ch 16 reproduction - vertebrate physiology · 2/7/14 1...

2/7/14

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Chapter 16 Reproduc4ve System 1.  Physiological aspects of

reproduc4on –  Induced vs spontaneous

reproduc4on 2.  Reproduc4ve Ecology –  Frequency –  Timing –  Environmental factors

3.  Reproduc4ve endocrinology –  Female/male cycles –  Pregnancy and birth

Cellular communica4on requires integra4on across systems

•  Sensory systems – Receive s4muli

•  Nervous system – APs sent via neural pathways within CNS

•  Endocrine system – Hormone secre4on

•  Reproduc4ve system – Tissues and organs, hormones

Endocrine system and reproduc4on

•  Endocrine system produces hormones necessary for ovula4on

•  Ovula&on: release of mature eggs from ovary –  Induced – depends on s4muli during copula4on

–  Spontaneous – endogenous processes (environmental factors)

Induced reproduc4on •  Copula4on triggers series of physiological changes in females

Spontaneous reproduc4on •  Photoperiod causes physiological changes –  Tes/cular recrudescence: testes regress in autumn, regrow when photoperiod increases

•  Reproduc4on only occurs when female in estrus

•  Females recep4ve to copula4on only when mature eggs present!

Mature eggs

Estrogen secre4on (ovaries)

Estrus



reproduc4on 2.   Reproduc&ve Ecology –  Frequency –  Timing –  Environmental factors

3.  Reproduc4ve endocrinology –  Female/male cycles –  Pregnancy and birth

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Frequency of reproduc4on •  Semelparous organisms reproduce once/life4me – Brown antechinus:

Brown antechinus

Photoperiod induces melatonin secre4on (pineal gland)

All males sexually mature at same 4me

Immune-‐compromised males die

FIGHTS!!

Lots of testosterone

Females mate with dominant

males

Frequency of reproduc4on •  Semelparous organisms reproduce once/life4me – Brown antechinus – Sockeye salmon: Males and females cease feeding during migra4on; die aZer spawning

Sockeye Salmon Brown antechinus

Frequency of reproduc4on •  Semelparous organisms reproduce once/life4me •  High parental investment in offspring – Sockeye salmon catabolize body 4ssues for energy to produce gametes

Sockeye Salmon Brown antechinus

Frequency of reproduc4on •  Iteroparous organisms reproduce >2 4mes/life4me – Reproduce in cycles under endocrine and neuroendocrine control

•  Parental fitness not 4ed to single offspring •  Conserve energy for future offspring

•  Leads to trade-‐offs in provisioning strategies

Parental investment •  Pre-‐natal provisioning trade-‐off: – Many yolk-‐poor eggs for many OS (with low survival)

OR –  Few yolk-‐rich eggs for few OS (with high survival) –  Provisioning can occur to OS via blood (placental mammals)

•  Pre-‐natal provisioning •  Post-‐natal provisioning (lacta4on, feeding) – What are the trade-‐offs? What are risks/costs?

Parental investment

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•  Some species follow rigid steps – Timing and ini4a4on of each step regulated by hormonal and/or neurological control mechanisms

•  Alternate strategies 1.  Sperm storage

(salamanders, turtles, snakes, birds, bats)

Timing of reproduc4on

Ma4ng

Fer4liza4on

Hatching/Birthing

Embryonic development

2.  Embryonic diapause –  Delayed implanta4on: Embryonic development

stops aZer contracep4on •  Timing coincides with environment


2.  Embryonic diapause –  Delayed implanta4on –  Postpartum estrus: ready to mate immediately

following birth •  High reproduc4ve poten4al •  High energe4c demand


3.  Seasonal synchrony: reproduc4on coincides with resource abundance –  Length of breeding season correlated with la4tude


•  Tundra: breed 1 x/year à Monestrus

•  Tropics: breed year round à Polyestrus

Environmental factors influence reproduc4ve ecology

•  Food availability alters 4ming of events – Malnutri4on inhibits gonadotropin and egg matura4on in ovaries

– Causes later onset of mensus

– Effects seen in utero; less in young raised during famine

Lummaa and Cludon-‐Brock 2002


•  Food availability alters 4ming of events

•  Social behaviors – Why do some wait un4l 5 YO, when reproduc4vely able to at 2 YO?

– Size and experience constraints

– Female preference

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•  Food availability alters 4ming of events

•  Social behaviors •  Bio4c and abio4c condi4ons – Photoperiod – Warm temperatures and rainfall induce ma4ng

Longer days in Spring


Environmental condi4ons affect more than just onset of reproduc4on

Temperature dependent sex determina4on

Speed of growth and development

à  Within species, growth is faster in warmer environments

à  Biochemical reac4ons are faster


Environmental condi4ons affect more than just onset of reproduc4on

Temperature dependent sex determina4on

Speed of growth and development

à  Faster in warmer environments à  Biochemical reac4ons are faster

à  Nest temperature determines sex of developing eggs

à  Sea turtles, nonavian rep4les




3.   Reproduc&ve endocrinology –  Female/male cycles –  Pregnancy and birth

Female reproduc4on

•  Ovula&on: Single ova released every menstrual cycle – LH induces several responses that vary depending on organ and &ming of cycle

•  Reproduc4on starts in embryo stage •  oogonia à 1° oocytes in ovaries

•  Stored un4l puberty

Physical changes in ovaries Folliculogenesis: Primordial follicles (oocyte and

surrounding cells) develop to maturity •  Begins at puberty

1.  1° oocyte gets bigger 2.  Secretes

glycoproteins (zona pellucida)

3.  Soma4c cells surrounding oocyte mature à granulosa cells

1° oocyte à 1° follicle

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Physical changes in ovaries

1.  Follicular phase •  1° follicleà 2° follicle à

mature follicle

2.  Ovula4on •  Oocyte released to

oviduct (fallopian tubes)

3.  Luteal phase •  Corpus luteum develops

Three phases within each cycle:

Physical changes in ovaries: Follicular phase

Follicular phase: 1° follicleà 2° follicle à mature •  Antrum opens in granulosa cells – Fluid-‐filled cavity

•  Theca develops around granulosa – Connec4ve 4ssues

•  Becomes mature follicle

Physical changes in ovaries: Follicular phase

Follicular phase: 1° follicleà 2° follicle à mature •  Several follicles start process, but only some mature – Biggest granulosa cells and antrum

– Rest of the follicles degenerate

Physical changes in ovaries: Ovula4on

Ovula4on: Release of mature follicle to oviduct LH surge

Enzymes breakdown follicle wall

Antral fluid and 2° oocyte ovulated

Physical changes in ovaries: Luteal phase

Luteal phase: Ruptured follicle cells reorganize into corpus luteum

•  Oocyte NOT fer4lized: – Corpus luteum degenerates

•  Oocyte fer4lized: – Corpus luteum secretes pregnancy hormones

Physical changes in uterus

1.  Menstrual phase •  Sloughing of

endometrial cells •  Estrus mammals

reabsorb cells

•  Three phases within each cycle:

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1.  Menstrual phase 2.  Prolifera4ve phase •  Thickening •  Occurs with follicular

phase in ovaries



1.  Menstrual phase 2.  Prolifera4ve phase 3.  Secretory phase •  Endometrium matures •  Ready to provide

nutrients to embryo


Physical responses synchronized between uterine and ovary phases Cycle under endocrine control

Cycle under endocrine control

Events differ across 4me at 4 sites:

1.  Hypothalamus 2.  Anterior pituitary 3.  Ovaries 4.  Uterus

Endocrine responses : Follicular phase

•  AP pulses maintain high concentra4on GnRH

•  LH and FSH surge just before ovula4on

Hypothalamus secretes GnRH (via

AP pulses)

Anterior pituitary secretes LH and FSH into circula4ng blood

Hypothalamo-‐hypophysical portal system

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Endocrine responses : Follicular phase Anterior pituitary

secretes LH and FSH

LH s4mulates androgen produc4on

in theca cells

LH FSH

FSH s4mulates aromatase secre4on from granulosa cells

Androgens diffuse to granulosa cells

Aromatase converts androgens

to estrogens

•  Posi4ve feedback loop: é  Estrogen à é  granulosa cellsà é  aromatase à é  conversion of androgen to estrogen à

é  Estrogen .....


secretes LH and FSH


in theca cells




to estrogens

•  Estrogen also increases secre4on of GnRH from hypothalamus à é  LH/FSH à ....


secretes LH and FSH


in theca cells




to estrogens

Endocrine responses : Follicular phase •  Corresponds to events in prolifera4ve phase in uterus:

1.  Estrogen s4mulates endometrial cells to thicken 2.  Granulose cells

secrete inhibin •  Inhibits FSH

secre4on à •  Stops conversion

of androgens into estrogens

A lot of stuff just happened.... LH surge causes: •  Meio4c division of

dominant oocyte •  Secre4on of

progesterone from granulosa cells 1.  Lowers estrogen

secre4on 2.  Breaks down follicle

membrane à antral fluids and oocyte release

3.  Ini4ates forma4on of corpus luteum

Endocrine responses : Ovula4on

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•  Secretes estrogen, progesterone, and inhibin •  Peak when

endometrium at thickest

Endocrine responses : Luteal phase ê LH surge

Corpus luteum func4on begins

•  Progesterone and estrogen:

–  Inhibit GnRH secre4on of LH and FSH –  New follicles can’t develop

ê LH surge


Endocrine responses : Luteal phase

•  Progesterone prepares uterine lining for implanta4on 1.  Thickens endometrial

cells 2.  Produces glycogens

and enzymes that increase number of endometrial cells

ê LH surge



If no fer4liza4on occurs – corpus luteum degenerates à Decrease in estrogen, progesterone, and inhibin (produced by corpus luteum) concentra4on –  GnRH resumes secre4on of LH and FSH –  Endometrium secrete prostaglandins à constrict blood vessels à sloughing off






Male reproduc4ve cycle •  Sperm and hormones produced in testes

•  Testosterone secreted from Leydig cells

•  Amount secreted varies over 4me – é during 1st part of embryonic development

– Lower un4l birth – é aZer puberty

?

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Endocrine control: male reproduc4on

•  Hormones secre4on controlled by gonadotropins from pituitary

Hypothalamus secretes GnRH (via

AP pulses)

Anterior pituitary secretes LH and FSH

Endocrine control: male reproduc4on Anterior pituitary

secretes LH and FSH

LH binds to Leydig cells

FSH s4mulates Sertoli cells

Secrete testosterone

1.  Secrete nourishment for sperm

2.  Secrete inhibin (stops FSH secre4on)

3.  Secrete hormones that maintain testosterone concentra4on

Inhibin ≈ Testosterone equilibrium à Constant sperm produc4on

•  Ejacula4on involves nervous system and endocrine system – Parasympathe4c nerves release NO

à Dila4on of blood vessels and increases blood flow à Erec4on

Endocrine control: male reproduc4on

•  Semen: Fluids from prostrate gland and seminal vesicle •  Provide energy for sperm





Pregnancy and birth

1.  Fer4liza4on 2.  Implanta4on/Early

pregnancy 3.  Birth

Pregnancy: Fer4liza4on •  Occurs in oviduct •  Oocyte surrounded by zona pellucida and granulosa cells

•  Sperm undergo capacita&on in female reproduc4ve tract – Enhances speed – Enables fusing with cell membrane

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Pregnancy: Fer4liza4on 1.  Enzymes in sperm

head breakdown zona pellucida

2.  Fuses to oocyte membrane

3.  Cytoplasm of gametes mix

1

3

2

Pregnancy: Fer4liza4on 4. Cor4cal reac4on: Oocyte cytoplasm releases cor4cal granules – Prevents mul4ple sperm from penetra4ng cell wall

Pregnancy: Implanta4on •  Corpus luteum secretes progesterone – Thickens endometrial cells

Pregnancy: Implanta4on •  Implanta4on of embryo à release human chorionic gonadotropin (hCG) – Extends life of corpus luteum to 50-‐70 days – Pregnancy tests

Pregnancy: Implanta4on Placenta:

1.  Secretes progesterone (endometrial membrane) 2.  Increases blood flow (nutrients and O2) to embryo 3.  Secretes estrogen (s4mulates myometrial muscle

growth)

Pregnancy: Birth •  Increasing estrogen s4mulates myometrium to produce connexons – Allows coordinated muscle contrac4ons –  Increases produc4on of oxytocin receptors

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Pregnancy: Birth •  Posi4ve feedback loop:

Myometrial muscle contrac4ons

1

3

2 1

APs sent to hypothalamus

2

Posterior pituitary secretes

oxytocin

3

Myometrial cells secrete prostaglandins

4

4

5

5

ch 16 reproduction - vertebrate physiology · 2/7/14 1...

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