1. Controlling your Homeostasis
The Endocrine System
Controlling your Homeostasis

2. Basics
Network of glands that secrete hormones which travel through blood to affect target cells
Paracrine secretions act locally
Autocrine secretions act on the cells that produce them
Exocrine glands secrete to the outside of the body through tubes or ducts

3. Functions Control metabolic processes
Control rates of reaction, aid in transport across membranes, regulate balances of substances
Vital in reproduction, development and growth

4. Types of Hormones Steroid – formed from cholesterol
Ex. Estrogen, testosterone, aldosterone, cortisol

5. Types of Hormones Nonsteroid – formed from amino acids
Amines, peptides, and proteins
Not lipid soluble
Nonsteroid Hormone Action
Combine with receptors in the target cell membrane
Receptors have binding site and activity site
Hormone-receptor complex signals a G protein to stimulate a membrane protein (adenylate cyclase) to induce formation of second messenger protein w/ the help of ATP

6. Types cont. Hormone action cont.
The second messenger associated with one group of hormones is known as cyclic adenosine monophosphate (cAMP)
The cAMP activates another set of enzymes (protein kinases) which transfer phosphate groups from ATP to substrate molecules
The series of reactions that follows induce the cellular changes associated w/ the hormone’s actions

7. Cont.

8. Feedback Mechanisms Negative feedback Positive feedback
An increase in concentration of a hormone triggers activities that inhibit further secretion
Positive feedback
An increase in concentration of a hormone triggers activities that stimulate further secretion

10. Hypothalamus and Pituitary

11. Hypothalamus Region in the forebrain Contains hormone-secreting cells
Interacts closely with pituitary gland
Releases hormones that affect pituitary activities
Primary function: monitor internal organs and states related to organ functioning

12. Pituitary Gland Master gland of the endocrine system
Pea-sized gland at base of hypothalamus
Two lobes
Posterior lobe stores and secretes hormones
that were synthesized in the hypothalamus
Anterior lobe produces and secretes its own
hormones
Summarized in Table 11.3

13. Anterior Pituitary Adrenocortitropic (ACTH) Steroids
Control secretions from adrenal cortex
Thyroid Stimulating (TSH): Thyroid
Follicle Stimulating (FSH): Ovaries, Testes
Stimulates production of sex cells
Luteinizing (LH): Ovaries, Testes
Promotes secretion of sex hormones; role in releasing egg in females
Prolactin (PRL): Mammary Tissue
Sustains milk production after birth
Growth (GH): all cells

14. Abnormalities GH Output
Gigantism: overproduction during childhood
Pituitary dwarfism: underproduction
Acromegaly: too much in adulthood

16. Thyroid Two lobes connected by isthmus Produces:
Thyroxine (T4) – contains 4 iodine atoms
Increases rate of metabolism
Triiodothyronine (T3) – 3 atoms of I
Same as above, but 5 times more potent
Calcitonin – lowers blood calcium and phosphate ion concentrations by inhibiting release from bones and increasing excretion of these in kidneys

17. Parathyroid Located on posterior side of thyroid
Parathyroid hormone (PTH)
Increases blood calcium concentration and decreases blood phosphate ion concentration
Affects bones, kidneys, and intestines
Negative feedback mechanism: increased blood calcium inhibits PTH production

18. Adrenal Glands Closely associated with kidneys Two portions:
Adrenal medulla – central portion
Adrenal cortex – outer portion

19. Adrenal Medulla Epinephrine (adrenalin) Norepinephrine (noradrenalin)
Both…
Increase: heart rate, breathing rate, force of cardiac muscle contraction, blood pressure, blood glucose
Decrease: digestive activity
Produced in response to stress
Preparation for “fight or flight responses”

20. Adrenal Cortex
Aldosterone – regulates concentration of extracellular electrolytes by conserving sodium ions and excreting potassium ions
Cortisol – decreases protein synthesis, increases fatty acid release (fat used for energy instead of glucose), and stimulates glucose synthesis from noncarbohydrates
Maintains blood glucose levels between meals
Controlled by ACTH from ant. pit.

21. Pancreas
Glucagon – produced by alpha cells, stimulates liver to break down glycogen into glucose  raising blood sugar
When blood sugar gets too high, beta cells detect and secrete insulin
Insulin – promotes movement of glucose into certain cells, stimulates formation of glycogen from glucose  lowering blood sugar

23. Pineal Gland Located deep between cerebral hemispheres
Melatonin – produced in response to light conditions  may help control circadian rhythm

24. Thymus, Testes, Ovaries
Thymosin
Testosterone
Estrogen

25. Stress
Condition of the body in response to a stressor – change in external environment
Stressors can be physical (extreme heat/cold, injuries, infections etc) or psychological (thoughts about danger, personal loss, unpleasant social interactions)

26. Stress cont. Short term “fight or flight” Long term adjustment
Adrenal medulla secretes epi and norepi
See info under epinephrine
Long term adjustment
Ant. Pit. Secretes ACTH which stimulates adrenal cortex to release cortisol
See info under cortisol
Fig