Nervous system ppt/question, Schemes and Mind Maps of Law

Download Nervous system ppt/question and more Schemes and Mind Maps Law in PDF only on Docsity!

Male Reproductive System

Dr Reem Abraham

Learning Objectives

1. Describe spermatogenesis and the role of Sertoli cells, Leydig cells and the blood-testis barrier in this process.
2. Describe the actions and cellular mechanisms of testosterone and related androgens
3. Describe the biosynthesis, mechanism of transport within the blood, metabolism and elimination of testosterone and related androgens.
4. Describe the endocrine regulation of testicular function: the role of GnRH, FSH, LH, testosterone, and inhibin.
5. Describe the factors that determine sex differentiation and development of the male embryo.
6. Describe the physiological functions of the major components of the male reproductive tract.
7. Describe the process of capacitation of spermatozoa.
8. Describe the structure and function of spermatozoa.
9. List the components of semen and their functions.
10. List the major target organs for testosterone and other androgens.
11. Summarize the functions of the accessory male sex organs.
12. Describe the phases of the male sexual response and the mechanisms that produce erection and ejaculation.
13. Summarize the general structure of testosterone, and relate its biosynthesis, transport, metabolism, secretion and physiological actions. At the end of this lecture, students should be able to:

• At week 7 in genetic males: sex-determining region of the Y chromosome (SRY gene) /Testis-determining factor (TDF), causes the testes to begin developing Until week 5 of gestation period • Male gonads: testes
• Female gonads: ovaries

• At the same time, Antimüllerian hormone produced by testicular Sertoli cells causes atrophy of a second set of ducts, the müllerian ducts In female fetus, müllerian duct system then develops into uterine tubes (oviducts) and a uterus ✓ In male fetus, wolffian duct system develops into the epididymis and vas deferens, under the influence of TESTOSTERONE Embryonic differentiation of male and female internal genitalia (genital ducts) from wolffian (male) and müllerian (female) primordia.

Structure of the testis

1. Seminiferous tubules : loops of

convoluted tubules within the

testes; Spermatozoa are formed

in the walls of seminiferous

tubules

• Majority of the testes is

comprised of seminiferous

tubules

• The epithelium of Seminiferous

tubules contain SERTOLI CELLS

• Functions of Sertoli cells

1. Provide nutrients to the developing sperms
2. Blood-testes barrier: Tight junctions between adjacent Sertoli cells near the basal lamina forms a barrier between the testes and the bloodstream

• Functions of Blood-testis barrier : a) It allows only essential substances, hormones like testosterone to pass through it b) Prevents entry of damaging substances, prevents antigenic products of germ cell division and maturation from entering the circulation and generating an autoimmune response c) Maintenance of composition of the fluid in the lumen of seminiferous tubules depends on the blood–testis barrier. Structure of the testis

2. Leydig cells/interstitial cells of

Leydig

• SECRETE TESTOSTERONE (steroid

hormone)

Structure of the testis

• Epididymis: maturation and storage

of sperms

• Attain motility, after remaining in

epididymis for 18 to 24 hours

• Storage of Sperm in vas deferens

Functions of the accessory male sex organs

Male sex hormones

1. Testosterone: Primary

2. Dihydrotestosterone (DHT)

3. Androstenedione

• Testosterone secretion starts in male fetal testes at about the seventh

week of embryonic life

• In the accessory sex organs, especially prostate:
• Testosterone DHT

5 α-reductase

✓ Development of male external genitalia in the fetus is controlled most directly by DHT. ✓ 5 - alpha reductase deficiency in males causes a failure to develop external genitalia in utero.

• Ninety-eight percent of the circulating

testosterone is bound to plasma proteins,

such as gonadal steroid binding globulin

(GBG) or sex steroid-binding globulin and

albumin.

• Free (unbound) testosterone is biologically

active,

• In some target tissues, testosterone is the

active androgenic hormone.

• In other target tissues, testosterone must

be activated to dihydrotestosterone by

the action of 5α-reductase

Biosynthesis of testosterone and its mechanism of transport within the blood

Functions mediated by testosterone and dihydrotestosterone

enlargement of the prostate and the penis at the time of puberty Major target organs of testosterone:

1. Male reproductive organs
2. Muscle
3. Bone
4. Brain
5. Skin

Hypothalamic-pituitary gonadal axis

Control of testicular function by negative feedback mechanism

Negative feedback

SPERMATOGENESIS

• Begins in puberty
• Occurs in seminiferous tubules
• The entire period of spermatogenesis, from

spermatogonia to spermatozoa, takes about 74 days,

approximately 2 months

• Within the testes, spermatogonia

remain inactive until puberty.

• At puberty, spermatogonia undergo

mitosis to form primary

spermatocytes

• Primary spermatocytes undergo

meiotic division to form four

spermatids within a time span of 64

days.

• Spermatids develop into

spermatozoa under the influence of

testosterone (spermiogenesis).

SPERMATOGENESIS