Gas exchange Flashcards
1
Q
What is the thoracic pressure like compared to atmospheric pressure?
A
- thoracic cavity pressure is negative pressure compared with thoracic pressure
2
Q
Due to lung tissue being elastic - what do they naturally want to do?
A
- lung tissue wants to collapse and deflate
3
Q
How is the thoracic cavity bounded and what does it naturally want to do?
A
- thoracic cavity bounded by ribs, sternum and diaphragm under tension
- this means it wants to spring out
4
Q
What does negative pressure aid in?
A
- negative pressure helps keep lungs semi-inflated even when exhaling
5
Q
Lung tissue has a high compliance - what does this mean?
A
- A small change in pressure leads to a large change in volume
- this is why its difficult to reinflate a collapsed lung
6
Q
What is the equation for compliance?
A
- compliance = change in volume / change in pressure
7
Q
Surfactant increases lung compliance.
What is it?
What does it do?
A
- polar phospholipid
- type 2 pneumocytes (alveolar epithelial cells)
- reduces energy needed to inflate lungs
- also prevents transudate (fluid) coming out of capillaries
8
Q
Disease states can alter lung compliance - what can a lack of surfactant leas to?
A
- a decrease in compliance
- e.g., respiratory distress syndrome
9
Q
Disease states can alter lung compliance - what does an increase in connective tissue lead to?
A
- decreases compliance
- e.g., fibrosis/scarring
10
Q
Disease states can alter lung compliance - what does reduced lung elastic tissue cause?
A
- increases compliance
-e.g., emphysema (makes deflation difficult)
11
Q
What type of process is inspiration?
A
- its an active process
12
Q
What does inspiration involve?
A
- involves increasing the volume of the thorax to lower pressure, causing expansion of the lungs
13
Q
Inspiration is achieved by pulling the ribs outward and displacing the diaphragm caudally into the abdomen - Describe the steps of this process:
A
- diaphragm contracts and flattens
- external intercostal muscles contract to aid ribs opening
- increased thoracic volume lowers pressure (more negative)
- this causes lungs to expand
- increased lung volume lowers pressure
- air is drawn into the alveoli where gas exchange occurs
14
Q
What type of process is expiration?
A
- this is a passive process at rest
- except in the horse where there is an activate phase even at rest
15
Q
Expiration involves the opposite to inspiration - what is the process?
A
- diaphragm relaxes, reducing volume of thorax
- thoracic wall and ribs return to resting position
- elastic lungs recoils, expelling air
16
Q
Further reduction of thoracic volume can be achieved by active muscle contraction - what does this process involve?
A
- internal intercostal muscles
- also accessory muscles of respiration e.g., abdominal muscles contract to increase abdominal pressure to force diaphragm more cranially
17
Q
Why does the horse show biphasic inspiration and expiration (passive and active phases)?
A
- because the horse has a firm thoracic wall
18
Q
Describe the process of expiration in a horse:
A
- relaxation, relying on elastic recoil of lungs and chest
- chest reaches resting volume
- further decrease by active contraction of internal intercostal and abdominal muscles
19
Q
Describe inspiration in a horse:
A
- relaxation, relying on elastic recoil of chest to open up
- chest reaches resting volume
- active inspiration phase by contraction of diaphragm and external intercostal muscles
20
Q
What nerve innervates the diaphragm?
A
- innervated by phrenic nerve
21
Q
What do gas molecules do to the walls they contact?
A
- they exert pressure on the walls they contact
22
Q
What is the total pressure equal to?
A
- equal to all gas molecules
23
Q
What is partial pressure?
A
- partial pressure (px) is that of a single gas
24
Q
What is atmospheric pressure of air at sea level?
A
- 760mmHg
25
Calculate the partial pressure of oxygen at 20.8% if the atmospheric is 760mmHg
- 20.8% x 760 = 158 mmHg
26
Why is understanding partial pressure important?
- important in predicting movement of gases
27
How will a gas move during partial pressures?
- a gas will move from area of high px to lower px
28
What is the ultimate goal of respiration?
- to keep correct concentrations of certain molecules in tissues for correct function
29
What gases can be found in tissues?
- oxygen
- carbon dioxide
- H+ (acid base balance)
30
What type of diffusion is gas exchange?
- simple diffusion
31
Gas exchanges can be from ... to ...
- from alveolus to blood (external respiration)
- from blood to tissues (internal respiration)
32
Fricks law described factors influencing the rate of diffusion of a gas across a membrane - what are these factors?
- surface area of the membrane
- thickness of the membrane
- partial pressure difference of gas across the membrane
- diffusion coefficient (properties of gas and membrane)
33
The rate of diffusion across a membrane can be affected by disease - what are these?
- alveolar destruction (surface area)
- fibrosis or oedema (thickness)
- ventilation disturbances, bronchoconstriction, atelectasis (Px)
- perfusion disturbances, emboli (Px)
34
Diffusion of O2 from alveolus into blood does what?
- follows pressure gradient
35
Internal respiration - describe the process of diffusion down a pressure gradient of O2:
- blood to interstitial fluid
- interstitial fluid to cell
- vice vera for CO2
36
What type of solubility does oxygen have in the blood
- a low solubility in the blood
37
What is most oxygen transported by?
- most oxygen is transported by a protein within RBCs called haemoglobin
38
What groups does haemoglobin contain?
- contains 4 iron-based haem groups
39
What does Haem bind to?
- molecular oxygen
40
What can the 1st O2 binding to 1st haem group cause?
- conformational change in haem
41
What can the 2nd and 3rd O2 molecules binding to haem cause?
- easier binding (increased affinity)
42
What happens when PO2 is low to Haemoglobin affinity for oxygen?
- Hb affinity for O2 is low
- in tissues encourages Hb to drop O2
43
When po2 is high what happens to Hb affinity for O2?
- Hb affinity for O2 is high
- in lungs encourages Hb to pick up O2
44
The oxygen dissociation has an S-shaped curve - what does this show?
- as more O2 binds to Hb, its affinity changes (increases at first, then decreases)
45
The dissociation curve can be shifted due to other factors - what happens during a left shift?
- left shift = generally increased affinity
- same Po2 - higher Hb saturation
- easier to pick up O2
46
What causes a right shift of the oxygen dissociation curve?
- right shift = generally decreased affinity
- same po2, lower Hb saturation
- easier to drop off O2
47
What can a left shift cause?
- higher pH (alkalosis)
- lower Co2
- lower temperature
48
What does a right shit cause?
- lower pH (acidosis)
- higher CO2
- higher temperature
49
Hoe does Co2 diffuse?
- diffuses down its conc gradient into bloodstream
50
What can Co2 be transported as?
- dissolved in the plasma - 7%
- bound to amine groups of Hb (carbaminohaemoglobin) - 23%
- as bicarbonate ions HCO3 - 70%
51
Transport as HCO3- contributes to the bicarbonate buffer system how?
- Bicarbonate (HCO3-) and carbonic acid (H2CO3) together ‘buffer’ dramatic changes to pH and so contribute to acid-base balance
52
Why is carbon monoxide gas so poisonous?
- Binds to Hb but with a 200-300 x greater affinity than O2
- even at low PCO it doesn't want to dissociate = irreversible binding to Hb and so displaces O2
