Gas Exchange Flashcards
What are alveoli
Air filled pockets in the lungs where all gas exchange takes place
What are the types of cell of the alveoli
Pneumocytes type 1
Pneumocytes type 2
Macrophages
What are types one Pneumocytes and what do they do
Simple squamous
Thin cells, wall of alveoli
Short gas exchange distance
What are type two Pneumocytes and what do they do
More specialised
Produce surfactant
Larger cells
What is a macrophage and what does it do
Digest things that shouldn’t be there
Remove dust and foreign objects
What is the role of surfactant
Reduce surface tension to stop the alveoli from collapse h
Explain elasticity of the alveoli
Has a dense network of capillaries, is surrounded by elastic fibres
Fibres recoil during exhalation, reduce size of alveoli to push air out
Why is gas exchange efficient at alveoli
Walls less that one micro meter thick
Sa 35 x surface of the body
(Put together)
Explain alveolar epithelium
Simple squamous
Consists of thin delicate type 1 Pneumocytes
Patrolled by macrophages (dust cells)
Contain type 2 pneumocytes that produce surfactant
What is Henry’s law
When gas under pressure comes into contact with liquid, gas dissolves until liquid equilibrium is reached
At a given temperature:
Amount of gas in a solution is proportional to Pp of that gas
E.g the pp of oxygen at sea level is 20%
What are the factors that lead to efficient gas exchange
- Substantial differences in pp of O2 across the respiratory membrane
- Distances involved in gas exchange are short
- O2 and Co2 are lipid soluble
- SA is large
- Blood flow and air flow are coordinated
What does diffusion happen over
Concentration gradient, determined by pp
What is the pulmonary circuit
Heart and lungs,
Carries deoxygenated blood from the heart to the lungs to be oxygenated
What is the systemic circuit
Carries oxygenated blood from the left ventricle
How is gas transported
Plasma
Red blood cells - hb
- transport gas from peripheral tissues
- remove gas from plasma, allowing them to diffuse into the blood
How does oxygen bind to haemoglobin
Hemes - binding sites
Oxyhaemoglobin - saturated with oxygen
Deoxyhaemoglobin - without oxygen bound to it
Carbominohaemoglobin - carrying co2
Why is carbon monoxide dangerous
Haemoglobin has a higher affinity for it, stop oxygen binding
What factors effect o2 release
- ppo2
- blood ph
-temperature - bpg levels, increase with increase
Why is the oxyhaemoglobin saturation curve a curve not a line
Shape of hb molecule changes slightly every time it binds to an oxygen molecule
Each o2 binding makes more binding easier
Explain dissociation at equilibrium
Oxygen molecules bind at the same rate other oxygen molecules are released
What is normal saturation at rest
96%
How does temp effect affinity
Temp increase = hb releases more O2, less affinity
Decrease, release less, more affinity
What is the bohr effect
Result of ph on saturation curve
Caused by co2 production
= carbonic acid
Lower ph = lower affinity, more released- shift Right
Higher ph = higher affinity, less released, shift Left
How is co2 transported in the blood
Generated by aerobic metabolism
- dissolve in plasma 7%
- red blood cells 93%,
- 23 % of this bind to hb = cmhb
- converted to carbonic acid 70%
What is meant by local control of respiration
At the tissues
Increased activity of peripheral tissue = less o2 more co2 pp
Changes in gas exchange
Increased blood flow
Explain neural control of respiration
Respiratory centres at brain-
Increased demand = increased Q and resp rates
Involuntary:
Reg resp muscle activity
Freq and depth
Voluntary:
- reflects activity in cerebral y
- effect output of med ob, pons, motor neurons
Where are respiratory centres
Rcc in medulla oblongata
Pons has some control
Explain control of respiration in the pons
Pons and medulla oblongata are linked
- paired nuclei that adjust output of respiratory rhythmicity centres
Apneustic centres:
- provides continuous stimulation DRG, increasing intensity of inhalation - inhibited during exhalation
Pneumotaxic centres:
- inhibit A centre and promote exhalation
Where are the different respiratory areas in the brain
Higher centres:
- hypothalamus, Linux system and cerebral cortex alter activity if pneumotaxic areas
A and p centre in pons
Medulla oblongata, DRG VRG
What are the respiratory centre of the medulla oblongata
Dorsal respiratory group (top)
- inspiratory centre
- quiet and forceful
- intercostalmusckes and diaphragm
Ventral respiratory group
- inspiratory and expiratory centre
- only in forced breathing
- accessory respiratory muscles
Explain the cycle of the respiratory groups
- DRG and inspiratory centre of VRG active, expiratory centre of VRG inhibited
- Muscles of inhalation contract, and opposing muscles relax. Inhalation occurs
- DRG and inspiratory centres of VRG inhibited. Expiratory centre of VRG active
- Muscles of inhalation relax and muscle of exhalation contact. Expiration
What are the respiratory reflexes
- Chemoreceptors - sensitive to pp, ph, cerebrospinal fluid
- Baroreceptors
- Stretch receptors, sensitive to changes in lung volume
- Irritating physical or chemical stimuli in resp tract
- Temp ect
What are the mechanoreceptors involved in respiratory regulation
Baroreceptors
Stretch receptors - changes in lung volume
What is the hering-breurer reflex
2 mechanoreceptors reflexes involved in forced breathing
- inflation reflex
Prevents over expansion of lungs
As lung volume increases DRG inhibited, VRG stimulation (expiratory portion) - deflation reflex
Inhibits respiratory centres
Stimulated inspiration centre during lung deflation
Explain the chemoreceptor reflexes involved in respiratory control
Influenced by chemoreceptor input from:
Cranial nerves
Central chemoreceptors that monitor cerebrospinal fluid
(Csf contains oxygen so can tell oxygen concentrations, decide if need more respiration)
- in brain stem
What factors stimulate chemoreceptors
- drop on PO2 to 40mmHg = increase rate 50-70%
- 10% increase PCo2 = increase rate 100%
- chemoreceptor stimulation decreased sensitivity which chronic stimulation
- increased lactic acid, ph
