L18a: Male Gonads: Testicles, Testosterone

Gametogenesis

development from primordial germ cells to mature gametes: oogenesis in females and spermatogenesis in males

Pampiniform plexus

arrangement of the testicular vein into an elaborate, convoluted network that creates many intimate finger-like "wrappings" surrounding the testicular artery

Acrosome reaction

exocytic secretory event within the sperm head that releases proteolytic enzymes for zona pellucida penetration

Capacitation

final functional maturation of the spermatozoa, it includes enhancement of flagellar activity (hyperactivation) & acrosome reaction

Differentiation

a spherical undifferentiated spermatid undergoes a remarkable transformation that results in the production of a highly specialized spermatozoon containing a head and a flagellum including a midpiece (with a mitochondrial helix) and a principal piece (tail)

Diploid

containing two complete sets of chromosomes, one from each parent

Haploid

containing a single set of chromosomes

Proliferation phase

stage that involves cells undergoing repeated mitotic divisions

Spermatogenesis

process that involves the division and transformation from diploid stem cell to haploid spermatozoon

Spermiogenesis

process by which haploid round spermatids complete an extraordinary series of events to become streamlined spermatozoa capable of motility

What is gametogenesis?

process of development from primordial germ cells to mature gametes: oogenesis in females and spermatogenesis in males

When considering the flow of spermatozoa, what segment of the male reproductive tract continues the tail of the epididymis?

ductus deferens

Sperm cells partially mature in the

epididymus

The ductus deferens begins at the

tail of the epididymis

Main components of the male reproductive system

1. testis: high-speed production

2. epididymis: head & body: finishing shop

3. epididymis: tail: warehouse & shipping

4. accessory sex glands: final changes & packaging

5. ductus deferens, urethra, penis: delivery system

Blood supply to the testes

testicular artery

The testicular artery forms the

pampiniform plexus

The testicular vein "wrappings" around the testicular artery allows for

temperature regulation & counter-current exchange of testosterone

Spermatogenesis requires a temperature that is _____ cooler than body temp?

4-6 degrees

Testicular parenchyma is divided into

lobules by connective tissue septae

Site of spermatogenesis

seminiferous tubules

Internal organization of the testes

1. lobules

2. seminiferous tubules

3. straight tubules

4. rete testes

5. efferent ductules

6. head of epididymis

Site of fluid absorption & sperm maturation

epididymis

Ductus deferens

long, straight, tubular organ that originates at the scrotum & ends at the beginning of the urethra

The ductus deferens is responsible for

transporting the ejaculate out of the epididymis and into the pelvic urethra

4 accessory sex glands

1. ampulla of ductus deferens

2. vesicular gland

3. prostate

4. bulbourethral gland

What are the accessory sex glands responsible for?

providing an optimal environment and nourishment for the spermatozoa

The main function of the penis is to

serve as a organ of copulation & passage for semen and urine

What structure is responsible for sperm production?

seminiferous tubules

What is the function of the pampiniform plexus?

temperature regulation & testosterone exchange

Puberty

the process of acquiring reproductive competence

The male reproductive system is under control of the

Hypothalamic-Pituitary-Gonadal Axis

Tonic center of the hypothaamis

produces GnRH

What minimizes the function of the surge center in the male fetus?

testosterone freely enters the brain & transforms into estradiol

What happens to GnRH release after puberty in males?

the hypothalamus "wakes up" and GnRH is released in a pulsatile fashion along with LH & FSH from the anterior pituitary gland

Tubular component of the testis

site of spermatogenesis

Interstitial component of the testis

site of testosterone production

Leydig cells have

LH receptors & produce testosterone

Sertoli cells have

FSH receptors & produce inhibin

LH pulse

- LH binds to receptors on leydig cells which then release testosterone

- testosterone diffuses into sertoli cells

- testosterone converted into DHT & E2 and released into bloodstream

FSH pulse

FSH binds to receptors on sertoli cells, which then produce spermatogenic substances and INHIBIN

Spermatogenic substances

androgen binding protein (ABP) maintains a higher tubular testosterone concentration despite pulsatile release

What is the action of inhibin in the male reproductive system?

selectively inhibits FSH release

General effects of testosterone

- heat detection

- courtship

- sexual arousal/erection

- mounting/intromission/ejaculation

- memory

- increased metabolic rate

- muscle growth

- bone thickness

- skin thickness

- hair growth

- hair darkening

What is the purpose of the spines on the penis of a cat?

stimulate mechanoreceptors to induce ovulation in queens

What are the major reproductive hormones produced by the anterior pituitary gland?

FSH & LH

In the hypothalamus, males only have the tonic center/nuclei (true/false)

true

Spermatogenesis takes place entirely within the

seminiferous tubules

In most domestic species, spermatogenesis takes

40-60 days

Most immature sperm cells (spermatogonia) are located at

the periphery of a seminiferous tubule near the basement membrane

Three major phases of spermatogenesis

1. mitosis

2. meiosis

3. differentiation

Mitosis phase of spermatogenesis

proliferation phase, a primary spermatocyte is produced, stem cell renewal

What allows some spermatogonia to revert to stem cells?

loss of intercellular bridges

Meiosis I

DNA replication, primary spermatocytes become secondary spermatocyte

Meiosis II

produces haploid spermatids formed from secondary spermatocytes

Differentiation/Spermiogesis phase

results in the production of a fully differentiated, highly specialized spermatozoon containing a head & flagellum including a midpiece & tail (principal piece)

What are the three major phases of spermatogenesis?

mitosis, meiosis, differentiation

Where does sperm capacitation occur?

the female reproductive tract