Overview and mechanics

Question 1

define internal respiration

Answer 1

the intercellular mechanisms which consumes oxygen (constant supply) and produces carbon dioxide (must be removed)

food + oxygen –> energy + carbon dioxide

Question 2

define external respiration

Answer 2

the sequence of events that lead to the exchange in oxygen and carbon dioxide between the external environment and the cells of the body
4 step process

involves 4 body systems;
respiratory, cardiovascular, haematology and nervous

Question 3

describe the 4 steps of external respiration

Answer 3

1. ventilation
2. exchange of oxygen and carbon dioxide between air in the alveoli and blood in the pulmonary capillaries (coming to the lungs)
3. transport of oxygen and carbon dioxide in the blood between the lungs and the tissues
4. exchange of oxygen and carbon dioxide between in the systemic capillaries and body cells

Question 4

explain the first step of external respiration

Answer 4

ventilation - the mechanical process of moving air between the atmosphere and air sacs, alveoli, in the lungs (moving gas in and out of the lungs)

Question 5

explain movements of gases in regards to Boyle’s Law

Answer 5

Boyle’s law - gases move from region of high to low pressure. At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas - as the volume of a gas increases, the pressure exerted by the gas decreases

before inspiration - intra-alveolar pressure is equivalent to atmospheric pressure
during inspiration - intra-alveolar pressure must become less than atmospheric pressure for air to flow into lungs. The thorax and lungs expand as a result of contraction of inspiratory muscle

Question 6

explain how lungs adhere to chest wall and follow its movement

Answer 6

2 forces hold the thoracic wall and the lungs in close opposition;

1. the intrapleural fluid cohesiveness - the water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart. Hence the pleural membrane tend to stick together
2. the negative intrapleural pressure - the sub-atmospheric intrapleural pressure create a transmural pressure gradient across the lung wall and across the chest wall. So the lungs are forced to expand outwards while the chest is forced to squeeze inwards

Question 7

explain the respiratory mechanics and relationship between atmospheric, intra-alveolar and intra-pleural pressure

Answer 7

atmospheric pressure - pressure caused by the weight of the gas in the atmosphere on the Earth’s surface, usually 760 mm Hg

intra-alveolar (intrapulmonary) pressure - pressure within the lung alveoli. 760 mm Hg when equilibrated with atmospheric pressure

intrapleural (intrathoracici) pressure - pressure exerted outside the lungs within the pleural cavity. Usually less than atmospheric pressure (756 mm Hg)

Question 8

explain the significance of transmural pressure gradient across lung wall and across the chest wall

Answer 8

across the lung wall, the intra-alveolar pressure of 760 mm Hg pushes outward, while the intrapleural (intrathoracic) pressure of 756 mm Hg pushes inward
this 4 mm Hg difference in pressure constitutes a transmural pressure gradient (transpulmonary pressure) that pushes out on the lungs, stretching them to fill the larger thoracic cavity

across the thoracic wall, the atmospheric pressure of 760 mm Hg pushes inward, while the intrapleural pressure of 756 mm Hg pushes outward. This 4 mm Hg difference in pressure constitutes a transmural pressure gradient that pushes inward and compresses the thoracic wall

Question 9

explain that pneumothorax abolishes the transmural pressure gradient needed for lung expansion

Answer 9

pneumothorax - air in the pleural space
can be;
spontaneous - a hole in lung wall permits air to move down its pressure gradient and enter the pleural cavity from the lungs, abolishing the transmural pressure gradient, lung collapses to unstretched size
traumatic - puncture in chest wall permits air from atmosphere to flow down pressure gadding d enter pleural cavity, abolishing transmural pressure gradient
iatrogenic
collapsed lung - when transmural pressure gradient is abolished, the lung collapses to its unstretched size, chest wall springs outwards

air enters the pleural space from outside or from the lungs
this can abolish transmural pressure gradient radon to lung collapsed
small pneumothorax can be symptomatic - includes shortness of breath and chest pain
physical signs include - hyper resonant percussion note and decreased/absent breath sounds

Question 10

explain that inspiration is an active process and that normal expiration is a passive process

Answer 10

inspiration is an active process depending on inspiratory muscle contraction - the chest wall and lungs stretch
the increase in the size of the lungs make the intra-alveolar pressure to fall due to the air molecules becoming contained in a larger volume (Boyle’s Law)
the air then enters the lungs down its pressure gradient until the intra-alveolar pressure becomes equal to atmospheric pressure

normal expiration is a passive process brought about by relaxation of inspiratory muscles
the chest wall and stretched lungs recoil to their preinspiratory size because of their elastic properties
the recoil of the lungs make the intra-alveolar pressure to rise because the air molecules become contained in a smaller volume (Boyle’s Law)
the air then leaves the lungs down its pressure gradient until the intra-alveolar pressure becomes equal to atmospheric pressure

Question 11

identify inspiratory muscles used during normal resting breathing

Answer 11

the volume of the thorax is increased vertically by contraction of the diaphragm (major inspiratory muscle), flattening out its dome shape
(phrenic nerve from cervical 3, 4 and 5)
the external intercostal muscle contraction lifts the ribs and moves out the sternum (bucket handle mechanism), increasing side-to-side dimension of thoracic cavity and increasing front-to-back dimension of thoracic cavity

Question 12

explain how lungs recoil

Answer 12

elastic connective tissue in the lungs - whole structure bounces back into shape

alveolar surface tension - the attraction between water molecules at liquid air interface
in the alveoli this produces a forces which resists the stretching of the lungs
if the alveoli were lined with water alone the surface tension would be too strong so the alveoli would collapse

Question 13

describe the role and importance of pulmonary surfactant, with the law of Laplace and alveolar stability

Answer 13

according to the law of LaPlace; the smaller the alveoli (smaller radius - ‘r’) have a higher tendency to collapse
P = 2T/r
P - inward directed collapsing pressure
T - surface tension

pulmonary surfactant is a complex mixture of lipids and proteins secreted by type II alveoli - it reduces the alveolar surface tension
it lowers alveolar surface tension by interspersing between the water molecules lining the alveoli
surfactant lowers the surface tension of smaller alveoli more than that of large alveoli
this prevents the smaller alveoli from collapsing and emptying their air contents into larger alveoli

Question 14

describe the opposing forces acting on the lungs

Answer 14

forces keeping the alveoli open;
transmural pressure gradient, pulmonary surfactant, alveolar interdependence

forces promoting alveolar collapse;
elasticity of stretched lung connective tissue, alveolar surface tension

Question 15

describe respiratory distress syndrome of the new born

Answer 15

developing metal lungs are unable to synthesise surfactant until late in pregnancy
premature babies may not have enough pulmonary surfactant - causing respiratory distress syndrome of the new born
the baby makes very strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs

Question 16

describe the alveolar interdependence

Answer 16

a factor to help keep the alveoli open - if the alveolus start to collapse, the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it