topic 6.4 - ventilation

Question 1

what is the function of ventilation?

Answer 1

it maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries

Question 2

draw a labelled diagram of an alveolus

Answer 2

pg311
- type 1 pneumocystis in alveolus walls
- phagocyte
- network of blood capillaries
- type 2 pneumocystis in alveolus walls

Question 3

give 4 ways of monitoring ventilation in humans at rest and after mild and vigorous exercise

Answer 3

1. ventilation rate
   - observation of number of times air is exhaled and inhaled in a minute
   - data logging with inflatable chest belt that is placed around the thorax
2. tidal volume
   - one normal breath is exhaled through a delivery tube into a vessel and the volume is measured. it is not safe to use this apparatus for repeatedly inhaling/exhaling air as the co2 concentration will rise too high
   - spirometers measure flow rate into and out of lungs and from these measurements lung volumes can be deduced

Question 4

structure and function of type 1 pneumocytes

Answer 4

extremely thin alveolar cells that are adapted to carry out gas exchange

• located in epithelium, in wall of alveolus
• flattened cells
• distance over which co2 and o2 have to diffuse is very small, which increases the rate of gas exchange

Question 5

structure and function of type 2 pneumocytes

Answer 5

secrete a solution containing surfactant that creates a moist surface:
- allows oxygen to dissolve and diffuse to blood
- provides area from which co2 can evaporate into the air and be exhaled

hydrophobic heads face the water and the hydrophobic tails face the air:
- reduces surface tension and prevents water from causing the sides of the alveoli to adhere when air is exhaled from lungs, helping prevent the collapse of the lung

Question 6

give a flow diagram describing airways for ventilation

Answer 6

nose/mouth -> trachea -> two bronchi -> lung -> tree-like bronchioles -> groups of alveoli

Question 7

give the structure and function of trachea and bronchi

Answer 7

rings of cartilage in their walls to keep it open even when air pressure inside is low or pressure in surrounding tissues is high

Question 8

structure and function of bronchioles

Answer 8

smooth muscle fibres in their walls, allowing the width of these airways to vary

Question 9

draw a diagram for inspiration

Answer 9

• ribs upwards and outwards
• air in
• diaphragm down

Question 10

draw a diagram for expiration

Answer 10

• ribcage inwards and downwards
• air out
• diaphragm up

Question 11

describe the basic physics involved in ventilation

Answer 11

• if particles of gas spread out to occupy a larger volume, the pressure of gas becomes lower
• if gas is compressed to occupy a smaller volume, the pressure rises
• if gas is free to move, it will flow from regions of higher pressure to regions of lower pressure

Question 12

describe the process of ventilation and how pressure is linked with it

Answer 12

1. muscle contractions cause pressure inside the thorax to drop below atmospheric pressure
2. air is drawn into the lungs from the atmosphere (inspiration) until lung pressure has risen to atmospheric pressure
3. muscle contractions then cause pressure inside the thorax to rise above atmospheric, so air is forced out from the lungs to the atmosphere (expiration)

Question 13

muscles can be in two states

Answer 13

contracting and relaxing

Question 14

contracting

Answer 14

• muscles do work
• exert a pulling force (tension) that causes a particular movement
• become shorter

Question 15

relaxing

Answer 15

• muscles lengthen passively
• pulled into an elongated state by the contraction of another muscle
• do not exert a pushing force (compression) while relaxing so do no work

Question 16

describe an antagonistic pair of muscles

Answer 16

when one muscle contracts and causes a movement the second muscle relaxes and is elongated by the first . the opposite movement is caused by the second muscle contracting while the first relaxes

Question 17

why are antagonistic pairs of muscles needed?

Answer 17

muscles can only cause movement in one direction. if movement in opposite directions is needed at different timed, at least two muscles will be required

Question 18

draw a table for
diaphragm, ribcage
inspiration, expiration

Answer 18

p315

Question 19

draw a table for
volume and pressure changes, movement of diaphragm, movement of ribcage
inspiration, expiration

Answer 19

p.316

Question 20

causes of lung cancer

Answer 20

• smoking: tobacco contains many mutagenic chemicals.
• passive smoking
• air pollution from diesel exhaust fumes, nitrogen oxides from all vehicle exhaust fumes, smoke from burning coal, wood, or other organic matter
• radon gas: radioactive gas that leaks out of rocks like granite. accumulates in badly ventilated buildings so people inhale it
• asbestos, silica, some other solids if dust or particles of them are inhaled, in construction sites, quarries, mines, or factories

Question 21

consequences of lung cancer

Answer 21

• difficulties with breathing, persistent coughing, coughing up blood, chest pain, loss of appetite, weight loss, general fatigue
• may lead to secondary tumours
• chemotherapy or radiotherapy

Question 22

emphysema

Answer 22

Emphysema is a lung condition whereby the walls of the alveoli lose their elasticity due to damage to the alveolar walls
- The loss of elasticity results in the abnormal enlargement of the alveoli, leading to a lower total surface area for gas exchange
- The degradation of the alveolar walls can cause holes to develop and alveoli to merge into huge air spaces (pulmonary bullae)

Question 23

theories for formation of emphysema

Answer 23

in smokers, the number of phagocytes in the lungs increases and they produce more elastase.
- phagocytes inside alveoli normally prevent lung infections by engulfing bacteria and produce elastase, a protein-digesting enzyme, to kill them inside the vesicles formed by endocytosis.
- alpha 1-antitrypsin (A1AT) is an enzyme inhibitor and prevents elastase and other proteases from digesting lung tissue.
- genetic factors affect the quantity and effectiveness of A1AT produced in the lungs

Question 24

symptoms of emphysema

Answer 24

• irreversible, chronic disease
• low oxygen saturation in the blood and higher than normal co2 concentrations.
• patient lacks energy
• shortness of breath
• ventilation laboured and more rapid than usual

Question 25

volume and pressure changes
- inspiration
- expiration

Answer 25

volume in thorax increases and pressure consequently decreases
volume in thorax decreases and pressure consequently increases

Question 26

movement of the diaphragm and abdomen wall muscles
- inspiration
- expiration

Answer 26

inspiration:
- diaphragm contracts and so it moves downwards and pushes the abdomen wall out
- muscles in the abdomen wall relax allowing pressure from the diaphragm to push it out

expiration:
- diaphragm relaxes so it can be pushed upwards into a more domed shape
- muscles in the abdomen wall contract pushing the abdominal organs and diaphragm upwards

Question 27

movement of the ribcage for the external intercostal muscles and internal intercostal muscles
- inspiration
- expiration

Answer 27

inspiration:
- the external intercostal muscles contract, pulling the ribcage upwards and outwards
- internal intercostal muscles relax and are pulled back into their elongated state

expiration:
- external intercostal muscles relax and are pulled back into their elongated state
- internal intercostal muscles contract, pulling the ribcage inwards and downwards