Hypoxia

Question 1

hypoxia

Answer 1

deficiency of oxygen at the tissue level

Question 2

causes of hypoxia

Answer 2

hypoxic hypoxia - arterial co2 reduced
anemic hypoxia - arterial o2 normal but oxygen content of blood reduced due to not enough erythrocytes, deficient/abnormal hemoglobin, carbon monoxide
ischemic hypoxia - blood flow to tissues reduced
histotoxia hypoxia - amount of oxygen to tissues is normal, cell can’t utilise it due to toxic agent affecting metabolic machinery

Question 3

hypercapnia

Answer 3

increased arterial co2

Question 4

hypercapnia and oxygen therapy

Answer 4

primary respiratory drive is hypoxia, as reflex ventilatory response to increased co2 may be lost in chronic situations
may cause them to stop breathing
mix of air and o2

Question 5

causes of hypoxic hypoxia

Answer 5

hypoventilation
diffusion impairment
shunt
ventilation-perfusion inequality

Question 6

hypoventilation

Answer 6

caused by:
defect along respiratory control pathway, from medulla to respiratory muscles
severe thoracic cage abnormalities
major obstruction of upper airway

hypoxemia accompanied by increased arterial co2

Question 7

diffusion impairment

Answer 7

thickening of alveolar membranes or a decrease in their SA
blood o2 and alveolar o2 fail to equilibrate
co2 is normal due to it diffusing more readily than o2 or reduced if hypoxemia stimulates ventilation

Question 8

shunt

Answer 8

anatomical abnormality of CVS causing mixed venous blood to bypass ventilated alveoli in passing from the right side to left side of heart
intrapulmonary defect where mixed venous blood perfuses unventilated alveoli - co2 doens’t increase because its effect is counterbalanced by ventilaion from hypoxemia

Question 9

ventilation-perfusion inequality

Answer 9

copd

arterial co2 normal or increased

Question 10

ventilation-perfusion inequality

Answer 10

cause hypoxemia w/out increases in co2
increase in o2 doesn’t add much to haemoglobin that is already almost 100% saturated
poorly ventilated diseased alveoli contribute blood with low oxygen to pulmonary vein/whole circulation
increased ventilation -> minimal increase in o2 saturation
HCO3- doesn’t reach saturating levels, so increased ventilation lowers CO2 to below normal levels, and when mixed w/ blood from other areas, co2 levels are normal

Question 11

emphysema

Answer 11

loss of elastic tissue and destruction of alveolar walls leading to increased compliance. atrophy and collapse of lower airways. lungs are attacked by proteolytic enzymes produced by leukocytes in response to factors - e.g. smoking

Question 12

consequences of alveolar wall loss

Answer 12

adjacent alveoli fuse to form fewer, larger alveoli. loss of pulmonary capillaries
reduces total SA
not uniform throughout lungs - ventilation-perfusion inequality

Question 13

airway resistance

Answer 13

increases work of breathing and hypoventilation

caused by collapse of lower airways, especially during expiration (loss in elastic tissue)

Question 14

2 factors passively holding the airways open

Answer 14

transpulmonary pressure

lateral traction of connective-tissue fibres attached to airway exteriors

Question 15

summary of symptoms of emphysema

Answer 15

decreased elastic recoil of lungs
increased airway resistance
low SA
ventilation-perfusion inequality: some hypoxia, if disease is extensive, increased co2

Question 16

atmospheric pressure and altitude

Answer 16

progressively decreases as altitude increases

Question 17

atmospheric pressure on Mt. Everest, and sea level

Answer 17

253mmHg

760mmHg

Question 18

alveolar and arterial pressure at altitude

Answer 18

o2 decreases as people ascend, unless they breathe pure oxygen

Question 19

mountain/altitude sickness

Answer 19

ascending rapidly to altitudes above 10000ft
breathlessness, headache, nausea, vomiting, insomnia, fatigue, impairment of mental processes, pulmonary edema, brain edema

Question 20

pulmonary edema

Answer 20

leakage of fluid from pulmonary capillaries into alveolar walls and eventually airspaces
pulmonary hypertension, as pulmonary arterioles constrict in presence of low oxygen

Question 21

treatments for mountain sickness

Answer 21

supplemental oxygen and diuretic therapy - reduce blood pressure by promoting water loss in urine. reduces amount of fluid leaving capillaries in lungs and brain

Question 22

compensatory mechanisms in high altitudes

Answer 22

peripheral chemoreceptors increase ventilation
erythropoietin
DPG increases and shifts oxygen-haemoglobin dissociation curve to right, facilitating oxygen unloading in tissues
increases in skeletal muscle capillary density, # mitochondria, muscle myoglobin transfer - increase o2
decreased plasma volume -> increased conc erythrocytes and hemoglobin

Question 23

what causes skeletal muscle capillary density increases?

Answer 23

hypoxia-induced expression of genes coding for angiogenic factors