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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/7/31/2019 2012 Digestive System in Man
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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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