12. physiology of reproduction
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Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
homeostasis but exerts other important effects
Hypothalamus
Reproductive AnteriorReproductiveapa yorgans
Sexhormones
Targetcells
reproductive capability
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Re roductive S stem
• Includes gonads, reproductive tract, andaccessory sex glands
– Depends on union of male and female gametes
– Male and female reproductive systems designedo ena e un on o gene c ma er a
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Re roductive S stem• Primary reproductive organs (gonads)
–• Pair of testes in male• Pair of ovaries in female
– Functions of mature gonads•
– Spermatozoa (sperm) in male – Ova e s in female
• Secreting sex hormones –
– Estrogen and progesterone infemales
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Re roductive S stem• Reproductive tract
–house gametes after they are produced
• Accessor sex lands – Empty supportive secretions into reproductive tract
• – Externally visible portions of reproductive system
• econ ary sexua c arac er s cs
– External characteristics not directly involved inrepro uc on a s ngu s ma es an ema es• Body configuration and hair distribution• on ro y es os erone n ma e an es rogen
in female.
• Functions
– Production of sperm (spermatogenesis) – Delivery of sperm to female
• Organs –
• Sperm-producing organs• Suspended outside abdominal tract
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– Accessory sex glands• Seminal vesicles, prostate gland,
bulbourethral glands – Secretions provide bulk of semen (liquid
substance that is conducive to sperm viability) –
• Organ used to deposit semen in female – Male reproductive tract
• p ym s, uctus vas e erens, e acu atoryduct empty into urethra (canal running lengthof penis that empties into exterior)
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Male Re roductive S stem
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Female Re roductive Functions and Or ans• Functions – Production of ova (oogenesis) – Reception of sperm – Transport of sperm and ovum to common site for
• Product of fertilization is known as an embryo .•
– Maintenance of the develo in fetus until it can survive in outside
,as a fetus .
world (gestation or pregnancy)
– Giving birth to the baby (parturition)
– Nourishing infant after birth by milkproduction (lactation)
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Female Reproductive System
Re roductive Cells Human chromoso mes: 2n=40• Body (somatic) cells
– Contain 46 chromosomes (diploid number) –
• Gametes (sperm and egg) – Have 23 chromosomes ha loid number – Contains only one member of each homologous pair
of chromosomesPig chromosomes:
2n=38
–
• Autosomes –
characteristics and specific traits such as eye color
• Sex chromosomes Mouse chromos omes:2n=40Cow chromosomes:
2n=60 – Remaining pair of chromosomes – Two genetically different types
•• Smaller Y chromosome
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ChromosomalDistribution in
Sex Determination• Sex determination
– Depends on combination of sex chromosomes – Genetic female
• Has two X chromosomes
– Genetic male• Has an X and a Y chromosome
• Y chromosome – Responsible for all the anatomic
an unct ona st nct onsbetween males and females
•
– Determined at time of conception – De ends on which t e of sex
chromosome is contained within thefertilizing sperm
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Sexual Differentiation
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Sexual DifferentiationThree levels of differences
between males and females – Genetic
• Depends on combination of
sex chromosomes at time ofconception
–• Whether testes or ovaries develop
chromosome determines gonadaldifferentiation
– Phenotypic• Apparent anatomic sex of
individual• Determined by gonadal sex
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Male Reproductive Physiology
• Testes –
seventh month of gestation –
• Location provides cooler environmentessential for spermatogenesis
– Perform dual function• Produce s erm
– Occurs within seminiferous tubules
• Secrete testosterone – Produced by Leydig (interstitial) cells that lie
in connective tissue between seminiferous
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
tubules
Male Reproductive Physiology• Testosterone
–cholesterol precursor molecule
– Five categories of testosterone effects
• Sex-specific tissues after birth• -• Secondary sexual characteristics• Non-re roductive actions
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Effects of Testosterone
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
S ermato enesis• Results in many highly specialized, mobile sperm
• Com lex rocess b which undifferentiated di loidprimordial germ cells (spermatogonia) are converted intohaploid spermatozoa (sperm)
• Three major stages – Mitotic proliferation
• -four identical primary spermatocytes
– Meiosis• Each primary spermatocyte forms two secondary spermatocytes
yielding four spermatids after the second meiotic division• Theoretically, sixteen spermatozoa result from each
spermatogonium that goes through process
– Packaging•
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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S ermato enesis• Spermatozoa
–
– Consists of four parts
cells throughout development
• Head – Consists primarily of the nucleus
(contains DNA)• Acrosome
– Enzyme-filled vesicle that caps tip ofthe head
– Used to penetrate ovum – Formed by endoplasmic reticulum and
Golgi complex before these organellesare discarded
• Midpiece – Area where mitochondria are concentrated
• Tail – Provides mobility for spermatozoan
Spermatogenesis
The relationship between Sertoli cells and the developing sperm.
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The modification of a germ cell to form amammalian sperm
The modification of a germ cell to forma mammalian sperm
Nucleus /
Mitochondria / Mictotubule/
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Spermatogenesis
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
S ermato enesis
• Functions of Sertoli cells located in seminiferous tubules – Form blood-testes barrier – Provide nourishment
– Phagocytic function – Secrete seminiferous tubule fluid which flushes released
additional processing – Secrete andro en-bindin rotein – Site of action to control spermatogenesis
• Release inhibin• Acts in negative-feedback fashion to regulate FSH secretion
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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S ermato enesis• Epididymis and ductus deferens
– Store and concentrate s erm – Increase sperm motility and fertility prior to ejaculation
• During ejaculation –
glands• Seminal vesicles
– – Supply prostaglandins
» Promote smooth muscle motility in both male and femalereproductive tracts (enhances sperm transport)
– rov e more t an a t e semen – Secrete fibrinogen
• Prostate gland – – Provides clotting enzymes and fibrinolysin
• Bulbourethral glands – Release lubricating mucus
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
H othalamic & ituitar Control on Testicular Function
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Reproductive System
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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• More complex than male reproductive
physiology• arac er ze y comp ex cyc ng
• Ovaries – Primar female re roductive or ans
Primaryoocyte
luteum
Rupturedfollicle
• Produce ova (oogenesis)• Secrete female sex hormones
–» Essential for ova maturation and release» Establishment of female secondary sexual
characteristics» Essential for transport of sperm from
vagina to fertilization site in oviduct
» Contributes to breast development in
Maturefollicle
Ovulation
Secondaryoocyte
– Progesterone
» Important in preparing suitableenvironment for nourishin a develo in
Ovary
embryo/fetus» Contributes to breasts’ ability to produce
milk
Oo enesisSpermatogenesis Oogenesis
Accomplished within Take anywhere from
• Identical steps ofchromosome replication
wo mon s o years ocomplete on cyclicbasis from onset of
gamete production in bothsexes
menopause
Postpubertal male can Female born with
– Timing and end resultare very different
pro uce severahundred million spermeach day
m e , arge ynonrenewablesupply of germ cells
Each primaryspermatocyte yieldsfour e uall viable
Each primary oocyteyields only onec to lasm-rich ovum
spermatozoa
and threecytoplasm-poorpolar bodies that
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
disintegrate
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Oo enesis
• Oogonia – Undifferentiated primordial germ cells in fetal
ovaries – Divide mitotically to give rise to 6 million to 7
million oogonia by fifth month of gestation – During last part of fetal life begin early steps of
first meiotic division but do not complete it• Now known as primary oocytes
– Contain diploid number of 46 replicated chromosomes – ema n n me o c arres or years un ey are prepare
for ovulation
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Oo enesis• Primary oocyte
– urroun e y s ng e ayer o granu osacells
– ocyte + granulosa cells → primary ollicle• Primary follicle
– After development starts there are twopossible fates
• Reach maturity and ovulate• Degenerate to form scar tissue (atresia)
• Between puberty and menopause – Follicles develop into secondary (antral)
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
follicles on cyclic basis
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• Just before ovulation – Primary oocyte completes its first meiotic division
yielding• First polar body• Secondary oocyte
– Ovulated – Sperm entry triggers second meiotic division which
» Secondary polar body (haploid)
» Mature haploid ovum which unites with haploidsperm cell during fertilization
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Oogenesis
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Oogenesis (egg) Follicle development in ovary
2n
Oogonium (Stem cell)Mitosis
2n
Primary oocyte
Primordial follicle
oocyte
2n
Growth Primary oocyte(arrested in prophase
I present at birth) Primordial follicle
Childhood (Ovary inactive)
Primar folliclePrimar ooc te4n
Meiosis I
Growing follicle
(still arrested in prophase I)
Ovulation
2nnFirst polar body
a ura eoocyte)
Vesicular follicle
2nSperm
e os sof polar body(may or may
not occur) Meiosis IIOvulated secondaryoocyte (arrested at
nnnn n
Spermcomp ete
(only if sperm penetration occurs)Polar bodies
(all degenerate)
• Normally interrupted only by pregnancy
• Finally terminated by menopause• Consists of two alternating phases
– Follicular phase• Dominated by presence of maturing follicles
– Luteal phase• Characterized by presence of corpus luteum
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Ovarian C cle
• Follicular phase – Operates first half of cycle
– Granulosa cells of some primary follicles proliferate – ocy e ns e eac o c e en arges – Theca cells in follicle secrete increased amounts of
– Rapid follicular growth continues during follicular phase• One follicle usuall rows more ra idl and matured about 14
days after onset of follicular development – Follicle ruptures to release oocyte from ovary – – Released oocyte enters oviduct where it may or may not be
fertilized
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Ovarian C cle• Luteal phase
– – Old follicular cells undergo structural
transformation to form cor us luteum – Becomes highly vascularized –
ovulation – Continues to increase in size for another four or
five days – If released ovum is not fertilized and does not
implant, corpus luteum degenerates within about14 days after its formation
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Development of the Follicle, Ovulation, and Formationand Degeneration of the Corpus Luteum
Ovarian C cle• Hormonal interactions
– Durin follicular hase, rise in FSH si nals ovarian follicleto secrete more estrogen
– Rise in estrogen feeds back to inhibit FHS secretion which
– LH rises in follicular phase• As it peaks in mid-cycle, it triggers ovulation
– Estrogen output decreases and mature follicle is convertedto a corpus luteum
–luteal phase
– Progesterone output inhibits release of FSH and LH• Low LH – corpus luteum degenerates• Progesterone levels decline
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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orre a on
Between
and CyclicOvarian and
Uterine Changes
Ovarian Cycle
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Uterine C cle
• Menstrual cycle• Reflects hormonal changes during ovarian cycle• Averages 28 days• Outward manifestation of cyclic changes in uterus is
menstrual bleeding once during each cycle• Consists of three phases
– – Proliferative phase –
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
• Menstrual phase
– Characterized by discharge of blood and endometrialdebris from vagina
– – Coincides with end of ovarian luteal phase and onset offollicular hase
– Release of uterine prostaglandin• Causes vasoconstriction of endometrial vessels
– Disrupts blood supply – Causes death of endometrium
– Help expel blood and endometrial debris from uterine cavity outthrough vagina (menstrual flow)
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Uterine C cle
• Proliferative phase – Begins concurrent with last portion of ovarian
follicular phase• Endometrium starts to repair itself and proliferate under
influence of estrogen from newly growing follicles
– Estrogen-dominant proliferative phase lasts fromend of menstruation to ovulation
– Peak estrogen levels trigger LH surge
responsible for ovulation
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Uterine C cle• Secretory or progestational phase
–new corpus luteum is formed
–progesterone and estrogen
• Pro esterone – Converts endometrium to highly vascularized, glycogen-
filled tissue
– – If fertilization and implantation do not occur
• New follicular phase and menstrual phase begin onceagain
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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• Cessation of woman’s menstrual cycle• Usually occurs between ages of 45 and 55
• Midlife hypothalamic change may trigger onset ofmenopause
• Preceded by period of progressive ovarian failure – Increasingly irregular cycles – Dwindlin estro en levels
• Loss of estrogen primarily affects skeleton and
cardiovascular system• Period of transition called the climacteric
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Fertilization
• Oviduct is site of fertilization – Normally occurs in upper third of oviduct (ampulla)
• Must occur within 24 hours after ovulation
– Sperm usually survive about 48 hours but cansurvive up to 5 days in female reproductive tract
• Sperm deposited in vagina travel through cervicalcanal, uterus, and to upper third of oviduct – ema e repro uc ve rac a s n sperm m gra on
• Contractions of myometrium
• Allurin released by mature eggs
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Fertilization• First sperm to reach ovum
– uses w p asma mem rane o ovum
– Triggers chemical change in ovum’s surroundingmembrane that makes outer layer impermeableto entry of any more sperm
– Head of fused sperm gradually pulled into ovum’scytoplasm
– Within hour, sperm and egg nuclei fuse
• Fertilized ovum now called a zygote
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
• Fertilized ovum divides mitoticall – Within week grows and differentiates into
blastoc st ca able of im lantation • Blastocyst implants in endometrial lining by means
– Enzymes digest endometrial tissue•
blastocyst• Release nutrients from endometrial cells for use by
developing embryo
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Earl Sta es of Develo ment fromFerti lization to Implantation
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Implantation of Blastocyst
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Develo ment• After implantation
– acen a eve ops
• Organ of exchange between maternal and
• Acts as transient, complex endocrine organthat secretes essential pregnancy hormones
– Human chorionic gonadotropin» Maintains corpus luteum until placenta
a es over unc on n as wo r mes ers – Estrogen
» Essential for maintainin normal pregnancy
– Progesterone» Essential for maintaining normal
pregnancy
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Gestation• Pregnancy
– ou wee s rom concep on
– Physical changes within mother to meet demandsof pregnancy
• Uterine enlargement• reasts en arge an eve op a ty to pro uce m• Volume of blood increases 30%•• Respiratory activity increases by about 20%
• Kidneys excrete additional wastes from fetus•
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Parturition
• Labor, delivery, birth• Requires
– Dilation of cervical canal to accommodatepassage of fetus from uterus through vagina andto the outside
– Contraction of uterine myometrium that aresufficiently strong to expel fetus
• Exact factors triggering increase in uterinecontractility and initiating parturition not fully
established
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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• Once contractions begin at labor onset, positive-feedback cycle progressively increases force
• Pressure of fetus against cervix reflexly increasesoxytocin secretion
• Role of oxytocin – Causes stronger contractions – -
until cervical dilation and delivery are complete
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Parturition• Stages of labor
– Cervical dilation• Longest stage• Lasts from several hours to as long as 24 hours in a first
– Delivery of baby• Be ins when cervical dilation is com lete • Usually lasts 30 to 90 minutes
– Delivery of placenta• Second series of uterine contractions separates placenta
from placenta –
after baby is born• After delivery, uterus shrinks to pregestational size (involution)
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Sta es of Labor
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Lactation• During gestation
–development of ducts and alveoli in mammary glands
• Prolactin
– production by alveolar epithelial cells – Withdrawal of placental steroids at parturition initiates
• Sustained by suckling – Triggers release of oxytocin and prolactin – Oxytocin
• Causes milk ejection by stimulating cells surrounding alveolito s ueeze secreted milk out throu h ducts
– Prolactin• Stimulates secretion of more milk to replace milk ejected asbab nurses
Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
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Chapter 20 The Reproductive SystemHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
Suckin Reflexes
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