Sperm Development

Question 1

How are sperm produced?

Answer 1

• Spermatozoa are produce in the seminiferous tubules of the testicles
• Spermatogenesis involves:
  
  • Proliferation of stem cell (mitosis)
  • Meiotic division of stem cells (become haploid) starts near puberty
    
    • during meiosis, homologous chromosomes form pairs (one from sire and one from dam - and exchange DNA
    • Therefore every chromosome in a sperm cell has DNA from both the sire and dam
  • Differentiation from a nucleated round cell to the specialized tad-pole shaped sperm cell

Question 2

What is the structure of the testicle? how does it sperm flow through to the vas deferens?

Answer 2

• Made up of closely packed seminiferous tubules
  
  • 90% of testicular tissue in bulls, rams, rats
  • to a low of 60% of testicular tissue in boars and stallions
• Seminiferous tubules ⇢ Rete testis (channels in center of testis) ⇢ Efferent ducts (3-20 ducts) ⇢ epididymis (single tube) ⇢ vas deferens (thick muscular wall)

Question 3

What is the Epididymis? function? structure?

Answer 3

• Metabolically active
• Sperm cell matures here
• Divided into 3 regions
  
  • Head
  • body
  • Tail (storage)

Question 4

What Physiologic changes occur in spermatozoa as they transverse the tubular tract?

Answer 4

• Gain the ability for progressive motility
• Acrosome matures (“tightens” onto head - gets rid of excess membrane)
• Plasma membrane - stiffens in some areas and increases flexibility in others
• All are testosterone- dependent

Question 5

What is the Blood-Testis Barrier? Structure? functions?

Answer 5

• Tight junctions between Sertoli cells divide the tubules into 2 compartments
  
  • Basal compartment - contains spermatogonium and preleptotene spermatocytes
  • Adluminal compartment - communicates with lumen and contains more advanced stages
• Wide range of permeability:
  
  • complete exclusion of antibodies
  • Free transfer of androgen-binding protein and inhibin
• Keeps haploid cells from initiating immune response

Question 6

What are the different types of scrotums?

Answer 6

• Reptiles and birds do not have scrotums
• Intra-abdominal testes
  
  • elephants, dolphins whales, armadillos
• Non-pendulous scrotums
  
  • pigs, horses, cats
• Pendulous scrotums
  
  • dogs, cattle, sheep, primates

Question 7

What is the Tunica Dartos?

Answer 7

• Smooth muscle just below the scrotal skin
• Helps regulate testicular temperature
• Contraction - reduces surface area available for heat loss (cold day)
• Relaxation - increases surface area for heat loss (hot day)

Question 8

What is the Pampiniform Plexus

Answer 8

• Counter current exchange of heat between testicular artery and vein
• Decreases temperature of blood arrive at testicle by about 5°C

Question 9

What is ‘Puberty’?

Answer 9

• The onset of puberty is controlled by the maturing hypothalamic-pituitary-gonad axis
• In the bull - “the age when an ejaculate has a minimum of 50 million sperm cells with at least 10% motility
  
  • far below the level acceptable for breeding

Question 10

How are disturbances of spermatogenesis manifested?

Answer 10

• Reduced sperm production
• increased sperm abnormaities

Question 11

What are the types of testicular degeneration?

Answer 11

1. Temporary - followed by regeneration
2. Permanent - with fibrosis

Question 12

What are the different reasons (pathogenesis) for abnormal sperm production?

Answer 12

• Stress - pain, hunger, cold
• Heat - obesity, scrotal abnormality, climate, fever
• Season - photoperiod, nutrition, temp
• Hereditary - sperm defects, testis size
• Puberty - resembles distrubed spermatogenesis
• Toxicity - plant, bacterial, environmental
• Nutritional - protein, vit A or Se deficiency

Question 13

How does Stress affect sperm production?

Answer 13

• Stress suppresses LH release
• LH is necessary for Testosterone - essential for normal spermatogenesis and epididymal function

Question 14

How does increased body temperature affect spermatogenesis?

Answer 14

• Kills developing sperm
  
  • for 1-2 weeks
• Poor quality sperm
  
  • at least a month
  • different defects seen based on where the sperm was at the time of insult (see chart)
• Gradual improvement
  
  • normal in 3 months

Question 15

How long does it take to produce sperm?

Answer 15

• ~39 days from spermatogonia to mature elongated spermatids
• ~7-16 days to transverse the epididymis (species dependent)