Breathing Flashcards
What is respiration?
Includes two processes:
External respiration, the absorption of O2 and removal of CO2 from the body as a whole;
Internal respiration, the utilization of O2 and production of CO2 by cells and the gaseous exchanges betweenthe cells and their fluid medium
How is breathing controlled spontaneously?
In the brain, the medulla controls spontaneous breathing, it is where respiratory pacemaker lies.
Central Chemoreceptors detect CO2 concentration;
Peripheral Chemoreceptors detect CO2 concentration and blood pH;
Both chemoreceptors feedback to brain stem respiratory centres, so increased CO2 and acid during exercise causes more breathing.
We can override this to an extent but respiratory pacemaker is a fail safe - you’ll eventually pass out and return to spontaneous breathing if you hold your breath.
Why do we need gas exchange?
To get oxygen to tissues and CO2 away from it.
What enables pulmonary gas exchange in the lungs?
Adequate ventilation (air going into lungs) and perfusion (adequate blood entering lungs that can be oxygenated).
Mainly due to diffusion of gas across the alveolar-capillary membrane. Thin walled alveoli and thin walled capillaries in contact allow for this.
How do we carry oxygen in the blood?
We have haemoglobin in the blood - a tetramer with 2 alpha and 2 beta subunits, each of which has a Haem group (a porphyria with a central Ferrous atom).
The Oxygen binds to the Ferrous atom when they come into contact, initially loosely.
Once one Oxygen has bound, easier for it to bind to the other haem groups on the other subunits as the initial combination alters the shape of the haemoglobin, making it more efficient in binding to oxygen.
What is the Oxygen-Haemoglobin dissociation curve?
Compares haemoglobin-oxygen saturation at different concentrations of oxygen. Steep curve - only 1 of 4 of the possible O bound at very low concentrations but sharply increases after 1 has bound to all possible bound.
What does a right shift in the oxygen haemoglobin dissociation curve mean?
The haemoglobin has less affinity for oxygen so gives it up more readily.
What causes haemoglobin to have a lower affinity for oxygen?
What does it do to the haemoglobin oxygen dissociation curve?
Increase in CO2
Increase in [H+] (pH)
Increase in temperature
Increase in 2,3-DPG (metabolite)
These all happen in muscles during exercise.
This shifts the oxygen-dissociation curve to the right.
How is carbon dioxide carried in the blood?
Main way is by CO2 dissociating with water to form H2CO3 which further dissociates into H+ and HCO3- to be carried in blood.
Dissolves back into CO2 and goes down concentration gradient into lungs and expelled into alveolar space.
A small amount will also be bound to haemoglobin and a small amount bound to amino acids in body system but most dissolved.
Why do we need oxygen?
Essential for aerobic respiration (glycolysis to get ATP).
What is required for adequate oxygen?
A supply of oxygen, working lungs, working heart, haemoglobin.
What happens at higher altitude to partial pressure of oxygen?
Lower partial pressure.
Should be about 21 kPa at sea level.
How do we quantify oxygen carriage?
Non-invasive: haemoglobin saturation (oxygenated haemoglobin is red and uses absorption spectroscopy so as long as Hb is normal, accurate)
Invasive: arterial blood gas (more complicated but if Hb is abnormal good as detects overall oxygen levels and CO2 levels in blood as well as saturation, also pH, bicarbonate, electrolytes and other form of haemoglobin)
Not enough oxygen getting into the lungs is a way that respiration can go wrong.
What are some reasons this can happen?
High altitude or low Oxygen environments like industrial accidents.
Diseases that obstruct flow of air (and so oxygen) to alveolus which cause not enough gas getting across airway, something in way of gas exchange (acute inflammation/pus/water), chronic alveolar thickening (pulmonary fibrosis);
Asthma causes an inflamed airway so not enough gas can get across airway,
Cystic Fibrosis causes mucus build up and inflammation in airway,
COPD increased mucus and destruction of alveoli and connecting tissue so collapse of conducting airways,
Pneumonia causes inflammation (narrowing airways), damage in the small airways and alveoli (fluid in alveoli). This means not enough oxygen gets into the blood, causing ventilation to perfusion (V/Q) mismatch - treat by increasing oxygen provision.
What is asthma?
Asthma causes basement membrane and smooth muscle thickening of the alveoli so not enough gas can get across this narrowed airway since it’s thicker and inflamed.
Treat with bronchodilators.
What is cystic fibrosis?
Cystic Fibrosis causes mucus build up and inflammation in airway, making it harder for oxygen to get in to alveoli.
We now have drugs that call alter the mutated protein in CF.
What is COPD?
COPD increased mucus and destruction of alveoli and elastic fibres in the lung so collapse of conducting airways, limiting airflow.
Treat with bronchodilators.
What is Pneumonia?
Pneumonia causes inflammation (narrowing airways), damage in the small airways and alveoli (fluid in alveoli). This means not enough oxygen gets into the blood, causing ventilation to perfusion (V/Q) mismatch.
Dense shadowing on x-ray since alveoli full of pus and fluid.
Treat by increasing oxygen provision and if bacterial, give antibiotics.
What is pulmonary fibrosis?
Causes chronic alveolar thickening, preventing adequate gas exchange.
See as shaggy shadowing on x-ray.
What is pulmonary oedema?
Extra fluid in the lungs because heart isn’t pumping properly, meaning fluid in way of gas exchange at alveoli.
Shadowing on x-ray but outline of lungs normally quite clear.
Treat with diuretics.
What is a pulmonary embolism?
Blood clots move into lung and block deoxygenated blood getting to area where it’s oxygenated.
Some shadowing and darkness on an x-ray as where blood isn’t getting to the lung, darkness. But normally we use CT scan - darkness on area is clot where tracer is so should be bright (pulmonary artery).
Treat with anti-coagulators.
How is oxygen therapy given?
Variable performance masks are cheap but the exact inspired O2 concentration is not known.
Fixed function masks have constant, known inspired concentration.
Reservoir mask have high inspired concentration of Oxygen.
Invasive Ventilation is required for severe respiratory failure not responding to oxygen therapy.
Generally treat with oxygen alongside trying to treat cause.
What is Invasive Ventilation?
Invasive Ventilation is required for severe respiratory failure not responding to oxygen therapy, but it is not a suitable treatment for all patients and is provided in intensive therapy units.
What does the circulation do?
Allows oxygen and CO2 to go to cells and be taken away, provides cells with nutrients, allows waste products to be taken away, also allows for metabolism, immune system, circulating hormones, body temperature regulation…
What are the two circulatory systems?
Pulmonary - smaller, arterial pressure of about 25/10mmHg, only lungs
Systemic - much larger, arterial pressure of about 120/70, all of body
Side note: there is circulation systems involving circulatory fluids like lymph as well as blood.
Aside from the heart, what controls circulation?
Brain and kidneys
Describe distribution of fluid in the body.
We are 60% water.
1/3 of that is extracellular, 2/3 intracellular.
25% of extracellular fluid is intravascular fluid (plasma), 75% extravascular (interstitial).
So of a 60kg body, 36L fluid, 3L of plasma.
What is the haematocrit?
Ratio of blood plasma and blood cells present. Broadly 55% plasma, 45% cells.
[Haematocrit: in men it’s actually 0.4-0.52, in women 0.36-0.47]
What is the circulating volume in an average adult?
5 litres (3L plasma, 2.4L blood cells, roughly)
What does the lymphatic system so?
Mops up any fluid not taken back up by small veins and return it to the large veins.
What is laminar flow?
How does this relate to blood vessels?
In a tube, fluid won’t flow equally across the tube. This is due to friction at the walls, so closer to centre has a greater flow.
This is governed by Poiseuille’s Law (flow through a rigid tube is due to a pressure gradient) and most greatly influenced by the radius, but also by the liquid’s viscosity and the tube length.
Means vessel size will have a dominant effect on the flow through them, more so than viscosity/length.
What are resistance vessels?
Arterioles and the smallest arteries.
They have small diameters and many branches.
Where is there a bottleneck in the vascular system?
Why is this?
Bottleneck at the arterioles.
This is because as well as having a small radius, they are not very numerous (capillaries and venules have many branches which overcomes their small radii).
The cross-sectional area increases greatly in the capillaries and venules.
How does the velocity of blood flow change across the vasculature?
Why is this useful?
Greatest in the arteries, then decreases at the arterioles, slowest in capillaries and then increases again in veins.
This means tissues bathed carefully in the fluid so function of gas exchange can be fulfilled.
How does the blood pressure change in the vascular system?
Continuously decreases but pressure drops with greatest gradient across the arterioles.
Pulsitivity of the pressure also decreases as the arteries get smaller until continuous flow at end of arterioles.
What function do veins have that compensate for their low pressure?
Valves
What tissue type is present in capillaries?
Only endothelium - this allows for greatest diffusion.
Which vessels ave a greater proportion of elastic tissue?
Why is this useful?
Larger arteries as they are closest to the heart which is a pump.
This means there is elastic recoil, propelling fluid forward in between cycles (each pump of the heart), dampening down the pulsatile swings very effectively so by the time it reaches the arterioles it’s much weaker and by the time it reaches small arterioles and capillaries, it has gone and there’s a continuous flow.
What types of tissues are present in the venous system?
In venules, only epithelium and fibrous tissue.
In veins, have epithelium, elastic, smooth muscle and fibrous tissue but much less than in arteries. This allows for them to be less sprung open than arteries to allow them to absorb changes in blood volume.
What types of vessels have muscular tissue?
What is the benefit to this?
Smaller arteries and arterioles.
These have a basal vascular tone which allows them to respond to systemic and local regulators by altering their tone.
Systemic regulators can alter blood pressure, especially in resistance vessels.
Local regulators modulate local blood flow, providing more blood to where there’s a greater need, especially in arterioles and pre-capillary sphincter.
What is the structure of arterial walls?
Tunica intima - endothelium and internal elastic lamina (keeps it sprung)
Tunica media - smooth muscle (sometimes elastic lamina beyond that in larger vessels)
Tunica external - loose connective tissue
(This is from deep to superficial)
What regulates vascular tone in smooth muscle in vessels?
Adrenaline and noradrenaline which act on alpha-1-adrenergic receptors (vasoconstrictive - increase blood pressure, reducing blood flow) and beta-2-adrenergic receptors (vasodilators - decrease blood pressure, increase blood flow).
Other vasoconstrictors are Angiotensin2, Endothelin, inflammatory mediators…
Other vasodilators are Histamine (like in allergies) which can be released and cause swelling, nitric oxide, prostaglandins…
What changes local to a muscular vessel cause vasodilation?
Interstitial pO2 decreasing, pCO2 increasing, pH decreasing.
These have the opposite effect in the pulmonary system.
