Hormones affecting reproduction

Part 5: Reproduction

Endocrine System

Reproductive System

Male FemaleGonad Testes OvaryGamete Sperm Ovum (egg)Hormones Androgens:

testosterone, androsterone

Estrogenprogesterone

Male Anatomy

Fig. 46.8

Cells of the Testes

Leydig interstitial cells synthesize hormones (androgens)

Sertoli cells synthesize sperm (spermatogenesis)

Male Reproductive Hormones: Androgens

androsterone

testosterone

Male Reproductive Hormones: Androgensboth hormones are released from

testes

Androgen: Testosterone

Steroid hormone Develops male primary and

secondary sexual characteristics

Primary Sexual CharacteristicsAssociated with the reproductive

systemDevelopment of vas deferens,

external reproductive structuresStimulate spermatogenesis: sperm

production in sertoli cells (lifetime process)

Secondary Sexual CharacteristicsNot directly related to the

reproductive systemDevelops characteristics at puberty

deepening of voice facial and pubic hair muscle growth increased secretion of body oils

(associated with body odour)

Male Reproductive Hormones

1. Hypothalamus: Gonatropin releasing hormone (GnRH)

2. Anterior Pituitary: Gonadotropic hormones FSH & LH

3. Sertoli cells: FSH stimulates spermatogenesis

4. Leydig cells: LH stimulates hormone (androgen) secretion

5. Androgen testosterone affects primary & secondary sexual characteristics

Hypothalamus

Anterior pituitary

testes

Sertoli cells

Leydig cells

GnRH

FSH LH

testosterone

sperm production

Gonadotropic Hormones

Two types: Follicle stimulating hormone (FSH) Luteinizing hormone (LH)

Peptide hormonesPresent in both male and female

Gonadotropins in Males

FSH: act on Sertoli cells to increase spermatogenesis (nontropic)

LH: stimulate Leydig cells to make androgens (tropic)

Image Source: http://www.andrologyaustralia.org/images/pageContentImages/MI_Image_Jul2005_04HormonalLinks.jpg

Male Reproductive Hormone:Neuroendocrine pathway - nontropic

Location HormoneHypothalamus Gonadotropin-Releasing

Hormone (GnRH)Anterior Pituitary

Gonadotropins:Follicle-stimulating hormone (FSH)

Effect: Sertoli cells

Spermatogenesis

Male Reproductive Hormone:Neuroendocrine pathway - tropic

Location HormoneHypothalamus Gonadotropin-Releasing


Gonadotropins:Lutenizing hormone (LH)

Testes: Leydig cells

Androgens: testosterone

Effect Primary and secondary sexual characteristics

Fig. 46.14

Male Reproductive Hormonal Control

hypothalamus

pituitary

testes

Sertoli cells

Leydig cells

GnRH

FSH LH

testosterone

sperm production

Negative Feedback

Testosterone negatively feedback to the hypothalamus and pituitary to decrease the production of GnRH and LH

Female Reproductive Systemcomparatively more complicated

than male reproductive systemmonthly cycle until menopause (~12

to 50 yrs)one ovum produced per germ cell

Female Anatomy

Fig. 46.9

Female Reproductive Hormones

estrogen

progesterone

Female Reproductive Hormonesboth produced in the ovaries

Image Sources: Wikipedia, http://en.wikipedia.org/wiki/Estrogen, http://trollydolly.us/wp-content/uploads/2009/04/estrogen-cartoon.gif

Estrogens

Female sex hormonesThree compounds

Estradiol is predominant

Develops secondary sexual characteristics Breast development Wider hips Fat deposition

Estradiol

Estrone

Estriol

Ovary Follicle Cells

primary oocyte: egg that can be fertilized by sperm

granulosa cells: provide nutrients for primary oocyte

Ovarian Cycle Regulation:Neuroendocrine pathwayLocation HormoneHypothalamus Gonadotropin-Releasing


Gonadotropins:Follicle-stimulating hormone (FSH)Lutenizing hormone (LH)

Ovaries: Follicle & Corpus Luteum

EstrogenProgesterone

Gonadotropin-Releasing Hormone (GnRH)

GnRH levels not shown in graph or right but correlates to the rise in LH/FSH levels

Released in slow waves during follicular phase

Rate of release is increased (peaked) when approaching ovulation

Rate decreases greatly during luteal phase

Gonadotropins in FemalesFSH:

Stimulates growth of follicle (maturation) in follicular phase

LH: lutenizes the follicle

into the corpus luteum

Induces ovulation Matures the corpus

luteum in luteal phase

Ovarian Cycle Follicular phase

Growth of several follicles but only one matures while others disintegrate

Egg in follicle enlarges Coat of follicle thickens Fluid-filled cavity inside follicle develops and bulges

Ovulation Follicle and wall of ovary rupture Egg is released

Luteal phase Follicular tissue develops into corpus luteum Corpus luteum secretes female hormones

Fig. 46.13b

Ovulation

Ovulation

EGG CELL

Fig. 46. 10

hypothalamus

pituitary

ovaries

follicle corpus luteum

GnRH

FSH LH

progesteronesome estrogen

estrogen

1 2

ovulation

Female Reproductive Hormone Control

ProgesteroneCorpus luteum

secretes progesterone (and some estrogens)

Correlates to thickening of endometrium in order to accept

fertilized egg and enable implantation and growth

Image Source: Wikipedia, http://en.wikipedia.org/wiki/Progesterone

Progesterone If no implantation then

corpus luteum disintegrates progesterone isn’t

secreted Decreased progesterone

levels leads to: stop of endometrium

growth endometrium breaks

down (menstruation)

Image Source: Wikipedia, http://en.wikipedia.org/wiki/Progesterone

Menstrual Cycle

Day 1 = first day of menstruation Menstrual flow phase

sloughing of endometrial lining menstrual bleeding

Proliferative phase endometrium regenerates and thickens

Secretory phase endometrium continues to thicken becomes more vascularized (blood vessels) develops glands to secrete fluid rich in glycogen

hypothalamus

pituitary

ovaries


GnRH

FSH LH


estrogen

1 2

ovulation


Follicle

Granulosa cells of follicle secretes estrogen

Estrogen Regulation: High levels

High estrogen: Positive feedback on LH & FSH by stimulating GnRH

Estrogen surge from follicle during day 12-14 LH & FSH surge Results in ovulation

Estrogen Regulation

Also responsible for the early thickening of the endometrium in the proliferative phase

Estrogen Regulation: Low levels

Estrogen secreted at low levels during most of the cycle

Negative feedback on GnRH, LH & FSH

Estrogen Regulation

Corpus luteum secretes estrogen and progesterone

Both act together to negatively feedback on GnRH, LH & FSH

Prevents ovulation

Dual Role of Estrogen

Low estrogen concentration negative feedback

High estrogen concentration positive feedback

http://www.sumanasinc.com/webcontent/animations/content/ovarianuterine.html


hypothalamus

pituitary

ovaries


GnRH

FSH LH


estrogen

1 2

ovulation

Day 12-14 when estrogen levels surge

Day 12-14 when estrogen levels surge

Fig. 46.15

Overview of Female Reproductive Cycles

Fig. 46.15

Hormonal Control in Follicular phase Immature follicles

have receptors for FSH but not LH

FSH stimulate follicular growth

Granulosa cells of the growing follicles secrete estrogen

Low levels of estrogen negatively feeds back on LH and FSH

Fig. 46.15

Hormonal Control near ovulation Estrogen surge

Positive feedback on LH & FSH by stimulating GnRH

Mature follicle have receptors for LH

LH induces ovulation Estrogen also

stimulates thickening of endometrium

Fig. 46.15

Hormonal Control in Luteal Phase LH lutenizes

remaining follicular tissue into corpus luteum

Corpus luteum secretes estrogen and progesterone

Both act together to negatively feedback on GnRH, LH & FSH

Fig. 46.15

Hormonal Control in Luteal Phase Corpus luteum

disintegrates Sharp decline in

estrogen & progesterone

Negative feedback removed Secretion of GnRH, LH &

FSH begins Disintegration of

endometrium

Menopause

Occur around age 46-54Ovaries lose responsiveness to

gonadotropins Decline in estrogen production Cessation of ovulation and menstruation

Hormones affecting reproduction

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