Respiratory 3 Flashcards
1
Q
Why does gas exchange occur?
A
- exchange of gases between alveoli, blood, and tissues occurs due to differences in the partial pressures of gasses
- atmospheric pressure (barometric pressure)= 760mmHg at sea level
2
Q
What is Dalton’s law of partial pressures?
A
- in a mixture of gasses, each gas will contribute to the total pressure of the system in direct proportion to its percentage in the mixed gas
- [percentage] x [%gas]= partial pressure of gas (Pgas)
- direction of diffusion is determined by partial pressure of the gas (gas moves from high to low pressure)
- ex: atomospheric 160mmHg, alveolar 105mmHg, arterial blood 100mmHg, tissue 40mmHg so that gas will move from atmosphere to the tissues
3
Q
Describe the partial pressure gradients as air enters the alveoli, and as air goes back into the atmosphere
A
- as atmospheric air enters the alveoli, partial pressure of oxygen decreases due to increase in water vapour and carbon dioxide and partial pressure of carbon dioxide increases from addition from blood
- as air moves from the alveoli to the atmosphere, partial pressure of oxygen increases and partial pressure of carbon dioxide decreases due to mixing of air with dead space
4
Q
Describe gas exchange through the alveolus
A
- blood returing from tissue (“venous” blood flowing through pulmonary artery): oxygen level is low, CO2 level is high
- as blood moves past alveolus it will pick up some oxygen and will offload CO2
- partial pressure of O2 will increase and CO2 will decrease
- blood is now “arterial” travelling through pulmonary vein
- CO2 concentrations within the blood affect pH so they are kept at a very limited concentration window
5
Q
How does pulmonary edema affect gas exchange?
A
- diffusion barrier
- plasma leaks into airway and creates a thick fluid layer so now oxygen and carbon dioxide have to diffuse across this fluid layer
- oxygen doesn’t dissolve well in water so the blood can only pick up so much oxygen
- still able to get rid of CO2 because it dissolves well in water
6
Q
What is a ventilation/perfusion mismatch?
A
- sometimes there are regions of the lung where there is an imbalance between how well it is ventilated and how well it is perfused with blood
- described as an abnormal V/Q ratio
- V: ventilation
- Q: how much blood is flowing by alveolus
- Normal V/Q ratio: good ventialtion of alveoli and lots of blood to support gas exchange
- High V/Q ratio: good ventilation but poor blood flow, naturally happens at apex of lung and pulmonary embolism
- Low V/Q ratio: not enough ventilation of a well perfused area, happens in asthma, lung cancer, base of lung
7
Q
How is ventilation/perfusion mismatch corrected for?
A
- pulmonary arterioles that supply alveoli have oxygen sensors to sense oxygen partial pressure in alveolus
- if arterioles sense there is a lot of oxygen present, they will relax
- if they sense low oxygen, they will constrict
8
Q
What occurs to the pulmonary aterioles when oxygen concentration is high?
A
- if blood flow is low, pulmonary arteriole smooth muscle cells have oxygen sensors which sense the high oxygen and they relax
- allows blood to flow by alveolus and pick up the oxygen and get rid of CO2
9
Q
What occurs to the pulmonary aterioles when oxygen concentration is low?
A
- pulmonary arterioles sense low oxygen and constrict
- this shunts blood away from that alveolus and send to others that are better perfused
- helps to restore ventilation and perfusion
- hypoxic pulmonary vasoconstriction
- only tissue where vessels constrict in response to low oxygen (all other tissues would dilate with low oxygen)
10
Q
How do your pulmonary arterioles respond when you go to a higher elevation and in COPD?
A
- atmospheric pressure is lower
- partial pressure of oxygen drops
- pulmonary arterioles sense the decrease in partial pressure of oxygen in alveolus so they will all start to constrict
- there are no well ventilated alveoli because it is an atmospheric issue
- might develop pulmonary hypertension
- in COPD or chronic bronchitis, inflammation of bronchi themselves limits the ability to ventilate the entire lung
- pulmonary hypertension leads to congestion of blood on right side, right ventricular dilation, and heart failure
11
Q
How is CO2 carried in the blood?
A
- 7% dissolved
- 70% as HCO3-
- 22% bound to hemoglobin
- concentration is highest at tissue and venous blood
- lowest at lungs
12
Q
How does CO2 move from tissue to blood?
A
- some is dissolved in plasma and moves across endothelium
- some will react slowly to form HCO3-
- the rest will react quicky in the erythrocyte to also form HCO3- via carbonic anhydrase
- some will stick to the hemoglobin molecule and ride with it (called carbamino hemoglobin)
-
13
Q
How does CO2 move from the blood to the alveoli?
A
- CO2 will dissociate from high pressure in the blood to low pressure in alveolus
- bicarb slowly reverts back into water and CO2
- occurs quicker in the erythrocyte due to carbonic anhydrase
- carbamino hemoglobin will let go to move from high to low concentration
14
Q
How is oxygen transported in the blood?
A
- 1.5% dissolved
- 98.5% bound to hemoglobin
- oxygen is highest in alveoli, slightly less in arterial blood, and lower in tissue
15
Q
Describe the structure of hemoglobin
A
- central heme ring within 4 globular proteins (2 alpha and 2 beta)
- iron ion in centre of heme ring that binds reversibly with oxygen
- partial pressure determines if oxygen binds to hemoglobin
- if partial pressure is high, it will favour binding
- heme has high affinity for CO (carboxy hemoglobin)
- fetal form has higher affinity for oxygen than the adult form (has to pull oxygen off of maternal hemoglobin)
- sickle cell anemia: single nucleotide polymorphism within globular part of chain so that in the deoxy form it takes on a strange conformation, crystals poke plasma membrane so they don’t last very long in circulation
16
Q
Describe oxygen saturation
A
- hemoglobin molecule has 4 opportunities for oxygen binding
- would never see 0 oxygen bound to hemoglobin in the body because it would mean there is no oxygen present anywhere in the environment
- as you add oxygen molecules, it favours more oxygen molecules binding (cooperativity of binding)
17
Q
Describe changes in hemoglobin saturation with respiratory failure
A
-with respiratory failure, partial pressure of oxygen can drop as low as 60mmHg without seeing much change in hemoglobin saturation
18
Q
What does the steep slope of the O2-Hb dissociation curve indicate?
A
- at the tissues, partial pressure of oxygen drops from 97% in the lungs to approximately 40% in the tissues
- at rest, 25% of oxygen is released from hemoglobin to the tissues
- this means that when you need to exert more energy that is more than what you would at rest, you have 75% of oxygen bound on hemoglobin ready to be released
- steep part of curve allows you to have a small change in the partial pressure of oxygen and a large change hemoglobin saturation
19
Q
What conditions need to be met to shift the O2-hemoglobin curve to the right?
A
- under certain conditions, hemoglobin will favour getting rid of oxygen to give it to a tissue
- highly metabolically active tissue generates CO2, has higher temperature, and lower pH
- these shift the curve to the right which means that if these conditions are met, you can increase the amount of oxygen that is taken off of hemoglobin
20
Q
What are the functions of the ventral and dorsal respiratory groups?
A
- dorsal respiratory group sends bursts of neural activity to the muscles of inspiration during normal quiet breathing (diaphragm, external intercostals)
- inspiratory area is active for 2 seconds sending signal then inactive for 3 seconds to allow the lung that was just stretched to recoil
- innervates muscles of inspiration through the phrenic nerve (C3,4,5) and the internal intercostals
- the ventral respiratory group sends outputs to accessory muscles during forced breathing
29
Q
What are central chemoreceptors?
A
- located in brainstem
- measuring pH of CSF
- blood brain barrier doesn’t allow HCO3- and H+ through
- CO2 can get through the BBB
- central chemoreceptors measure pH through CO2 diffusion into the chemoreceptor and conversion into H+
30
Q
How do chemoreceptors respond to ensure adequate pH and oxygen levels?
A
-ventilating more allows more oxygen into the blood to correct pH, increased CO2 and decreased O2 levels
