Ventilation and Gas Exchange

Question 1

What is ventilation?

Answer 1

The process of bringing in fresh air into the alveoli and removing the stale air. Maintains concentration gradient of CO2 and O2 between O2 in the alveoli and CO2 in the blood capillaries.

Question 2

What is gas exchange?

Answer 2

Process of diffusion between O2 in the alveoli and CO2 in the blood capillaries.

Question 3

What is respiration?

Answer 3

Oxidation of organic compounds that occurs within cells, producing energy in the form of ATP.

Question 4

Why do we need a ventilation system?

Answer 4

Ventilation is necessary as it maintains the concentration gradient of CO2 and O2 for gas exchange to occur, which itself is required for cellular respiration to occur, which itself is necessary for energy production. Thus the ventilation system is necessary for energy production.

Question 5

What are Type I Pneumocytes

Answer 5

Extremely thin alveolar cells that are adapted to carry out gas exchange. Contained in the epithelial layers of alveoli in the lungs.

Question 6

What are Type II Pneumocytes?

Answer 6

Rounded cells occupying part of the alveolar surface area. They secrete a fluid which coats the inner surface of the alveoli.

Question 7

What is the basement membrane?

Answer 7

Thin, fibrous extracelular matrix of tissue separating the alveoli and blood capillary.

Question 8

What is the surfactant layer?

Answer 8

• Moist film allowing oxygen in the alveolus to dissolve and then diffuse to the bloof capillaries.
• Provides an area from which CO2 can evaporate into the air and be exhaled.
• Monolayer of phospholipid-like molecules on the surface of the moisture layer of the alveoli with hydrophilic heads facing the water and and hydrophobic tails faicing the air in the alveoli. Reduces surface tension and prevents water from causing the sides of the alveoli to adhere when air is exhaled, preventing lung collapse.

Question 9

What are four structural adaptations of the alveoli that suits them to their function of gas exchange?

Answer 9

Spherical shape of alveoli, and flattened, single-cell thickness of each alveolus (Type I pneumocytes), moist inner lining of alveolus from Type II pneumocytes, and associated capillary bed nearby.

Question 10

Advantage of spherical shape of alveoli?

Answer 10

Increased surface area for diffusion

Question 11

Advantage of flattened, single-cell thickness of each alveolus (Type I pneumocytes)?

Answer 11

Small distance to diffuse over

Question 12

Advantage of moist inner lining of alveolus from Type II pneumocytes?

Answer 12

Prevents lung collapse. Maintains CO2 and O2 concentration gradients.

Question 13

Advantage of associate capilary bed nearby?

Answer 13

Oxygen able to be quickly brought into the blood stream.

Question 14

Describe the mechanism of inspiration.

Answer 14

• Muscle contractions cause the pressure inside the thorax to rise above atmospheric pressure, causing air to be drawn into the lungs until they reach atmospheric pressure.
• Diaphragm moves downwards and flattens. Ribcage moves upwards and outwards.

Question 15

Describe the mechanism of expiration.

Answer 15

• Muscle contractions cause pressure inside the thorax to rise above atmospheric pressure, so air is forced our from the lungs to the atmosphere.
• Diaphragm moves upwards and becomes domed. Ribcage moves downwards and inwards.

Question 16

What is the state of the diaphragm, abdominal muscles, external intercostal muscles, internal intercostal muscles, and air pressure with inhalation?

Answer 16

• diaphragm contract
• abdominal muscles relax
• external intercostal muscles contract
• internal intercostal muscles relax
• air pressure decreases

Question 17

What is the state of the diaphragm, abdominal muscles, external intercostal muscles, internal intercostal muscles, and air pressure with exhalation?

Answer 17

• diaphragm relaxes
• abdominal muscles contract
• external intercostal muscles relax
• internal intercostal muscles contract
• air pressure increases

Question 18

What is hemoglobin? What does it do?

Answer 18

• Protein molecule found within erythrocytes

- Carries most of the oxygen in the bloodstream

Question 19

What is the structure of an erythrocyte?

Answer 19

Plasma membrane surrounding a denucleate cytoplasm filled with hemoglobin molecules. Few organelles or other components other than hemoglobin.

Question 20

What is the structure of hemoglobin?

Answer 20

Composed of four polypeptides, each with a heme group near its center, and each heme group having an iron atom within it.

Question 21

What is iron’s role in hemoglobin?

Answer 21

When hemoglobin reversibly binds to an oxygen molecule, it is the iron atom within the heme group that is binding with the oxygen.

Question 22

How many O2 molecules can be carried by one hemoglobin molecule? How many CO2 molecules?

Answer 22

4 O2 molecules. 1 CO2 molecule.

Question 23

What is meant by hemoglobin’s affinity for oxygen?

Answer 23

Hemoglobin’s shape changes depending on how many oxygen are bound to hemoglobin’s iron atoms. These different shapes affect hemoglobin’s ability to bind with oxygen. This is known as hemoglobin’s affinity for oxygen. The greater the tendency to bind with oxygen, the higher the affinity.

Question 24

What is included in an oxygen dissociation curve?

Answer 24

Mapping of the partial pressure of oxygen (independent variable) with respect to percentage saturation of hemoglobin (dependent variable).

Question 25

Define partial pressure.

Answer 25

The pressure exerted by a single type of gas within a mixture of gases.

Question 26

What pressure units are used for the partial pressure of oxygen?

Answer 26

pO2/mm Hg

Question 27

What is the relation of the partial pressure of oxygen and the saturation of hemoglobin?

Answer 27

As partial pressure increases, the percentage of saturation of hemoglobin increases sigmoidally.

Question 28

What is myoglobin? What is its structure?

Answer 28

• Oxygen-binding protein found in muscles used to store oxygen within the muscle tissues until muscles begin to enter an anaerobic situation, dissociating oxygen to delay the onset of lactic acid fermentation
• Each molecule consists of a single polypeptide, a heme group, and an iron atom.

Question 29

Describe the importance of fetal hemoglobin’s affinity for oxygen?

Answer 29

Fetal hemoglobin has a higher affinity for oxygen than maternal hemoglobin. As a result, maternal hemoglobin releases oxygen in the placental capillaries while fetal hemoglobin is more likely to bind to that same oxygen such that oxygen is transferred from mother to child.

Question 30

What occurs to blood at the tissues?

Answer 30

The partial pressure of oxygen decreases and the partial pressure of carbon dioxide increases, making the pH decrease and in turn making hemoglobin’s affinity for oxygen decreases and thus releases its oxygen.

Question 31

What occurs to the blood at the lungs?

Answer 31

Partial pressure of oxygen increases and the partial pressure of carbon dioxide decreases, making the pH increase and in turn making hemoglobin’s affinity for oxygen increase and so hemoglobin takes up oxygen from the lungs.

Question 32

What is the effect of CO2 on the pH of the blood?

Answer 32

Causes the pH of the blood to decrease.

Question 33

What happens to hemoglobin when CO2 has a greater presence?

Answer 33

Hemoglobin is induced to dissociate oxygen

Question 34

What are the three ways in which CO2 is brought out of the tissues?

Answer 34

• Dissolves in the blood plasma
• Enters erythrocytes and becomes reversibly bound to heme groups
• Enter erythrocytes and converted into hydrogen carbonate ions and then move into the blood plasma

Question 35

How is CO2 converted to hydrogen carbonate?

Answer 35

• The cytoplasm of the erythrocytes contains the enzyme carbonic anhydrase which catalyzes a reaction in which carbon dioxide and water combine to form carbonic acid.
• Carbonic acid dissociates into a hydrogen carbonate ion and a hydrogen ion.
• Hydrogen carbonate ions exit the cytoplasm of the erythrocyte through specialized protein channels via facilitated diffusion, exchanging one hydrogen carbonate ions for one chloride ion. This is known as the chloride shift.

Question 36

How is the ventilation rate controlled by negative feedback?

Answer 36

• Ventilation rate controlled by an area of the medulla oblongata of the brainstem known as the respiratory control center, where two mechanisms come into play when the rate of ventilation needs to increase.
• Receptor cells, chemosensors or chemoreceptors, in the inner wall of the aorta and carotid arteries detect when there is an increase in CO2 level and the associate degree in blood pH. When stimulated, these receptors send action potentials to the medulla’s breath center.
• The medulla itself contains these types of chemosensors. As the blood passes through the capillary beds of the medulla, increased carbon dioxide and decreased pH are detected.
• To increase ventilation rate, the medulla’s respiratory center sends action potentials to the diaphragm, intercostal muscles, and muscles in the abdomen, altering the frequency of breathing.

Question 37

How does pO2 change with increasing altitude?

Answer 37

Decreases, meaning oxygen is more spread out.

Question 38

How can the body acclimatize to life at high altitudes?

Answer 38

• Increasing the number of erythrocytes and hemoglobin
• Increasing capillaries in the lungs and muscles
• Increasing lung size and surface area for oxygen and carbon dioxide exchange
• Increase in myoglobin within muscle tissue

Question 39

Descibe what happens to the lung tissue with emphysema. What are the causes? What are treatments?

Answer 39

• Many of the alveoli become severely damaged, with gaping holes left where healthy tissue once existed.
• Caused by smoking and exposure to smoke, air pollution, coal, and silica dust.
• Treatments are centered round slowing further damage by stopping the exposure to the causative agents and medications that help relieve some of the symptoms.