Anatomy of The Reproductive System

Anatomy of The Reproductive System

ANATOMY OF THE REPRODUCTIVE SYSTEM RITA ADJEI INTRODUCTION The formation of a new individual begins with a sperm from a male and an ovum (more precisely an oocyte) from a female. Sperm and oocytes are the gametes or sex cells. They provide a mechanism for forming a new individual

and mix genetic contributions from past generations. Sperms and oocytes are produced in the reproductive system, which is organized similarly in the male and female. Each system has paired structures called gonads where the sperm and the oocytes are manufactured, tubules to transport these cells and hormones and secretions that control the process. The male and female reproductive systems are a connected series of organs and glands that

produce and nurture sex cells and transport them to sites of fertilization. ORGANS OF THE MALES REPRODUCTIVE SYSTEM Organs of the male reproductive system produce and maintain male sex cells, transport these supporting fluids to the outside and secrete male sex hormones. A males primary sex organs (gonads) are the two

testes in which sperm cells and male sex hormones form. The accessory sex organs of the male reproductive system are the internal and external reproductive organs. TESTES The testes (singular testis) are ovoid structures about 5cm in length and 3cm in diameter. They lie outside the abdomen within a sac

called the scrotum. Lying outside the abdominal cavity exposes the testes to a lower temperature than the rest of the body which is necessary for sperm to develop. Structure: A tough white fibrous capsule encloses each testis. Along the capsules posterior border, the connective tissue thickens and extends into the testis forming thin

septa that divides the testis into about 250 lobules. Each lobule contains one to four highly coiled convolution seminiferous tubules, each approximately 70cm long uncoiled. A specialized stratified epithelium with spermatogenic cells, which give rise to sperm cells lines the seminiferous tubules. Other specialized cells called interstitial cells lie in the spaces between the seminiferous tubules. Interstitial cells produce and secrete male sex hormones ( esp. testosterone)

MALE EXTERNAL REPRODUCTIVE ORGANS The male external reproductive organs are the scrotum, which encloses the testes and the penis. The urethra passes through the penis. SCROTUM It is a pouch of skin and subcutaneous tissues

that hangs from the lower abdominal region posterior to the penis. A medial septum subdivides the scrota into two chambers each of which encloses a testis. Each chamber also contains a serous membrane which covers the testis and helps ensure that it moves smoothly within the scrotum. The scrotum protects and helps regulate the temperature of the testes, factors necessary for sex cell production.

Exposure to cold causes the smooth muscles in the walls of the scrotum to contract, the scrotal skin to wrinkle and the testes to move closer to the pelvic cavity, where they can absorb heat. Exposure to warm causes the smooth muscle to relax and the scrotum to hang loosely, providing an environment conducive for sperm production and survival.

PENIS The penis is a cylindrical organ that conveys urine and semen through the urethra to the outside. During erection, it enlarges and stiffens so that it can be inserted into the vagina during sexual intercourse. The body or shaft of the penis has three columns of erectile tissue- a pair of dorsally located corpora cavernosa and single, ventral, corpora spongiosum.

A tough capsule of dense connective tissue surrounds each column. Skin, a thin layer of subcutaneous tissue and a layer of connective tissue enclose the penis. The corpus spongiosum, through which the urethra extends, enlarges at its distal end to form a sensitive, cone-shaped glans penis. The glans covers the ends of the corpora cavernosa and bears the urethral opening. The

skin of the glans, is very thin and hairless, and contains sensory receptors for sexual stimulation. A loose fold of the skin called the prepuce (foreskin) covers the glans as a sheath and it is sometimes removed by a surgical procedure called circumcision. MALE INTERNAL ACCESSORY ORGANS The internal accessory organs of the male

reproductive system are specialized to nurture and transport sperm cells. These structures include epididymis, vas deferens, ejaculatory ducts, urethra, seminal vesicles, prostate glands and bulbourethral glands. EPIDIDYMIS Each epididymis (plural epididymides) is a tightly coiled duct/tube about 6cm long.

It emerges from the top of the testis, descends along the posterior surface of the testis and then courses upwards to become the vas deferens. Sperm cells mature and are stored in the epididymis. VAS DEFERNS Each vas deferens (vasa deferentia) also called ductus deferens is a muscular tube about 45cm long.

It passes upward along the medial side of a testis and through a passage in the lower abdominal wall (inguinal canal), enters the pelvic cavity and ends behind the urinary bladder. Just outside the prostate gland, the vas deferens unites with the duct of a seminal vesicle to form ejaculatory duct which passes through the prostate gland and empties into the urethra. SEMINAL VESICLES

A seminal vesicle is a convoluted sac-like structure about 5cm long that is attached to the vas deferens near the base of the urinary bladder. The glandular tissue lining of the inner wall of a seminal vesicle secretes a slightly alkaline fluid. This fluid helps regulate the pH of the tubular contents as sperm cells travel to the outside. Seminal vesicle secretions also contain fructose (a monosaccharide) that provides energy to sperm cells and prostaglandins which stimulate muscular

contractions within the female reproductive organs, aiding the movement of sperm cells toward the egg cell. PROSTATE GLAND The prostate gland is a single, donut-shaped gland that surrounds the upper portion of the urethra just below the bladder. It is enclosed in connective tissue and composed of many branched tubular glands,

whose ducts open into the urethra. The gland secretes a thin, milky fluid with an alkaline pH. Prostatic fluid enhances the motility of sperm cells and helps neutralize the acidic secretions of the vagina. BULBOURETHRAL GLANDS The two bulbourethral glands (Cowpers gland) are each about a centimeter in diameter and are inferior to the prostate gland on either side of the

urethra. The glands are pea-sized organs. They secrete an alkaline mucus that coats the urethra before sperms are released. This fluid also lubricates the end of the penis in preparation for sexual intercourse. All of the secretions from seminal vesicles, prostate gland, bulbourethral glands combine to form the seminal fluid that caries sperm.

SEMEN Semen is the fluid the male urethra conveys to the outside during ejaculation. It consists of sperm cells from the testes and secretions of the seminal vesicles, prostate gland and bulbourethral glands. Semen is slightly alkaline (pH about 7.5) and its contents include prostaglandins and nutrients. The volume of semen released at one time varies from 2 to 5 milliliters. The average number of sperm cells in the fluid is

about 120 million per milliliter. Sperm cells are non motile while in the ducts of the testes and epididymis but begins to swim as they mix with accessory secretions. ERECTION, ORGASM AND EJACULATION IN MALES During sexual stimulation, parasympathetic nerve impulses from sacral portion of the spinal cord, release the vasodilator nitric oxide (NO), dilating the arteries leading into the penis.

At the same time, the increasing pressure of the arterial blood entering the vascular spaces of erectile tissue compresses the veins of the penis, reducing flow of venous blood away from the penis. Consequently, blood accumulates in erectile tissue and the penis swells and elongates, producing an erection. Erectile dysfunction exists when the erectile tissue doesnt expand enough to compress the

veins. At the peak of sexual stimulation, a pleasurable feeling of physiological and psychological release called orgasm occurs. Emission and ejaculation accompany male orgasm. Emission is the movement of sperm cells from the vas deferens and secretions from the seminal vesicle and prostate gland into the urethra.

Once semen is in the urethra, rhythmic muscle contraction causes it to be expelled from the penis in spurts (ejaculation). During ejaculation, a sphincter closes off the bladder so that no urine enters the urethra. Following ejaculation the penis returns to its normal flaccid state. After ejaculation, a male typically experiences a period of time called the refractory period during

which stimulation does not bring an erection. ORGANS OF THE FEMALE REPRODUCTIVE SYSTEM The organs of the female reproductive system produce and maintain the female sex cells, the egg cells (oocytes); transport these cells to the site of fertilization, provide a favourable environment for a developing offspring to the outside and produce female sex hormones. A females primary sex organs (gonads) are the

two ovaries which produce the female sex cells and sex hormones. The accessory sex organs of the female reproductive system are the internal and the external reproductive organs. OVARIES The ovaries are solid ovoid structures each about 3.5cm long 2cm wide and 1cm thick. They lie in shallow depressions in the lateral

wall of the pelvic cavity. Structure: Ovarian tissues are subdivided into two indistinct regions- an inner medulla and an outer cortex. The medulla is composed of loose connective tissue and contains many blood vessels, lymphatic vessels and nerve fibers. The cortex consists of more tiny masses of

cells called ovarian follicles. A layer of cuboidal epithelium covers the ovarys free surface. Just beneath the epithelium is a layer of dense connective tissue. FEMALE EXTERNAL GENITALIA The external accessory organs of the female reproductive system include the labia majora, labia minora, clitoris and vestibular glands.

These structures surround the openings of the urethra and vagina, and compose the vulva. LABIA MAJORA The majora enclose and protect the other external organs. They correspond to scrotum in males and are composed of rounded folds of adipose tissue and a thin layer of smooth muscle covered by skin and hair.

The labia majora lie close together. At their anterior ends they merge together to form a round elevation of adipose tissue called mons pubis, which overlies the symphysis pubis. LABIA MINORA They are flattened, longitudinal folds between the labia majora. They are composed of connective tissue richly supplied with blood vessels, giving a pinkish

appearance. Posteriorly, minora merge with the labia majora, while anteriorly they converge to form a hair like covering around the clitoris. CLITORIS It is a small projection at the anterior end of the vulva between the labia minora. It is usually about 2cm long and 0.5cm in diameter.

The clitoris corresponds to the penis in males and has similar structure. It is composed of two columns of erectile tissue called corpora cavernosa. At its anterior end, a small mass of erectile tissue forms a glans which is richly supplied with sensory nerve fiber. VESTIBULE The Labia minora encloses a space called the

vestibule. The vagina opens into the posterior portion of the vestibule and the urethra opens in the midline just anterior to the vagina and about 2.5cm posterior to the glans of the clitoris. A pair of vestibular glands, corresponding to bulbourethral glands in males lie on either side of the vaginal opening. Beneath the mucosa of the vestibule on either side is a mass of vascular erectile tissue called

vestibular bulb. FEMALE INTERNAL ACCESSORY GLANDS This includes a pair of uterine tubes, an uterus, and a vagina. VAGINA The vagina is a fibromuscular tube about 9cm long, extending from the uterus to the outside. It conveys uterine secretions, receives the erect penis during sexual intercourse and provides an

open channel to the offspring during child birth. The vagina extends upwards and back into the pelvic cavity. It is posterior to the urinary bladder and urethra, anterior to the rectum and attached to these structures by connective tissues. A thin membrane of connective tissue and stratified squamous epithelium called the

hymen partially covers the orifice. The vagina wall has three layers: The inner mucosa layer is a stratified squamous epithelium. This layer lacks mucous glands; the mucus in the lumen of the vagina comes from uterine glands and vestibular glands at the mouth of the vagina. The middle muscular layer consists mainly of smooth muscle fibers. A thin band of striated muscle at the lower end of the vagina helps close the vagina

opening. Another voluntary muscle, bulbospongiosus) is primarily responsible closing this orifice. The outer fibrous layer consists of dense connective tissue interlaced with elastic fibers. It attaches the vagina to the surrounding organs. UTERUS The uterus is a hollow, muscular organ shaped somewhat like an inverted pear. The size of the uterus changes greatly during

pregnancy. In its non-pregnant adult state, the uterus is about 7cm long, 5cm wide and 2.5cm in diameter. It is located medially within the anterior portion of the pelvic cavity, superior to the vagina and usually bends forward over the urinary bladder. The upper two-thirds or body of the uterus has a dome-shaped top.

The uterine tubes enter the top of the uterus at its broadest part. The lower third of the uterus is called cervix. This tubular part extends downward into the upper portion of the vagina. The cervix surrounds the opening called cervical orifice through which the uterus opens into the vagina. The uterine wall is thick and has three layers:

The endometrium, the inner mucosal layer is covered with columnar epithelium and contains abundant tubular glands. The myometrium, a thick middle, muscular layer consists largely of bundles of smooth muscle fibers. The perimetrium is an outer serosal layer that covers the body of the uterus and part of the cervix. The uterus receives embryo and sustains its divert.

UTERINE TUBES The uterine tubes (oviducts or fallopian tubes) open near the ovaries. Each tube is almost 10cm long and passes medially to the uterus penetrates its wall and opens into the uterine cavity. Near each ovary, a uterine tube expands forming a funnel shaped Infundibulum which partially encircles the ovary.

Finger-like projections called Fimbriae, fringe the infundibulum margin. Although the Infundibulum does not touch the ovary, one of the larger extensions corrects directly the ovary. Simple columnar epithelial cells, some ciliated, line the oviduct. The epithelium secretes mucus and the cilia beat toward the uterus. These actions help draw the secondary oocytes

and expelled follicular fluid into the Infundibulum following ovulation. Ciliary action and peristaltic contractions of the uterine tubes muscular layer help transport the secondary oocytes down the uterine tube.

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