Lecture 21: Control of Physiological Functions: Homeostasis



Homeostasis of Some Body Parameters is Necessary for Life

Homeostasis is Based Upon Negative Feedback

Homeostasis Requires: Sensors, Signal Transmission, Control Centers and Effectors

(Madonna computer model of homeostasis)

The Major Control Systems in the Body are the Nervous and Endocrine Systems

The Nervous System Uses Electrical Transmission of Signals

Example of Nervous Control: Knee Jerk Reflex

The Endocrine System Uses Chemical Transmission of Signals

Hormones fall naturally into 2 groups: hydrophobic and hydrophilic

 Type of Hormone  Mode of Action  Examples


 (lipid soluble)

Permeable to cell membranes. Pass into cell, bind to an internal receptor and turn on genes. Proteins produced by the genes are responsible for the effects. Steroid hormones: male & female sex hormones, aldosterone, cortisone.

Thyroid hormones.


(water soluble)

 Impermeable. Bind to receptors in the cell membrane. This causes release of second messengers (c-AMP, Ca, inositol triphosphate, etc.) inside the cell. The second messengers are responsible for the hormone effects.

Amines: norepinephrine,

Proteins and peptides: growth hormone, ACTH, insulin, FSH, parathyroid hormone, oxytocin, ADH

Example of Hormonal Control: Regulation of Thyroid Hormones