Chapter 23: Reproductive Systems
Reproductive System
Functions
–Produce, nurture, and transport ova and sperm
–Secrete hormones
–Provide safe nurturing environment for fertilized eggs
Reproductive Organs
Primary reproductive organs
–Gonads (ovaries and testes)
–Functions
Hormone secretion
Gamete (ova and sperm) production
Secondary reproductive organs
–All other organs, ducts, and glands in the reproductive system
–Nourish and transport eggs (fertilized and unfertilized) and sperm
Male Reproductive System
Produces, nourishes and transports sperm
Deposits sperm within the female reproductive tract
Secretes hormones
Testes
Also called the testicles
Male gonads
Produces sperm and secretes testosterone
Located in the scrotum (sac between the thighs, outside the abdominal cavity)
Testes develop in the abdominal cavity but descend into the scrotum during the last 2 months of fetal development
If testes don’t descend its called chryptorchidism
Can result in infertility
Sperm prefer slightly cooler temperature of the scrotum
Divided into about 250 lobules
Seminiferous tubules
Tightly coiled
Form sperm
Interstitial cells
Between the seminiferous tubules
Produce androgens (male hormones) especially testosterone
Spermatogenesis
Millions of sperm produced each day
Formed by the epithelium of the seminiferous tubules
Spermatogenic cells
–Produce the sperm
Supporting cells
–Sustentacular cells, Sertoli cells, and “nurse” cells
–Support, nourish and regulate the spermatogenic cells
The formation of sperm
Spermatagonia: undifferentiated spermatogenic cells with 46 chromosomes
Testosterone causes these cells to enlarge and form primary spermatocytes
Division through meiosis divides chromosomes in half
Mature sperm only has 23 chromosomes
Sperm must undergo several maturational changes before they are functional
Sperm
Head
–Mostly nucleus
–Acrosome
Specialized structure on the front part of the head
Has enzymes that allow sperm to penetrate egg and allows fertilization
Midpiece
–Spiral shaped and contains lots of mitochondria (energy production)
Tail
–Flagellum allows sperm to swim
Genital Ducts
Sperm are collected in the seminiferous tubules and then move into the genital ducts where they mature and are transported out of the body
Two epididymides
Two vas deferens
Two ejaculatory ducts
One urethra
Epididymis
First part of the duct system
About 20 feet long and highly coiled
Sits along top and posterior of the testis
Sperm mature here becoming motile and fertile
Walls contract pushing sperm into the vas deferens
Vas Deferens
Continuous with the epididymis
Ascends as part of the spermatic cord through the inguinal canal in the groin region
Spermatic cord also includes blood vessels, lymphatic vessels, nerves, muscles and connective tissue
Ejaculatory Ducts
Vas Deferens travels through the pelvic cavity, over the urinary bladder and joins with the duct of the seminal vesicle to form the ejaculatory duct
Two ejaculatory ducts pass through the prostate gland and join the urethra
Urethra
Extends from the base of the urinary bladder to the tip of the penis
Carries urine and semen but only one at a time, never both simultaneously
Accessory Glands
Seminal Vesicles
–Located at the base of the bladder
–Secrete a thick yellowish material rich in fructose (sugar), vitamin C and prostaglandins
–Nourish and activate the sperm as they pass through the ducts
Prostate Gland
–Donut-like gland that encircles the prostatic urethra just below the bladder
–Secretes milky alkaline substance that helps increase sperm motility
–Counteracts acidic environment of the vagina and protects sperm
–Contracts during ejaculation to force secretions into the urethra
Bulbourethral Glands
–Also called Cowper glands
–Secrete thick mucus into penile urethra
–Mucous serves as a lubricant during intercourse
Semen
Mixture of sperm and the secretions of the accessory glands
Approximately 60% from the seminal vesicles
Most of the rest comes from the prostate gland
Milky-white liquid with an alkaline pH (7.2-7.6)
–Helps protect against acidic female reproductive tract
Nourishes the sperm
Aids in the transport of sperm
Lubricates the reproductive tract
2-6 ml of sperm (1 tsp) per ejaculation
50-100 million individual sperm per ejaculation
External Genitals
Scrotum
–Sac that hangs between the legs and contains the testes
Penis
–Carries urine to the outside of the body and is the organ of sexual intercourse
Penis
Shaft or body of the penis contains three columns of erectile tissue and an enlarged tip called the glans penis
Loose skin covering the penis extends downward and forms a cuff of skin around the glans called the foreskin or prepuce
Erection
When a man is sexually stimulated the parasympathetic nerves fire
Penile arteries dilate and the spongy erectile tissue fills with blood
Collection of blood in erectile tissue causes the penis to enlarge and become rigid
Process is called an erection
Orgasm, Emission and Ejaculation
Orgasm in men is accompanied by emission and ejaculation
Emission
–Movement of sperm and glandular secretions form the testes and genital ducts into the urethra, forming semen
–Sympathetic nervous system influences the ducts causing rhythmic peristaltic-type contractions
Ejaculation
–Expulsion of semen from the urethra to the outside
–Urethra fills with semen
–Motor nerve impulses from the spinal cord stimulate skeletal muscles at the base of the erectile colums to contract rhythmically expelling semen from the penis
–Imediately after ejaculation sympathetic nerve impulses cause penile arteries to constrict (blood flow lowered)
–Also accompanied by increased drainage of blood from the penis
–Penis becomes flaccid
Male Sex Hormones
Called Androgens
Most important one is testosterone
Most secreted by the interstitial cells of the testes
Low levels of testosterone production until puberty when production increases rapidly.
Leads to all the changes associated with puberty (primary sex characteristics)
Hormonal Control
Hypothalamus secretes a releasing hormone
Triggers the anterior pituitary to secrete the gonadotropins; follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
FSH promotes spermatogenesis by stimulating the spermatogenic cells to respond to testosterone
–Spermatogenesis caused by interaction of FSH and testosterone
LH is also called interstitial cell-stimulating hormone (ICSH) in males
–Promotes the development of the interstitial cells and secretion of testosterone
Negative feedback loop regulates testosterone production
–High testosterone causes decrease in anterior pituitary and hypothalamic hormone secretion
–Low testosterone causes increase in anterior pituitary and hypothalamic hormone secretion
Female Reproductive System
Produces eggs
Secretes hormones
Nurtures and protects a developing baby during 9 months of pregnancy
Ovaries
The female gonads
Located on each side of the uterus in the pelvic cavity
Anchored in place by ligaments (ovarian and broad ligaments)
Not directly attached to the fallopian tubes but are close
Egg Development
Each ovary contains many ovarian follicles
Born with 2 million follicles
Number declines with age
At puberty only about 400,000 follicles remain
About 400 will mature over a lifetime because only one egg produced each month between puberty and menopause
Each follicle has immature egg (oocyte) and the cells surrounding it (follicular cells)
As each follicle matures the egg undergoes meiotic division so that a mature egg only has 23 chromosomes
The follicle enlarges and a fluid filled center is formed
The follicular cells begin to secrete estrogen
Mature follicle known as the graafian follicle
Ovulation
The ovarian follicle bursts ejecting a mature egg (ovum) with a surrounding layer of cells
The ovum travels into the peritoneal cavity where the fimbriae of the fallopian tubes sweep it up and into the fallopian tube
After Ovulation
The follicular cells the that remain in the ovary develop into the corpus luteum
The corpus luteum secretes large amounts of progesterone and smaller amounts of estrogen
If no fertilization occurs the corpus luteum deteriorates in about 10 days into the corpus albicans
Corpus albicans does not secrete hormones
If fertilization does occur then the corpus luteum stays and produces hormones until the placenta takes over
Ovarian Hormones
Estrogen
–Promotes maturation of the egg
–Helps develop female secondary sex characteristics
Progesterone
–Secreted by the corpus luteum
–Works with estrogen to establish the menstrual cycle
–Helps maintain pregnancy in the early months
–Helps prepare breasts for milk production
Genital Tract
Fallopian tubes, the uterus and the vagina
Fallopian Tube
Also called the uterine tubes or the oviducts
About 4 inches long and extends from the uterus to the ovary
End nearest the ovary called the infundibulum
Fingerlike projections called the fimbriae
Don’t attach directly to the ovaries
Swishing motion of the fimbriae sweep ovum into the fallopian tubes at ovulation
Egg slowly moves toward the uterus by peristaltic contractions and movement of the cilia of the fallopian tubes (4-5 days)
Transports the egg to the uterus
Also the usual site of fertilization (egg and sperm fuse)
Fertalized egg may implant in the fallopian tube instead of the uterus
Called an ectopic pregnancy
Usually results in a miscarriage
Can lead to maternal bleeding, possible hemorrhage and death
Uterus
Also called the womb
Shaped like an upside-down pear
Held in place between the rectum and the bladder by the broad ligament
Provides a safe and nurturing environment for the developing baby during pregnancy
Fundus
Upper part, above the entrance of the fallopian tubes
Body
Central region
Cervix
Lower narrow region that opens into the vagina
Epimetrium (perimetrium)
Outer serosal layer
Myometrium
Middle, smooth muscle layer
Endometrium
Basal layer
Next to the myometrium
Thin and vascular
Functional layer
Layer that thickens in response to ovarian hormones
Sloughs off during menstruation
Vagina
4 inch muscular tube that extends from the cervix to the vaginal opening
Mucosal lining lies in folds (rugae)
Allows the vagina to stretch and receive the baby during childbirth
Also recieves the penis during intercourse and is and exit for menstrual blood
Normally acidic environment discourages growth of pathogens
External Genitals (Vulva)
Labia majora
–Folds of hair covered skin
–Merge anteriorly to form the mons pubis
Labia minora
–Smaller folds of skin interior to the labia majora
Separated by a cleft containing the urethral and vaginal openings
Prevent drying of the mucous membranes
Clitoris
–Resembles the penis
–Contains erectile tissue and capped by thin membrane called the glans
–Labia minora partially surround and form a forskin
–Sensory receptors that allow females to experience pleasurable sexual sensations
Vestibule
–The cleft between the labia minora
–Contains the openings of the urethra and the vagina
–Vestibular glands on either side of the vaginal opening secrete mucous-containing substance that moistens and lubricates the vestibule
Peritoneum
–Area between the vaginal opening and the anus
Female Sexual Response
Erection
–Erectile tissue in the clitoris and the tissue surrounding the vaginal opening swell with blood
–Parasympathetic nervous system induces dilation of the arteries
–Erectile tissue in the vaginal mucosa, breast and nipples also swells
–Other responses: enlargement of the vagina and secretion by the vestibular glands
Orgasm
–Stimulates reflexes
–Causes muscle contractions in the perineum, uterine walls and uterine tubes
–Aids in directing and transporting sperm through the genital tract
Hormonal Control
Menstrual Cycle
–Egg matures, endometrial lining builds up, ovulation, no fertilization, endometrial lining sloughs off, cycle starts again
Average 28 days
Ovaries secrete most of the hormones involved in the menstrual cycle
Hypothalamus secretes releasing hormone
Stimulates anterior pituitary to release FSH and LH
FSH and LH stimulate ovaries to produce estrogen and progesterone
Ovarian Cycle
Follicular Phase
–Begins with hypothalamus secreting releasing hormone
–The anterior pituitary releases the gonadotropins (FSH and small amount of LH)
–Stimulates the maturation of the ovarian follicle
–Maturing ovary secretes large amounts of estrogen
–Estrogen helps follicle to mature
–Ends with ovulation due to a spike in LH
Luteal Phase
–Immediately follows ovulation
–Corpus luteum develops
–LH stimulates corpus luteum to release progesterone and small amounts of estrogen
–Hormones exert negative feedback on anterior pituitary
–Once corpus luteum dies progesterone and estrogen level decline
–Anterior pituitary starts releasing more FSH and LH and cycle repeats
Uterine Cycle (Menstrual Cycle)
Estrogen and progestrerone secreted by the ovaries controls the uterine cycle
Ovarian cycle controls the menstrual cycle
Menstrual Phase
–Characterized by bleeding
–Begins on day 1 and continues for 3 – 5 days
–The functional layers of the endometrial lining and blood leave the uterus through the vagina
Proliferative Phase
–Begins with the end of the menstrual phase
–Estrogen secreted by the ovaries stimulates the repair and growth of the inner endometrial lining
Secretory Phase
–Progesterone from the corpus luteum causes the endometrial lining to become lush and thick
–Ready to receive fertilized egg
–If it doesn’t happen then the cycle repeats itself
Implantation
The endometrial lining does not slough off if the blood levels of estrogen and progesterone are high enough
If fertilization occurs the fertilized egg implants in the uterine lining
Some of the cells at the site of implantation secrete the hormone human chorionic gonadotropin (hCG)
This stimulates the corpus luteum
It doesn’t die and keeps producing progesterone and estrogen preventing menstruation
Birth Control
Barrier methods
–Prevents sperm from coming in contact with the egg
–Can be mechanical or chemical
–Condoms
–Diaphragm
–Spermicidal creams, foams and jellies
Hormonal Contraceptives
–Birth control pill, patch or implant
–Pharmacologic agent that contains estrogen and progesterone
–Blood levels of estrogen and progesterone increase
–Lowers levels of FSH and LH and prevents ovulation
Surgical Methods
–Vasectomy
Interruption of the vas deferens
Sperm can’t exit the epididymis
–Tubal ligation
Interruption of the fallopian tubes
Sperm can’t reach the egg
IUD
–Intrauterine device
–Stimulates the uterus to prevent implantation
Behavioral Methods
–Abstinence
–Rhythm method (high rate of pregnancy)
–Coitus interuptus (high rate of pregnancy)
RU-486
–Morning after pill that causes loss of implanted embryo