Physiology- Module 15

- main function- breakdown organic nutrients for absorption into the body
- mouth: breakdown food by chewing (mastication) and mix with saliva
- salivary glands: produce saliva to moisten and begin digesting some food particles
- esophagus: straight muscluar tube that connects the mouth and pharynx to stomach
- stomach: stores, mixes and digests some food and delivers good to small intestine
- liver: produces and secretes bile
- gallbladder: stores and concentrates bile
- pancreas: secretes digestive enzymes, hormones and bicarbonates
- small intestine: allows digestion and absorption of foo particles
- large intestine: stores and concentrates undigested material and absorbs salt and water
- rectum: site where the defection reflex is triggered

- it involves the release of digestive enzymes into the lumen of the GI tract. this fluid may include: water, electrolytes, enzymes, bile salts and digestive enzymes

- the process where food is broken down into smaller molecules by the digestive enzymes so they can be taken up by the body

- the proces where food is broken down into smaller molecules by the digestive enzymes so they can be taken up by the body

- the movement of the food through thr GI tract by the contraction of smooth muscle that line the walls of the tract

- the removal of the unwanted waste products from the body after almost all of the unwanted material is absorbed

- digestion begins in the mouth by saliva ( 3 salivary glands: parotid, submandibular and sublingual)
- contain enzymes that begin to digest carbohydrates and lipids
- food is broken down and mixed with saliva to form bolus, then swallowed
- swallowing begins when the larynx moves up and closes the glottis
- food travels by peristalsis (wave of smooth muscle contraction) down the esphagus to the stomach

- divided into 3 areas
1. fundus- at the top end of the stomach
2. the body- largest part of the stomach, secretes mucus, HCl, and pepsinogen
3. the antrum- locates at the far end of the stomach, secretes mucus as well as the hormone gastrin- pyloric sphincter empties into the small intestine

-main function: to liquefy, mix and store the food so it can be slowly released into the small intestine where most digestion adn absorption takes place

- the stomach does secrete mucus , HCl, pepsinogen, gastrin and intrinsic factor
- HCl begins to breakdown protein and connective tissue adn kills bacteria
- HCl also converts pepsinogen to is active form, pepsin
- pepsin begins to digest the large protein molecules breaking them down to peptides
- gastrin stimulates the secretion of stomach acid
- intrinsic factor hepls absorption of vitamin B12
- contents of stomach are then slowly emptied into small intestine
- must be regulated so all food entering the small intenstine can be fully digested and absorbed

- lies below the stomach and has both endocrine and exocrine (digestive) functions
- the exocrine products are secreted into a long pancreatic duct. This duct merges with the common bile duct (from the liver and gallbladder) just before entering the duodenum.
- produces and secretes the carbohydrate-digesting enzyme amylase, the protein-digesting enzymes trypsin, chymotrypsin, and proteases, and the fat-digesting enzyme lipase

- stomach empties contents here
- 3 segments- duodenum, jejunum, ileum
- contains villi
- almost all digestion and absorption takes place
- digestion of food ocurs by presence of specific enzymes that come from pancreas, cells in the walls of small intestine and bile from liver
-IMPORTANT- very specific digestive enzymes for each part of our meal
- some enzymes digest only proteins, some only carbs, some only lipids- into respective building blocks
- once digested, building blocks are then absorbd- some like they were resborded in the kidney

- carbohydrates are composed of a single building block called simple sugars or monosaccharides- glucose and fructose
- 2 units called disaccharides- sucrose, lactose and maltose
- 2 or more units called polysaccharides- starch
- amylase breaks down the polysaccharides to maltose, sucrose and lactose
- the disaccarides cant be absorbed until they are broken down into monosaccharides
- enzyme maltase breaks down maltose
- enzyme sucrase breaks down sucrose
- enzyme lactase breaks down lactose
- 3 enzymes located on brush border of microvilli located on the intestinal cells

- people who cannot eat dairy- serious cramps, bloating, gas
- cannot digest lactose becuase unable to produce lactase
- if lactose cannot be digested, it can stay in the tract

- almost identical to process of glucose reabsorption at the kidney
- intestinal cells have many Na/K pumps on the basal side ( side not lining intestine)
- pumps establish a concentration gradient for Na- high on outside, low on inside of cell
- gradient powers the Na/glucose co-transporter on the luminal side (side that faces intestine), moves glucose into the cell as Na moves down the concentration gradient
- once glucose is inside cell, it will diffuse throught the basal side by facilitated diffusion

- proteins are long strings of amino acids joined together
- in order to absorb these long chains, they must be broken down by their amino acid building blocks
- process begins with HCl, which begins to uncoil the long protein strands to provide pepsin access to the protein chain to digest into smaller polypeptides
- polypeptides enter small intestine where they will be completely broken down to amino acids and absorbed
- this requires 2 pancreatic enzymes called proteases
1. the enzyme, endopeptidase, breaks the bonds between amino acids inside the polypeptides
2. the enzyme, exopeptidase, breaks bonds between amino acids at the ends of the poplypeptide
- in order for pancreatic enzymes to function properly the highly acidic chyme (HCl) that entered the small intestine from the stomach must be neutrailized by bicarbonate from the pancreas
- it it isnt neutralized, the acid will break up the pancreatic enzymes and render them ineffective