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Animal Science 434. Lecture 12: Spermatogenesis. Production of Fertile Sperm. hormonal regulation of the testis mitotic division of spermatogonia meiotic divisions of spermatocytes morphologic transformation of spermatids into spermatozoa. Hormonal Regulation of the Testis. LH. LH. LH.

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animal science 434

Animal Science 434

Lecture 12: Spermatogenesis

production of fertile sperm
Production of Fertile Sperm
  • hormonal regulation of the testis
  • mitotic division of spermatogonia
  • meiotic divisions of spermatocytes
  • morphologic transformation of spermatids into spermatozoa
slide4

LH

LH

LH

LH

GnRH

GnRH

GnRH

GnRH

FSH

FSH

FSH

FSH

slide5

Time of Day (24 hr)

Pulses are important !

slide6

FSH on Sertoli Cells

  • estradiol
  • inhibin
  • ABP
  • tight junctions

Negative Feedback of

Estradiol and Inhibin

To

Epid.

Negative Feedback of Androgens

FSH

LH

ABP

+

T

E2

Inhibin

T

TJ

ABP

Hypothalamus

GnRH

Ant.

Pituitary

Leydig

Cells

Sertoli

Cells

Germ

Cells

Seminiferous

Tubule

slide8

Sertoli Cell

Myoid Cells

slide10

Every 13.5 Days sperm are released from this point

Spermatozoa

Round

Spermatid

Secondary

Spermatocyte

Primary

Spermatocyte

Every 13.5 Days

a new group of cells

initiate the cycle

Spermatogonia

slide11

Typical Sequence of Spermatogenesis

A

Spermatogonia

(A, intermediate, B)

A

A

Spermato-cytogenesis

I

I

B

B

Primary

Spermatocyte

Mitosis

P

P

Meiosis

S

S

SecondarySpermatocyte

RS

RS

Round Spermatid

Spermio-genesis

Spermatozoa

SP

SP

Spermiation

Rete Testis

slide12

Many Sperm are Produced

Potential Sperm Produced

1

A

2

A

A

4

I

I

8

B

B

16

P

P

32

S

S

64

RS

RS

SP

SP

mitotic divisions
Mitotic Divisions
  • species dependent
    • between 2 and 6 divisions (4 to 64 potential daughter cells produced)
  • classifications vary among species and investigators
    • A1, A2, A3, A4, B 1, B2, P
    • Ad, Ap, B, P
    • As, A0, A1,A2, I, B, P
  • cytoplasmic bridges form between daughter cells
slide14

Degenerating Spermatogonia (Apoptosis, as high as 75%)

Cytoplasmic Bridges Present Among Daughter Cells

All develop surrounded by 1 Sertoli cell !

germ cells sertoli cell
Germ Cells / Sertoli Cell

Species Primary Round Max. Potential Spermatocytes Spermatids Spermatids

Equine 3.0 ± 0.2 10.9 ± 0.9 64

Bovine 1.2 ± 0.1 5.2 ± 0.6 64

Human 1.3 ± 0.1 4.2 ± 0.2 16

apoptosis of germ cells
Apoptosis of Germ Cells
  • Season
  • Disease
  • Trauma or heat
  • Hormone levels
  • Normal part of spermatogenesis
stem cell renewal
Stem Cell Renewal
  • To keep spermatogenesis going indefinitely
  • Replenish testis incase of injury, trauma, or high heat
slide18

FSH

Periodic

Entry of

Cells into

Mitosis

A2

Spermatogonial

Renewal in the

Rat and Bull

A1

Stem Cell

Pool

A3

A4

In

B

P

slide19

FSH

Ap

Spermatogonial

Renewal in the

Primate

Ad

Stem Cell

Pool

B

P

golgi phase
Golgi Phase

Development of Acrosome

Migration of Centrioles

cap phase
Cap Phase

Acrosome Development Continues

Flagellum Elongates

acrosomal phase
Acrosomal Phase

Acrosome

Manchette

Elongation

maturation phase
Maturation Phase

Manchette disapears

Mitochondria migrate

Dense fibers form

spermatogenesis29
Spermatogenesis

57 days

Stallion

stages
Stages
  • Specific cellular associations within a small segment of a seminiferous tubule
  • stages are not the same length in time
stages35
Stages
  • Specific cellular associations within a small segment of a seminiferous tubule
  • stages are not the same length in time
cycle
Cycle
  • progression through sequence of all stages
cycle39
Cycle
  • progression through sequence of all stages
  • 4.5 cycles to form spermatozoa
    • some species variation
duration of spermatogenesis

Bull Ram Boar Stallion Man

cycle (days) 13.5 10.4 8.3 12.2 16

Spermatogenesis61 47 39 57 75

Duration of Spermatogenesis
coordination of stages form waves
Coordination of Stages Form Waves
  • some portion of seminiferous tubule is always releasing sperm
interstitial tissue

Blood Vessel

Interstitial Tissue
  • Vascular System Provides
    • Nutrients
    • Oxygen
    • Growth Factors
    • Hormones
slide46

Compartments

Myoid Cells

Tight Junctions

Luminal

Adluminal

Basal

compartmentalization
Compartmentalization
  • Basal
    • mitosis
      • spermatogonia (A, I, B)
      • primary spermatocytes
  • Adluminal
    • meiosis
      • primary spermatocytes
      • secondary spermatocytes
      • spermatids
    • spermiogenesis
  • Lumen
    • spermiation
blood testis barrier

!!!!!

Blood Testis Barrier
  • Sertoli cells and associated tight junctions
  • first appears at puberty
  • induced by FSH
  • after puberty can be maintained by FSH and/or testosterone
  • essential for meiosis
tight junction role in meiosis
Tight Junction Role in Meiosis
  • Sertoli cells can manipulate environment around 1° spermatocyte
    • Enters meiosis
    • Completes meiosis
  • Destruction of TJ causes impairment of meiosis
    • Heat, heavy metals, pesticides, lack of FSH or Testosterone
capacity for sperm production
Capacity for Sperm Production

Species Testis Sperm/gm DSP Weight (gm) (X 106) (X 109)

Dairy Bull 650 18 10

Beef Bull 500 18 8

Ram 550 26 14

Boar 750 30 25

Stallion 165 18 3

Man 40 4 .045 - .2

duration of spermatogenesis52

Bull Ram Boar Stallion Man

cycle (days) 13.5 10.4 8.3 12.2 16

Spermatogenesis61 47 39 57 75

Duration of Spermatogenesis
slide53

FSH

Ap

Spermatogonial

Renewal in the

Primate

Ad

Stem Cell

Pool

B

P

capacity for sperm production54
Capacity for Sperm Production

Species Testis Sperm/gm DSP Weight (gm) (X 106) (X 109)

Dairy Bull 650 18 10

Beef Bull 500 18 8

Ram 550 26 14

Boar 750 30 25

Stallion 165 18 3

Man 40 4 .045 - .2

variation in sperm production
Variation in Sperm Production
  • Testis Size
  • Efficiency of spermatogenesis
    • mitotic division
    • degeneration of germ cells
  • Length of spermatogenesis
apoptosis of germ cells56
Apoptosis of Germ Cells
  • Season
  • Disease
  • Trauma or heat
  • Hormone levels
  • Normal part of spermatogenesis
over population of spermatogonia

Normal

Apoptosis Inhibited

PS

Sertoli

Sertoli

PS

SG

AP

AP

SG

Sertoli

Sertoli

SG

AP

SG

AP

SG

SG

SG

SG

SG

Basement Membrane

SG

SG

SG

SG

SG

Basement Membrane

Over Population of Spermatogonia

Tight Junction

Sertoli

Sertoli

SG

SG

SG

SG

SG

SG

SG

SG

SG

Basement Membrane

animation of spermatogenesis
Animation of Spermatogenesis

View the Animation of SpermatogenesisUsing the Link at the Bottom of the Screen

  • The objective is to see how the process of spermatogenesis takes place over time and involves both stages and cycles.
    • In the animation, the timing of events is correct but we have taken liberties in moving groups of cells from side to side to make room for development of other cells.
    • The animation begins with primordial germ cell migration into the primary sex chord and replication of gonocytes to form stem cell A-Type spermatogonia.