MEDS Human Biology Module 4 PDF

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MEDS Human Biology Module 4DigestionDescribe the specialised anatomical structures within the digestive system  Anatomy: the structure and function of body systems that work together to underpin normal human activity  Nutrition: how the cells of the body get the nourishment they require to survive...

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MEDS Human Biology Module 4 Digestion Describe the specialised anatomical structures within the digestive system  Anatomy: the structure and function of body systems that work together to underpin normal human activity  Nutrition: how the cells of the body get the nourishment they require to survive  Enzymes: digestive enzymes chemically break down food – fat, proteins and carbohydrates  Waste: undigested material and unabsorbed products of digestion are excreted into the digestive tract and removed from the body in urine and faeces  Digestion: the mechanical and chemical breakdown of food to absorb nutrients for growth and functioning  Essential for energy, growth and maintenance of our bodies  In a healthy body; water, monosaccharides, amino acids, fatty acids and glycerol, vitamins and minerals absorbed within an appropriate range

 Enzyme means ‘to modify from within’ – changes substance Anatomy  Alimentary canal or digestive/gastrointestinal tract (GIT) includes major digestive organs (stomach), from mouth to anus (about 9m with 30-40m2 of surface area)  Accessory organs: secrete fluid/enzymes into digestive tract, salivary glands, liver and pancreas release secretions through ducts into intestine for chemical digestion, helps with digestion but does not host it  Major organs: oral cavity, oesophagus, stomach, small intestine, large intestine (colon), rectum, anus Oral cavity  Lips, cheeks, teeth and tongue  Serous (watery) component: moistens food for swallowing, dissolving food for tasting, contains enzyme amylase (carbohydrates – simple sugars, start of chemical digestion)  Mucous component: lubricates food, lysosome is antibacterial  Lysozyme: lyso – ‘to burst the cell open,’ zyme – ‘modify’ Oesophagus  Muscular contractions of the oesophagus occur is peristaltic waves  Waves of relaxation followed by waves of contraction along a tube  Waves push food towards stomach Stomach  Mechanical and chemical  Huge muscular sac (1-3litres)

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Food churned (mechanical) for 2-4 hours Food mixed with stomach secretions (chemical breakdown) – chyme Peristaltic waves gradually move chyme into small intestine Pyloric sphincter keeps food into stomach until its ready to move on Mechanical digestion: peristalsis Contractions occur every 20 seconds from body of stomach towards pyloric sphincter Chemical digestion: gastric juice

Describe the digestive enzymes and their activities  Secreted by gastric glands in the stomach wall – HCl, enzymes, alkaline mucus, intrinsic factor  Enzymes in the digestive system break particles into small molecules – absorbed into circulation and transported all over the body, then broken down by other enzymes to release energy/assembled into new molecules to build tissue 1. Hydrochloric Acid (HCl) a. Secreted by gastric glands (specifically parietal cells) b. pH ~ 2/3 c. Kills some ingested bacteria and some viruses d. Softens fibres in meat and vegetables e. Activates digestive enzymes of stomach (pepsinogen > pepsin) f. If any enzyme ends in ‘-ogen’ it is inactive and stored until activation 2. Enzymes a. Chief cells are gastric glands (stomach glands) that produce enzymes, most importantly pepsinogen b. Pepsinogen is converted by HCl to pepsin (active) c. Pepsin breaks proteins down (food is made of proteins) 3. Alkaline mucus a. Fluid from mucus cells b. Protects stomach lining from HCl and pepsin c. Mucous barrier > 1mm thick 4. Intrinsic factor a. From gastric glands b. Secreted in the presence of food c. Not digestive – binds to B12 d. Assists absorption of B12 in small intestine e. B12 is important in RBC production, DNA synthesis Amylase: produced in the mouth, helps break down large starch molecules into smaller sugar molecules Pepsin: produced in the stomach, breaks down proteins to amino acids Trypsin: produced in the pancreas, also breaks down proteins Sucrase breaks down sucrose Maltase: breaks down maltose Lactase: breaks down lactose Understand how nutrients are absorbed for use in the body  Absorption by stomach: very limited, only low molecular weight substances can pass through (water, alcohol, Panadol)  Feed-forward system: sight, smell, taste or thought of food stimulates the medulla, vagus nerve transmits signals from the brain to stomach, initiates secretion of HCl, pepsinogen, mucous, intrinsic factor, gastrin into the stomach – gastrin is secreted from gastric glands and stimulates further gastric secretion  Food entering stomach: stimulates stretch receptors – increased stomach secretion, polypeptides produced from initial digestion stimulate gastrin release, chyme moves continuously into small intestine  Stomach to small intestine: chyme pH drops to 2.0 – detected by chemoreceptors, neural signals reduce gastric secretion, duodenum releases secretion and cholecystokinin, these inhibit stomach gastrin secretions and increase accessory organ secretions to small intestine – food is moving from the stomach to the duodenum

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Small intestine: digestion and absorption, 6m long, three parts; duodenum, jejunum and ileum, modifications to increase SA: circular folds (formed of mucosa and submucosa), villi (finger like projection from mucosa), microvilli (cytoplasmic extensions of mucosal cells) Small intestine digestion 1. Food entering the small intestine is only partially digested 2. Mechanical mixing of chyme and chemical processes 3. Mucosa of the duodenum secretes mucus, ions and H20 – lubricates and protects the intestinal wall from acidic chyme 4. The small intestine also secretes digestive enzymes a. Peptidases: peptides – amino acids b. Sucrase: breaks down sucrose c. Maltase: breaks down maltose d. Lactase: breaks down lactose

Accessory organs Liver  Produces bile to aid digestion – stored in gallbladder  Contains bile salts to emulsify fats, small fat droplets more effectively digested by enzymes  Bile also allows excretion, bilirubin from RBC breakdown  E.g. cholesterol and fats Pancreas  Produces bicarbonate to neutralise acidic chyme  Lots of enzymes  Carboxypeptidase: peptides  amino acids  Pancreatic amylase: starch  monosaccharides  Pancreatic lipases: emulsified fat  fatty acids and glycerols Absorption in small intestine  Most absorption occurs in duodenum and jejunum  Chyme takes 5-6 hours to be processed and absorbed  Two absorption routes across intestinal epithelium for transport to other parts of the body o Water soluble nutrients: sugars o Non-water-soluble nutrients: fats o These go into the blood where they are absorbed  92% of H2O is absorbed in the small intestine  AT the end of the ileum all that remains is water, indigestible food (cellulose) and bacteria Large intestine  Colon: mucosal lining with tubular glands (crypts) which contain mucus producing goblet cells  Rectum: straight muscular tube

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Anal canal: thick, involuntary smooth muscle forms the internal anal sphincter, voluntary skeletal muscle forms the external anal sphincter

Monosaccharides, disaccharides, polysaccharides  Most carbs derive from plants, but lactose is derived from animals  Most common monosaccharides in the diet are glucose and fructose  Disaccharide sucrose (table sugar)  Sucrose consists of one glucose and one fructose molecule joined together – sugarcane and sugar beats Carbohydrates – polysaccharides and disaccharides are split into monosaccharides which are absorbed into the blood  Enzymes can break the bonds between glucose molecules of starch and glycogen but they don’t have the enzymes necessary to digest cellulose  Therefore, it is important to thoroughly cook or chew plant matter  Cooking and chewing break down the plant cell walls and expose the starches contained inside the cells to digestive enzymes  Undigested cellulose provides fibre which increases the build up of faeces making it easier to defecate Fructose and other monosaccharides absorbed into the blood are converted into glucose by the liver  Whether absorbed directly from the digestive tract of synthesised by the liver, is an energy source to produce ATP  Because the brain relies almost entirely on glucose for its energy, the body carefully regulates blood glucose levels Describe the waste products from our digestive system and how these are made  Activity in large intestine: water, minerals and vitamins absorbed so waste stored here before defecation o Resident bacteria produce enzymes that synthesise vitamin K (blood clotting) and B complexes (coenzymes in metabolic pathways o Produce by-products of metabolism – short chain fatty acids (15% of daily energy needs), methane  Waste: undigested food (cellulose), fluid and older cells from the lining of your GI tract

Metabolism Differentiate between anabolism and catabolism  Metabolism: breaks down molecules (turning glucose to pyruvate in glycolysis) and builds new molecules (synthesizing proteins, carbs, lipids and nucleic acids) – mitosis and myosis  Catabolism: breaks molecules down – begins with digestion then occurs within cells, large molecules to small ones (degradation), energy from the chemical bonds is released  Anabolism: builds molecules up – requires energy to form new chemical bonds, formation of new cells, maintenance of existing cells, production of molecules (e.g. hormones or enzymes), small molecules – joined  ABCD: Anabolism = biosynthesis – Catabolism = Degradation

Explain the process of metabolism and ATP creation through biochemical cycles Activated carrier molecules  Carry chemical bond energy is easily exchangeable forms  As a transferable chemical group as high energy electrons e.g. ATP  Takes energy from food molecules, releases energy to the body, when anabolism then produces new cells  NADH: carries new energy around

Adenosine triphosphate: an energy transfer molecule – takes energy from food and gives it to cells

Carbohydrate metabolism  Carbohydrates digested to monosaccharides of which glucose is the most important  Glucose storage: short term (glycogen – skeletal muscle, liver), long term (fat)  Glycolysis: if oxygen available – aerobic respiration, oxygen not available – anaerobic respiration Glycolysis (2 ATP)  Glucose  pyruvic acid, ATP and NADH o Pyruvic acid: either used in aerobic and anaerobic respiration o NADH: nicotinamide adenine dinucleotide Anaerobic respiration 1. Glycolysis 2. Lactic acid formation a. Uses energy derived from NADH from glycolysis b. Produces lactic acid – transported to liver, converted to glucose when oxygen is available c. Produces ATP for a short time e.g. intense exercise

Aerobic respiration 1. Glycolysis 2. Acetyl-CoA formation a. Pyruvic acid moves into mitochondrion 3. Citric acid cycle (2 ATP) a. Tricarboxylic acid (TCA) cycle / Krebs cycle b. FADH = another carrier molecule c. Stops without oxygen as it runs out of carrier molecules 4. Electron transport chain a. Needs oxygen to accept electrons Electron transport chain – electrons = hot potato  Aerobic respiration only  Series of electron transport molecules attached to inner membrane of mitochondrion  Site of oxidative phosphorylation  Electrons transferred from activated carrier molecules (NADH, FADH) to electron transport molecules  Some electron transport molecules are also H+ pumps o Pump H+ between mitochondrial compartments o H+ can then move back by diffusion o Movement of H+ coupled to ATP production  2 electrons and 2 H+ coupled to ATP production

The Kidney Describe the anatomy of the kidney, the structure of the nephron and name and describe the structure and functions of regions of the nephron  Kidney: removers of waste and maintainers of balance 1. Maintaining ECF fluid composition and volume 2. Maintaining mass balance/clearance 3. Filtration follows by reabsorption 4. Secretion of some waste products 5. Produces some hormones – erythropoietin Nephron  Functional unit of the kidney  Approximately 1.3 million of them in each kidney  Consists of renal corpuscle, proximal convoluted tubule, loop of Henle and distal convoluted tubule  Approximately 15% of the nephrons, called juxtamedullary (next to the medulla in the kidney) nephrons, have loops of Henle that extend deep into the medulla of the kidney  The other 85%, cortical nephrons, have loops of Henle that don’t extend

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20% of plasma volume removed into nephron 70% of that is reabsorbed almost immediately in Proximal Convoluted Tubule Fine tuning in remaining sections Taking nearly everything out of the blood, checking composition, putting nearly everything back in and removing the rest in the urine

Describe the glomerular filter. Distinguish the properties of the blood components it allows to pass. Appreciate the methods used to measure it.  Filtration occurs when blood pressure is non-selectively forces water and other small molecules out of glomerular capillaries and into the Bowman capsule, forming a fluid called filtrate  Average 21% of blood pumped by heart each minute flows through the kidneys  Of the total volume of blood plasma that flows through the glomerular capillaries, about 19% passes through the filtration membrane into the Bowman capsule o become filtrate Renal corpuscle  In the renal cortex – layer of connective tissue  A thick layer of adipose tissue surrounds the kidney and protects from mechanical shock  Fluid is forced into the renal corpuscle and then flows into the proximal convoluted tubule  Glomerulus: “Ball of wool”, tangle of porous capillaries  Bowman’s capsule: surround glomerulus, absorbs filtrate from it  Site of ultrafiltration: fluid under pressure at a semi-permeable membrane  Small molecules (...