1. Types of Cellular Secretion of Hormones Blood Transport of Hormones General Mechanisms of Hormonal Actions
Asha Alex
Physiology

2. What is a HORMONE? Hormone= chemical messenger produced in the body
that interacts w/ receptor in target tissue
to cause a change in function of that tissue.

3. Types of Cellular Secretion
Autocrine
Paracrine
Endocrine
Neuroendocrine
Neural
Pheromonal

4. Autocrine & Paracrine:
The Local Targeters

5. Endocrine & Neuroendocrine: The Long Distance Travelers

6. Types of Cellular Secretion of Hormones
Types of Hormones
Action of Hormone
Example
Autocrine
Acts on cells that synthesized them
Insulin-like Growth Factor (IGF-1)-stimulates cell division in the cell which produced it.
Paracrine
Acts on nearby cells
Insulin, secreted by pancreatic βcells-affects secretion of glucagon by pancreatic α cells
Endocrine
Carried in bloodstream or thru lymph to target cells in organs
Insulin, Estradiol, Cortisol
Neuroendocrine
Hormones synthesized in neuron:
a) releases hormone next to
target cell OR
b) releases it into bloodstream,
which carries it to target cell.
Hormone synthesized in neuron, goes from hypothalamus to anterior pituitary gland thru the portal system
Neural
Chemical released by 1 neuron, & acts on adjacent neuron.
Neurotransmitters: Acetylcholine
Pheromonal
Release of volatile hormones (into atmosphere; are transmitted to another individual & recognized as olfactory signal.
Pheromones

7. Regulation of Hormone Secretion: NEGATIVE FEEDBACK
If hormone A acts to raise the plasma concentration of substrate B, a decrease in substrate B will stimulate the secretion of hormone A.
Whereas an increase in substrate B will suppress secretion of hormone A.
Maintains homeostasis.

9. Blood Transport of Hormones
When hormones are secreted into blood, many are immediately bound to plasma proteins.
Proteins can recognize hormone specifically & bind it w/high affinity (ex: binding of sex hormones by sex hormone binding globulin- SHBG).

10. Blood Transport of Hormones
Equilibrium btw free & bound hormone
a fixed proportion of hormone travels free/unbound, while most is carried bound.
Bound hormone is
physiologically inactive
protected from metabolic enzymes in organs (liver)
Drugs, (aspirin) can displace other substances like anticoagulants from their binding sites
may cause hemorrhage.

11. General Mechanisms of Hormonal Action
Hormones interact w/target cells thru primary interaction w/receptors that recognize the hormones.
Several receptor systems: differ in mechanism & timing.
1) Membrane Receptors
2) Intracellular Receptors

12. MEMBRANE RECEPTORS conformational change in other membrane proteins
Charged ions (peptides, neurotransmitters)
bind to receptors on
cell membrane
conformational change in
other membrane
proteins
activates enzymes in cell
Synthesis of second messengers
that activate
phosphorylating enzymes

13. Uncharged molecules (steroid hormones)
INTRACELLULAR RECEPTORS
Uncharged molecules (steroid hormones)
diffuse into cell &
bind to intracellular receptors
hormone-receptor complex
binds to specific
hormone response elements (HREs)
on DNA
Modulates gene expression
in target cell.
RNA & protein synthesis altered.

14. TO WRAP IT UP: Types of Cell Secretion Blood Transport
Autocrine
Paracrine
Endocrine
Neuroendocrine
Neural
Pheromonal
Blood Transport
binding of hormone to plasma protein
Membrane Receptors
Intracellular Receptors

15. Bibliography
Endocrinology-At A Glance
Medical Physiology-Guyton