6 1 Digestion and Absorption Understanding The contraction

6. 1 Digestion and Absorption Understanding: - The contraction of circular and longitudinal muscle layers of the small intestine mixes the food with enzymes and moves it along the gut - The pancreas secretes enzymes into the lumen of the small intestine - Enzymes digest most macromolecules in food into monomers in the small intestine - Villi increase the surface area of epithelium over which absorption is carried out - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients Applications: - Processes occurring in the small intestine that result in the digestion of starch and the transport of the products of digestion to the liver Skills: - Production of an annotated diagram of the digestive system - Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph Nature of science: - Use models as representations of the real world: dialysis tubing can be used to model absorption in the intestine

The Digestive System How do we get from this… …to this?

Key stages 1. Ingestion – Eat the food 2. Digestion – Food converted into smaller molecular form 3. Absorption – Small molecular forms absorbed through cells of digestive system and pass into blood system 4. Transport – Circulatory system delivers small molecular nutrients to body cells 5. Elimination – Undigested material/waste leaves body

Digestion – why? You are moving house…

Digestion – why? You are moving house…

Digestion – why? Break down larger molecules that cannot be absorbed into smaller molecules that can Copy and complete the table: Molecule ingested Proteins Lipids (triglycerides) Carbohydrates (polysaccharides and disaccharides) Nucleic acids (DNA and RNA) Molecular form after digestion

Digestion – why? Break down larger molecules that cannot be absorbed into smaller molecules that can Copy and complete the table: Molecule Ingested Molecular form after digestion Proteins Amino acids Lipids (triglycerides) Glycerol and fatty acids Carbohydrates (polysaccharides and disaccharides) Monosaccharides Nucleic acids (DNA and RNA) Nucleotides

Structure of digestive system Create an annotated diagram of the digestive system: 1. Role of the digestive system 2. Organs • Mouth • Esophagus • Stomach • Small intestine • Pancreas • Liver • Gall bladder • Large intestine • Anus 3. What does each organ do? 4. The process of peristalsis Skills: - Production of an annotated diagram of the digestive system Biodigital human

The Digestive System The mouth contains teeth. These chew the food and break it into smaller pieces. The tongue pushes food to the back of the mouth so you can swallow it. Enzyme (amylase) in saliva

The Digestive System The oesophagus, or food pipe, joins the mouth and the stomach. Food is squeezed along this tube into the stomach: peristalsis

The Digestive System The stomach is a bag of acid. The hydorchloric acid in the stomach, and enzymes break down the food even more. Bacteria and other pathogens killed

The Digestive System Pancreas secretes lipase, amylase and protease (enzymes)

The Digestive System Liver secretes bile Creates optimum p. H for enzymes Helps to break up lipids Gall bladder stores the bile

The Digestive System In the small intestine, the broken down food gets absorbed into the blood so the body can use it. Main area for digestion

The Digestive System The large intestine is about 1. 5 metres long. In the large intestine, the body absorbs a lot of water back from the digested food.

The Digestive System At the end of the digestive system, the left overs that the body can’t use leaves the body through the anus when you go to the toilet. Faeces is held in the rectum before.

Can you swallow if you are upside down?

Peristalsis Food does not move through your digestive system using gravity Muscles control the movement of your food throughout your digestive system Oesophagus, stomach and intestines (Autonomic nervous system – you are unaware) Understanding: - The contraction of circular and longitudinal muscle layers of the small intestine mixes the food with enzymes and moves it along the gut

Small Intestine Draw the diagram: Label the: - Lumen - Circular smooth muscle - Longitudinal smooth muscle - Villi Understanding: - The contraction of circular and longitudinal muscle layers of the small intestine mixes the food with enzymes and moves it along the gut

Enzymes Specific enzymes for specific foods Act as catalysts for reactions (reactions require less energy when there are enzymes) Throughout digestive system – process starts in the mouth Focus on pancreas and small intestine Understanding: - The pancreas secretes enzymes into the lumen of the small intestine

Round 1: Pancreas Enzyme Substrate Amylase Lipase Phospholipase Protease Understanding: - The pancreas secretes enzymes into the lumen of the small intestine Action

Round 1: Pancreas Enzyme Substrate Action Amylase Starch Breaks down starch to maltose Lipase Triglycerides Broken down to fatty acids and glycerol Phospholipase Phospholipids Broken down to fatty acids, glycerol and phosphate Protease/endopeptidases Proteins/polypeptides Broken down to shorter peptides Some of these products are still too big to be absorbed so need to be broken down more by different specific enzymes Understanding: - The pancreas secretes enzymes into the lumen of the small intestine

Round 2: Wall of small intestine Enzyme Substrate Nuclease Maltase Lactase Sucrase Exopeptidases Dipeptidases Understanding: - Enzymes digest most macromolecules in food into monomers in the small intestine Action

Round 2: Wall of small intestine Enzyme Substrate Action Nuclease DNA/RNA Breaks down into nucleotides Maltase Maltose Breaks down into glucose Lactase Lactose Breaks down to glucose and galactose Sucrase Sucrose Breaks down into glucose and fructose Exopeptidases Peptides Break down into single amino acids (leaves dipeptides) Dipeptidases Dipeptides Break down into amino acids Understanding: - Enzymes digest most macromolecules in food into monomers in the small intestine

Super fun fact: How long is this boat?

Undigestables Food takes hours to pass through the long small intestine Many molecules remain undigested Human body cannot synthesize the necessary enzymes E. g. Cellulose: passes on to large intestine as the main component of faeces Understanding: - The pancreas secretes enzymes into the lumen of the small intestine

Small Intestine 4 3 Four layers: 1. Serosa (outer coat) 2. Muscle layers 3. Sub-mucosa (blood and lymph vessels) 4. Mucosa (Lining of small intestine) Skills: - Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph 2 1

Small Intestine Draw a cross section of an intestinal villus. Label each part and describe the function - Epithelium Microvilli Capillaries Lacteal Goblet cells Understanding: - Villi increase the surface area of epithelium over which absorption is carried out

Villi summary Key points: 1. 2. 3. 4. Epithelium is one cell thick Many villi with microvilli = large surface area Good blood supply Large amounts of mitochondria Understanding: - Villi increase the surface area of epithelium over which absorption is carried out

Surface Areas A small intestine that is 5 m long and 2. 5 cm diameter. Surface area: No villi= 0. 5 m 2 With villi = 200 m 2 Understanding: - Villi increase the surface area of epithelium over which absorption is carried out

Spot the Difference his t ld ou oeliac c y c Wh ke a ? ma thin Coeliac small intestine Some villi are lost, so the individual cannot absorb the products of digestion properly

Passive Simple diffusion - Follow concentration gradient - Small molecules/non-polar molecules Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Passive Facilitated diffusion - Down concentration gradient - Protein also used due to size/polarity Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Active transport - Uses membrane pumps - Move against concentration gradient - Use ATP Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Active Endo/exocytosis - Molecules trapped in an infolding of the membrane - Pass through to the other side as a vesicle - Requires ATP Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Absorption in the villi PASSIVE (No ATP): - Simple diffusion - Facilitated diffusion ACITVE (ATP used): - Active transport - Exocytosis Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Methods of absorption Triglycerides INTO VILLUS MEMBRANE - Simple diffusion (Passive) - Facilitated diffusion (Passive) OUT OF VILLUS MEMBRANE - Exocytosis (Active)

Triglycerides 1. Must be digested before being absorbed 2. Produces fatty acids and a monoglyceride Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Triglycerides 3. Can be absorbed by simple diffusion as they can pass between phospholipids in plasma membrane Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Triglycerides 4. Fatty acids also absorbed by facilitated diffusion using fatty acid transporters (proteins in membrane of microvilli) Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Triglycerides 5. Once through the membrane and inside the epithelium cells, fatty acids are combined with monoglycerides to produce triglycerides, which cannot diffuse back again Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Triglycerides 6. These triglycerides join with cholesterol to form droplets. 7. These then become coated in phospholipids and protein Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Triglycerides 8. These lipoproteins are released from epithelial cells into either the capillary or lacteal by exocytosis Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Methods of absorption Triglycerides INTO VILLUS MEMBRANE - Simple diffusion (Passive) - Facilitated diffusion (Passive) OUT OF VILLUS MEMBRANE - Exocytosis (Active)

Methods of absorption Glucose - Active transport (Active) - Facilitated diffusion (Passive)

Glucose 1. Glucose cannot pass through the plasma membrane by simple diffusion because it is polar (therefore hydrophilic) Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Glucose 2. Sodium potassium pumps pump sodium ions by active transport from the cytoplasm inside the villus to the intestinal lumen. Pumps potassium ions the other way. Sodium concentration builds up. Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Glucose 3. Sodium glucose co-transporter proteins transfer a sodium ion and glucose molecule together into epithelium cells. (Facilitated diffusion = passive) Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Glucose 4. Glucose channels allow glucose to move by facilitated diffusion into the villus and on into the blood capillaries. Understanding: - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients

Methods of absorption Glucose - Active transport (Active) - Facilitated diffusion (Passive)

6. 1 Digestion and Absorption Understanding: - The contraction of circular and longitudinal muscle layers of the small intestine mixes the food with enzymes and moves it along the gut - The pancreas secretes enzymes into the lumen of the small intestine - Enzymes digest most macromolecules in food into monomers in the small intestine - Villi increase the surface area of epithelium over which absorption is carried out - Villi absorb monomers formed by digestion as well as mineral ions and vitamins - Different methods of membrane transport are required to absorb different nutrients Applications: - Processes occurring in the small intestine that result in the digestion of starch and the transport of the products of digestion to the liver Skills: - Production of an annotated diagram of the digestive system - Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph Nature of science: - Use models as representations of the real world: dialysis tubing can be used to model absorption in the intestine

Modelling the small intestine Write a simple method. How can we use dialysis tubing to model absorption of digested food in the intestine? - You will not Title complete this as Hypothesis Equipment an experiment Method Why is this a good model? Why could it be a bad model? Nature of science: - Use models as representations of the real world: dialysis tubing can be used to model absorption in the intestine