Endocrine System

Topics: Hypothalamus, Endocrine system, Hormone Pages: 18 (2983 words) Published: February 24, 2014
Study Guide, Chapter 16 The Endocrine System

Endocrine System: Overview
Acts with nervous system to coordinate and integrate activity of body cells Influences metabolic activities via hormones transported in blood Response slower but longer lasting than nervous system

Study of hormones and endocrine organs

Endocrine System:
Controls and integrates
Growth and development
Maintenance of electrolyte, water, and nutrient balance of blood Regulation of cellular metabolism and energy balance
Mobilization of body defenses

Exocrine glands
Nonhormonal substances (sweat, saliva)
Have ducts to carry secretion to membrane surface
Endocrine glands
Produce hormones
Lack ducts
Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands Hypothalamus is neuroendocrine organ
Some have exocrine and endocrine functions
Pancreas, gonads, placenta
Other tissues and organs that produce hormones
Adipose cells, thymus, and cells in walls of small intestine, stomach, kidneys, and heart

Chemical Messengers
Hormones: long-distance chemical signals; travel in blood or lymph Autocrines: chemicals that exert effects on same cells that secrete them Paracrines: locally acting chemicals that affect cells other than those that secrete them Autocrines and paracrines are local chemical messengers; not considered part of endocrine system

Chemistry of Hormones
Two main classes
Amino acid-based hormones
Amino acid derivatives, peptides, and proteins
Synthesized from cholesterol
Gonadal and adrenocortical hormones

Mechanisms of Hormone Action
Though hormones circulate systemically only cells with receptors for that hormone affected Target cells
Tissues with receptors for specific hormone
Hormones alter target cell activity
Hormone action on target cells may be to
Alter plasma membrane permeability and/or membrane potential by opening or closing ion channels Stimulate synthesis of enzymes or other proteins
Activate or deactivate enzymes
Induce secretory activity
Stimulate mitosis

Hormones act at receptors in one of two ways, depending on their chemical nature and receptor location 1. Water-soluble hormones (all amino acid–based hormones except thyroid hormone) Act on plasma membrane receptors

Act via G protein second messengers
Cannot enter cell

2.Lipid-soluble hormones (steroid and thyroid hormones)
Act on intracellular receptors that directly activate genes
Can enter cell

Plasma Membrane Receptors and Second-messenger Systems
cAMP signaling mechanism:
1. Hormone (first messenger) binds to receptor
2. Receptor activates G protein
3. G protein activates adenylate cyclase
4. Adenylate cyclase converts ATP to cAMP (second messenger) 5. cAMP activates protein kinases that phosphorylate proteins

cAMP signaling mechanism
Activated kinases phosphorylate various proteins, activating some and inactivating others cAMP is rapidly degraded by enzyme phosphodiesterase
Intracellular enzymatic cascades have huge amplification effect

PIP2-calcium signaling mechanism
Involves G protein and membrane-bound effector – phospholipase C Phospholipase C splits PIP2 into two second messengers – diacylglycerol (DAG) and inositol trisphosphate (IP3) DAG activates protein kinase; IP3 causes Ca2+ release

Calcium ions act as second messenger
Ca2+ alters enzyme activity and channels, or binds to regulatory protein calmodulin Calcium-bound calmodulin activates enzymes that amplify cellular response

Other Signaling Mechanisms
Cyclic guanosine monophosphate (cGMP) is second messenger for some hormones Some work without second messengers
E.g., insulin receptor a tyrosine kinase enzyme that autophosphorylates upon insulin binding  docking for relay proteins that trigger cell responses

Intracellular Receptors and Direct Gene Activation
Steroid hormones and thyroid hormone
1. Diffuse into target cells and bind with intracellular...
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