Endocrinology, lecture on Hypothalamo-Hypophysial Communication
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 and James A. Carr:
Read pages 119-124, 135-139, 203-210 for this lecture
acronyms    end
X. Hypothalamo-Hypophysial Communication  

	A. Hypothalamus produces hypophysiotropic hormones: releasing hormones
	    and release-inhibiting hormones	

		1. hormone release stimulated by depolarization  ® slow travelling
		   action potential in neurosecretory neurons  

		2. located below the thalamus,
		    just below and beside the 3rd ventricleof the brain
			a. nuclei with endocrine function:  

		3. POA + AH  produce and release GnRH and TRH

			a. coordinate GnRH and PRL surges

		4. SCN coordinates rhythmic hormone release  (e.g. CRH, melatonin)

		5. SON + PVN make OT and AVP    (magnocellular)

			a. parivcellular division  makes CRH and TRH  (TRH from PVN) 

		6. PVa  + DMN synthesize CRH, TRH and  somatostatin(GHRIH)

		7. VMN also makes CRH, TRH & somatostatin, but also GHRH

			a. regulates insulin and glucagon (glucoreceptors)
			b. GnRH to MCG (midbrain central gray, aka PAG)

		8. ARC synthesizes CRH, TRH, GHRH 

			a. GnRH is made in mediobasal portion

			b. DA (PRIH) from tubero-infundibular region

		9. Hypothalamus also has normal neurons which send signals 
		    by action potential to other parts of the brain

			a. e.g. posterior hypothalamus  regulates sympathetic NS, VMN
			   regulates female sex behavior

			b. neurohormones (such as RHs and neurohypophysial nonapeptides) 
			   may be the neurotransmitters for these normal neurons 
			   (e.g. AVP, CRH, DA, GnRH, OT, TRH, somatostatin)

	B. Hypothalamo-Hypophysial Portal System
		1. Neurohemal organ in the Median Eminence

			a. superior hypophysial artery delivers blood to capillary bed 
			    in the median eminence

			b. RHs released from neurosecretory neurons into capillary bed

				i. neurohemal organ

			c. RHs carried by Hypothalamo-Hypophysial Portal Vein(s) 
			   to the adenohypophysis (pars distalis) 
				i. also to the intermediate lobe (pars intermedia) 

	C. Adenohypophysis = Anterior Pituitary

		1. Derived from Rathke's pouch

			a. fusion of a ventral growth of the diencephalon, the 
			    infundibulum, with an ectodermal sac (Rathke's)

			b. APUD - common origin from neuroectoderm

				i. hypothesis - all peptide hormone-producing cells are of 
				   neural origin - amine precursor uptake and decarboxylation  series

					(1) supported by hormone production as 
					      neurotransmitters in the brain

		2. corticotropic cells - produce/release ACTH

			a. adrenocorticotropic hormone or corticotropin

			b. comes from a preprohormone called POMC or pro-opiomelanocortin

				i. also cleaved from POMC:
				   a-MSH, b-endorphin, g-lipotropin...

		3. somatotropic cells - GH

		4. gonadotropic cells - LH and FSH

		5. lactotropic cells - PRL

		6. thyrotropic cells - TSH

		7. PACAP (pituitary AC activating peptide)
			i. pituitary paracrine enhances tropic hormone release
		8. Pars tuberalis - thin layer of cells connecting the
		   adenohpyophysis/median eminence with the 3rd ventricle 

			a. tanycytes - capable of absorbing and moving material (including
			   hormones) from median eminence to cerebrospinal fluid (CSF)
			   or vice versa

		9. Pars Intermedia - a-MSH producing area 
		   between the pars distalis and pars nervosa
	D. Neurohypophysis = Pars Nervosa (posterior pituitary)

		1. axons from hypothalamic neurosecretory neurons of the supraoptic 
		   and paraventricular nuclei project into the pars nervosa

		2. Supraoptic Nucleus (SON)

			a. produces mostly AVP

		3. Paraventricular nucleus (PVN)

			a. produces mostly OT

		4. secreted into neurohemal organ of the general circulation

	E. Regulation of Hypophysiotropic Secretion

		1. hypothalamus is innervated by other areas of the brain

			a. hippocampus, amygdala, BNST, septum, tegmentum...

			b. hypothalamus also innervates other areas of the brain

		2. a variety of neurotransmitters effect hypophysiotropic secretion

			a. the same factor may stimulate the release of one 
			   and inhibit the release of another

				i. Serotonin (5-HT) stimulates CRH, GHRH, inhibits TRH

				ii. NE stimulates GnRH and TRH, inhibits or stimulates CRH

				iii. ACh stimulates GHRH and CRH, inhibits somatostatin

				iv. Glu stimulates GnRH

				v. GABA inhibits CRH

	F. Regulation of Tropic Secretion
		A. RHs are synergistically enhanced by a adenohypophysial paracrine
			1. PACAP stimulates tropic hormone release by potentiating cAMP activity
			    in pituitary corticotropes, gonadotropes, lactotropes, melanotropes,
				somatotropes, thryrotropes
				a. PACAP in the secretin/glucagon hormone family

XI. Tropic Hormones