This document discusses the importance of the small intestine in the digestion process. It covers topics such as enzyme activation, regeneration of the intestinal lining, mucus lining, inhibitors of activation, and the role of cholecystokinin. References are provided for further reading.
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Assign.2:Question 1Surname, First Name A. The small intestines produce enzyme activators such as enterokinase, which activates trypsinogen to trypsin which is required for the digestion of proteins in the small intestine. Active trypsin is dangerous to small intestine epithelial wall cells and therefore only activated in presence of substrates (1). B. The small intestine epithelium is highly regenerative, regenerating its lining 5-7 days and this enables the intestinal epithelium to hold on despite continuous abrasion that it suffers when breaking down food and absorbing nutrients (2). Breaking down of food needs bile and pancreatic juices to take place. C. The mucus lining of the small intestine secreted by Brunner glands found in the duodenum ensure there is a protective barrier against active pancreatic and bile juices against entry into mucosa layer of the small intestine (3). D. The inhibitors of activation found in the small intestine ensure that both pancreatic juice and bile are not active inside the lumen unless there are substrates present for digestion. E. Cholecystokinin produced by the small intestine contracts the gall bladder to release bile, stimulates pancreatic enzyme release and relaxes the sphincter of Oddi to allow the passage of pancreatic juice and bile to act on substrates in the small intestine (4). It is only produced when food enters the small intestine from the stomach, offering protection from bile and pancreatic juice. References 1.Canani RB, Terrin G, Cardillo G, Tomaiuolo R, Castaldo G. Congenital diarrheal disorders: improved understanding of gene defects is leading to advances in intestinal physiology and clinical management. Journal of pediatric gastroenterology and nutrition. 2010 Apr 1;50(4):360-6. 2.Yu J. Intestinal stem cell injury and protection during cancer therapy. Translational cancer research. 2013 Oct 1;2(5):384. 3.Jakab RL, Collaco AM, Ameen NA. Physiological relevance of cell-specific distribution patterns of CFTR, NKCC1, NBCe1, and NHE3 along the crypt-villus axis in the intestine. American Journal of Physiology-Gastrointestinal and Liver Physiology. 2010 Oct 28;300(1):G82-98. 4.Afghani E, Lo SK, Covington PS, Cash BD, Pandol SJ. Sphincter of Oddi function and risk factors for dysfunction. Frontiers in nutrition. 2017 Jan 30;4:1.
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Assign. 2:Question 2Surname, First Name A. Chordae tendinae are thread-like bands that are within the heart ventricles. On the right they attach to the three cusps of the tricuspid valves and on the left attach to the two cusps of the mitral valve. They are made up of collagen protein fibers and elastin protein fibers. The chordae tendinae hold the cusps of the atrioventricular valves to avoid the valves from blowing out due to high blood pressure contained in the ventricles (1). They are important in holding the cusps of the atrioventricular valves on the ventricular side to ensure that blood flows in the right direction in my model (from atrium to ventricle and no backflow). B. The structures missed are intercalated discs which contain fascia adherens, gap junctions and desmosomes (2). The intercalated discs ensure the cardiac myocytes are connected to one another. Major proteins of intercalated discs are N-cadherin, vinculin and plakophilin -2. Their absence in the model caused it to fall apart because the intercalated discs allow the cardiomyocytes to hold out against the strong mechanical forces generated by beating of the heart (3). C. Gap junction is an agglomeration of multiple individual gap junction’s channels with associated proteins and they are composed of twelve connexin molecules. Connexin 43 is the major protein of gap junction. Gap junctions allow spread of action potential between cardiomyocytes. Without gap junctions the normal heart will fail because depolarizing current would not be transmitted between cardiomyocytes and the heart will not contract (4). D. To calculate the pulse pressure one has to minus diastolic blood pressure from systolic blood pressure. Systolic pressure-diastolic pressure 125mmhg-95mmhg=30mmhg Pulse pressure=30mmhg E. Mean arterial pressure is calculated by adding diastolic pressure to one third of pulse pressure. Diastolic pressure+ 1/3 pulse pressure 95mmhg+ 1/3(30mmhg) 95mmhg+10mmhg=105mmhg Mean arterial pressure=105mmhg References 1.Icardo JM, Colvee E, Revuelta JM. Structural analysis of chordae tendineae in degenerative disease of the mitral valve. International journal of cardiology. 2013 Aug 20;167(4):1603-9. 2.Pappano AJ, Wier WG. Cardiovascular Physiology-E-Book: Mosby Physiology Monograph Series. Elsevier Health Sciences; 2018 Sep 6. 3.Su V, Lau AF. Connexins: mechanisms regulating protein levels and intercellular communication. FEBS letters. 2014 Apr 17;588(8):1212-20. 4.Foulquier S, Daskalopoulos EP, Lluri G, Hermans KC, Deb A, Blankesteijn WM. WNT signaling in cardiac and vascular disease. Pharmacological reviews. 2018 Jan 1;70(1):68-141.
Assign. 2:Question 3Surname, First Name Ai Our eyes are able to see a scene as a whole by processing information obtained from the nasal and temporal visual fields from both the left and the right eye. This capability is referred to as the binocular vision (1). Aii To pick fine details from a near or far distance the light needs to be converged at the retina. This requires changing the shape of the lens through contracting or relaxing of ciliary muscles (2). Bi To differentiate objects in the background by contrast the light has to be focused on the fovea, the rich cone rich part of the retina. Bii This is possible through simultaneous contrast that intensifies the contrast between two colors. The stimulation of an area of retina by one color modifies the surrounding areas (3). Ci Concentrating on a particular object and seeing them is achieved through accommodation. The convexity of the lens must be altered so as to alter the refractory power of the lens. When concentrating on a far object the lens is flattened due to contraction of suspensory ligament. Focusing on near objects requires the lens to be more spherical to converge light to the retina (4). Cii To focus on specific objects in a surrounding than others means that the other objects’ light is directed towards the blind spot part of the retina. References 1.Gollisch T, Meister M. Eye smarter than scientists believed: neural computations in circuits of the retina. Neuron. 2010 Jan 28;65(2):150-64. 2.Hofer, S.B., Mrsic-Flogel, T.D., Bonhoeffer, T. and Hübener, M., 2009. Experience leaves a lasting structural trace in cortical circuits.Nature,457(7227), p.313. 3.Palczewski K. Chemistry and biology of vision. Journal of Biological Chemistry. 2012 Jan 13;287(3):1612-9. 4.Shahjouei S, Amini M. Biophysics of Vision. InBiophysics and Neurophysiology of the Sixth Sense 2019 (pp. 27-58). Springer, Cham.
Assign. 2:Question 4Surname, First Name Ai The pleura enclose each lung and they are made up of two membranes, the inner visceral layer and outer parietal layer (1). Aii Pleural cavity is a narrow space located between the two pleural membranes (visceral and parietal). Normal pleural pressure at the beginning of inspiration is -5 centimetres of water and the normal pleural pressure at the end of inspiration is -8centimetres of water (2). Aiii Pleural cavity pressure ensure that the lungs do not collapse and by remaining lower than the intra- alveolar pressure they keep the lungs inflated. Aiv Pleural fluid is a thin film of serous fluid that is secreted by the visceral layer of the pleura. Its role in ventilation is to create the negative pressure within the pleural cavity. Bi When a diver descends in water, the water pressure increases while the volume of air in the lungs decreases and when the diver is ascending, the water pressure decreases while the volume of air in the lungs expand. Bii While ascending the volume of air in the lungs is increased and therefore if the diver holds their breath the increased volume of air in lungs leads to bursting of alveoli and entry of air into the pleural space. Biii Constantly exhaling while ascending helps the diver reduce excess pressure changes and avoid the danger of alveoli burst by removing the excess air from the lungs (3). Biv Pulmonary barotrauma. Pulmonary barotrauma is the damage to the lungs of a diver when they hold their breath while ascending due to excessive pressure changes. When the diver holds their breath there is overexpansion and rupturing of the alveoli is likely to occur (4). References 1.De Paoli L, Quaia E, Poillucci G, Gennari A, Cova MA. Imaging characteristics of pleural tumours. Insights into imaging. 2015 Dec 1;6(6):729-40. 2.Finley DJ, Rusch VW. Anatomy of the pleura. Thoracic surgery clinics. 2011 May 1;21(2):157-63. 3.Shaikh N, Ummunisa F. Acute management of vascular air embolism. Journal of Emergencies, Trauma and Shock. 2009 Sep;2(3):180. 4.Aquila I, Pepe F, Manno M, Frati P, Gratteri S, Fineschi V, Ricci P. Scuba diving death: always due to drowning? Two forensic cases and a review of the literature. Medico-Legal Journal. 2018 Mar;86(1):49-51.