Edapt WK 6 Reproductive System PDF

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MALE AND FEMALE REPRODUCTIVE SYSTEMS The male and female reproductive systems have more in common than you think! Both contain organs known as gonads (ovaries and testes) that produce sex cells known as gametes (egg and sperm). The gametes will unite to produce a zygote, a single celled embryo. The two systems are widely different, but they share many features, such as hormonal regulation and production of hormones.

THE MAJOR ANATOMY OF THE MALE AND FEMALE REPRODUCTIVE SYSTEMS

The most obvious differences between the two reproductive systems appear in the external anatomy. The most prominent male external features are the penis and scrotum, while the female features include the mons pubis and two sets of labia (minor and majora), which are most visible. The female clitoris, vaginal and urethral openings, as well as duct openings of two types of glands are still considered part of the female external genitalia, but these are less easily observed in comparison to males. The scrotum is a pouch of skin that surrounds internal structures: the testes, epididymis and a portion of the ductus deferens. These structures are all found outside the pelvic cavity in the male, while all female internal organs are located within the pelvic cavity (ovaries, uterine tube, uterus and vagina). The male accessory glands (seminal vesicles, prostate and bulbourethral glands), and a portion of the ductus deferens are found in the pelvic cavity. The male and female reproductive systems are closely associated with the urinary system. In males, the urethra is several times longer than in females and is used for both voiding urine and passage of semen. The female urethra is significantly shorter and only carries urine. As such, females are more likely to suffer from urinary tract infections (UTIs) due to the short distance the bacteria have to travel to reach the bladder. Testes contain a series of closed continuous ducts that carry sperm from the seminiferous tubules where sperm are made, through the epididymis and ductus deferens to the urethra and out of the body. The female ovary does

not have an attached tube to carry ovulated oocytes. Instead there is a gap between the fimbriae of uterine tubes and the ovaries through which the oocyte can fall through and enter the pelvic cavity. Even though we see major anatomical differences between the male and female reproductive systems, we must remember that many structures share a common embryonic origin (homologues) and perform very similar functions. For example, the ductus deferens in males and uterine tubes in females have the common function of transporting their respective gametes.

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This diagram provides an overview of the anatomy of the female reproductive system.

MALE AND FEMALE HOMOLOGUES OF VARIOUS REPRODUCTIVE SYSTEM

Homologous structures in males and females that originate from the same embryonic tissues and share similar functions.

Female Structure

Male Structure

Ovaries

Testes

Ovum

Sperm

Female Structure

Male Structure

Labia majora

Scrotum

Labia minora

Spongy urethra

Vestibule

Intermediate/membranous urethra

Vestibular bulb

Corpus spongiosum of penis

Clitoris

Glans penis and corpora cavernosa

Paraurethral glands

Prostate

Greater vestibular glands Bulbourethral glands

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Development of the External Genitalia By 6 weeks, the embryo has three primordial structures – the genital tubercle, urogenital folds, and labioscrotal folds – which will become the male or female genitalia. At 8 weeks, these structures have grown but the sexes are still indistinguishable. Slight sexual differentiation is noticeable at 10 weeks, and the sexes are fully distinguishable by 12 weeks. Matching colors identify homologous structures of the male and female. REGUL ATION OF THE REPRODUCTIVE PROCESSES

Hormonal regulation of both male and female reproductive systems begins in the hypothalamus, which is directly associated with the pituitary gland. Hormonal regulation begins as early as embryonic and fetal

development, then at puberty, and through the reproductive years. In both sexes, the hypothalamus secretes Gonadotropin Releasing Hormone (GnRH), which stimulates specialized cells (gonadotrophs) located in the anterior pituitary to secrete Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). In males, LH stimulates specialized cells in the testes to secrete male hormones called androgens; the main androgen in males is testosterone. In females, LH targets the ovaries and stimulates the corpus luteum to secrete estrogens (estradiol, estriol, estrone), progesterone, and relaxin. FSH (in conjunction with the actions of testosterone) stimulates sperm production (spermatogenesis ) in the male testes. While in the female ovaries, FSH stimulates the development of follicles containing oocytes, in preparation for ovulation. FSH also stimulates these follicles to secrete estrogens. Testosterone is responsible for embryonic development of the male reproductive organs, onset of puberty, development of male secondary sexual characteristics such as body hair and deep voice, libido, spermatogenesis, and protein anabolism in muscle cells. Estrogens are responsible for development and maintenance of female reproductive organs and secondary sexual characteristics such as breast development, thickening of the uterine lining, protein anabolism in bone and muscle cells, lowering blood cholesterol, and onset of puberty. Progesterone is responsible for preparing the uterus for possible implantation of an embryo, while relaxin helps to relax uterine muscle, in preparation for implantation. Negative feedback mechanisms are used to control the secretion of GnRH, FSH and LH. Elevated levels of testosterone, estrogens and progesterone in the blood inhibit further secretion of GnRH and LH. Both gonads also produce a small quantity of the hormone inhibin, which inhibits FSH secretion by the anterior pituitary. When the levels of testosterone, estrogens, progesterone and inhibin fall, the hypothalamus and pituitary gland resume releasing GnRH, LH and FSH. 

Hormonal Interactions in the Ovarian Cycle

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Hormonal Regulation of Spermatogenesis and Androgen Production

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Hormonal Regulation of Spermatogenesis and Androgen Production The hypothalamus secretes gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH stimulate spermatogenesis and testosterone (and other androgen) production, as shown in this image.

GROSS AND MICROSCOPIC ANATO MY OF THE MALE REPRODUCTIVE SYSTEM

In this unit we will explore the structure and function of the male reproductive system. The testes produce millions of sperm cells per day and a series of ducts allow the sperm to leave the body, but only after mixing with secretions from 3 accessory glands.

THE TESTES AND SCROTUM SC ROTUM

The scrotum is part of the male external genitalia and its main function is to house, protect and provide a cooler and more ideal environment for sperm production within the testes. The ideal temperature for sperm production in humans is approximately 2° C lower than normal body temperature (37° C). The scrotal skin divides it into two separate compartments, with each compartment housing a testis. The compartments can be identified by the external seam called raphe and the internal scrotal septum. The region between the testes and pelvic cavity, called the spermatic cord, forms a bridge between external and internal organs and contains the ductus deferens, blood vessels, lymphatic vessels, nerves, and muscle. Two major muscles are found underneath the skin of the scrotum: cremaster and dartos muscles.

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The dartos is most superficial smooth muscle responsible for causing wrinkles on the scrotum during cold conditions, pressing the testes closer to the body. The cremaster muscle is a deep skeletal muscle that contracts when cold, to move the testes upward and closer to the trunk for warmth.

TESTES

The testes, are oval shaped organs, approximately 5 cm in length and 3 cm in diameter. They are covered by a double layered serous membrane called the tunica vaginalis and encapsulated by a strong white fibrous tissue capsule called the tunica albuginea. This tissue spreads through the organ to divide it into about 200 to 250 lobules. Each lobule encloses a seminiferous tubule and joins to create a complicated system of channels. Each of these channels gives rise to ducts (rete testes) that connect to the epididymis. These seminiferous tubules are made up of cells that function in the production of sperm (Sertolli cells - spermatogenesis). Additional cells known as Interstitial cells (Leydig cells) are found between the spaces within the seminiferous tubules and function in secreting testosterone.

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The Scrotum and Spermatic Cord Testes and Seminiferous Tubules

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Testes and Seminiferous Tubules (a) The gross anatomy of a testis is shown diagrammatically in a cut-away, partial sagittal section. (b) A photomicrograph reveals a seminiferous tubule in the testis THE EPIDIDYMIS

The epididymis is a crescent shaped organ laying on the superior surface of the testis. It consists of a head, body and tail; all of which are a series of tubules that gradually increase in diameter and are widest at the tail. The tubules would measure approximately 20 ft if straightened out. This organ serves to connect the seminiferous tubules to the ductus deferens. Functions of the epididymis include:    

Sperm maturation; a physiological process whereby sperm acquire the ability to fertilize an ovum Propelling sperm into the connected ductus deferens Sperm storage Recycling of old and damaged sperm

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The Testis and Associated Structures (a) The scrotum is opened and folded downward to reveal the testis and associated organs. (b) Anatomy of the testis, epididymis, and spermatic cord. © Scanning election micrograph of the seminiferous tubules. (d) Light micgrograph. This region of the tubule did not have mature sperm in it at the time.

MALE REPRODUCTIVE DUCTS AND ACCESSORY GLANDS

The tail of the epididymis gives rise to the ductus deferens, a thick muscular tube found within the spermatic cord. The ductus deferens continues through the inguinal canal to enter the pelvic cavity. There it loops posteriorly around the bladder and ureters before widening into the terminal ampulla. The duct of the ampulla joins the duct of the laterally located seminal vesicle (gland). Together the seminal vesicle and ductus derens form the short ejaculatory duct which penatrates the prostate gland and ends at the prostatic urethra. The male urethra is approximately 8-9 inches long and is divided into 3 segments:   

Prostatic urethra Membranous or intermediate urethra Spongy or penile urethra

All sections of the urethra serve as passageways for both urine and semen, but never at the same time. The seminal vesicles or seminal glands are highly folded glandular epithelial tissue. Their secretions constitute approximately 60% of the total semen volume and are responsible for a phenomenon known as capacitation, whereby the sperm acquire the ability to self propel using their flagella. Their slightly alkaline secretions contain fructose, prostaglandins, and clotting proteins. The fructose is easily metabolized by sperm and acts as a fuel source for ATP production, the prostaglandins help with sperm motility and the clotting proteins form a temporary semen clot in the vagina, allowing the sperm to remain in the female reproductive tract. The clot will dissolve and the sperm will be free to swim through the cervical canal a shortly thereafter. The prostate gland is located just inferior to the bladder and encircles the prostatic urethra like a doughnut. Its secretion contribute approximately 30% of the semen volume. It secretes citric acid for sperm ATP production and proteolytic enzymes to bread down the semen clot which is formed after ejaculation. The bulbourethral glands are the smallest of the 3 glands, located at the base of the penis, between the pelvic cavity and external genitals. They secrete a small amount of clear fluid that neutralizes the acidity of the urethra from residual urine and lubricates the tip of the penis. While they do not contribute a significant volume to semen, they aid in sexual intercourse via lubrication of the most distal portion of the penis.

THE STRUCTURE AND FUNCTIONS O F THE PENIS

The penis has a cylindrical shape and contains the urethra for semen and urine passage, as well as erectile tissue for sexual function. It is composed of the internal root, the external shaft and the glans. The glans is the most distal portion of the penis and is covered by a fold of skin called the prepuce (foreskin) which contains the external urethral orifice. The shaft contains three columns of erectile tissue. The corpus spongiosum is the smallest and surrounds the spongy urethra, it expands at the distal end to form the glans. The two larger cylinders of erectile tissue are known as the corpora cavernosa (singular -corpus cavernosum) which extend through the shaft of the penis, each of which contains a deep artery. During sexual arousal, the deep arteries dilate and fill the microscopic sinuses (lacuane) of the erectile tissue with blood, leading to an erection. Dorsal veins drain blood from the penis. The mechanisms of erection and ejaculation are mediated by an autonomic reflex arc. It begins with the parasympathetic fibers stimulating the dilation of the deep arteries and blood filling the lacuane, resulting in the penis becoming erect. Bulbourethral glands secrete fluid to neutralize the acidity of the urethra and lubricate the glans penis. Ejaculation is brought about by increase sympathetic innervation. The smooth muscle of the ductus deferens begin peristaltic contractions that move sperm into the ejaculatory duct; it is at this point that the prostate and seminal glands secrete substances into the seminal fluid. The internal urethral sphincter contracts to prevent urine from leaving the bladder. Muscles at the root of the penis contact to force semen out during ejaculation. This is a unique example of the synergistic effects of parasympathetic and sympathetic systems, whereas these two branches of the autonomic nervous system typically have antagonist effects. Following ejaculation, blood flow to the penis decreases and blood leaves the lacunae via dorsal veins, which in turn causes the penis to become flaccid.

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Anatomy of the Penis (a) Superficial dissection of shaft, lateral view. (b) Cross section at midshaft. THE PATHWAY OF SPERM

The path of sperm from their formation in the lumen of the seminiferous tubules to the outside of the body: START: Seminiferous tubules

↓ Rete testis

↓ Efferent ductules (ducts)

↓ Epididymis

↓ Ductus deferens

↓ Ductus deferens in the spermatic cord

↓ Ductus deferens in the pelvic cavity

↓ Ejaculatory duct

↓ Prostatic urethra

↓ Intermediate/membranous urethra

↓ Spongy/penile urethra

↓ END: External urethral orifice

PRODUCTION, COMPOSITION, AND FUNCTIONS OF SEMEN

Semen is a complex mixture of sperm cells and secretions from the male reproductive accessory glands. The main function of semen is to safely carry mature sperm into the female vagina. Once there, semen provides the necessary tools needed for the sperm to remain in the vagina by forming a temporary clot, which is dissolved 10 – 30 minutes later, freeing the sperm. It provides energy to power their flagella, protects them from acid and bacteria in the vagina and helps them travel through the cervix and uterus to reach their ultimate destination, the uterine tubes. Composition of semen: 

10% sperm and spermatic duct secretions

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60% seminal gland secretions 30% prostate secretions trace amounts of bulbourethral gland secretions

Sperm count:  

normal is 50 – 150 million/mL below 20 million/mL could indicate infertility

Volume: 2 – 5 mL per ejaculate pH: 7.2 – 7.7

GROSS AND MICROSCOPIC ANATO MY OF THE FEMALE REPRODUCTIVE SYSTEM

The female reproductive system is similar to the male reproductive system, but it is relatively more complex. There are more reproductive organs, not just to release gametes, but also to house and nourish the embryo during gestation and provide nutrition after birth. Hormonal changes occur in monthly cycles, unlike the continuous hormonal secretion that occurs in males.

GROSS ANATOMY, MICROSCOPIC ANATOMY, AND FUNCTIONS OF THE OVARIES

The ovaries, or female gonads, are almond-shaped organs located in the posterior region of the pelvic cavity, lateral to the uterus. They are held in place by a series of ligaments. The ovarian ligament anchors them medially to the uterus and the suspensory ligament attaches them to the pelvic wall, laterally. A portion of the peritoneum called the mesovarium, wraps around the ovaries and merges with the broad ligament, inferiorly. The suspensory ligament encases the arteries, veins, nerves and lymphatics that enter and exit the ovary. Similar to the male testes, the tunica albuginea serves as the ovarian capsule. The interior of the ovary is divided into the outer cortex and inner medulla, but there is no sharp distinction between them. The medulla contains large blood vessels while the cortex is home to ovarian follicles that are in all stages of development. Ovarian follicles of different sizes are observed inside an ovary after puberty. Each follicle contains a large oocyte in various stages of meiosis and is surrounded by small follicular or granulosa cells which nourish and protect the oocyte, as well as manufacture hormones. Mature follicles are very large, fluid-filled structures that burst through the ovary wall during monthly ovulation; there are no ducts to lead the oocyte out of the ovary like the sperm have in the male testes. After ovulation, the follicle remains in the ovary and becomes a temporary endocrine gland called the corpus luteum. If fertilization does not occur, it degenerates into a fibrous scar tissue structure known as the corpus albicans. The overall function of the ovaries is to produce mature egg cells (ova or oocytes) and release them into the uterine tubes to await fertilization by sperm. The follicles and corpus luteum within the ovaries produce hormones such as estrogens, progesterone, inhibin and relaxin.

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Structure of the Ovary The follicles are not drawn to scale; indeed the mature follicle at the top and ovulating follicle at the lower right have diameters about equal to the entire 3 cm length of the ovary, from ovarian ligament to suspensory ligament, and bulge from the ovarian surface like enormous blisters.

THE UTERUS AND UTERINE TUBES

The uterine tubes, also called oviducts or fallopian tubes, connect the ovaries to the uterus. The uterine tubes are stabilized by the broad ligament and are composed of three distinct regions: infundibulum, ampulla and isthmus. Nearest to the ovary, the infundibulum is the open end of the tube and is lined by finger-like projections called fimbriae. The space between the fimbriae and ovary, provides an opening into the pelvic cavity through which endometrium ...