromatase.