Physiology of Breathing

Question 1

mechanics of breathing

Answer 1

diaphragm used for quiet breathing
inspiratory muscles contract
increases thoracic volume
decreased thoracic pressure
air pushed in along pressure gradient
expiration is passive
intercostal & accessory muscles are used in more forceful breathing

Question 2

effect of posture on breathing

Answer 2

movement of diaphragm complicated by abdominal cavity & its contents
facilitated in sitting position as opposed to a lying position

Question 3

FEV1

Answer 3

forced expiratory volume in 1 second

Question 4

tidal volume

Answer 4

represents air moving in and out of the lung in quiet breathing

Question 5

tidal volume

Answer 5

450ml
300ml of this reaches alveoli for ventilation
150ml lost to anatomical dead space i.e. non conducting zone

Question 6

pulmonary gas exchange

Answer 6

occurs between the alveolar air & pulmonary capillary blood
gases move across alveolar wall by diffusion
diffusion is determined by partial pressure gradients

Question 7

partial pressure in alveoli & artery

Answer 7

is the same due to the equity of exchange

Question 8

ventilation v perfusion

Answer 8

ventilation is the flow of air in and out of the alveoli while perfusion is the flow of blood to the alveolar capillaries

Question 9

relationship between ventilation & perfusion

Answer 9

they are matched
they vary in different parts of the lung in an upright person
V and Q are greater at base of lung and reduce as they move towards the apex
these differences are less marked when prone

Question 10

PP of mixed venous blood and arterial blood

Answer 10

MVB:
PO2 = 40mmHg
PCO2 = 46mmHg
arterial =
PO2 = 100mmHg
PCO2 = 40mmHg

Question 11

how does N2O travel in the body

Answer 11

carried in simple solution in the blood
it does not bind to haemoglobin

Question 12

haemoglobin

Answer 12

globular protein made of 2 alpha and 2 beta chains with 4 haem groups
Fe reversibly binds O2
200-300 Hb molecules / RBC

Question 13

oxygen transport

Answer 13

O2 transported via:
attached to haemoglobin (97%)
dissolved in plasma (3%)
with increased inspired PO2 e.g. breathing pure O2 or hyperbaric O2 there is little increase in O2 bound to Hb and amount dissolved is increased in proportion to PO2

Question 14

CO2 transport

Answer 14

CO2 transported in erythrocytes & plasma
& is transported as:
dissolved CO2 (10%)
combined to protein (20%)
bicarbonate ions (70%)

Question 15

control of breathing

Answer 15

1. cerebral cortex
2. central chemoreceptors (decrease pH, increase PCO2 CSF)
3. joint & muscle receptors - movement
4. breathing muscles
5. lung stretch receptors - inflation
6. peripheral (arterial) chemoreceptors - decrease PO2 & increase PCO2

Question 16

what is hypoxia

Answer 16

decreased O2 delivery to tissues

Question 17

hypoxic hypoxia

Answer 17

decreased O2 reaching alveoli and decreased diffusion into blood

Question 18

cyanosis

Answer 18

blue colouration of skin & mucous membranes
due to >5gm deoxygenated Hb

Question 19

central cyanosis

Answer 19

affects whole body & evident in oral tissues
generally due to decreased O2 delivery to blood
- low atmospheric PO2
- decreased airflow in airways (obstruction)
- decreased O2 diffusion into blood
- decreased pulmonary blood flow

Question 20

peripheral cyanosis

Answer 20

due to decreased O2 delivery to a localised & peripheral part of the body
often due to decreased blood flow to tissues - stagnant hypoxia
peripheral vascular diseases can cause