Intro to Endocrine

PHYSIOLOGY  INTRO TO ENDOCRINE PHYSIOLOGY  DR. VIC MENDOZA JANUARY, 2011

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Secretes substances (hormones) to act in concert with the nervous system 

MAJOR SIGNALING/CONTROL SYSTEM -

Nervous System o

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ENDOCRINE GLAND

Integrates tissue functions by a network of  cells and cell processes that constitute the nervous system

Endocrine System

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A group of cells that produce and secrete a hormone

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2 features of the endocrine glands: o

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Aka HORMONAL SYSTEM Integrates organ function via chemicals that are secreted from endocrine tissues into the extracellular fluid

ENDOCRINE VS NERVOUS CONTROL -

Both share a role for control and coordination throughout the body

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Should not be considered as separate entities o

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Some endocrine glands respond to nervous stimuli Endocrine system maintains nervous system

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Growth and development

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Metabolism

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Reproduction

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Homeostasis

Numerous organs and tissues located throughout the body

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Works in conjunction with the nervous system

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Concerned with 3 functions: o

Maintain homeostasis 

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Regulates concentration of  chemicals in body fluids and metabolism

Major regulator of growth and development 

Sexual development and reproduction

PHYSIOLOGY: INTRODUCTION TO ENDOCRINE PHYSIOLOGY

Typically are highly vascular, and their capillaries are usually fenestrated

HORMONE -

A substance secreted DIRECTLY INTO THE BLOOD by discrete SPECIALIZED CELLS (which may be grouped into an endocrine gland) in RESPONSE TO A SPECIFIC STIMULUS (neural or bloodborne) and in amounts which VARY WITH THE STRENGTH OF STIMULUS

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Present in only MINUTE CONCENTRATIONS in blood and when carried to their target cells exert specific effects which always involve the REGULATION OF PRE-EXISTING CELLULAR REACTIONS other than by the provision of metabolic energy

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Secreted into extracellular fluid and readily enter the blood by passive diffusion driven by steep concentration gradients

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Diffusion through pores in capillary endothelium also largely accounts for delivery of hormones to the extracellular fluid that bathes both target and nontarget cells

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In general, hormones distribute rapidly throughout the extracellular fluid and are not preferentially directed toward their target tissues

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Most hormones are cleared from blood soon after secretion and have a half-life in blood of less than 30 minutes

ENDOCRINE SYSTEM Controls numerous body processes

Ductless glands (vs exocrine glands which deliver their products through ducts to the outside of the body or to the lumen of the GIT)

**Both these features facilitate in the two-way trafficking of  signals to the gland and hormones to the blood. Except for these vascular features, endocrine glands have no other special distinguishing features

Both systems involve reflexes

**The nervous system and endocrine system often respond together so as to integrate the organism’s response to changes in its external and internal environment

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Helps the body react to stress properly

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Half-life of a hormone in blood  defined as the period of time needed for its concentration to be reduced by half life. This depends on its rate of degradation and on the rapidity with which it can escape from the circulation and equilibrate with fluids in extravascular compartments Page 1