Comparative Physiology Withers CH 11 Endocrinology Communication Pathways Among Cells endocrine: fluid-born transport of chemical mediators (ex., insulin in regulation of glucose metabolism) paracrine: local diffusional transport of chemical mediators (ex., histamine in the inflammatory response) autocrine: local action of a chemical mediator on its own secretory cell (ex., norepinephrine to autoregulate further release from the nerve) neuroendocrine: endocrine-like secretion from a neuron-like secretory cell (ex., oxytocin in the milk let-down response) Negative Feedback Endocrine systems Neuroendocrine Neurosecretion Classical endocrine Neurosecretion Neurosecretion Secretory center of neuron bodies Synthesis of neurohormone Axonal pathways to deliver the neurohormone to a remote site ( can be distant) Usually peptides (ex. Oxytocin) Conspicuous histologically by neurosecretory granuels Neurosecretion Protein hormones make on RER. Sequestered in granuels Released by exocytosis
Invertebrates Polychaete worms Juvenile hormone transported from cerebral ganglion to the dorsal bloodvessel Comparison of Vertebrate and arthropod endocrine tissue Vertebrate Cords of cells Interspersed sinusoids Arthropod Compact masses Not interspersed with capillaries Mechanisms of Hormone Action Specificity Function of 3-D structure and binding properties are important so it can specifically bind to a specific receptor. Peptide and protein hormones can vary in structure and so create great variety in hormone sturcture Overlap in binding cross reactivity Slight variation in AA sequence can alter binding Mechanisms of Hormone Action Hormone binding Conformational change in receptors High affinity RIA K d = [R][H]/[R.H] High vs low Membrane Bound Receptor Systems
G protein Types Gs,Gi Go Subunits Α,β,γ Adenyl cyclase camp Receptor Hypothesis:Membrane Cytosolic Receptor Systems Steroid Hormones Two step Modified two step All nuclear model Receptor Hypothesis:Intracellular Neurosecretory in nature Complexity increases in higher invertebrates I.e annelids, mollusks, arthropods have better developed systems then cnidarians and platyhelimitheyes Reasoning? Better circulatory systems! Lower invertebrates Hydrozoans (Cnidarians) Neurosecretory cells (growth, asexual reproduction, regeneration Platyhemitheyes Cerebal neurosecretory cells (regeneration, osmotic challenge, reproduction, shedding of proglottids) Nematodes Hormones control ecdysis of cuticle
Annelids Cephalized nervous system, coelom, well developed circulatory system Most endocrine functions include control over development, growth, regeneration and gonadal maturation Pg 511 Polychaete Neurosecretion Lower invertebrates Mollusks Regulation of reproduction Protandry Male develops first then there is a later reversal to female Neurohormones regulate the anatomical and physiological conversion of male secondary sexual features to female secondary sexual features Nonreproductive systems Body growth and shell growth Lower invertebrates Crustaceans Neurosecretory and classical Neurohemal organs Sinus gland in eyestalk Postcommisure organ Pericardial organ Classical Y organ in the antennary segment Androgenic gland ovaries
Chordates Hypothalamo hypophysial axis Adenohypophysis neurohypophysis Quiz Read pages 515-521 Give a brief description of the following: Endocrine control over A) molting B) reproduction C) color change Chordate Endocrine systems Neurosecretory reduced, classical endocrine enhanced Master control gland Hypothalamus/anterior pituitary Cells are concentrated into glands Echinoderms Insects
Evolution of Endocrine systems Identifying and measuring Hormones