chapter d6 digestion

8/13/2019 Chapter D6 Digestion

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Chapter D6 Digestion

Checklist

Types of Nutrients

How Enzymes aid digestion

Why do we need to eat?

We need food to:o provide us with energyfor growth, movement & maintaining a healthy body;o grownew cells and tissues; and repairworn out tissues.o Keep us healthy

Main types of Nutrients

There are three main types of nutrients: carbohydrates, proteinsand fats..

Carbohydrates The main

carbohydrates in food

are starchand

sugars(Sucrose,

Glucose)

Starch: Potatoes,

noodles, bread & rice.

Sugars: Ripe fruits &

sweets

For Energy

Protein Animal Produce & PlantProduce

Animal Produce: Fishmeat, egg white, cheese.

Plant Produce: Soya

beans & Nuts.

For the growth& repair for

damaged

tissues.

Fats & Oils Animal & Plant Fats Animal fats: Butter & Oily

fishes.

Plant fats: Cooking Oils

For energy

Why must food be digested ?

We can only use the nutrients in the food we eat when they pass through the gut wallsinto the blood vessels.

Here, the nutrients can be carried through the bloodstream to all parts of the body. The gut walls and blood vessels are made up of cells. The cell membrane has small openings (or pores) that allow small molecules to enter,

but not large molecules.

Nutrients like glucose and amino acids are small molecules. They can pass through the cell

membranes easily and enter the bloodstream


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But most major nutrients in food are large molecules which cannot pass through the cellmembranes.

They must be broken down into molecules that are small enough to pass through thecell membranes.

This process is called digestion. Digestionis the breaking down of large, complex food molecules into small, simpler

molecules.

Our body is able to carry out digestion by producing complex proteins called enzymes. The enzymes involved in digestion are called digestive enzymes.

Digestion of Nutrients (Drawing)

Carbohydrates

1. Carbon, hydrogen & oxygen2. Provides Energy3. Monosaccharide -------------) Disaccharides -----------------) PolysaccharidesProtein

1. Carbon, hydrogen, oxygen, sulfur, nitrogen(unique to protein), phosphorus at timesThe digestive System

2. For repair & growth3. Last resort as energy source as conversion ratio is low4. Amino acids------------------) Peptones/ Peptides---------------------) PolypeptidesFats

1. Carbon, hydrogen & oxygen2. Saturated, Unsaturated fats3. Insulation. High in energy content but no used as first choice as it is difficult to break down.

EnzymesNutrients like glucose and amino acids,

are small, soluble molecules. They can

pass through the cell membrane.

Nutrients like starch, proteins and fats,

are large, complex molecules. They

cannot pass through the cell membrane.


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Drawings of Enzymes Reaction

Effect on temperature on enzyme activity

1. Inactive in low temperatures2. Denatured at high temperatures3. Optimum Temperature is where enzyme activity is highest, best

Effect on pH enzyme activity

1. Enzymes work well within a narrow range of pH2. Beyond this narrow range, the enzyme is denatured and loses its function3. Optimum pH is where enzyme activity is at its best.


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Digestive System in General

-Broken down into 2 Major parts

The Alimentary canal: A long tube that starts from the mouth & ends at the anus.-It is 9 meters long

-Food enters via mouth, waste substances come out via the anus.

Organs joined to the alimentary canal: They provide enzymes & liquids which ar needed fordigestion.

The Mouth

Food is chewed in the mouthwith the teeth. Chewing helps to cut and grind the food the smaller pieces. This increases the surface area and allows the food to be digested faster. As food is chewed, salivary glandsin the mouth secrete saliva. Saliva serves two purposes:

Wets the food, so that it is easier to swallow. Digests starch into sugars with the help of an enzyme called salivary amylase.

While chewing food, the tongue rolls the food into small balls when are pushed to theback of the mouth and squeezed into the oesophagus. This is known as swallowing.


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The oseophagus

The oesophagusis a long muscular tube leading to the stomach. By contracting and relaxing, the muscles help to push the food down to the stomach. This is how food moves along the rest of the gut too. No digestion occurs in the oesophagus. However, the digestion of starch by amylase may continue as the food moves to the

stomach.

The Stomach

The stomach is a muscular bag that lies in the upper part of the abdomen. Its muscles contract and relax, causing food to break up into even smaller pieces. This movement also mixes the food well with gastric juicefor better digestion. Gastric juice is secreted by glands in the stomach walls, into the stomach cavity. It

contains:

o proteaseswhich digest proteins; ando hydrochloric acid, which helps proteases to work ph level of 1-2

Hydrochloric acid kills any bacteria in the food. Food stays in the stomach for a few hours before passing into the small intestine, bit by

bit.The Small Intestine

The small intestineis a long muscular tube, which is about 6 m long. The liver and the pancreas are connected to the small intestine. Food is mixed with 3 fluids in the small intestine to aid digestion:

o Intestinal juicefrom the walls of the intestine. It contains the enzymes maltase,proteases and lipases.

o Pancreatic juicefrom the pancreas.o Bilefrom the liver.

Pancreas

The pancreasproduces pancreatic juice. The juice contains the enzymes maltase, protease and lipase. The digestion of food in the small intestine are as follows:

o Digestion of fats: Fat 3Fatty acids, 1Glycerol


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The digestion of food in the small intestine are as follows:o Digestion of starch:

Starch Maltose Maltose Glucose

o Digestion of small protein molecules Protein molecules amino acids

The Liver

The liver produces a yellowish-green fluid called bile. Bile is stored in the gall bladder. The gall bladder has a duct (a small tube) that carries bile into the small intestine. Bile does not contain digestive enzymes, but helps to break up fast into smaller oil

droplets in a process known as emulsification.

This increases the surface area of the oil and allows the fats to be digested quickly by thelipases in the pancreatic and intestinal juices.

Absorption in the Small Intestine

The small intestine allows only small molecules like sugar and amino acids to passthrough its wall and into the bloodstream.

Large molecules like starch and proteins cannot pass through the walls of the smallintestine.

Digestion ends in the small intestine. The final products of digestion are glucose, amino acids, fatty acids and glycerol. After digestion, the smaller digested food molecules can pass through the wall of the

small intestine and into the bloodstream.

Undigested matter is mostly made up of fibre. Together with water and mineral salts, the undigested food passes into the large

intestine.

Fibre can be found in vegetables. It is important for the gut muscles to move the foodalong the gut.


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The Large Intestine

The large intestine is about 1.5 m long. Its function is to absorb water and mineral salts. This takes place in the colon. What is left now is a nearly solid waste called faeces. This is temporarily stored in the rectum, before being expelled through the anus is a

process called egestion.

Digested food entering the blood

1. Digested food is made up of small, soluble molecules.2. Theses molecules diffuse through the walls of the small intestine into numerous blood

vessels.

3. They are then carried away by the blood to the rest of the body.4. This is known as : Absorption of food.

Features of walls of the small intestine.-Making ABSORPTION easier

1. Large Surfaces area for absorption to digested food moleculesAided by: Presence of many villi (finger like projections), Length of small intestine(7m)

2. Thin wall: Only one cell thick: Shortens the distance between wall & blood vessels.

chapter d6 digestion

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