Physiology Flashcards
Describe Fick’s Law
Fick’s law states that the rate of diffusion of a gas through a tissue sheet is proportional to the area of the sheet and the partial pressure difference across it, and inversely proportional to the thickness of the sheet.
Under which circumstances is oxygen transfer diffusion limited?
Diffusion limitation of O2 may occur during intense exercise, thickening of the blood-gas barrier and alveolar hypoxia (high altitude).
How to you convert mmHg to kPa
Divide the figure by approx 7.5
Right atrial pressure
4-12 mmHg
Right ventricular pressure
28/4 mmHg ( 15-30 / 0-8) mmHg
Pulmonary artery pressure
25/12 mmHg
Left atrial pressure
Mean of 8 mmHg
Left ventricular pressure
125/8 mmHg (90 - 140 / 4 - 12) mmHg
The Pasteur Point
The Pasteur Point is the oxygen concentration below which oxidative phosphorylation cannot occur in the mitochondria. It is considered to be around 1 mmHG (0.13 kPa).
Hüffner’s constant
It describes the volume of O2 (in ml) that can combine with each 1g of Hb. IN Vitro 1.30, in vivo 1.34.
Typical oxygen consumption at rest
250 - 500 ml/min
Critical DO2 (Oxygen delivery)
The degree of oxygen delivery below which supply is inadequate to meet oxygen demand. (Typically 4-8ml/kg/min)
Oxygen extraction ratio
The Fraction of delivered oxygen that is taken up by the tissues. Typically 0.2-0.2. Varies between organs. I.e. heart is particularly sensitive to ischaemia due to an O2ER of 0.6.
Hypoxia
Insufficient supply of oxygen to the tissues to maintain normal cellular function.
Hypoxaemic hypoxia
Insufficient tissue oxygenation arising from an abnormal reduction in the partial pressure of oxygen in the arterial blood.
Anaemic hypoxia
Insufficient tissue oxygenation arising from a failure of the oxygen-carrying capacity of blood in the face of a normal partial pressure of oxygen.
Ischaemic hypoxia
Insufficient tissue oxygenation arising from a failure of perfusion.
Histotoxic hypoxia
Insufficient tissue oxygenation in the face of normal oxygen delivery due to the failure of oxidative phosphorylation.
Location of GLUT1 Receptors
Universally distributed
Location of GLUT2 Receptors
Present in Gut, Liver and Pancreatic Islets
Location of GLUT3 Receptors
Present in CNS & Brain (Insulin independent)
Location of GLUT4 Receptors
Present in insulin-responsive tissues such as skeletal muscle, adipose tissue, heart
Insulin
Is composed of two polypeptide chains (A and B) linked by disulphide bridges. The A chain contains 21 amino acids, the B chain contains 30 amino acids.
One physiological action of insulin is to increase the permeability of cell membranes to potassium, magnesium and phosphate ions. This forms the basis of treating life threatening hyperkalaemia with a glucose/insulin infusion.
During fasting, serum insulin and glucose levels fall whilst lipolysis increases.
Acetazolamide
Is a Zinc containing enzyme that inhibits carbonic anhydrase. It is found in: Erythrocytes, the nephron, Pulmonary endothelium, gut, pancreas, cardiac and skeletal muscle.
There are 7 isoenzymes known.
Isoenzyme IV is found in the brush border of the proximal convoluted tubule.
Isoenzyme II is found in luminal cells.
What Lung Volumes can be measured with a Spirometer?
Most lung volumes except TLC, FRC and RV.
How can you measure FRC
Helium dilution or body plethysmography
What does STOP-BANG stand for?
S - Snoring
T - Tiredness
O - Observed Apnoea
P - Hypertension
B - BMI >35
A - Age >49
N - Neck Circumference 41 or greater in women, 43 or greater in men
G - Gender: Male
Tell me about Calcitonin
Calcitonin is a polypeptide hormone released from the C cells of the thyroid in response to hypercalcaemia (not hypocalcaemia).
Its hypocalcaemic effects are mediated by preventing bone resorption by osteoclasts.
It is secreted in excess in patients with medullary carcinoma of the thyroid.
Causes of Increased PVR
Vasoconstrictor drugs
5-HT
Histamine
Maximal Expiration
Hypoxia
Hypercapnia
Acidosis
Causes of decreased PVR
Anaemia
Prostacycline
Acetylcholine
Vasodilator drugs
Hyperoxia
Hypocapnia
Alkalosis
