HUBS1416 Topic 1 Lecture The Digestive System & Its Accessory Organs 4 slides per page.pdf

7/7/24 The Digestive System &...

7/7/24 The Digestive System & Its Accessory Organs Advanced Human Bioscience (HUBS1416) School of Biomedical Science and Pharmacy School of Biomedical Science and Pharmacy College of Health, Medicine & Wellbeing College of Health, Medicine & Wellbeing 1 2 Lecture Overview Digestive System l Part 1: Purpose of the digestive system and obesity Gastrointestinal tract l Part 2: General action of the nervous system, the mouth, oesophagus and swallowing Accessory organs: l Part 3: The stomach and small intestines, pancreas liver & gall bladder gall bladder l Part 4: The liver & large intestines & summary of pancreas GIT system l Part 5: Metabolism, fate of nutrients, control of feeding & satiety 3 4 1  7/7/24 Food components You Are What You Eat (and what you do) l Macronutrients 61.4% of the Australian Ø components that supply energy population are either Ø consumed in the greatest amounts overweight or obese Ø carbohydrates, lipids and proteins Ø have to be broken down to be absorbed and then used 25% of Australian l Micronutrients children are currently Ø only required in tiny amounts overweight or obese Ø don’t provide energy, but are essential (5% in 1960s) for normal function Ø include the vitamins & minerals l Water and gases Immediately used OR converted to adipose tissue for energy storage 5 6 What is Obesity? The Global Obesity Problem BMI: Body Mass Index 25-30 kg/m2 = overweight >30 kg/m2 = obese 7 8 2  7/7/24 What Causes Obesity? Energy Expenditure Unhealthy eating patterns: Resting metabolic rate l ~ 60-75% of daily energy ↑ consumption of foods expenditure high in fat and energy and low in nutrients l homeostasis requires energy Thermic response of a meal l 10% of daily energy expenditure Energy Intake > Energy Expenditure l energy cost of digestion, absorption, mobilisation and storage of food Physical activity l most variable component of energy expenditure (260 à 5000 kcals/day) ↓ in or lack of Genetic factors l voluntary muscular activity physical exercise (conscious and unconscious) 9 10 The many health consequences of obesity Factors affecting metabolic rate Factor Effect on Metabolic rate Age Ü With increasing age Gender Higher in men Size Higher in bigger people Pregnancy, lactation, menstruation Û In these conditions Activity Û with increasing activity Body temperature Û with increasing temperature Thyroid hormone level Û With increasing thyroid hormone level Starvation Ü In this state Emotional states Û with stress, anxiety DON’T NEED TO KNOW DETAILS 11 12 3  7/7/24 The GI Tract Digestive System Processes l The tissue is essentially the same l Contents are both mixed, liquidised along entire length and moved along the gastrointestinal tract by l Four layers, two of which are muscle contractions of the smooth muscle layers of the gut wall l Chemical digestion occurs by means of enzymes l After digestion, absorption of the simple sugars, amino acids, fatty acids, vitamins, ions, etc, can occur 13 14 Mixing and moving of gut contents The Mouth Segmentation Peristalsis l Mechanical digestion l Teeth l Incisors tear off a bite l Molars chew and grind l Tongue l Manipulates crushed food into a bolus 15 16 4  7/7/24 Swallowing has both voluntary & involuntary What’s saliva for? phases: l Salivary glands produce saliva, Voluntary - tongue & cheeks push containing mucus, salivary amylase, the bolus back towards the pharynx lipase, antibodies and lysozyme Involuntary - pharyngeal muscles l Mucus binds and moistens the propel the bolus into the oesophagus, crushed food it is pushed down the oesophagus by peristalsis l Amylase begins the digestion of the carbohydrates and lipase will begin the digestion of the fats 17 18 The Oesophagus The Stomach Collapsible tube extending from the l Three layers of muscle: contraction of all layers gives a churning action pharynx to the stomach, passing through the diaphragm l Sphincters at top and bottom keep the Cardiac Sphincter Peristalsis in the oesophagus pushes the fluid in the stomach while churning inal gitud food down, & the lower oesophageal cle Lon sphincter opens when the food touches it mus C l Contains strong hydrochloric acid to kill microbes Pyloric sphincter m irc us ul cl ar e muscle Oblique The food then passes into the stomach l Protein digestion starts here (pepsin) l Food turns into chyme – a thick, partially digested fluid that enters the small intestine through the pyloric sphincter Lower oesophageal Oesophagus - a solid meal of mixed macromolecules will take around 5 hours to (cardiac) sphincter fully leave the stomach Stomach 19 20 5  7/7/24 The stomach needs protection Actions of Gastric Juice from its own acid and protease Various specialised cells in the stomach produce the components of gastric juice that each have specific functions: l Hydrochloric acid – Thick Viscous l Mucus – Alkaline l Pepsinogen – l Gastric lipase – l Intrinsic factor (IF) – 21 22 What stimulates the stomach? What inhibits the stomach? l The sight or smell of food l The arrival of chyme in the small intestine The brain stimulates gastric activity via Both the nervous and endocrine systems work to slow the parasympathetic division; down gastric activity and reduce acidity when the chyme causing acid, mucus and enzyme secretion starts to come through into the duodenum l The presence of food in the stomach Why do we only want small Causes the stomach to release the hormone gastrin; amounts of chyme at a time stimulates gastric juice production by the stomach and muscular contractions of the stomach in the intestine? 23 24 6  7/7/24 The pancreas Small intestine and gall bladder l There are three regions: duodenum, jejunum & ileum l It is 5-6m in length l Digestion is completed (duodenum) Gall l Digested food is absorbed (primarily bladder jejunum) Bile l Requires secretions from duct l Gall bladder & Liver l Pancreas Pancreas Pancreatic duct 25 26 What is in pancreatic juice? Activation of proteases in the duodenum l Sodium bicarbonate (neutralises stomach acid) Ready to l Enzymes to digest (break down) Intestine all the major food types: digest wall proteins Enterokinase l Amylase for carbohydrates l Lipase for lipids l Proteases for proteins l Nucleases for nucleic acids The proteases produced in the stomach and pancreas are in an inactive form which has to be activated in the GIT lumen – Why? 27 28 7  7/7/24 Mechanical digestion also occurs What’s in bile? in the small intestine l Bile salts These emulsify fats to allow the lipase to get at the fat droplets l Bile pigments e.g. bilirubin Play no role in digestion – they are excreted via this route. Bilirubin is a breakdown product of haem Segmentation mixes and breaks contents down l Cholesterol Peristalsis moves contents Being excreted by this route & may also protect the duodenum from along the bile salts 29 30 Arrival of chyme in the duodenum triggers hormonal responses that (with the nervous system) coordinate intestine and stomach function 1. Chyme enters the 6. CCK stimulates Intestinal Mucosa duodenum from the liver to increase stomach bile production l Internal surface area of small intestine is the size of a tennis court. 2. Fatty acids & amino acids in chyme entering Ø This surface area is achieved by lots 7. CCK causes the duodenum stimulates gall bladder to of circular folds in internal lining, villi the release of contract & & microvilli cholecystokinin (red dots) sphincter of Oddi from duodenal cells to relax à bile l Contains Peyers patches: nodules of enters duodenum lymphatic tissue that protect the GI 3. Acid in chyme entering the duodenum stimulates tract from pathogens that escape release of secretin (yellow stomach dots) from duodenal cells into bloodstream 4. CCK causes the Circular exocrine pancreas to folds secrete enzyme-rich juice Peyers 5. Secretin causes exocrine pancreas patches to secrete bicarbonate-rich juice and inhibits further gastric acid secretion and gastric motility 31 32 8  7/7/24 The structure of the small Villi contain blood and lymph vessels intestine reflects its function to transport the absorbed nutrients Surface area is Absorption of the products of digestion maximised by: occurs in a number of ways: Ø diffusion Ø facilitated diffusion Epithelial cells with Ø active transport microvilli (brush border) Blood capillaries sugars and peptides are Circular folds Lymph capillary absorbed into the blood (lacteal) Microvilli along with water fats are absorbed into Mucus-secreting cells the lymphatic vessels Villi (lacteals) 33 34 Absorbed nutrients are carried from the small intestine straight to the liver via the hepatic portal vein 35 36 9  7/7/24 The liver receives the products of digestion for processing: Large Intestine l Detoxification/biotransformation l Water is absorbed from the l Storage of excess nutrients large intestine contents Glucose àglycogen, fat soluble vitamins l Any carbohydrates are acted on by bacteria l Synthesis of bile à production of gases l Destruction of old red blood cells 37 38 Faeces Water use and absorption in the GIT About 1.2 litres of water is taken in via food and drink, and another 7 After absorption of most of the litres of water are added to the gastrointestinal tract in the form of all the water, chyme becomes faeces secretions required for digestion It contains any insoluble fibre, dead and live microbes, epithelial cells shed from the tract and some fatty acids Mucus is secreted by the large intestine to act as a lubricant, allowing the faeces to move along About 8 litres of water is absorbed back into the bloodstream from the gastrointestinal tract. Very little water is normally lost in faeces 39 40 10  7/7/24 Summary - roles of the regions of the GIT Summary - roles of the accessory organs Saliva Contains amylase and Liver Mouth lipase. Also moistens Makes bile. Chewing and lubricates food Converts glucose à breaks up food glycogen for storage. Stomach Breaks down and builds HCl for protection and up many biological enzyme activation. molecules. Pepsin activated. Detoxifies Churning to create chyme Large intestine Limited absorption Pancreas Absorption of water Produces digestive Small intestine Gall bladder hormones trypsin & and ions Stores and Site of most chemical chymotrypsin (proteases), concentrates bile. amylases and lipase. digestion and absorption. Contracts to release Produces bicarbonate to Proteases, nucleases, bile into duct amylases and lipase neutralise acid delivered here from Slide 41 pancreas. 41 42 Metabolism Metabolism This is all of the chemical reactions occurring in all the cells of your body There are two main types of metabolic reactions: at any moment. These reactions use the nutrients l Anabolic: gained from digestion to provide This is the building up of the energy needed for: substances from simple to more Ø Homeostasis complex ones. These reactions require energy input Ø Voluntary activity Ø Growth l Catabolic: Ø Maintenance and repair This is the breaking down of Ø Secretion and contraction complex substances into simpler ones. These reactions release energy 43 44 11  7/7/24 Not all nutrients provide the same Which nutrients for which functions? amount of energy l For growth and repair, amino 1g carbohydrate provides: 17 kJ (4kcal) of energy acids would be used in preference 1g protein provides: 17 kJ (4kcal) of energy to fatty acids or glucose (growth & 1g fat provides: 38kJ (9kcal) of energy repair would involve making structural proteins) i.e. Amino acids, then lipids, then Can either be used straight away or stored glucose l For energy to power all activities, glucose is used in preference to amino acids or fatty acids. i.e. Glucose, then lipids, then amino acids 45 46 Metabolic Turnover How is glucose utilised? Some glucose is converted to glycogen and stored Glucose leaves the liver in the hepatic vein It is used to produce energy for cells (ATP) It is used to maintain blood glucose level in the normal range (3.5-8 mmol/l) Glucose comes in from the intestine It is converted to glycogen and stored in muscles (in the hepatic portal vein) It is converted to fat and stored as adipose tissue 47 48 12  7/7/24 How are lipids utilised? How are amino acids utilised? l To produce new cellular proteins to l To make lots of ATP (one fatty acid replace old ones molecule can yield 126 ATP molecules as compared to 1 l Eg. enzymes, hormones & glucose which yields about 32 ATP) antibodies l To be stored as fat l Can be utilised in by the mitochondria to make ATP when l To make lipid components of cells there is not enough glucose or (e.g. phospholipids for membranes, lipids myelin for nerve cells) l Excess amino acids can be processed by the liver (deamination) to keto acids so they can be stored for future energy usage – by conversion to lipids 49 50 How are amino acids utilised? What regulates our intake of food? All our proteins are made from just 20 different The hypothalamus in the brain amino acids contains a feeding centre and a satiety centre Ten of these amino acids can be made in the body and do not have to be taken in as part of Various signals will feed into the diet. These are the non-essential amino acids either the feeding or The others cannot be made in the body, and the satiety centre, have to be present in the diet – these are the to drive us either to eat or to stop essential amino acids eating 51 52 13  7/7/24 Factors feeding into the feeding and Some of the hormonal signals which influence satiety centres the hypothalamus & control feeding Higher brain regions Hypothalamus Signals from fat tissue Signals from GIT Nutrients in blood 53 54 Leptin Deficiency Leptin-deficient child aged 3. Same child aged 7 after treatment with Weight 42 Kg recombinant human leptin. Weight 32 Kg 55 14