Digestion, 6.1 Digestion and Absorption

Villi increase the surface area of epithelium over which absorption is carried out What is absorption? What does the rate of absorption depend on? Main way to increase this factor?

Absorption = process of taking substances into cells and blood Nutrients are absorbed principally in the small intestine and rate of absorption depends on the SA of the epithelium. - Lots of folds on the inner surface for increased SA - Lots of villi to increase SA

The contraction of circular and longitudinal muscle layers of the small intestine mixes the food with enzymes and moves it along the gut What is peristalsis and what do the muscle layers do? What is the purpose of peristalsis?

Circular + Longitudinal muscle in the wall of gut = smooth muscle consisting of relatively short cells which exert continuous moderate force with some more vigorous contractions - doesn't remain relaxed. - Waves of muscle contraction = peristalsis contract circular muscles behind food preventing it being pushed back to the mouth + Longitudinal contractions where the food is located moves it along. * Contractions controlled unconsciously by enteric nervous system - Peristalsis occurs in one direction, when puking occurs, abdominal muscles used - Food is moved few centimetres at a time hence progression through intestine is much slower allowing time for digestion. Main function of peristalsis = churning with semi digested food to mix it with enzymes and speed up digestion

Enzymes digest most macromolecules in food into monomers in the small intestine The different main reactions? The reactions that occur from enzymes that are not found in pancreatic juice?

Enzymes in pancreatic juice carry out hydrolysis reactions: Starch --> Maltose by amylase Triglycerides --> Fatty acids + glycerol/ fatty acids and monoglycerides by lipase Phospholipids ---> Phosphate + Glycerol + Fatty acids by phospholipase Proteins and polypeptides --> Shorter peptides by protease * Wall of intestine produces variety of other enzymes to digest more substances, most of these enzymes remain immobilised in the plasma membrane of epithelium cells lining the intestine. DNA and RNA --> Nucleotides by nucleases Maltose --> Glucose by maltase Lactose --> Glucose + Galactose by lactase Sucrose --> Glucose + Fructose by sucrase Peptides ---> Dipeptides by exopeptidases Dipeptides --> Amino acids by dipeptidases * Some substances remain undigested because humans cannot synthesise necessary enzymes

Villi absorb monomers formed by digestion as well as mineral ions and vitamins What is the role of the epithelium? What does it absorb? What does it get rid of and how?

Epithelium covers villi preventing harmful substances and being permeable to useful nutrients: Villi absorbs these products: - Glucose fructose galactose and other monosaccharides - Amino acids (any of the 20) - Bases from digestion of nucleotides - Fatty acids, monoglycerides + glycerol Also absorb substances which don't need digestion: - Minerals - Vitamins * Some substances that are harmful pass through the epithelium and are removed from the blood and detoxified by the liver. * Unwanted, harmless substances absorbed pass out in the urine * Bacteria passed through is removed from the blood by phagocytic cells in the liver

Use of dialysis tubing to model absorption of digested food in the intestine What can you test? Explain the results

Investigating need for digestion 1) Cut length of dialysis tubing and seal one end by tying a knot, pour in suitable mixture of foods. 2) Enzyme in one of the tubings and none in the other and place in to separate test tubes containing water 3) After time test for sugars - bag with no enzyme + water will contain no sugars whereas bag with enzyme + water will have sugar Investigating membrane permeability 1) Place mixture in dialysis tubing which can all be tested for and leave for a while 2) Use separate tests for the water and contents of dialysis tubing Cola contains glucose, phosphoric acid + caramel Test for glucose with glucose strips (should be outside) Check colour of contents (Should be brown as caramel is a complex carbohydrate that needs to be digested) Test for pH

Dialysis tubing can be used to model absorption in the intestine Why do models need to be used? What similarities what differences?

Living systems are complex and many factors influence results when experiments are done - difficult to control variables. Models are used to represent part of living system such as gastric model or the use of dialysis tubing made from cellulose to mimic the wall of the gut. Its pores allow water and small molecules or ions to pass through freely but not large molecules - can model absorption by passive diffusion and osmosis.

The pancreas secretes enzymes into the lumen of the small intestine What are the two types of glandular tissue in the pancreas. Contents?

Pancreas contains two types of gland tissue: Small groups of cells secrete insulin glucagon into the blood Remainder synthesises and secretes digestive enzymes into the guy in response to eating a meal - mediated by hormones synthesised in stomach and by enteric nervous system. Digestive enzymes are synthesised in pancreatic gland cells on ribosomes on RER, processed in Golgi apparatus and secreted by exocytosis. One large duct secretes pancreatic juice into lumen of small intestine. Contents of pancreatic juice: Amylase to digest starch Lipases to digest triglycerides and phospholipids Proteases to digest protein and peptides

Production of an annotated diagram of the digestive system Role of digestion and components involved? The different structures and functions?

Role of digestive system = to break down large carbon compounds in food, to yield ions and smaller compounds that can be absorbed * Proteins, lipids and polysaccharides involve several stages at different parts of the gut for digestion * Surfactants required to break up lipid droplets and enzymes required to catalyse reactions - enzymes are produced in some on the glandular cells in the lining of the stomach and intestine * Surfactants and other enzymes secreted through accessory glands that have ducts leading to digestive system Different structures and functions: Mouth = Mechanical digestion of food by chewing and mixing with saliva which contains lubricants and enzymes at the start of digestion - controlled voluntarily. Esophagus = Movement of food by peristalsis from mouth to stomach Stomach = churning and mixing secreted water and acid to kill pathogens + initial stages of protein digestion Small intestine = Final stages of digestion of lipids, carbohydrates, proteins and nucleic acids, neutralising of stomach acid + absorption of nutrients Pancreas = Secretion of lipase, amylase and protease Liver = secretion of surfactants in bile to break up lipid droplets Gall bladder = storage and regulated release of bile Large intestine = reabsorption of water, further digestion of carbohydrates by symbiotic bacteria + formation and storage of feces.

Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver What are the different types of starch? Process that occurs and enzyme breakdown? Where does glucose travel after broken down?

Starch digestion demonstrates catalysis, enzyme specificity and membrane permeability. - Starch is a macromolecule composed of many alpha glucose monomers linked together by condensation reactions these require digestion Starch consists of two types of molecules: - Amylose which contains unbranched chains of glucose - Amylopectin which has with branched chains of glucose Amylase breaks to 1,4 bonds in both amylose and amylopectin. Amylose froms maltose and maltotriose whereas amylopectin is not fully broken down. Fragments of amylopectin containing 1,6 bonds that cannot be broken down by amylase are called dextrins. Maltase digests maltose Glucosidase digests maltotriose Dextrinase digests dextrins to glucose. * Glucose absorbed into villus epithelium cells by co-transport sodium ions and moves by facilitated diffusion into the fluid in interstitial spaces inside villus. Glucose in blood is carried via hepatic portal vein to the liver where excess glucose can be absorbed by liver cells and converted to glycogen for storage.

Different methods of membrane transport are required to absorb different nutrients Movement of triglycerides? Movement of glucose?

To be absorbed nutrients pass from lumen of the small intestine to the capillaries or lacteal in the villi. *- Triglycerides are digested and fatty acids and monoglycerides are absorbed into villus epithelium cells by simple diffusion as they can pass between phospholipids in the plasma membrane - Fatty acids also absorbed by facilitated diffusion due to fatty acid transporters - Fatty acids combine with monoglycerides to produce triglycerides which cannot diffuse back to the lumen once in epithelium cells. - Triglycerides react with cholesterol to form droplets coated with phospholipids and protein - Lipoprotein particles are released by exocytosis to enter lacteal or be carried away by lymph * Glucose cannot pass through plasma membrane as it is polar and hydrophilic - Sodium potassium pumps pump sodium ions by active transport from cytoplasm to interstitial spaces inside villus and potassium ions in opposite direction to create low concentration of sodium ions inside villus epithelium cells - Sodium glucose co transporters carry sodium and glucose molecule to the cytoplasm through facilitated diffusion. Occurs due to the concentration set by potassium-sodium pumps. - Glucose channels also allow glucose to move by facilitated diffusion from cytoplasm to blood capillaries in villus

Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph What are the different layers?

Wall of the small intestine is made up of many layers o living tissues: - Serosa = outer coat - Muscle layers = Longitudinal and circular muscle - Sub mucosa = tissue layer containing blood and lymph vessels - Mucosa = lining of small intestine with the epithelium that absorbs nutrients on inner surface

enzyme in saliva that breaks down starch into sugars - beginning the process of chemical digestion

amylase

muscular opening at end of rectum through which waste material eliminated from

anus

system of body that processes food, gets rid of waste

digestive system

getting rid of the unused food from the digestive process (mainly fibre)

egestion (pooping!)

tiny organ behind the liver that stores bile to break down fats

gall bladder

chemical made in stomach that helps break down food and kill bacteria

hydrochloric acid

last section of digestive system, where water is absorbed from food and remaining material eliminated from body

large intestine

a large organ located above and in front of the stomach filters toxins from the blood, makes bile

liver

place where food is masticated (broken up into small pieces) (physical digestion)

mouth

muscular tube that moves food from mouth to stomach

oesophagus

the liquid part of blood that transports dissolved food, hormones and waste CO2

plasma

stores faeces (solid wastes) from body

rectum

peristalsis

rhythmic muscular contractions that squeeze food through oesophagus into stomach

glands of mouth that produce saliva, a digestive secretion

salivary glands

organ that completes the chemical digestion of food and absorbs the most nutrients

small intestine

an enlarged, muscular saclike organ which churns the food

stomach

small finger-like projections on walls of small intestines that increase surface area for absorption

villi