Physiology revision - Respiratory System

Question 1

What are the lobes of the lungs?

Answer 1

Superior, middle and inferior lobe in right lung

Superior and inferior in left lung to accommodate heart

Question 2

What is the pleural sac? What are its functions?

Answer 2

A double-walled enclosure of the lungs filled with fluid; pleural fluid

It reduces friction from movement on the surface of the lungs

It fixes the lungs firmly on the thoracic wall without any physical attachments

Question 3

What are the consecutive branches of the airways?
What are their functions?

Answer 3

Conducting zone:

• Bronchi
• Bronchioles
• Terminal bronchioles

Respiratory zone:

• Respiratory bronchioles
• Alveolar ducts
• Alveolar sacs

Functions:

1. Warm inspired air
2. Humidify inspired air
3. Filtration of inhaled foreign materials

Question 4

What lies on the epithelial surfaces of the airways, to the respiratory bronchioles to “filter” air?

Answer 4

1. Cilia - beat mucus upwards towards the pharynx to be swallowed
2. Goblet cells (glands) and indiv. epithelial cells that secrete mucus
3. Macrophages that phagocytize inhaled pathogens
4. Airway epithelium also secretes a watery fluid upon which mucus can easily be pushed by cilia

Question 5

What are the components of alveoli? What are the two types? What does the substance on the type 2 cell do?

Answer 5

Single-layer alveolar epithelial cells and a single-layer capillary epithelial cells (sometimes these cells fuse)

Type 1 alveolar cells - For gas exchange (air-facing cells)

Type 2 alveolar cells - Surfactant cells that produce detergent-like substance called surfactant that prevents the collapse of the alveoli

Surfactant - Reduces surface tension so smaller alveoli do not collapse into larger ones. Smaller bubbles have higher pressure

Question 6

Where is the pressure in the lungs always negative? What purpose does this serve?

Answer 6

Pressure is always negative (sub-atmospheric) in the pleural cavity; prevents the collapse of the lung when inspiratory muscles contract to move diaphragm downwards

This creates an adhesive force (fluid in cavity that creates tension and adhesion)

Question 7

What is hemoglobin and what percentage of O2 molecules bind to it?

Answer 7

Hemoglobin is an O2 binding protein contained within red blood cells. 98% of O2 from the alveoli is transport bound to Hb and the other 2% is dissolved in the plasma

Question 8

At equilibrium, what is the solubility vs. the partial pressure of O2 in air and water?

Answer 8

At equilibrium, PO2 in air and water is equal, but the solubility of O2 is not, meaning the concentration is not equal

Question 9

How is CO2 carried in the blood?

Answer 9

CO2 is much more soluble than O2

70% is carried in the form of bicarbonate ions (HCO3-)

23% is carried bound to Hb

7% is dissolved

Important note: Hb binds to the the H+ ions released from the rctn btw CO2 and H20 to create HCO3-, reducing the acid concentration of H2CO3 (process known as respiratory acidosis)

Question 10

What is Dalton’s Law of partial pressure?

Answer 10

The pressure of a gas mixture is equal to the sum of the pressure of the individual gases

Question 11

What is Frick’s Law of diffusion?

Answer 11

The greater the solubility of a gas, means a greater rate of diffusion for that gas

Ex. CO2 is a lot more soluble than O2, therefore diffuses across the membrane a lot easier

Question 12

What is the average partial pressure of O2 and CO2 in the lung capillaries vs. the tissue capillaries?

Answer 12

Lung capillaries:

PO2 = 100mmhg
PCO2 = 40mmhg

Tissue capillaries:

PO2 = 40mmhg
PCO2 = 46mmhg

Question 13

How do you calculate O2 consumption and CO2 consumption?

Answer 13

O2:

Inspired O2 - expired O2 = Consumed O2

CO2:

Expired CO2 - inspired CO2 = Produced CO2

Note: To calculate these you need to know the volume of the these in/expirations as well as the of the molecule in this air

Question 14

What organ in the brain controls involuntary ventilation?

Answer 14

The Medulla

• It contains the ‘respiratory rhythmicity center’ that activates intercostal muscles and the diaphragm

Question 15

What structure in the brain modulate and inhibits the respiratory rhythmicity centre?

Answer 15

The pons

Question 16

What are the two ‘protective interruption of the respiratory rhythm’ mechanisms?

Answer 16

• Slowly adapting pulmonary stretch receptors;

Located in airway smooth muscle, these receptors fire when the tidal volume approaches physical limitations for lung tissue expansion. The Hering-Breuer reflex initiates a signal that inhibits inspiration

• Rapidly adapting pulmonary stretch receptors;

Located in the trachea and large airways, these receptors initiate reflexes such as coughing, sneezing, bronchoconstriction when exposed to irritants such as smoke, inhaled particles, cold air

Question 17

What creates ventilatory drive?

Answer 17

Peripheral chemoreceptors:

1. Aortic chemoreceptors (aortic arch)
2. Carotid chemoreceptors (carotid bodies)

Sense PaO2 and signal to the medulla

Question 18

What do the medulla’s chemoreceptors respond to in the brain to create ventilatory drive?

Answer 18

Medulla’s chemoreceptors respond to PaCO2 through the concentration of hydrogen ions that cross from the cerebral spinal fluid, to the interstitail fluid.

CO2 crosses the BBB from the capillaries, forms H2CO3 with H2O in the CSF and then dissociates into H+ and HCO3-. H+ then crosses into IF of medulla.