Mr. Briner Unit 6.1 Digestion and Nutrition

Mr. Briner Unit 6.1 Digestion and Nutrition
ASM IB DP Biology Unit 6.1 Digestion and Nutrition

Digestion and nutrition
Digestion of large molecules Food molecules are usually polymers Polysaccharides, proteins and lipids Too large to move from the digestive tract into the circulatory system Can not move across the membranes of small intestine epithelial cells

Digestion of large molecules Most large food polymers are insoluble Must first be digested to smaller soluble molecules to be absorbed into the blood

Digestion of large molecules Polymers need to be broken down into monomers during digestion Polysaccharides  monosaccharides Polypeptides  amino acids Lipids  glycerol and fatty acids

Digestion of large molecules Monomers are small enough to move into small intestine epithelial cells Through diffusion, facilitated diffusion, or active transport through membrane proteins

Enzymes in digestion At body temperature (~37°C), reaction rates are too slow to be efficient Hydrolytic reactions in the digestion of large food molecules are very slow Due to considerable activation energy Reactions are exothermic

Enzymes in digestion Enzymes lower activation energy Catalyzing hydrolysis reactions

Enzymes in digestion Enzyme Source Substrate Products Optimum pH Salivary amylase Salivary glands Starch Maltose 7.5 Pepsin Stomach Proteins Smaller polypeptides 2 Pancreatic lipase Pancreas Phospholipids (triglycerides) Glycerol, Phosphate, Fatty acids 7.2

Absorption vs. Assimilation Absorption Movement of chemical substances from the digestive tract lumen into cells Movement into the circulatory or lymphatic systems for distribution to all somatic cells By diffusion, facilitated diffusion, or active transport

Absorption vs. Assimilation Assimilation Following digestion and absorption, nutrients are taken into somatic cells and are used in metabolism Converted to the biomass of the organism

6.1.S1 Production of an annotated diagram of the digestive system.

The Digestive System Mouth Beginning of the digestive system Used in eating and speaking Breaks down food through salivary enzymes (chemical) and mastication(physical)

The Digestive System Esophagus Muscular tube transporting food from the mouth to the stomach Squeezes food (bolus) ‘down’ with circular and longitudinal muscles (peristalsis)

The Digestive System Stomach Large, expandable, muscular, glandular organ Stores and mixes food (physical) Begins protein breakdown (chemical)

The Digestive System Stomach Gastric pits secrete: HCl Producing a stomach pH of about 2 Facilitating pepsin activity Killing foreign pathogens, such as bacteria Mucus Protects stomach cells from acidic conditions

The Digestive System Stomach Gastric pits secrete: Pepsin Catalyzes the hydrolysis of polypeptides Chyme The product of stomach digestion Acidic fluid released from stomach into small intestine (via pyloric sphincter)

Stomach Lumen of the stomach - stores the food from a meal Gastric pits – Secrete mucus, enzymes and acid Mucus secreting cells – Protects stomach surface from auto-digestion

Stomach Parietal cells – Produce HCl which kills microorganisms Also converts inactive pepsinogen to active pepsin Chief cells – Produces protease enzyme

The Digestive System

6.1.U2 The pancreas secretes enzymes into the lumen of the small intestine.

The Digestive System Pancreas Producing several important hormones For example, insulin and glucagon Secreting pancreatic juice Containing digestive enzymes Amylases, Lipases and Proteases! Helps break down nutrients in the chyme

The Digestive System Liver

The Digestive System Liver Produces bile Alkaline compound that emulsifies lipids Increases lipids SA making enzymatic digestion more efficient Glycogen storage, decomposition of red blood cells, plasma protein synthesis, hormone production, and break down of toxic substances

The Digestive System Gall bladder Concentrates and stores bile (from liver) Thereby aiding the emulsification of lipids

6.1.U3 Enzymes digest most macromolecules in food into monomers in the small intestine.

The Digestive System Small intestine Enzymes from the pancreas, liver and gall bladder are released here:

The Digestive System Small intestine Digestion is completed here Products of digestion are absorbed into the blood stream

The Digestive System Small intestine Pancreas releases bicarbonate (NaHCO3-) Neutralizes acidic chyme Producing a pH = 8 Optimizing activities of intestinal enzymes

The Digestive System Small intestine Pancreas secretes hydrolytic enzymes Proteases Polypeptides digested into amino acids Amylases Polysaccharides digested into monosaccharides Lipases Triglycerides digested into fatty acids and glycerol Nucleases Nucleic acids (DNA and RNA) into nucleusides

The Digestive System Small intestine Bile produced in liver from gall bladder Released through pancreatic duct Emulsifying fat droplets into smaller particles Have higher SA:V ratio as smaller drops So pancreatic lipase can act more efficiently

6.1.U1 The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut.

The Digestive System Small intestine Motility by peristalsis Rhythmic contractions of circular and longitudinal smooth muscles lining small intestine Slowly force chyme down intestinal tract

The Digestive System Small intestine Absorption Lining of small intestine is folded Increasing surface area for absorption Each fold is folded again into villi Villus is the absorptive unit

6.1.S2 Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph.

The Digestive System Small intestine Composed of four main tissue layers (from outside to centre): Serosa – holds intestines together Muscle layer – moves chyme by peristalsis Submucosa – connects muscles to mucosa Mucosa – designed for absorption

Small intestine Villus Increase SA for absorption of the products of digestion Microvilli border of the epithelial cell Increases SA for absorption

Small intestine Lacteal Connect to the lymphatic system for lipid transport Blood vessels to transport absorbed products Muscle for peristalsis

The Digestive System Large intestine

The Digestive System Large intestine Reabsorption of water, Na+, K+ from intestinal lumen to capillaries Also absorption of vitamin K produced by mutualistic bacteria Motility by peristalsis Rhythmic contractions of circular and longitudinal smooth muscles lining large intestine Force fecal matter down intestinal tract

Large intestine Lumen of the colon Goblet cells producing mucus Muscular walls to maintain peristalsis

The Digestive System Rectum End of the large intestine Stores feces until expulsion Anus End of the digestive system Allows expulsion of feces

The Digestive System

6.1.U4 Villi increase the surface area of epithelium over which absorption is carried out.

Villus structure Special adaptations of villi to maximize nutrient absorption

Villus structure Special adaptations of villi to maximize nutrient absorption Folding to increase surface area Proteins for transport through membranes Capillaries for good blood supply Lacteals for lipid transport

Villus structure Surface area Folding of intestine Increases surface area by 3x Villi Additional folding of intestine walls creates finger-like projections called villi Increasing surface area by an additional 10X

Villus structure Surface area Microvilli Folding of the cell membrane of the villi cells Creates a border of microvilli Expands surface area by another 20x Thus, total surface area increase: 3 x 10 x 20 = 600x

Folds increase surface area by 3x Villi increase surface area by10x Microvilli increase surface area by 20x

6.1.U5 Villi absorb monomers formed by digestion as well as mineral ions and vitamins.

Villus structure Transport through cell membranes Muscular walls of small intestine Maintain the movement of chyme by peristalsis Keeps high concentration of nutrients near villi

6.1.U6 Different methods of membrane transport are required to absorb different nutrients.

Villus structure Transport through cell membranes Membrane proteins to allow diffusion, facilitated diffusion and active transport Diffusion of fatty acids, fat-soluble vitamins, some mineral ions Facilitated diffusion of some monosaccharides, some vitamins and mineral ions Active transport of amino acids, glucose, some mineral ions

Villus structure Transport through cell membranes

Villus structure Blood capillaries

Villus structure Blood capillaries Oxygenated blood enters villus Supplying oxygen for cellular respiration and cell growth and repair Need to make ATP for active transport Deoxygenated blood leaves villus Rich in absorbed nutrients Amino acids, monosaccharides, mineral ions, vitamins

Villus structure Lacteals Branches of the lymphatic system Receive the lipoproteins before transporting them to the circulatory system Fatty acids and glycerol are reformed into triglycerides in epithelial cell smooth ER/Golgi A. Triglycerides are coated with proteins and then leave epithelial cells and enter lacteals

Villus structure

Villus structure Special adaptations of villi to maximize nutrient absorption MR SLIM

Villus structure Special adaptations of villi to maximize nutrient absorption Microvilli Folds of epithelial membrane increases SA Rich blood supply Capillary network transports absorbed products

Villus structure Special adaptations of villi to maximize nutrient absorption Single layer epithelium Minimizes diffusion distance between lumen and blood Lacteals Absorbs lipids from the intestine into the lymphatic system

Villus structure Special adaptations of villi to maximize nutrient absorption Intestinal glands Pits release digestive enzymes Membrane proteins Facilitates transport of digested materials into epithelial cells

6.1.A1 Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver.

Starch digestion and transport Starch is a polysaccharide Made of glucose Accounts for ~ 60% of the carbohydrates consumed by humans

Starch digestion and transport Digestion of starch Begins in the mouth Salivary amylase Continues in the small intestine Pancreatic amylase in the intestines Does not occur in the stomach pH is too acidic for amylases

Starch digestion and transport Two types of starch Amylose and amylopectin Amylase breaks amylose into maltose Maltase converts maltose into glucose In the small intestine Glucose also formed from other carbs

Starch digestion and transport Glucose Can be broken down to produce ATP Cell respiration Can be stored in animals As the polysaccharide glycogen

Starch digestion and transport Pancreas: Produces amylase used in intestines Produces hormones released into the blood to control glucose storage and use Insulin and glucagon

Starch digestion and transport Pancreas: Insulin lowers blood glucose levels Increases glycogen synthesis and storage in the liver and fat tissues Glucagon increases blood glucose levels Limits the synthesis and storage of glycogen by the liver and fat tissues

6.1.A2 Use of dialysis tubing to model absorption of digested food in the intestine.

Modelling digestion Digestion has two main roles: Breaking down large macromolecules into smaller ones Absorbing the small macromolecules

Modelling digestion Dialysis tubing is a plastic material Micropores that make it semi-permeable Pores are from nm

Modelling digestion Dialysis tubing is a plastic material Large molecules cannot pass through Starch, polypeptides, etc. Small molecules can pass through Glucose, salts, etc. Not selectively permeable based on charge Ions can pass through

Modelling digestion Experiment set 1: Absorption If a bag made of dialysis tubing is filled with a starch solution, it will inflate because of osmosis Water will move into the bag

Modelling digestion Experiment set 1: Absorption If a bag made of dialysis tubing is filled with a glucose solution, glucose will diffuse out of the bag Be detectable in the surrounding water

Modelling digestion Experiment set 2: Digestion If a bag made of dialysis tubing is filled with a starch and amylase solution Amylase will digest the starch into maltose Maltose is small enough to diffuse out of the bag Maltose will be detectable in the surrounding water

Mr. Briner ASM

MAJOR SOURCES Brent Cornell (Melbourne, AU)
Thank you to my favorite sources of information when making these lectures! Chris Paine (Shanghai, CH) www. bioknowledgy.weebly.com John Burrell (Bangkok, TH) Dave Ferguson (Kobe, JA) Brent Cornell (Melbourne, AU) Andrew Allott – Biology for the IB Diploma C. J.Clegg – Biology for the IB Diploma Weem, Talbot, Mayrhofer – Biology for the International Baccalaureate Howard Hugh’s Medical Institute – Mr. Hoye’s TOK Website – And all the contributors at

Mr. Briner Unit 6.1 Digestion and Nutrition

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