humandigestionteacher-110323090218-phpapp01

7/28/2019 humandigestionteacher-110323090218-phpapp01

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HumanumanDigestiveigestiveSystemystem


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What you will be learning...(a) identify the main regions of the alimentary canal and the associated

organs: mouth, salivary glands, oesophagus, stomach, duodenum,

pancreas, gall-bladder, liver, ileum, colon, rectum, anus(b) *describe the functions of these parts in relation to ingestion, digestion,absorption, assimilation and egestion of food, as appropriate

(c) explain why most foods must be digested

(d) describe:

(i) digestion in the alimentary canal

(ii) the functions of a typical amylase, protease and lipase, listing thesubstrate and end-products

(e) describe the structure of a villus (including role of capillaries and lacteals) inabsorption

(f) State the function of the hepatic portal vein as the route taken by most ofthe most absorbed from the small intestine

(g) state the role of the liver in:(i) carbohydrate and fat metabolism

(ii) breakdown of red blood cells

(iii) metabolism of amino acids and the formation of urea

(iv) breakdown of alcohol, including the effects of excessive alcoholconsumption


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Recall. . .What are the main organs of the alimentary canal?

Mouth

Oesophagus

Stomach

Small intestine Large intestine

Anus

Although not part of the alimentary canal, the liver,gall bladder and pancreas are closely associated withit. They play an important role in digestion bysecreting digestive enzymes.


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5 Digestion Processes (IDAAE) Ingestion: taking in of food into the body.

Digestion: breaking down of food into simplersubstances

Absorption: diffusion of food from smallintestine into the blood

Assimilation: using digested nutrients to makenew material

Egestion: removal of undigested waste material


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DigestionMechanical / physical digestion physically

breaks down the food in the mouth (chewing).

Smaller pieces of food increase surface area

for digestion. It also takes place in the

stomach (churning of food by the muscularstomach walls)

Chemical digestion uses enzymes to

chemically break down complex food

substances into their simplest form. e.g.

Starch maltoseamylase


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Chemical digestion:

Starch (carbohydrate) digestion: in mouth and

small intestine. Protein digestion: in stomach and smallintestine

Fat digestion: only in small intestine

Why must food be digested???

Large molecules of food are unable to pass

through cell membranes, thus must be brokendown into small molecules so that they candiffuse through cell membranes into the bloodstream


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Mouth (Ahhh....)

Mouth ingests food Teeth masticates food into small pieces toincrease surface area for digestion

Saliva (pH 7) moisten and soften food

Starch maltose

Tongue mixes food with saliva and rollsfood into a bolus before swallowing

Saliva - water, mucus, salivary amylase

Salivary amylase


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Swallowing


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trachea

(windpipe)

glottis

During breathing, the

larynx is lowered and

the glottis is open.

pharynx

oesophagu

s

larynx

(voice-box)

air

What Happens During Breathing

and Swallowing?Normally, air passes into

the trachea (windpipe)

while food passes into

the oesophagus.


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During swallowing, the

larynx is raised and the

glottis is covered by theepiglottis. This prevents

food particles from

entering the trachea.

pharynx

trachea

(windpipe)

oesophagu

sglottis

epiglottis

food

particles

larynx

(voice-box)


and Swallowing?


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Occasionally, small

particles of food or water

may get into the larynxor trachea.

trachea

(windpipe)

larynx(voice-box)

food

particles


and Swallowing?


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and Swallowing?

This automatically induces

violent coughing to force

the food particles or waterout and to prevent

choking.

trachea

(windpipe)

larynx(voice-box)

food

particles


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The two layers of musclescause rhythmic, wave-like

contractions of the gut walls.

Such movements are known as

peristalsis.

Peristalsis:

enables food to be mixed

with the digestive juices; and

moves the food along the

gut.

Part of the gut wall

Peristalsis

circular

muscles

longitudinal

muscles


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Wall here constricts.

Circular muslces

contract; longitudinal

muscles relax

Wall here dilates

Direction of movement of food

Circular muscles relax

Longitudinal muscles

contract


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Peristalsis Move the food down!

When circular musclescontract, longitudinalmuscles relax. Gut wallconstricts i.e. gut becomes

narrower and longer. Foodis squeezed or pushedforward.

Gravity and slipperymucous lining helps pushfood down too.

http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/basics/peristalsis.html
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/basics/peristalsis.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/basics/peristalsis.html


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Stomach Stores food temporarily

Stomach muscles churns and mixes food (alsoby peristalsis) with gastric juice to form chyme.

Gastric juice contains hydrochloric acid (HCl)

and enzymes like rennin and pepsin HCl is very acidic (pH2), thus it kills bacteria

and other microorganisms, as well as

stopping the action of salivary amylase

Provides acidic medium for gastric enzymes

to work

Only protein digestion here


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HCl converts inactive pepsinogen and prorennin

to their active forms


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The stomach isguarded at the

entrance and exit

points by sphincter

muscleswhichcontrol the amount

of food entering

and leaving thestomach.

S ll I t ti


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Small Intestine

Subdivided into duodenum, jejunum and

ileum

In the small intestine, chyme stimulates

1. Pancreas to secrete pancreatic juice

2. Gall bladder to secrete bile

3. Intestinal glands to secrete intestinal juice

All three juices secreted are alkaline,

pH 8.5


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bile

intestinal juice

pancreatic

duct

pancreatic juicebile duct

1

3

2

Pancreatic and

intestinal juice containmany digestive

enzymes.

Bile does not contain

enzymes. Bile emulsifies

fats, increasing the

surface area for lipaseaction

D d


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Duodenum

Starch maltose

Protein polypeptides Fats fatty acids + glycerol

Ileum

Maltose glucose Polypeptides amino acids

Fats fatty acids + glycerol

Lactose glucose + galactose

Sucrose glucose + fructose

pancreatic amylase

proteases

lipase

maltase

protease

lipase

lactase

sucrase

Note that the small intestine is the main site of

digestion of food and absorption of nutrients.


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Large Intestine (colon)

Large inverted Ushaped tube.

No digestion takesplace here

Absorbs waterandminerals salts

Stores the faeces(dead cells, mucus,germs, undigestedfood)


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Is the colon the main region for waterabsorption?

No! About 94% of the total amount ofwater passing through the alimentary canalis absorbed by the small intestine! Thelarge intestine absorbs most of the

remaining 6% of water.

Rectum temporarily stores faeces

Anus egests (= removal of undigestedmatter) faeces

O i t d ith th


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Organs associated with the

alimentary canal

These organs do

not digest food but

aid in digestion

Gall bladder

Pancreas

Liver

G


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Gall bladder Temporarily stores bile (smelly green

substance) secreted by liver. Secretes bile in the presence of chyme.

Bile breaks up large fat droplets into very

small fat droplets to increase surface areafor lipase action (Emulsification) Bileemulsifies fats

*Bile is not an enzyme, so it is not affectedby temperature

P


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Pancreas Connects to small intestine by pancreatic

duct Produces pancreatic juice

Secretes hormones like insulin (controlsblood glucose concentration) and glucagon

(controls carbohydrate metabolism)

Liver Produces bile, which is stored in the gall

bladder

Absorption


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AbsorptionAdaptations of the small intestine

Small intestine is very long (~5 m)

Internal surface of the small intestine has

many folds.

On these folds, there are many finger-like

projections called villi

These 3 adaptations increase surface

area for absorption


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Lacteal fatty acids

and glycerol recombinein the epithelium to

form fat which then

enters the lacteal as

fine fat droplets

Blood capillaries transport sugars

and amino acids

away from the

smallintestine

One cell thick epithelium

forefficient absorption of

food particles

This continual transport of digested food substances

maintains the concentration gradient for the absorption

of digested food substances.


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The concentration of simple nutrients (e.g.glucose, amino acids, fatty acids and glycerol) ishigher in the lumen of the small intestine then inthe blood capillaries that pass through the villi.

Thus, nutrients diffuse across a region of highconcentration (lumen of the small intestine) tothe bloodstream, which has a lowerconcentration. Note that absorption by activetransport is also possible.

The blood capillaries in the small intestine uniteto form larger blood vessels, which unite to formthe hepatic portal vein, which transports thenutrients to the liver.

What happens to amino acids and glucose


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What happens to amino acids and glucose

after absorption?

Products released from liver into general

blood circulation

Molecules pass into the epithelial cells

Through walls ofcapillaries in the villus and into bloodstream

The capillaries join up to form veins

Veins unite to form 1 large vein: Hepatic Portal Vein

Hepatic portal vein carries blood to liver

Liverstores or alters products of digestion


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Gl A i A id


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Glucose Amino Acids

Glucose is used by allcells as a source ofenergy.

Excess glucose

returned to liver andstored as glycogen.Insulin stimulates liverto convert glucose intoglycogen. When the

body needs energy,glycogen is convertedback to glucose.

Amino acids which enterthe cells are convertedinto new protoplasm thatis used forgrowth and

repair. Amino acids used toform enzymes andhormones.

Excess amino acidsdeaminated by liver.

What happens to fatty acids and glycerol


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after absorption?

Molecules pass into the epithelial cells

Recombine into fats again in the epithelial cells

Fats enter the lacteals

Lymph (fluid in lacteals) + fat = chyle

Lymphatic vessels discharge chyle into

bloodstream


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Fats

Blood carries fats to all parts of the body,especially to the liver.

When there is enough glucose, fats are not

broken down but are used to build

protoplam. When there is insufficient glucose, fats

are broken down to provide energy.

Excess fats stored in adipose tissues.

Villi absorption by diffusion


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Villi absorption by diffusion

DiffusionDiffusion

From intestine

T

To liver

Assimilation


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Assimilation After travelling through the blood stream to

the rest of the body, cells can now makeuse of

glucose as source of energy

amino acids to build new cytoplasm and tissuecells

fatty acids to build new cell membranes

Functions of the Liver


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1. Regulation of blood glucose concentration

70-90mg of glucose / 100cm3 of blood (normal conditions)

2. Production of bile

Liver produces bile which is stored in the gall bladder

Functions of the liver


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3. Iron storage

Red blood cells are destroyed in the spleen andtheirhaemoglobin is sent to the liver to be broken

down. The iron released is then stored in the liver.

Bile pigments are also formed from the breakdown

of haemoglobin.4. Protein synthesis

Liver synthesizes proteins found in blood plasma,

e.g. albumins, globulins, fibrinogen



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5. Deamination of amino acids

Excess amino acids are transported to the liver, where their

amino groups are removed and converted to urea.



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6. Detoxification Liver cells contain alcohol dehydrogenase

to break down alcohol. Excessive alcohol is harmful. Alcohol

stimulates acid secretion in the stomach andincreases risk ofgastric ulcers.

Prolonged alcohol abuse may lead to livercirrhosis (destruction of liver cells), whichcan lead to liver failure and death.

7. Heat production

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