12. Physiology of Reproduction

8/18/2019 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



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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

-

– 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


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


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


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



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Effects of Testosterone


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•



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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


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



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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


H othalamic & ituitar Control on Testicular Function



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Reproductive System




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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


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


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)


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


Oogenesis



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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



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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


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



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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


– ,


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orre a on

Between

and CyclicOvarian and

Uterine Changes

Ovarian Cycle



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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 –


• 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)



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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


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



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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


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



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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


• 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



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Earl Sta es of Develo ment fromFerti lization to Implantation


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



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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•


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



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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


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)



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Sta es of Labor


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



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Suckin Reflexes

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12. Physiology of Reproduction