May 2, 2014 – Chemical signals and hormones IV

Announcements:- Final is NOT CUMULATIVE*- In lecture review session (Wed. May 7)- TA led review session (10am – 12pm, Wed. May 14, 151 Everett Lab

1. Pre-lecture quiz2. Review of stress responses3. Hormone-mediated physiological tradeoffs4. Interactions between the HPA and HPG axes5. Sex hormones

* I will ask about recurrent themes (e.g. tradeoffs, negative feedback, etc.)

Stress response

Operates via two interrelated systems:

• SAM (Sympathetic-adrenomedullary) (Short Term Response)

• HPA (hypothalamic-pituitary-adrenocortical) (Chronic Response).

SAM, adrenals, and epinephrine

Summary of the “fight or flight” response

1.) Increases in HR, BP, O2 consumption, blood glucose and fatty acid concentrations.

2.) Redirection of blood flow from the skin and digestive system toward heart, brain, and muscles.

3.) Relaxation pulmonary smooth muscle to dilate bronchi and increase O2 uptake.

Take home messages:

1.) Short term stress responses are EXTREMELY beneficial over the short term.

2.) Prolonged stress responses can be harmful.

HPA axis and glucocorticoids

• Adrenal cortex produces glucocorticoid hormones (GC).

• Cortisol is most important human (GC), involved in regulating metabolism, immune response, and general homeostasis.

• Elevated cortisol leads to:– Short term metabolism of fat stores into

glucose– Increased hunger– Suppression of immune response;– Cardiovascular changes (e.g. increases in

BP)

Hormone-mediated TradeoffsInteractions between stress, reproduction and immune function

Hormone-mediated Tradeoffs:Interactions between stress, reproduction and immune function

Testosterone treated Control

Territory size Larger Smaller

Singing frequency Higher Lower

# of aggressive interactions Higher Lower

Number of matings Higher Lower

Number of offspring Higher Lower

Offspring quality Lower Higher

Survival Lower Higher

Hormone-mediated Tradeoffs:Interactions between stress, reproduction and immune function

Montane Urban

Breeding season Shorter Longer

Aggressiveness Higher Lower

Male parental investment Higher Lower

Testosterone Higher Lower

Cortisol Higher Lower

Stress response Higher Lower

Hormone-mediated TradeoffsInteractions between stress, reproduction and immune function

HPG axis

Gonads

• Male testes produce sperm cells• Female ovaries produce ova• Fertilization

– Sperm cell + ovum = zygote

• Sex chromosomes– Humans: XX = female, XY = male– Birds: ZW = female, ZZ = male– Many vertebrates lack sex chromosomes entirely

Sex Hormones – Released by Gonads

• Androgens - e.g., testosterone (“male” hormones) • Estrogens - e.g., estradiol (“female” hormones) • Adult testes release more androgens and ovaries more

estrogens • Progestins – also present in both sexes

– progesterone prepares uterus and breasts for pregnancy• Adrenal cortex – also releases sex steroids

HPG axis & Reproductive System

Males

Also known as Leydig cells

Steps for spermatogenesis

1. GnRH released at hypothalamus -----> + section of FSH & LH at anterior pit.

2. a. FSH stimulates sertoli cells which stimulate spermatogenesis b. LH simulates Leydig cells which secrete testosterone

Testosterone stimulates sertoli cells to stimulate spermatogenesis

3. a. testosterone has negative effects on GnRH b. testosterone has negative effects on LH & FSH c. Sertoli cells release inhibin which has negative effects on LH & FSH

HPG axis & Reproductive System

Males Females

Figure 48-12

FolliclecellsOocytes

1. Formation of primaryoocytes within follicles

5. Degeneration ofcorpus luteum

3. Maturation offollicle

Secondary oocyteto oviduct

4. Ovulation

2. Follicle growth

Figure 48-13-2

Ovulation

Pituitaryhormonecycle

Ovariancycle

Follicle growth

FOLLICULAR PHASE

Corpus luteum degeneration

LUTEAL PHASE

FSH

LH

Ho

rmo

ne

leve

ls

Days0 7 14 21 28

Figure 48-14

OvulationFollicle growth

FOLLICULAR PHASE

Corpus luteum degeneration

LUTEAL PHASE

Estradiol

Progesterone

Ovarian hormones andpituitary hormones exertfeedback on each other

Negative feedbackon LH

Positive feedbackon LH

Negative feedbackon LH,FSH

Follicles andcorpus luteumsecretehormones