Scenario Questions For A Medical Student Biology Essay

This assignment will reply five set inquiries in response to a scenario of medical pupil ( PF ) and his expedition to establish cantonment at Mount Everest. The replies cover subjects runing from anatomy, cardio-respiratory physiology and pharmacological medicine.

Effectss of high height on airing and its control

Ventilation includes both the refilling of gases in the lungs and the oxygenation of blood through the pneumonic capillary bed1. In healthy persons such as PF the chief variable impacting airing is the environment.Barometric force per unit area ( the force per unit area the Earth ‘s atmosphere exerts on objects ) varies with height ; at 5300 meters ( base cantonment ) the barometric force per unit area is 52 kPa. However the theoretical value for the partial force per unit area of divine O ( PIO2 ) is 9.6 kPa which takes into history the dilution factor of H2O vapour 6.

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3 kPa and the part or air that constitutes O ( 21 % ) .2Under normal fortunes the partial force per unit area of arterial C dioxide ( PaCO2 ) is detected by cardinal chemoreceptors of the myelin oblongata. Cardinal chemoreceptors have the lead function in the control of respiration. The function of peripheral chemoreceptors ( located in the carotid and aortal organic structures ) are negligible in comparing. However, in hypoxic conditions peripheral chemoreceptors chiefly regulate airing. Peripheral chemoreceptors detect hypoxic, hypercapnic, and acidic conditions. ( Refer to chart in appendix a screening when hypoxic thrust is stimulated ) .

Research has shown that it is the glomus cells in peripheral chemoreceptors which react to these alterations 3,4.Under normal conditions, glomus type 1 cells regulate their O sensitive Na K pumps keeping a resting membrane potency. In hypoxic conditions the Na+-K+-pump is inhibited therefore doing depolarization of a nearby subdivision of the glossopharyngeal nervus and the carotid fistula nervus. Action potencies travel to the respiratory Centre ( RC ) of the myelin. The RC houses both inspiratory ( I ) and expiratory ( E ) neurones in different compartments of which the ventral and dorsal respiratory groups are of high importance.

The lone piece of land karyon is located in the dorsal respiratory group which consists of largely I neurones, which undertakings into the phrenic and intercostal nervousnesss, innervating the stop and intercostal musculuss severally. Furthermore the ventral respiratory group consists of a aggregation of nuclei known as the Botzinger complex incorporating both E and I neurones. The E neurones extend into the intercostal motor neurones and aid in termination. The combined stimulatory consequence of these neurones alters the respiratory form and leads to a hyperventilatory response 4. Whilst peripheral chemoreceptors do play a major function in hypoxic conditions, there are several different receptors and physiological reactions that besides contribute to modulating and changing the beat of external respiration.When PF reached base cantonment blood trials were taken demoing blood O, C dioxide and pH. These trials were repeated the undermentioned twenty-four hours.

Discussion of the blood gases obtained and the differences between them

The initial blood trials are implicative of a typical response to high height. As stated antecedently when the PO2 falls below 8 kPa, as in the instance of PF, this leads to the stimulation of hypoxic thrust in order to increase O concentration. The following twenty-four hours ‘s set of blood trials showed a decrease in arterial PO2 and PCO2 of 1.8 kPa and 0.6 kPa severally. There was besides an addition in blood pH by 0.4.

The pH and the PCO2 can be explained by the effects of hyperventilation. Carbon dioxide is a respiratory acid ; hyperventilation removes C dioxide cut downing the sourness of the blood. The addition in arterial pH is known as respiratory alkalosis.However the decrease in PO2 is unexpected. Exposure to high height does ab initio take to hyperventilation whereas ; in the short term there is a decrease in both PO2, and PCO2. After 1 twenty-four hours there is a grade of acclimatization. Typically there would be an addition in infinitesimal airing ensuing in an addition in alveolar and arterial PO2. ( Refer to appendix B for a graphical representation ) 5 ( pp 254- 257 ) .

The continued decrease in PaO2 can be explained by understanding the formation of oxyhemoglobin. This is formed in a reaction between O and deoxyhaemoglobin at equilibrium. Based on Le Chatellier ‘s rule on equilibrium kineticss, the decrease in atmospheric O favours the rearward reaction and therefore a lessening in oxyhemoglobin. As a compensatory mechanism the person would bring on polycythemia to keep equal degrees of O in the blood.

Based on the consequences it would look that PF has non acclimatised 6.The alveolar gas equation can be used as a step of the relationship between the degrees of dental consonant ( PAO2 ) and arterial O. In healthy topics the PaO2 and the PAO2 are indistinguishable. When using the dental consonant gas equation to the first set of blood trials PAO2 matches the PaO2. However the 2nd unit of ammunition of blood trial show a difference between the PaO2 and PAO2 of 2.

5 kPa ( mention to computation in appendix degree Celsius ) .Based on this information and the computations it is implicative that PF is enduring from Type 1 Respiratory failure. Type 1 respiratory failure can be defined as holding hypoxia combined with normal or low degrees of C dioxide. This is chiefly due to a airing perfusion mismatch or a shunt ; the effect of which is to cut down the O transporting capacity of the blood7 ( pp 50-53 ) .

The inside informations of this shall be explained subsequently. In order to be able to understand the mechanics involved in respiratory failure, one has to appreciate the anatomical web of blood vass that supply the lungs.

Anatomy of blood supply to the lungs

The lungs are the receiver of two distinguishable circulatory systems. The bronchial circulation is really much a high force per unit area vascular web which has a prevailing function in supplying nutriment, except to the air sac. On the other manus the pneumonic circulation is a low force per unit area low opposition web, chiefly focused on gas exchange8.On the median surface of each lung is a aggregation of cannular vass known as the hilus. The hilus is located in the in-between mediastinum. Furthermore the hilus besides contains the chief blood vass, bronchus, nervous and lymphatic tissue 9.

The right lung is supplied by the right pneumonic arteria, which is found superior to the two pneumonic venas that leave at the hilus. The bronchial tube is more posterior in relation to the blood vass. The left lung mirrors the right lung, except for the, left pneumonic arteria which is located inferiorly to the bronchial tube. ( Mention a diagram in appendix D ) . Widening from the right ventricle, the pneumonic bole bifurcates at the part of the sternal angle ( T4/5 ) organizing the left and right pneumonic arterias.

The pneumonic arterias further divide in to arteriolas, which supply little sections of lung tissue know as the bronchopulmonary sections. There are 10s of these bronchopulmonary sections ( as illustrated in appendix vitamin E ) . Branchs of the pneumonic vena signifier anastomoses with the subdivisions of the pneumonic arteria. They so bit by bit unify to organize the superior and inferior pneumonic venas at the hilus, which later empty in to the left atrium 9, 10 ( pp139-150 ) .The bronchial arterias arise variably either straight from the thoracic aorta or from the intercostal arterias.

They are involved in the nutriment of the tracheobronchial tree ( the corporate term used to depict the divisions of the bronchial tube ) . In add-on the bronchial arterias are involved in providing mediastinal lymph nodes, pneumonic nervousnesss, splanchnic pleura and a part of the gorge. Venous blood from the first two to three coevals of the tracheobronchial tree is drained in to the intercostal, azygos and hemizygous venas. The staying bronchial venous blood drains into the pneumonic circulation.

Vasoconstriction of the pneumonic capillaries and arteriolas lead to HAPE, bring forthing symptoms such as coughing up of pink bubbling fluid10.

The likely mechanism of HAPE

PF has been diagnosed with high height pneumonic hydrops ( HAPE ) . HAPE is a signifier of noncardiogenic pneumonic hydrops that consequences from high height.

HAPE is induced by figure of reactions in response to hypoxic conditions. The primary factor is deficiency of O which inhibits the O sensitive K channels in the vascular smooth musculus of the pneumonic arteriolas. Inhibition of the K channels leads to the gap of Ca channels. Calcium moves in down the concentration gradient triping the myosin visible radiation concatenation kinase protein, ensuing in contraction of smooth musculus.

Subsequently, there is an addition in pneumonic arterial force per unit area ( by about 50 mmHg ) and an addition in capillary force per unit area ensuing in the bulge of fluid and localised hydrops. This procedure is known as hypoxic vasoconstriction ( HPV ) 11 ( pp 80-83 ) . Additionally, there is grounds to demo that hypoxia besides inhibits the endothelial cells ‘ ability to let go of azotic oxide hence cut downing the magnitude of vasodilatation therefore lending to HAPE.

Furthermore surveies besides suggest the balance of fluid in the air sac is affected by hypoxia. Alveolar epithelial tissue is involved in the resorption of alveolar fluid by a procedure of co-transportation of Na through Na channels. This procedure generates an osmotic gradient required for the transit of H2O into the cells. In hypoxic conditions there is a down ordinance of both the specific Na channels ( ENac ) and the Na K pump that drives this procedure.

Consequently alveolar fluid accumulates and patients can show with HAPE 12, 13. Regardless of the extended research into HAPE there remains no consensus on the existent cause.The symptoms of HAPE correspond with type 1 respiratory failure ensuing in a airing perfusion ( V/Q ) mismatch and a shunt. V/Q mismatch is when the blood flow in the capillaries ( perfusion ) is non adequately oxgygenated through airing, due to the barrier posed by the alveolar fluid. The congestion caused by the accretion of fluid leads to a diffusion block, whereby the diffusion distance for the motion of gases is increased. A ‘shunt ‘ refers to the bypassing of blood from parts in the lungs which are non adequately oxygenated to countries that are better oxygenated.

This procedure becomes pathological in HAPE. The V/Q mismatch, diffusion block and shunt are responsible for the symptoms of HAPE, such as sickness shortness of breath and tachypnoea etc 5.

Compare and contrast the actions of Nifedipine and Sildenafil

Nifedipine is a Ca ion adversary. It is a common drug used to handle HAPE, belonging to the dihydropyridine category. It is taken orally as a tablet, and one time digested it undergoes extended first-phase metamorphosis.

Nifedipine is primary metabolised by the cytochrome P450 in the liver whilst, using the isoenzymes CY3PA4, CYP1A2 and CYP2A6. It chiefly blocks electromotive force dependent L-type Ca channels found on alpha-1 receptors located on cardiac and vascular smooth musculus. It works by forestalling the transmembrane inflow of Ca ion therefore suppressing the contraction of smooth musculus, and bring oning vasodilatation.

With respects to its specific intent in the intervention HAPE, the vasodilatory consequence reduces the HPV, change by reversaling the symptoms of HAPE. Nifedipine is metabolised really rapidly and has a half life of two hours 14. This can besides be used in the intervention of angina high blood pressure etc. Nifedipine has negative ionotropic effects on myocardial tissue and can deject sinoatrial node and atrio-ventricular node conductivity in myocardium. However Nifedipine will preferentially adhere on to receptors on the vascular smooth musculus. 15,16.

Sildenafil is a drug whose effects are related to nifedipine. Sidenafil is more normally known as Viagra. Sildenafil is a phosphodiesterase V ( PED5 ) inhibitor ; it is taken orally and converted into an active metabolite via the liver, utilizing the same household of cytochrome P450 enzymes. Once activated its effects are exerted chiefly on vascular smooth musculus as opposed, to Nifedipine which affects cardiac and vascular smooth musculus. Sildenafil works by suppressing the PED5, cut downing the degrees of cyclic-GMP ( cGMP ) therefore maintaing a province of vasodilatation. Its actions chiefly concentrate on the smooth musculus of principal cavernosa, bring oning hard-on in males.

There has been some research bespeaking that it can cut down HPV, thereby change by reversaling the symptoms of HAPE17.18. Sildenafil has a half life of 4-5 hours. Research has shown that Sildenafil can be used as a prophylaxis to forestall HAPE as it has been shown to cut down pneumonic arterial force per unit area. However research is still ongoing and Sildenafil remains a front-line drug in the intervention of HAPE. Side-effects of Nifedipine include ; hypotension, blushing concerns, and break of cardiac beat. The unwanted effects of Slidenafil are ; concerns, blushing and retinal harm 19.


In decision this assignment has explained the mechanics of airing at high height. The functions of peripheral and cardinal chemoreceptors have been explained with respects to, their different methods of centripetal sensing and their interactions with different encephalon Centres.Interpreting blood gas informations is highly of import in diagnosing. Bing able to integrate relevant informations into the alveolar gas equation, and placing differences is alveolar and arterial gradient enables a better grasp of the extent of PF ‘s wellness.The footing of understanding how HAPE causes symptoms, is interlinked to the anatomy of the blood supply to the lungs.

By recognizing the anatomical differences in the bronchial and pneumonic circulation, and their functions, correlativities can be made between symptoms and the site of the hurt.HAPE is a complex upset chiefly characterised by hypoxic vasoconstriction, nevertheless its underlining pathology remains idiopathic. The chief intervention is a Ca channel blocker. Nifedipine is chiefly a vasodilative used as a from-line drug in the intervention of HAPE. Sildenafil is besides a vasodilative ; nevertheless has a lesser consequence on pneumonic capillary force per unit area 19.


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