Physiology of the male reproductive system D. Gehan Shaker Badawi (2015) – (2016)

Physiology of the male reproductive system

D. Gehan Shaker

Badawi

(2015) – (2016)

Specific objectives

At the end of this session, you should be able to:

1. Mention cell types of the testis

2. Mention the functions of Sertoli cells

3. List hormones involved in gametogenesis and steroidogenesis.

4. List hormones produced by the testis & describe their functions

5. Discuss biological effects of androgen (prenatal and postnatal effect).

6. Explain the mechanism of erection.

Male Reproductive System

Male Reproductive System

1ry sex organ 2ry sex organs

1. Gametogenesis 2. Steriodogenesis

Testes Glandular System

Tubular System

Epididymis Vas deference

A single coiled tube that essential for Motility and Maturation of the sperms

Essential for: Storage of sperms (in its ampulla) Transports of sperms to ejaculatory ducts.

Seminal vesicles

Secretes mucoid viscid fluid rich in Fructose, PGs, ascorbic acid & Fibrinogen

Prostate

thin milky alkaline fluid contains plasmin, buffers, HyaluronidaseCholesterol

Bulbourethral

Secretes mucous

The testes:

Represent 1ry sex organs in male

Have 2 main functions:

Spermatogenesis i.e. formation of mature

sperms.

Steroidogenesis i.e. synthesis and secretion of male

sex hormones (testicular androgens)

Histologically

Spermatogenic cells Sortoli cells Leydig Cells

Formation of mature sperm

1. Supportive2. Protective3. Nutritive Cells

Androgens Secretion

Cells of the Testis

Sortoli cellSpermatocytes

Leydig cell

Cells of the testis

Leydig Cells

Sertoli cell

Hormonal Control of testicular cells

Hypothalamus

GnRh

Anterior Pituitary

Follicle Stimulating Hormone (FSH)

Luteinizing Hormone (LH)

Sertoli Cells Interstitial Cells

TestosteroneAndrogen Binding

Protein (ABP)

Spermatogenesis

Spermatogenic cells

Inhibin

Testosterone

-ve feedback

-ve feedbackMainly inhibits FSH Specifically inhibit LH

Hormonal Control of testicular cells

Hypothalamus secretes gonadotropin releasing hormone (GnRH)

Anterior pituitary secretes FSH and LH

FSH causes Sertoli cells to secrete:

Androgen Binding protein (ABP)

Inhibin

LH causes interstitial cells to secrete testosterone

ABP binds testosterone its half-life stimulate spermatogenesis

Control of testicular function:

by Negative FB by

1. testosterone (on (hypothalamus & ant pituitary; against LH)

2. Inhibin (on anterior pituitary against FSH)

Sortoli cells

Histology

Site

Function of Sertoli cells

Large pyramidal Non motile Non proliferating Tubular cells

line the seminiferous tubules

1. Provide mechanical support for the growing gametes.

2. Provide nutrition support for growing gametes (high content of glycogen).

1. Supportive

Means: Convert spermatids to spermatozoa Mechanism: by removal of excess cytoplasm.

2. Spermiogenesis

Means: release of sperms from Sertoli cells to lumen of seminiferous tubules

Control: under the effect of LH.

3. Spermiation

Function of Sertoli cells

Secretion of fluid, rich in K+ , HCO3-,

Essential subs for maturation of sperms.4. Secretory

Sertoli cells synthesize and secrete the following (under the effect of FSH):

1. Inhibin Hormone ---- FSH secretion

2. Estradiol from androgenic precursors.

3. Mullerian duct-inhibiting factor preventing differentiation of the female internal sex organs in the male fetus.

4. Androgen-Binding Protein (ABP) binds testosterone its half-life

5. Blood-testis barrier: Is a memb. formed by tight junctions between the bases of Sertoli cells. It has two main functions:

1. It prevents harmful subs. in the bl. from reaching seminiferous lumen.

2. It keeps immunogenic germ cells in the seminiferous tubules from entering systemic circulation.

6. They Synthesize and secrete H-Y antigen: gonadal cells to differentiate as testes.

B) Leydig Cells (interstitial cells Leydig)

Site

Time of appearance

Function

Located between seminiferous tubules (20% of testicular mass).

They appear at 7-9th week of pregnancy.

They secrete androgens:

1. In the fetal life under effect of human chorionic

gonadotropin (HCG) secreted by the placenta.

2. At puberty under effect of pituitary gonadotropins).

C) The Spermatogenic cells

The spermatogonia are nonmotile stem cells that divide during the process of spermatogenesis to form mature sperms

Spermatogenesis

Def.

Time

Site

Duration

Maturation of Sperms Occurs in epididymis (needs 18h to 10 days).

Process of formation of spermatozoa from primitive germ cells.

Starts at average of 13 year throughout whole life but ing markedly in old age (Andropause)

Needs 74 days (+ 12-21 days for transport of sperms into the ejaculatory ducts).

Seminiferous tubules.

Storage of Sperms

Occurs in the vas deferens in suppressed inactive state by multiple inhibitory factors.

Factors affecting

1. Hormonal (Hypothamamic, testosterone, & others)2. Temperature 3. Dietary4. Extrinsic

1. Hormonal Factorsa) Hypothalamic-hypophysial-testicular Axis

At puberty ++ hypothalamic LHRH ++ pituitary gonadotropins; FSH and LH.

i) Function of FSH:

1. It maintains the gametogenic functions of the testes.

2. Stimulate Growth and secretory functions of Sertoli cells.

ii) Function of LH:

Stimulate Leydig cells testosterone ++ spermatogenesis.

b) Testosterone:Stimulate growth & division of spermatogenic cells.

Needed in high conc w is maintained by:

1. Lipid solubility of the hormone.

2. Presence of Androgen-Binding Protein (from

Sertoli cells).

3. Counter current exchange: exchange of

testosterone from systemic veins into

spermatic arteries w runs parallel but in

opposite direction to each other).

Spermatic artery

Systemic veinSystemic vein

Counter current exchange

NoteCounter current system

Counter current exchanger1. Thermoregulation (testes) 2. Testosterone (testes) 3. Thermoregulation (skin)4. Vasa recta in kidneyMultiplier system:

kidney

c) Other Hormones:

1. Inhibin: ---FSH secretion by a direct effect on

ant. pituitary.

2. Activins: are formed from inhibin precursors

and ++ FSH secretion.

3. Growth h: stimulates early division of

spermatogonia.

4. Thyroid h: essential for metabolic reaction

of spermatogenesis.

2. Temperature

The optimum temp. for spermatogenesis is 35°C (i.e.< body temp.) provided by:

1. Site of the testes: in the scrotum outside abdominal cavity.

2. Scrotal skin is thin, rich in sweat glands and with little subcutanous fat.

3. Counter current system (heat exchange between spermatic art. and veins).

4. Dartos ms buffer (contracts in cold and relaxes in hot weather).

Spermatic artery

Systemic veinSystemic vein

Counter current exchange

3. Dietary factors1. Starvation gonadotropin sec

2. Vit. A def. keratinization & atrophy of spermatogenic epith.

3. Vit. C deficiency testosterone synthesis

4. Extrinsic factors Mostly inhibit spermatogenesis:

Irradiation, Hypoxia and toxins , Certain infections

e.g. mumps destroy seminiferous tubules.

We got too much…..please GOD make him finish…….

Physiological function of testosterone

During fetal life

After birth

Sexual function

Metabolic function

Differentiation

Testicular descend

a) Testosterone Major hormone produced by the Leydig cells More than 98% of it is bound to plasma proteins & 2% is unbound.

b) Dihydrotestosterone Only 20% of dihydrotestosterone is synthesized in testis. 80% from the peripheral conversion of testosterone. Dihydrotestosterone is 2 times active than testosterone.

c) Androstenedione: Important steroid precursor for blood estrogens in men.

Hormones secreted by the testis

Physiologic Effects of Testosterone

A) During the Fetal Life

1- Differentiation & development of 2ry sex organs:

Leydig cells of testes secrete testosterone at 7-9th

week of gestation ++ Wolffian duct internal

genitalia in male.

2- It helps descend of testes from abd. cavity into

scrotum during the last 2 to 3 months of pregnancy.

1- 1ry sex organ Spermatogenesis 2. 2ry sex organs Growth & enlargement.3. Control of gonadotropin secretion (-ve FB)4. Development of male sex characters: a) Hair:

Hair especially in face, on chest, axilla and around anus.

Pubic hair is triangular in appearance with apex towards umbilicus.

The hair disappears from ant. part of scalp “temporal recession”.

(1) Sexual functions

B) After Birth

2ry sex charactersb) Voice: Deep & low pitched ( thickness of vocal cords).c) Skin:

is thickened with acne formation الشباب . حبd) Body conformation

Shoulders broaden and ms enlarge.e) Behavioural changes

sexual desire & males become aggressive.

1- Protein-anabolic effect which : Ms bulk (50% in ms mass. Bone growth with deposition of Ca2+ and finally closure of epiphysis. Thickness of the skin and vocal cords. BMR by 5-10%.

2- Increased RBCs count: 3- Effect on water and electrolytes:

Moderate Na+, K+, Ca2+,& water retention. The size of the kidneys.

(2) Metabolic

Effects

Mechanism of Erection

Mechanism of Erection

The penis consists of erectile tissue made up of three columns or cords of spongelike vascular spaces

Erection is accomplished by engorgement of the penis with blood (vasocongestion).

In the absence of sexual excitation, the erectile tissues contain little blood, because their arterioles are constricted. the penis remains small and flaccid.

During sexual arousal, these arterioles reflexly dilate and the erectile tissue fills with blood, causing the penis to enlarge.

The veins that drain the erectile tissue are mechanically compressed reducing venous outflow more vasocongestion.

Erection is achieved through Erection Reflex

Parasymp plays the most important role through its strong VD on the arterioles

The chemical mediator is nitric oxide (NO) that acts through generation of cGMP

cGMP is inactivated by phosphodiesterase 5 (PDE5)

Sildenafil (Viagra) inhibits PDE5 cGMP time of erection (but can’t initiate erection as it can't generate nitric oxide (NO)

Mechanism of Erection

Release of NO within the penile tissue

Generation of c GMP

Relaxation of smooth of bl vs

Dilatation arterioles & arteries

Expanding of sinusoids in corpora cavernosa

Compression of subtunical venular plexuses

Increasing of intracavernous pressure

Increased resistance to outflow from penis

MALE SEXUAL PERFORMANCE

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Erectile dysfunction or Impotence:

Failure to achieve or maintain an erection suitable for sexual intercourse. Affect 50% of men between 40 and 70 years old. May be due to:

1. Psychological factors.2. Physical factors.

A. Nerve damageB. Medication that interfere with autonomic function C. Problem with blood flow to the penis.

Sildenafil (Vigra): prescribed to treat erectile dysfunction. It does not produce an erection but it amplifies and prolongs an erectile response triggered by usual means of stimulation.

ABNORMALITIES OF TESTICULAR FUNCTION

1. Cryptorchidism:

descent of testes is incomplete, testes remain in the abdomen. Occurs in neonatal life.

1. Bilateral: Impaired Testosterone secretion and spermatogenesis.

2. Unilateral :Normal Testosterone and impaired spermatogenesis.

2. Male hypogonadism:

Clinical picture depends on whether testicular deficiency develops before or after puberty.

causes:– Testicular disease (Hypergonadotrophic Hypogonadism)– Disorder of hypothalamus or pituitary (Hypogonadotrophic

Hypogonadism)

3. Androgen secreting tumors :

Leydig cell tumors (a rare condition) leads to precocious pseudopuberty in prepubertal boys. 30

REFERENCES

Human physiology, Lauralee Sherwood, seventh edition.

Text book physiology by Guyton &Hall,11th edition.

Text book of physiology by Linda .s Costanzo, third edition.

Physiology by Berne and Levy, sixth edition.

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Thanks a lot my friend ………

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