6.1: Digestion & absorption Why digest?

Digestion From food to poo Crash Course VIDEO: http://www.youtube.com/watch?v=s06XzaKqELk Small molecules Pieces of food Chemical digestion (enzymatic hydrolysis) What are the reasons for digestion? Change food into useable forms Some food molecules may be too big for absorbtion Common molecules to be digested? Starch, proteins, triglycerides. Nutrient molecules enter body cells Mechanical digestion Food Undigested material INGESTION DIGESTION ABSORPTION ELIMINATION

Chemical reactions breaking down the food Absorption Define these terms Ingestion Eat the food Digestion Chemical reactions breaking down the food Absorption Small molecules passing into blood/lymphatic vessels Transport Circulatory system delivering absorbed molecules

Carbohydrates Lipids Protein Nucleic acids What are molecules made of? Carbohydrates Poly, di or monosaccharides  monosaccharides Lipids Triglycerides  glycerol & fatty acids Protein Protein  amino acids Quick review! Nucleic acids DNA, RNA  nucleotides

What is this? Draw, and recognise the structure of an amino acid Which general group do amino acids belong to? Proteins! Amino acid!

Mono, Di or Poly? Maltose Disaccharide

What is this? Saturated fatty acid

Mono, Di or Poly? Glycogen Polysaccharide

What is this? Technical name = D-ribose Ribose

What is this? Unsaturated fatty acid

Mono, Di or Poly? Fructose Monosaccharide

What is this? No need to draw, recognise structure Glucose

How are molecules broken down? Salivary enzymes Pepsin (protease) Pancreatic lipase Source Salivary glands Stomach cells Pancreas cells Substrate Amylose (starch) Proteins (polypeptides) lipids Products Maltose, glucose Amino acids Glycerol & fatty acids Optimum pH 7 3

Summary of digestion Some molecules cannot be digested (example: Cellulose) The enzyme cellulase digest cellulose, but humans lack the gene that codes for this enzyme. Undigested cellulose is an important part of dietary fibre, which has beneficial effects on the digestive system.

Digestive System aka alimentary canal

Peristalsis – waves of muscle contraction, the muscle in the walls of the alimentary canal are rarely relaxed. Sometimes they contract vigorously, sometimes more moderately! Peristalsis regulates the flow of substances through the tract and also allows mixing with enzymes. This is controlled by the enteric nervous system, only present in the gastrointestinal tract, not controlled by the brain.

Stomach

Duodenum

Small intestines

Large intestines

anus

6. 1: Methods of absorption HWK sheet http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html http://www.youtube.com/watch?v=bNMsNHqxszc FUNNY VIDEO: http://www.youtube.com/watch?v=jsVgi8hoFFc TIP: Read pages 284 – 288 to help the explanation in the conclusion

Summary of digestion Longitudinal and circular muscle fibers along the walls of the alimentary canal contract and relax squeezing the food and breaking up large solid lumps. Digestive juices release by salivary glands, stomach and pancreas contain enzymes which help break food molecules

You will be expected to draw this from memory! Page 280 (154 in the old book) – draw and annotate a diagram of the human digestive system. You will be expected to draw this from memory!

Pancreas Secretes enzymes into the S.I Contains two gland tissues types Hormone secretions Enzyme secretions Digestive enzymes synthesized in pancreatic gland cells on ribosomes (rER) then processed by the Golgi apparatus and excreted by exocytosis. Pancreatic juice contains: Amylase Lipases Proteases Sketch figure 4, page 282 to show the secretion of digestive enzymes into ducts within the pancreas.

Small intestine Duodenum is the first part. Food stuff mixed with bile (from liver/gall bladder) and trypsin (protease), lipase, amylase and bicarbonate (from pancreas) Most molecules absorbed through capillary bed expect fatty acids (absorbed into lacteal) Villi contain capillary bed (circulatory system) and a lacteal (lymphatic system). Bile breaksdown lipids Bicarb. neutralises acid

Tissue layers in transverse section of the small intestines, as seen with an electron microscope. (also on pg. 281 fig. 2) It would be a good idea to be able to draw and label this diagram.

Google image search ‘tissue layer in transverse sections of the small intestines’ pick one that is labelled that shows the main layers

Enzymes in the small intestines Substrate Product Amylase Starch Maltose Lipase Triglycerides Fatty acids & glycerol or fatty acids & monoglycerides Phospholipase Phospholipids Fatty acids, glycerol & phosphate Protease Proteins & polypeptides Shorter peptides These are only a few of the enzymes involved with digestion. These are all enzymes secreted by the pancreas, this means they are present in the intestinal ‘juice’ and will leave the body along with the waste material. This is why the pancreas continually produces these enzymes.

Remove single amino acid at a time until a dipeptide remains Immobilized enzymes Enzyme Substrate Product Nucleases DNA, RNA Nucleotides Maltase Maltose Glucose Lactase Lactose Glucose & galactose Sucrase Sucrose Glucose & fructose Exopeptidases Peptides Remove single amino acid at a time until a dipeptide remains Dipeptidases Dipeptides Amino acids These enzymes are immobilized in the plasma membrane of the epithelium cells lining the intestine. These enzymes are active on the wall and remain active when they become dislodged from the lining of the intestine (abrasion).

In summary…. Small intestine is able to absorb a wide range of substances including: Glucose, fructose, galactose, the twenty amino acids, fatty acids, monoglycerides, glycerol, nucleotides, mineral ions (Ca, K, Na) and vitamins (vitamin C aka ascorbic acid)