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THE DIGESTIVE SYSTEM





anus

appendix

colon

gall bladder

gullet

liver

pancreas

rectum

salivary glands

small intestine

stomach

teeth

tongue

Use the list below to name the parts of the digestive system in the diagram below.
Digestive system - no labels
If you like, you can colour in the various regions, and make the list into a key.

The numbered regions are referred to in the table below.

RULES OF LABELLING

- labels (names) in ink
- written horizontally

- lines in pencil - ruled

- no overlapping label lines

- no arrowheads

- do not write on top of diagram

Briefly describe the processes that occur in the sections of the digestive system above.


Name the "digestive juices" produced in the various numbered regions, together with their ingredients

Region number and name Digestive juice Ingredients
1 mouth saliva water, amylase, mucus
2 stomach gastric juice protease, HCl, mucus
3 liver bile alkali, bile salts, pigments, NO ENZYMES
4 pancreas pancreatic juice amylase, protease, lipase
5 small intestine intestinal juice various enzymes to complete digestion

What part do a) your tongue and b) your teeth play in digestion?

a > forms food into bolus b > cuts, grinds food

How many types of amylase are there?

> 2

How many glands produce amylase? (trick question!)

> either 2 or 7 (pancreas and 6 salivary glands)

Mucus is produced all along the gut. Think of some uses for it.

> lubrication > protection against digestive juices

Why is water added in the first parts of the gut?

> to dissolve food / move it on / allow enzymes to hydrolyse food

Which is the first class of food to be acted on in the digestive system?

> carbohydrate (starch)

Which is the last class of food to be acted on in the digestive system?

> fats and oils

Digestive System There are at least 3 ring-shaped muscles (sphincters) along the gut. Do not get these confused with the layer of circular muscle - all along the gut - which has a role in moving food along.

Mark the positions of these (stationary) sphincter muscles with an X on the diagram alongside.

What happens when we relax each one of them?

> food enters stomach

> food leaves stomach

> faeces leaves gut at anus

How is it that we can (apparently) drink when standing on our head? (Do not try this in the lab!)

> peristalsis - waves of muscular contraction

What is the function of the epiglottis?

> prevents food entering lungs ("going the wrong way")

What is the epiglottis doing, most of the time?

> keeping out of the way, allowing air into the lungs

What is indigestion?

> (solid) food not being digested (to liquid) - probably due to conditions not being correct (wrong pH)

What causes indigestion?

> food in too large particles due to inadequate chewing? / excess acids in stomach prevent alkaline conditions needed by enzymes in small intestine

The first part of the small intestine is called the duodenum, and it receives secretions from 2 glands.

Name these glands

> pancreas > liver

Why do stomach and duodenal ulcers not heal very well?

> secretion of enzymes and HCl damages the cells

Why do we sometimes bring up a greenish liquid when we are very sick?

> this is bile, from the small intestine

There are no digestive enzymes in bile, so what is its function in the digestive process?

> bile emulsifies fats (physical digestion) - making them easier to digest

What is the function of the gall bladder?

> stores bile

How could you get on without it?

> OK - but must stick to low fat diet

Label the diagram of a villus alongside.
villus Where are the villi found?

> small intestine

What (pipework) are they connected to?

> blood vessels > lymphatic system

What is the advantage of the villus having only a single layer of cells on its surface?

> lets digested food through easily

What is the advantage of there being lots of villi?

> to provide a large surface area for absorption

What sorts of substances pass into the blood capillary inside a villus?

> glucose, amino acids , "some" fatty acids and glycerol

What sorts of substances pass into the lacteal inside a villus?

> "most" fatty acids and glycerol

What is the function of the blood capillaries inside the villi?

> to absorb the products of digestion

What is the name of the blood vessel which runs between the digestive system and the liver?

> hepatic portal vein

What (sub-units) are proteins converted to in digestion?

? > amino acids

What might happen to them in the liver (if they are not wanted by the body at the time)?

> deaminated to urea etc.

What (sub-units) are carbohydrates converted to in digestion?

? > glucose

What might happen to them in the liver(if they are not wanted by the body at the time)?

> stored as glycogen, then released as glucose when needed

Why are vitamins not changed in digestion?

? > no need for conversion - already soluble - not composed of subunits

What might happen to them in the liver?

> stored - think of cod liver oil!

How many of the functions of the liver are associated with the digestive process?

> 6 out of 8 ?

What is the function of the ileum (main part of small intestine)?

> absorption of digestion products from gut contents

What is the function of the colon (large intestine)?

> absorption of water from gut contents

What is the function of the rectum?

> storage of faeces

Why is diarrhoea so runny?

> no water reabsorbed in the colon

What part of the gut has no function in Man?

> appendix

In rabbits, this part is very large, and full of organisms that feed on cellulose.

What is the advantage of this to the rabbit?

> cellulose is the main food component in grass etc, and it needs time to maximise breakdown by bacteria etc.


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