Lecture 1 - Homeostasis, Body Fluids, pH & Temperature Flashcards
Define homeostasis + name 4 things that need to be maintained constant in the internal environment.
Homeostasis is the physiological process by which internal systems of the body are maintained at equilibrium, despite variations in internal and external factors.
- Concentration of O2, CO2 + electrolytes
- Concentration of nutrients (glucose, AA’s etc)
- pH
- Temperature
What are the 4 components required for a homeostatic feedback loop to work?
- The variable (e.g.: temperature/blood glucose)
- The sensor (e.g.: nerve cells in skin)
- The control centre (e.g.: hypothalamus)
- The effector (e.g.: muscle)
Describe how an increase or decrease in temperature. is controlled by a negative feedback loop?
Describe at least 3 effector mechanisms for heating up and cooling down.
1) Receptors in skin alert brain of temp change
2) Hypothalamus (control centre) then alerts effectors
3) Effectors return temp to set point
- Vasodilation vs Vasoconstriction
- Sweating vs Shivering
- Pilorelaxation vs piloerection
Give 2 examples of positive feedback loops + how they work.
When does positive + negative feedback stop?
1) Blood clotting - break in blood vessel wall causes release of chemokines which attract platelets to adhere to blood vessel wall. This causes further attraction of platelets until clot is formed and loop is stopped.
2) Stretching of cervix during birth - causes oxytocin release from pituitary. This binds to cervix wall and causes further stretching.
Positive feedback stops = when the initiator ceases
Negative feedback stops = when the effector ceases
What is core body temperature? When does it fluctuate?
- 37 degrees C +/- 0.5
- Throughout the day or during menstrual cycle for women (decreases during ovulation)
What is the normal body pH range & What are the 2 major organs that control Acid-Base balance?
- 7.35-7.45
1) Lung-respiratory balance
2) Kidney-metabolic balance
What are the 2 main buffer systems used to regulate pH levels?
- Carbonic-Bicarbonate Buffer System
- Phosphate buffer system
In a standard 70kg male, what % does water make up?
How much water is in the IC and EC? - describe compartments for EC
- 60% (42L)
- 2/3 of water is ICF = 28L
- 1/3 of water if ECF = 14L
- of the 1/3, 75% is IF (10.5L) & 25% is in plasma (3.5L)
How much blood is there in a standard 70kg male?
- 5L
State the total body water (TBW) % in normal, lean and obese males, females and infants.
Males - 60%, 70%, 50%
Females - 50%, 60%, 42%
Infants - 70%, 80%, 60%
Remember - more % body fat = less % water
In terms of red blood cells, explain the terms isotonic, hypotonic & hypertonic
Isotonic = Same amount of water on both sides of membrane. Hypotonic = Less water inside the cell Hypertonic = Less water outside the cell
What happens to hypotonic and hypertonic RBC’s?
Hypo = Cell bursting/lysis Hyper = Cell shrinkage/shrivelling
What happens in the body during dehydration (due to sweating, vomiting, burns etc) ]
What happens to the body in water toxicity?
- Water loss, leading to increase in plasma osmolality –> ADH release –> oliguria (decreased urine)
- High osmotic pressure –> Cells absorb water and swell –> enzymes and proteins stop working –> Cells continue to swell until they burst –> patients need isotonic solution.
What is oedema? Describe the process of oedema.
- Oedema is fluid retention in interstitial space.
- This occurs when hydrostatic pressure (pressure from blood vessels) exceeds oncotic pressure (pressure trying to put water back into capillaries), therefore water is drawn out into interstitial spaces and accumulated.
What is osmolality and what units are used to measure it?
How is osmolality measured for solutes that are ionised?
What is the normal range for osmolality?
- The concentration of a solution expressed as total number of solute particles per kg - mOsm/kg
- E.g.: NaCl - can dissociate into Na+ and Cl-, therefore each mM in solution would provide 2 mOsm. E.g.: 140mmol/L Na+ and 5mmol/L K+ = (140 x 2) + (5 x 2) = 290 mOsm/kg.
- 280-300 mOsm/kg.
