Endocrine System Slide I

Not including MLC

Endocrine System

Endocrine System

slowly acting by using chemical messengers called hormones

Endocrine glands

ductless glands that produce/release hormones into the blood stream through diffusion

Endocrine organs

lack the structural or anatomical continuity typical of most organ system instead endocrine tissue is tucked away in separated regions of the body

Chemical classification of hormones

1. Amino acid based molecules

2. Steroids

3. Eicosanoids

Steroids

• Derived from cholesterol

  • ex. sex hormones

Eicosanoids

diverse lipids made from 20-carbon fatty acid (arachidonic acid)

• have localized effect

Leucotrienes

• lipid derivatives that act as chemicals signals that mediate inflammation and some allergic reactions

Prostaglandins

• made from highly active lipids found in the cells’ plasma membranes

  • plays roles in regulation of blood pressure (increase), blood clotting, inflammation, and labor contractions

Autocrines

chemicals that exert their effects on the same cells that secrete them

• smooth muscle prostaglandins effect smooth muscle cell contraction

Paracrines

• affect cell types other than those releasing the chemicals

Target cells and target organs response

can only be stimulated when there is a specific protein receptor present in the plasma membrane or in its interior

What happens in the target cell?

1. Produce changes in membrane permeability or potential

2. Stimulate synthesis of proteins or regulatory molecules (enzymes)

3. Activate or deactivate enzymes, induce secretory activity

4. Stimulate mitosis

Steroid Hormone Action

Nonsteroid/Water-Soluble Hormone Action

Structures of ATP & cAMP (Cyclic- adenosine-monophosphate)

Target Cell Specificity

• must have specific membrane or intracellular receptors to which hormones can bind

Target cell response depends of 3 factors

1. Blood levels of the hormone

2. Relative number of target cell receptors

3. Affinity of the receptor for the hormone

Concentration of a hormone

reflects its rate of release, the rate of inactivation and removal from the body

Half-life of a hormone

duration of time a hormone remains in the blood and is shortest for water soluble hormones

Target organ duration and response

varies widely among hormones

Permissiveness

occurs when one hormone cannot exert its full effect without another hormone being present

Synergism

occurs when more than one hormone produces the same effects in a target cell, and their combined effects are amplified

Antagonsim

Occurs when one hormone opposes the action of another hormone

Events occurring in a negative feedback mechanism

1. some internal or external stimulus

2. Hormone secretion

3. Hormone levels rise

4. Inhibit further hormone release (even while promoting responses in their target organs

(blood levels of many hormones vary only within a very narrow range)

Endocrine gland stimuli

• humoral

• neural

• hormonal