6.1 digestion

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Digestion Topic 6 Human Health and Physiology

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Page 1: 6.1 digestion

Digestion

Topic 6 Human Health and Physiology

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6.1.1 Explain why digestion of large food molecules is essential.

6.1.2 Explain the need for enzymes in digestion.(The need for increasing the rate of digestion atbody temperature should be emphasized.)

6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase.

Aim 7: Data logging with pH sensors and lipase, and data logging with colorimeters and amylase can be used.

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6.1.4 Draw and label a diagram of the digestive system.(Show the mouth, esophagus, stomach, small intestine, large intestine, anus, liver, pancreas and gall bladder. The diagram should clearly show the interconnections between these structures.)

6.1.5 Outline the function of the stomach, small intestine and large intestine.

6.1.6 Distinguish between absorption and assimilation.

6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.

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Digestion

The mammalian digestive system has 5 basic functions: ingestion –taking food into the digestive system (mouth) peristalsis – the movement of food along the alimentary

canal digestion – the breakdown of large, insoluble food

molecules into smaller, soluble molecules absorption –the uptake of digested food from the gut

into the blood stream egestion – (or defecation) the elimination of undigested

food, bacteria and dead cells from the digestive system (large intestine).

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Why Digestion?

Food is composed of large, insoluble molecules: Carbohydates. Proteins. Lipids.

Humans need to break these molecules down into smaller units that: are small enough to be absorbed by the villi in the small intestine. Are in a form that can be used by the cells of the body.

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Two Types of Digestion.

The alimentary canal is a long muscular tube running from the mouth to the anus.

Digestion starts in the mouth. The two types of digestion occurring in the mammalian

digestive system are: Physical Digestion (Mechanical Digestion)

the action of teeth chewing food, physically breaking the food into smaller pieces

Chemical Digestion Involves chemical reactions (Hydrolysis) and the help of catalysts to

break food into smaller pieces

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Enzymes in Digestion

Digestion is a slow process, so special specific catalysts called enzymes are used to speed up digestion at body temperature.

The are many different enzymes. Enzymes are:

highly specific – one enzyme catalyses one chemical reaction. always proteins sensitive to pH – work best at an certain pH Reusable – not used in the chemical reactions they catalyse Sensitive to heat - broken down (destroyed) by heat - denatured

Enzyme names are generally characterised by the ending -ase (however there are exceptions)

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Types of Digestive Enzymes

Digestive enzymes can be classified into groups depending on their action: Carbohydrases (Amylases) – work on carbohydrates Proteases – work on proteins Lipases – work on lipids

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Digestive Enzymes

Name of Enzyme

Where it is made (Source)

Where it works

What it works on

(Substrate)

What is made

(products)

Optimum ph

Amylase Salivary Amylase

Salivary Glands

Mouth Starch Maltose 7

Protease Pepsin Wall of the stomach

Stomach Protein polypeptides 1-2

Lipase Pancreatic Lipase

Pancreas Small Intestine

Lipids (fats and oils)

Fatty Acids and Glycerol

7

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The Digestive System

The digestive system can be broken into two parts: The Alimentary canal – a

continuous tube running from the mouth to the anus

Accessory structures – salivary glands, liver, gall bladder, pancreas. These are outside the alimentary canal and either produce or store secretions which aid in digestion of food.

Handout - The Digestive System Handout – Structure and Function

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The Digestive System

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Assimilation

Many people confuse the terms: digestion, absorption and assimilation

Digestion – the process of breaking down large molecules into smaller ones

Absorption – when the small molecules are taken up from the digestive system into the blood stream

Assimilation – when these molecules are incorporated into tissues of the body

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The Villus The surface of the small intestine is folded to form villi. The surface of the villus is thin, only one layer of epithelial cells. On the surface of epithelial cells are even smaller folds of the

plasma membrane called microvilli. This folding greatly increases the surface area for absorption of

food molecules. Protein channels in the microvilli membranes allow rapid absorption

of food molecules by facilitated diffusion Protein pumps in the microvilli allow absorption of food molecules

against a concentration gradient by active transport. Numerous mitochondria in epithelial cells provide ATP for active

transport A network of blood capillaries are close to the surface of the villus

so the distance for diffusion of food molecules into the bloodstream is small.

A lacteal (a branch of the lymphatic system) in the centre of the villus carries away fats after absorption.

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Structure of a Villus