THE MALE REPRODUCTIVE

SYSTEM

Learning objectives • Describe spermatogenesis and the role of Sertoli cells,

Leydig cells and the basement membrane in this process.• Describe the endocrine regulation of testicular function:

the role of the GnRH pulse generator, FSH, LH, testosterone, and inhibin.

• List the major target organs and cell types for testosterone and other androgens.

• Understand aging- related changes in the hypothalamo-pituitary-goandal axis that lead to puberty, reproductive maturity, and reproductive senescence (andropause)

Which of the following is a correct statement about the production of human sperm?

a. Spermatogonia undergo meiosisb. Spermatogenesis occurs in the epididymisc. Normally, 10 to 20 million sperm are produced

dailyd. FSH is requirede. Complete maturation of spermatozoa occurs in

about 1 month

OVERALL CONTROL OF ADULT MALE HORMONAL SECRETION

Leydig cells

• 20% of the adult testis is connective tissue interspersed with Leydig cells.

• The function of the Leydig cells is synthesis and secretion of testosterone , the male sex steroid hormone.

• Testosterone has both local (paracrine) effects and endocrine effects.

Functions of the Sertoli cells in the seminiferous tubules include

a. Secretion of FSH into the tubular lumenb. Secretion of testosterone into the tubular

lumenc. Maintenance of the blood-testis barrierd. Synthesis of estrogen after pubertye. Expression of surface LH receptors

Functions of Sertoli Cells• Provide nutrition for the development of germinal

cell into spermatozoa and conversion of spermatids into sperms

• Production of Androgen-Binding Protein thereby maintain high supply of androgen to the deveolping germ cells

• Form Blood-Testes Barrier -prevents entry of toxin

• Foetal Sertoli cell produce MIS

• Produce Inhibin which inhibits FSH secretion

• Synthesize estrogen from testosterone by aromatisation

LKS

Spermatogenesis

The process of sperm formation

Hormonal Factors That Stimulate Spermatogenesis

1. Testosterone2. Luteinizing hormone3. Follicle-stimulating hormone4. Estrogens5. Growth hormone

STRUCTURE OF SEMINIFEROUS TUBULE

• The tight junctions between Sertoli cells divide the lumen into a) Basal compartment

b) Luminal or adluminal compart.• The spermatogonia are located in the basal

compartment• The spermatocytes develop in the luminal

compartment within the cytoplasmic folds of the Sertoli cells

The Seminiferous Tubules

Spermatogenesis

divided into three phases: (1) Mitotic divisions of spermatogonia generatethe spermatocytes, which are destined to become mature sperm; (2) meiotic divisions of the spermatocytes, which decrease the chromosome number and produce haploid spermatids; (3) spermiogenesis, in which spermatids are transformed into mature sperm through the loss ofcytoplasm and the development of flagella

SPERMATOGENESIS- 1st STAGE

• Spermatogonia in the basal comparment of Seminiferous tubules are called Type A SPERMATOGONIA.

• These divide 4 times to form slightly more differentiated cells called Type B SPERMATOGONIA

SPERMATOGENESIS- 2nd STAGE

• MIGRATION: The Type B spermatogonia migrate centrally across the tight junctions of the Sertoli cells into the adluminal compartment

• Having penetrated the barrier they become enfolded in the cytoplasmic processes of Sertoli cells.

• Further development occurs in association with the Sertoli cells.

SPERMATOGENESIS- 3rd STAGE

• FORMATION OF PRIMARY SPERMATOCYTE- For a period averaging 24 hrs the Type B spermatogonium becomes progressively enlarged and modified to form the PRIMARY SPERMATOCYTE

• At the end of 24 hrs in the primary spermatocyte the DNA has replicated and each of the 46 chromosomes has 2 chromatids bound together at the centromere

SPERMATOGENESIS-4th STAGE

• FIRST MEIOTIC DIVISION & FORMATION OF SECONDARY SPERMATOCYTE- The Primary spermatocyte undergoes the first meiotic division

• Each pair of chromosome separate so that each secondary spermatocyte has 23 chromosomes

• Each of the 23 chromosomes has 2 chromatids

SPERMATOGENESIS- 5th STAGE

• SECOND MEIOTIC DIVISION & FORMATION OF SPERMATIDS- within 2-3 days a second meiotic division occurs so that 2 spermatids are formed

• Each spermatid contains 23 chromosomes having 1 chromatid each

• Half of the spermatids have X chromosomes and the other half Y chromosomes

• Thus the eventual sperm which fertilizes the ovum provides half the genetic material

SPERMATOGENESIS- 6th STAGE

• SPERMIOGENESIS: CONVERSION OF SPERMATIDS TO MATURE SPERMATOZOON

• The spermatids have characteristics of epitheloid cells

• Each spermatid elongates into a sperm composed of a head & a tail.

• This change requires that the spermatid is in close association with the Sertoli cell

SPERMIOGENESIS

FACTORS AFFECTING SPERMATOGENESIS

• From a single spermatogonium 512 sperms are formed.

• The process takes 74 days on average• The two testes of the adult form 120 million sperms

each day• STORAGE: A small quantity is stored in the

epididymis, but most in the vas deferens & ampulla of the vas deferens

Maturation of Sperm in the Epididymis

• Maturation of Sperm in the Epididymis -capability of some motility

• Storage of Sperm-up to 120 million sperm each day; They can remain stored, maintaining their fertility, for at least a month; After ejaculation, the sperm become motile, and they also become capable of fertilizing the ovum, a process called maturation.

• Capacitation of the spermatozoa:-uterine and fallopian tube fluids wash away the various inhibitory factors, lose much of their excess cholesterol, becomes much more permeable to calcium ions,

FACTORS AFFECTING SPERMATOGENESIS

• TEMPERATURE: Requires a temperature considerably lower than interior of body. The testes are maintained at a temperature of 32 c. They are kept cool by a heat exchange in a counter-current fasion between the spermatic arteries and veins.

FACTORS AFFECTING SPERMATOGENESIS

• REDUCED SPERMATOGENESIS AND SPERM COUNT- EFFECT OF HIGH TEMPERATURE

1) CRYPTORCHIDISM-testes in the abdomen at high temp

2)Tight cloth Binders cause degenration of tubular walls & sterility results

3)Hot baths reduce count 4)Seasonal Variation: Sperm count greater in

winter regardless of scrotal temperature

FACTORS AFFECTING SPERMATOGENESIS

• INFECTION: Mumps causes bilateral orchitis• STRICTURE OF THE GENITAL DUCT causes

degeneration of tubular epithelium• GENETIC ABNORMALITIES: Klinefelter’s Syndrome

Q. Which of the following functions of the Sertoli cells mediates negative feedback control of follicle-stimulating hormone (FSH) secretion?

(A) Synthesis of inhibin(B) Synthesis of testosterone(C) Aromatization of testosterone(D) Maintenance of the blood-testes barrier

Q. Functions of the Sertoli cells in the seminiferous tubules include

a. Secretion of FSH into the tubular lumenb. Secretion of testosterone into the tubular

lumenc. Maintenance of the blood-testis barrierd. Synthesis of estrogen after pubertye. Expression of surface LH receptors

Testosterone

Testosterone

Actions of Androgens on Target TissuesMediated by Testosterone

• Differentiation of epididymis, vas deferens, and seminal vesicles

• Deepening of voice• Increased muscle mass• Pubertal growth spurt• Spermatogenesis• Negative feedback on anterior

pituitary• Libido• Cessation of pubertal growth

spurt (epiphyseal closure)

Mediated by Dihydrotestosterone

• Differentiation of penis, scrotum, and prostate

• Male hair pattern• Male pattern baldness• Sebaceous gland activity• Growth of prostate

Age-related changes in LH and testosteronesecretion in the normal male

1. Fetal life

Normal male development requires the presence of 3 hormones:testosterone,dihydrotestosterone, and the Müllerian inhibiting factor (MIH).

1. (hCG) + LH → Leydig cells → testosterone → Wolffian ducts

2. testosterone → dihydrotestosterone → urogenital sinus & genital organs

3. Sertoli cells → MIH → absence of female internal structures

• Wolffian ducts differentiate into the majority of male internal structures; namely, epididymis, vasa deferentia, and seminal vesicles.

• Dihydrotestosterone induces the urogenital sinus and genital tubercle to differentiate into the external scrotum, penis, and prostate gland.

Adults with bilateral cryptorchidism

• Elevated temperatures• FSH secretion is elevated, probably as a result

of decreased Sertoli cell production of inhibins.

• Testosterone secretion by the Leydig cells of cryptorchid testes also tends to be low, and as a result, LH secretion of is elevated.

ERECTION, EMISSION, AND EJACULATION

• Erection• Erection is caused by dilation of the blood vessels (a parasympathetic

response) in the erectile tissue of the penis (the corpora- and ischiocavernous sinuses).

• This dilation increases the inflow of blood so much that the penile veins get compressed between the engorged cavernous spaces and the Buck’s and dartos fasciae.

• As a result,for a brief period, inflow of blood to the penis exceeds outflow.

• Mediators that remove the chronic state of vasoconstriction are probably vasoactive intestinal peptide (VIP) and/or nitric oxide (NO). Acetylcholine may also be

involved.

Emission

• Emission is the movement of semen from the epididymis, vasa deferentia, seminal vesicles, and prostate to the ejaculatory ducts.

• The movement is mediated by sympathetic (thoracolumbar) adrenergic transmitters.

• Simultaneously with emission, there is also a sympathetic adrenergic-mediated contraction of the internal sphincter of the bladder, which prevents retrograde ejaculation of semen into the bladder.

• Destruction of this sphincter by prostatectomy often results in retrograde ejaculation.

Ejaculation

• Ejaculation is caused by the rhythmic contraction of the bulbospongiosus and the ischiocavernous muscles.

• Contraction of these striated muscles that are innervated by somatic motor nerves causes the semen to exit rapidly in the direction of least resistance, i.e., outwardly through the urethra.

• Ejaculation ,is mediated by somatic motor efferents.

Consequences of deficient testosterone production

• During second to third month of gestation -- ambiguity in the male genitalia and male pseudohermaphrodism.

• third trimester --leads to problems in testicular descent (cryptorchidism) along with micropenis.

• Puberty-- to poor secondary sexual development and overall eunuchoid features.

• Postpubertal --decreased libido, erectile dysfunction, decrease in facial and body hair growth, low energy, and infertility

Hormonal Changes in Specific Altered States