6.4 - Gas exchange

Question 1

what is gas exchange in organisms?

Answer 1

• where gases are absorbed or released from the environment - all orgs must do it
• Multicellular organisms such as plants and animals use complex organ systems to exchange gases for cell metabolic processes
• in humans, oxygen is absorbed
  from air and carbon dioxide is removed

Question 2

what is ventilation?

Answer 2

• a way of gas exchange
• maintains concentration gradients by pumping air in and out of the alveoli

Question 3

how do humans gas exchange?

Answer 3

• lungs to draw air that contain oxygen into the alveoli (air sacs)
• Alveoli increases the surface area for efficient gas exchange with capillaries
• Both oxygen and carbon dioxide gases diffuse down a concentration gradient (passive diffusion)
• Oxygen is transported from alveoli to red blood cells in adjacent capillaries and carbon dioxide diffuses from the capillary into the alveoli for removal

Question 4

what do the alveoli do?

Answer 4

• site for efficient gas exchange as it increases the total surface area for passive diffusion
• The wall of an alveolus (sing.) is called the epithelium and it contains two types of cells: type I and type II pneumocytes
• Majority of alveolar cells are type I pneumocytes and are involved in gas exchange

Question 5

what are type I pneumocytes?

Answer 5

• very thin and flat cells with a thickness of ~0.15mm of
  cytoplasm
• The capillaries adjacent to the alveoli are made up of one very thin layer of cells
• means that the distance that oxygen and carbon dioxide diffuses during gas exchange is very small, thus increases the rate of gas exchange

Question 6

what are type II pneumocytes?

Answer 6

• rounded cells and occupy around 5% of the total alveolar surface area
• they secrete a fluid called surfactant
• The surfactant coats the inner surface of alveoli and allows the oxygen in the alveoli to dissolve and to diffuse into blood in surrounding capillaries
• CO2 can also evaporate from this fluid into the air to be exhaled
• molecules in the surfactant have similar structure to phospholipids in the cell membrane
• monolayer of surfactant provides a moist lining in the alveoli that reduces the surface tension and prevents water from causing the sides of the alveoli to adhere during exhalation
• so lung doesn’t collapse

Question 7

how are airways used in ventilation?

Answer 7

• Air enters the ventilation system through the nose and mouth
• Air passes down the trachea into the lungs
• Inspiration (inhaling) and expiration (exhaling) are controlled by two sets of antagonistic muscle groups that change the volume and pressure inside the thorax

Question 8

what is the trachea and what does it do?

Answer 8

• trachea is lined with rings of cartilage in walls to ensure it always remains open despite low air pressure inside compared to surrounding tissues
  -The trachea splits into the two bronchi (also has walls strengthened by cartilage), each leading the right or
  left side of the lung

Question 9

what is bronchi and what do they do?

Answer 9

• Inside each lung, the bronchi divide into smaller airways called bronchioles that are made of smooth muscle fibres
• At the end of each bronchiole is a cluster of alveoli for gas exchange

Question 10

what is boyle’s law?

Answer 10

• 𝑃 ∝1/v
• When the volume of the thoracic cavity increases, the pressure in the thorax decreases.
• When the volume of the thoracic cavity decreases, the pressure in the thorax increases

Question 11

how does the pressure change work in ventilation?

Answer 11

• Air will move from a region of high pressure to a region of lower pressure (passive transport)

Question 12

what happens in inspiration?

Answer 12

• muscles surrounding the lungs contract to cause the pressure inside the thorax to drop below atmospheric pressure causes the air to move into the lungs to reach an equilibrium with atmospheric pressure

Question 13

what happens in expiration?

Answer 13

• muscle contractions cause the pressure inside the thorax to increase above atmospheric pressure so the air is forced out of the lungs and into the atmosphere.

Question 14

what happens when muscles are worked or relaxed?

Answer 14

• when they work, they contract to exert a pulling force to cause a certain movement by shortening the muscle
• when they are relaxed, as they lengthen it does not exert a pushing force, thus no work is done (passive process)

Question 15

what is an Antagonistic muscle?

Answer 15

• an opposite muscle must exert a pulling force for work to be done
• When muscle contracts and shortens, a second muscle relaxes and lengthens. These muscles work as antagonistic pairs (like bicep and tricep)
• During inspiration and expiration, different muscles are needed to complete opposing movements

Question 16

what does an antagonistic muscle do during inspiration?

Answer 16

• The diaphragm contracts and so it flattens and moves down → increase volume
• external intercostal muscles contract pulling the ribcage upwards and outwards → expands the chest to increase volume
• Additional muscle groups help to pull the ribcage up and out e.g. sternocleidomastoid elevates the sternum and pectoralis minor pulls the ribs outwards
• Decreases the pressure in the thoracic region.

Question 17

what does an antagonistic muscle do during Expiration?

Answer 17

• Diaphragm relaxes and it curves upwards into a dome → reduces volume
• The internal intercostal muscles contract pulling the ribs inwards and downwards → reduces the breadth of the chest
• Abdominal muscles contract and push the diaphragm upwards to for exhalation
• Additional muscle groups such as quadratas lumborum may help to pull the ribs downwards
• Increases pressure in the thorax

Question 18

what is lung cancer?

Answer 18

• one of the top 5 common cancers in the world that results in mortalities
• results from the uncontrolled proliferation of lung cells that forms a tumour, and when tumours impact normal tissue function, it results in disease
• common cancer bc lungs are vital exchange system and any disruption to normal function causes disease in an individual also lots of blood access to rest of body

Question 19

what are Causes of lung cancer?

Answer 19

• Smoking tobacco: 87% of cases; higher cigarette smoked pack years, increased lung cancer incidences.
• Passive smoking: 3% of cases; countries with banned smoking indoors and public areas has observed a drop in reported cases.
• Air pollution: 5% of cases due to diesel exhaust fumes, nitrogen oxides from vehicle exhausts and smoke from burning coal and wood.
• Radon gas: radioactive gas that leaks from rocks like granite.
• Asbestos, silica and some other solids: dust or other particles are inhaled.

Question 20

what are the consequences of lung cancer?

Answer 20

• The consequences of lung cancer are severe as it is an essential exchange surface.
• It includes: difficulties breathing, persistent coughing, coughing up blood, chest pain, loss of appetite, weight loss and general fatigue.
• Mortality rates are high with only 15% of patients with lung cancer surviving for more than 5 years.
• Surgical removal of a lung lobe affected will still result in pain and fatigue

Question 21

what is Emphysema?

Answer 21

• In healthy lung tissue, each bronchiole leads to a group of alveoli that can exchange gases efficiently
• emphysema causes alveoli with larger air sacs (pulmonary bullae), thicker alveolar walls and fewer alveoli
• This decreases surface area for exchange, and the distance for gas diffusion is increased; so gas exchange is ineffective.
• Patients have less elastic lungs and so ventilation is more difficult.

Question 22

what are the main causes of emphysema?

Answer 22

• The main causes of emphysema are
  smoking and air pollution e.g. asbestos.
• Toxins in the smoke and pollution cause inflammation and damage to the white blood cells in the lungs.
• The cilia that line the airways and used to expel mucous becomes damaged, and so the mucous builds up in the lungs causing infections.
• This recruits phagocytes to the region that produce elastase (protease) enzymes.
• Elastase is part of the inflammatory response that breaks down elastic fibres of the alveolar walls.

Question 23

what are the Consequences of emphysema?

Answer 23

• damage to the alveoli is irreversible.
• causes low oxygen saturation in the blood and so higher than normal carbon dioxide concentrations.
• Patients will have a lack of energy, fatigue, shortness of breath and cyanosis.
• Mild activity may become difficult for these patients over time