Download BIOL 245 Endocrine System 1 I. Hormones A. From endocrine

BIOL 245
Endocrine System 1
I. Hormones
A. From endocrine glands
B. Target tissues
C. Classes
1. protein based
a. glycoproteins:
b. polypeptides
2. biogenic amines (monoamines)
- amino acid-based:
- tyrosine derived:
3. steroids (cholesterol-based)
a. cortisol
b. sex steroids
D. Synthesis and transport
1. steroids
a. bound to hydrophilic transport proteins
b. unbound form taken up by target cells
2. thyroid
- thyroxine-binding globulin (TBG)
E. Inactive forms (long)
1. preprohormone --> prohormones --> active hormone
- preproinsulin ---> proinsulin ---> insulin
2. some forms not activated until inside target cells
F. Requirements for proper activity
1. receptors on/in target cells
2. binding of hormone to receptor causes change in the activity of target cell
G. Interactions
1. synergistic
a. additive or complementary
b. examples:
2. permissive: enhances effect of another hormone
a. ↑ responsiveness of target organ to another hormone
b. ↑ activity of another hormone
3. antagonistic
a. lactation (via prolactin) inhibited by ↑ E2
b. insulin vs. glucagon
II. Mechanisms of Hormone Action
A. Interaction with receptors on/in target cells
1. high specificity
2. high affinity
3. low capacity
4. types of interactions vary depending on hormone class
a. nuclear receptors:
b. cytoplasmic receptors:
c. membrane receptors:
B. Steroid/Thyroid mechanisms
1. each type is nonpolar
2. transported by plasma carrier proteins
3. nuclear: (steroids)
a. binding of hormone changes conformation of receptor
b. hormone-receptor complex binds to acceptor sites (usually on DNA)
c. activates gene transcription
4. thyroxine
a. only about 0.04% of T4 is “free” in plasma
b. converted to T3 in cell (small amount of free T3 in plasma)
c. T3 receptor is bound to chromatin
C. Second-messenger activation
1. hormone is first messenger
2. cAMP
a. catechols and some protein-derived
b. ATP ---> cAMP
c. cAMP activates protein kinases ----> protein phosphorylation
3. Ca++
a. intracellular [Ca++] normally very low
b. example: α-adrenergic stimulation via epi
- activates phospholipase (enzyme)
- phospholipase breaks down phospholipids ---> IP3
- IP3 triggers ↑ in intracellular [Ca++]
- Ca++ binds to and activates calmodulin
- activation of protein kinases
D. Receptor regulation
- up or down-regulation