1. Human Anatomy & Physiology
Chapter 16 – The Endocrine System

2. General Characteristics
What is the endocrine system?
Endocrine glands produce hormones
Hormones
Chemical messengers
Released into the blood and transported throughout the body
Influence the activity of target tissues
Figure 16.1

3. General Characteristics
Endocrine glands vs. exocrine glands
Hormone Chemistry
Most hormones are amino acid based
Amino acid derivatives
Short chains of amino acids (peptides)
Proteins
Steroid Hormones (synthesized from cholesterol)
Aldosterone and gonadal hormones

4. Effects of Hormones
To bring about their effects, hormones alter cell activity
They are like chemical “triggers”
Hormones can have the following effects on a cell:
Open or close membrane channels
Stimulate the synthesis of new proteins
Activate or inactivate enzymes
Induce secretory activity
Stimulate mitosis

5. Effects of Hormones
Some of these mechanisms function through second messengers
Cyclic AMP
Others activate G-protein systems
Affect ion channels
Induce the synthesis of second messengers

6. Effects of Hormones
Hormone chemistry determines how a hormone can communicate with its target cells
Amino acid based hormones are water soluble and CANNOT move through the membrane
Therefore they require membrane-bound receptors
Examples from other text

7. Effects of Hormones
G-protein systems - Figure 16.2

8. Effects of Hormones Awesome Animation
Steroid hormones are lipid soluble and CAN move through the membrane
Their receptors are located inside the cell
Once bound to their receptor, the hormones stimulate transcription and the production of new proteins
Figure 16.3 and from other text

9. Effects of Hormones Target cell specificity
For a cell to be affected by a hormone, it must have a receptor for that hormone
Examples
Hormones are removed from the blood by the kidneys or liver
Half-life (a few seconds to ~30 minutes)
Onset of hormone effects varies
Duration of effect ranges from seconds to several hours

10. Control of Hormone Release
Control of most hormones is regulated by negative feedback
What does that mean?
There are a couple hormones regulated by positive feedback
Figure from other text

11. Control of Hormone Release
Stimulation of hormone release
Humoral stimuli – changing levels of ions or nutrients in the blood
Insulin and blood glucose
PTH and calcium
Neural stimuli – neurons stimulate the release of hormones
Catecholamines (epinephrine) and the sympathetic nervous system
Hormonal stimuli – hormones from one gland stimulate the release of other hormones
TSH and the thyroid hormones
Figure 16.4