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Compare pulmonary and systemic blood flow

Pulmonary blood flow refers to the flow of deoxygenated blood from the right side of the heart to the lungs, and the oxygenated blood from the lungs being pumped into the left side of the heart and is pumped around the body. Systemic blood flow refers to oxygen being deposited into the tissue and carbon dioxide being transported back to the lungs, the opposite of pulmonary circulation.


Describe the main anatomical features of the airways and gross anatomical features of the lung

air can enter through the nose or the mouth, then through the nasopharynx through the larynx which is where the vocal cords are located and marks the end of the upper respiratory system. Here the channel splits into the trachea which consists of stiff cartilage, guarded by a flap called the epiglottis, and the oesophagus. Through the trachea the airways split between the two lungs into the bronchus which further divide into secondary bronchus, which then divide into bronchioles which finally end as alveoli. Surrounding the lungs is the pleural cavity, diaphragm a dome shaped muscle, ribs and muscles.


Identify the different classes of airways and pneumocytes

Type 1 alveoli cells – thin for diffusion
type 2 alveoli cells surfactant – secrete surfactant, easing tension making breathing easier

For the airways we have:
blood vessels

as we progress from nose to lungs we lose cilia, mucous is lost and the epithelium become more squamous.


State the mechanical factors that affect respiratory minute volume.

pressure (boyle’s law)
resistance and the radii of airways
the stretch of the lungs
trans pulmonary pressure


Explain why intrapleural pressure is always less than alveolar pressure.

intrapleural space is always being pulled at by the elastic pull of either the lungs or the ribs, however due to the tension of the fluid between the two membranes doesn’t separate. The alveolar pressure is always higher because it’s adhered to the ribs the pleural cavity allowing it to expand and compress.


Be able to describe the anatomy of the pleural cavity

it consists of a visceral membrane binding it to the lungs, and a parietal membrane binding it to the ribs, with about 3ml of fluid in between the two membranes which encompass the lungs.


Understand the relationship between the parietal and visceral pleura and why this is important for inflation of the lung

the small amount of fluid enables gliding but doesn’t allow for separation of the two membranes. They keep the lung adhered to the ribs through the membranes.


Be able to describe how the muscles of respiration act to increase and decrease thoracic volume

the muscles such as the diaphragm contracts, and the external intercostal muscles, scalene muscles, sternocleidomastoid muscles pull on the ribs increasing thoracic space allowing for the lungs to increase in volume for inspiration, where as if the diaphragm relaxes, and the internal intercostal muscles contract pulling on the ribs and the abdominal muscles contract, the thoracic space decreases, decreasing lung volume increasing pressure triggering expiration.


Relate Boyle’s law to the mechanics of breathing, inspiration and expiration

Boyle’s law dictates that as volume decreases, the pressure increases meaning there is an inverse relationship between the two. As someone inspires, the volume of the lungs increases and pressure decreases, so air can move from a place of high pressure to low pressure. As they expire, the volume decreases, and pressure increases so the gases move from an area of high pressure to low pressure.


Define the various lung volumes and capacities and, provide approximate normal values for them.

tidal volume – volume of either a inspiration or expiration – 500ml
total lung volume – 6000ml
expiratory reserve volume – 1100ml
residual volume – 1200ml
inspiratory reserve volume – 3000ml
air from dead space – 150ml
vital capacity – tidal volume + expiratory reserve volume + inspiratory reserve volume – 4600ml
functional residual capacity – expiratory reserve volume + residual volume – 2300ml
inspiratory capacity – tidal capacity + inspiratory reserve volume – 3500ml


State the role of pulmonary surfactant and the Law of Laplace

The role of pulmonary surfactant is to ease the fluid tension required for the absorption of oxygen to prevent the collapse of the alveoli. The law of Laplace (P=2T/r) is that increasing the volume of fluid within the alveoli increases the pressure, especially within smaller alveoli which is problematic as we need smaller alveoli instead of larger ones for increased surface area. Surfactant overcomes this as in a smaller space the concentration is increased and obstructs the affinity water molecules have for one another. This makes breathing easier, reduces recoil and increases lung compliance.


Summarise the basic characteristics of obstructive and restrictive lung disease.

obstructive lung disease has a massive effect of air exhaled and slightly reduces the vital capacity. An example of this is COPD as its major effect is on the airways, this reduces the ratio between FEV1/FVC (forced expiratory volume 1 second/forced vital capacity).

restrictive lung disease reduces the amount of air exhaled and the vital capacity dramatically, such as pulmonary fibrosis as this limit the lung expansion. This doesn’t reduce the ratio and often requires a comparison of forced expiratory flow (average of a forced expiration) to recognise.


Describe the tests used to identify abnormal lung function.

spirometry, it can be dynamic where the time taken to exhale a certain volume is measured or it can be static where only the volume is considered. It can measure tidal volume, expiratory reserve volume, inspiratory reserve volume, vital capacity and inspiratory capacity.


Know the normal values for alveolar and arterial gas partial pressures

Pa oxygen - 100 mm hg
Pa carbon dioxide – 40 mm hg
PA oxygen – 40 mm hg
PA carbon dioxide – 46 mm hg


Describe the difference between pulmonary and alveolar ventilation

pulmonary ventilation involves the tidal volume of each breath, then the number of breath per minute this tells us the total air getting into and out of the lungs. The alveolar ventilation refers to the fresh air for exchange reaching the alveolar, taking into account the dead air.


Describe the factors that affect the oxyhaemoglobin dissociation curve.

Factors that affect the oxyhaemoglobin dissociation curve are temperature, and increase in temperature will shift the curve to the right, resulting less affinity between haemoglobin and oxygen, and a decrease will shift it to the left meaning during severe hypothermia oxygen isn’t being diffused to the tissues. Increasing pH will also shift the curve to the right, as well as increasing the partial pressure of carbon dioxide and 2,3-DPG which is a chemical released during hypoxia to encourage oxygen diffusion.


State the factors that affect gas exchange

the partial pressure gradient
gas solubility
surface area
thickness of membrane


state the differences between partial pressure and gas content.

partial pressure determines the pressure of which the gaseous form is pushing the gas into solution, it doesn’t equal gas content which refers purely to the gas in solution, which is partly determined by solubility and partial pressure.


Compare oxyhaemoglobin dissociation for adult haemoglobin with that of foetal haemoglobin and myoglobin in relation to their physiological roles

myoglobin has the highest affinity for oxygen as it’s located in the muscles, then foetal haemoglobin as they both require the taking the oxygen from oxyhaemoglobin in order to meet energy demand.


Identify the forms in which CO2 is carried in the blood.

7% of CO2 dissolves directly into the plasma, 23% can bind to haemoglobin to form deoxyhaemoglobin and 70% forms HC03- bicarbonate ions in solution.


Identify the factors which favour CO2 unloading to the alveoli at the lungs.

the increase partial pressure of oxygen favours oxygen loading at the haemoglobin. On top of that carbon dioxide is being constantly removed at the lungs from plasma, meaning that the forms of CO2 transport are converted back into CO2 to try and from equilibrium, as well as the difference in partial pressure meaning that carbon dioxide will follow the gradient into the alveoli. Other factors like pH also favour oxygen loading which subsequently means carbon dioxide unloading.


Explain the relationship between ventilation and perfusion and its significance in health.

ventilation and perfusion should ideally match each other in rate of flow per L/min. conditions like emphysema, fibrotic lung disease, pulmonary oedema and asthma can all reduce the amount of oxygen being absorbed this results in deoxygenated blood being reabsorbed and mixed with oxygenated blood causing hypoxia.


Describe the term ‘shunt’.

shunt refers to the flow of blood through poorly ventilated areas, it when the rate of ventilation is less than perfusion, which is the opposite of alveolar dead space. Results in diverted blood flow as the systemic vessel around the effected alveoli is constricted and the bronchiole dilates.


Describe the role of haemoglobin in the transport of O2 in the blood.

only 3ml of oxygen can dissolve into plasma which isn’t enough to meet demands. As a result, haemoglobin can take absorb much more oxygen (1g of Hg can absorb 1.34g of oxygen), maintaining the partial pressure gradient of oxygen from the alveoli to the blood. Its cooperative binding works in that the more oxygen it has the easier it is for oxygen to bind, and as it begins to unload it’s easier to lose its oxygen. It’s ideal for the factors that affect dissociation are the ones found in the tissues where oxygen is needed most, whist these factors aren’t found in the lungs meaning it can readily pick up oxygen.


Explain why the shape of the oxyhaemoglobin dissociation curve is important to O2 loading in the lungs and unloading in the tissues.

the sigmoid shape of the oxyhaemoglobin curve means that a large decrease in oxygen partial pressure translates only to a small decrease in oxygen saturation of oxyhaemoglobin. Even at partial pressure of 40mmHg, oxygen saturation is still at 75% leaving a large reserve.


Explain the action of carbonic anhydrase in CO2 transport

carbonic anhydrase (H20) helps convert the carbon dioxide into carbonic acid which then dissociates into bicarbonate and hydrogen ions, the excess hydrogen ions bind to deoxyhaemoglobin whilst the bicarbonate is pumped out the erythrocyte through a chloride channel into plasma.


Know the difference between anatomical, alveolar and physiologic dead space

alveolar dead space shouldn’t really be present in a healthy human, it occurs once a alveolar is no longer participating in gas exchange. Anatomical dead space is the air present in the airways that is unable to participate in gas exchange, it equates to roughly 150ml and is regularly replaced with fresh air or stale air from the alveoli. Physiological dead space is calculated by adding together the anatomical and alveolar dead space.


State the factors that determine arterial PO2

oxygen bound to haemoglobin
saturation of haemoglobin (temp, pH, PCO2, DPG)
total number of binding sites
oxygen dissolved in plasma
alveolar ventilation
perfusion of alveolar
composition of air
diffusion of oxygen


explain how respiratory motor movements are affected by the central nervous system

the diaphragm is innervated by the phrenic nerve, since the diaphragm is responsible for 70% of the work required for breathing it highlights how heavily influential the central nervous system is for control of breathing, if there is damage to the vertebrae C3,4,5 breathing ceases and results in death, this demonstrates that it is entirely dependent on the brain and it is not autonomous. The intercostal muscles that aid in breathing also are innervated and thus controlled by the intercostal nerves that stem from the spinal cord which their impulses originate from the brain stem.


List the factors involved in changing ‘respiratory drive’, rate and depth of breathing.

respiratory drive is controlled involuntary by the medulla and the pons, specifically the dorsal respiratory group (DRG) which controls the inspiratory muscles and the ventral respiratory group (vRG) which influences the expiratory and inspiratory muscles such as the pharynx, larynx and tongue. These centres are influenced by primarily chemoreceptors; however, they can also be influenced by chemoreceptors in the peripheral carotid and aorta. The further can be influenced by the limbic system through emotions, mechanoreceptors in the chest wall, or voluntarily by the higher centres of the brain but these can override by the brainstem.