Homeostasis Flashcards
Define homeostasis.
The tendency towards a relatively stable equilibrium between interdependent elements
Especially as maintained by physiological processes
What is negative feedback?
Output reduces the original effect of the stimulus
What is positive feedback?
Output increases the original stimulus
Give 3 methods of cell communication.
Autocrine
Paracrine
Endocrine
What does Autocrine mean?
A cell-produced substance that has an effect on the cell that secretes it
What does paracrine mean?
A hormone which has effect only in the vicinity of the gland secreting it
What does endocrine mean?
Glands which secrete hormones or other products directly into the blood
What ways can water enter the body?
Drinks, food, IV
What ways can water leave the body?
Kidneys - excretion GI - faeces, vomit Blood loss from wounds, internal bleeding Sweating Breathing
What does ‘insensible loss’ mean?
Water loss that can’t be measured! For example sweat, breathing
Name the 2 fluid compartments water is found in in the body. % in each?
Intracellular fluid - 67%
Extracellular fluid - 33%
There are 2 types of extracellular fluid - describe them and give values.
Interstitial (75-80%) - solution surrounding cells
Intervascular (20-25%) - blood plasma
What hormones influence the balance of water in the body?
ADH - anti diuretic hormone (also known as vasopressin)
Aldosterone
ANP - atrial natriuretic peptide
Briefly describe the function of ADH. Also where is it released?
Retain water in the body by increasing water reabsorption in the collecting ducts of the nephron
Also constricts blood vessels
Stored and released from posterior pituitary
How does ADH increase reabsorption of water in the collecting duct of the tubule?
Induces translocation of aquaporin water channels in the plasma membrane of the collecting duct. (This also occurs in the DCT)
Briefly describe the function of aldosterone. Also where is it released?
From adrenal cortex of adrenal gland.
Causes retention of sodium, secretion of potassium, water retention and an increase in BP and blood volume
Activates Na+/K+ pumps in membranes of DCT and collecting ducts of nephrons
Briefly describe the function of ANP. Also where is it released?
Secreted by atrial heart muscle cells
Acts to reduce water, sodium and adipose loads in the bloodstream - thus reducing blood volume and BP
Also a vasodilator
Define osmotic pressure.
Pressure that would need to be applied to a solvent to prevent it passing into a given solution by osmosis
Used to express concentration
Define oncotic pressure.
A form of osmotic pressure exerted by proteins (notably albumin)
Tends to pull fluid into circulatory system
What is oedema?
Excess fluid in the interstitium (fluid that surrounds tissue cells)
Name 4 types of oedema.
Inflammatory
Venous
Lymphatic
Hypoalbuminaemic
What causes inflammatory oedema?
Vascular permeability
Fluid and cells leave the vessels, protein follows. More fluid is in the interstitium.
What is interstitial fluid?
A solution that bathes and surrounds the tissue cells of multicellular animals.
What causes venous oedema?
High pressure in the circulatory system forces fluid out into interstitium
