IP1 UNIT3 - lect 2

The male reproductive system includes organs such as the testis, epididymis, and accessory glands (e.g., prostate, seminal vesicles) that play crucial roles in the production, maturation, and transport of sperm.

Sperm must travel approximately 30cm from the male seminiferous tubules to the female oviduct, which is equivalent to swimming 109 miles for a human.
The female reproductive tract is an inhospitable environment for sperm, presenting various challenges that must be overcome for successful fertilization.
Only 1 in 1 million sperm reach the oocyte, highlighting the difficulty of sperm reaching their destination. In a typical ejaculate of 15 million sperm per ml, this results in about 45 sperm potentially reaching the oocyte from a 3ml ejaculate.

Sperm are released from Sertoli cells into the seminiferous tubules.
They are then transported in a fluid secreted by Sertoli cells, moving through the rete testis, vasa efferentia, and finally into the epididymis.

Caput: Fluid from Sertoli cells is reabsorbed, concentrating sperm by 100-fold. Muscles in the epididymis facilitate sperm transport.
Corpus: This section modifies the environment for sperm maturation.
Cauda: This serves as a storage location for mature sperm. A complete passage through the epididymis takes 10 days.

Physical Changes: Sperm undergo loss of surplus cytoplasm and condensation of nuclear chromatin due to the formation of disulphide bridges.
Membrane Modifications: Surface glycoproteins are added to the plasma membrane, leading to changes in membrane fluidity and lipid composition. Cholesterol is metabolized to favor unsaturated fatty acids.
Metabolic Adjustments: Metabolic activity declines to prolong sperm viability, which increases reliance on external fructose for energy.
Motility Enhancements: cAMP levels in the tail of the sperm increase, improving motility.

Sperm are ejaculated in seminal plasma, which is produced by accessory glands, including the prostate gland, seminal vesicle, ampulla, and bulbourethral gland.
The volume of the ejaculate is determined by these glands rather than the testes themselves.

Ejaculate volumes vary among species:
- Bull: 2-10ml
- Dog: 2-15ml
- Boar: 150-500ml
- Horse: 30-300ml

The structure and contribution of accessory glands vary by species, which affects the composition and volume of seminal plasma produced.

Glycoprotein Decapacitation Factors: Protect sperm until fertilization.
Fructose and Sorbitol: Serve as energy substrates for sperm.
Citric Acid: Prevents coagulation of sperm, necessary to avoid forming seminal 'stones'.
Acid Phosphatase: Involved in phospholipid metabolism.
Buffers: Neutralize the acidic pH of vaginal fluids.
Ascorbic Acid: Acts as a reducing agent, protecting sperm from oxidative damage at ejaculation.
Prostaglandins: Stimulate contractions in the female reproductive tract to aid sperm transport.

Sperm leave the testis in a fluid secreted by Sertoli cells, which is then reabsorbed in the caput epididymis.
During transit, sperm mature in the epididymis, where they are stored in the cauda epididymis and vas deferens.
Seminal plasma is produced in the ampulla, seminal vesicles, and prostate glands, providing a fluid vehicle for sperm, including buffering and metabolic support.