e7-1 hormonal control of reproduction femalemale dendrobates azureus

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Hormonal Control of Reproduction

female maleDendrobates azureus

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Hormonal Control of Reproduction

1. Critical importance to fitness

“its ability to perpetuate itself as measured

by its reproductive success” (Pianka 2000)

Energetically expensive

Therefore, must be precisely timed to insure maximal survival of young

young born at time most favorable for survival in cyclical environment

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2. Control of Reproduction

HYPOTHALAMUS

ADENOHYPOPHYSIS

GONAD: TESTIS OROVARY

MEDIAN EMINENCE

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DAYLENGTH

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DAYLENGTHTEMPERATURE

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DAYLENGTHTEMPERATURENUTRITION

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DAYLENGTHTEMPERATURENUTRITIONENDOGENOUS CLOCK

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Gonadotropin-Releasing Hormone (GnRH)

DAYLENGTHTEMPERATURENUTRITIONENDOGENOUS CLOCK

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GnRHStimulates

Gonadotropins: Luteinizing Hormone (LH) Follicle-Stimulating Hormone

(FSH)

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3. Functions of gonadotropins

a. Stimulate gametogenesis

production (meiosis) and maturation of gametes

Male: spermatozoa

Female: oocyte

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b. Stimulate steroidogenesis

steroid hormone production by gonads

Male: androgens (testosterone)

Female: estrogens (estradiol)

progestins (progesterone)

androgens

Actions similar in male and female, only timing and targets that differ

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4. Female system

Precise, often brief, secretion of gonadotropins in regular cycles

Cycles range from multiannual to days

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a. Ovary Structure

(1) connective tissue capsule

(2) ovarian follicle (1 to millions)

oocyte: premeiotic gamete

follicle cells: two layers of steroidogenic cells surrounding oocyte

inner layer: granulosa

outer layer: theca

(3) Ducts for oocyte transport and packaging

oviduct, uterus

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b. Control of ovarian function

LH Theca Cells+

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b. Control of ovarian function

LH Theca Cells Androgen+

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b. Control of ovarian function

LH Theca Cells Androgen

FSH+LH

Granulosa Cells

+

+

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b. Control of ovarian function

LH Theca Cells Androgen

FSH+LH

+

+

Estrogen

Granulosa Cells

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b. Control of ovarian function

LH Theca Cells Androgen

FSH+LH

Granulosa+

+

Estrogen

Blood

Granulosa Cells

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b. Control of ovarian function

LH Theca Cells Androgen

FSH+LH

Granulosa+

+

Estrogen

BloodOogenesis

Granulosa Cells

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c. Estrogens

(1) Local effects (paracrine)

Stimulate oocyte and follicle cell growth

Oocyte and follicle size increase

(2) Distant effects (endocrine)

(a) Feedback: slight negative feedback on LH

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(b) Primary Sexual Characteristics

Growth of ducts and organs directly responsible for gamete production and transport:

ovary, oviduct, uterus

(c) Secondary Sexual Characteristics

Anatomical structures not directly involved in gamete production, but associated with reproductive activity

physical and behavioral:

mating receptivity

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(d) Metabolic effects

tissue growth

follicle, ducts, mammary gland

energy storage

appetite stimulant

fat deposition

yolk production

vitellogenin : precursor protein

of yolk proteins.

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Ovary

FSHLH ESTROGEN

VITELLOGENESIS

LIVER

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Ovary

ESTROGEN

VITELLOGENIN

VITELLOGENESIS

(calcium, lipids,carbohydrates,phosphorous)

LIVER

FSHLH

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Ovary

ESTROGEN

VITELLOGENIN

VITELLOGENESIS

(calcium, lipids,carbohydrates,phosphorous)

LIVER

Folliculargrowth

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Vitellogenin concentration in blood plasma or serum can be measured by immunoassays known as ELISAs

Requires an antibody specific for vitellogenin.

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Vitellogenesis Cycle on the Kemp's ridley sea turtle

0

2

4

6

8

10

12

Jun Sep Dec Mar May Jul

POSTNESTING

PREMATING

MATING NESTING

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Female Reproductive Cycles

(1) Follicular Phase of the cycle

oocyte and follicle growth under

influence of estrogen

Oocyte can not be fertilized in the follicle

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(2) Ovulation

rupture of follicle and release of oocyte

stimulated by LH surge

Regulation of LH surge:

(a) environmental cues

e.g., daylength, temperature, substrate, mates, etc.

(b) endocrine cues

e.g., estrogen positive feedback

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LH surge transforms follicle cells into new endocrine gland:

Corpus luteum (CL)

External fertilizers:

eggs shed, CL very brief

cycle ends here

Internal fertilizers:

eggs retained, CL persists

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(3) Luteal Phase , the CL is steroidogenic

Estrogens

maintain 1° and 2° sexual characteristics

Progestins

negative feedback on LH with estrogen

prepare female for embryo support

stimulate structures essential for

embryo survival

e.g., uterus, mammary gland, albumin glands

All preparation in anticipation of fertilization

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(4) No fertilization

CL regresses, negative feedback gone, cycle restarts if CNS permits

(5) Fertilization

CL persists: progesterone

New endocrine gland: placenta

Progestins maintained until termination

Cycle can be manipulated: GnRH, steroids