Reproductive System 

Human reproductive system, organ system by which humans reproduce and bear live offspring .



·         Male Reproductive System Testosterone is responsible for the development of secondary sexual characteristics like the development of facial hair, deep voice, and an abrupt increase in height in

males.



 

A male reproductive system is a group of organs and hormones that play a role in human reproduction. These organs and hormones are present either inside or outside the pelvis.

 

Organs of Male reproductive System

 

-     Two testes                                       - Two epididymides                   - Two different ducts (vas deference)

 

-     Two spermatic cords               - Two seminal vesicles             - Two ejaculatory duct

 

-     A prostate gland                          - A penis

 

Testes

·         The testes are the male reproductive glands that are about 4.5 cm long, 2.5 cm wide and 3 cm thick and surrounded by three layers of tissues namely, tunica vaginalis, tunica albuginea, and tunica vasculosa.

·         A testis is composed of 900 coiled seminiferous tubules in which the sperms are formed.

·         Between these tubules are interstitial cells or Leydig cells which produce the hormone testosterone after puberty. Testosterone is responsible for the development of secondary sexual characteristics like the development of facial hair, deep voice, and an abrupt increase in height in males.

 ·         The seminiferous tubules are folded and tightly packed to form the epididymis which comes out of the scrotum in the form of vas deferens.

 ·         Seminiferous tubules in testes are also responsible for the storage of sperms. Leydig cells in the tubules provide essential nutrients for the sperms during storage.


Spermatic cords

-       The testes are suspended in the scrotum with the help of the spermatic cords. This cord is composed of a testicular artery, testicular veins, lymphatics, a deferent duct, and testicular nerves, and the vas deferens (ductus deferens). Spermatic cords are covered by a layer of connective tissues and smooth muscles. 

-       Vas deferens forms a part of the spermatic cord which allows the transfer of sperm from the testes to the ejaculatory duct.

-       Since the cords are provided with numerous blood vessels and nerves, it provides the continuous flow of blood throughout the male reproductive system.

Seminal Vesicles

-          Seminal Vesicles are small fibromuscular organ surrounded by a columnar epithelium present on either side of the urinary bladder. From each of the seminal vesicles, a small duct is originated that connects to the vas deference to form the ejaculatory duct.

 ·         The seminal vesicles secretes mucoid fluid rich in fructose, citric acid, and other essential nutrients which provides nutrients and energy for the sperms until one of the sperm fertilizes the ovum.

 

Prostate gland 

·         The prostate gland is present in the pelvic cavity in front of the rectum and is surrounded by an outer fibrous layer, a layer of smooth muscle, and the glandular substance made up of columnar epithelial cells.

·         A prostate gland secretes a thin milky fluid that is comprised of calcium ions, citrate ions, and phosphate ions along with some fibrinogen and prostaglandins, which adds to the bulk of the semen. 

·         The slightly alkaline nature of the fluid has a vital role in the successful fertilization of the ovum. The liquid in the ejaculatory duct is acidic owing to the citric acid and metabolic products of the sperm, which ultimately, results in inhibition of sperm fertility.

 Penis

 ·         It is formed of three cylindrical masses called erectile tissue and some involuntary muscles. The erectile tissue is composed of fibrous connective tissue and is covered by skin with a large amount of blood supply.

 ·         A penis has two lateral columns called corpora cavernosa and the column between them containing the urethra is called corpora spongiosum.

 ·         The tip of the penis is structured into a triangular structure called glans penis above which is a movable folded skin called a prepuce.

·         The blood to the penis is supplied by a deep, dorsal, and bulbar arteries and whereas the blood is drained to the iliac veins through a bundle of veins in the penis.

 ·         It is provided with autonomic and somatic nerves.

 ·         The rapid flow of blood causes the ballooning of the fibrous tissues to the extent that causes the penis to be erect and hard.

 

Hormones involved in male reproductive system

 ·         Testosterone: This hormone is secreted by Leydig cells or interstitial cells present in the testes, which is involved in the development and division of germinal cells during the early stages of spermatogenesis.

 ·         Luteinizing hormone: This hormone is secreted by the pituitary gland, which stimulates the Leydig cells to release testosterone hormone.

·         Follicle Stimulating hormone: This hormone is also secreted by the anterior pituitary and functions in the stimulation of Sertoli cells which allows the conversion of spermatids into sperms.

·         Estrogen: Estrogen formed from the Sertoli cells also play some role in spermatogenesis.

 

Female Reproductive system

 

The organs in the female reproductive system are divided into external organs and internal

 organs. External organs of the female reproductive system




- Labia majors                                      - Labia minora             - Vestibular gland (Bartholin’s gland)

- Clitoris      - Hymen              - Vaginal orifice

 

Internal organs of the female reproductive system

-     Vagina                      - Uterus                   - Uterine tubes (Fallopian tubes)         -          Ovaries

 

External Genetilia (Vulva): The external organs in the female reproductive system are collectively termed, vulva consisting of labia majora, labia minora, clitoris, vaginal orifice, vestibular gland, and hymen. Labia majora

 

·         These are large muscular folds surrounding the vulva, comprised of skin, fibrous tissue, fat, and a large number of sebaceous glands.

 

Labia minora

 ·         A smaller fold present beneath the labia majora is the labia minora. It is also provided with a large number of sebaceous glands.

·         The cleft between the two folds is called the vestibule, which is the opening for the vagina, vestibular glands, and urethra.

 ·         Clitoris has numerous sensory nerve endings and corresponds to the penis in Male. They have no reproductive significance.

·         The hymen is a thin mucosal membrane present in front of the opening of the vagina. Vestibular glands

 ·         Vestibular glands (Bartholin’s gland) are small pea-sized glands with ducts opening into the vestibule. These are present on either side of the vaginal opening

 ·         The secretion of these glands helps to keep the vagina moist.

 

Internal Genitalia

·          The internal genitalia is present in the pelvic cavity of a female and consists of a uterus, a vagina, two    uterine tubes two ovaries.

Ovaries

 

-          An ovary is the gonad of the female reproductive system which produces an ovum that develops into a zygote after fertilization.

 ·         Ovaries are female gonads or glands that exist in pairs in humans and each lie on the ovarian fossa present on the lateral wall of the pelvis.

·         They are 2-3 cm long, 2 cm wide, and 1 cm in thickness. The ovaries are attached to the upper part of the uterus by the ovarian ligament called mesovarium and are connected to the fallopian tubes by a deep tissue called an infundibulopelvic ligament.

·         An ovary is surrounded by a capsule which encloses an outer cortex and an inner medulla. The capsule is a fibrous connective tissue called tunica albuginea.


1.      Medulla: It lies in the middle of the ovary and consists of blood vessels, fibrous tissue, and\

 nerves

2.       Cortex: Cortex is present around the Medusa and has a framework of fibrous tissue or stroma surrounded by germinal epithelium. It contains ovarian follicles in different stages of development with an ovum. The follicular cells are flattened epithelial cells derived from the germinal epitheliumsurrounding the ovary.

 

The ovaries have two distinct functions.

 

·         Gamete production: Ovaries are the site of periodic development and release of the egg cell or female gamete by the process of ovulation. The developing egg cell mature in the fluid-filled follicles. At once, only one egg cell is released. However, different cells can also mature simultaneously.

·         Hormone secretion: Ovaries secrete a set of hormones including the estrogen, testosterone, progesterone, and inhibin which are involved in the development of secondary sexualcharacteristics and the maintenance of the reproductive function of the ovaries. 

Uterine tubes (Fallopian Tube)

 -          Uterine tubes, also known as oviducts, are the part of the female reproductive system that carry ova from the ovary to the uterus each month. After fertilization of the ovum and sperm, these tubes transport the fertilized egg to the uterus for implantation.

 -          Each uterine tube is 10-13 cm long with a 1-2 cm diameter that extends laterally from the superior part of the uterus.

 1.      The infundibulum is a funnel-shaped structure that opens into the peritoneum of abdominal Ostia. It is found with associated fimbriae which are finger-like mucosal projections. These fimbriae projects over the ovaries with the longest of the fimbriae called ovarian fimbriae that attach to the superior aspect of the ovum.

2.      The ampulla is the longest part of the tubes with a length of 5cm. It has a thin wall with the folded luminal surface, and the fertilization occurs in this lumen.

 3.      The isthmus is the narrower part of the tube that extends towards the uterus.

 4.      The intramural (interstitial) part that transverses the myometrium of the uterus.

 

Uterus

 The uterus is a hollow muscular pear-shaped organ of the female reproductive system which is narrow both anteriorly and posteriorly.

 ·         It lies in between the urinary bladder and the rectum. In an adult female, the uterus weighs about 30-40 grams and is approximately 7.5cm long, 5cm wide with 2.5cm thick walls.

 ·         The wall of the uterus is comprised of three layers viz—Perimetrium myometrium and endometrium.

·         Perimetrium is the outermost layer of the uterus which is folded anteriorly to form the vesicouterine pouch.

 ·         Myometrium is the middle layer which is also the thickest layer in the uterine wall, which is composed of smooth muscles, connective tissues, blood vessels, and nerves.

 ·         The endometrium is the innermost layer that is composed of columnar epithelium provided with a large number of mucus-secreting tubular glands.

·         Externally, the uterus is divided into three parts, the fundus, the body, and the cervix. The fundus is the dome-shaped part present above the opening for the uterine tubes. The body is the main part of the uterus, which is connected to the cervix. The cervix or ‘the neck of the uterus protrudes out through the anterior wall of the vagina.

 ·         The primary purpose of the uterus is to provide a feasible environment for a newly developing baby.

·         Uterine secretions provide nourishment to the ovum before its implantation on the wall and, later after fertilization, the rapidly expanding ball of cells is nourished by the endometrial cells.

 ·         The uterus undergoes a periodic shedding after puberty in the female, which is called the menstrual

 cycle. This shedding prepares the uterus to nourish and protect a fertilized ovum. Vagina

 

The vagina is a fibromuscular tube that is lined with stratified squamous epithelium that connects the internal and external organs of the female reproductive system. The vagina is present obliquely upwards bent at an angle of 45° with the bladder in front and rectum and anus behind.

 ·         The vagina is surrounded by three layers, the outer layer of areolar tissue, a middle layer of smooth muscle, and the inner layer of stratified squamous epithelium that forms ridges or rugae.

 ·         Vagina has no secretory cells; however, the surface is kept moist by the cervical secretions.

 ·         Between puberty and menopause, Lactobacillus acidophilus is found abundantly in the vagina. This organism secretes lactic acid that maintains the pH of the vagina between 4.9-3.7. This acidity inhibits the growth of other microorganisms that may reach the vagina through the perineum.

 

Hormones of Female reproductive system

 

FSH and LH: These hormones stimulate the production of ovarian hormones estrogen and progesterone and also support the proliferation of follicles on the wall of the ovary.

 

Estrogen hormone: This hormone supports the proliferation of egg follicles and helps in the maintenance and development of female characteristics in the human body.

 

Progesterone hormone: Progesterone hormone regulates the inner lining (endometrium) of the uterus and also functions in the release of the egg during ovulation.

 

Menstrual Cycle

The menstrual cycle is the process of discharge of blood and other things from the vagina of a woman every month from puberty to menopause excluding pregnancy. It is a natural periodical process that brings changes in the female reproductive system which is responsible for the pregnancy.

 

Hormones Involved in Menstrual cycle

 

The hypothalamus secretes a luteinizing hormone-secreting hormone which stimulates the anterior part of the pituitary to secrete:

1.      Follicle Stimulating Hormone (FSH) causes the maturation of ovarian follicles and stimulates the release of estrogen which is responsible for ovulation.

2.      Luteinizing Hormone (LH) which triggers ovulation and formation of corpus luteum and release of progesterone.

 ·         The menstrual cycle is described by ovarian and uterine cycles. The ovarian cycle involves the formation and maturation of follicular cells in the ovary, whereas the uterine cycle describes the changes in the endothelial layer of the uterus.

Ovarian Cycle

 

The ovarian cycle involves the formation and maturation of follicular cells in the ovary. This cycle is divided into three phases:

 Follicular phase

·         After puberty, as a result of the release of a large amount of FSH and LH by the pituitary, the ovaries with the follicles start to grow.

·         During the first stage, the targeted follicular cells enlarge up to two-fold to three-fold in diameter. These enlarged follicular cells are termed primordial follicles.

·         After a few days, the level of FSH surpasses LH which accelerates the growth of 6-10 primary follicles that compete for dominance. Under the influence of FSH, these cells develop layers of granulosa cells as well as express the LH receptors on the granulosa cells.

 ·         The second layer of cells called theca develops around these follicles which can produce other sex hormones like estrogen and progesterone.

 ·         LH from the pituitary and the estrogen within the follicles cause accelerated growth of the primary follicles into vesicular follicles.

 · The ovum present inside the follicles develops aggressively increasing in size another threefold to four-fold. After a week or more of growth, one of the follicles starts outgrowing other follicles (a process called atresia).

 ·  The single follicle further increases in size and forms the mature follicle.

·         Ovulation in women with regular 28 days of sexual cycles occurs 14 days after the onset of menstruation. Few days before ovulation the follicle starts to swell with a protruding center called the stigma.

· The in-surge of the LH hormone and the release of estrogen from the follicle degrades the cells at the stigma and results in a hole. The secondary oocyte leaves the follicle through the hole and reaches the peritoneal cavity. The secondary oocyte then reaches the fallopian tube through the fimbriae. If there is left-right coordination between the ovaries is not yet known. However, occasionally, both the ovaries release an ovum, which results in the formation of fraternal twins.

 ·    If a sperm fertilizes the oocyte, it develops into a mature ovum. If fertilization doesn’t occur,

 thesecondary oocyte degenerates within the fallopian tube.

 

Luteal Phase

 ·         The luteal phase is the last phase of the ovarian cycle and it corresponds with the secretory phase of the uterine cycles.

 ·         During the first few hours of ovulation, the remaining follicular cell, including the granulosa and theca develops into lutein cells. This cell then becomes filled with lipid components that give them a yellow appearance. The total mass of the cell is called corpus luteum.

· Corpus luteum produces progesterone that inhibits the release of FSH and LH by the pituitary. Consequently, the concentration of FSH and LH falls over time and the corpus luteum degenerates.

·    The falling levels of progesterone then trigger menstruation. The process from the start of ovulation to the withdrawn of progesterone takes around two weeks. Even though the sexual cycle in all women is not the same; the duration of the luteal phase remains more or less the same in all women.

·       In the case of a successful pregnancy, the degeneration of corpus luteum is prevented by the release of human chorionic gonadotropin (hCG) from the placenta. Corpus luteum is essential to produce progesterone which maintains the new pregnancy.

 

Uterine Cycle

 

The uterine cycle includes the changes in the endothelial layer of the uterus. It is divided into three  phases.

 

Menstruation

 

·         Menstruation, also called menses, menstrual bleeding, or a period, is the first phase of the uterine cycle. This occurs as a result of the degeneration of corpus luteum which inhibits the release of FSH and LH from the pituitary and thus prevents the proliferation of other follicular cells.

·         The menstrual flow often serves as a sign to indicate the women is not pregnant; however, bleeding might also occur during pregnancy due to several reasons.

 ·         The menstrual flow consists of blood from broken capillaries, secretions from endometrial glands, endometrial cells as well as an unfertilized ovum.

 ·         This phase usually lasts about 3-5 days but might range from 2-7 days in some women. On average, 35 milliliters of blood is lost during menstruation, but 10ml to 80ml is considered normal.

·         A protein called plasmin is responsible for the prevention of clotting during menstruation. 

·         Pain in the back, stomach, and upper thigh is common during the first few days of menstruation and severe pain is commonly observed in adolescent girls (67% of women observe severe cramping).

·         This is the second phase of uterine cycles where the estrogen causes the proliferation of the endometrial layer in the uterus.

 ·         After the maturation of follicles in the ovary, they cause the release of estrogen which causes the growth of a new layer of endometrium called proliferative endometrium. The endometrium becomes thick with the rapid cell multiplication and increases the mucus-producing cells as well as blood capillaries.

 ·         The estrogen also causes the formation of crypts in the cervix that facilitate the secretion of vaginal discharge.

 ·         This phase ends when ovulation occurs and the level of estrogen declines.

Secretive Phase

·         The final phase of the uterine cycle corresponds with the luteal phase of the ovarian cycle, which occurs after ovulation.

 ·         The corpus luteum releases progesterone hormone, which is particularly essential to make the uterus receptive for the implantation of the fertilized ovum. The endometrium becomes oedematous and the secretory glands produce a large amount of watery liquid to assist the passage of spermatozoa.

 ·         If fertilization occurs, the fertilized ovum travels to the uterus through the uterine tube and become embedded.

 ·         However, if fertilization doesn’t occur, menstruation occurs and a new cycle is initiated.