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Chapter 52: Reproductive System
52-1 Male Reproductive System 52-2 Female Reproductive System 52-3 Gestation
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52-1 Male Reproductive System
I. Formation of Sperm (head, mid-piece, and tail) Spermatogenesis begins when [TESTOSTERONE] increases during puberty. (FOUR sperm cells result during DIVISION)
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Critical Thinking (1) From an evolutionary perspective, WHY is so much energy expended on the production of SO MANY sperm by the male reproductive system?
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(1) Testes (endocrine gland)
Testosterone levels maintain spermatogenesis (male gametogenesis).
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II. Male Reproductive Structures
Manufacture, store, protect, AND deliver gametes to an unfertilized egg (fertility up to a period of years).
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(1) Seminiferous Tubules (INSIDE testes)
Tightly-coiled tubules WHERE spermatogenesis takes place.
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(2) Scrotum Testes DEVELOP within abdominal cavity (but LOWER into scrotum after birth to reduce HOT temperature—LOWER necessary for meiosis).
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(A) Path of Sperm through the Male Body (following spermatogenesis)
Sperm move from S.T. to EPIDIDYMIS, through VAS DEFERENS and URETHRA, and OUT penis.
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(1) Epididymis (of EACH testis)
A long coiled tubule where sperm MATURE and are STORED upon release.
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(2) Vas Deferens (of EACH testis)
DUCT extending from EPIDIDYMIS and CARRIES sperm to URETHRA (where sperm MIX with fluids).
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Critical Thinking (2) Why might sperm be able to survive as long as they do in the female, even though they have very LITTLE cytoplasm to store nutrients?
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(3) Semen (testes, seminal vesicles, bulbourethral glands, prostate gland)
(a) Fructose (NRG for sperm), (b) Alkaline fluids (NEUTRALIZES acidity), (c) Prostaglandins (stimulates smooth muscle CONTRACTION of female tract), and (d) Sperm cells (actual male GAMETES).
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(B) Delivery of Sperm Of million sperm released internally, a LARGE % are DESTROYED by ACIDIC environment of female tract.
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(1) Penis (highly VASCULAR)
SPONGY tissue, controls urethra CONTRACTIONS via smooth muscle lining.
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(2) Ejaculation (~ 3-4 mLs)
Sperm are ~ 10% of semen, ~90% is made up by SUPPORT FLUIDS for protection AND food supply.
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52-2 Female Reproductive System
I. Formation of Eggs BORN ~ 400,000 immature ova; OOGENESIS begins when [ESTROGEN] rise HIGH enough for maturation AND ovulation. [NOTE: ONE ovum with THREE disintegrating polar bodies RESULTS].
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(1) Ovaries An endocrine organ (estrogen AND progesterone) as well as SITE of oogenesis.
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(2) Ovum (regulated by FSH and LH)
10-28 immature eggs resume MEIOSIS every 28 days, BUT typically only ONE mature egg is released from a FOLLICLE.
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II. Female Reproductive Structures
Produce, release gametes during a CYCLE to maximize OPPORTUNITY for fertilization (in addition to SUPPORT pregnancy).
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(1) Fallopian Tube (i.e., uterine tube)
Following release, OVUM is swept into 1 of 2 uterine tubes, LINED with contracting CILIATED walls. (often SITE of FERTILIZATION)
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(2) Uterus Hollow, MUSCULAR organ where a ZYGOTE implants and develops AGAINST the wall.
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(3) Cervix Lower ENTRANCE to uterus, regulated by a SPHINCTER muscle. (4) Vagina Opening to cervix, CHANNEL which baby passes through during delivery.
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III. Preparation for Pregnancy
Each month comes a PREPARATION for a POTENTIAL pregnancy by undergoing a MENSTRUAL CYCLE (~ 28 days).
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(1) Menstrual Cycle (FOUR stages—F, O, LP, and M)
Regulated by HORMONES egg matures AND enters a fallopian tube, where FERTILIZATION can occur (if NOT, it degenerates AND is shed).
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(A) Follicular Phase (1-14 days; BEGINS when FSH triggers follicle growth)
Immature egg COMPLETES its 1st division; [ESTROGEN] rises until it PEAKS as maturing egg moves CLOSE to ovarian surface.
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Critical Thinking (3) A human female produce on average only ONE mature egg every 28 days. In contrast, a female salmon lays 50 million eggs at each spawning. Hypothesize as to why there is such great discrepancy in egg production between the two species.
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(1) Follicle (stimulated by FSH)
TISSUE surrounding IMMATURE egg (supplies nutrients AND secretes estrogen increases [LH] in bloodstream UTERINE lining THICKENS).
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(B) Ovulation (triggered by SPIKE of LUTEINIZING HORMONE ~ Day 14)
Follicle ruptures, RELEASING egg into fallopian tube to UTERUS, awaiting fertilization (NOTE: Nutrients in egg help it survive for 48 hours).
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Critical Thinking (4) What might happened if MORE than ONE egg were simultaneously released from the ovaries?
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(C) Luteal Phase (~ Day 15-28, marked by FORMATION of corpus luteum)
Once follicle ruptures, CORPUS LUTEUM develops in order to stimulate THICKENING of UTERINE LINING (e.g., endometrium).
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(1) Corpus Luteum (sustains LIFE of endometrium)
Remnants of ruptured follicle, GROWS larger and begins to SECRETE large amounts of E and P (while FSH and LH levels drop).
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(D) Menstruation (3-5 days at BEGINNING of FOLLICULAR phase)
If egg is NOT fertilized, corpus luteum will DIE and [ESTROGEN] and [PROGESTERONE] drop—uterine lining is SHED from body.
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(1) Menopause (~age 50, the END of menstruation)
Most FOLLICLES have either matured and ruptured OR degenerated, PREVENTING further secretion of estrogen and progesterone.
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52-3 Gestation I. Fertilization (ACROSOME (sperm) and ZONA PELLUCIDA (egg)) RESTORES human DIPLOID number (46), 9-MONTH gestation (SITE of fertilization in fallopian tube).
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Critical Thinking (5) What do you think might happen if MORE than ONE sperm were able to penetrate the cell membrane of an egg?
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(A) Cleavage and Implantation (~6 days AFTER fertilization)
Zygote BEGINS cleavage (mitosis) and IMPLANTS itself into UTERINE LINING. (marking BEGINNING of pregnancy).
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(1) Morula (32-cell ZYGOTE)
BALL of dividing cells DEVELOPS into a BLASTOCYST, next stage of development.
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(2) Blastocyst ATTACHES and BURROWS (using enzymes) into UTERINE wall, building CONNECTIONS to access a nutrient supply.
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(3) Implantation (marks the BEGINNING of pregnancy)
Occurs ~ 6 days POST-fertilization, marked by BLASTOCYST burrowing INTO thick UTERINE LINING.
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II. Pregnancy (a NINE-MONTH period of gestation)
Divided into 3 trimesters, BASED on human development.
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(1) Trimesters 3 periods, MARKED by development from BLASTOCYST to NEWBORN.
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(A) First Trimester (ALL body systems BEGIN to form)
Primary GERM layers arise (i.e., EME), PLACENTA attaches to FETUS and secretes HCG so that UTERINE LINING is NOT shed. *NOTE*: ENDOderm—Linings of Digestive, Respiratory, and Urinary tracts, Liver, Pancreas, and many glands. MESOderm—Muscle and Connective tissue, and Organs. ECTOderm—Nervous System and Integumentary.
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Critical Thinking (6) About 20 years ago, a large number of women who took a tranquilizer called “thalidomide” EARLY in pregnancy gave birth to babies with serious limb defects. Other mothers who took the drug LATER ON in pregnancy had normal children. What might this tell you about the SEQUENCE of development in a human fetus?
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(1) Amnionic Sac (one of the FOUR membranes formed during 1st Tri-M)
Fluid-filled CUSHION of embryo, supported by YOLK sac (first blood cells AND reproductive cells), allantois (origin of blood VESSELS), and chorion (surface COVERED with villi).
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(2) Chorionic Villi (small, fingerlike PROJECTIONS of CHORION)
Extend into UTERINE LINING and PLACENTA where products are exchanged through BLOOD of fetus AND mother.
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(3) Umbilical Cord (connects fetus TO placenta)
Blood NEVER mixes between mother and fetus, BUT materials are EXCHANGED by diffusion.
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(4) Human Chorionic Gonadotropin (HCG, a PLACENTAL hormone)
2nd week; MAINTAINS uterine lining by secretion of E and P, and likewise INHIBITS release of FSH and LH, PREVENTING ovulation.
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(5) Fetus (~8 weeks TO birth, 5 cm at end of 1st trimester)
Marked by formation of ALL major ORGAN SYSTEMS, and beginning the 2nd trimester, systems begin to MATURE and GROW.
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(B) Second Trimester (~ by trimester’s end, fetus is up to 32 cm long)
Fetal HEARTBEAT strong, ossification of SKELETON, layer of soft HAIR over skin, MOVEMENT beginning, and SLEEP CYCLES begin.
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(C) Third Trimester Fetal SENSORY systems active, MOTOR systems improve, and FAT deposits develop ( BODY TEMPERATURE).
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Critical Thinking (7) Observe the activity photographed in the fetus below; suggest an ADAPTIVE ADVANTAGE for this behavior.
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(D) Birth (~ 270 days after fertilization, marked by LABOR)
Initiated by release of prostaglandins, estrogen, and oxytocin—result in UTERINE CONTRACTION, rupturing of amniotic sac (WATER BREAKS), and RELAXATION of CERVIX. (1) Labor (i.e., strong contractions, SELF-PERPETUATING) Uterine muscles push fetus OUT through cervix and vagina HEAD-first, FOLLOWED by afterbirth.
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(2) Afterbirth (i.e., PLACENTA, amnion, and uterine lining)
Expelled ~10 minutes FOLLOWING delivery, as newborn has umbilical cord CUT and TIED, closing off VESSELS GIVE NEWBORN a fully-functional CARDIOPULMONARY circulation.
