Cell signalling and the endocrine system Flashcards
What are the 3 main types of hormone?
Peptide
Amine
Steroid
What hormone is produced by the pineal gland?
Melatonin
What glands produce peptide hormones?
Hypothalamus
Pituitary
Thyroid
Parathyroid
Pancreas
What glands produce amine hormones?
Thyroid
Parathyroid
Adrenal
What glands produce steroid hormones?
Ovaries
Testes
Adrenal
What are amine hormones?
Pre-synthesised hormones that are stored in vesicles
What stimulates release of amine hormones?
They are released in response to a stimuli by Ca2+ dependant exocytosis
How are amine hormones transported?
Amines are hydrophilic and are transported mainly free in the plasma
What are peptide hormones?
Peptides are pre-synthesised, usually from a longer precursor, and are stored in vesicles
What stimulates release of peptides?
They are released in response to stimuli by Ca2+ dependant exocytosis
How are peptide hormones transported?
Peptides are hydrophilic and are transported mainly free in the plasma
What stimulates steroid hormones?
- Increased cellular uptake and availability of cholesterol
- Increased rate of conversion of cholesterol to pregnenolone (Rate limiting)
How are steroid hormones transported?
Steroids are hydrophobic and are transported in plasma, mainly bound to plasma proteins
Only free steroid hormones are biologically active
What are some examples of specific carrier proteins of hormones?
- Cortisol-binding globulin (CBG) - Binds cortisol and some adrenaline
- Thyroxine-binding globulin (TBG) - Binds T4 and some T3
- Sex steroid-binding globulin (SSBG) - Binds testosterone and oestradiol
What are some examples of general carrier proteins of hormones?
- Albumin - Binds many steroids and thyroxine
- Transthyretin - Binds thyroxine and some steroids
What is the function of carrier proteins?
These carrier proteins are a buffer and reservoir that helps to maintain a relatively constant concentration of free lipophilic hormone in the blood, meaning that free and bound hormones are kept in equilibrium
Surges in hormone secretion are buffered by binding to carriers
Free hormone removed from plasma by elimination is replaced by bound hormone dissociating from carrier proteins
What form of hormone can pass capillary walls?
Free hormones
What is the half-life of amine hormones?
A few seconds
What is the half life of proteins and peptide hormones?
A few minutes
What is the half-life of steroid and thyroid hormones?
Hours to days
Why do steroids and thyroid hormones have much longer half-lives?
Protein binding suppresses elimination
What are the 3 main types of hormone receptors?
- G-protein coupled receptors (GPCR)
- Receptor kinases
- Nuclear receptors
What types of hormones stimulate G-protein coupled receptors?
Amines
Some proteins/peptides
What are the 3 classes of nuclear receptors?
Class I
Class II
Hybrid
What usually stimulates class I nuclear receptors?
Activated by many steroid hormones; in the absence of activating ligand, these are mainly located in the cytoplasm, bound to inhibitory heat shock proteins, and move to the nucleus when activated
What usually stimulates class II nuclear receptors?
Activated mostly by lipids; constitutively present in the nucleus
What usually stimulates hybrid ulcer receptors?
Activated by thyroid hormone (T3) and other substances (Similar in function to class 1)
What effect does Gs protein have on a cell?
Stimulation of adenylyl cyclase
What effects does Gi protein have on a cell?
Inhibition of adenylyl cyclase
What is the function of adenylyl cyclase?
Conversion of ATP to cAMP
Increased cAMP increases PK Activity, which causes cellular effects through phosphorylation of ser/thr residues
What effect does Gq have on a cell?
Stimulation of phospholipase C (PLC)
What is the function of phospholipase C in a cell?
Conversion of PIP2 to IP3 and DAG release
IP3 causes Ca2+ release from the ER
DAG phosphorylates ser/thr residues
What type of receptor does insulin bind to?
Receptor kinase
How do receptor kinases work?
Unbound insulin binds to the receptor, causing autophosphorylation of intracellular tyrosine residues
This causes activation of multiple adaptor proteins, notably IRS1, which are also tyrosine phosphorylated
This increases Akt/PKB activity
What are some metabolic effects of insulin binding?
- Recruitment of glucose transporters
- Increased glycogen formation
- Increased fat formation
- Changes in gene expression
- Decreased glycogenolysis
- Increased formation of protein
