The Reproductive System

Mrs. Nina Abdelnaby

38.1 REPRODUCTIVE SYSTEM

Role of a Male in reproduction  The role of a male in sexual

reproduction is to produce sperm cells (haploid cells) and to deliver them to the female reproductive system to fertilize an egg cell (haploid cell).

What is Puberty?  Puberty is the adolescent stage of

development when changes in the body make reproduction possible.  Secondary sexual characteristics:  Growth of bodily hair  change of voice  Muscular build (male)/fat deposition

(female)  Development of mammary glands (females)  Growth spurt

Onset of Puberty  The onset of puberty is predetermined genetically (i.e. runs in families)  The hypothalamus stimulates the pituitary gland to release hormones. Puberty starts in males and females by the production of FSH (follicle stimulating hormone) & LH (leutinizing hormone) by the pituitary gland.

Male reproductive structures: Testes  Testes (singular, testis):

two egg-shaped organs where gametes are produced  The testes develop within the abdominal cavity. Before a male is born, the testes descend into an external sac called the scrotum.  The temperature within

the scrotum is 2oC to 3oC cooler than the temperature inside the body—37oC. This cooler temperature is necessary for development of normal

 Each testis contains 250 compartments containing tightly coiled tubules called seminiferous tubules. Sperm forms through meiosis in the specialized lining of this

Role of Hormones

Formation of Sperm  Males begin to produce sperm during puberty  Two hormones released by the anterior pituitary regulate the functioning of the testes  Luteinizing hormone (LH) stimulate secretion of the hormone testosterone (main male sex hormone)  Testosterone is produced by the testes  Follicle-stimulating hormone (FSH), along with testosterone, stimulates sperm production in the seminiferous tubules

 A male will continue to produce sperm as long as his testosterone level is high

Formation of gametes  Meiosis results in the reduction of the

number of chromosomes from diploid (2n) to haploid (1n).  As the cells that produce sperm undergo meiosis, the chromosome number drops from 46 to 23.  4 sperm cells result from each cell that begins meiosis.

Structure of a mature sperm The mature sperm consists of 3 regions 2. Head: the tip of the head contains enzymes. During fertilization these enzymes help the sperm penetrate the protective layers that surround the egg cell. The head also contains 23 chromosomes. 3. The midpiece: is packed with mitochondria. These mitochondria supply the energy required for sperm to reach an egg. 4. Tail: consists of a single, powerful flagellum that propels the sperm.

Path of Sperm through the Male Body  Sperm move from the seminiferous tubules in

the testes to the epididymis (a long, coiled tubule that is closely attached to the testis)

 Within each epididymis, a sperm matures and gains

the ability to swim as its flagellum completes development. Some sperm is stored in the epididymis.

 Some sperm leaves the epididymis and pass

through the vas deferens (a duct that extends from the epididymis)  Vas deferens loops around the urinary bladder and merges with the urethra.  Sperm exists the body through the urethra (so does urine—but not at the same time)

Sperm is mixed with fluid produced by 3 exocrine glands  Seminal vesicles: produce a fluid rich

in sugars—fructose— that the sperm use for energy  The prostate gland: secretes an alkaline fluid that neutralizes the acids in the urethra of the male & female vagina.  The bulbourethral glands: secretes an alkaline fluid that neutralizes traces of acidic urine in the urethra.

Semen  Sperm mixed with secretions from

the seminal vesicles, prostate gland, and bulbourethral glands form a fluid called semen.

Release of Sperm  When a male becomes aroused, the spongy tissue in the penis fills with blood—this causes the penis to become erect.  Semen is forcefully expelled from the penis by contractions of the smooth muscles that line the urethra. This process is called ejaculation.  Each ejaculation expels 2-5 mLof semen. Each mLcontains 50-130 million sperm. Most of them are killed by the

Review questions  Why are the testes found in the scrotum and not inside the male body?  Describe the mature sperm.  Describe the path that sperm take in exiting the body.  What is the function of the vas deferens?  Which structures in a male produce fluids that mix with sperm to form semen?  Why are so many sperm produced by the male reproductive system?  In what way are sperm different from the body’s other cells?  The wearing of tight underwear has been linked to low sperm counts in some men. Explain how