Lecture 1 Flashcards
What is Homeostasis?
“Standing still”
Dictionary = The tendency towards a relatively stable equilibrium between independent elements, especially as maintained by physiological processes.
When and by whom was the concept of Homeostatis developed?
It was developed by American physiologist Walter Bradford Cannon in the 1920’s.
However, it can be traced back to the 1860’s to French physiologist Claude Bernard, who introduced the term ‘Milieu interieur’.
What are the properties of external vs internal?
External has variable chemical composition, variable temperature and a high entropy whereas Internal has a constant chemical composition, a constant temperature and a low entropy.
What is the general Homeostatic principle?
(Think of a see-saw!)
There is a variable on a set point which is the ‘steady-state balance.’ If there is a disturbance, sensors detect it and this triggers an effector which counteracts the disturbance.
This applies to every body parameter: water balance, ion concentrations and temperature.
On what level is Homeostasis important?
On all levels :-
Whole organisms, specific organs/physiological systems, individual cells.
What variables need to be controlled in homeostasis?
Nutrient/water intake (TO) waste product excretion.
Body temperature
Ion concentrations, pH
How is homeostasis maintained at the cellular level?
Cellular composition has to be kept within narrow range for cell function, this includes ions, small ions, water and pH.
Tell me a brief revision of cell compartments.
Cells are compartmentalised (eg - mitochondria, vesicles) and these have specific functions that require specific conditions, e.g. pH and calcium concentration.
Name the pH variations of the following compartments:- Mitochondrial matrix Extracellular fluid Cytosol Secretory vesicles Lysosomes, Endosomes
Mitochondrial matrix = 7.7 Extracellular fluid = 7.4 Cytosol = 7.1 Secretory vesicles = 5-6 Lysosomes, Endosomes = 4.6-6
Name the variations in calcium concentrations in the following compartments:- Mitochondrial matrix Endoplasmic/Sarcoplasmic reticulum Extracellular fluid Cytosol
Mitochondrial matrix = perhaps up to mM (milli-molar)
Endoplasmic/Sarcoplasmic reticulum = up to mM
Extracellular fluid = around 2mM
Cytosol = 10-100 nM (nano-molar)
How much of the following are in the Intracellular fluid (mmol/L)? Sodium Potassium Chlorine Bicarbonate Calcium - Ionised Pi - Ionised
Sodium = 10-15 Potassium = 120-150 Chlorine = 20-30 Bicarbonate = 12-16 Calcium Ionised = around 10^-7 Pi - Total and Ionised = 0.5-0.7
How much of the following are in the Extracellular fluid (mmol/L)? Sodium Potassium Chlorine Bicarbonate Calcium - Total Pi - Total
Sodium = 135-147 Potassium = 3.5-5 Chlorine = 95-105 Bicarbonate = 22-28 Calcium Total = 2.1-2.8 Calcium Ionised = 1.1-1.4 Pi Total = 1.0-1.4 Pi Ionised = 0.5-0.7
What is epithelia and what does it do?
The interface between the internal environment of the body and the external space (skin, lungs, intestine).
Epithelia maintains constant composition and volume of the extracellular fluid.
What does the extracellular fluid do?
The extracellular fluid provides a stable environment for cells and this is important for the health of cells.
How is homeostasis achieved? How is this possible?
The regulated exchange of ions and molecules between: - the intracellular fluid (cytosol) and extracellular fluid and
- the cytosol and intracellular compartments.
This is possible due to the nature of the cell membrane, it is made of lipids and up to 50% protein.
