This is on the basic details of the endocrine system including the different types of hormones. It describes the mechanisms of actions of hormones. The general control mechanisms of hormone production and release are also included.
2. Nervous and Endocrine Systems
• Act together to coordinate functions of all body systems
• Nervous system
– Nerve impulses/ Neurotransmitters
– Faster responses, For a short duration, acts on specific target
• Endocrine system
– Hormone – mediator molecule released in one part of the body
but regulates activity of cells in remote areas of body
– Slower responses, effects last longer, broader influence
4. Hormone specificity
• Hormones affect only specific target tissues with
specific receptors
• Hormone specificity is due to the receptors: present
on cell membrane or in cytoplasmic organelles
• Receptors constantly synthesized and broken down
– Down-regulation
– Up-regulation
5. Hormone types
Circulating – circulate in blood throughout body
Local hormones – act locally
Paracrine – act on neighboring cells
Autocrine – act on the same cell that secreted them
6. Chemical nature of Hormones
–Lipid-soluble – use transport proteins
» Steroid
» Nitric oxide (NO)
–Water-soluble – circulate in “free” form
» Amine
» Peptide/ protein
» Eicosanoids
8. Mechanisms of Hormone Action
• Response depends on both hormone and target cell
• Lipid-soluble hormones bind to receptors inside target cells
9. Hormone action
• Water-soluble hormones bind to receptors on the plasma
membrane
– Activates second messenger system
– Amplification of original small signal
• Responsiveness of target cell depends on
– Concentration of Hormone
– Abundance of target cell receptors
– Influence exerted by other hormones
• Permissive, synergistic and antagonistic effects
11. • Most hormonal regulation by negative feedback
– Few examples of positive feedback also exist
Control of
hormone
secretions
Nervous
system
Other
Hormones
