Lecture 2- Endocrine System Flashcards
Carrier Proteins for Lipid Soluble Hormones(2)
- General Carrier Proteins
2. Specific Carrier Proteins
General Carrier Proteins
- Albumin-Steroids, Some thyroid Hormones
2. Transthyretin- thyroid hormones, some steroids
Specific Carrier Proteins
- Cortisol binding globulin(CBG)–>cortisol and aldosterone
- Thyroxine Binding globulin(TBG)–> thyroid hormone
- Sex steroid binding globulin (TEGB)–> Testosterone and estradiol
Control of Hormone Secretion
- Regulated by: signals from nervous system, chemical changes of molecules, other hormones
- Hormone regulation (negative or positive feedback)
Control of Hormone Secretion- Negative Feedback
- Most endocrine glands under negative feedback
- cells can sense the magnitude of the biological effect and DECREASE the response
Control of Hormone Secretion- Positive Feedback
- Increased production and release of Oxytocin, enhance milk production and release, enhance contractions during childbirth
- Contraction–> head of baby activates receptors to CNS–>hypothalamus–> produce for Oxytocin
Hormone Activity
- Hormones affect only specific target tissue (depends on receptors)
- Response depends on both hormones and target cells
- Target cells respond differently to the same hormone
- Hormonal effects vary
Hormone Activity: Receptor
- Lock and Key mechanism
- Hormone locks onto a specific receptor
Regulation of Hormone Effects
Downstream Effect determines by:
- # of receptors
- Amount of hormone secreted
Regulation of Hormone receptors (2)
- Down-regulation
2. Up-Regulation
Down-Regulation
- Increase in hormone leads to DECREASE in number of receptors
- Target cell is LESS sensitive, decreases response
Up-Regulation
- decrease in hormone leads to INCREASE in number of receptors
- Target cell is sensitive, better chance for hormone to find receptor
Where do Water-soluble hormones bind?
-to receptors on the PLASMA membrane
Where do lipid-soluble hormones bind?
- To receptors inside target cells
- Cytoplasmic or nuclear
Surface Receptors for water- soluble hormones (3)
- Single transmembrane protein
- Membrane bound protein
- 7 transmembrane protein (GPCR)
Components of a GPCR
- Produces responses through the action of a G-Protein
- Effector protein is activated by a G protein
- Effector produces a 2nd Messanger
G Proteins
- Can be stimulatory(S) or inhibitory (I)
- consist of alpha, beta, and gamma subunits
- Alpha can be Gs, Gi, Gq, and Gt
- They contain GTPase activity that hydrolyzes GTP
- can be active and inactive
Inactive state of G proteins
- G protein is bound to a receptor that is not activated by a hormone
- alpha/beta/gamma subunits form a complex
- GDP is bound to the alpha subunit
Active State of G proteins
- Ligand binding stimulates the exchange of GDP for GTP on the ALPHA subunit
- Alpha subunit dissociates from beta/gamma subunits
- Starts/ends in the Inactive state
Effect Systems and their second messenger (3)
- Adenylate cyclase—>cAMP
- Phospholipase—-> Inositol phosphate
- Ion channels–> ions
Adenylate Cyclase and cAMP system
-Water-soluble hormone binds to the receptor and activates a G protein (Gs)
Signal Amplification
-ADVantage= low concentration of hormone can produce large effect downstream
Interaction of cAMP signaling
- Inactivation occurs by the action of the enzyme phosphodiesterase
- cAMP is inactivated to AMP
Activation and inhibition of adenylate cyclase (AC)
- Gs will activate AC and increase cAMP
- Gi will inhibit AC and decrease cAMP
- EX- adrenergic receptors
