Respiration Physiology

Question 1

What is the air pressure in your lungs just before you breath in?

Answer 1

•Just before you breath in, the air pressure inside your lungs is equal to the air pressure of the atmosphere at sea level: 760 mmHg.

Question 2

Why does the pressure inside the alveoli have to be lower than atmospheric pressure?

Answer 2

To draw air into the lungs

Question 3

How does the pressure of gas vary with volume?

Answer 3

The pressure of gas varies inversely with volume

Question 4

What is cellular respiration?

Answer 4

• Within the cell, oxygen is required to breakdown organic molecules such as glucose in order to generate ATP
• Carbon dioxide is generated by cellular metabolism and this must be removed from the cell
• Therefore, there has to be gas exchange, our respiratory system facilitates this exchange.

Question 5

How does inhalation work?

Answer 5

The pressure inside the alveoli has to be lower than atmospheric in order to draw air into the lungs

The pressure of gas varies inversely with volume

Therefore, differences in pressure caused by changes in lung volume cause air to be drawn into the lung

For inhalation to occur lungs need to expand, increasing lung volume, decreasing pressure to below atmospheric pressure

The increase in lung volume is caused by the contraction of the diaphragm and external costal muscles

Question 6

What is the diaphragm and what does it do?

Answer 6

Dome-shaped skeletal muscle forming the floor of the thoracic cavity

Contraction causes the dome to flatten

A 1 cm drop produces a pressure difference of 1-3 mmHg and about 500 mL of air the enter the lung

A 10 cm drop produces a 100 mmHg pressure difference and about 2-3 L of air to enter the lungs

The action of the diaphragm is responsible for about 75% of the air that enters the lungs

Question 7

What percentage of air into the lungs are the intercostal muscles responsible for?

What happens to the ribs on contraction?

Answer 7

Contraction is responsible for about 25% of air that enters the lungs

The ribs are elevated and move outwards

Question 8

What is the intrapleural pressure?

Answer 8

The pressure that always exists between the two pleural

layers of the pleural cavity

This is always lower than atmospheric pressure

Question 9

As the diaphragm and intercostal muscles contract, what happens to the intrapleural cavity?

Answer 9

As the diaphragm and intercostal muscles contract, the volume of the intrapleural cavity also increases, this causes the intrapleural pressure to drop to ~754 mmHg

The parietal and visceral pleurae normally adhere to each other because of the sub-atmospheric pressure and surface tension created by two moist surfaces

As the thoracic cavity expands this results in parietal pleura lining of the cavity being pulled outwards in all directions, taking the visceral lining and hence the lungs with it

The volume of the lungs increases and the alveolar pressure drops from 760 to 758 mmHg

Question 10

How does the nose affect the air entering?

Answer 10

•As the air enters the body through the nose it is warmed up and filtered

Question 11

Outline the passage of the air taken in through the nose?

Answer 11

• The air passes through the pharynx and larynx into the trachea and on into the bronchi, these tubes are reinforced to prevent collapse and lined with cilliated epithelium and mucus producing cells
• The bronchi branch into smaller and smaller tubes terminating in the alveoli

Question 12

Label the respiratory system

Answer 12

Question 13

Label this image

Answer 13

Question 14

What types of cell make up the alveoli?

Answer 14

The walls of alveoli consist of two types of alveolar epithelial cells:

Type I alveolar cells – squamous cells, line the walls almost continuously

Type II alveolar cells – cuboidal epithelium, interspersed amongst the Type I cells, and secrete alveolar fluid

Question 15

Describe the respiratory membrance?

Answer 15

Is very thin – approximately 0.5 micrometers in diameter

Consists of four layers:

1. The alveolar wall (Type I & Type II alveolar cells and alveolar macrophages)
2. The epithelial basement membrane (alveoli)
3. The capillary basement membrane
4. The endothelial cells (of the capillary)

Question 16

How many alveoli do the lungs contain?

What is the surface area available for gas exchange?

How is rapid diffusion of gases enabled?

Answer 16

The lungs contain about 300 million alveoli

The surface area available for gas exchange is about 70 square meters

The pulmonary capillaries are narrow so that erythrocytes pass through in single file

This, together with the thinness of the respiratory membrane, enables rapid diffusion of gases

Question 17

Explain the role of surfactant in the alveoli?

Premature infants?

Answer 17

• Surfactant is a complex fluid made up of phospholipids and apoproteins produced by alveolar cells

Surfactant reduces the surface tension in the lung increasing alveolar stability and reducing the likelihood of collapse

• Because surfactant is produced relatively late in foetal life, premature infants born without adequate surfactant in the lungs can experience respiratory distress which can lead to death

Question 18

What are the basics of gas exchange?

Answer 18

Remember that diffusion is the movement of material from a higher to a lower concentration

The concentrations of gases are measured as partial pressures

Therefore, the greater the difference in partial pressure the greater the rate of diffusion

Question 19

Fill in the table

Answer 19

Question 20

What is oxygen carried by?

How much does this increase carrying capacity?

How many of these does each RBC contain?

How many of these does each mL of blood contain?

Answer 20

• Oxygen is carried by the transport protein haemoglobin
• Haemoglobin increases the oxygen carrying capacity of the blood by about 70 times

Each red blood cell (erythrocyte) contains about

250,000,000 haemoglobin molecules and each mL of

blood contains ~1.25 X 1015 molecules of haemoglobin

Question 21

What carries the oxygen around the body, percentages and why?

Answer 21

Oxygen does not easily dissolve into water so only about 1.5% of the oxygen inhaled dissolves into the blood plasma, 98% of the oxygen carried in the blood is bound to the heme units of protein haemoglobin found in red blood cells

Question 22

Explain the use of heme units and partial pressures to take O2 to the tissue?

Answer 22

The most important factor that determines how much oxygen binds is the partial pressure of oxygen, the more oxygen there is the more will bind to the heme units.

In the pulmonary capillaries the partial pressure of oxygen is high and a lot of the oxygen binds to the haemoglobin.

In the tissue capillaries the partial pressure of oxygen is lower and the oxygen is unloaded from the heme units.

Question 23

What 4 things affect haemoglobins affinity for oxygen?

Answer 23

1. The acidity (pH)
2. The partial pressure of carbon dioxide
3. Temperature
4. Bisphosphoglycerate (BPG)

Question 24

Explain how acidity/pH has an effect on Hb affinity for oxygen?

Answer 24

As the acidity increases (pH drops), the affinity of haemoglobin for oxygen decreases, the oxygen is unloaded from the heme units.

Metabolically active tissues produce lactic and carbonic acid.

The hydrogen ions (H+) are able to bind to the amino acids of haemoglobin and alter the shape of the protein slightly decreasing its affinity for oxygen.

Question 25

Explain how the partial pressure of carbon dioxide effects the affinity of Hb to oxygen?

Answer 25

Carbon dioxide can also bind to haemoglobin, the effect is similar to acidity. As PCO2 rises the haemoglobin releases O2 more readily.

In fact PCO2 and pH are related, low blood pH (acidy) results from high PCO2.

As CO2 enters the blood much of it is temporarily converted to carbonic acid (H2CO3) in a reaction catalysed in the red blood cell by an enzyme called carbonic anhydrase.

Carbonic acid is a weak acid that can dissociate releasing hydrogen ions

Question 26

Explain how temperature effects the affinity of Hb to oxygen?

Answer 26

As temperature increases so does oxygen unloading from haemoglobin

In metabolically active tissues a lot of heat is released (all cells release some heat), these cells also release acids, lowering the pH.

Metabolically active cells need lots of oxygen!

Question 27

Explain how Bisphosphoglycerate effects the affinity of Hb to oxygen?

Answer 27

BPG deceases the affinity of haemoglobin for O2

BPG is formed in red blood cells when they breakdown glucose to form ATP.

BPG can bind to haemoglobin to allow more oxygen to be unloaded.

Higher levels of BPG are found in people living at high altitudes, certain hormones can also effect levels of BPG.

Question 28

Explain carbon monoxide poisoning?

Answer 28

Carbon monoxide has a 200 times greater affinity for haemoglobin than oxygen in concentrations as low as 0.1% (PCO 0.5 mmHg) the carbon monoxide will bind to half of the heme groups reducing the oxygen carrying capacity of the blood by 50%.

Without urgent administration of pure oxygen, CO poisoning is FATAL

Question 29

Explain the 3 ways of carbon dioxide transport?

Answer 29

Each 100 mL of de-oxygenated blood contains 53 mL of gaseous CO2 which is transported in three ways.

1. Dissolved CO2 in blood plasma ~7%
2. Carbamino compounds bound to proteins in the blood, because haemoglobin is the most prevalent protein in the blood most of the CO2 will be bound to it. The affinity is dependent on PCO2 ~23%
3. Bicarbonate ions (HCO3-) in blood plasma, as CO2 enters red blood cells it reacts with water in the presence of an enzyme carbonic anhydrase to form carbonic acid which can dissociate into a hydrogen ion and a bicarbonate ion. As the concentration of bicarbonate ion increases in the red blood cell it diffuses out into the plasma down a concentration gradient. In exchange chloride ions move into the red blood cell to maintain the electrical balance between the blood plasma and red blood cell cytosol ~70%

Question 30

What are the non-respiratory lung functions?

Answer 30

1. Reservoir of blood available for circulatory compensation

2. Filter for circulation: thrombi, micro-aggregates etc

3. Metabolic activity :

• activation of angiotensin I/II
• inactivation of noradrenaline, bradykinin, 5 H-T and some prostaglandins

4. Immunological: IgA secretion into bronchial mucus

Question 31

Explain the control of respiration?

Answer 31

• Respiratory centre in the brain consists of the medullary rhythmicity area in the medulla oblongata and pneumotaxic area and apneustic area in the pons.
• The inspiratory area sets the basic rhythm of respiration
• The pneumotaxic and apneustic areas coordinate the transition between inhalation and exhalation
• Respiration may be modified by a number of factors, e.g. O2, CO2 and H+ levels, blood pressure changes, temperature, pain and many more factors

Question 32

Label this image

Answer 32