Physiology- Lungs/gas exchange

Question 1

What is Fick’s law? And the equation

Answer 1

Fick’s law is the rate at which substances can diffuse

Rate of Diffusion is directly proportional to (surface area x concentration gradient)/ distance

Question 2

What can we deduce form Ficks law?

Answer 2

In order to support a fast diffusion rate surfaces must have:

• a large surface area
• a short diffusion pathway
• a high concentration difference

Question 3

What is epithelial tissue?

Answer 3

The layer of cells covering all the external and internal surfaces of the body

Question 4

Name the 5 types of epithelial tissues:

Answer 4

• Squamous epithelium
• Endothelium
• Columnar epithelium
• Ciliated epithelium
• Epidermis

Question 5

Describe the lungs: use all necessary vocabulary

Answer 5

Trachea branches to 2 bronchi-> bronchioles->alveoli

Pleural membrane surrounds lungs

Question 6

How have the lungs adapted for gas exchange?

Answer 6

• large surface area-> 600 million alveoli provide a huge surface area
• short diffusion pathway-> walls of alveoli are flattened epithelial cells like the capillary walls
• mechanism Maintain high conc. gradient-> constant blood flow in capillaries and ventilation in it sacs

Question 7

Why is exhaled air more humid than inhaled air?

Answer 7

Water inevitably diffuses down its conc. gradient from the tissue fluid and alveoli cells into the air in the alveoli
- due to the lungs being so deep inside the body, the water vapour remains in the lungs and lowers the diffusion gradient causing less water to be lost

Question 8

Why do the epithelial cells secrete a soapy surfactant in the lungs?

Answer 8

To reduce water surface tension (breaks hydrogen bonds) making it less sticky, without this the alveoli would collapse (common problem in premature babies)

Question 9

How does the body reduce infection and pathogen invasion in the lungs??

Answer 9

• Epithelial cells of bronchioles secrete mucus
• Mucus traps bacteria and particles
• mucus is swept up by cilia of the ciliated epithelial cells to throat
• mucus is then swallowed and pathogens are killed in stomach acid
• also phagocytes migrate to alveolar air spaces to kill non trapped bacteria

Question 10

Explain the purpose of the pleural membrane/fluid and thorax

Answer 10

The outer pleural membrane is attached to the thorax while the inner membrane I attached to the lungs, between the membranes is the pleural fluid which is incompressible, so when the thorax expands or contracts so does the lungs
- the alveoli collapse if not held open by the thorax

Question 11

What direction does air always flow? And how is it tidal?

Answer 11

Air always flows from a high pressure to a low pressure

- tidal meaning the air goes in and out via the same route

Question 12

What is the process of inspiration?

Answer 12

• diaphragm contracts and external intercostal muscles contract pulling ribs out
• volume of thorax and lungs increases stretching the elastic walled alveoli
• decreases pressure of air in alveoli below atmospheric pressure
• air flows from high pressure outside to low pressure inside alveoli

Question 13

What is the process of expiration?

Answer 13

• diaphragm and external intercostal muscle relax allowing ribs to fall in
• volume of thorax and lungs decrease causing the alveoli and bronchioles to shrink (elastic recoil)
• pressure inside increases above atmospheric pressure so air flows out

Question 14

Forced expiration occurs after normal expiration, but how does this occur? And why?

Answer 14

• abdominal muscles contract, pushing diaphragm up
• internal intercostal muscles contact pulling ribs down
• larger and faster respiration (used in exercise)

Question 15

What is pulmonary ventilation? And how is it calculated?

Answer 15

The volume of air ventilating the lungs per minute

-> PV= ventilation rate x tidal volume

Question 16

What is ventilation rate and how is it calculated?

Answer 16

The time taken for one whole ventilation cycle (breaths per minute)
-> VR= 60/cycle time (s)

Question 17

What is tidal volume?

Answer 17

The normal volume of air breathed in each breath (breathing depth)

Question 18

What is the difference between gas exchange and ventilation?

Answer 18

Gas exchange: certain gases are moved between environment and blood
Ventilation: the muscular movement that speeds up gas exchange
- increases rate of gas exchange by increasing the concentration difference

Question 19

Gas exchange summary:

Answer 19

• passive
• uses diffusion
• slow
• gases move down their own conc. gradients (may be in different directions)

Question 20

Ventilation summary:

Answer 20

• uses mass flow
• active process (contracting muscles use ATP)
• all gases in air move together in same direction
• fast process

Question 21

What is asthma and the symptoms?

Answer 21

Asthma is an allergic response to allergens

-wheezing, difficulty breathing, tight chest and coughing

Question 22

Describe what happens in an asthma attack:

Answer 22

• allergens (fur, dust, pollen or faeces) trigger an inflammatory response
• white blood cells (mast cells) release histamines causing the smooth circular muscles of bronchioles to contract (bronchoconstriction)
• epithelial cells secrete more mucus which blocks airways
• tidal volume is reduced and air is replaced more slowly, concentration gradient across alveolar epithelium is reduced so less oxygen diffuses into blood for respiration

Question 23

How to reduce asthma?

Answer 23

Anti-inflammatory drugs

Question 24

What is process of pulmonary tuberculosis?

Answer 24

• bacterial cells are breathed in, invading the epithelial cells of alveoli and bronchioles, where they multiply into tubercles (dormant lumps)
• the tubercles stimulate an inflammatory response by white blood cells, forming fibrous scar tissue
• scar tissue reduces elasticity of alveoli and thickens walls reducing rate of diffusion
• after months bacteria emerges from tubercles and start reproducing inside lung epithelial cells killing them (reducing their surface area)
• TB also spreads via blood stream to other organs destroying them too

Question 25

How is TB spread?

Answer 25

TB is transmitted by aerosol droplets from coughing and sneezing
- worsened by overcrowding in slums and hospitals

Question 26

Can TB be treated?

Answer 26

Yes, with antibiotics and the BCG vaccine

Question 27

How does emphysema reduce gas exchange??

Answer 27

• tar in cigarettes stimulate white blood cells to release inflammatory protease enzymes in the alveoli
• the protease enzyme digests elastin (the elastic tissue in alveolar epithelium)
• alveoli can no longer expand and recoil, reducing tidal volume, reducing oxygen diffusion gradient

Question 28

What happens in the worse cases of emphysema?

Answer 28

• the alveoli epithelial cells are completely destroyed
• alveoli form fewer larger air sacs, with thicker walls
• this reduces surface area and increases length of diffusion pathway, reducing oxygen diffusion for cellular respiration (Ficks Law)

Question 29

How do people cope with emphysema?

Answer 29

Incurable, quitting smoking stops symptoms worsening, patients breath pure oxygen to compensate

Question 30

What is lung cancer? And how does it reduce gas exchange?

Answer 30

• the growth of excess tissue, due to uncontrolled division of epithelial cells
• mutagenic agents in environment cause the epithelial cells to mutate and divide continuously into a tumour
• the tumour growth constricts bronchioles and alveoli slowing rate of gas exchange

Question 31

What can cause lung cancer?

Answer 31

• smoking, asbestos and radon gas (all mutagenic agents/carcinogens)

Question 32

What is pulmonary fibrosis?

Answer 32

• inhaled particles stimulate inflammatory response causing growth of fibrous scar tissue in alveoli
• scar tissue thickens alveolar walls, longer diffusion pathway and smaller surface area
• scar tissue also reduces elasticity of alveoli so normal passive exhalation is reduced, smaller oxygen diffusion gradient

Question 33

Why is pulmonary fibrosis known as an occupational disease?

Answer 33

A common disease found in work place environments and triggered by work place particles
Coal dust - coal mining
Asbestos - demolition worker
Beryllium - nuclear power worker