Homeostasis, oedema, body fluids 1 Flashcards
What is negative feedback?
A feedback loop which only stops when the effector returns to normal, which is detected by the sensor/control centre
What is positive feedback?
A feedback loop which only stops when the initiator ceases
What is the normal range for body pH and how is it controlled?
7.35 (veins) - 7.45 (arteries) Respiratory balance (lungs, short term) Metabolic balance (kidneys, long term)
How do you treat acidosis?
Hypoventilation, so increase breathing rate to decrease CO2 levels in the blood, breathe out a lot
Kidneys excrete H+ and retain HCO3-
How do you treat alkalosis?
Hyperventilation, so reduce breathing rate, breathe into bag to increase CO2 levels
Kidneys retain HCO3- and excrete H+
What is the normal range for gastric pH?
1.5 - 3.5
In what pH range can human tissue survive?
6.8 - 7.8
How can you work out changes in pH from [H+] and vice versa without using a calculator?
pH at [H+] = 100 is pH 7.0
[H+] x 2 = pH + 0.3
Briefly describe the two most common buffering systems in the body
Carbonic acid/bicarbonate - regulates blood pH
Sodium phosphate - regulates other cells and intercellular pH
When are antacids used?
They neutralise acids because they’re alkaline
Used if epithelial cells are damaged by gastric juice in the oesophagus and pharynx (vomiting)
Which antacid is used most commonly and why?
Aluminium Hydroxide, as even though it’s only mildly alkaline it’s insoluble
How do you measure the pH of an arterial blood sample?
Arterial Blood Gas
Why does fluid balance in the body have to remain right?
To avoid dehydration, metabolic failure and toxicity
How does total body water (TBW) differ between age and sex and why?
Infants - highest Adults - lowest Elderly - high Males have higher TBW than females Higher body fat % = lower TBW % Water stored mainly in muscle cells so lean % > normal % > obese %
What has the highest TBW?
An unfertilised egg (zygote)
What does isotonic mean?
Same amount of water inside and outside the cell
What does hypertonic mean?
[Solute] is higher outside the cell so water moves out, shrinking the cell and resulting in more water outside the cell
What does hypotonic mean?
[Solute] is higher inside the cell so water moves in, so the cell swells up and lyses
What happens over time if an organism is dehydrated?
Cells absorb water from interstitial space
Then each other (cell death)
Then organs (tissue death)
Then brain, liver, kidneys and heart (death)
How does water move across a membrane?
2 ways;
Osmosis - it is a small and neutral molecule so it can just diffuse through the cell membrane
Via the aquaporin protein - when it is moving in bulk
When water moves in bulk across a membrane, what protein transports it? How is this regulated?
Aquaporin protein
Different isoforms exist (fast/slow)
Prevalence of isoforms is regulated by the amount of glycerol in the cell
What is hydrostatic pressure?
Pressure exerted by the blood pushing against walls of capillaries, so pushes water out
What is oncotic pressure also known as?
Colloid osmotic pressure
What is oncotic pressure?
Pulls fluid into capillaries and/or prevents fluid from leaving because of the proteins that do not leave the capillary and so draw water in (mainly albumin)
What happens if there is too much water in an organism?
Osmotic pressure is high, cells absorb water and swell, enzymes and proteins stop working and cells continue to swell until they burst
How do you treat a patient who has too much water in their system?
Give them an isotonic solution of saline through an IV drip, 0.9% NaCL
What is the difference between osmolality and osmolarity?
Osmolality (mOsm/kg) doesn’t depend on pressure and temperature, and it considers the mass of solution
Osmolarity (mmol/L) does depend on pressure and temperature and it considers volume
How is osmotic pressure of tissue measured?
In plasma and urine
If both are high it suggests dehydration and vice versa
If given plasma concentrations of various solutes, how can you work out the osmolality of each and total osmolality?
Glucose or urea - same (1:1)
Solutes that ionise (eg. NaCl) each mmole in solution = 2 mOsmoles
e.gg [plasma] sodium = 140mmol/L (x2), potassium = 5 (x2), urea = 5 (x1) and glucose = 5 (x1) so total osmolality = 300mOsm/kg
What is an oedema?
Swelling (most commonly of ankles) resulting from retention of fluid
During oedema, what happens to the hydrostatic and oncotic pressures?
Hydrostatic pressure > oncotic pressure so water is drawn out into the IS spaces
This results in the plasma proteins being in the IS space, and lymphatics are blocked or damaged
Name 5 factors that need to be kept constant in the internal environment?
Concentration of oxygen Concentration of carbon dioxide Concentration of electrolytes Concentration of nutrients Concentration of waste products pH Temperature Volume and pressure of body fluid compartments
What is the normal human body temperature range?
37 +/- 0.5 °C
In the menstrual cycle, when does the body temperature rise? What temperature does it rise to?
3-4 days before ovulation
37.4°C
