TOPIC 53 Animal Nutrition

5.1 Diet

5.2 Human Alimentary Canal

5.3 Mechanical and Physical Digestion

5.4 Chemical Digestion

5.5 Absorption and Assimilation

Use the following to check what you can do,

ffick one of the columns for each criterial

o Define balanced diet

. List the different classes of food that make a balanced diet

List the chemical elements which make up carbohydrates, fats and

proteins

. State the importance of protein, carbohydrates and fats in our diet

State the importance of taking Vitamins C and D, minerals (calcium &

iron) and fibre in our diet

Give the sources for carbohydrates, proteins, fats, vitamins C and D

and mineralsalts (iron and calcium)

Explain the relation between diet and age, diet and sex and diet and

activity of an individual

. Deflne malnutrition

. Explain constipation and the problems associated with this condition

. Explain obesity and the health problems associated with this condition

Name and state the function of the parts of the system that make up thehuman alimentary canal and the associated oroans

. Define ingestion, digestion, absorption, assimilation and egestion

To identify which part of the alimentary canat is involved in the process

mentioned above

tdentiff the different types of teeth and state their functions in relation totooth structure

r State the process and causes of tooth decay

. State ways to prevent tooth decay

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Describe the proper care of teeth

. Describe chewing

. Describemechanicaldigestion

r Describe the process of peristalsis

. Definechemicaldigestion

r Distinguish chemical digestion and mechanical digestion

Describe the role of salivary and pancreatic amylase and maltase in fire

State the end-products f-or the digestion of starch

. Describe the functions of pepsin and lipase

. State the end products for digestion of proteins and fats

. State the optimum pH for these enzymes

. Describe how the digested food molecules are aGorbed in the bbol

o State the roles of liver in the digestion and assimilation of food

Explain what happens to excess glucose

Explain what happens to excess amino acids

. Explain wtrat happens to excess fats

Describe briefly how and in what form, exces@the bodv

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5,2 HUMAN ALIMENTARY GANAL

* TIre food we eat goes through five different processes in our body:

(1) lngestion: taking food into the body (eating).

(2t Digestion:the breaking down of large complex food molecules into simple, soluble molecules.

(3) Absorption: digested food from the alimentary canal diffuses into the blood stream.

(4) Assimilation: the use of absorbed food to form new cells or part of cells.

(5) Egestion: passing out undigested food as faeces.

* 1yre atimentary canal is the canal (tube) along which food passes to be processed.

,/ Assimilation does not take place in the alimentary canal'

./ The human alimentary canalis about 900cm (9 m) long.

I The canal is able to fit into our bodies because it is folded into loops.

rt

Diagram below shows the human alimentary canal and the organs associated with it (shaded)

tongue

salivary gland

windpipe

oesophagus

I

mouth re-rttlrj

diaphragm

stornach

pancreas

large

intestine

eal bladder

liverduodenum

ileum

colon

fectum

Ft-**l

small fintestine I

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Parts of the Human Alimentary Ganal and the Associated orqans

lngestion takes place in the mouth

Physical digestion starts here

(when teeth break the food into smaller pieces and the tongue rollthe food to mix it with saliva)

Chemical digestion of starch starts in the mouth (saliva contains enzyme salivary amylase tobreak down starch to maltose)

1uy Oesophaqus:

It is a tube through which food is transferred from the mouth to the stomach.

This tube is muscular; it contractsand relaxes to push the food to the stomach. The contraction

and relaxation of the muscular oesophagus is called peristalsis.

Mouth(a)

r.

(c) Stomach:

It is a muscular bag-like structure which stores ingested food for a few hours.

- proteins and fats remains in the stomach for about 2 to 3 hours

- carbohydrates remains in the stomach for only one hour

Glands in the wall of the stomach produce gastric juices containing hydrochloric acid andenzyme pepsin.

Protein is digested in the stomach.

(d) Liver:

^ Produces bile. Bile does not contain any enzymes

^ Bile breaks down bigger fat molecules to smaller fat molecules

(e) Gall bladder:

^ Gall bladder is connected to liver.

^ The bile produced by the liver is temporarily stored in the gall bladder

^ The bile is then released to the duodenum (first part of the small intestine) when it is needed.

^ Secretes pancreatic juice into the duodenum.A Pancreatic juice contains enzymes for the digestion of carbohydrates, fats and proteins

Pancreas(0

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1s; Small intestine:

A lt is about 6 metres long and consists of duodenum and ileum.

(i) Duodenum:

F First part of small intestine where acidic food from stomach is neutralized by the bile juice

(released from gall bladde$ and mix with pancreatic juice (released from pancreas)

F Bile not only neutralise the acidic food, it also helps to break down fats to smaller molecules.

Pancreatic juice contain enzymes to break down proteins, carbohydrates and fats

(ii) Ileum:

digestion of food.

the walls of ileum

th; Larqe intestine:

^ lt is about 1.5 metres long and consists of colon and rectum.

(i) Colon:

F lt absorbs water and minerals from undigested food.

(ii) Rectum:

F A short muscular tube which stores faeces before egestion.

(i) Anus:

^ An opening through which the faeces is passed out.

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5.3 MECHANICAL AND PHYSICAL DIGESTION

Digestion

We must digest our food so that lt is small enough to pass through the thin walls of the ileum into the blood.

There are two types oi digestion:

(1) Physicaldigestion(2) Chemicaldigestion.

m

m

Physical Digestion

Digestion is the breaking down of large complex foods into smaller simpler food units.

Physical digestion breaks down food into smatler pieces. lt is sometimes calledmechanical digestion. This type of digestion does not chemically change the food.

Chewing

+ Example of physical digestion is chewing in our mouth with our teeth.

3E ffre functions of teeth are to cut, tear and grind food into smaller pieces.

ffi tt is important to chew our food because:

(a) it breaks the food up into smatler pieces that are easier to swallow.

(b) it makes digestion by enzymes easier. when food has been broken up into smaller pieces, thereis a larger surface area for the enzymes to act on.

(c) chewing allows the food to be mixed with the saliva.food to move easily along the alimentary canal.

+ There are fourdifferent types of teeth:

(1) incisor(2) canine

(3) premolar

(4) molar

Each type has a different shape, size and function.

Saliva also contains mucus which helps

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The table below shows the four types of teeth in humans

T5,pe of tooth Description Function

fl-*Itr*y urcrsor

. chisel-shaped

. narrow bitine surface cutting food

ff- pointed

y canine

r chisel-shaped and pointed. narrow biting surface

cutting andtearing food

(e)-- curp

W premolar

a three blunt cuspsbroad biting surfacea

crushing andgrinding food

-ai- broad

hl 3sil:"" morar

r four blunt cuspsr broad biting surface

crushing andgrinding food

Dental Decav

+ Teeth have a very hard outer layer to protect them while chewing food.

+ Over time this hard layer can be dissotved away by acid produced by bacteria in the mouth.

$ This is called dental decay or tooth decay.

S The acid is produced when bacteria digest leftover food stuck in between the teeth.

S Too much sweet food and not cleaning the teeth properly will cause tooth decay to happen more

quickly.

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The diagram below shows the stages in the decay of a molar tooth

1. bactcria * sugar-r-acid(in the (ur the

mouth) foo$

NO PATN

acid attacks the hard surface

of the tooth, forming a cavity

SLICT{T

TOOTHAC}IE

bone-like

inner

region

acid eats through the innnerregion

SEVERE

TOoftIActm

inntrmost regioncontaining ncrv!s

4, acid reaches the innermostrqgion, where it attacks thenerve$

AGONY!

painful

swelling

5. decay reachs base of toothand causs a painful swelling

The Proper Care of Teeth

+ You can have strong, healthy teeth by doing the following:

(1) Keep your teeth clean

,/ You should brush your teeth at teast twice a day, early in the morning and before going to bed.

./ lf possible, brush your teeth after every meal or at least rinse your mouth with water to remove

any food remains on your teeth.

,/ Food particles that are trapped between your teeth are best removed with a piece of dental floss.

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,/ lt is better to use fluoride toothpaste when brushing your teeth. Fluoride hardens the tooth

surface making it more resistant to tooth decay.

(21 Eat less sweet and stickY food

,/ lf sugar is present in your mouth for too long, your teeth will start to decay.

(3) Visit the dentist regularly

./ Do not wait to visit your dentist until you get a toothache.

Peristalsis

^ The walls of the whole alimentary canal consist of layers of muscles and cells which secrete slimy liquid

called mucus,

a The layers of muscles bring about wave-like contractions called peristalsis which push food along the

alimentary canal.

.r The slimy mucus makes it easier for the food to move along.

Below shows peristalsis - wave-like contractions which move food along the alimentary canal

Muscle

contracts

Food Muscle

relaxes

*lE

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5.4 CHEMICAL DIGESTION

Chemicaldigestion is a process by which complex food molecules are broken down intosimple soluble substances. Enzymes are used to produce these chemical changes.

Most of the food we ingest is insoluble and made up of molecules that are too large and complex to pass

through the wall of the small intestine (ileum) into the blood vessels.

Below shows digestion reduces complex food substances into simple units

-

digestion

o oooooo oo

glucose units

ooo

Bw

fE a".!

digcsrion nmamino acid units

Fnrt-Fats

%

cligestion

tfntf

farry acids and glycerol

f ln most animals, digestion is extracellular.

(Extracellular means that digestion takes ptace outside the body cells. ln most animals, digestion

takes place in ihe alimentary canal.)

* Example of extracellular digestions are:

salivarv amvlase

(b) Stomach: protein pepsn > polypeptide (peptones)

(c) Duodenum: fats bile (no enzyme) , emulsified fats

oancreatic amvlase

(d) lteum: maltose maltase , glucose

polypeptide (peptones) peptidase , amino acids

frts &'"e r fatty acids and glycerol

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