Chapter 16: Reproductive System

•Function: produce new individuals of a species and pass on genetic material

•Structures:

–Gonads: primary sex organs (testes & ovaries)

•Produce gametes: sex cells (sperm & ova)

•Secrete sex hormones (development & function of reproductive organs; sexual behavior & drives)

–Accessory reproductive organs

•Produce materials to support gametes (i.e. semen)

Male Reproductive System

•Gonad: testes; gamete: sperm

–Both exocrine (sperm-producing) function and endocrine (testosterone-producing) function

•Accessory ducts/glands: aid in delivery of sperm to body exterior or to female reproductive tract

Testes

•paired oval glands (10-15 g)

•develop around 3rd month high on posterior abdominal wall (descend during 7th month)

•Produce sperm & hormones

–Responds to hormones from pituitary gland (FSH & LH)

•FSH – stimulates spermatogenic cells to produce sperm

•LH – stimulates release of testosterone (final trigger for spermatogenesis and enhances spermatogenesis)

•Divided into lobules that contain seminiferous tubules

–Make sperm and empty sperm into rete testis which leads to duct system

•Interstitial cells surround seminiferous tubules and produce androgens (testosterone)

•Cryptorchidism

–Testes do not descend

•3% of full term infants, 30% premature

•both sides results in sterility

–Chance of testicular cancer 30-50 times higher

–80% spontaneously descend in first year

–Hormones or surgery needed otherwise

•Spermatogenesis

–Sperm production (takes 64-72 days)

–Begins during puberty and continuesthroughout life

–Millions of sperm produced per day

–Formed in seminiferous tubules of testis

–Spermatogonia: primitive stem cells (mitotically divide throughout life)

•During puberty, FSH is secreted some new cells become primary spermatocytes that will undergo meiosis and form four haploid spermatids (immature)

–Spermiogenesis (occurs in epididymis): spermatids stripped of excess cytoplasm and tail forms to form mature sperm; contain DNA

•Acrosome: releases enzymes that help sperm penetrate through the capsule of follicle cells that surround the egg

–Threats to Spermatogenesis

•Common antibiotics (penicillin & tetracycline) can suppress sperm formation

•Radiation, lead, certain pesticides, marijuana, tobacco, excessive alcohol can cause production of abnormal sperm

•Testosterone Production

–interstitial cells in testes produce testosterone

–activated by luteinizing hormone (LH) – released by anterior pituitary gland with FSH (sperm production)

–stimulates adolescent growth spurt, prompts reproductive organs to develop, underlies sex drive

–causes secondary male sex characteristics

Duct System

•Accessory organs transport sperm from the body

–Epididymis

•Temporary storage site for immature sperm from testis

•Takes about 20 days to make it through, sperm maturation occurs and gain ability to swim

–Ductus deferens (vas deferens)

•Empties into ejaculatory duct, which passes through prostate gland to merge with urethra

•vasectomy

–Urethra

•Extends from base of bladder to tip of penis

•Carries both urine and sperm to body exterior (part of both systems)

•Bladder sphincter prevents passage of urine/sperm at same time and prevents sperm from entering bladder

•Pathway: Seminiferous tubules  rete tubule (spermatogenesis)  efferent ducts  epididymus (maturation)  vas deferens  ejaculatory ducts  urethra

•Vasectomy

–Portion of ductus deferens (vas deferens) removed

–Sperm produced but degenerate

–Can be reversed (45-60% effective)

Accessory Glands

•Seminal vesicles (60%)

–Located at base of bladder

–Secretion is rich in fructose, vitamin C, prostaglandins, and other substances that nourish and activate sperm passing through tract; alkaline (high pH); viscous

•Prostate (25%)

–Encircles upper part of urethra

–Produces fluid that plays role in activating sperm; milky fluid, slightly acidic (citric acid & enzymes)

–aids in survival in female reproductive tract

•Bulbourethral glands (Cowper’s glands)

–Tiny glands inferior to prostate

–Produce thick, clear, alkaline mucus that cleans urethra of traces of acidic urine prior to ejaculation

Semen

•Mixture of sperm and accessory gland secretions

•Transport medium for nutrients and chemicals that protect sperm and aid in their movement

•Fructose in seminal vesicle secretion provides the sperm’s energy fuel

•Alkalinity of semen (pH 7.2-7.6) helps neutralize the acidic environment (pH 3.5-4) of female vagina (protects sperm & maintains motility)

•Contains:

–antibiotic chemicals that destroy certain bacteria

–hormone relaxin

–enzymes that enhance sperm motility

–substances that inhibit an immune response in female reproductive tract

•Dilutes sperm to aid in motility

–2-5 ml semen ejaculated, between 50-150 million sperm per milliter

•Male Infertility

–First step to test fertility in a couple unable to conceive is semen analysis

–Sperm count: <20 million per milliliter makes impregnation improbable, 20-40 million borderline

–Motility – at least 60% swimmers

–Morphology – 65-70% not deformed

–Semen volume - low would indicate defect or inflammation

–pH – slightly alkaline

–Fructose present

–liquefaction within 2 hours – enzyme defect if not occurring

–May be caused by obstructions of duct system, hormonal imbalances, environmental estrogens, pesticides, excessive alcohol, many other factors

External Genitalia

•Scrotum: protection and support of testes

–Divided sac of skin

–Provides testes with temperature below body temperature (viable sperm cannot be produced at normal body temperature)

•need temperature 3 degrees lower than body temp.

–Cremaster muscle & change in scrotal surface area regulate temperature (temperature can cause infertility)

•Penis

–Delivers sperm into female reproductive tract & supports urethra

–Shaft, glans penis, prepuce (foreskin) around glans

–Erectile tissue surrounds urethra to enable delivery of sperm to female reproductive tract

–Circumcision

•Part or all of prepuce removed

•Usually performed by eighth day of life

•No consensus on medical benefits

Female Reproductive System

•Gonad: ovaries; gamete: ova

–releases both exocrine products (ova) and endocrine products (estrogen and progesterone)

–in 3rd month, pre-programmed cells develop and descend to pelvis and start making follicles (if no Y chromosome)

•must nurture and protect developing fetus during pregnancy

•accessory organs: structures to transport, nurture, or serve the needs of reproductive cells and/or developing fetus

Ovaries

•contain ovarian follicles

–each follicle consists of immature egg (oocyte) surrounded by follicle cells

–follicle enlarges as oocyte matures and develops fluid-filled region called antrum

–ovulation: ejection of egg from ovary

–after ovulation, follicle becomes corpus luteum and degenerates

•attached to uterus with ligament but no real attachment to fallopian tubes

•Ovulation

–approximately every 28 days

–ovum released from ovary and sucked up into fallopian tube with current produced by fimbriae that surround ovary and cilia inside tube

–fertilization occurs in fallopian tube (uterine tube)

–egg can drop into abdominopelvic cavity, befertilized, and implantoutside uterus (ectopic pregnancy)

•Ovarian Cyst

–fluid-filled sac on or in ovary

–relatively often, most under 2 inches

–usually noncancerous

•Oogenesis

–formation of eggs (ova)

–one egg is formed per meiosis

–oogonium – predetermined diploid cell

–does not go through 2nd cell division unless fertilized

–nucleus immediately splits if fertilized (2nd nucleus expelled)

–unequal cell division – only get one egg from meiotic division

Contrasting Spermatogenesis & Oogenesis
Spermatogenesis / Oogenesis
equal division / unequal division
4 sperm / one egg (3 polar bodies)
both divisions prior to maturity / only 1 division prior to fertilization
300 million per day / 1-2 produced per month (don’t waste energy on 2nd division

Duct System

•UterineTubes (Fallopian tubes)

–receive ovulated oocyte and provide site for fertilization

–sperm must swim against current created by cilia

–fertilization occurs within 24 hours (due to viability of egg)

–location of surgical sterilization

•Uterus

–path for sperm & egg (if not fertilized)

–receives, retains, and nourishes fertilized egg

–initiation of labor (contractions)

–wall composed of three layers: perimetrium, myometrium, endometrium

•endometrium is inner lining: if egg is fertilized, burrows into endometrium (implantation); if not fertilized, sloughed off periodically in response to changes in levels of ovarian hormones in blood (menstruation)

•endometriosis: thickened, fibrous endometrium

–Tubal Ligation

•surgical sterilization: fallopian tubes cut and cauterized

•can be reversed

–Toxic Shock Syndrome

•caused by bacterium: Staphylococcus aureus

•high fever (up to 105), sore throat, tender mouth, headache, rash, abdominal pain, vaginal irritation

•most common in females who use tampons

Mammary Glands

•organs of reproductive system

•Modified sweat glands lie over chest muscles

•15-20 lobes

•Respond to hormones

–Oxytocin (hypothalamus) begins lactation

–Prolactin (pituitary) helps oxytocin to begin lactation and maintain lactation

–Relaxin allows milk to come in (around 48 hours after birth)

•Men have non-functional mammary glands

•Breastmilk provides IgA antibodies and nutrients difficult to replicate in infant formula

Female Hormones

•FSH: stimulates follicles to have 1st cell division to produce secondary oocyte

•LH: increases at ovulation

•Estrogen: released by ovary; controls uterine cycle; builds endometrial lining

–Appearance of secondary sex characteristics

•Progesterone: released by ovary (and placenta); controls uterine cycle; maintains pregnancy if fertilization occurs

Fertilization

•Spermatozoon and ovum merge into single nucleus

•Occurs in fallopian tube about 12-24 hours after ovulation

•Only 1% of 300-500 million sperm reach secondary oocyte

•Sperm cannot merge with egg until in female reproductive tract for 10 hours

–capacitation: functional change sperm undergo in female reproductive tract; membrane formed round head of sperm and enzymes released to help penetrate cells around oocyte; enzymes liquefy semen so sperm become more motile

•Oocyte secretes chemical to attract sperm

•Syngamy: only one sperm fertilizes egg (entry of other sperm blocked to prevent polyspermy)

Zygote

•Fertilized egg (day zero)

•First cell of the individual

•Two nuclei fuse

Morula

•Developing embryo reaches uterus around 3 days after ovulation

•Approximately 16 cells; uses uterine secretions for nutrition and continues dividing

Blastocyst

•Embryo hollows out to form a ball-like structure once it has about 100 cells

•Secretes hormone: human chorionic gonadotropin (hCG)

–Stimulates corpus luteum of ovary to continue producing hormones

–Pregnancy tests

•Attaches to the endometrium day 7 after ovulation

•Inner cell mass of blastocyst begins to form the three primary germ layers

Implantation

•Completed and uterine mucosa has grown over embry0 by day 14 after ovulation (normally day to start menstruating)

•Enzymes secreted to penetrate uterine lining and immunosuppressors secreted to prevent woman’s body from rejecting embryo as “foreign”

Gastrulation

•Within one week of implantation (around day 12)

•Gut begins to form (tube) – will become digestive system

•embryonic disc – germ layers (cells surrounding tube)

–Primary Germ Layers: endoderm, mesoderm, ectoderm

Neurilation: nervous system development (18-20 days)

•Organs start development (organogenesis)

Embryonic Membranes

•Yolk sac: early food source for embryo

–Early site of blood formation prior to spleen taking over

–Developmental circulatory system of embryo prior to placenta

•Amnion: becomes amniotic sac

–Shock absorber for fetus, regulates temperature, prevents adhesions

–Amniocentesis

•Chorion: Embryo’s contribution to placenta

–Surrounds embryo and later becomes part of placenta

–Chorionic villi testing

•Allontois: Embryo’s contribution to umbilical cord

–Small outpouching of yolk sac

–Early blood formation (helps yolk sac)

–Becomes connection in placenta for blood (umbilical cord)

Placenta

•Developed by 3 months

•Comes from chorion and endometrium of mother

•Allows oxygen and nutrients to diffuse into fetal blood from maternal blood with no mixing of blood

•Small and nonpolar substances can pass through (i.e. drugs and alcohol)

•Protective barrier (most microorganisms cannot cross)

•Stores nutrients

•Produces hormones necessary to maintain pregnancy

Umbilical Cord

•Comes from allantois and mother’s tissue

•Three vessels (one vein & two arteries)

–Nutrients diffuse into umbilical vein (towards fetus) and wastes leave through umbilical arteries (away from fetus)

•Wharton’s jelly around umbilical cord (connective tissue)