Digestion

and absorption

Objectives

Understandings:

• The contraction of circular and longitudinal muscle 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 and skills:

• Application: Processes occurring in the small intestine that result in the

digestion of starch and transport of the products of digestion to the liver.

• Application: Use of dialysis tubing to model absorption of digested food in the

intestine.

• Skill: Production of an annotated diagram of the digestive system.

• Skill: Identification of tissue layers in transverse sections of the small intestine

viewed with a microscope or in a micrograph.

Metabolism chemical reactions breaking down food and releasing energy from nutrients Digestion mechanical & chemical breakdown of food into nutrients

Digestion

Prepares food for cellular intake because most food molecules are large polymers and insoluble

Digestion

They must first be digested to smaller soluble molecules before they can be absorbed into the blood

6

The Digestive Process

• Ingestion – Taking in food through

the mouth • Propulsion (movement of

food) – Swallowing – Peristalsis – propulsion

by alternate contraction &relaxation

• Mechanical digestion – Chewing – Churning in stomach – Mixing by segmentation

• Chemical digestion – By secreted enzymes:

see later • Absorption

– Transport of digested end products into blood and lymph in wall of canal

• Defecation – Elimination of

indigestible substances from body as feces

• Mechanical processing and movement: chewing, mixing

• Secretion: fluid, digestive enzymes and hormones, bile, acid, alkali, mucus

• Digestion: breaking down food to smallest absorbable units

• Absorption: through mucosa, into blood or lymph vessels

• Elimination: undigested material eliminated

Peristalsis

push food along by rhythmic waves of smooth muscle contraction in walls of digestive system

Sphincters muscular ring-like valves, regulate the passage of material between sections of digestive system

Movement & Control

Chemistry of Digestion

Enzymes are biological catalysts that increase the rate of reaction

Hydrolysis of insoluble food molecules to soluble end products

Amylases

Proteases

Nucleases

Lipases

pH 8

glycerol and fatty

acids

lipids (triglycerid

es) pancreatic

juice pancreatic

lipase Lipase

pH 2

shorter polypeptid

e chains protein gastric juice pepsin Protease

pH 7 maltose starch saliva salivary amylase Amylase

optimum pH product substrate source

example of enzyme

type of enzyme

The Digestive Enzymes

The Digestive Enzymes

The Digestive Enzymes

Digestive System

mouth - the first part of the digestive system, where food enters the body. Chewing and salivary enzymes in the mouth are the beginning of the digestive process (breaking down the food).

esophagus - the long tube between the mouth and the stomach. It uses rhythmic muscle movements (called peristalsis) to force food from the throat into the stomach.

stomach - a sack-like, muscular organ that is attached to the esophagus; food is mixed with acids & enzymes chemical digestion. Food remains for few hours; peristalsis mixes food until almost fluid – called chyme; pyloric sphincter opens allowing small amounts of acid chyme into duodenum; repeated until stomach empty

Main function: storage; chemical digestion of proteins

Digestive System

small intestine - the long, thin tube that food goes through after it leaves the stomach. Main function: chemical digestion of carbs, lipids, proteins & absorption.

large intestine - the long, wide tube that food goes through after it goes through the small intestine

anus - the opening at the end of the digestive system from which feces exit the body.

Digestive System

pancreas - enzyme-producing gland located below the

stomach and above the intestines. Enzymes help in the digestion of carbohydrates, fats and proteins in the small intestine.

liver - a large organ located above and in front of the stomach. It filters toxins from the blood, and secretes bile (which breaks down fats) and some blood proteins.

gall bladder - a small, sac-like organ located by the duodenum. It stores and releases bile (digestive chemical produced in liver) into the small intestine

Digestive System

Accessory Organs

Absorption The soluble products are first taken up by various mechanisms into the epithelial cells that line the gut. These epithelial cells then load the absorbed molecules into the blood stream. Assimilation The soluble products of digestion are then transported to the various tissues by the circulatory system. The cells of the tissues then absorb the molecules for use within this tissues the broken down molecules actually become part of the body

Absorption & Assimilation

• Blood supply in the villus which absorb the end products of digestion from the epithelial cells

• The lacteals (green) that receive the lipoproteins before transporting them to the circulatory system.

• Muscular walls that maintain the movement of chyme by peristalsis.

Structure of the Small Intestine

Structure of the Small Intestine

Structure of the Small Intestine

The structure of the villus (villi) increases the

surface are for the absorption of digested food molecules.

folds increase SA:VOL ratio by X 3 Villi project into the lumen of the gut

increasing the surface area by X 10 Microvilli are outward folds of the plasma

membrane increasing the surface area another X10

Structure of the villus

A. Mouth – 1. teeth begin mechanical digestion (chewing, grinding) 2. saliva (digestive enzyme) begins chemical digestion, breakdown of carbohydrates into smaller sugar molecules (amylase) and breakdown of bacteria cell walls (lysozyme) B. Esophagus – food tube 1. peristalsis – contractions of smooth muscle toward the stomach

The Process of Digestion

C. Stomach 1. chemical digestion– pepsin breaks down proteins and needs hydrochloric acid to work which stops amylase. Mucus needed to protect stomach 2. mechanical digestion – churned stomach contents become chyme. D. Small Intestine 1. most chemical digestion and absorption of food 2. digestive fluids from pancreas, liver and lining of duodenum a. pancreas – regulates blood sugar 1. breaks down carbohydrates, proteins, lipids, and nucleic acids 2. produces sodium bicarbonate, neutralizes acids b. liver – makes bile for breaking down fats (stored in gall bladder)

The Process of Digestion

E. Absorption in the Small Intestine

1. villi– folded surfaces, increase surface area for absorption

a. products of carbohydrates and proteins

(undigested fat and some fatty acids absorbed by

lymph)

F. Large Intestine

1. absorption of water

2. bacteria produce compounds (vitamin K)

a. massive antibiotic use can cause vitamin K

deficiency

3. undigested material leave body through rectum

The Process of Digestion