Dr. Uche Amaefuna Biology – Premed Windsor University School of Medicine and Health Sciences

Pre Med – Biology Chapter 18 Human Reproduction There is more to lectures than the power point slides! Engage your mind

Human Reproduction

Human reproduction involves intricate anatomy and complex behavior  Reproductive Anatomy of the Human Male.  The scrotum and the penis are the external components of the reproductive system.  The internal reproductive organs consist of gonads, accessory sex glands, and ducts.

Male Reproductive System

 External structure of the penis:  The shaft of the penis is covered by relatively thick skin.  The sensitive glans penis is covered by thinner skin.  The glans is covered by the prepuce which may be removed by circumcision.  There is verifiable health benefit to circumcision.

 The penis is composed of three layers of spongy erectile tissue.  During sexual arousal the erectile tissue fills with blood from arteries.  The resultant increased pressure seals off the veins that drain the penis.  The engorgement of the penis with blood causes an erection.  An erection is essential to the insertion of the penis into the vagina.  The penis of some mammals possesses a baculum, a bone that helps stiffen the penis.

 Impotence can result from the consumption of alcohol and other drugs, and emotional, nervous system, or circulatory problems.  Treatment includes drugs and penile implant devices.  Viagra ® acts by promoting the action of nitric oxide.

Testes

 Testes are the male gonads.  Consists of many highly coiled seminiferous tubules surrounded by layers of connective tissue.  Sperm form in seminiferous tubules.  Leydig cells (interstitial cells), scattered between seminiferous tubules produce androgens (ex. testosterone).

 Testes are located in the scrotum, outside the body cavity.  This keeps testicular temperature cooler than the body cavity.  The testes develop in the body cavity and descend into the scrotum just before birth.  From the seminiferous tubules sperm pass to the coiled tubules of the epididymis.  It takes about 20 days for sperm to pass through the tubules of the epididymis.  In the epididymis sperm become motile and gain the ability to fertilize.

Semen  Seminal fluid is thick, yellowish, and alkaline.  It contains mucus, fructose, a coagulating enzyme, ascorbic acid, and prostaglandins. Accessory glands:  seminal vesicle  prostate gland  bulbourethral gland

Seminal vesicle: A pair of glands that secrete a liquid component of semen into the vas deferens. Secretion is alkaline, which neutralizes the acidic condition of the female genital tract. Seminal fluid contains fructose. Seminal Vesicle

Prostate gland: Location- surrounds and opens into the urethra where it leaves the bladder. Secretion- slightly alkaline fluid that activates the sperm and prevents them from sticking together  Prostate problems are common in males over 40.  Prostate cancer is one of the most common cancers in men. Prostate

Bulbourethral gland (Cowper’s gland): Location- paired glands that lie beneath the prostate Secretion- a thick, clear alkaline mucous that drains into the membranous urethra. Function- It acts to wash residual urine out of the urethra when ejaculating semen-- raises pH; neutralizes acidity of urine. Bulbourethral gland

 Ejaculation propels sperm from the epididymis to the vas deferens.  The vas deferens run from the scrotum and behind the urinary bladder.  Here each vas deferens joins with a duct from the seminal vesicle to form an ejaculatory duct.  The ejaculatory ducts open into the urethra.  The urethra drains both the excretory and reproductive systems. Ejaculation

 A male usually ejaculates about 2 – 5 mL of semen; each milliliter containing about 50 – 130 million sperm. Bulbourethral fluid also carries some sperm released before ejaculation. This is one of the reasons why the withdrawal method of birth control has a high failure rate. Ejaculate

Spermatogenesis

Mature Spermatozoa tail mitochondria nucleus acrosome head

Seminiferous Tubules

spermatogonium 1º spermatocyte 2º spermatocyte spermatids Sertoli cell spermatozoa Seminiferous Tubules

Sperm Maturation & Development (maturation: days)

Hormones Involved in Spermatogenesis Gonadotropin Releasing Hormone (GnRH) Follicle Stimulating Hormone (FSH) Interstitial Cell Stimulating Hormone (ICSH), also called LH Testosterone Inhibin

HypothalamusHypothalamus Anterior Pituitary GnRH FSHICSH/LH Hormonal Control of Spermatogenesis

Interstitial Cells ICSH/LH Testosterone Hormonal Control of Spermatogenesis

Sertoli Cells Testosterone Spermatogenesis FSH Inhibin Hormonal Control of Spermatogenesis

Feedback Inhibition Inhibin Acts on anterior pituitary Inhibits FSH production Testosterone Acts on hypothalamus Inhibits GnRH production Hormonal Control of Spermatogenesis

Some Other Effects of Testosterone muscle and bone growthmuscle and bone growth facial and pubic hair growthfacial and pubic hair growth thickening of vocal cordsthickening of vocal cords growth of pharyngeal cartilagegrowth of pharyngeal cartilage hair follicle effectshair follicle effects stimulates sebaceous glandsstimulates sebaceous glands

Reproductive Anatomy of the Human Female  External reproductive structures:  labia  clitoris  vaginal opening  Internal reproductive structures:  ovaries  fallopian tube (uterine tube)  cervix  uterus  vagina  fimbrae

Biology 100 Human Biology cervix vagina fimbriae uterine tube ovary uterus bladder urethra clitoris l. minora l. majora vaginal orifice Female Reproductive System

Biology 100 Human Biology uterine tube ovary egg uterus cervix vagina endometrium myometrium perimetrium

Oogenesis in the Ovary

Oogenesis Ovary- contains 400,000 oocytes; release about 500 in a lifetime Ovary- under influence of FSH. The follicles mature every 28 days Primary follicle produces estrogens And primary oocyte completes its 1 st division produces 2ndary oocyte and polar body

Oogenesis Aprox 1/2 way through the 28 day cycle the follicle reaches the mature Vesticular or Graffian follicle stage. Estrogen levels rise and release LH and FSH and triggers ovulation. The 2ndary oocyte travels down the uterine tube to the uterus. If fertilized by sperm, it will produce a zygote

Oogenesis

Ovum

Hormones Involved in the Female Reproductive Cycle Gonadotropin Releasing Hormone (GnRH)Gonadotropin Releasing Hormone (GnRH) Follicle Stimulating Hormone (FSH)Follicle Stimulating Hormone (FSH) Luteinizing Hormone (LH)Luteinizing Hormone (LH) EstrogenEstrogen ProgesteroneProgesterone

HypothalamusHypothalamus Anterior Pituitary GnRH FSHLH Female Hormonal Cycle

Follicle Cells LH Estrogen FSH Female Hormonal Cycle

The Uterine Cycle The Uterine Cycle

Ovarian Cycle

Hormone Fluctuation

Some Other Effects of Estrogen breast development external genitalia growth stimulates bone growth increases HDL and lowers LDL

Menopause: cessation of ovarian and menstrual cycles.  Usually occurs between ages 46 and 54.  Due to ovaries decreased responsiveness to gonadotropins. Menopause affects:  changes in sexual desire  triggers mood swings  causes debilitating hot flashes  may lead to bone and heart problems  short-term memory loss  insomnia

 Mammary glands.  Are present in both males and females.  Are not a component of the reproductive system.  Contain epithelial tissue that secrete milk.  Milk drains into a series of ducts opening at the nipple.

Female Reproductive System Produce hormones (estrogen and progesterone) for secondary sexual characteristics. Produce one large oocyte at regular intervals and release it in such a way that it enters the oviduct (“Fallopian tube”,“uterine tube”). Receive semen from the male and transport it into the oviduct. Produce hormones (estrogen and progesterone) which prepare the uterus for pregnancy each cycle by thickening its inner lining; Getting rid of this thickened lining each cycle if pregnancy does not occur. Protect and nourish the embryo and fetus during pregnancy, then expel it through the vagina Produce milk to nourish the newborn

Ovary: Located within pelvis, 2 to 5 cm (1 to 2 inches) lateral to the uterus Approximately 3cm x 2cm x 1cm Central region, or “medulla”, consists of connective tissue with many blood vessels. Outer region, or “ CORTEX ”, has all of the oocytes. One or two of these oocytes may be developing before ovulation; undeveloped ones are stored here. Also contains the remnant from the previous cycle’s ovulation, called a “ Corpus Luteum”, which secretes progesterone to keep uterus ready for implantation of the embryo

Maturation of an oocyte is called oogenesis, which leads to ovulation During oogenesis, the oocyte is surrounded by follicular cells granulosa cells in one or more layers, forming a CUMULUS OOPHORUS.

The developing oocyte and its follicle: Four stages before ovulation

2. PRIMARY FOLLICLES : Develop only after puberty; 3 to 4 enter this stage each cycle No change in primary oocyte Follicle has begun development – cells are larger

The developing oocyte and its follicle: Four stages before ovulation : 3. SECONDARY FOLLICLE: 1 or 2 primary follicles progress to this stage each cycle Primary oocyte larger, finishes first division of meiosis to become a secondary oocyte, also forming a polar body. Follicle grows larger as follicular cells divide to form many layers; spaces begin to develop in center of follicle

The developing oocyte and its follicle: Four stages before ovulation. 4. MATURE/VESICULAR/GRAAFIAN FOLLICLE. Most follicles which made it to “secondary” will reach this stage Follicle is very large; Many layers of cells surrounding fluid-filled center called ANTRUM Secondary oocyte covered with thick, clear membrane called zona pellucida; pushed to one side in follicle and surrounded by mass of follicular cells called cumulus oophorus

Big Question: How is this process of oogenesis regulated? Oogenesis, as well as ovulation and many other things, are regulated by the pituitary gland, which lies just below the brain

Oogenesis and growth of the follicle in the ovary are initiated and stimulated by FSH from the pitutitary During this oogenesis under the stimulation of FSH, follicular cells surrounding the oocyte secrete the hormone ESTROGEN, which stimulates the inner lining of the uterus to thicken and begin secreting mucus, getting ready for pregnancy This estrogen from the follicular cells also inhibits the pituitary gland from secreting any more FSH. Thus, no more follicles will be stimulated to develop until it stops.

Rupture of the follicle is ovulation. The secondary oocyte, surrounded by the zona pellucida and cumulus oophorus, is released from the surface of the ovary, where it can be captured by the open end of the oviduct. The cumulus oophorus now called the corona radiata.

Luteinizing hormone also causes the follicular cells of the now empty follicle to develop into CORPUS LUTEUM. This structure secretes the hormone progesterone. Ovulation is triggered when the pituitary gland secretes a different hormone, called LH.

Before ovulation: FSH stimulates cells of follicle to secrete estrogen, which stimulates the lining of the uterus to develop. After ovulation: LH stimulates cells of the corpus luteum to secrete Progesterone, which maintains the uterine lining in this “ready for pregnancy” condition. If fertilization and pregnancy occur, the placenta of the embryo secretes a hormone called HUMAN CHORIONIC GONADOTROPIN (hCG), which stimulates the corpus luteum to keep secreting progesterone, which in turn keeps the lining of the uterus thick and full of blood vessels. If fertilization and pregnancy do not occur, after a few days the corpus luteum deteriorates and stops producing progesterone. Without its stimulus, the uterus can not maintain its thick lining, so this falls off and is shed as menstruation.

When the oocyte is released from the surface of the ovary during ovulation, it is picked up by the oviduct, or Fallopian Tube, a hollow muscular tube which leads from near the uterus to the ovaries.

Oviduct: Lateral End: Wide opening, or infundibulum, surrounds the surface of the ovary. The edge is surrounded by finger-like projections. Middle Part: Wide Medial End: Narrow leads into uterus. Cavity of oviduct is continuous with cavity of uterus.

By mechanisms not completely understood: The oviduct moves the oocyte toward the uterus The oviduct moves sperm away from the uterus Fertilization occurs in ampulla of oviduct, forming the zygote, which goes through repeated mitotic cell divisions to eventually form the embryo. Oviduct moves this growing mass of pre-embryo cells toward uterus: takes 3 or 4 days. Secretions from oviduct are necessary to keep sperm, oocyte, and embryo alive.

Uterus: Anterior to rectum; Posterior & superior to bladder Narrowed inferiorly to form cervix, which projects into vagina

Uterus: Outer layer = PERIMETRIUM : Thick layer of muscle Inner layer = ENDOMETRIUM : Lots of glands & blood vessels Two layers of endometrium: : Closer to myometrium; Remains after menstruation; Regrows functional layer : Closer to cavity; Thickens every cycle; Embryo implants here during pregnancy; Dies and falls off during menstruation Inferior end narrows to form CERVIX, which projects down into vagina.

Mass of Uterus: Immediately before menstruation: 100 – 150 grams Immediately after end of menstruation: 50 – 100 grams End of pregnancy: 1,000 – 1,500 grams At end of pregnancy: Uterus extends from vagina inferiorly to bottom of sternum superiorly Lies anterior to all other abdominal organs except bladder

Vagina: Thin-walled, tubular Inferior to uterus; Anterior to rectum Posterior to bladder & urethra Receives penis and semen during sexual intercourse Passage for delivery of fetus or menstrual flow