Lecture 1 Introduction to Endocrinology and Diabetes Flashcards
Define the endocrine system
• A system that integrates and controls organ function via the secretion of chemicals (hormones) from cells, tissues or glands which are then carried in the blood to target organs, distal from the site of hormone synthesis, where they influence the activity of that target organ
What is the neuroendocrine system
Endocrine and nervous system combine. Nerves release hormones which enter blood and travel to their target cells
What are autocrine hormones
Cells secrete chemicals that bind to receptor on the same cell
What are paracrine hormones
Chemicals diffuse in ECF to affect neighbouring cells
Name features of an Endocrine Hormone
- Produced 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 -10-12 M)
- Act by binding to receptors on target tissues
- Have their action terminated, often via negative feedback loops.
What are peptide hormones made of
Chains of amino acids (most common)
What are amine hormones composed of
All derived from one of two amino acids (tryptophan or tyrosine)
What are steroid hormones composed of
Cholesterol
Describe the synthesis of peptide hormones
Preprohormone is directed into the ER by a signal sequence
Enzymes in the ER chop off signal sequence creating pro hormone (inactive)
Prohormone transported to Golgi complex and bud offing active peptides
What are C-peptides
inactive fragment cleaved from the insulin prohormone. Levels of C-peptide in plasma or urine are often measured to indicate endogenous insulin production from the pancreas (produced in equal amounts). However, because insulin is metabolised faster, levels of C-peptide are typically about 5x higher than endogenous insulin.
Why is measuring C-peptides important
Measuring C-peptide levels ensures quick stabilization of glucose levels of type 1 diabetic- endogenous insulin production by pancreas
Why are peptide hormones able to transport via blood easily
Water soluble
How do most peptide hormones work
modulating either the GPCR or tyrosine kinase linked signalling pathways. These pathways phosphorylate existing proteins in the cell and modify their function e.g. open or close ion channels, activate or inactivate enzymes.
Name Amine Hormones
Catecholamines: Dopamine, Norepinephrine, Epinephrine
Tyrosine
Thyroxine (T3)
Triiodothyronine (T3)
Which amines have a similar mechanism to peptide hormones
Catecholamines
Which amines have a similar mechanism to steroid hormones
Thyroid hormones
Name the only amine hormone not derived from Tyrosine
Melatonin which is derived from tryptophan
Why are steroid hormones synthesised directly and released
Lipophillic so cannot be retained within lipid membranes
Why are steroid hormones transported by carrier proteins
Poorly soluble in water which increases their half-life (60-90 mins vs 2 mins)
Steroid hormones are produced by
- Gonads (testes and ovary) – sex steroids
- Placenta - hCG, sex steroids
- Kidney - Vitamin D3
- Adrenal cortex - corticosteriods
Where are steroid hormones receptors located and why
their receptors are located inside cells (cytoplasmic or nuclear receptors) and trigger either activation or repression (inhibition) of gene function within the nucleus = genomic effect.
Lipophilic and can travel easily inside and out of cell
What type of steroid hormone can diffuse across capillary walls to target cells
Unbound free steer/thyroid hormone
What is the Law of Mass Action
dictates that as free hormone leaves the plasma (taken up by cells) more hormone is released from the carriers. Typically only minute quantities of hormone are required for physiological functions.
