Human Reproduction

Chapter 9

Human Reproduction

Female Reproductive System

The parts of female reproductive system include:

1.        The Ovaries (Female Gonads)

2.       Oviducts or the uterine tubes or fallopian tubes

3.       The Uterus

4.       The Vapina

5.       External Organs Which are collectively called the vulva, or pudendum.

Ovaries

• The ovaries (female gonads) are paired glands. Each ovary resembles in size and shape as that of unshelled almond.
• Each ovary has two important functions.

1. Production of gametes, secondary oocytes that develop into mature ova (eggs) after fertilization, and 
2. Production of hormones- progesterone, estrogens, inhibin and relaxin.

Uterine Tubes

•         Two uterine (fallopian) tubes, or oviducts, that extend laterally from the uterus.
•         The tubes, which measure about 10 cm (4 in.) long.
•         Important function of these tubes is to provide route for sperm to reach an ovum and transport secondary oocytes and fertilized ova from the ovaries to the uterus.

Uterus

• It is located between the urinary bladder and the rectum.

• It is the size and shape of an inverted pear.

Functions of Uterus:

• It provides pathway for sperm deposited in the vagina to reach the uterine tubes.

• It is the site of implantation of a fertilized ovum, development of the fetus during pregnancy, and labor.

• During reproductive cycles when implantation does not occur, the uterus is the source of menstrual flow

Vagina

• The vagina is a tubular, 10 cm long fibromuscular canal lined with mucous membrane that extends from the exterior of the body to the uterine cervix.

• It is located between the urinary bladder and the rectum.

Functions of Vagina

1. It is the receptacle for the penis during sexual intercourse
2. It is the outlet for menstrual flow
3. It is the passageway for childbirth

Vulva      

The term vulva, or pudendum, refers to the external genitals of the female.Vulva is composed of following parts: 

• Mons pubis: It is anterior to the vaginal and urethral openings. It is an elevation of adipose tissue covered by skin and coarse pubic hair that cushions the pubic symphysis.   

• Labia majora: From the mons pubis, two longitudinal folds of skin, called labia majora, extend inferiorly and posteriorly.

• The clitoris is a small cylindrical mass composed of two small erectile bodies, the Corpora cavernosa, and numerous nerves and blood vessels.

Oogenesis and Follicular Development

• The formation of gametes in the ovaries is termed oogenesis. Oogenesis occurs in essentially the same manner as spermatogenesis; meiosis takes place and the resulting germ cells undergo maturation.

The Female Reproductive Cycle    

• The female reproductive cycle is controlled by hormonal changes.

• It involves ovarian and uterine cycle

1. Ovarian cycle: It consists of sequence of actions in ovaries that occur during and after maturation of oocyte.

2. Menstrual (uterine) cycle: It consists of simultaneous sequence of changes in uterine endometrium preparing it for arrival of fertilized ovum

Male Reproductive System 

The parts of the male reproductive system are:

1.The testes  

2. A system of ducts:

• Epididymis
• Ductus deferens
• Ejaculatory ducts
• Urethra    

3. Accessory sex glands    

• Seminal vesicles 
• Prostate gland   
• Bulbourethral glands  

4. The penis

5.   5. The scrotum

Testes         

• The testes are paired oval glands located in the scrotum.    

• Each testis measure about 5 cm long and 2.5 cm in diameter and has a mass of 10—15 grams.          

• Each testis consists of internal compartments called lobules. Each of the 200—300 lobules contains one to three tightly coiled tubules and the seminiferous tubules.

• Sperms are produced in the seminiferous tubules

System of Ducts

Ducts of the Testis        

• The sperm and fluid is pushed along the lumen of seminiferous tubules and then into a series of very short ducts called straight tubules.      

• The straight tubules lead to a network of ducts in the testis called the rete testis.

• From the rete testis, sperm move into a series of coiled efferent ducts in the epididymis that empty into a single tube called the ductus epididymis.

Epididymis

• The epididymis is a comma-shaped organ about 4 cm long that lies along the posterior border of each testis.

• Each epididymis consists mostly of the tightly coiled ductus epididymis.

Ductus Deferens      

• Within the tail of the epididymis, the ductus epididymis becomes less convoluted, and its diameter increases. Beyond this point, the duct is known as the ductus deferens or vas deferens.

Urethra       

• In males, the urethra is the shared terminal duct of the reproductive and urinary systems; it serves as a passageway for both semen and urine.    

• About 20 cm long, it passes through the prostate, the deep muscles of the perineum, and the penis.

Accessory Sex Glands

The ducts of the male reproductive system store and transport sperm cells, but the accessory sex glands secrete most of the liquid portion of semen.       

The accessory sex glands include:

1.        The seminal vesicles

2.       The prostate

3.       The bulbourethral glands     

   The seminal vesicles

• The paired seminal vesicles or seminal plands are convoluted pouch like structures, about 5 cm in length, lying posterior to the base of the urinary bladder.

• Through the seminal vesicle ducts they secrete an alkaline, viscous fluid that contains fructose (a monosaccharide sugar), prostaglandins, and clotting proteins that are different from those in blood.

The prostate

• The prostate is a single, doughnut-shaped gland about the size of a golf ball.

• It measures about 4 cm from side to side, about 3 cm from top to bottom, and about 2 cm (0.8 in.) from front to back.

• It is inferior to the urinary bladder and surrounds the prostatic urethra. 

• The prostate secretes a milky, slightly acidic fluid (pH about 6.5) that contains several substances like Citric acid, proteolytic enzymes, such as pepsinogen, lysozyme, amylase, and hyaluronidase.

Bulbourethral Glands   

• The paired bulbourethral glands, or Cowper ‘s glands, are about the size of peas.

• They are located inferior to the prostate on either side of the membranous urethra within the deep muscles of the perineum, and their ducts open into the spongy urethra.

Penis     

• The penis contains the urethra and is a passageway for the ejaculation of semen and the excretion of urine.

• It is cylindrical in shape and consists of a body, glans penis, and a root

Scrotum

• The scrotum (bag), the supporting structure for the testes, consists of loose skin and underlying subcutaneous layer that hangs from the root (attached portion) of the penis

Spermatogenesis

• The process by which the seminiferous tubules of the testes produce sperm is called spermatogenesis.

• The total duration of spermatogenesis in humans is 65-75 days.

• Spermatogenesis starts with the spermatogonia, which contain the diploid (2n) number of chromosomes.

The final stage of spermatogenesis spermiogenesis, is the development of haploid spermatids. 

Menstrual Cycle           

• It is the regular natural change of female reproductive system. It is the reason of pregnancy and required for the production of ovocytes and also for the preparation of uterus for pregnancy. Pregnancy is only possible due to menstrual cycle.

• It normally starts between twelve and fifteen years of the ape. The frequency of menstrual cycle is after 21 to 40 days and an average after every 28 days.       

• Menstruation (bleeding) usually lasts for 2 to 7 days (average four days).          

• Common symptoms of menstruations are acne, tender breasts, bloatinp (inflation) and feeling of tiredness.       

•  It is governed by hormonal changes. Menstrual cycle is divided in three phases based onevents in the ovary i.e. ovarian cycle or in the uterus i.e. uterine cycle.