HUBS1416 Digestion and metabolism.docx

**[HUBS1416 -- Digestion and Metabolism]** Food goes through 4 processes when we eat it: 1. **Ingestion**- Putting the food inside the body. 2. **Digestion**- Mechanically and chemically breaking down the food into its component parts. 3. **Absorption**- Taking the now broken down parts o...

**[HUBS1416 -- Digestion and Metabolism]** Food goes through 4 processes when we eat it: 1. **Ingestion**- Putting the food inside the body. 2. **Digestion**- Mechanically and chemically breaking down the food into its component parts. 3. **Absorption**- Taking the now broken down parts of the food into the bloodstream, 4. **Excretion/ Elimination**- The removal and disposal of any material in the food that the body can't use. **Anatomy and Physiology of the Gastrointestinal (GI) tract, from mouth to anus:** ------------------- ---------------------------------------------------- ---------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Area** **Accessory organs / Parts** **Digestion** **Function** **Mech** **Chem** Mouth Teeth (incisors, canines, molars) Yes No To chop, tear and grind food into a smooth bolus that can be swallowed. Muscles (cheeks, lips, tongue Yes No To move food around the teeth and to help shape the bolus so it can be swallowed. Salivary Glands No Yes To make saliva which lubricates the bolus for swallowing and contains amylase and lipase to start digesting sugar and fat respectively. Throat Pharynx (top of the throat, Pharyngeal muscles) Yes No When swallowing, the voluntary muscles of the mouth push the bolus to the pharynx where the involuntary muscles take over and squeeze the bolus into the oesophagus. Oesophagus (oesophageal muscles) Yes No Involuntary oesophageal muscles continue to squeeze the bolus toward the stomach using a sequential contraction wave called peristalsis. Cardiac Sphincter Muscle valve Muscular valve. Closes off the stomach from the oesophagus. If it leaks, the stomach acid can burn the oesophagus resulting in reflux, also known as heartburn. Stomach Fundus (top part) Yes Yes The main body of the stomach, contains the largest number of gastric juice producing cells and does most of the churning of the chyme. Pylorus (bottom part) Yes Yes Lower portion of the stomach, funnels chyme toward the pyloric sphincter and duodenum. Longitudinal, circular and oblique muscles Yes No Muscles in the wall of the stomach that are protected from the gastric juice by the mucosal layer. They help churn the ingested food into chyme. Chief gastric cells No Yes Cells which produce Pepsinogen and gastric lipase. Parietal cells No Yes Cells which produce hydrochloric acid and intrinsic factor. Goblet Cells No Yes Cells which produce mucus to protect the lining of the stomach. Pyloric Sphincter Muscle valve Muscular valve. Controls the flow of chyme into the duodenum. Activity is modulated by sectretin. Duodenum Pancreas No Yes Secretes pancreatic juice containing amylases, lipases, nucleases and proteases via the common bile duct into the duodenum. Action stimulated by cholecystokinin (CCK) produced by the presence of protein and fat in the duodenum. The duodenum has enterokinase (endopeptidase) on the lumen wall that activates proteases released by the pancreas. Gall Bladder No Yes Stores bile salts produced by the liver and releases them into the duodenum via the common bile duct in response to CCK. Common bile duct No Yes Duct which transports bile and pancreatic juice from the pancreas and gall bladder into the duodenum. Sphincter of Oddi Muscle Valve Muscular valve that separates the common bile duct from the duodenum. Small intestine Jejunum/ Ileum Yes Yes The jejunum and ileum absorbs small molecules from the chyme that have been broken down by the enzymes in the gastric and pancreatic juices. Also breaks down chyme physically my squashing it out through peristalsis, increasing its surface area. Villi Yes Yes Microscopic, finger-like blocks of cells that stick out from the wall of the intestine to increase its surface area, allowing more absorbtion. They contain GI capillaries and Lacteals. They are responsible for absorbing nutrients. GI capillaries **Absorbs** nutrients Blood vessels which pass through the villi and carry blood and nutrients back to the liver via the portal vein. Lacteals **Absorbs** nutrients Lymph capillary in the villi. Transports lipids (fats) directly from the gut lumen into the bloodstream via the lymph system. Peyer's Patches Immune system tissue Patches of lymphoid tissue in the wall of the small intestine that drain fluid from chyme and allow the immune system to control gut flora levels and destroy pathogens. More numerous in the ileum than the jejunum. Portal Vein Transports **absorbed** nutrients Carries blood and absorbed nutrients from the intestines to the liver. Large Intestine Caecum **Absorbs** nutrients, secretes mucus. The first part of the colon. Absorbs water, nutrients and electrolytes that remain in the digested chyme. Secretes thick mucus to lubricate the stool as it passes through the rest of the colon. Colon (Ascending, Transverse, Descending, Sigmoid) **Absorbs** nutrients, secretes mucus. Extracts the remaining nutrients and water from the stool and passes it on to the rectum. Rectum Removes water, compacts wastes Removal of water and storage and compaction of faeces Anus Muscle valve Muscular valve, seals rectum, allows for storage and excretion of faeces. ------------------- ---------------------------------------------------- ---------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **[Chemicals Used in the process of Digestion]** **Enzymes:** These are the chemical tools that the body uses. They can be used to break down large molecules into small, usable molecules- a process called **catabolism.** Enzymes used to do this are called **catabolic enzymes.** They can also be used to build new large complex molecules out of smaller components- a process called **anabolism.** Enzymes that can do this are called **anabolic enzymes.** The enzymes used in the digestive system are generally **catabolic enzymes** -------------- -------------------------------------------------------- ---------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------- Enzyme Type Produced by Activated by Breaks down Amylase Salivary Glands, Pancreas Already active on synthesis Complex carbohydrates (starches) into simpler sugars, ultimately into monosaccharides for cellular respiration. Can be converted to glycogen for storage. Lipase Von Ebener's glands (mouth), Pancreas, Small intestine Already active on synthesis but become more effective once bile salts enter the chyme. Complex fatty molecules (triglycerides) into free fatty acids and glycerol. Fatty acids can be used to make lots of ATP. Nucleosidase Liver Already active on synthesis Nucleic acids, releasing phosphates, pentoses and nitrogenous bases. Proteases Stomach (pepsin) Low pH of the stomach acid Proteins into amino acids. Amino acids can be reused to build new tissues and enzymes or can be deaminated by the liver and stored as fat. Pancreas Enterokinase found on the inner wall of the duodenum -------------- -------------------------------------------------------- ---------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------- **Note on Bile Salts**- not an enzyme but are used to break pools of lipids (fat) into tiny globules, increasing its surface area so the lipases have more access to it. The bile salt molecules have have a lipophilic (fat loving) end and a lipophobic (fat hating) end. When the lipophilic end attaches to a lipid droplet, the lipophobic end of the molecule pushes other fat droplets away, stopping them from pooling. **Hormones:** These are signalling chemicals that stimulate actions from specific target organs and tissues. They are the chemical communication system that the body uses and are carried with the blood to their target tissues/ organs. +-----------------+-----------------+-----------------+-----------------+ | **Hormone** | **Produced by** | **Target** | **Effect** | +-----------------+-----------------+-----------------+-----------------+ | Cholecystokinin | I-cells in the | Pancreas, Gall | Pancreas- | | (CCK) | wall of the | bladder, | stimulates the | | | duodenum when | Pyloric | pancreas to | | | they detect | sphincter | produce | | | presence of fat | | pancreatic | | | and protein in | | juice- a | | | the chyme. | | collection of | | | | | catabolic | | | | | enzymes- that | | | | | is released | | | | | into the | | | | | duodenum via | | | | | the common bile | | | | | duct. | | | | | | | | | | Gall Bladder- | | | | | stimulates the | | | | | contraction of | | | | | the bladder, | | | | | forcing the | | | | | stored bile | | | | | salts in it | | | | | into the | | | | | duodenum via | | | | | the common bile | | | | | duct. | | | | | | | | | | Pyloric | | | | | Sphincter- | | | | | reduces the | | | | | rate of stomach | | | | | emptying by | | | | | causing the | | | | | pyloric | | | | | sphincter to | | | | | close when CCK | | | | | is at high | | | | | levels. | +-----------------+-----------------+-----------------+-----------------+ | Secretin | S-cells in the | Pancreas | Pancreas- | | | wall of the | | stimulates the | | | duodenum when | | release of | | | they detect | | sodium | | | gastric acid | | bicarbonate | | | from the | | through the | | | stomach. | | common bile | | | | | duct to | | | | | neutralize the | | | | | gastric acid in | | | | | the chyme. | +-----------------+-----------------+-----------------+-----------------+ | Ghrelin | The stomach | Hunger centre | Stimulates | | | when it is | in the | hunger and the | | | empty- | hypothalamus | drive to eat. | | | specifically | (brain). | | | | when the | | | | | stretch sensors | | | | | on the stomach | | | | | tissue are not | | | | | being | | | | | activated. | | | +-----------------+-----------------+-----------------+-----------------+ | Leptin | Adipose (fat) | Satiety centre | Stops feelings | | | cells. | in the | of hunger and | | | | hypothalamus | increases | | | | | feelings of | | | | | satiety. | +-----------------+-----------------+-----------------+-----------------+ **[Glossary]** **Anabolic-** A chemical or process that builds bigger molecules out of small molecules. **Antacid-** A weak base (alkaline) taken orally to partially neutralize or buffer stomach acid. Used in the treatment of heartburn and stomach ulcer disease- eg Gaviscon, Rennie, Quick Eze, Alka seltzer. **Bile-** A mixture of bile salts, cholesterols, bilirubin, enzymes and water. Stored in the Gall Bladder and released in response to CCK. **Catabolic-** A chemical or process that breaks down big molecules into smaller ones. **Cholecystectomy --** Surgical removal of the Gall Bladder. **Chyme-** Mashed up and partially dissolved food and gastric secretions produced by the stomach and passed into the duodenum. **Enzyme-** A chemical tool used by the body to take apart or put together molecules. **Gall Stones (cholelithiasis) -** Solidified bile salts and cholesterol that can form in the Gall Bladder and block the common bile duct if they travel into it. Can also cause pain on Gall Bladder contraction in response to CCK. **Gastrointestinal (GI) Tract-** The whole passage from the mouth to the anus. **Metabolism-** the sum total of all the chemical reactions occurring in the body. Rate of reactions is generally regulated by hormones released by the thyroid gland. **Proton Pump Inhibitors-** Drugs which reduce the strength of stomach acids by inhibiting the Parietal Cells from pumping H~+~ ions (protons) into the gastric secretions. Less H~+~ ions = weaker acid. Eg. Pantoprazole, Esomeprazole. **Ulcer/ Ulceration-** An open sore which fails to heal.