1 Homeostasis

Question 1

Definition of homeostasis

Answer 1

The process whereby cell, tissues and organisms maintain the status quo.
Homeo: sameness
Stasis: standstill

Question 2

What parameters need to be kept constant?

Answer 2

Concentration of O2, CO2, salts and electrolytes.
Concentrations of nutrients and waste products.
pH of internal environment.
Temperature of internal environment.
Volume and pressure of body fluid compartments

Question 3

What is a negative feedback loop?

Answer 3

A response to a stimulus causing a reaction to bring the system back to baseline/ stabilise it.

Question 4

Examples of negative feedback loop

Answer 4

Core body temperature:
Too hot: vasodilation, sweating, pilorelaxation, stretching out.
Too cold: vasoconstriction, shivering, piloerection, curling up.

Eating:
Incr BM (stimulus) —> detected by pancreas —> pancreas secretes insulin —> Liver uptake of glucose incr (stored as glucagon)—> BM returned to baseline.

Question 5

Positive Feedback Loop definition

Answer 5

The output enhances or exaggerates the original stimulus.

Loop is stopped when initiator ceases.

Question 6

Examples of positive feedback loops:

Answer 6

Regulation of blood clotting:
Break/tear of blood vessel wall —> FEEDBACK CYCLE INITIATED—>clotting occurs as platelets adhere to site and release chemokines —> chemokines attract more platelets —> clotting proceeds, newly formed clots grow —> feedback cycle ends when clot seals wall break.
Giving birth:
Baby pushes against cervix causing stretch—> stretching cervix causes impulses to be sent to the brain —> brain stimulates pituitary to release oxytocin —> oxytocin causes uterus to contract—> feedback look stops when baby is born.

Question 7

Core Body Temperature

Answer 7

36. 5-37.5 —> fluctuates throughout day and circadian rhythm.
    - Pregnant women have a higher baseline of 37.4
    - Heat stroke: 40+
    - Hypothermia: 36.4 below
    - No vital signs: 28 below

Question 8

pH

Answer 8

Normal blood pH: 7.35-7.45
If lower: acidosis
If higher: alkalosis
—> Blood is slightly alkaline due to proteins.
Lungs maintain this short term
Kidneys maintain this long term

Question 9

Lungs and pH

Answer 9

Fast acting
If blood is too acidic (can be due to incre metabolism or lactic acid build up) then respiratory rate will increase to excrete excess CO2 and increase the blood pH

Question 10

Kidneys and pH

Answer 10

Can excrete or retain both H+ and HCO3-
If blood too acidic: excrete H+ and retain HCO3-
If blood too alkylotic: retain H+ and excrete HCO3-

—> powerful mechanism but takes a few days to bee effective

Question 11

Acidity

Answer 11

Gastric pH: 1.5-3.5
—> if stomach loses mucus lining then acid can cause ulceration or perforation of the tissue.

PH is a key stimulator of tumorogenesis:

5. 8pH cancer cells can form
6. 5pH death

Question 12

pH [H+] calcs

Answer 12

[H+] change of factor of 2 causes pH change of 0.3
Eg pH 7.4 : 40 [H+]
PH 7.1 : 80 [H+]

Question 13

Buffering systems in body examples intracellular and extracellular?
Neutraliser examples?

Answer 13

Intracellular fluid buffer:
- Protein buffer systems: amino acid buffers, plasma protein buffers, haemoglobin buffers.
- Phosphate buffer system.
Extracellular fluid buffer:
- Protein buffer systems as above.
- Carbonic acid bicarbonate buffer system.

Neutraliser: anacids and aluminium hydroxide.

Question 14

Total body mass:
Solids?
Fluids?
Differences in percentages?

Answer 14

40% solid
60% fluids —> 2/3 ICF
                      —> 1/3 ECF: 80% interstitial fluid
                                                 20% plasma
Differences in water content:
Infants: 70%
Men: 60%
Women: 50%
Increase body fat, decrease TBW%

Question 15

Isotonic? Hypotonic? Hypertonic?

Answer 15

Iso: amount of water inside and outside cell is equal
Hypo: less water outside cell so moves into cell causing cell swelling and bursts.
Hyper: less water inside cell as water has moved out of cell causing cell to shrink.

Question 16

Dehydration

Answer 16

Less urine output, increased osmolarity, increased ADH
—> use an isotonic solution (0.9% NaCl)
—> bulk water movement is fast acting. Controlled by aquaporins (ATP) and glycerol

Question 17

Osmolarity vs Osmolality

Answer 17

Osmolarity:
[solution] expressed as osmoles of solute particles perL of solution.
Calculate with volume of solution.
Mol/L
Temperature and pressure dependant
Osmolality:
[solution] expressed as a total number of solute particles per kg
Calculate with mass of solution
Osmol/L
No dependance

Question 18

Osmolality calculations

Answer 18

Can be used clinically for serum and urine.
Increased serum and urine osmolality if dehydrated.

When calculating remember:
Glucose and urea: 1mmol/L: 1mosmole
Solutes (NaCl, K): 1mmol/L: 2mosmole

Question 19

Odema:
What is it?
What causes it?
What diseases is it seen in?

Answer 19

Aka dropsy.
It is fluid retention. Normally the swelling of ankles.
Happens when hydrostatic pressure is greater than the osmotic pressure so more water is driven out into the interstitial spaces. May also be because lymphatic system may be blocked so fluids cant get back into the system. Also maybe due to oncotic pressure (pressure exerted by proteins eg albumin).

Diseases: heart failure, liver cirrhosis and renal disease.