Introduction to endocrinology Flashcards
an overview of diabetes and endocrinology
What is an endocrine system?
- Integrates and controls organ function
- Via chemicals (hormones)
- Which are carried through the blood to target organs
- Distal from the hormone site of synthesis
- Response may be fast or slow
What is a hormone?
- Endocrine hormone: target organs are distal to the site of synthesis
- Paracrine hormone: act local to the site of synthesis
- Autocrine hormone: act on/ in the same cell it was produced
- Exocrine hormones: released from exocrine glands via ducts to the external environment
What is a neurohormone?
- Endocrine and nervous system combine
- Nerves release hormones which travel in the blood and travel to their target cells
- e.g. Adrenalin
What is endocrinology?
The branch of physiology and medicine concerned with endocrine glands and hormones
Describe endocrine communication
- Hormones travel in the blood to their target organs/ tissue
- Tissues detect hormones through the presence of a specific receptor for that chemical in/on the cell
- No receptor= no response
Describe neural communication
- Neurotransmitters released from presynaptic neurons travel across the synaptic cleft to the postsynaptic cell to influence its activity
- Neurotransmitter is a chemical released by a neuron but only acts within the synaptic cleft
What is the “life history” of a typical hormone?
- Secreted by a cell or group of cells
- Secreted from those cells into the blood
- Transported via the blood to distant targets
- Exert their effects at very low concentrations (act in the range 10^-9 - 10^-12M)
- Act by binding to receptors on target tissues
- Have their action terminated (often through negative feedback loops)
Describe peptide or protein hormones
- composed of chains of amino acids
- Common
- Synthesised in advance of the need and then stored in vesicles until they are required
- An example of a peptide hormone is insulin, TRH or FSH
- Water soluble and so dissolve easily in plasma making transport via the blood simple and easy
- It cannot cross cell membranes, however, as they are water soluble
- They bind to membrane bound receptors on target cells
- Once bound these receptors generally create relatively fast biological responses (seconds-minutes)
- Most work by modulating the GPCR or the tyrosine kinase linked signalling pathways
- These pathways phosphorylate existing pathways in the cell and modify their function
- e.g. open/close ion channels, activate or inactivate enzymes
- The tyrosine kinase pathway may also alter gene expression (not for insulin though)
How are peptide or protein hormones produced?
- Initial protein produced by ribosomes is large and inactive (preprohormone)
- Preprohormones contain one or more copies of the active hormone in their amino acid sequence
- Preprohormones are cleaved into smaller units in the RER (prohormones)
- Prohormones are smaller but still inactive
- Prohormones are packaged into vesicles in the Golgi apparatus along with proteolytic enzymes which break the prohormone down into the active hormone and other fragments
- Hormones and fragments are stored in the endocrine cell until release is triggered then all vesicle contents are released into the plasma (co-secretion)
How do steroid hormones interact with their receptors and what happens when they do?
• Steroids cross the plasma easily as they are lipophilic
• Their receptors are located inside the cells
• They trigger either activation or inhibition of gene function within the nucleus (genomic effect)
- Genes control the synthesis of protein so these hormones either increase or decrease protein synthesis
• This is a relatively slow process (hours-days)
• Effects persist for longer
• Some evidence shows that steroids sometimes bind to cell surface receptors which would mean a quick response
Describe the production and excretion of steroid hormones
• All derived from cholesterol
- Which steroid is produced depends on the cell as they all have different enzymes and so synthesise different derivative of cholesterol
• Synthesised directly when needed
• They cannot be retained within the lipid membranes
• Once synthesised they diffuse across the membrane into the ISF and the blood
How are steroid hormones transported in the blood?
- They are transported bound to carrier proteins such as albumin
- This stabilises their transport through the plasma and protects them from enzymatic degradation which greatly increases their life span
What are steroid hormones produced by?
• Steroid hormones are produced by:
- Gonads (testes and ovaries): sex steroids
- Placenta: hCG, sex steroids
- Kidney: vitamin D3
- Adrenal cortex: Corticosteroids
What are amine hormones derived from?
- All derived from one of two amino acids (tryptophan and tyrosine)
- The only amine hormone not derived from tyrosine is melanin which is derived from tryptophan
What are catecholamines?
- Dopamine from the brain
- Norepinephrine from neurons
- Epinephrine from the adrenal medulla
- Similar mechanisms of actions to peptide hormones (hydrophilic)
