Chapter 12 Semen and its Components

Chapter 12 Semen and its Components

A. Semen: Spermatozoa + seminal plasma

B. Sources and relative contribution to semen: See TABLE 12-1

Greatest contribution: In bull: vesicular gland; In boars : prostate and bulbourethral glands

C. Chemical composition of semen: See TABLE 12-2

Bull and ram semen: higher in fructose and sorbitol from vesicular gland; Boar semen: higher in Na and K from prostate gland

12-1 Spermatozoa

A. Semen characteristics by species: See TABLE 12-3

B. Size of spermatozoa:

Overall length: 60-70Ґм in bull, boar and ram sperm; 50Ґм in stallion sperm Head: 8-10Ґм long; 4Ґм wide; 0.5Ґм thick

12-1-1 Normal morphology: See FIGURE 12-1

Figure 12-1 Structural diagram of spermatozoon.

A. Head:

a. Nucleus: contain genetic code
b. Postnuclear cap: cover posterior portion of nucleus
c. Acrosome: cover anterior portion of nucleus and contain enzymes as hyaluronidase,corona penetrating enzyme and acrosin

B. Neck:(sometimes included in "Tail") Proximal centriole: join head and tail, where head and tail separate during fertilization and in heat-damaged semen

C. Tail:

a. Mid-piece: Mitochondrial sheath: contain enzymes converting energy substrates as fructose into ATP b. Main-piece: Axial filament of 2 central fibrils, 9 pairs of inner fibrils and 9 coarse outer fibrils: its contraction by energy from ATPЎж tail movement
c. End-piece:

12-1-2 Abnormal morphology

A. Reduced fertility: From 25% or more abnormal sperm

B. Classification of abnormal sperm: See FIGURE 12-2

Figure 12-2 Morphological abnormalities of spermatozoa identified through examination of semen for quality.

a. Abnormal heads: asymmetrical, tapering , pyriform, giant, micro and double heads
b. Abnormal tails: enlarged, broken, bent, filiform, truncated and double mid-pieces; coiled, looped and double tails; cytoplasmic droplets (formed on neck during spermiogenesis and usually lost during maturation)

12-2 Seminal plasma

A. Function: Serve as buffer, optimal osmotic and nutrient medium

B. pH: nearly 7.0; slightly acidic in bulls and rams; slightly alkaline in boars and stallions

C. Osmotic pressure: similar to blood and physiological saline(0.9% NaCl)

D. Energy substrates: fructose, sorbitol etc

12-2-1 Inorganic ions

A. Major ions: Na+, Cl-, K+; minor ions : Ca++, Mg++

B. K+/Na+ ratio: High in sperm cell and low in seminal plasma

C. Function: Maintain optimal osmotic pressure for sperm survival

12-2-2 Buffering agents

A. Principal organic ion as buffering agent: Bicarbonate(HCO3-)

B. Source: Vesicular gland

C. Function: guard against change in pH of semen, but not sufficient

12-2-3 Energy substrates

A. Energy substrates: Fructose, sorbitol, glycerylphosphocholine(GPC)

B. Source: Fructose and sorbitol: vesicular gland; GPC: epididymis: uniquely high in semen

C. Metabolism:

a. Fructose: used under anaerobic and aerobic conditions
b. Sorbitol and GPC:used only aerobically
c. GPC: utilized after splitted into choline and glycerylphosphate by an enzyme in female tract

12-2-4 Other organic compounds

A. Inositol and citric acid: considerably high, but not utilized.

B. Ergothionine: found in boar and stallion semen

12-3 Energy metabolism by spermatozoa

*. Plasmalogen: a lipid reserved within sperm cell: used when other substrates are limiting

A. Anaerobically:Fructose ўў 2 lactic acid + 2 ATP (net yield)

B. Aerobically : Fructose ўў CO2 + H2O + 38 ATP (net yield)

C. ATP + H2O ўў ADP + H3PO4 + 7,000 calories /mole

12-4 Factors affecting rate of metabolism

A. Measurement of metabolism rate

a.Under aerobic condition: 1). O2 consumption 2). CO2 liberation 3) Methylene blue reduction tiume
b. Under anareobic condition: 1) pH reduction 2) Increase in lactic acid 3) Decrease in fructose

B. Relationship of fertile life to metabolic rate of sperm:

a. Reduced metabolic rate : extend the storage life of semen;
b. Reduced metabolic rate in epididymis: extend life of epididymal sperm
c. Sperm in fresh ejaculate of semen: fertile for a few hours under high rate of metabolism

12-4-1 Temperature

A. High temperature: Inc. metabolic rate and dec. life span of sperm

B. At 50ЎЙ: Irreversible loss of sperm motility

C. At body temperature: Sperm live for a few hours only: due to inc.metabolism

D. Low temperature: Extend fertile life of sperm by dec. metabolism ( when bull semen frozen at -196ЎЙ, less than 0.02% of metabolic rate at body temperature): Problems: cold shock and freeze kill

a. Cold shock: 1) Irreversible loss of sperm motility by sudden reduction of semen temperature from 15ЎЙ to 0ЎЙ (critical range), 2) Protecting from cold shock: Slow cooling after addition of lecithin and lipoproteins by diluting with egg yolk or milk diluter

b. Freeze kill: 1) Sperm killed during freezeing and thawing 2) Protected satisfactorily by equilibrating bull semen in a diluter containing glycerol Ўж Desirable fertility from semen frozen for decades

12-4-2 pH

A. Higher metabolic rate: From pH of semen near neutrality(7.0), where most enzymes in sperm are most active.

B. Deviations toward alkalinity or acidity: Can reduce metabolic rate, but buffering capacity of diluter is rather important because pH range to be altered without permanent impairment of sperm is narrow

12-4-3 Osmotic presssure

A. Semen diluted with isotonic diluter maintains maximum metabolic activity

B. Hypo- or hypertonic diluter: Can reduce metabolism but detrimental to sperm

12-4-4 Concentration of spermatozoa

A. Inc.concentration of sperm Ўж Inc. K+/Na+ ratio Ўжinhibit sperm metabolism

B. Moderate dilution with buffered, isotonic medium containing fructose, before cooling: Not greatly alter metabolic rate, but extend sperm life

C. Excessive dilution (over 1,000x): Depress motility and metabolic rate

12-4-5 Hormones

A. Androgens over physiological level: Ўй sperm metabolism

B. Fluid from female tracts: Inc. sperm metabolism; due to estrogen or other factors Ўж Ўиsperm motility

12-4-6 Gases

A. CO2

a. 5-10% partial pressure of CO2: Ўйsperm metabolism
b. Epididymal sperm: Long life by high CO2
c. CO2 gassing in diluter: Effective for sperm preservation at room temperature

B. O2

a. Necessary for aerobic metabolism
b. High level of O2: Toxic
C. Other gases: N2, H2, He: No effects

12-4-7 Light

A. Light under oxygen: Produce harmful H2O2; Semen should be protected from light

B. H2O2 production: Prevented by addition of catalase to diluter

12-4-8 Antibacterial agents

A. Penicillin and dihydrostreptomycin or neomycin: Used for control of bacterial growth, with no effects on sperm metabolism

B. Antibacterial agents: Ўиsemen fertility from bulls infected with vibriosis

C. Control of bacteria in semen by antibiotics Ўж Sparing energy substrates: Extend fertile life of sperm