Organs of the Male Reproductive System
Male Internal Accessory Organs
Male External Reproductive Organs
Erection, Orgasm, and Ejaculation
Hormonal Control of Male Reproductive Functions
Hypothalamic, Pituitary Hormones, and Male Sex Hormones
Organs of the Female Reproductive Systems
Female Internal Accessory Organs
Female External Reproductive Organs
Erection, Lubrication, and Orgasm
Hormonal Control of Female Reproductive Functions
Female Sex Hormones, Female Reproductive Cycle, and Menopause
Testes are the primary organs of the male reproductive system as they are responsible for creating the sex cells (sperm) of the male and the male hormone testosterone. Most males have two testes that are held just below the pelvic cavity by the scrotum.
Each testis is enclosed by a fibrous capsule. The capsule is surrounded by the scrotum. The capsule invades the testis and divides it into lobules. Each lobule is filled with seminiferous tubules. Spermatogenic cells that give rise to sperm cells line the tubules. Between the tubules are cells called interstitial cells that make testosterone.
The spermatogenic cells of the seminiferous tubules begin the process of making sperm cells but the sperm cells do not mature until they go to the epididymis. A mature sperm has the following three parts:
1) Head - oval in structure; it holds a nucleus that holds 23 chromosomes; the head is covered with an enzyme filled sac called an acrosome; the acrosome helps the sperm penetrate and egg.
2) Midpiece - portion of the sperm between the head and tail; it is filled with mitochondria that generate the energy needed by the cell to move.
3) Tail - the tail is a flagellum; the flagellum moves in such a way to propel the sperm forward.
Click here to see the structure of a sperm
Spermatogenesis is the process of sperm cell formation. At the beginning of spermatogenesis, spermatogenic cells are called spermatogonia. Spermatogonia contain 46 chromosomes. These cells undergo mitosis and the resulting cells are then called primary spermatocytes. Primary spermatocytes also contain 46 chromosomes. Primary spermatocytes (about the time of puberty) undergo a process called meiosis. In meiosis, each primary spermatocyte divides to make two secondary spermatocytes. Each secondary spermatocyte divides to make two spermatids. So, from one primary spermatocyte, you end up with 4 spermatids. The spermatids then develop flagella to become mature sperm cells. The spermatids end up containing only 23 pairs of chromosomes.
Click here to see the events of spermatogenesis
The following is a list of internal accessory organs of the male:
Each epididymis sits on top of each testis. An epididymis is a highly coiled tube that receives spermatids from the seminiferous tubules as these cells are formed. Inside the epididymis, the spermatids mature to become sperm cells.
The vas deferens are tubes that are connected to epididymises. They carry sperm cells from the epididymis to the urethra in the pelvic cavity of the male. When a male has a vasectomy, this is the tube that is cut and tied.
The seminal vesicle is a sac-like organ that secretes an alkaline fluid rich in sugars and prostaglandins. The sugars are used to make energy by sperm cells and the prostaglandins stimulate muscular contractions in the female reproductive system. These muscular contractions help to propel sperm forward in the female reproductive tract. Seminal vesicles release their product into the vas deferens.
The prostate gland surrounds the proximal portion of the urethra. It makes a milkly, alkaline fluid and secretes this fluid into the urethra. This fluid helps to protect the sperm as they enter the female reproductive system.
The bulbourethral glands are inferior to the prostate gland. They make a mucus-like fluid that is secreted during sexual excitement into the urethra. The fluid lubricates the end of the penis in preparation for sexual intercourse.
Click here to see the organs of the male reproductive system
Click here to see seminiferous tubules
Click here to see a summary of male reproductive organ functions
Semen is a mixture of sperm cells and fluids from the seminal vesicles, prostate gland and bulbourethral glands. This mixture is alkaline and contains nutrients and prostaglandins. One milliliter of sperm usually contains about 120 million sperm cells!
Click here to view a semen analysis
There are two male external reproductive organs as follows:
The scrotum is a pouch of skin that holds two testes. It contains a serous membrane which secretes serous fluid to ensure the testes move freely within it.
The penis is a cylindrical organ that conveys urine and semen to the outside. The body or shaft of the penis contains specialized tissue called erectile tissue. The urethra runs through the length of the penis. The end of the penis is enlarged into a cone-shape structure called the glans penis. If a male has not been circumcised, a piece of skin called the prepuce will cover the glans penis.
Click here to see a cross section of the penis
The parasympathetic nervous system causes the erectile tissue of the penis to become engorged with blood during sexual excitement which produces erection of the penis. The height of sexual excitement results in orgasm. During orgasm, sperm cells are propelled out of the testes towards the urethra. The secretions of the prostate, seminal vesicles, and bulbourethral glands are also released into the urethra. The movement of the sperm and secretions into the urethra is called emission. The process of ejaculation occurs when semen is forced out of the urethra. After ejaculation sympathetic nerve fibers cause the erectile tissue to release blood and the penis gradually returns to a flaccid state.
The hypothalamus, anterior pituitary and the testes secrete hormones that regulate male reproductive functions.
At the onset of puberty, the hypothalamus releases a hormone called gonadotropin releasing hormones (GnRH). GnRH stimulates the anterior pituitary to release FSH and LH.
FSH (follicle stimulating hormone) causes spermatogenesis to begin. LH (luteinizing hormone) stimulates interstitial cells to produce testosterone.
Male sex hormones are called androgens. The most important androgen is testosterone.
Testosterone stimulates the development of male secondary sex characteristics. Male secondary sex characteristics are characteristics that are usually unique to males. Examples of these characteristics are chest hair, thick facial hair, enlarged muscles, enlarged bones, and thickening of vocal cords to produce a deep voice. Testosterone also stimulates the maturation of male reproductive organs.
Testosterone levels in the male are regulated by a negative feedback mechanism. When testosterone levels increase above normal in the blood, the hypothalamus no longer secretes GnRH. Therefore, the anterior pituitary no longer secretes LH and FSH. Therefore testosterone levels fall. When testosterone levels fall below normal, the hypothalamus begins to secrete GnRH again which causes the anterior pituitary to release LH and FSH again. Now testosterone levels begin to rise again.
The ovaries are the primary sex organs of the female as they produce the sex cells (eggs) of the female. They also produce estrogen and progesterone.
Click here to see the location of the ovaries in the pelvic cavity
Most females have two ovaries. They are oval is shape and about 3.5 cm long. They are in the pelvic cavity.
An ovary is divided into a outer area called the cortex and an inner area called the medulla. The medulla contains nerves, lymphatic vessels, and many blood vessels. The cortex contains small masses of cells called ovarian follicles. Epithelial tissue and dense connective tissue cover each ovary.
Before a female child is born, primordial follicles develop in the cortex of her ovaries. The primordial follicles contain a large cell called a primary oocyte and smaller cells called follicular cells. The primary oocyte eventually undergoes meiosis to become a mature egg.
Oogenesis is the process of egg cell formation. At the onset of puberty some primary oocytes are stimulated to continue meiosis. When a primary oocyte divides it becomes one polar body (a nonfunctional cell) and a secondary oocyte. It is the secondary oocyte that is released from the ovary each much during ovulation. When the seconday oocyte is fertilzed, it will divide and form a mature fertilized egg cell a polar body. So, the process of meiosis begins before a female is born and completes only if a secondary oocyte is fertilized. The resulting mature egg cell will contain 23 chromosomes.
Click here to see the events of oogenesis
At puberty the anterior pituitary starts to release increased amounts of FSH (follicle stimulating hormone). This stimulates some primordial follicles to become primary follicles. A primordial follicle becomes a primary follicle when it enlarges and the numbers of follicular cells increase. A primary follicle also has a fluid filled cavity in it.
Under the influence of FSH the primary follicle will develop into a secondary follicle. The primary follicle becomes a secondary follicle when the primary oocyte divides and makes a seconday oocyte and a polar body. During ovulation, the secondary oocyte is released from the ovary into a uterine tube.
Click here to see the events of an ovarian cycle
The female accessory sex organs include the uterine tubes, uterus, and vagina.
Each uterine tube opens near the ovaries. The also open into the uterus. The end of a uterine tube near the ovary is expanded. This expansion is called an infundibulum; it functions to "catch" a secondary oocyte as it leaves an ovary. Uterine tubes are lined with ciliated cells. The cilia of these cells sweep the oocyte toward the uterus.
The uterus is a hollow, muscular organ that functions to receive an embryo and sustain its development.
The upper two-thirds of the uterus is called the body of the uterus. The narrow, lower portion of the uterus that extends into the vagina is called the cervix. The opening of the cervix is called the cervical orifice.
The wall of the uterus has three layers - 1) endometrium, 2) myometrium and 3) perimetrium. The endometrium is the innermost lining of the uterus. It contains numerous tubular glands that secrete mucus. The myometrium is the middle, thick, muscular layer. The perimetrium is a thin layer that covers the myometrium. It secretes serous fluid that coats the uterus.
The vagina is a tubular organ that extends from the uterus to the outside. It functions to receive the erect penis during sexual intercourse, and provides an open passageway for uterine secretions and an offspring.
The opening of the vagina is posterior to the urinary opening and anterior to the anal opening.
The wall of the vagina has three layers - 1) an innermost mucosal layer (secretes mucus), 2) a middle muscular layer and 3) an outermost fibrous layer.
Click here to see the organs of the female reproductive system
Click here to see a summary table of female reproductive organ functions
The female external reproductive organs are as follows:
The labia majora are rounded fold of adipose tissue and skin that serve to protect the other external reproductive organs. At their anterior ends the labia majora form the mons pubis which is a fatty area that overlies the pubic bones. The labia majora and mons pubis are typically covered in pubic hair in post puberty females.
The labia minora are folds that are between the labia majora. They are pinkish in color due to their high degree of vascularity. Anteriorly they merge together to form a hood over the clitoris.
The clitoris is anterior to the urethral opening. It contains erectile tissue and is rich in sensory nerves.
The vestibule is the space enclosed by the labia minora. There are two vestibular glands at the opening of the vagina that secrete mucus during sexual excitement. This mucus facilitates insertion of the penis into the vagina.
During sexual excitement, nervous stimulation causes the clitoris to become erect and the vestibular glands to become active. At the same time, the vagina elongates. If the clitoris is sufficiently stimulated, an orgasm will occur. During orgasm the walls of the uterus and uterine tubes contract to help propel sperm toward the upper ends of the uterine tubes.
At the onset of puberty, the hypothalamus secretes increasing amount of GnRH (gonadotropin releasing hormone). GnRH causes the anterior pituitary to release FSH and LH. FSH and LH then stimulate the ovary to produce estrogen, progesterone, and mature follicles. Estrogen and progesterone stimulate enlargement of reproductive organs and the female secondary sex characteristics. Female secondary sex characteristics are those characteristics that usually unique to females. The include breast development, increased vascularization of the skin, and increased fat deposits in the breast, thighs and hips,
The female reproductive cycle is also called a menstrual cycle. It consists of regular changes in the uterine lining which leads to a monthly period or bleeding. The following are the major hormonal changes that occur during one reproductive cycle.
1) Anterior pituitary releases FSH. FSH stimulates an ovarian follicle to mature.
2) The maturing follicle secretes estrogen. Estrogen causes the uterine lining to thicken.
3) Anterior pituitary releases a sudden surge of LH. The LH surge triggers ovulation.
4) Following ovulation, follicular cells of the follicle become a corpus luteum.
5) The corpus luteum secretes progesterone which causes the uterine lining to become more vascular and glandular.
6) If the released oocyte is not fertilized, the corpus luteum degenerates.
7) The degenerating corpus luteum causes estrogen and progesterone levels to fall; the fall of estrogen and progesterone cause the uterine lining to break down and bleeding (menses) starts.
8) When the anterior pituitary releases FSH, the reproductive cycle begins again.
Menopause is the termination of the menstrual cycle due to normal aging of the ovaries.
Mammary glands are accessory organs of the female reproductive system. They secrete milk after after pregnancy. Mammary glands are located beneath the skin in the breast area. A nipple is located near the center of each breast. The pigmented area that surrounds a nipple is called an areola.
Each gland is made of 15 to 20 lobes. Each lobe contains alveolar glands that make milk and alveolar ducts that deliver milk to openings on nipples.
Click here to view mammary glands
Coitus interruptus is the process of withdrawing the penis from the vagina before ejaculation. This method is not very reliable as small amounts of semen may enter the vagina before ejaculation.
The rhythm method requires abstinence from sexual intercourse around the time a female is ovulating. However, predicting ovulation is difficult.
Mechanical barriers prevent sperm from entering the female reproductive tract. They include condoms, diaphragms, and cervical caps.
Chemical barriers destroy sperm in the female reproductive tract. They include spermicides.
Birth control pills are oral contraceptives. These pills are normally low doses of estrogen or progesterone that prevent the hypothalamus from releasing the LH surge necessary for ovulation. So these pills, prevent ovulation.
Depo-provera is an injectable contraceptive. It prevents ovulation and alters the lining of the uterus so implantation of a blastocyst is not likely.
Contraceptive implants are small rods of progesterone that are implanted beneath the skin. They also prevent ovulation.
An intrauterine device (IUD) is a small, solid object a physician implants in the uterus. It prevents implantation of a blastocyst.
Tubal ligation is a surgical method used in females to prevent pregnancy. In this process, the uterine tubes are cut and ligated to prevent sperm from reaching the ooctye.
Vasectomy is a surgical method used in males to prevent pregnancy. In this process, the vas deferens are cut and ligated to prevent sperm from being ejaculated.