Endocrinology, lecture on homeostasis
USD Department of Biology
Endocrine Glands
2nd Messengers
Nuclear Receptors
Genetic Regulation
Hormone Synthesis
Receptor Regulation
Hypothalamo-Hypophysial Communication
Tropic Hormones
Neurohypophysial Nonapeptides
Thyroid Axis
Adrenal Axis
Adrenal Medulla
Osmotic-Pressure Balance
Reproductive Endocrinology
Somatic Axis
Growth Factors
Immune Factors
Ca++, PO4 Homeostasis
Pancreatic Hormones
GI Hormones
Guts 'n Brains
Brain Hormones
Endocrine Evolution
Figures for Endocrionology
text:Vertebrate Endocrinology5th Edition - David O. Norris:
Read pages 13-20 for this lecture
acronyms    end
IV. Homeostasis  			

	A. balanced physiological systems operating in the organism to maintain a
	   dynamic equilibrium

		1. usually a constant steady state maintained within certain
		   tolerable limits

			a. maintained by:

				i. hormonal production (rate) and storage (capacity)

				ii. negative feedback

					(1) neuroendocrine reflex stimulates endocrine action

					(2) positive feedback stimulates endocrine action

				iii. receptor regulation

				iv. biological rhythmicity

				v. pulsatile secretion

				vi. carrier proteins

	B. Hormone Production

		1. Rate of hormone production depends primarily on stimulation by
		   neural input, paracrines, or other hormones 

			a. and inhibition

		2. after stimulation/inhibition: 
			G-protein transduction, 2nd messenger activation, enzyme action,
			DNA transcription, messenger RNA processing, transport and
			translation, transfer RNA transport and protein synthesis,vesicle
			production at the golgi, enzymatic cleaving, and exocytosis
			 all take time

			a. peptide hormones are made in the rough endoplasmic reticulum (rER)

			b. steroids are made in the sER  and/or  mitochondria

			c. thyroid hormones are made at the cell membrane

			d. monoamine hormones are made primarily in the cytosol

	C. Storage

		1. little or no storage of hormones

			a. usually less than the normal need for one day

			b. especially true for thyroid and steroid hormones

	D. Negative Feedback

		1. Hormones may inhibit the factor (hormone, paracrine,
		   neurotransmitter) which stimulated it

		   a. directly or indirectly inhibit

		2. Endocrine Axes and feedback

			a. neurotransmitter stimulates neurohormone secretion


				i. 5-HT ®+CRH						

			b. neurohormone stimulates tropic hormone secretion			

				i. CRH ®+ACTH

			c. tropic hormone stimulates peripheral hormone secretion		 

				i. ACTH ®+B/F

			d. hormone stimulates cellular action and inhibits
			   neurotransmitter, neurohormone, and tropic hormone secretion

				i. B/F ®+ hippocampus ®-5-HT, CRH, ACTH

				ii. long-loop feedback

		3. Short-loop feedback

			a. ACTH inhbits CRH secretion

		4. Ultrashort-loop feedback

			a. ACTH inhibits secretion of ACTH, CRH inhibits CRH secretion

	E. Receptor regulation

		1. hormones act only on tissues with receptors

		2. receptor numbers may be up- (more) or down-regulated (less)

	F. Biological Rhythmicity and Pulsatility

		1. Periodicity of hormone secretion may vary over minutes or a year

		2. Rhythmic patterns may determine effect at the target tissue

			a. e.g.  pulsatile secretion is required for GnRH function

			b. many environmentally stimulated biological functions are
			   mediated/timed via rhythmic patterns of hormone secretion

	G. Many hormones are carried/protected in the plasma by carrier proteins

		1. receptors usually have a greater affinity
		   than carrier proteins for hormone

V. Second Messenger Systems