2012 digestive system in man

7/31/2019 2012 Digestive System in Man

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What is nutrition?

Intake of food

and the process thatconverts food substances

into living matter.


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5 Stages of nutrition

As food goes along the alimentary canal,

it undergoes the following processes:

INGESTION

DIGESTION

ABSORPTION ASSIMILATION

EGESTION


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Intake of food

into the body.Feeding, Drinking.


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Breakdown oflarge, complex and

insoluble foodmolecules intosmall, soluble

particles.


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Digested food enters

blood and is carried to theliver before going to the

rest of the body.


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process by which

absorbed food is

converted to formnew cells, for

growth and to

provide energy.


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Removal of

undigested food

wastes as faeces


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INGESTION

HOLOZOIC NUTRITION- intake of ready-

made solid organic food.


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DIGESTION

Digestion:process by which body breaks

down food into simple, soluble, diffusible

substances that can be absorbed and used by

body cells.

Digestive system: alimentary canal and

associated organs - liver, pancreas, gall

bladder.


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Mechanical / Physical digestion:cutting and

crushing of solid food into smaller pieces by

chewing (mastication) and churning (peristalsis).


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Chemical digestion:process of breaking down

large, insoluble, complex food into smaller,

simpler, soluble food particles that can

diffuse across cell membranes through the

action of enzymes.


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WHY IS DIGESTION NEEDED IN ANIMALS?

Animals are unable to manufacture their own food in their bodies.

They must obtain food substances from other animals or plants to

provide for their energy requirements, growth and health.

Most of the nutrients in food such as starch, protein and fat occur

as large, insoluble molecules. Such molecules cannot pass

through the cell membrane into the body cells.

Animals must break down these complex molecules into simple,

diffusible and soluble molecules using action ofenzymes.

Glucose and amino acids, are small and soluble in water. Theycan then pass through the cells in the walls of the gut and blood

vessels to get into the blood stream.


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LAYERS OF TISSUES IN ALIMENTARY CANAL

Serous coat

Longitudinal smooth muscles

Circular smooth muscles

Epithelium- innermost layer of cells incanal. Replaced when worn away by foodmovement. Folded, lined with digestiveglands and cells that produce mucus.

Blood vessels


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JOURNEY OF FOOD

As food enters the

mouth, mechanical

digestion occurs.The

teeth mashes up the

food and mixes it withsaliva that is secreted

by the salivary gland.


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Teeth

Tongue

cut, grind and break food into

smaller pieces to expose largesurface area for enzymes to acton.

Rolls food into bolus


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Behind Swallowing. . .

Investigation1.Place your fingers against your

larynx (voice-box)

2.Swallow your saliva

3.Account for the movement in your

throat


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1. The moves up.

2. This movement causes a flap

of tissue called the to

close off the entrance of the

3. This prevents the entry of food

particles into the

voice-box / larynx

epiglottis

trachea / wind-pipe

trachea / wind-pipe


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Journey of Food

Food then goes through a long winding

tube called oesophagus.

The long tube of esophagus ensures

that food has sufficient time to be

digested and absorbed into the body.


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The cells of the

oesophagus wall secretes

a liquid called mucus.

Mucus makes it easier and

smoothen the journey of

the food as it travels to

the stomach.

JOURNEY OF FOOD


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wave-like, rhythmic waves of contraction and

relaxation of muscular wall of gut, regulated

by nervous system. Food can move slowly and

easily through the entire alimentary canal.

Circular muscles contract, longitudinal

muscles relax = wall contracts, vice versa.


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visit website for peristalsis animation:

http://www.westga.edu/~lkral/peristalsis/

Peristalsis simulation

The muscles in the wall of the canal cause wave-like contractions

called Peristalsis. This process can be visualized as a squeezing

action, forcing the food along.
http://www.westga.edu/~lkral/peristalsis/http://www.westga.edu/~lkral/peristalsis/


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Peristalsis: Squeezing action

JOURNEY OF FOOD


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Sphincter muscles to

control the flow of food.

As food enters the stomach,

Gastric juices are secreted

by gastric glands in the walls

of the stomach.

Gastric juices contain acids

such as HCl and enzymes to

digest proteins.

The P.H of stomach is 2.0

Diagram of a Stomach

JOURNEY OF FOOD


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A thick , muscularand elastic bag.

Due to its acidic

conditions in thestomach, the enzyme

amylase does not

function here andthere is no breakdown

of starch molecules

into maltose.

JOURNEY OF FOOD


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Gastric juice = enzyme pepsin +

dilute solution of hydrochloric acid

Amylase requires an alkaline medium

to function

HCl stops the action of salivary amylase.


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1) Provides an acidic mediumfor action of the enzymepepsin.

2) Kills bacteria.


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Caused by excessive production ofhydrochloric acid.

HCl causes the stomach walls to beeroded gastric ulcer

Worry and stress can increase theflow of gastric juice into the

stomachCan also be caused by a bacteria,which causes recurrent infections


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Small IntestineThe small intestine consists ofthree portion namely :

Duodenum , Jejunum and

ileum.

The small intestines receive bile

and pancreatic juices andcontain enzymes for digestion.

p.H is 8.5 , alkaline condition

JOURNEY OF FOOD


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JOURNEY OF FOOD

Small intestine

Ileum


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All the food thathave been digested

in the small

intestine will getsabsorbed into the

blood stream at the

ileum.

JOURNEY OF FOOD


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The function of the large

intestine is to absorb water

and mineral salts from

undigested food.

It also stores faeces which are

mainly undigested food such

as cellulose from the

vegetables.

Inverted U colon , largeintestine

JOURNEY OF FOOD


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ileum


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Anus

The function of

anus is to expel

or egest the

undigested

food (faeces).

JOURNEY OF FOOD


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JOURNEY OF FOOD


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JOURNEY OF FOOD


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The liver produces a green liquid called

bile that helps to break up the fats into

smaller droplets . This process is called

Emulsification.The bile is stored in the gall bladder

before released into the small intestine.

JOURNEY OF FOOD


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The elongated pancreas secretespancreatic juice which contains

enzymes to digest carbohydrates,

proteins and fats.

JOURNEY OF FOOD


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MOUTH TEETH - for mastication. Teeth cut, grind

and break food into smaller pieces to exposelarge surface area for enzymes to act on.

TONGUE - rolls food into bolus.

SALIVARY GLANDS produce saliva - softens

and moistens food.

Saliva contains water, mucus, salivaryamylase (ptyalin).

Water - as solvent, for hydrolysis. Mucus - sticks food together and lubricates

bolus for swallowing

Starch ------> Maltose


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EPIGLOTTIS - helps to separate pathway ofdigestion and respiration I.e. alimentarycanal for food and trachea (windpipe) forair.

Bolus of food pushed into pharynx bytongue.

Epiglottis covers trachea duringswallowing.

If it does not function properly - coughingreaction.

PHARYNX


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OESOPHAGUS

Tube connecting pharynx to stomach.

Walls made up of circular and longitudinalmuscles.

PERISTALSIS - muscular waves ofcontraction along length of alimentarycanal. Transports food to stomach.

CARDIAC SPHINCTER- rings of muscle atentrance of stomach. Controls entry offood into stomach.


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J-shaped muscular bag.

Muscular walls churn and further break food

into smaller pieces. Food mixed with gastric

juice and mucus to formchyme.

Store food for 2 - 6 hours.

GASTRIC JUICE- secreted by gastric and mucusglands. Digestive enzymes in gastric juice begin

digestion of proteins. PYLORIC SPHINCTER- rings of muscles at exit

of stomach. Controls entry of food intoduoenum.

STOMACH


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STOMACH - GASTRIC JUICE

HYDROCHLORIC ACID- acidic medium (pH 2)for enzyme action. Kills bacteria. Activatesenzymes.

Water -as solvent, for hydrolysis.

Mucus - protects stomach wall from acidicgastric juice. Lubricant for movement of foodin stomach.

PEPSIN- proteins digested into polypeptides /peptones.

RENNIN- coagulates milk protein (caseinogen)into insoluble curds (casein) for hydrolysis by

pepsin.


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SMALL INTESTINE

Long coiled muscular tube with many folds oninner surface, lined by glands.

3 regions - duodenum, jejunum, ileum.

Increases surface area for absorption of food.

DUODENUM- producesintestinal juicefor final

stage of digestion.

JEJUNUM AND ILEUM- for absorption of

digested food materials.


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INTESTINAL JUICE(SUCCUS ENTERICUS)-alkaline, withmany enzymes.

EREPSIN- peptones digested into amino acids.

LACTASE - lactose (milk sugar)digested into glucoseand galactose.

SUCRASE- Sucrose (table sugar) digested into glucoseand fructose.

MALTASE- Maltose digested into glucose.

INTESTINAL LIPASE- fats digested into fatty acids andglycerol

ENTEROKINASE - activate trypsinogen to trypsin frompancreatic juice.

Water - as solvent, for hydrolysis.

DUODENUM - SMALL INTESTINE


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ADAPTATIONS OF SMALL INTESTINE

Covering inner surfaces of ileum are villi

(finger-like projections) . Eachvilliiscovered with epithelial cells withmicrovilli(microscopic projections) - furtherincrease surface area.

Wall of each villus is very thin, only one

cell thick. Allowsfast diffusion or active

transport.

Intestinal wall and villi richly supplied withblood capillaries and lacteals.


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LIVER AND GALL BLADDER

BILE- dark green liquid produced by liver. GALL BLADDER- store bile temporarily.

When food is in duodenum, released viabile duct.

Emulsifies or breaks fats into tinydroplets, provides increased surface areafor lipase to act on.

Neutralises acidic chyme, providesalkaline medium (pH 8).

PANCREAS


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PANCREAS Joined to duodenum by pancreatic duct.

PANCREATIC JUICE- alkaline, contains many enzymes

for hydrolytic food digestion.

Water - as solvent, for hydrolysis.

PANCREATIC AMYLASE- starch digested into maltose.

TRYPSIN- polypeptides digested intopeptones.(TRYPSINOGEN activated by ENTEROKINASEfrom intestinal juice)

PANCREATIC LIPASE- fats digested into fatty acidsand glycerol

Insulin (hormone)- excess glucose converted intoglycogen in liver stored.

Glucagon (hormone) glycogen converted intoglucose in liver and released into blood.


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LARGE INTESTINE Regions - Caecum, appendix, colon,

rectum and anus.

CAECUM & APPENDIX- non-functionalorgans in Man. Contains many bacteria to

produce vitamins e.g. B1, B2, K. COLON- thick walled, U-shaped tube.

Absorbs water, vitamins and mineral saltsfrom the undigested food.

MUCUS- lubricates unabsorbed, undigestedfood.


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Peristalsis - compacts undigested foodinto faeces and moves food along colon.

RECTUM- stores faeces temporarily.

FAECES- undigested food, roughage, bilepigments, bacteria, dead cells from

intestinal wall.

ANUS- regulate emptying of rectum.

LARGE INTESTINE


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2012 digestive system in man

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