Chapter 6 Nutrition (b)

Form 4 Biology Chapter 6: Nutrition (b)

1

The Human Digestive System


2

Mouth

Perform mechanical digestion by using teeth. Cut the food into smaller

pieces so that the surface area is larger for digestion. Starch is mainly

digested by salivary amylase into maltose.

Glands: Salivary glands

Secretion: Saliva

Amylase

Starch + water Maltose


3

Stomach

Main organ that digest protein. It consists of a mucus inner layer which

protect itself from the action of hydrochloric acid and enzyme. Because

of the mucus layer, absorption of nutrients is limited. The function of

hydrochloric acid is (a) stop the catalysing action of salivary amylase

on carbohydrate (b) prepare an acidic medium for pepsin to

function (c) kill all microorganisms

Glands: Stomach

Secretion: Gastric juice

Pepsin

Protein + water polypeptide

Rennin

Caseinogen Casein


4

Duodenum

It is the first section of small intestine and also the shortest part.

Glands: Pancreas

Secretion: Pancreatic juice

Pancreatic amylase

Starch + water Maltose

Trypsin

Polypeptide + water peptide

Lipase

Fat + water Fatty acids + glycerol


5

Function of gallbladder

Gallbladder stores bile salt produced by liver. Bile salt emulsifies oil by

breaking down large oil droplets into smaller one. This is to increase the

total surface area which is easy for lipid digestion by lipase. The bile is

alkali so it can neutralise the acid from the stomach.


6

Ileum

Ileum is the last section of small intestine that is about 2 to 4m long. The

pH is usually between 7 and 8.

Glands: Small intestine

Secretion: Intestinal juice

Maltase

Maltose + water glucose

Sucrase

Sucrose + water glucose + fructose

Lactase

Lactose + water glucose + galactose

Erepsin

Peptide + water amino acids


7

Digestion in Ruminants and Rodents


8


9

Comparison Between The Digestive Process in Humans, Ruminants

and Rodents


10


11

Problems of Food Digestion

Incomplete Digestion of Food

1. Incomplete digestion of food causes indigestion.

2. Cause of indigestion:

a) Swallowing food without sufficient chewing

b) Eating too much

c) Intake of too much of fatty and spicy food

d) Excessive consumption of alcohol

e) Underscretion of certain digestive enzymes

f) Insufficient bile salts

g) Swallowing too much air while eating

3. Effect

a) The absorption of nutrients decreases

b) Uncomfortable in the abdomen such as nausea, bloating and

frequent burping

c) The release of internal toxins which increase the load to the kidneys,

liver and immune system.


12

Gallstones Preventing the Flow of Bile

1. Bile contains water, cholesterol, fats, bile salts, proteins and bilirubin.

2. If the liquid bile contains too much cholesterol. Bile salts or

bilirubin, it can harden into gallstone.

3. When gallstones get stuck in any of the ducts that carry bile from the

liver to the small intestine, they block the flow of bile.

4. It may also block pancreatic duct causing gallstone pancreatitis.


13

ABSORPTION AND ASSIMILATION

Adaptations of the Digestive System for Absorption

1. Absorption of digested food:

(a) takes place in the small intestine

(b) starts in the duodenum and is completed in the ileum

2. The adaptations of the small intestine to absorb digested food are:

(a) A large surface area with

i. Small intestine is long

ii. wall of the small intestine is folded inwards

iii. the inner surface of the small intestine is covered with finger-

like projections called villi.

iv. the epithelial cells of each villus are covered with microvilli.

(b) the microvilli is one-cell thick

(c) a comprehensive network of blood capillaries (capillary

network) within each villus to transport away absorbed nutrient

molecules all over the body.

(d) the lacteal within each villus transports away fatty acids,

glycerol and oil-soluble vitamins.


14

The Structure of Villus

1. A villus is covered with epithelium. In the middle of a villus is a milky

white structure called lacteal. The lacteal is continuous with lymphatic

vessels.

2. Surrounding each lacteal is a network of blood capillaries. The blood

capillaries of all villi drain into a vein called the hepatic portal vein.

3. Water & water-soluble substances such as simple sugars (glucose,

fructose and galactose), amino acids, mineral ions vitamin B and C

are absorbed into the blood capillaries. The hepatic vein then carries

these food substances to the liver.

4. Fatty acids and glycerol diffuse into the epithelial cells of villi where

they combine to form fat droplets. The fat droplets are then deposited

into the lacteal, giving it a milky appearance.

5. Other lipids such as cholesterol and lipid-soluble vitamins such as

vitamin A, D, E and K are also deposited into the lacteal.


15


16

Absorption in the Colon

1. The colon:

(a) has no digestive activity

(b) has no villi but the epithelium lining of its mucosa is for

absorption

2. The colon absorbs

(a) water

(b) vitamins, including biotin, folic acid, vitamin K, and several B

vitamins produced by bacteria.

(c) electrolytes/minerals like sodium and chloride

3. Nutrients absorbed are transported to the liver via the hepatic portal

vein.


17

Functions of the Liver

1. Functions of liver:

(a) Remove and stores iron and vitamins A, D, E, and K

(b) Makes plasma protein (albumin, globulin, fibrinogen, prothrombin

and haemoglobin)

(c) Detoxifies poisonous substances (e.g. alcohol, drugs, traces of

insecticides, herbicides and other toxic chemicals)

(d) Maintain a constant blood glucose

(e) Converts amino acids to glucose (when body runs out of glucose)

(f) Maintain a constant blood amino acid level (excess amino acid is

converted into urea, while remainder of amino acid is changed into

carbohydrate)

(g) Regulation of lipids (excess lipids are removed from the body,

changed into carbohydrates or sent to fat storage sites)

(h) Removes haemoglobin molecules that are old or die (haemoglobin

is converted into bile pigments while the iron is saved up)

(i) Produce bile

(j) Produce heat

(k) Produce cholesterol


18

Assimilation of Food

The Process of Assimilation in the Liver

Amino Acids

Amino acids have to pass through the liver before they reach the blood

circulatory system.

The liver synthesizes plasma proteins from amino acids.

Plasma proteins have various functions, for example, blood clotting and

osmoregulation.

When a short supply of glucose and glycogen occurs, the liver converts

amino acids into glucose.

Excess amino acids connot be stored in the body and are broken down in

the liver through a process called deamination.

During deamination, urea, the common nitrogenous waste product of

humans, is produced and transported to the kidneys to be excreted.


19

Glucose

Glucose in the liver is used for respiration. According to the needs of the

body, excess glucose is converted into glycogen and stored in the liver.

When the blood sugar level falls and the body, the stored glycogen is

converted back into glucose.

Once the glycogen store in the liver is full, excess glucose is converted

into lipids by the liver.

Lipids

Lipids which enter the heart through the subclavian veins are transported

in the bloodstream to body cells.


20

The Process of Assimilation in the Cells

Amino acids

Amino acids which enter the cells are used for the synthesis of new

protoplasm and the repair of damaged tissues.

They are also important building blocks in the synthesis of enzymes and

hormones.

Amino acids are also used in the synthesis of proteins of plasma

membrane.

Glucose

When the glucose molecules reach the body cells, they are oxidized to

release energy during cellular respiration.

Energy is required for the various chemical processes which take place

in the cell, for example, in muscle contraction and synthesis of proteins.

Excess glucose is also stored as glycogen is a long-chained

carbohydrate molecule that is insoluble in water.

Lipids

Lipids such as phospholipids and cholesterol are major components of

plasma membranes

Fats that are stored around organs act as cushions that protect organs

from injuries.


21

Excess fats are stored in the adipose tissue underneath the skin as

reserve energy.

When the body lacks glucose, fats are oxidized to release energy.

FORMATION OF FAECES AND DEFECATION

Colon

1. The intestinal contents consist of a mixture of water, undigested food

substances, dead cells and dead bacteria and indigestible fibre.

2. Movement of undigested materials is helped by peristalsis.

3. The colon reabsorbs almost 90% of water and minerals into the

bloodstream.

4. The remaining will form the faeces.

Rectum

1. The faeces pass to the rectum for temporary storage.

2. As the faeces accumulate, pressure in the rectum increases, causing a

desire to expel the faeces from the body.

Defecation

1. The elimination of faeces is known as defecation.


22

2. The muscles around the anus, the opening of the rectum will contract

and eject the faeces via the anus.

Defecation Related Problems

Constipation

Condition where faeces becomes hard, dry, and difficult to pass and

bowel movements do not happen very often.


23

Colon cancer

A type of cancer that develops in the tissues of the colon. It is cause by

carcinogens and eating a high fat, low fibre diet.


24

Haemorrhoids

Condition where the veins around the anus or lower rectum is swollen

and inflamed. It can be caused by prolonged constipation or diarrhoea.

5. The importance of high fibre diets:

(a) prevents constipation, colon cancers and haemorrhoids

(b) stimulates peristalsis

(c) helps in weight control through the “stomach-full” feeling

(d) reduces heart disease

(e) absorbs and eliminates toxic substances

(f) regulates glucose absorption for diabetics

(g) prevents cancers of the colon and of the rectum


25

The Role of Microorganisms in the Colon

The colon plays host to two groups of bacteria:

(a) Beneficial or “good” bacteria

(b) Pathogenic or “bad” bacteria

Beneficial Bacteria

1. Examples of beneficial bacteria are Bacteroides, Lactobacillus

acidophilus and Escherichia coli.

2. Functions are:

(a) digesting fragments of carbohydrate, protein and lipid that were

not digested in the small intestine

(b) fermenting cellulose fibres that were indigestible in the stomach and

in the small intestine

(c) producing amino acids and vitamins K and B-complex.

(d) producing antibiotic that controls the growth of pathogenic bacteria


26

The Effect of Antibiotics on Microorganisms in the Colon

1. Antibiotics are a group of drugs commonly taken to treat bacterial

infections.

2. Antibiotics kill bad bacteria, but good bacteria as well.

3. If beneficial bacteria is completely killed, pathogenic bacteria will

repopulate the colon rapidly, bringing about an infection.

Health Problems Related To Eating Habits

A) Gastritis

1. Gastritis is the inflammation of the lining of the stomach wall.

2. There are various causes of gastritis:

a) Irregular meals – when a person skips a certain meal the stomach

will be empty. The aciic gastric juice produce by the stomach will

act on the lining of the stomach instead, gradually corroding it.

Sometimes gastric ulcers are also formed.

b) Excessive smoking

c) Alcoholism

d) Stress

e) Insufficient chewing – if food is not chewed properly, the stomach

wall will be burdened to churn food more thoroughly to break up

the food.

f) Prolonged intake of drugs such as painkillers.


27

g) Helicobacter pylori bacteria which break down the mucus on the

surface of stomach lining, exposing the lining to the direct action

of gastric juices.

3. Gastritis can be treated by antacids. Antacids contain alkalis which

can neutralise the hydrochloric acid in gastric juice.


28

B) Obesity

1. When a person eats more than the body needs, excess food will be stored

in the body as fats. This can lead to obesity.

2. A person is said to be obese if his/her body weight exceeds the right

weight for his/her height by 20% or more.

3. BMI (Body Mass Index) can be calculated using the following formula:

A BMI of 18.5 – 24.9 is considered ideal. A person is said to be obese if

his BMI is 30 or more.

4. Obesity predisposes a person to various health problems such as high

blood pressure, heart diseases and disbetes mellitus. However, obesity

can be overcome by watching one’s diet and exercising regularly to help

burn off fat.


29

C) Anorexia nervosa

1. Anorexia nervosa is characterised by the loss of the desire to eat, due

to an obsession of maintaining a slim body. It is more common among

young single females.

2. An anorexic intentionally starves herself and will therefore become

emaciated over time. She has a low basal metabolic rate and her

mentruation may stop

3. If untreated, an anorexic patient may ultimately die of severe

undernourishment and malfunctioning of organ systems.

4. Treament consists of psychological therapy and regulation of diets.


30

Karen Anne Carpenter was an American singer and drummer who died of

anorexia nervosa in 1983. She was believed to be the first known celebrity died of

anorexia.

D) Bulimia

1. Like anorexia nerosa, bulilia typically affects young females.

2. It is characterised by uncontrollable overeating followed by forced

purgin or vomiting.

3. Out of fear of being overweight, a bulimic patient who has been binging

may induce voiting by digging into her throat or by taking purgatives.

Bulimia can cause undernourishment. It can aso lead to kidney and liver

problem and hormonal imbalance.

4. Stress and depression are among the underlying factors. Thus, the

treatment of bulimia includes medical treatment coupled with

counselling.

Date post:	20-Feb-2016
Category:	Documents
Upload:	jenny-wong
View:	236 times
Download:	3 times

Chapter 6 Nutrition (b)

Documents