Sperm Maturation and Spermatogenesis

Sertoli Cells

Respond to FSH

Promote cell activity and regulate mitotic division and proliferation of spermatozoa

Leydig Cells

Respond to LH

Stimulate testosterone production

Hormone Requirements for Spermatozoa Production

1. GnRH secretion from the hypothalamus

2. FSH and LH secretion from pituitary

3. Testosterone and estrogen secretion

Testosterone

Maintains spermatogenesis

Increase in testosterone in ST is essential for spermatogenesis

GnRH

Gonadotropin-releasing hormone

FSH

Promotes Sertoli cell activity and regulates mitotic division and proliferation of spermatozoa

LH

Stimulate testosterone production in Leydig cells

Estradiol

Produced by Sertoli Cells

Inhibin

Causes a decrease in FSH levels

Feedback loops…

Maintain hormones throughout the body

DHT

Dihydride testosterone

Frequent pulses of hormones leads to continual production of..

male gametes

Spermatogenesis General Functions

Continual gamete supply via stem cell (spermatogonia) renewal

Billions of sperm daily, maximize reproduction

3 Stages of Spermatogenesis

Proliferation

Meiotic Stage

Differentiation Stage (or Spermiogenesis)

Proliferation Stage

Mitotic divisions of spermatogonia

Meiotic Stage

Results in the production of haploid spermatids

Differentiation Stage

Spermatid → Spermatozoon

Proliferation happens in the ____ compartment

Basal

Meiotic Stage and Differentiation Stage happen in the ____ compartment

Adluminal

Differentiation Phases

1. Golgi Phase

2. Cap Phase

3. Acrosomal Phase

4. Maturation Phase

Golgi Phase

Initial acrosome formation

Initial tail development, translocation of centrioles

Proximal centriole

Attachment point of tail (flagellum)

Distal centriole

Central portion of tail or axoneme (tail fibres)

Cap Phase

Acrosome membrane formed (outer and inner)

Production of hydrolytic enzymes

Acrosome Reaction

Exocytosis during fertilization, digest zona pellucida

Acrosomal Phase

Acrosome covers 2/3 nucleus, nucleus elongates

Neck and annulus formation

Annulus

Junction between midpiece and principal piece

Maturation Phase: Final Sperm Assembly

FSH Dependent

Spermatid → Spermatozoon

Mitochondria surround mid-piece in helical fashion

Spermiation

Sperm released from Sertoli cells into seminiferous tubule lumen

Spermatozoa Head

Acrosome, Nucleus, Cytoskeletal structures, Cytoplasm

Spermatozoa Flagellum

Axoneme

Other dense fibers

Head Cytoskeleton

Structural role in defining shape of sperm head

Functional role in aiding sperm penetration of egg

Acrosome

Contains enzymes necessary for sperm to penetrate through the egg during fertilization

Sits as a cap over the nucleus of the top (anterior portion) of the sperm head

Flagellum Neck/Capitulum

Fits into implantation socket of sperm head

Flagellum Middle Piece

Is the region of the tail between the neck

Flagellum Principal Piece

Continues posteriorly from the middle piece to near the end of the tail (axoneme)

Flagellum End Piece

Is posterior to principal piece and contains the central axoneme covered by the plasma membrane

Axoneme Principal Piece

9 Pairs

2 Central

9 course outer fibers

How does the testis produce sperm on a continual basis?

Cycle of the seminiferous epithelium

Cycle

Progression through all 8 cell stages (spermatogonia → mature spermatid)

Cycle Duration

Time required to complete all stages

Spermatogenesis requires ~ ____ Cycles

4.5

Spermatogenic Wave

Distribution of stages along the length of the ST at a given time

Function of Spermatogenic Wave

Provide constant supply of sperm of epididymis

Daily Sperm Production

# sperm produced each day by testes

DSP is dependent on

testicular size or sertoli cell numbers

Fertilizing ability dependent on

Morphology and Motility

Only sperm in the ______ epididymis can be ejaculated

Cauda

Motility

Ability of sperm to swim progressively forward forward

Most common assessment of viability

Morphology

Appearance of sperm cells

All ejaculates have about _____% of abnormal sperm

5-15%

Head Abnormalities

Primary

Tail Abnormalities

Secondary

Androgen synthesis _________ LH and FSH is not changed

in response to

Heat stress does not kill sperm it inhibits __________

spermatogenesis

Fertility Effects of Heat Stress on Males

Decrease sperm motility and number; Increase abnormalities

Fertility Effects of Heat Stress on Females

Decrease fertilization rates, Increase embryonic loss