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Chapter 12—Male Reproductive System. Said an ovum one night to a sperm, “You’re a very attractive young germ. Come join me, my sweet, let our nuclei meet And in nine months we’ll both come to term.” --Isaac Asimov. Ch. 12-- Study Guide. Critically read:

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Said an ovum one night to a sperm, “You’re a very attractive young germ. Come join me, my sweet, let our nuclei meetAnd in nine months we’ll both come to term.”--Isaac Asimov

ch 12 study guide
Ch. 12-- Study Guide

Critically read:

(A)pages pp. 239-247 right before Sexual Differentiation section;

(B) Negative feedback regulators (pp. 254-255) right before prepuberty subsection

Comprehend Terminology (the text in bold/italic)

Study and understand the text and corresponding figures.

testes fig 12 2 x a
§ Testes (Fig. 12.2, x)-A

Dimension-- Oval organ; 3 cm (anterior to posterior) x 2.5 cm (wide) x 4 cm (long)

Each testis is surrounded by two tunics (C.T.): (From outermost and moving in)

  • Its anterior and lateral surfaces are covered by tunica vaginalis
  • Tunica albuginea– testis itself has a white fibrous capsule
slide6

testicular thermoregulation
§ Testicular Thermoregulation
  • Sperm cannot be produced at core body temperature (too warm; 37 degrees Celsius):
    • Pampiniform plexus = near testicular artery, a network of veins– forming countercurrent heat exchangerthatcools arterial blood entering testis by 1-2 degree Celsius (Fig. x, y)
  • When too cold: muscle contraction to:
    • Pull testes close to body
    • Contract and scrotum becomes taut
    • wrinkles skin reducing surface area of scrotum
testes fig 12 1 12 4 b
§ Testes (Fig. 12.1, 12.4)-B
  • Septa divide testes into 250-300wedge-shaped lobules containing seminiferous tubules(where sperm are produced); each tubule lined with a thick germinal epithelium:
    • Several layers of germ cells for sperm production
    • Tall Sertoli (sustentacular) cells; function?
  • Between the seminiferous tubules are interstitial (Leydig) cells, the source of testosterone

Fig. 27.10 and X

slide12

Stages of sperm maturation: 

Lumen of seminiferous tubule

Spermatozoon

Tight junctions --see next slide

Spermatids

Secondary

spermatocyte

Primary

spermatocyte

Sertoli cell

Spermatogonium

spermatogenesis a
§ Spermatogenesis--A
  • Def. of spermatogenesis– The production of sperm cells through a series of mitotic and meiotic cell divisions
    • Location?
    • How long does it take?
    • Microscopic examination– two important cell types (see next slide)
spermatogenesis b
§ Spermatogenesis--B
  • Two important cell types in seminiferous tubules
    • Germ cells–
    • In various stages of sperm development, such as spermatogonia, primary spermatocytes, secondary spermatocytes
    • Sustentacular (Sertoli) cells– these cells provide crucial support for spermatogenesis

Figure x

spermatogenesis c
§ Spermatogenesis--C
  • Three major stages—
    • Mitotic proliferation—
    • Spermatogonia located in the outermost layer of the seminiferous tubule, outside the blood-testis barrier (BTB)
    • One of the daughter cells (Type A spermatogonium) remain at the outer edge of the tubule; importance?
    • The other daughter cell (Type B spermatogonium) starts moving toward lumen forming 4 identical primary spermatocytes (2N)
spermatogenesis d
§ Spermatogenesis--D
  • Meiosis—
  • Each primary spermatocyte (2N) must pass through BTB (tight junction) and ultimately yield 4 spermatids (1N)
  • Spermiogenesis—
  • Spermatids become extremely specialized and motile spermatozoa
  • Sperm travel lightly

Figure w, x, y, z

slide19

A

B

Meiosis

C

slide20

Spermatogenesis

Stages:

Chromosomes:

46; 2n

(diploid number;

single strands)

One daughter cell remains

at the outer edge of the

seminiferous tubule to

maintain the germ cell line

Spermatogonia

One daughter cell moves

toward the lumen to

produce spermatozoa

Mitosis

46; 2n

(diploid number;

single strands)

Primary

spermatocyte

46; 2n

(diploid number;

doubled strands)

First meiotic

division

Meiosis

Secondary

spermatocyte

23; n

(haploid number;

double strands)

Second meiotic

division

23; n

(haploid number;

single strands)

Spermatids

Spermio-

genesis

23; n

(haploid number;

Single strands)

Spermatozoa

sperm s journey male reproductive tract
§ Sperm’s journey (male reproductive tract)
  • Testes– sperm-producing organs; inside the scrotum (skin-covered sac)
  • Routes (spermatic ducts) the sperm travel: A-Testes  B-Efferent ductules  C-Epididymis D-Ductus deferens E-Ejaculatory duct  F-Urethra  Exterior

Fig. x

slide24

Anterior/posterior view?

Urinary bladder

Ureter

2. Prostate gland

1. Seminal vesicle

3. Bulbourethral gland

E

D

F

Penis

C

B

A

Glans penis

leydig cells
§ Leydig cells
  • Principal role of Leydig cells– synthesize testosterone (& estrogen) in response to LH
  • In the fetus--initially Leydig cells depend on chorionic gonadotropin; later on LH
  • After birth– Leydig cells regress and die until puberty
  • Initial steps of testosterone formation– similar to adrenal cortex; from cholesterol to pregnenolone
  • Four other enzymes convert pregnenolone (21 C) to testosterone (19 C) (Fig. 12.5)
slide27

Pregnenolone

Testosterone

germinal epithelium sertoli cells
§ Germinal epithelium (Sertoli cells)
  • Principal role of germinal epithelium (Sertoli cells)– produce sperm
  • Sertoli cells– only cells known to express FSH receptors in human males; also have testosterone receptors
  • FSH, LH, and testosterone all play vital roles in spermatogenesis. How so for LH and testosterone?

Fig. 12.6

secretion and metabolism of t
§ Secretion and metabolism of T
  • Testosterone (T) is the principal androgen secreted by the mature testis. In that 5% is from adrenal cortex.
  • Aging– no sharp drop in T (unlike estrogen in the postmenopausal woman)
  • In blood 98% of T binds to binding proteins — albumin, sex hormone-binding globulin (SHBG also called TeBG; having higher affinity for T), and ABP (androgen binding protein) in Sertoli cells
  • The other 2% of T can diffuse out of the blood
  • Liver is principal site of degradation of T; T also can convert to other steroids (Fig. 12.7)
mechanism of action by t
§ Mechanism of action by T
  • Nuclear receptors-- Testosterone (T) often converts to 5alpha-dihydrotestosterone before binding to their nuclear receptors (Fig. 12.8)
  • T also may bind to membrane receptors-- either directly or through the bind of the sex hormone binding globulin
effects of testosterone
§ Effects of testosterone
  • Testosterone promotes -- growth, differentiation, and function of accessory organs of reproduction.
  • Maintenance of normal reproductive function in the adult depends on continued T secretion.
  • T stimulates transport and delivery of sperm
  • On sexual characteristics– during early adolescence, T stimulates growth of pubic hair, axillary, and facial hair; lowers the pitch of the voice
  • T stimulates secretion of the hormone erythropoietin; T increases sexual drive (libido) in both men and women .
hypothalamus pituitary testis
§ hypothalamus-pituitary-testis
  • Hypothalamus GnRH– stimulates secretion of both LH and FSH
  • Testosterone, which is secreted in response to LH, acts as a feedback regulator of LH.
  • FSH stimulates the Sertoli cells to synthesize and secrete inhibin (glycoprotein), which regulates FSH secretion.

Fig. 12. 17

slide38

Stimulation

Inhibition

Stimulation