Male Reproductive system

Male Reproductive system

Objectives

At the end of this lecture, student will be able to

• List the organs of male reproductive system

• Describe the structure of male reproductive system

• Describe the process of spermatogenensis

• Explain the negative feedback control on blood levels of testosterone

Content

• Anatomy and Physiology of Male reproductive system

• Spermatogenesis

REPRODUCTIVE SYSTEM

• Reproduction - process by which new individuals of a species are produced and the genetic material is passed from generation to generation

The organs of reproduction are grouped as

• Gonads (produce gametes)

• Ducts (transport and store gametes)

• Accessory sex glands (produce materials that support gametes) and

• Supporting structures (have various roles in reproduction)

Male reproductive system

Sagittal section of male reproductive system

Anatomy of male reproductive system

Scrotum 

• A sac that hangs from the root of the penis 

• Consists of loose skin and underlying subcutaneous layer

• Supports the testes

• Single pouch of skin separated into lateral portions by a median ridge called the raphe

• Scrotal septum divides the scrotum into two sacs, each containing a single testis

• Septum - made up of a subcutaneous layer and muscle tissue, the dartos muscle

• Each testis in the scrotum is associated with cremaster muscle, a series of small bands of skeletal muscle

Testes/ Testicles

• Paired oval glands (gonads) in the scrotum

– Seminiferous tubules - sperm cells are made

– Sertoli cells (sustentacular cells)- nourish sperm cells and secrete inhibin

– Leydig (interstitial) cells, produce the male sex hormone testosterone

• Testes descend into the scrotum through the inguinal canals

• Failure of the testes to descend, cryptorchidism

• Sertoli cells - secrete androgen-binding protein (ABP) à binds to testosterone àkeeps its concentration high in the seminiferous tubule

- Secrets inhibin à inhibition of FSH helps à regulate the rate of spermatogenesis.

• Testosterone

-  Controls the growth, development, and maintenance of sex organs

-  Stimulates bone growth, protein anabolism, sperm maturation

-  Stimulates development of masculine secondary sex characters

System of ducts

• Ducts of the Testis

- Seminiferous tubules

- Straight tubules

- Rete testis

• Sperm flow out of the testes through the efferent ducts

• Ductus epididymis - site of sperm maturation and storage

• Ductus (vas) deferens

- Stores sperm

- Propels them toward the urethra during ejaculation

• Ejaculatory duct

- Union of the duct from the seminal vesicle and vas deferens

- Passage for ejection of sperm and secretions of the seminal vesicles into the first portion of the urethra, the prostatic urethra

• Urethra in males is subdivided into 3 portions:

- Prostatic

- Membranous

- Spongy (penile) urethra- ends at the external urethral orifice

Sagittal section of a testis showing seminiferous tubules

Accessory Sex Glands

Includes:

Seminal Vesicles/Seminal glands

- Convoluted pouch like structures

- Posterior to the base of the urinary bladder

- Anterior to the rectum

• Secrete alkaline, viscous fluid

- Neutralize acid in the female reproductive tract

- Fructose for ATP production by sperm

- Sperm motility and viability

- Semen coagulate after ejaculation

Prostate gland

• A single, doughnut-shaped gland

• About the size of a golf ball; Inferior to the urinary bladder

• Surrounds the prostatic urethra

• Secretes a milky, slightly acidic fluid (pH 6.5) contains

- Citric acid in prostatic fluid - ATP production via the Krebs cycle

- Proteolytic enzymes - break down the clotting proteins from the seminal vesicles

- Seminal plasmin in prostatic fluid- an antibiotic, destroy bacteria

Bulbourethral Glands

• Paired bulbourethral glands/Cowper’s glands; about the size of peas.

• Inferior to the prostate on either side of the membranous urethra

• Their ducts open into the spongy urethra

• Secrete an alkaline fluid into the urethra

- Protects the passing sperm by neutralizing acids from urine

• Secrete mucus

- Lubricates the end of the penis and the lining of the urethra

- Decreases the no. Of sperm damaged during ejaculation

Penis

• Contains the urethra

• Passageway for the ejaculation of semen and the excretion of urine

• Consists of

- A body

- Glans penis

- A root

• Body of the penis, composed of 3 cylindrical masses of tissue, each surrounded by fibrous tissue, tunica albuginea

- Two dorsolateral masses, corpora cavernosa penis

- Smaller midventral mass, the corpus spongiosum penis, contains spongy urethra

Glans penis

• Enlarged acorn-shaped region

• At the distal end of the corpus spongiosum penis

•   Its margin is the corona

• Covering the glans in an uncircumcised penis is the loosely fitting prepuce or foreskin

Root of the penis – attached portion

Has - Bulb of the penis

- The expanded portion of the base of the corpus spongiosum crura of the penis

Internal structure of the penis

Semen

• Mixture of sperm and seminal fluid

• Consists of the secretions of the seminiferous tubules, seminal vesicles, prostate, and bulbourethral glands

• Provides the fluid in which sperm are transported

• Supplies nutrients

• Neutralizes the acidity of the male urethra and the vagina

Internal structure of the penis

SPERMATOGENESIS

• Process whereby immature spermatogonia develop into sperm

• Occurs in the testes

• Takes 65–75 days

• Sequence includes

- Meiosis I

- Meiosis II

- Spermiogenesis

• Forms 4 haploid sperm (spermatozoa) from each primary spermatocyte

• Mature sperm consist of a head and a tail

• Function - fertilize a secondary oocyte

Hormonal Control of the Testes

• Release of FSH is stimulated by GnRH and inhibited by inhibin

• Release of LH is stimulated by GnRH and inhibited by testosterone.

Negative feedback control of blood level of testosterone

Gonadotrophs of the anterior pituitary produce luteinizing hormone (LH).

Summary

• Reproduction is the process by which new individuals of a species are produced and the genetic material is passed from generation to generation

• Reproductive organs – Gonads, Ducts, Accessory sex glands and

Supporting structures

• Male structures of reproduction include the testes, ductus epididymis, ductus (vas) deferens, ejaculatory duct, urethra, seminal vesicles, prostate, bulbourethral (Cowper’s) glands, and penis

• Spermatogenesis, occurs in the testes, is the process whereby immature spermatogonia develop into sperm

• Testosterone controls the growth, development, and maintenance of sex organs; stimulates development of masculine secondary sex characteristics

• Levels of testosterone in blood is controlled by negative feedback mechanism