BIOLOGY 206: CHAPTER 27:REPRODUCTIVE SYSTEM:LAUREL SPRING 2007
I.Overview
A.Functions and common concepts
1.Common purpose of the male and female reproductive systems is to produce offspring.
2.Primary reproductive organs are called gonads
a.testes are the male gonads
b.ovaries are the female gonads
3.Gonads produce
a.gametes or sex cells (egg and sperm)
b.sex hormones
4.The male sex hormones are called androgens and the female sex hormones are estrogens and progesterone
a.sex hormones are vital to the development of the reproductive organs and sexual behaviors.
5.All the remaining organs are called accessory reproductive organs
6.When sperm fuses with the egg, fertilization occurs and a new individual forms.
7.Once fertilization occurs, it is the female who carries and protects the new embryo and fetus until birth.
II.Anatomy of the Male Reproductive System
A.Overview
1.The testes are the male gonads, and they lie within the scrotum.
2.The testes produce sperm and the androgens.
3.The sperm are delivered to the body exterior through a system of ducts including (in order) the epididymis, the ductus deferens, and the urethra which opens to the outside at the tip of the penis.
4.The accessory glands empty their secretions into these ducts and include the seminalvesicles, prostateand bulbourethralglands
B.Scrotum
1.Pouch of skin that holds testes outside body and helps maintain fairly constant sperm temperature by elevating and lowering itself.
2.Superficial fascia incompletely divides the scrotum into right and left halves, 1/2 for each testis.
3.Sperm need a cool temperature to develop, so must be outside the body.
4.The cremaster muscles raise and lower the testes to help it maintain the desired temperature of 3 degrees Celsius below body temperature.
C.Testes
1.Each testis is approximately 4 cm X 2.5 cm and is surrounded by 2 tunics.
a.Tunica vaginalis is the outer coat from the peritoneum
b.Tunica albuginea is the inner fibrous capsule. It has septal extensions that divide each testis into 300 lobules
2.Each lobule contains 1-4 coiled seminiferous tubules which produce the sperm
3.The seminiferous tubules converge to form the rete testis on the posterior side of the testis and carry sperm to the epididymis on the external surface.
4.Interstitial cells surround the seminiferous tubules and produce the androgens, primarily testosterone.
5.Testicular arteries off the abdominal aorta feed the testes. The blood is cooled by a special structure (pampiniform plexus) before it enters the testes.
6.Blood returns to the inferior vena cava via the testicular veins.
7.The testes are supplied by both divisions of the ANS.
8.Nerves, blood vessels, and lymphatic vessels are all enclosed in the spermatic cord that extends from the epididymis through the inguinal canal.
D.Penis
1.The penis is a copulatory organ designed to deliver sperm and to serve as an exit for urine.
2.The penis and scrotum make up the male external genitalia.
3.The shaft has an enlarged tip, the glans penis, which is covered by a cuff of skin, the prepuce/foreskin.
a.Removal of the foreskin is called circumcision.
4.Internally the penis contains:
a.Penile urethra
b.3 columns of erectile tissue - a spongy network of connective tissue and smooth muscle interspersed with vascular spaces which fill with blood in sexual excitement, causing erection.
5.The corpus spongiosum is the slender mid-ventral column of erectile tissue surrounding the urethra. It expands at the tip to form the glans penis.
6.The corpus cavernosa are paired columns of erectile tissue that make up the bulk of the penis.
III.The Male Duct System
A.Epididymis
1.The epididymis is a comma-shaped coiled tube that uncoils to more than 6 meters.
2.Sperm are immature and non-motile when they enter, but after 20 days they have matured and can swim.
3.Sperm are expelled from the tail of the epididymis when the male is sexually stimulated in a process called ejaculation.
4.Sperm can be stored for several months, but are eventually phagocytized.
B.Ductus deferens and ejaculatory duct
1.Ductus deferens (vas deferens) is an 18" long tube that runs up from the epididymis through the inguinal canal into the pelvic cavity, arches over a ureter and descends on the posterior surface of the bladder where it joins the duct of the seminal vesicle to form the ejaculatory duct.
2.Each ejaculatory duct passes through the prostate gland and joins the urethra.
3.These structures undergo peristaltic waves of smooth muscle in ejaculation to propel the sperm out of the body.
4.A vasectomy is a sterilization method that ties off the ductus deferens. It is a relatively simple and very effective procedure.
a.Sperm continue to be produced but they can no longer exit the body and undergo phagocytosis.
C.Urethra
1.Outlet for urine and sperm in males.
2.It has 3 subdivisions:
a.Prostatic urethra drains bladder and is surrounded by prostate gland.
b.Membranous urethra passes through urogenital diaphragm.
c.Spongyor Penile urethra (75% of urethral length) runs through shaft of penis and opens to exterior atexternal urethral orifice.
IV.The Male Accessory Glands
A.Overview
1.The male accessory glands produce the bulk of semen (sperm and secretions).
2.They have an overall sperm-diluting role which increases sperm motility.
B.Seminal Vesicles
1.The paired seminal vesicles are located at base of bladder and produce 60% of semen's fluid volume.
2.Provides food/energy in the form of fructose to nourish sperm for swimming to egg.
3.It also secretes prostaglandins which decrease the viscosity of cervical mucosa and cause reverse peristalsis of uterus.
a.Both actions increases the sperms chances of reaching the egg.
C.Prostate Gland
1.The prostate gland is a single walnut-size and donut-shaped organ that surrounds the prostatic urethra just below bladder.
2.Secretions protect and activate sperm.
3.The prostate hypertrophies in almost all elderly men and makes urination difficult. This can lead to cystitis and/or kidney damage. It may also cause a hernia to develop because of the straining during urinatation.
a.Microwave and/or radio-wave radiation now usually replace the more traditional surgery associated with destroying excess tissue.
4.Prostate cancer is the third most common cancer in men
a.Screening involves a rectal digital exam and PSA blood test.
b.Therapies vary widely from surgery to radiation to “watch”.
D.Bulbourethral Glands
1.These paired glands (Cowper’s glands) are pea-sized and inferior to prostate.
2.Their secretions are released prior to ejaculation to neutralize acid urine in urethra.
E.Semen
1.Semen is the milky white mixture of sperm and accessory gland secretions.
2.There is usually 2-5 ml of semen/ejaculate and 60-130 million sperm per ml!
V.The Male Sexual Response
A.Erection
1.The blood vessels supplying the erectile tissue are normally constricted.
2.In sexual arousal the parasympathetic NS causes local vasodilation such that the columns fill with blood. But the swelling of corpora cavernosa compresses the drainage veins and inhibits bloods exit.
3.The parasympathetic reflex also causes secretion from the bulbourethral glands.
B.Ejaculation
1.This process is under sympathetic control.
2.All ducts and glands contract and empty contents into the urethra.
3.The bladder sphincter constricts to prevent expulsion of urine.
4.The entire series of events as well as the sensations of pleasure are referred to as a climax or orgasm.
VI.Gametogenesis
A.Spermatogenesis
1.Sequence of events in seminiferous tubules that leads to production of gametes.
2.Involves 2 cell divisions and reduction of chromosome number from 2N (46) to N (23) in general process of meiosis.
B.Spermiogenesis
1.Differentiation of the N spermatid cells formed in spermatogenesis to motile, streamlined sperm cells.
2.Sperm has 3 components:
a.Head: contains nucleus/DNA with a tip called acrosome with enzymes to penetrate egg
b.Mid-piece: contains mitochondria to produce energy (ATP) for swimming to egg
c.Tail: flagellum for swimming to egg
VII.Hormonal Regulation of Male Reproductive Function
A.Brain-Testicular Axis
1.The hypothalamus produces gonadotropin-releasing hormones (GnRH) that stimulate the anterior lobe of the pituitary.
2.The anterior lobe of the pituitary produces:
a.FSH (follicle-stimulating hormone)
b.LH or ICSH (interstitial-cell stimulating hormone)
3.FSH stimulates spermatogenesis indirectly by stimulating cells in the seminiferous tubule to release androgen-binding protein(ABP)
a.This makes the spermatogenic cells receptive to the stimulatory effects of testosterone .
4.ICSH binds to the interstitial cells and causes them to secrete testosterone.
5.There are several feedback systems involved in regulation
a.An increase in testosteronedecrease in GnRH
b.Inhibin is a hormone produced by the seminiferous tubules when the sperm count is high and inhibits both the hypothalamus and the anterior lobe of the pituitary thus controlling the rate of spermatiogenesis
6.One possible sequence is as follows:
Increase in spermincrease in inhibindecrease in FSHdecrease in ABPstops testosterone from binding decreased spermatogenesisdecrease in number of sperm, etc.
B.Other Effects of Testosterone
1.At puberty it causes all the male reproductive organs to grow to adult size and function.
2.Stimulates the development of hair: pubic, axillary, facial, chest, etc.
3.Deepens voice as larynx enlarges
4.Enhances bone mass
5.Boosts metabolic rate
6.Influences behavior
VIII.Anatomy of the Female Reproductive System
A.Overview
1.The ovaries are the gonads and the accessory ducts (uterine tubes, uterus and vagina) transport and/or support the reproductive cells and developing fetus
2.Ovaries and ducts are all within the pelvic cavity and are called internal genitalia.
3.Externalgenitalia orvulva are all the external sex organs.
B.Paired ovaries
1.Almond-shaped (double the size) on either side of uterus.
2.Anchored in the peritoneal cavity by ligaments which include:
a.ovarian ligament
b.Suspensory ligament
c.Mesovarium
3.Suspensory ligament and mesovarium are part of the broad ligament that supports all the internal genitalia.
4.Ovarian arteries branch off aorta, and ovarian veins join the inferior vena cava.
5.Tunicaalbuginea is the fibrous external surface.
6.Ovaries have an outer cortex which contain the ovarian follicles and an inner medulla containing the largest blood vessels and nerves.
7.Internally each ovary has many saclike structures called ovarianfollicles which have an immature egg (oocyte) surrounded by cell layers.
a.A single layer of cells are called follicular cells.
b.More than one layer of cells are called granulosa cells.
8.Follicles have different stages of maturation:
a.Primordial follicles have 1 layer of follicular cells around the oocyte. These are commonly found in nests/groups of cells at edge of ovary.
b.Primaryfollicle has 2 or more layers of granulosa cells around the oocyte. This follicle will be slightly deeper in the cortex and larger than the clustered primordial follicles.
c.Secondaryfollicle has a small fluid-filled space called the antrum.
d.Vesicular (Graafianfollicle) is the most mature follicle with a much enlarged antrum. The follicle bulges from the surface of the ovary.
e.Each month one vesicular follicle ejects its oocyte into the peritoneal cavity in a process called ovulation.
f.Corpusluteum is the structure that develops after ovulation from the ruptured follicle. This will eventually degenerate.
C.Paired uterine tubes (fallopian tubes/oviducts)
1.Receives ovulated oocyte and provides site for fertilization.
2.Approximately 10 cm ( 4") long, extending from ovary to upper sides of uterus.
3.The ampulla is the distal end that swells and curves around the ovary.
a.generally where fertilization occurs
1
b.Ampulla ends in open funnel called the infundibulum that has finger-like projections called fimbriae that drape over ovary and pull oocyte into the uterine tubes.
4.Proximal end narrows near uterus and is called the isthmus.
5.Note: the male system is closed, but female's is open; egg must be caught and brought into fallopian tube by the waving fimbriae.
6.Peristalsis and cilia from fallopian epithelial cells move egg toward uterus.
7.Microvilli produce moistening/nourishing secretions for egg and sperm.
E.Uterus
1.Hollow, thick-walled muscular organ that functions to receive, retain and nourish fertilized egg.
2.Pear shape and size in premenopausal women who have never been pregnant.
a.Larger in women who have had children
3.Located anterior to the rectum and posterosuperior to the bladder.
4.Has 4 major regions:
a.Body = major portion
b.Fundus = superior, rounded area above entrance of fallopian tubes
c.Isthmus = narrow inferior region between the body and cervix
d.Cervix = narrow outlet
(1)Cervicalcanal runs through middle of cervix and communicates with vagina. It has a superior opening from the uterus is called the internal os and its inferior opening into the vagina is called the external os.
(2)Cervical glands produce mucus that block spread of bacteria and entry of sperm except at mid-cycle.
5.Uterine wall has 3 layers:
a.Perimetrium = outermost serous layer and is the visceral peritoneum
b.Myometrium = bulky middle of smooth muscle that provides contractions for childbirth
c.Endometrium = mucosal lining of uterine cavity
6.After fertilization, embryo implants into endometrium where it remains throughout the gestation (development) period.
7.Endometrium has 2 layers:
a.stratum functionalis is closest to uterine cavity. It undergoes monthly cycles in response to hormones and is shed during menstruation.
b.stratum basalis is closest to myometrium. Doesn't change much during a monthly cycle and reforms the stratum functionalis after menstruation.
F.Support of uterus
1.There are numerous ligaments that support the uterus. Just 2 of these include:
a.Broad ligament that attaches sides of uterus to abdominal wall.
b.Round ligament that attaches uterus to labia majora.
2.These ligaments allow the uterus to be mobile and to change it’s position as the bladder fills and empties.
3.The other major support for the uterus are the muscles of the pelvic floor comprising the urogenital/pelvic diaphragms
G.Vagina
1.Thin-walled muscular tube (8-10 cm) between bladder and rectum extending from cervix to body exterior.
2.Functions:
a.Passageway for delivery of infant and menstrual flow.
b.Organ of copulation since it receives the penis in intercourse.
3.3 layers/coats:
a.Adventitia is the outermost fibroelastic layer.
b.Muscularis is the middle layer of smooth muscle.
c.Mucosa is the inner epithelium with transverse ridges called rugae for stretching and stimulation of the penis
4.In virgins the vaginal orifice mucosa expands to form the hymen, an incomplete partition of opening.
a.The hymen is vascular and tends to bleed during first intercourse.
b.Its durability is highly variable, however.
5.The fornix is at the upper end of vaginal canal and surrounds the cervix.
6.Resident bacteria produce a pH of 3.5 – 5, and this helps keep vagina free of infection but also makes it hostile to sperm.
a.Adolescents have an alkaline vagina which predisposes them to sexually transmitted disease.
H.External genitalia or Vulva
1.Mons pubis is the fatty area over the pubic symphysis and covered with pubic hair after puberty.
2.Labia majora extends posteriorly from mons pubis. It is 2 elongated, hair-covered fatty skin folds.
a.It is the female homologue to the scrotum.
3.Labia minora is enclosed by the labia major. It is composed of 2 thin, delicate hair-free folds.
4.Vestibule is the region enclosed by labia minora and contains:
a.Urinary meatus/orifice anteriorly,
b.Vaginal orifice posteriorly
c.Greater vestibular glands that are the homologue to the male bulbourethral glands. They lubricate and moisten.
5.The clitoris is the small area of erectile tissue just anterior to the vestibule and is the homologue to the penis
a.It is hooded by a fold called the prepuce of the clitoris.
b.In the male the penis serves as an outlet for urine and sperm. The female’s urinary and reproductive systems are separate and neither run through the clitoris.
I.Perineum
1.Diamond-shaped region between anterior ends of labia majora, coccyx posteriorly, and ischial tuberosities laterally.
IX.Ovarian cycle in an adult female
A.Overview
1.Ovarian cycle refers to series of events associated with the maturation of an egg over a 28-day period (or some variation therein)
2.Divided into 2 phases:
a.follicular phase which occurs prior to ovulation (Days 1-14)
b.luteal phase which is post-ovulatory (Days 14-28)
3.Cycle can vary and last up to 40 days. However, it is the follicular phase that varies, not the luteal phase.
B.Follicular phase
1.First, primordial follicles are activated and develop into primary follicles.
a.Surrounding granulosa and thecal cells begin to produce estrogens.
b.Granulosa cells also produce a glycoprotein-rich substance that forms a thick, transparent membrane around the oocyte called the zona pellucida.
2.Next, a clear liquid begins to develop and a fluid-filled cavity called the antrum develops.
3.The antrum continues to fill until the oocyte is completely isolated along with its granulosa cells. The resulting structure is called a corona radiata. A vescicular follicle results.
a.At this point the follicle bulges out at the surface of the ovary.
4.The final event before ovulation is the completion of cellular division of Meiosis I.
B.Ovulation
1.Ovary wall ruptures and ovulation occurs at Day 14.
2.Usually only one follicle ovulates its oocyte each month. However, if multiple oocytes are ejected and fertilized, fraternal (non-identical) twins can result
C.Luteal phase
1.Day 14-28
2.Follicle collapses and becomes corpus luteum that secretes primarily progesterone and some estrogen.
3.If fertilization does not occur the corpus luteum degenerates and its hormonal output ends.
a.At this point it becomes a corpus albicans.