Endocrine System

Chapter 45

What you need to know!

• Two ways hormones affect target organs.• The secretion, target, action, and

regulation of at least three hormones.• An illustration of both positive and negative

feedback in the regulation of homeostasis by hormones.

Endocrine

• System produces hormones that regulate homeostasis, reproduction, development, and behavior

• Master organs:• Hypothalamus• Pituitary gland• Receive sensory input

from receptors throughout the body

Hormones

• Transported by blood• Minute amounts needed• Are steroids, peptides, or amino acids• Work by either:

1. Binding to cell-surface receptors causing a signal transduction pathway (cascade of chemical events in response to stimulus) or

2. Diffusing across the cell membrane and binding to intracellular receptors which then act as transcription factors to activate specific genes

Blood Glucose Example

• Stable at 90mg/100ml• Regulated by pancreas• Pancreas serves multiple functions: digestions and blood

sugar regulation• Glucagon is released by alpha-cells in response to low

blood glucose levels• Insulin is released by beta-cells in response to high

blood glucose levels

Blood Glucose Example

• After eating food blood glucose levels in the body rise leading to the release of insulin by the beta cells; this stimulates the liver to build up glycogen (animal starch) storage and other body cells to absorb glucose

• After exercise or starvation blood glucose levels drop, alpha-cells release glucagon; this stimulates liver to break down glycogen into glucose

Blood Glucose Example

Diabetes

• Type 1 (juvenile)• Autoimmune destruction of beta cells• Type 2 (adult onset)• Exhaustion of beta cells due to high lifelong high

glycemic index diet

Stress (Fight or Flight) Response

• Regulated by hypothalamus/adrenal glands• Stress activates the hypothalamus• Fast reply: nerve connection to adrenal medulla

activates adrenalin (epinephrine) release

Adrenalin Action:• Glycogen breakdown• Blood glucose increase• Heart rate increase• Breathing rate increase• Lower blood flow to intestines (vasoconstriction)• Higher blood flow to muscles (vasodilation)

Long Term Stress

• Pituitary gland releases ACTH• Make adrenal cortex release corticoids• Corticoid action includes:• Increase in blood volume• Proteins/fat converted into glucose (rise in glucose

levels)• Suppresses immune system

• Antinflamatory response