Homeostasis, oedema, body fluids (BL 1)

Question 1

What is negative feedback?

Answer 1

A feedback loop which only stops when the effector returns to normal, which is detected by the sensor/control centre

Question 2

What is positive feedback?

Answer 2

A feedback loop which only stops when the initiator ceases

Question 3

What is the normal range for body pH and how is it controlled?

Answer 3

7.35 (veins) - 7.45 (arteries)
Respiratory balance (lungs, short term)
Metabolic balance (kidneys, long term)

Question 4

How do you treat acidosis?

Answer 4

Hypoventilation, so increase breathing rate to decrease CO2 levels in the blood, breathe out a lot
Kidneys excrete H+ and retain HCO3-

Question 5

How do you treat alkalosis?

Answer 5

Hyperventilation, so reduce breathing rate, breathe into bag to increase CO2 levels
Kidneys retain HCO3- and excrete H+

Question 6

What is the normal range for gastric pH?

Answer 6

1.5 - 3.5

Question 7

In what pH range can human tissue survive?

Answer 7

6.8 - 7.8

Question 8

How can you work out changes in pH from [H+] and vice versa without using a calculator?

Answer 8

pH at [H+] = 100 is pH 7.0

[H+] x 2 = pH + 0.3

Question 9

Briefly describe the two most common buffering systems in the body

Answer 9

Carbonic acid/bicarbonate - regulates blood pH

Sodium phosphate - regulates other cells and intercellular pH

Question 10

When are antacids used?

Answer 10

They neutralise acids because they’re alkaline

Used if epithelial cells are damaged by gastric juice in the oesophagus and pharynx (vomiting)

Question 11

Which antacid is used most commonly and why?

Answer 11

Aluminium Hydroxide, as even though it’s only mildly alkaline it’s insoluble

Question 12

How do you measure the pH of an arterial blood sample?

Answer 12

Arterial Blood Gas

Question 13

Why does fluid balance in the body have to remain right?

Answer 13

To avoid dehydration, metabolic failure and toxicity

Question 14

How does total body water (TBW) differ between age and sex and why?

Answer 14

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 %

Question 15

What has the highest TBW?

Answer 15

An unfertilised egg (zygote)

Question 16

What are the three types of tonicity?

Answer 16

Isotonic, hypertonic, hypotonic

Question 17

What does isotonic mean?

Answer 17

Same amount of water inside and outside the cell

Question 18

What does hypertonic mean?

Answer 18

[Solute] is higher outside the cell so water moves out, shrinking the cell and resulting in more water outside the cell

Question 19

What does hypotonic mean?

Answer 19

[Solute] is higher inside the cell so water moves in, so the cell swells up and lyses

Question 20

What happens over time if an organism is dehydrated?

Answer 20

Cells absorb water from interstitial space
Then each other (cell death)
Then organs (tissue death)
Then brain, liver, kidneys and heart (death)

Question 21

How does water move across a membrane?

Answer 21

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

Question 22

When water moves in bulk across a membrane, what protein transports it? How is this regulated?

Answer 22

Aquaporin protein
Different isoforms exist (fast/slow)
Prevalence of isoforms is regulated by the amount of glycerol in the cell

Question 23

What is hydrostatic pressure?

Answer 23

Pressure exerted by the blood pushing against walls of capillaries, so pushes water out

Question 24

What is oncotic pressure also known as?

Answer 24

Colloid osmotic pressure

Question 25

What is oncotic pressure?

Answer 25

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)

Question 26

What happens if there is too much water in an organism?

Answer 26

Osmotic pressure is high, cells absorb water and swell, enzymes and proteins stop working and cells continue to swell until they burst

Question 27

How do you treat a patient who has too much water in their system?

Answer 27

Give them an isotonic solution of saline through an IV drip, 0.9% NaCL

Question 28

What is the difference between osmolality and osmolarity?

Answer 28

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

Question 29

How is osmotic pressure of tissue measured?

Answer 29

In plasma and urine

If both are high it suggests dehydration and vice versa

Question 30

If given plasma concentrations of various solutes, how can you work out the osmolality of each and total osmolality?

Answer 30

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

Question 31

What is an oedema?

Answer 31

Swelling (most commonly of ankles) resulting from retention of fluid

Question 32

During oedema, what happens to the hydrostatic and oncotic pressures?

Answer 32

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