Digestive System.docx

The gastrointestinal tract links the initial intake of macromolecules at the mouth, to their absorption into circulation, with excretion at the anus. Don’t forget mechanical and chemical breakdown and that; 'no-digestion = no-absorption'... Smooth muscle lines this passageway, controlling the passa...

The gastrointestinal tract links the initial intake of macromolecules at the mouth, to their absorption into circulation, with excretion at the anus. Don’t forget mechanical and chemical breakdown and that; 'no-digestion = no-absorption'... Smooth muscle lines this passageway, controlling the passage of ingested stuffs from top to bottom Control of the musculature along this passage is broadly neural (PNS, SNS and the gastrointestinal systems own - enteric nervous system (ENS)) or hormonal and has an afferent feedback component... Non-fat, water-soluble foodstuffs enter the liver via the portal venous blood and three key events occur: - Liver sinusoids remove bacteria or particulate - Specialised cells absorb and store, temporarily, 1/2 to 3/4 of the nutrients - completing most of the chemical intermediary processing. - Blood finally leaves via the hepatic vein, emptying into the inferior vena cava Fat bypasses the liver, being absorbed by the intestinal lymphatics, arriving in circulation via the thoracic duct 1) Blood sugar regulation can be whittled down to the relationship between the hormones glucagon and insulin.  2) Blood sugar and blood glucose are almost entirely interchangeable, with the latter contributing 90% to the former. To understand normal blood sugar regulation we need to understand the Fasted blood glucose is maintained around 80-100 mg/dL, 'topped up' over extended periods by the action of glucagon, produced by pancreatic alpha cells. Taken very far, new glucose may even be produced, mostly via amino acids, in a process called gluconeogenesis. Glucagon = Stimulates the release of glucose, originating from glycogen stored in the liver. Post meal, depending on the size and contents of that meal (think monosaccharides versus polysaccharides), blood glucose may rise to ~140 mg/dL. Around this time, if not before, insulin is released, signalling the liver to stop releasing glucose and controlling blood glucose 'spikes'. Insulin = Signals the liver to stop releasing glucose. Moving glucose around is great, but we also need to take it into our cells, i.e., those of the liver. This is achieved in what I split into three simple steps: 1) Insulin binds to its receptor on the surface of the cells  2) This causes GLUT4 (specific glucose transporter) to be translocate to the cell membrane 3) Glucose uptake increases as it enters from the blood, into the cell With the actions of insulin and glucagon controlling blood glucose, we would expect a return to resting levels (80-100 mg/dL) between 60-180 min after a meal, again depending on size and contents. With some idea of normal, we then moved on to looking at glucose intolerance. Starting with a clear definition: Glucose tolerant = Our bodies can maintain our blood glucose within normal levels. 1) Someone may be able to control blood sugar in the normal range but may require more effort from pancreatic beta cells, to produce insulin. Not diabetic, likely more predisposed. 2) When the body cannot compensate by any means = pre diabetic or diabetic, based on severity. This is met with a range of negative effects on the body, numerous and often complex symptoms. On one hand, failure to manage insulin sensitivity and therefore blood glucose can lead to a variety of health conditions, in a negative cycle. Addition of simple dietary changes, or regular exercise on the other, can manage if not totally ameliorate any issues Structure-function Kidneys, ureters, feeding into the bladder and leaving the body via urethra give us our structural setup to perform the renal systems functions.... Regulation (i.e., of water, sodium or hydrogen ions) Filtration (i.e., of metabolic wastes such as urea or creatinine) Gluconeogenesis (Production of glucose from amino acids (a link to our first session!)) Endocrine function (think Renin and its relationship with another hormone ADH or AVP) *If considered as one key purpose, the kidneys are primarily concerned with filtering the blood. The functional unit aiding the completion of this filtration is the nephron, with about 1 million found in the kidneys... The Nephron Features two distinct parts, the renal corpuscle and the renal tubule. To wrap your head around these, try to find a nice video (such as the one embedded in the slides) or figure (as previous) and wrap your head round how things look - I think this will give you a better idea of the relationship before we say anything physiological.  The renal corpuscle Features the glomerulus and Bowmans capsule. The former represents a bundle of interconnecting capillaries (to exchange things (en masse)), while the latter is a capsule filled with fluid. Movement in the renal corpuscle is via an afferent arteriole, emptying via an efferent arteriole.  The renal tubule From the Bowmans capsule, the filtrate enters via the renal tubule. Passing through a system of proximal tubules, the loop of Henle and into collecting ducts. This setup is aimed at maximising tubular reabsorption and secretion, with things like sodium being exchanged differently at specific portions. In turn, certain hormones or drugs also act on different portions. Picking up from the collecting ducts... Collecting ducts may have multiple nephrons draining into them, with filtrate then entering the renal pelvis and then the ureters... Glomerular filtration: Filtration across capillaries, moving from high to low pressure in bulk, we then enter the tubules; Tubular reabsorption: When a substance is moved from the tubular lumen (inside) into the peritubular capillaries (outside) Tubular secretion: When a substance is moved from the peritubular capillaries (outside) into the tubular lumen (inside). Glomerular filtration= Bulk flow Tubular reabsorption and secretion= Diffusion and mediated transport Renal clearance: Mass of substance excreted per unit time / plasma concentration of substance