1. The Endocrine System
General Function and Organization

3. Bethold found that a rooster's comb is an androgen-dependent structure
Bethold found that a rooster's comb is an androgen-dependent structure. Following castration, the comb atrophies, aggressive male behavior disappears, and interest in the hens is lost.
Importantly, Berthold also found that these castration-induced changes could be reversed by administration of a crude testicular extract (or prevented by transplantation of the testes).

4. I. Organization of Endocrine System
The functions of the body are regulated by the nervous and the endocrine system.
The endocrine system consists of endocrine glands and cells that secrete hormones in various tissues.

5. Endocrine System Regulates long-term processes: growth development
Reproduction
Uses chemical messengers to relay information and instructions between cells

6. Endocrine glands: Glands that do not use ducts to convey the secretion to a neighboring target, they are also called ductless glands.
The secretions, known hormones, circulate all over the body in the blood but may produce effects only in selected sites.
The target organ(s) may or may not be near the site of production of the hormone.

7. A hormone –
--chemical substance
--is secreted into the internal body fluids by one specialized cell or a group of cells and
--has a physiological control effect on other cells of the body.

8. Endocrine vs. Nervous System
Major communication systems in the body
Integrate stimuli and responses to changes in external and internal environment
Both are crucial to coordinated functions of highly differentiated cells, tissues and organs
Unlike the nervous system, the endocrine system is anatomically discontinuous.

9. What are the modes of intercellular communication used by the endocrine and nervous systems?

11. What is the functional significance of the differences between the two systems?

12. Endocrine System - Is unable to handle split-second responses
Nervous System
- Handles crisis management
Are similarly organized:
1. rely on release of chemicals
2. share many chemical messengers
3. are regulated primarily by negative feedback
4. share a common goal: to preserve homeostasis

13. Hormones travel via the bloodstream to target cells
The endocrine system broadcasts its hormonal messages to essentially all cells by secretion into blood and extracellular fluid.
Like a radio broadcast, it requires a receiver to get the message –
in the case of endocrine messages, cells must bear a receptor for the hormone being broadcast in order to respond.

14. Transportation of Hormones
1. Endocrine: glands or specialized cells release hormones into the circulating blood that influence the function of cells at another location in the body.

15. Transportation of Hormones
2, Neuroendocrine: neurons secrete substances (neurohormones) that reach the circulating blood and influence the function of cells at another location of the body.

16. Transportation of Hormones
3. Paracrine, in which cells secret substances that diffuse into the extracellular fluid and affect neighboring cells.

17. What are the major structural classes of hormones?

18. Chemical Nature of Hormones
Can be divided into 3 groups:
Derivatives of amino acid
Proteins and polypeptide hormones
lipid derivatives (steroids)

19. Why is it important to know the chemical structures of different hormones?
Steroids can not be stored while Peptides are stored in secretory vesicles
To determine:-
Synthesis , storage and release
The way a hormone is transported
Its half life and mode of clearance
Its medium of action (Receptors)

20. Derivatives of Amino Acid Tyrosine
Small molecules structurally related to amino acids
Synthesized from the amino acids tyrosine

21. Tyrosine Derivatives Iodothyronines (Thyroid hormones)
Catecholamines (water soluble):
epinephrine (E)
norepinephrine (NE)

22. Peptide Hormones Chains of amino acids Synthesized as prohormones:
inactive molecules converted to active hormones before or after secretion
Water Soluble
Stored in the membrane bound secretory vesicles
Circulate in blood freely unbound
Usually administered by injection
Hydrophilic
Short half life
Signal through membrane receptors

23. 2 Groups of Peptide Hormones
glycoproteins:
more than 200 amino acids long, with carbohydrate side chains:
thyroid-stimulating hormone (TSH)
luteinizing hormone (LH)
follicle-stimulating hormone (FSH)

24. 2 Groups of Peptide Hormones
all hormones secreted by:
hypothalamus
heart
thymus
digestive tract
pancreas
posterior lobe of pituitary gland
anterior lobe of pituitary gland

25. Synthesis, Storage and Release of Peptide Hormones

26. Stimulus

27. Lipid Derivatives (Steroids)

28. Made by:-
Adrenal Cortex
Ovaries
Testes
Placenta
Kidneys

29. Steroid Hormones Synthesized from cholesterol Can not be stored
Released by:
reproductive organs (androgens by testes, estrogens, and progestins by ovaries)
adrenal glands (corticosteroids)
kidneys (calcitriol)

30. Steroid Hormones Remain in circulation longer than peptide hormones
Are absorbed gradually by liver
Are excreted in bile or urine

31. Hormones
Circulate freely or bound to transport proteins

32. Free Hormones Remain functional for less than 1 hour:
diffuse out of bloodstream:
bind to receptors on target cells
are absorbed:
broken down by cells of liver or kidney
are broken down by enzymes:
in plasma or interstitial fluids

33. Thyroid and Steroid Hormones
Remain in circulation much longer
Enter bloodstream:
more than 99% become attached to special transport proteins

34. Bloodstream
Contains substantial reserve of bound hormones