Homeostasis Flashcards
Define homeostasis
Maintenance of a constant internal environment
Describe a simple feedback loop
Set point
Control centre
Effector
Regulated variable
Sensor
Back to the control centre
What are the two communication types in homeostasis
Endocrine - hormones
Nervous - electrical
Define autocrine signalling
Cells talking to themselves
Define paracrine signalling
Cells talking to neighbouring cells a short distance away
- signal diffuses across gaps between cells
- inactivated locally, so does not enter the blood stream
Does paracrine signalling enter the blood stream
No
Give two examples of paracrine signalling
Interleukins
Platelet derived growth factor
Describe interleukins
Signalling in the immune system
Mainly between white blood cells
Describe platelet derived growth factor
Released from platelets
Regulates cell growth
Describe endocrine signalling
Cells talking to other cells elsewhere in the body
Name the endocrine organs
Hypothalamus
Pituitary
Thyroid
Adrenals
Pancreas
Ovaries
Testes
Define a hormone
Molecule that acts as a chemical messenger
What are the classifications of hormones
By structure
- amino-acid derivatives
- peptide
- steroid
Describe peptide hormones
Made of amino acids
Vary in size from few amino acids to small proteins
Some have carbohydrate side chains (glycoproteins)
Hydrophilic (like water)
Do peptide and amino acid hormones produce a quick or slow response in the body
Quick
Describe the route of a peptide hormone
Hormone pre-made and stored in a cell ready to be released when needed
Hormone dissolved in blood
Receptor on cell membrane
Chemical reactions produces quick response from cell - signal transduction cascade
Describe steroid hormones
All made from cholesterol
Different enzymes modify molecule to produce a variety of hormones
Cannot dissolve in water
Can dissolve in lipids
Do steroid hormones produce a quick or slow response
Slow
Describe the route of a steroid hormone e.g. testosterone
Testosterone made by cell and diffuses out once made
Transported in blood bound to transport protein as cannot dissolve in water
Receptor is in target cell
Slow response as directly affects DNA
Of a 70kg male what is the total body water % and L
60%
42L
Of a 70kg male what is the intracellular fluid % and L
40%
28L
Of a 70kg male what is the extracellular fluid % and L
20%
14L
Of 14L of extracellular fluid what is intravascular
3L
Of 14L of intracellular fluid what is interstitial
11L
Describe ECF
Na main
Anions Chloride and bicarbonate
Glucose and urea
Protein
Describe ICF
Main K
Describe interstitial fluid
Surrounds the cells but does not circulate
What is the calculation for estimated plasma osmolality
2Na + 2K + urea + glucose mmol/L
What osmolality are equal
Intra and extracellular
What is normal plasma osmolality
275-295 mmol/Kg
What are the consequences of dehydration
Thirst
Dry mouth
Inelastic skin
Sunken eyes
Raised haematocrit
Weight loss
Confusion - brain cells
Hypotension
What are the consequences of water excess
Hyponatraemia
Cerebral overhydration
- headache
- confusion
- convulsions
Define hydrostatic pressure
Pressure difference between plasma and interstitial fluid
Water moves from plasma into interstitial fluid
Define oncotic pressure
Pressure caused by the difference in protein concentration between the plasma and interstitial fluid
Water moves from interstitial fluid into plasma
Describe oedema
Excess accumulation of fluid in interstitial space
Disruption of the filtration and osmotic forces in circulating fluids
- obstruction of venous blood or lymphatic return
- inflammation = increased capillary permeability
- loss of plasma protein
Define serous effusion
Excess water in body cavity
What are the reasons for oedema and serous effusion
Increased fluid leakage into interstitial spaces OR impaired reabsorption of fluids
Describe transudate serous effusion
Fluid is pushed through the capillary due to high pressure within the capillary
Low protein content
Describe exudate serous effusion
Fluid leaks around the cells of the capillaries caused by inflammation and increased permeability of pleural capillaries to protein
High protein content
Normal reference range for sodium
135-145 mmol/L
What is the range for serum calcium
2.1-2.6 mM
50% serum calcium ionised (free)
50% bound to albumin (so cannot diffuse into cells)
What are the three routes to get to serum calcium
GI - Vit.D
Kidney - PTH/Vit.D/FGF23
Bone - PTH/Vit.D
