Accessory Digestive Organs These are organs located outside of the GI tract These organs create, or store and secrete enzymes, hormones and chemicals that are required for digestion.

Pancreas

Long flat gland, nestled between the stomach and duodenum. When chyme from the stomach enters the duodenum, the hormone CCK (cholecystokinin) is secreted (by the walls of the duodenum) and causes the pancreas to release its pancreatic juices and the liver to release bile The pancreas does 3 things to aide in digestion

1. Releases pancreatic juice Travels from the pancreas to the duodenum via the pancreatic duct Contains 28 different enzymes including: Amylases: convert big, complex carbs into simple sugars Lipases: split lipids into glycerol and fatty acids Trypsin/peptidase – breaks proteins into amino acids

2. Neutralizes the acidic chyme The pancreatic juices are alkaline (basic) because of its high concentration of bicarbonate ions (HCO 3 - ) Changes the chyme from pH 2 (which is the pH in the stomach) to pH 8 If the acidic chyme was not neutralized, it could cause ulcers in the intestinal walls

3. Releases Hormones INSULIN – controls blood sugar levels by allowing glucose to enter the cells allowing the glucose to be stored as glycogen. GLUCAGON – when more glucose is needed in the blood, glucagon will allow glycogen to be broken down into glucose again

Exocrine vs Endocrine Glands A gland is an organ that secretes a substance such as a hormone or an enzyme. Endocrine Glands: secrete hormones and release them directly into the blood stream. Ex: the pituitary glands, adrenal glands, the ovaries, the testes……

Exocrine vs Endocrine Glands Exocrine Glands: secrete their products into a duct. Ex: sweat glands, digestive glands

ENDOCRINE GLAND - Secretes products (hormones) directly into the blood stream Duct Acinus (plr acini) - Where product accumulates Acinar cell -Makes products -Ex: pancreatic lipase EXOCRINE GLANDS - Secrete products into a duct

Exocrine Gland Produce the products and secrete them into the acinus - Hollow space surrounded by secretory cells. - Collects products and sends it to the duct Can either lead to a lumen (space between cells, ex: the lumen of the small intestine) or out of the body

Examples of Exocrine Glands GlandPlace Released pHSecretionEnzymeSubstrateProduct Salivary glands Mouth7SalivaSalivary Amylase Gastric glands Stomach2Gastric Glands Pepsin/ pepsinogen pancreasSmall intestine (duodenum) 8 Pancreatic Juice Bicarbonate ions Pancreatic amylase Trypsin Lipase Phospholipase Not an enzyme Starch Protein Lipid Phosopholipids Maltose Smaller Polypeptides Glcerol & Fatty acids Phosphate, glycerol & fatty acids Neutralizes stomach acid

Stomach Ulcers An open sore in the lining of the stomach causing pain and sometimes bleeding For a very long time, the medical community believed that ulcers were caused by stress In fact, they are caused by medications that affect the mucous lining of the stomach or a bacteria called H. pylori

Stomach Ulcers H. pylori can enter the body through food or water. It is able to survive the acid environment in the stomach by burrowing into the mucosa and stopping the production of protective mucus. Without the protective mucus, HCl will destroy the stomach lining creating the ulcer. Can be treated with antibiotics

H. pylori may reduce the production of gastric acids because it damages the cells producing gastric juice. However, gastrin will still be released and attempt to stimulate these cells to produce gastric juice. As a result, it can lead to gastric cancer (stomach cancer) H. pylori can increase the amount of gastric acid which can lead to duodenal ulcers (because of the large volume of acid entering the duodenum)

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Pepsin and Trypsin Types of proteases (breakdown proteins) They are produced as inactive precursors – pepsinogen and trypsinogen – because in their active form they would digest the cell and enzymes that make them They are activated by the presence of HCl (produced in the stomach) and enterokinase (produced in sm. Intestine)

Lipid Digestion Not easy because they are not water soluble Lipid molecules group together to from droplets of fat Lipase acts on the surface of lipid spheres

Lipid Digestion - BILE BILE – produced by the liver Aides in lipid digestion by emulsifying fats (dividing fat droplets into smaller droplets) Creates a larger surface area for lipase to work

Bile is continuously produced in the liver but is stored in the gall bladder When food enters the duodenum, the gall bladder contracts and bile is squeezed out of the gall bladder and travels to the duodenum via the bile duct.

Absorption of Digested Foods

Cross Section of ileum (draw and label)

Epithelial cell features (of small intestine) Epithelial Cells are the cells that line cavities and surfaces They are the cells that create the villi that line the small intestine lumen

Epithelial Cell Features Form villi – increase surface area Contain microvilli – increase surface area Tight Junctions – connections between epithelial cells which fuse adjacent cells together at their membranes to form a seal Rich in mitochondria to produce ATP for active transport Pinocytotic vesicles –to aide in endocytosis

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Ileum - Cross section lumen Villus (plr villi) Circular muscle Longitudinal muscle mucosa Folds in small intestine

How are nutrients absorbed into epithelial cells? Passive Transport Active Transport

Passive Transport Transport across a membrane that does not require energy Driven by the concentration gradient SIMPLE DIFFUSION – the molecules move through the membrane moving from an area of high concentration to low concentration. Ex: lipids

Simple Diffusion

Passive Transport Facilitated Diffusion – the molecules are too large to pass through membrane on their own They enter the membrane via a pore or a carrier protein/protein channel Ex: amino acids, glucose

Facilitated Diffusion

Active Transport Requires ATP energy Often moves molecules against their concentration gradient (from low concentration to high concentration)

Active Transport ACTIVE TRANSPORT via Transport Proteins/ Protein Pumps These proteins embedded in the cell membrane require ATP to activate them

Endocytosis The plasma membrane forms a vesicle around the nutrient molecule(s) to bring them into the cell Pinocytosis: for liquids or small molecules Phagocytosis: for larger molecules

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Unabsorbed Materials The following molecules are not absorbed by the body (because there is no system of membrane proteins or receptors to absorb them): Cellulose Lignin (large polysaccharide that strengthens wood) Bile pigments Bacterial and intestinal cells These materials are egested in feces

Why isn’t Cellulose Digested? Cellulose is a large polysaccharide (made of glucose molecules) that provides structure in plant cell walls. The main difference between amylose (starch) and cellulose are the linkages

Cellulose indigestion Amylase cannot work on the 1, 4 beta linkages of cellulose Cellulose does not dissolve in water The enzyme cellulase can break down cellulose however mammals do not poses the enzyme

Ruminant Animals Some forms of bacteria can produce cellulase and they can live symbiotically in the guts of herbivores (such as cattle, llamas, sheep, goat, giraffes, deer….)

Endoscopy Medical scientists have developed methods of seeing inside the human body that are much safe and less traumatic than surgery An endoscope is a tool that is designed to look inside the body It is a narrow tube, with a light source, a lens, and a camera

It can be inserted through a natural opening in the body such as the mouth or anus or through a small incision into the body cavity The procedure is called an endoscopy. Can be used to remove a tissue sample biopsy, remove gall bladders Compared to regular surgery, this procedure is less painful and has a shorter recovery time.

Capsule Endoscope Technological advancements have allowed for the creation of a tiny camera, small enough to fit inside a capsule that can be swallowed. As the capsule passes through the digestive tract, it takes thousands of pictures that are transmitted wirelessly to a receiver. The capsules could also be equipped with sensors(for temp and pH) and could deliver drugs to specific target regions.