Endocrinology (lecture 25) Flashcards
GAP junction communication
Message transmitted directly from cell to cell
Specificity depends on anatomical location/proximity
Synaptic communication
Message transmitted across synaptic cleft
Specificity depends on anatomical location and receptors
Paracrine and autocrine communication
Message transmitted by diffusion in interstitial fluid
Specificty depends on receptors but also proximity
Autocrine = acts on itself Paracrine = acts on cells in local area
Endocrine communication
Message transmitted by circulating body fluids - blood
Specificity depends on receptors
Definition of endocrine system
Endocrine cells within endocrine glands release substances (hormones) which are conveyed by the blood stream & act on distant cells
What are the 2 main controllers of the body?
Hypothalamus
Pituitary
They control the rest of the endocrine system
What does the rest of the endocrine system do?
- Thyroid controls metabolism
- Parathyroids control calcium levels
- Thymus controls body temperature
- Adrenals release adrenaline/epinephrine
- Pancreas
- Ovaries & testes produce sex hormones
What are the non-classical producers?
- Kidney
- Heart muscle
- Endothelium
- Platelets
- Adipocytes
- White blood cells
What is a hormone?
Chemical messenger
Synthesised by specialised cells
Secreted into the blood in small amounts which acts on a specific receptor in target organs to regulate cellular function
How do hormones interact with target cells?
- High affinity
- Synergistic
- Permissive
- Antagonistic
- Competitive
High affinity interaction
Hormones are effective at low concentrations. They are normally found in the blood in the pico molar range
Synergistic interaction
The effect of two hormones is greater than one alone
e.g. thyroid hormone and norepinephrine on heart rate
Permissive interaction
The presence of one hormone is necessary for another to have an effect
e.g. thyroid hormone and aldosterone on Na/K pumps in kidney
Antagonistic interaction
Two hormones oppose each other’s effects
e.g. insulin vs glucagon
Competitive interaction
Two hormones, similar in structure, compete for the same receptor
e.g. epinephrine and norepinephrine
What are the 3 classes of hormones based on chemical structure?
Steroids
Peptides
Amino acids
What are steroid hormones
Synthesised from cholesterol
Lipiphilic – can cross membranes easily
Receptors tend to be inside the cell – in the nucleus
Very difficult to store as leak out of vesicles – produced on demand
Eg. Cortisol
What are peptide hormones
Synthesised from amino acids
Most abundant hormone class
Hydrophilic – like water – don’t cross the membrane easily
Receptors are on the membrane – second messenger pathways involved
Eg. Growth hormone
What are amino acid hormones
Synthesised from tyrosine
Some act like steroid hormones but some act like peptide hormones
Eg. Thyroid hormone & epinephrine
Properties of steroid hormones?
Cholesterol produced predominantly in the liver
- Released immediately following synthesis
- Circulate in bound form – needs a carrier protein - bound to plasma proteins
- Act on intracellular receptors which then bind to DNA (hormone response elements) & regulate gene transcription
Have slow long lasting effects
What action do steroid hormones have on receptors?
Inhibitory protein complex (Heat shock protein 90) is bound during the resting state, hiding the DNA binding domain
Hormone binds (allosterically) causing a conformational; change so the hinge opens up, exposing the DNA binding sites
Properties of peptide hormones
Peptide hormones are between 3 & 332 amino acids in length – most are longer
Synthesised as preprohormones (inactive form) & stored prior to release & modified before release
Act on cell surface receptors then via 2nd messenger systems to cause effect in target cells
Properties of amino acids
Amino acid hormones include thyroid hormone & epinephrine
Most synthesised from tyrosine
Stored for instant release
Different modes of action – TH has intracellular receptors, others act at the surface
What action do peptide and amino acids have on the cAMP pathway?
1) Hormone binds to receptor
2) Leads to G protein which activates adenylate cyclase
3) cAMP produced
activates protein kinase A
4) phosphorylates many things changing the cells activity
