ENDOCRINE PHYSIOLOGY - 1

1. ENDOCRINE PHYSIOLOGY - 1 LECTURE

2. COORDINATION IN THE ANIMAL BODY • Multi-cellular animal body have division of labor in cells and tissues. • There is a need of coordination in the body systems to control and regulate functions. And this need increases with the increasing complexity of structures and functions. • There are three main systems for “coordination”: • Nervous system (Neurosecretions) • Sensory system • Endocrine system

3. As multicellular organisms appear, complexity increased with increasing requirements to coup with environment. Increasing cell number then led to specialization of cells, then grouping together to make tissues and then organs.

4. CELLULAR AND GLANDULAR SECRETIONS • All cells secrete material in their surroundings. • Either to make a protective barrier, OR to communicate with other cells. • Cells that secrete similar substances are collected together in the course of evolution to make entities called GLANDS. • The cells in a gland act as a unit. • Glands possessed by an individual vary not only with species but also at different stages of development.

5. CELLULAR AND GLANDULAR SECRETIONS • Secretions of various glands are response of animal to various situations. • For example, feeding cause release of various hormones, blood glucose rise cause insulin secretion.

6. TYPES OF SECRETIONS From Evolutionary point of view: • When cells and their organization was simple, these were near to each other AND control could be achieved with simpler structures and secretions (molecules and compounds); Autocrine and Paracrine secretions and neurosecretions were enough, (e.g., lower invertebrates).

7. TYPES OF SECRETIONS - Contd • With increasing complexity, cells move far away from each other making tissues with division of labor; control and regulation become difficult to achieve, then “Endocrine System” developed.

9. AUTOCRINE SECRETIONS (auto- means “self”): Affect the secreting cell itself. An example is auto-inhibition of norepinephrine release from adrenergic neurons, by norepinephrine itself. Adrenergic neurons Norepinephrine

10. Eckert p 302 fig 9-1

11. PARACRINE SECRETIONS(para- means“Beside; near; alongside”): These affect neighboring cells. An example is Inflammatory response, in which localized vasodilation is induced by histamine released from mast cells in the area of tissue damage.

13. NEURO-ENDOCRINE SECRETIONS: As the name indicates, this is the secretion that is produced in Specialized Neurons but released into bloodstream to reach their destination, i.e., target tissues.

14. ENDOCRINE SECRETIONS (Endo- means “inside or within”): These are released in bloodstream and act on distant target tissues. Examples are insulin, thyroxine, etc.

16. EXOCRINE SECRETIONS: These secretions are released onto the surface of the body, including the surface of the gut and other internalized structures. Example is pheromones used to communicate with others animals, these are also used by animals to repel predators (by unpleasant odor).

18. ENDOCRINE SYSTEM

19. ENDOCRINE SYSTEM • We discussed that Endocrine Secretions are those which are released from specialized structures and released in circulation to reach target tissues. • Now we see what are endocrine glands and their secretions “HORMONES” (From Greek hormon, present participle of horman, to urge on, from horme, impulse).

20. ENDOCRINE GLANDS Endocrinology was probably began with AA Berthold classic experiments in 1849. He demonstrated that removal of testis leads to repression of male characteristics and replacement of these cause development of these structures.

22. William Bayliss and EH Starling described the first hormone to be discovered, named secretin, a hormone released from intestinal mucosa and cause increased flow of digestive juices from pancreas. • In 1905, Starling introduced term “hormone” and described three (3) characteristic properties that defines hormone.

23. HORMONE – 3 CHARACTERISTICS • Hormones are synthesized by specific tissues or glands • Hormones are secreted into the bloodstream, which carries them to their site(s) of action. • Hormone change activities of the target tissue or organs.

24. Most of the hormones in the metazoans fall in FOUR main structural categories. Amines: including catecholamines - epinephrine and norepinephrine, thyroid hormones and small molecules derived from amino acid. Eicosenoids: are produced from metabolism of arachidonic acid, including prostaglandins, leukotrienes thromboxanes and lipoxins. STRUCTURAL CATEGORIES OF HORMONES

25. STRUCTURAL CATEGORIES OF HORMONES • Steroids: are cyclic hydrocarbon derivatives synthesized from cholesterol (testosterone, estrogen). • Peptides and Proteins:constitutes the largest number of hormones and are the most complex. The term autacoid hormone is used to describe various active endogenous substances such as histaimne and serotonin.

26. HORMONE ACTION PATHWAYS

28. NEURAL REFLEX ARC

29. FIRST ORDER NEUROENDOCRINE LOOP

30. SECOND ORDER NEUROENDOCRINE LOOP

31. THIRD ORDER NEUROENDOCRINE LOOP

32. DIRECT ENDOCRINE LOOP