MALE REPRODUCTIVE SYSTEM

What are the 2 main functions of the testes?

Gametogenesis and steroidogenesis

What is gametogenesis in the testes?

Production of sperm by meiosis

What is steroidogenesis in the testes?

Production of steroid hormones, mainly testosterone

What regulates testicular function?

Pituitary gonadotropins FSH + LH, released in a pulsatile manner

What are the main factors affecting spermatogenesis?

1. Noxious Agents

2. Seasonal Variation

3. Scrotal Position

4. Nutrition

What do noxious agents do to the testes?

Cause degeneration of the seminiferous epithelium

What are the effects of noxious agents on sperm?

1. ↓ Sperm Count

2. Abnormal Sperm Morphology

3. Genetic Defects

What can sperm genetic defects cause?

1.     Embryonic/Fetal Death

2.     Teratogenesis

What type of cells are especially damaged by radiation?

Dividing cells

What is the sperm cell sensitivity to harmful factors from most to least?

Spermatids → spermatozoa → spermatogonia

How resistant are Sertoli cells to harmful factors?

They are resistant to most harmful factors

When are fertility and ejaculate quality highest?

During the breeding season

What factors affect seasonal variation in reproduction?

Photoperiod, FSH, LH, and testosterone

What does hot weather do to semen quality?

Decreases semen quality

What temperature is required for normal spermatogenesis?

Testes must be maintained about 2–4°C below body temperature

Where must the testes normally be located for normal spermatogenesis?

In the scrotum

What is cryptorchidism?

Failure of one or both testes to descend into the scrotum

What is the reproductive effect of bilateral cryptorchidism?

Sterility

What happens with unilateral cryptorchidism?

↓ Testicular and epididymal weight and impaired spermatogenesis

Why does cryptorchidism impair spermatogenesis?

The undescended testis is exposed to higher body temperature, causing sperm degeneration

What does excessive heat do to sperm?

Causes sperm degeneration + impaired spermatogenesis

What structures help regulate testicular temperature?

Scrotum, tunica dartos, cremaster muscle, pampiniform plexus, and spermatic artery

What happens to the testes in hot conditions?

The testes descend

What happens to the testes in cold conditions?

The testes elevate

What does poor nutrition do to male reproduction?

Causes ↓ libido, ↓ ejaculate volume, poor semen quality, and seminiferous degeneration

What does vitamin A deficiency cause in males?

Testicular atrophy, poor semen quality, delayed puberty, and accessory gland hypoplasia

What other nutritional factors can impair male reproduction?

Mineral deficiencies, phytoestrogens, goitrogens, and nitrates

What does estrogen do to male reproductive development?

Delays development of the seminiferous epithelium and accessory glands

What do progestins do to male reproduction?

They inhibit LH, causing ↓ spermatogenesis

What do fetal testes produce?

Testosterone and androstenedione

What are the functions of fetal testicular androgens?

Male genital development, accessory sex gland development, Müllerian duct regression, and secondary sex characteristics

What are secondary sexual characteristics?

Characteristics that develop under the influence of sex hormones after/around sexual maturation

What are special secondary sexual characteristics?

Structures used for attraction, display, or combat

What are examples of special secondary sexual characteristics?

Bird plumage and deer antlers

What are general secondary sexual characteristics?

Quantitative differences such as muscle mass and skeletal size

What are the main functions of androgens?

Maintain male secondary sex characteristics, support spermatogenesis, maintain high testosterone in the germinal epithelium, and help regulate Leydig cell testosterone secretion

What cells support spermatogenesis within the seminiferous tubules?

Sertoli cells

What is gonadocrinin?

A GnRH-like peptide produced by Sertoli cells that regulates testosterone and increases Ca²⁺ permeability of Leydig cells

What is the function of androgen-binding protein (ABP)?

It binds testosterone and maintains high testosterone concentration inside the seminiferous tubules

What other hormones do Sertoli cells produce?

Inhibin and estrogen

What do Leydig cells produce?

Testosterone

What hormone stimulates Leydig cells?

LH (ICSH)

What enhances Leydig cell testosterone production?

FSH and prolactin

Which testicular cells can synthesize testosterone from cholesterol?

Leydig cells

What does prolactin do to Leydig cells?

Increases LH receptor number, LH receptor affinity, and testosterone secretion

What is the pathway of LH action on Leydig cells?

LH → adenyl cyclase → protein kinase activation → RNA synthesis → cholesterol → pregnenolone → testosterone

What is required for normal spermatogenesis?

Interaction of germinal epithelium, Leydig cells, Sertoli cells, and pituitary gonadotropins

What is the role of Leydig cells in spermatogenesis?

They provide testosterone

What is the role of Sertoli cells in spermatogenesis?

They provide support and produce factors including estrogen and ABP

How much do adrenal androgens contribute to male reproductive function?

Only a small amount

What is puberty?

The beginning of reproductive capability

What factors does puberty depend on?

Hypothalamus, pituitary, gonads, target-organ maturation, nutrition, and environment

Which testicular cells function before sperm production begins?

Leydig cells

What is sexual maturity?

Achievement of full reproductive capacity

What is the sequence from puberty to full reproductive capacity?

Puberty → adolescence → sexual maturity

What factors affect hormone levels in males?

Age, season, time of day, and circadian rhythm

What are the major androgenic effects?

Masculinization and muscle growth

What are the major body effects of testosterone?

Larger body size, greater muscle mass, and aggressive mating behavior

How does excessive body fat affect male fertility?

↓ Fertility

Why does fat around the scrotum decrease semen quality?

It insulates the testes, reducing proper testicular cooling

What physical characteristics can testosterone influence?

Hair growth, hair pigmentation, and feather pigmentation

How does male hair typically differ under androgen influence?

It becomes darker and coarser

What happens to Leydig cell function with aging?

↓ Leydig cell function

How does testosterone provide negative feedback?

Testosterone decreases LH and FSH secretion

What is inhibin?

A hormone produced by Sertoli cells that mainly inhibits FSH

Where is inhibin found?

Testicular fluid, seminal plasma, and ovarian follicular fluid

What is the main function of inhibin?

↓ FSH

What effect does inhibin have on LH?

It has little or no effect on LH

What type of feedback does inhibin provide?

Negative feedback to the pituitary

What are examples of special sex characteristics?

Hair color, horns, vocalization, urination behavior, and pheromones

What do special sex characteristics depend on?

Gonadal steroids

What happens during sexual excitement in boars?

The testes release androgenic steroids

How are boar androgenic steroids converted in the salivary glands?

They are converted into 5α-androsterone-type steroids

What protein binds boar pheromones?

Pheromaxein

What are the main ligands involved in boar pheromones?

Androstenol and related androgens

What is the effect of boar pheromones on sows?

They stimulate an estrous sow for mating

What causes boar taint?

Androstene steroids stored in fat

What does boar taint produce?

A urine-like odor in cooked pork

What effect does orchiectomy have on boar taint?

It eliminates androgenic activity

What factors affect Leydig cells?

Cryptorchidism and restricted diet

Which species produce testicular estrogens?

Stallions, bulls, boars, dogs, and humans

Which testicular cells produce estrogen?

Sertoli cells

What stimulates testicular estrogen production?

FSH

How is testosterone converted into estradiol?

By aromatase

What is the major urinary estrogen in stallions?

Estrone

What other estrogen is produced in small amounts by stallions?

Estradiol

Which estrogen is not detectable in stallions?

Estriol

What is the order of the excurrent tract?

Seminiferous tubules → rete testis → efferent ducts → epididymis → vas deferens → urethra

What is the rete testis?

A network connecting the seminiferous tubules to the efferent ducts

What do the efferent ducts connect?

The rete testis to the epididymis

What are the 3 parts of the epididymis?

Head (caput), body (corpus), and tail (cauda)

What is spermateliosis (spermiogenesis)?

Transformation of spermatids → spermatozoa

What occurs after spermateliosis?

Spermiation

What is spermiation?

Release of mature sperm from Sertoli cells into the seminiferous tubule lumen

Where does epididymal maturation occur?

Between the rete testis and cauda epididymis

What happens to sperm during epididymal maturation?

They undergo functional maturation

What are the main functions of the epididymis?

Sperm transport, maturation, protection, and storage

Where is sperm primarily stored?

The cauda epididymis

Where do most ejaculated sperm come from in humans, dogs, cats, and stallions?

The cauda epididymis and vas deferens