Respiratory system

Question 1

What are the 5 components of the respiratory system?

Answer 1

• Airways
• Lungs
• Pulmonary circulation
• Thoracic cage
• Respiratory muscles

Question 2

What is Boyle’s Law?

Answer 2

P1V1=P2V2

‘The pressure of a given quantity of gas varies inversely with its volume at constant temperature’.

Question 3

What does the diaphragm do during inhalation?

Answer 3

It contracts and draws lungs downwards to increase lung volume

Question 4

What is vital capacity of the lungs?

Answer 4

Vital capacity = The sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume

Question 5

What is Total Lung Capacity?

Answer 5

Total Lung Capacity = The sum of vital capacity and residual volume

Question 6

What is residual volume?

Answer 6

Residual Volume = The volume of air left in the lungs after the expiratory reserve volume is exhaled, this cannot be measured by spirometry.

Question 7

What are the 3 parts of the respiratory process?

Answer 7

1. Ventilation of lungs with air
2. Gas exchange between air and blood (pulmonary circulation)
3. Perfusion of lungs with blood

All vital for efficient uptake of O2 and elimination of CO2

Question 8

What is ventilation?

Answer 8

The exchange of air between the atmosphere and the alveoli

Question 9

Describe the structure of the airways

Answer 9

• Air enters trachea through nose and mouth
• Trachea divides in the left and right bronchus
• They divide sequentially into small bronchi and bronchioles
• Bronchioles end in alveoli which is the major site of gas exchanges

Question 10

Describe the alveoli

Answer 10

Tiny hollow sacs
Alveolar walls contain capillaries
Large surface area of alveoli in contact with the capillaries means gas exchange of CO2 and O2 by diffusion is rapid

Question 11

Describe the process of inspiration and expiration

Answer 11

Inspiration

• Inspiratory muscles contract, diaphragm moves down and flattens and external intercostal muscles lift ribs cage and pull up sternum
• Thoracic cavity volume increases
• Intrapulmonary volume increases as lungs are stretched
• Intrapulmonary volume decreases
• Air flows into lungs down pressure gradient until intrapulmonary pressure is 0

Expiration

• Inspiratory muscles relax, diaphragm rises, the rib cages descends
• Lungs recoil
• Thoracic cavity volume and intrapulmonary volume decreases. The volume decrease compresses the alveoli and intrapulmonary pressure increases.
• Air flows out of lungs down pressure gradient until the intrapulmonary pressure is 0

Question 12

Describe the process of forced expiration

Answer 12

• An active process produced by contraction of abdominal wall muscles.
• The contraction causes an increase in intra-abdominal pressure which forces abdominal organs against the diaphragm and depress the ribcage. Internal intercostal muscles help depress rib cage and decrease thoracic volume.

Question 13

What influences uptake of O2 and CO2

Answer 13

• Partial pressure gradient and gas solubilities
• Matching of alveolar ventilation and pulmonary blood perfusion
• Structural characteristics of the respiratory membrane

Question 14

What is the partial pressure of O2 in the alveoli

Answer 14

Around 104mmHg

Question 15

What is the PO2 in the pulmonary arteries?

Answer 15

40mm Hg

Question 16

What happens when the PO2 in alveoli is low?

Answer 16

The terminal arterioles constrict and blood is redirected to an area with high PO2 so it can be easily diffused

Question 17

What happens when the PO2 is low and the PCO2 is high in the alveoli?

Answer 17

Pulmonary arterioles constrict and there is reduced alveolar ventilation, reduced perfusion

Question 18

What happens when there is a high PO2 and low PCO2 in the alveoli?
And what causes this?

Answer 18

Pulmonary arteries serving these alveoli dilate and there is enhanced alveolar ventilation and enhanced perfusion

This is caused by enhanced alveolar ventilation and inadequate perfusion.

Question 19

Why is PO2 in tissues always lower than in the systemic arterial blood?

Answer 19

Because tissue cells are continuously using O2 for metabolic activities while producing CO2.
It allows O2 to move rapidly from the blood to the tissues.

Question 20

Describe haemaglobin and its relationship with oxygen

Answer 20

Haemoglobin has four polypeptide chains each bound to an iron containing heme group which can bind with oxygen.
When Hb is saturated with O2 it become Oxyhaemoglobin HbO2.
After the first O2 has bound the the iron in the Hb, Hb changes shape to make it easier for the next O2 molecule to bind.

Affinity for oxygen changes with saturation level.

Question 21

What effects the rate Hb binds to O2?

Answer 21

PO2
Temperature
Blood pH
PCO2
Blood concentration of BPG (organic chemical)

Question 22

What 3 ways can CO2 leave tissues in the blood?

Answer 22

1. Dissolved in plasma (7-10%)
2. Chemically bound to hameoglobin by being carried in RBC as carbaminohaemoglobin (20%)
3. As a bicarbonate ion, HCO3-) in plasma (70%)

Question 23

Describe the formation of carbaminohaemoglobin.

And its loading and unloading process.

Answer 23

CO2 rapidly binds to HB without a catalyst.
It binds to the amino acid of globin.
The loading and unloading are influenced by the PCO2 and degree of Hb oxygenation.

CO2 rapidly dissociate from haemoglobin in the lungs due to the PCO2 in alveoli being lower than in the blood. This means it can easily diffuse out of the blood, down its pressure gradient into the alveoli and be breathed out of the body.

In CO2 loading, the PCO2 is higher in tissues than the blood so it diffuses in down pressure gradient to be removed from the tissues.

Question 24

Describe the process of CO2 being removed from tissues as a bicarbonate ion?
What is that ion?

Answer 24

The ion is HCO3-
CO2 enters the red blood cells and combines with H20 to form H2CO3, carbonic acid, catalysed by carbonic anhydrase
Carbonic acids is very unstable so dissociated in to H+ and HCO3-.
The HCO3- the moves into the blood plasma with a CL- ion during the chloride shift.

This process can occur in the plasma but is much faster if it happens in the RBC.

Question 25

How does the bicarbonate ion leave the bloodstream into the lungs?

Answer 25

Reverse chloride shift occurs and HCO3- re-enter the RBC and reforms with the H+ to form H2CO3 where carbonic anhydrase catalyses the reaction to form CO2 and H20 where then the CO2 diffuses out of the RBC into the alveoli down its pressure gradient. The same can happen in the plasma but is slower.

Question 26

How is carbaminohaemaglobin removed from the RBC?

Answer 26

Co2 dissociates from haemoglobin in the lungs as the PCO2 of alveolar air is lower than in the blood. So diffuses down its pressure gradients, into the alveoli and is exhaled out of the lungs

Question 27

What is the chloride shift?

Answer 27

Ion exchange When HCO3- is created it rapidly moves out of the RBC into the plasma. To counterbalance the anion outrush, Cl- ion moves from plasma into the plasma via facilitated diffusion through RBC membrane protein. This process is reversed in the lungs as HCO3- re-enters the RBC so Cl- moves out into the plasma.

Question 28

What senses blood gas levels?

Answer 28

Chemoreceptors in brain and periphery

Question 29

What do the central chemoreceptors do and where are they found?

Answer 29

Medulla surface Respond to CO2 by increasing blood O2 Very sensitive High PCO2 -> increased ventilation Low pCO2 -> decreased ventilation Located in medulla oblongata which sends signals to respiratory centre in the brainstem to send signals along medullary inspiratory neurone to help maintain homeostasis.

Question 30

What do peripheral chemoreceptors do and where are they found?

Answer 30

Found in the arteries Respond to O2 and initiate reflexes during hypoxia to maintain homeostasis. During moderate decrease in O2 they only have minor effects on breathing. Try to maintain normal partial pressure levels. They direct blood flow to kidneys and the brain as they are areas more sensitive to hypoxia. Sends afferent signal along glosspharyngeal and vagus nerve to medulla oblongate and pons in brainstem to send imuples along the medullary inspiratory neurones to help restore blood pO2 - Blood flow directly to kidneys and brain - Cardiac output is increased to increase blood flow - Respiratory rate and tidal volume are increased to increase oxygen intake from lungs

Question 31

What is hypoxia?

Answer 31

Having low levels of oxygen

Question 32

What happens to the respiratory system at high altitudes and how does it try to adapt?

Answer 32

- Air density and PO2 is lower, harder to breath, can cause Acute Mountain Sickness, symptoms include - headaches, shortness of breath, nausea and dizziness. When being in high altitude for a few days the body begins to make adaptions in a process called acclimatisation. - Peripheral chemoreceptors stimulate an increase in ventilation to try and restore gas exchange levels - Haemoglobin's affinity for O2 is reduced due to increase in BPG concentration - Kidneys accelerate production of erythropoietin which stimulates bone marrow to produce more RBCs - Increase in capillary density to muscles - Plasma volume may decrease