3. What are hormones?
• Hormones are organic chemical messengers
produced and secreted by endocrine cells into
the bloodstream.
• Hormones regulate, integrate and control a
wide range of physiologic functions.
5. Classification Of Chemical Messenger
System
1. Neurotransmitters: released by axon terminals of
neurons into the synaptic junctions.
2. Endocrine hormones: released by glands or
specialized cells into the circulating blood.
3. Neuroendocrine hormones are secreted by
neurons into the circulating blood.
4. Paracrines are secreted by cells into the
extracellular fluid.
6. 5. Autocrines:secreted by cells into E.C.F and affect
the function of the same cells that produced them
e.g Estrogen.
6. Cytokines are peptides secreted by cells into E.C.F
and can function as autocrines, paracrines, or
endocrine hormones e.g:
interleukins and lymphokines secreted by helper
cells act on other cells of the immune system.
Leptin produced by adipocytes is sometimes called
adipokines1.
8. 1-General Classification Of
Hormones
1) Local hormones
Exert specific local effects e.g.
Acetyl choline ,cholecystokinin, secretin etc.
2) General hormones
Effect is away from their point of secretion
Effecting all the cells of the body examples e.g. GH
,TH ,TSH etc.
16. Synthesis Of Hormones
Peptide hormone - e.g. Insulin
– Synthesis - RER, preprohormone
– Cleaved to pro hormone in ER.
– Transferred to Golgi apparatus.
– Packaged in secretory vesicles
– In Golgi apparatus, cleaved to active hormone and
inactive fragments
– Released into ECF when cell is signaled to do so
– Transported in blood, half-life - minutes
18. – Mechanism of action :
Bind to cell surface receptors.
Many use cAMP and some use tyrosine kinase
– Action - open or close membrane channels or
modulate metabolic enzymatic activity.
19. Steroid hormones e.g. Estradiol
Are not packaged, but synthesized and immediately
released
Precursor molecules (cholesterol) and
intermediate compounds of steroid hormones
are stored in cytoplasm .
upon stimulation final hormones can be formed
in minutes.
Circulate in blood bound (inactive) to protein
carriers
Half-life - hours
21. Steroid Vs Protein Hormones
Steroid Hormones:
• These are all derived from
cholesterol.
• Examples: testosterone,
estrogen, progesterone,
mineralocorticoids,
glucocorticoids.
• Steroids can cross the plasma
membrane!
• Receptors are mainly in
cytoplasm,
Protein Hormones:
• These are made of Amino
Acids.
• Examples: Insulin,
Hypothalamic hormones,
Pituitary hormones
• Protein hormones cannot cross
the plasma membrane!
• Receptors are on cell
membrane..
22. Amine Hormones
• Amine hormones
– Most derived from tryptophan or tyrosine
– They behave like:
peptide hormones e.g catecholamines or
steroid hormones e.g thyroid hormones
26. • Negative feedback loops:
– Stabilizing a function and maintain it within a normal
range
– Most commonly applied ,self limiting
– Biological actions that directly or indirectly inhibit
further secretion of the hormone
– Response is in opposition to stimuli.
– Homeostatic control.
• Positive feedback loops
– Response reinforces the stimulus, rare ,explosive and
self re-enforcing
– Biological action that directly or indirectly causes more
secretion of the hormone
27. Transport of hormones
• Water soluble hormones e.g. peptides and
catecholamine are transported through---------
----
• Steroid hormones and thyroid hormones
-------------------.
28. Transport of hormones
• Water soluble hormones e.g. peptides and
catecholamine are transported through
diffusion
• Steroid hormones and thyroid hormones
bound to proteins.
29. • Onset, Duration, and Half-life of hormones
– Onset varies greatly, from almost immediately to
hours or days
– Duration can range from several minutes to
several hours
– Half-life is the length of time the hormone
concentration takes to drop by half From a
fraction of a minute to several hours
– Concentration is determined by its rate of release
and the speed of deactivation and removal
30. Clearance of hormones
• Metabolic destruction
• binding with tissues
• Excretion by the liver into bile
• Excretion by the kidneys
• Degradation at target tissues
32. .
Location of Hormone receptors:
• In or on the surface of the cell membrane(protein
,polypeptides ,catecholamine, steroids)
• In the cytoplasm (steroids)
• In the cell nucleus (thyroid hormones,steroids)
