Endocrine System

Front 1

Cyclic AMP Second Messenger Mechanism (Hormones

Back 1

Polypeptide Hormones exert their effect through this mechanism.

Endocrine gland releases Hormone (1st messenger).
Hormone binds to a specific receptor on the target cell membrane.
The hormone receptor complex activates the enzyme Adenylate Cyclase in the membrane.
Adenylate Cyclase activates ATP to 3'5' cAMP in cytoplasm.
cAMP (2nd messenger) can affect other enzyme systems and cell functions by:
1. changing the cell membrane permeability and transport mechanism.
2. activating other enzyme systems.
3. altering the genetic expression of target cell DNA and thus influencing RNA and Protein synthesis by that cell.

Front 2

Steriod Hormone Mechanism of Action

Back 2

Steriods are nonpolar lipids that can pass through the cell membrane without binding to a receptor.

Endocrine Gland releases Hormone (1st Messenger)
Hormone enters cell membrane and goes through it.
Hormone binds to a protein within the cytoplasmic compartment (because its a liquid in water-like cytoplasm).
The hormone-protein complex gets translocated into the nucleus.
It binds to the regulatory region of a specific chromatin protein by Homo-dimerization.
***Steroids have to bind as a dimer. 2 have to bind DNA at the same time. Dimerization of receptors activates the promoter region and causes RNA synthesis.
This interaction triggers specific RNA synthesis.
Results in specific protein synthesis.
Has an effect on cell function.

Front 3

Thyroid Hormone Mechanism of Action

Back 3

Thyroid gland produces T4 and secretes it into the blood.
Thyroxin Binding Globulin, a water soluble blood carrier protein, carries T4 through blood plasma because T4 is lipid-based. Lipid based T4 can diffuse right into the cell without a carrier.
In the cytoplasm T4 is enzymatically converted into T3.
T3 enters the nucleus and will bind to specific nuclear receptor proteins, which are attached to the chromatin.
***Binds to DNA by Hetero-dimerization. T3 binds one receptor and 9-cis-Retinoic Acid binds to another --> 9 cis made from Vitamin A, so you need ample Vita A for Thyroid Hormone to function correctly! Wouldnt be able to heterodimerize!
When T3 attaches to the nuclear receptor, genes are activated which results in the transcription of mRNA.
Translation of protien.
Protein can then affect thyroid hormone response.

Front 4

Phospholipase C- Ca 2+ Second Messenger System

Back 4

Hormone binds to a receptor protein in plasma membrane of target cell.
Binding causes activation and dissociation of G Proteins.
Beta Gamma subunits diffuse through membrane and activate Phospholipase C.
Phospholipase C catalyzes the breakdown of membrane phospholipid into Diacylglycerol and Inositol triphosphate (IP3).
IP3 enters the cytoplasm and binds to receptors in Endoplasmic Reticulum.
BInding causes opeining of Ca channels release of stored Ca2+ into cytomplasm.
Ca2+ activates Calmodulin.
Activates Protein Kinase.
Phosphorylate different enzyme systems for a Hormone response.

***this system is used by Alpha 1 Receptors for Norepinephrine
Sympathetic NX = free glucose gets released by liver when Norepinephrine binds the Alpha 1 receptors

Front 5

Tyrosine Kinase Second Messenger System

Back 5

Insulin binds to alpha subunits of Tyrosine Kinase Receptor (integral protein) in plasma membrane of target cell.
****Receptor = 2 parts taht clamp around Insulin. Homodimerization around Insulin in the membrane.
Beta subunits auto-phosphorylate each other.
Activates the Tyrosine Kinase activity of the Insulin Receptor
Activated receptor phosphorylates insulin receptor substrate proteins, which activate a variety of signaling molecules.
Signaling molecules cause Glut 4 receptors in synaptic vesicles to be exocytosed into the membrane.
Receptors promote glucose uptake into the cell by Facilitate Diffusion.