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
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 andS upporting 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
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