6.1 Digestion and Absorption

Skill: Create an annotated digestive system diagram. Alimentary Canal = food tube, from mouth to anus Function of digestive system = to break down large carbon molecules into smaller ones that can be absorbed into bloodstream Digest = “break down” Practice drawing: https://www.youtube.com/watch?v=kv- x0KLbCPE&list=PLb1wF0xa6WI9nnb-yE_rjY2h4DX8ZI7R0&index=2

Digestive System

Digestive system structures & functions

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

Predict what cross-section of intestinal wall would look like!

Description of tissue layers in small intestine Serosa (serous membrane) = outer lubricating coat Muscle layers = longitudinal muscle and circular muscle Sub-mucosa = contains blood & lymph vessels Mucosa = line of small intestine, with epithelium that absorbs nutrients on inner surface

Identify tissue layers in transverse section of small intestine micrograph

Answers to previous slide: A = mucosa (contains villi) B = goblet cell (secrete mucous to line lumen) C = submucosa D = muscle layer (inner circular & outer longitudinal)

Identify tissue layers in transverse section of small intestine micrograph

Stomach is similar…

Understanding: The contraction of circular & longitudinal muscle layers of small intestine mixes food with enzymes and moves it along the gut. Circular & longitudinal muscles are SMOOTH muscles. Outer longitudinal muscles contract in front of bolus, and intestines shorten. Inner circular muscles contract behind bolus, intestines narrow, pushing the food along.

Peristalsis = wave-like muscle contractions in esophagus, stomach, small & large intestines that move the food along, while mixing food with enzymes https://www.youtube.com/watch?v=o18UycWRsaA and https://www.youtube.com/watch?v=ZZCgF24HI_o Wwwwwwwwwww * Wave-like muscle contractions * Occurs in esophagus, stomach, sm & L intestines * Speeds digestion * Only occurs in ONE DIRECTION * Speaking of which, what muscles are used when vomiting? Abdominal muscles * Through which organ does peristalsis move food the slowest? Small intestine (Allows time for digestion & absorption)

Understanding: The pancreas secretes enzymes into lumen of small intestine. Pancreatic amylase – digests starch Pancreatic lipase – digests triglycerides & phospholipids Pancreatic proteases (trypsin, chemotrypsin, aminopeptidase, carboxypeptidase) – digests polypeptides What organelle in pancreatic gland cells synthesize these enzymes? Ribosomes on the rough ER What organelle processes these proteins before they are secreted? Golgi apparatus By what process are the enzymes secreted by the pancreatic gland cells Exocytosis

Understanding: Enzymes digest most macromolecules in food into monomers in small intestine Digestive enzyme Chart Activity! What is the substrate and product of each of these enzymes?  Pancreatic amylase Pancreatic lipase Phospholipase Pancreatic protease Nuclease Maltase Lactase Sucrase Carboxypeptidase Aminopeptidase Dipeptidase Cellulase

What is Cellulose? We don’t have an enzyme to digest it, so it passes to the large intestine. AKA “fiber” or “roughage”.

Whiteboard Activity: State the source, substrate, product, and optimum pH for one named amylase, protease, & lipase. (a chart would be ideal!)

U: Villi increase surface area of epithelium over which absorption is carried out Absorption = process of taking substances into cells & the blood Site of absorption = small intestine Rate of absorption depends on surface area of epithelium Adult Sm intestine = 7m (23ft) long; 25- 30mm (1in) wide Villi (villus, singular) = small finger-like projections of mucosa Villus = 0.5 – 1.5mm long (40 villi/mm2) Function of folds & villi = increase surface area for absorption by 10X

U: Villi absorb monomers formed by digestion as well as mineral ions & vitamins Single epithelium layer is semipermeable Allows in products of digestion (monomers): monosaccharides, amino acids, fatty acids, monoglycerides, glycerol, nitrogen bases Also allows in substances not needing digestion: Mineral ions (e.g. Ca+2, K+, Na+) Vitamins (e.g. A, B, C, D, E) If harmful substances get through, detoxified by liver Unwanted, harmless substances get through (e.g. food coloring & flavoring), pass in urine Small amt of bacteria get through, removed by phagocytes in liver

U: Different methods of membrane transport are required to absorb different nutrients Different methods of moving nutrients into & out of villi: Simple diffusion Facilitated diffusion Active transport Exocytosis

Exocytosis (requires effort & energy by cell, therefore ACTIVE transport)

Absorption TRIGLYCERIDES GLUCOSE Triglycerides digested into fatty acids & monoglycerides Fatty acids & monoglycerides absorbed into epithelial by simple diffusion (fatty acids also absorbed by facilitated diff) Inside epithelium cells, fatty acids combine with monoglycerides to make triglycerides again Triglycerides combine w/ cholesterol to form droplets, coated in phospholipids & protein (“lipoproteins”) Lipoproteins released by exocytosis through membrane on inner side of epithelial cells Lipoproteins enter lacteal and carried away in lymph or enter blood capillaries in villi Starch digested into glucose Glucose can’t pass by simple diffusion because it’s polar/hydrophilic Active transport: Na+/K+ pumps pump Na+ from cytoplasm to interstitial spaces inside villus, and K+ in opposite direction  creates low conc of Na+ inside epithelial cells Facilitated diffusion: Na+/glucose co-transporter proteins in microvilli transfer a Na+ and glucose molecule together from lumen to cytoplasm of epithelial cells Glucose channels allow glucose to move by facilitated diffusion from cytoplasm to interstitial spaces inside villus and into blood capillaries in villus

Absorption of triglyerides Absorption of glucose

App: Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver Starch = many α-glucose monomers linked by condensation rxns in plants (Bread, potatoes, pasta, rice, cereal, oatmeal) Must be digested because too large to be absorbed Starch digestion = exothermic (releases heat) & enzymes speed it up Digestion of 1,4 bonds: Amylase breaks 1,4 bonds (if at least 4 glucose), leaving mixture of maltose (2 glucose) & maltotriose (3 glucose) Digestion of 1,6 bonds: fragments with 1,6 bonds = “dextrins”. What enzyme breaks down these sugars ? Maltose? Maltase Dextrins? Dextrinase Maltotriose? Glucosidase (HA, tricked you!)

NOS: Use models as representations of the real world: Dialysis tubing can be used to model absorption in the intestine Experiments on living systems are complex and involve many variables. If you did your IA using a living thing, you understand this! Sometimes it’s better to experiment on PARTS of a system (cells rather than whole organisms) … or use a MODEL to represent part of a living system Example: Dynamic Gastric Model = computer-controlled model of human stomach that carries out mechanical and chemical digestion of real food! Can test effects of diet, drugs, alcohol, etc on digestion Example: dialysis tubing made from cellulose (semipermeable due to size of pores) – mimic small intestine to model absorption by passive diffusion and osmosis Can test effects of different factors on diffusion of molecules into or out of tubing Disadvantage: cannot model active transport or exocytosis

App: Use of dialysis tubing to model absorption of digested food in intestine. Whiteboard Activity: (10 minutes) Investigation 1: Predict what will happen Experiment: (30 minutes) Investigation 2: Set up and carry out experiment. Turn in: Research Question Hypothesis Qualitative & Quantitative data Conclusion

TOK Application Which is the normal human condition… Lactose-tolerant or lactose intolerant? 3 arguments: Humans are only mammals who continue to drink milk into adulthood High proportion of humans are lactose-intolerant Ancestors were probably lactose-intolerant & tolerance evolved