Introduction to Digestion, Absorption, Transport, and Storage PDF

Faculty of Applied Health Sciences Department of Health Sciences Introduction to Digestion, Absorption, Transport, and Storage 1  Faculty of Applied Health Sciences Department of Health Sciences Learni...

Faculty of Applied Health Sciences Department of Health Sciences Introduction to Digestion, Absorption, Transport, and Storage 1  Faculty of Applied Health Sciences Department of Health Sciences Learning goals 1. Understand the difference between appetite and hunger/satiety. 2. Identify the path that food takes during digestion and describe the muscular actions of digestion. 3. Describe the actions and origins of the digestive secretions. 4. Describe the anatomical details of the GI tract and the features and activities of intestinal cells that facilitate nutrient absorption. 5. Explain how nutrients are delivered from the GI tract to body cells by the vascular and lymphatic system. 2  Faculty of Applied Health Sciences Department of Health Sciences What drives us to eat? Hunger - the physiological need to eat (physiological sensation), experienced as a drive to obtain food, - non-specific (any food), - it occurs because of biological changes throughout the body, which signal that you need to eat to maintain energy levels Satiety - the feeling of fullness and satisfaction that occurs after a meal and inhibits eating until the next meal 3  Faculty of Applied Health Sciences Department of Health Sciences NEED TO KNOW- the difference between huger and appetite Appetite – the (mainly psychological) desire to eat – a learned motivation that is experienced as a pleasant sensation that accompanies the sight, smell or thought of appealing foods – it can be a result of hunger but often has other causes such as emotional or environmental; driven by a number of factors 4  Faculty of Applied Health Sciences Department of Health Sciences Hunger and satiety – regulated by the brain, specifically the hypothalamus – brain receive signals (neurological or hormonal) based on level of food and nutrients in gut and blood (signals inform the brain and the brain determines when to eat or not to eat) – sometimes over-ridden by appetite Know: Hunger is regulated by the brain particularly the hypothlamus 5  Faculty of Applied Health Sciences Department of Health Sciences Hunger and satiety Foods have differing effects on our feelings of hunger and satiety: – proteins have a high satiety value – feel full longer when you eat proteins (most satiating macronutrient) (Main: Meat, fish, nuts, seafood, eggs, dairy) – carbohydrates and fat have a low satiety value – feel hungry sooner – bulky foods (i.e. fibre) provide a sense of satiety – feel full longer (Fiber rich food like raw fruits) – solid foods are more filling than semi-solid foods or liquids – feel full longer The idea of a hierarchy of satiating effects of macronutrients in the order of protein > carbohydrate > fat (Blundell & Macdiarmid, 1997) 6  Faculty of Applied Health Sciences Department of Health Sciences What happens to the food we eat? Terms Digestion – foods are broken down by chemical or mechanical processes to the smallest absorbable unit Absorption – moving products of digestion across intestinal wall into blood stream or lymphatic system Elimination – removal of undigested and unabsorbed products from the body Transport – move products through the blood stream or lymphatic system to part of body that require them Storage – excess products that are digested and absorbed are kept in specialized regions of the body for later use 7  Anatomy of the Gastrointestinal Tract Faculty of Applied Health Sciences Department of Health Sciences For are knowledge only! FIGURE 2-1 The Gastrointestinal Tract © 2020 Cengage. All rights Most absorption is within the small intestine reserved. The large intestine includes the colon, rectum and anus. 8  Faculty of Applied Health Sciences Digestion Department of Health Sciences The process by which complex food particles are broken down to smaller absorbable particles Digestion includes: – Mechanical digestion: the physical breakdown of food. – Chemical digestion: enzymatic reactions that break down large food molecules (ex. Stomach acid, bile salts) 9  Faculty of Applied Health Sciences Department of Health Sciences Digestion Digestion begins in the mouth. cephalic phase – sight, smell or thought of food initiates the digestive process with the salivary and gastric responses mediated via the autonomic nervous system chewing is the mechanical digestion that breaks food into smaller pieces some chemical digestion takes place by components of saliva (e.g. digestion of carbohydrates by salivary amylase) 10  Faculty of Applied Health Sciences Department of Health Sciences Digestion Saliva – 3 pairs of salivary glands (exocrine glands that secrete saliva into the mouth) – Saliva contain: water bicarbonate (pH maintenance) mucus (lubrication) antibodies (protection) enzymes (e.g. salivary amylase which initiates the digestion of starch) NEED TO KNOW- Salivary Amylase and its relation to digestion of carbohydrates 11  Faculty of Applied Health Sciences Department of Health Sciences Digestion The gastroesophageal sphincter separates the esophagus from the stomach; the bolus (the portion of food shallowed at one time) cannot slip back, from the stomach to esophagus Digestion in the stomach includes – extensive mechanical digestion to mix food with gastric juice (via muscle contractions) – chemical digestion via gastric juices (released by glands directly into the stomach) – gastric juices: the digestive secretion of the gastric glands containing a mixture of water, hydrochloric acid HCL, and enzymes (e.g. pepsin which acts on proteins and lipase which acts on emusilfied fats) 12  Faculty of Applied Health Sciences Department of Health Sciences Digestion Gastric juice which is secreted from the gastric glands (exocrine glands) in the stomach, contains – Hydrochloric acid (HCl) – to denature proteins and activate pepsin – Enzymes (e.g. pepsin and lipase)– digestion – Mucus (mucopolysacharide)– to protect the stomach lining – Intrinsic factor – protein critical in the absorption of vitamin B12 (discuss in a future lecture) Chyme: semi-solid product of mechanical and chemical digestion in the stomach; partially digested food mixed with water and gastric juices; expelled by the stomach into the duodenum (the top portion of the small intestine). 13  Faculty of Applied Health Sciences Department of Health Sciences Digestion From the stomach, chyme is slowly released through the pyloric sphincter (sphincter between the stomach and the duodenum) to the small intestine. Chemical digestion continues in the small intestine using bile (produced by liver and stored within the gallbladder) and pancreatic enzymes (pancreas). 14  Faculty of Applied Health Sciences Department of Health Sciences Digestion Liver produces bile (also serves other functions) Gallbladder stores bile Bile: secreted into duodenum when needed, whenever fat arrives there, it is an emulsifier: disperses the fat in the water forming an emulsion After the fats are emulsified, the enzymes (e.g. pancreatic lipase) can work on them, and fats can be absorbed. 15  Faculty of Applied Health Sciences Digestion Department of Health Sciences Pancreas: produces pancreatic juice which flows from the pancreas into the small intestine through the pancreatic duct o pancreatic juice contains: I. enzymes that act on all 3 macronutrients (amylase for carbohydrates, protease for proteins, and lipase for fats) II. sodium bicarbonate to neutralize acidic chyme as it enters the small intestine 16  Faculty of Applied Health Sciences Department of Health Sciences Digestion Small intestine – Three parts (duodenum, jejunum and ileum) – major site of digestion – final stage of digestion (smallest unit to be absorbed) 17  Faculty of Applied Health Sciences Department of Health Sciences Digestion Movement of digestive materials NEED TO KNOW THIS Peristalsis – successive waves of involuntary muscular contractions passing along the walls of the GI tract that push the contents along – moves the contain along due to the circular and longitudinal muscles contract – enhancing absorption along intestine The small intestine has two muscle layers that work together in peristalsis and segmentation. Circular muscles are inside, and Longitudinal muscles are outside. 18  Faculty of Applied Health Sciences Department of Health Sciences Digestion NEED TO KNOW- the difference between the tw Movement of digestive materials Segmentation – circular muscles contract, creating segments of chyme within the intestine – segments of chyme mixed with digestive juices, and nutrients come into contact with the small intestine’s lining for absorption Brakes down the chyme which increases absorption 19  Faculty of Applied Health Sciences Department of Health Sciences Absorption – small amount of absorption occurs in the stomach (e.g. water, fluoride, medium-chain fatty acids, some drugs including aspirin, and alcohol) – most absorption of nutrients occurs in the small intestine 20  Absorption Faculty of Applied Health Sciences Department of Health Sciences The lining of the small intestine has special structures to facilitate absorption – Villi are finger-like projections made up of cells that found on the folds of the small intestine, and they are in close contact with nutrient molecules; absorb nutrients and shuttle them into the bloodstream so they can travel where thy are needed. – Each villus (singular form of villi) composed of several hundred cells, each covered with microscopic hair-like projections called microvilli which are the primary site of absorption of most nutrients – Microvilli can trap nutrient particles and transport them via blood into the cells (the singular form is microvillus) Absorption occurs primarily within the microvilli (possible midterm question) - If you do not see the answer as microvilli then that is not the answer 21  Faculty of Applied Health Sciences Microvilli cell membrane Department of Health Sciences Absorption- Types Simple/passive diffusion – pass through membrane freely – move along concentration gradient (high to low) – i.e. lipids, water Outside of the cell is the gut lumen and the inside of the cell is inside the cell of intestinal villus 22  MAY NEED Faculty of Applied Health Sciences TO TELL HER WHAT TYPE OF ABSORPTION IS REQUIRED Department of Health Sciences Absorption- Types Facilitated diffusion – molecules that are only soluble in water – requires a carrier molecule (carrier protein) – requires concentration gradient (from a high to low concentration) – DOSE NOT require the expenditure of cellular energy – i.e. water-soluble vitamins, fructose, glucose Outside of the cell is the gut lumen and the inside of the cell is inside the cell of intestinal villus Facilitative glucose transporters 23 (GLUTs) for glucose  Faculty of Applied Health Sciences NO THE DIFFERENCES Department of Health Sciences Absorption- Types Active transport – needed when concentration is higher inside than outside – requires a carrier protein – requires energy – i.e. glucose and amino acids Outside of the cell is the gut lumen and the inside of the cell is inside the cell of intestinal villus. Sodium-glucose transport 24  Faculty of Applied Health Sciences Department of Health Sciences Absorption- Types Endocytosis – small amount of intestinal content engulfed by cell membrane – i.e. some proteins, antibodies in breast milk Outside of the cell is the gut DO NOT NEED TO KNOW TO MUCH ABOUT IT lumen and the inside of the BUT KNOW TYPES AND EXAMPLES FOR EACH cell is inside the cell of intestinal villus 25 Faculty of Applied Health Sciences Department of Health Sciences Absorption 26  Faculty of Applied Health Sciences Department of Health Sciences Absorption/Elimination Undigested food components move through a sphincter called the ileocecal valve (ileum to large intestine) to the large intestine. In the large intestine: – bacteria ferment undigested food particles – material is stored 12-24 hours prior to elimination while water and some nutrients are absorbed – bacteria produce vitamin K and B vitamins (e.g. B12) which are then absorbed into the blood 27  Faculty of Applied Health Sciences Department of Health Sciences Gut flora Shortly after birth, GI tract is colonized with wide variety of bacteria (flora) Mainly large intestine contain a large number and variety of bacteria Imbalance to the population causes: – diarrhea – constipation – systemic inflammation (obesity) 28  Can be found naturally or added to some produ Faculty of Applied Health Sciences Department of Health Sciences Probiotics Live microorganisms naturally found in or supplemented to food products, and also found in dietary supplements, that have health benefits when taken in sufficient amounts For example, they are found in fermented dairy; When ingested in appropriate quantities (1-10 billion live bacteria) can improve the host’s intestinal microbial balance Must be non-pathogenic when consumed and must be consumed in large amounts to survive and influence intestinal bacterial populations Bacteria adhere to intestinal wall for a short period of time – need to be consumed daily Resist destruction by stomach acid, bile, other digestive substances 29  Faculty of Applied Health Sciences Department of Health Sciences Probiotics Benefits to health – degrade undigested or unabsorbed dietary carbohydrate, including digestion-resistant starch – produce some vitamins e.g. vitamin K, and short- chain fatty acids – protect intestinal tissue from pathogenic bacteria – stimulate immune defenses 30  Faculty of Applied Health Sciences Department of Health Sciences Prebiotics Non-digestible substances in foods Typically oligosaccharides (e.g. fructo- oligosaccharide FOS), inulin (polysaccharides) or resistant starches Found in fruits and vegetables (e.g. in asparagus, garlic, leeks, bananas etc) Act as food for the probiotics; promote growth of good bacteria within the large intestine 31  Faculty of Applied Health Sciences Department of Health Sciences Synbiotics Combined use of both pro- and prebiotics such as: – Bifidobacterium and fructo- oligosaccharides – Lactobacillus and inulins Ex. Liquid yogurts (has added probiotic and fruits with prebiotics) 32  Faculty of Applied Health Sciences Department of Health Sciences Transport Vascular system – Blood (transport of water- soluble nutrients) Lymphatic system – Lymph (transport of lipids) 33  My have a question on exam related to anatomy and physiolog Faculty of Applied Health Sciences Department of Health Sciences Transport (need to know) Hepatic portal system – portal vein (receives first absorbed water-soluble nutrients like glucose) – ensures liver is first to receive materials absorbed from GI tract (“gatekeeper”) – Liver, as major metabolic organ, prepares absorbed nutrients for use by rest of body (also can storage nutrients within it) 34  Faculty of Applied Health Sciences Department of Health Sciences Transport Lymphatic system – network of vessels – functions transport fat-soluble nutrients (main function) return fluid to the blood part of the immune system 35  Faculty of Applied Health Sciences Department of Health Sciences Regulation Homeostasis tendency to maintain important variables in the face of large environmental changes (want to maintain something within a particular range) dynamic equilibrium i.e. blood sugar 36  Faculty of Applied Health Sciences Department of Health Sciences Regulation Negative feedback – response to a stimulus in order to reverse or cause the opposite effect of the original stimulus Ex. Increased blood glucose, negative feedback will reverse this and decrease the blood glucose back to homeostatic levels 37  Faculty of Applied Health Sciences Department of Health Sciences Regulation Central nervous system (CNS) – main processing area – brain and spinal cord Peripheral nervous system (PNS) Integration of CNS, – nerves outside CNS PNS (enteric) and – GI tract component called enteric nervous system hormones aids in regulating GI Hormones activity – chemical messengers secreted to regulate processes remotely 38 Faculty of Applied Health Sciences Gastrin Department of Health Sciences Hormone produced by G cells in the stomach parietal cells Triggered by entry of food into the gastrin stomach Promotes the HCl release of HCL from the stomach G cells (parietal cells) Controls the release of pepsin from the stomach pH/protein 39 Faculty of Applied Health Sciences Department of Health Sciences Below pH 3, More dietary gastrin secretion protein, gastrin is inhibited is released pH/protein 40  Faculty of Applied Health Sciences Department of Health Sciences Secretin Hormone released from duodenum when stomach inhibit gastric motility acid contents come to inhibit gastrin duodenum (when pH is below 4.5) It inhibits gastric motility and (pH) acidic chyme gastrin pancreatic juices It stimulates bicarbonate (HCO − 3) secretion from pancreas to neutralize chyme secretin 41 Faculty of Applied Health Sciences Department of Health Sciences Secretin (cont’) Below pH 4.5, Above pH 4.5, secretin is secretin released secretion is inhibited pH 42  Faculty of Applied Health Sciences Department of Health Sciences Cholecystokinin (CCK) Hormone produced by pancreatic duodenum due to lipid digestive rich chyme enzymes It stimulates the release of digestive enzymes from the pancreas and of bile from the bile gallbladder fatty meal / lipid rich chyme CCK 43 Faculty of Applied Health Sciences Department of Health Sciences CCK (cont’) Lipid-rich Lipid-poor chyme, chyme, CCK is CCK is inhibited released lipid 44  Faculty of Applied Health Sciences Department of Health Sciences Gastric-inhibitory peptide (GIP) Hormone produced by duodenum It inhibits gastric motility and secretion of acid It stimulates the release of insulin from pancreas in ↑ Carbohydrate meal response to glucose infusions GIP stimulate insulin secretion 45 Faculty of Applied Health Sciences Department of Health Sciences GIP (cont’) Hyper-osmotic Hypo-osmotic chyme due to chyme, GIP glucose, GIP is secretion is released inhibited chyme mOsm 46