Human Alimentary Canal: Structure & Function, Peristalsis, Role of Digestive Enzymes, Bile: Production & Storage, Bile: Function and the Small Intestine: Structure & Adaptations

Question 1

What is the digestive system?

Answer 1

The digestive system is an example of an organ system in which several organs work together to digest and absorb food.

Question 2

Describe digestion

Answer 2

Digestion is a process in which relatively large, insoluble molecules in food (such as starch, proteins) are broken down into smaller, soluble molecules that can be absorbed into the bloodstream and delivered to cells in the body
These small soluble molecules (such as glucose and amino acids) are used either to provide cells with energy (via respiration), or with materials with which they can build other molecules to grow, repair and function.

Question 3

What is the human digestive system made up of? (in general)

Answer 3

The human digestive system is made up of the organs that form the alimentary canal and accessory organs

Question 4

What is the alimentary canal?

Answer 4

The alimentary canal is the channel or passage through which food flows through the body, starting at the mouth and ending at the anus.
Digestion occurs within the alimentary canal.

Question 5

What are accessory organs useful for?

Answer 5

Accessory organs produce substances that are needed for digestion to occur (such as enzymes and bile) but food does not pass directly through these organs.

Question 6

What is the function of the mouth/salivary glands?

Answer 6

THE MOUTH IS WHERE MECHANICAL DIGESTION TAKES PLACE
- TEETH CHEW FOOD TO BREAK IT INTO SMALLER PIECES AND INCREASE IT’S SURFACE AREA TO VOLUME RATIO.
AMYLASE ENZYMES IN SALIVA START DIGESTING STARCH INTO
MALTOSE.
THE FOOD IS SHAPED INTO A BOLUS (BALL) BY THE TONGUE AND LUBRICATED IN SALIVA SO IT CAN BE SWALLOWED EASILY.

Question 7

What is the oesophagus and what is it’s function?

Answer 7

TUBE THAT CONNECTS THE MOUTH TO THE STOMACH WHERE THE FOOD BOLUS GOES AFTER BEING SWALLOWED WAVE - LIKE CONTRACTIONS WILL TAKE PLACE TO PUSH THE FOOD BOLUS DOWN WITHOUT RELYING ON GRAVITY.

Question 8

What is the function of the stomach?

Answer 8

FOOD IS MECHANICALLY DIGESTED BY CHURNING ACTIONS WHILE PROTEASE ENZYMES START TO CHEMICALLY DIGEST PROTEINS. HYDROCHLORIC ACID IS PRESENT TO KILL BACTERIA IN FOOD AND PROVIDE THE OPTIMUM PH FOR PROTEASE ENZYMES TO WORK.

Question 9

What are the parts and functions of the small intestine?

Answer 9

FIRST SECTION IS CALLED THE DUODENUM AND IS WHERE THE FOOD COMING OUT OF THE STOMACH FINISHES BEING DIGESTED
BY ENZYMES PRODUCED HERE AND ALSO SECRETED FROM THE PANCREAS
PH OF THE SMALL INTESTINE IS SLIGHTLY ALKALINE - AROUND
PH 8 - 9
SECOND SECTION IS CALLED THE ILEUM AND IS WHERE
ABSORPTION OF DIGESTED FOOD MOLECULES TAKES PLACE
THE ILEUM IS LONG AND LINED WITH VILLI TO INCREASE THE SURFACE AREA OVER WHICH ABSORPTION CAN TAKE PLACE

Question 10

What is the function of the large intestine?

Answer 10

WATER IS ABSORBED FROM REMAINING MATERIAL IN THE COLON
TO PRODUCE FAECES.

Question 11

What is the function of the anus and rectum?

Answer 11

FACES IS STORED IN THE RECTUM AND REMOVED THROUGH THE ANUS

Question 12

What is the function of the pancreas?

Answer 12

PRODUCES ALL THREE TYPES OF DIGESTIVE ENZYME; AMYLASE, PROTEASE AND LIPASE
SECRETES ENZYMES IN AN ALKALINE FLUID INTO THE DUODENUM
FOR DIGESTION TO RAISE PH OF FLUID COMING OUT OF THE STOMACH

Question 13

What is the function of the liver?

Answer 13

PRODUCES BILE TO EMULSIFY FATS (BREAK LARGE DROPLETS
INTO SMALLER DROPLETS) - AN EXAMPLE OF MECHANICAL
DIGESTION
AMINO ACIDS NOT USED TO MAKE PROTEINS BROKEN DOWN HERE (DEAMINATION) WHICH PRODUCES UREA

Question 14

What are the stages the food goes through during its passage through the alimentary canal?

Answer 14

Ingestion, mechanical digestion, chemical digestion, absorption, assimilation and egestion

Question 15

What is ingestion?

Answer 15

Ingestion - the taking in of substances, e.g. food and drink, into the body through the mouth

Question 16

What is mechanical digestion?

Answer 16

Mechanical digestion - the breakdown of food into smaller pieces without chemical change to the food molecules

Question 17

What is chemical digestion?

Answer 17

Chemical digestion - the breakdown of large, insoluble molecules into small, soluble molecules

Question 18

What is absorption?

Answer 18

Absorption - the movement of small food molecules and ions through the wall of the intestine into the blood

Question 19

What is assimilation?

Answer 19

Assimilation - the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells

Question 20

What is egestion?

Answer 20

Egestion - the passing out of food that has not been digested or absorbed (as faeces) through the anus

Question 21

What is peristalsis?

Answer 21

Peristalsis is a mechanism that helps moves food along the alimentary canal.

Question 22

Describe the process of peristalsis

Answer 22

Firstly, muscles in the walls of the oesophagus create waves of contractions which force the bolus along
Once the bolus has reached the stomach, it is churned into a less solid form, called chyme, which continues on to the small intestine

Question 23

What is produced in peristalsis and why?

Answer 23

Mucus is produced to continually lubricate the food mass and reduce friction.

Question 24

What is needed in peristalsis and why?

Answer 24

Dietary fibre as it provides the roughage required for the muscles to push against during peristalsis

Question 25

Describe the function of the circular muscles in peristalsis

Answer 25

Circular muscles contract to reduce the diameter of the lumen of the oesophagus or small intestine

Question 26

Describe the function of the longitudinal muscles in peristalsis

Answer 26

Longitudinal muscles contract to reduce the length of that section the oesophagus or the small intestine

Question 27

What is it called when the bolus has reached the stomach and is churned into a less solid form?

Answer 27

Chyme

Question 28

How is food mechanically digested?

Answer 28

By chewing, churning and emulsification

Question 29

Why is food partially digested mechanically?

Answer 29

Food is partially digested mechanically (by chewing, churning and emulsification) in order to break large pieces of food into smaller pieces of food which increases the surface area for enzymes to work on

Question 30

Is digestion mainly chemical or mechanical and describe why?

Answer 30

Digestion mainly takes place chemically, so that bonds holding the large molecules together are broken to make smaller and smaller molecules

Question 31

Describe chemical digestion

Answer 31

Bonds holding the large molecules together are broken to make smaller and smaller molecules. Chemical digestion is controlled by enzymes

Question 32

What are enzymes?

Answer 32

Enzymes are biological catalysts – they speed up chemical reactions without themselves being used up or changed in the reaction.

Question 33

What are the three main types of digestive enzymes?

Answer 33

There are three main types of digestive enzymes – carbohydrases, proteases and lipases.

Question 34

What are carbohydrases?

Answer 34

Carbohydrases are enzymes that break down carbohydrates to simple sugars such as glucose.

Question 35

What is amylase and what does it do?

Answer 35

Amylase is a carbohydrase which is made in the salivary glands, the pancreas and the small intestine.
Amylase breaks down starch into maltose. Maltase breaks down maltose into glucose.

Question 36

What are proteases?

Answer 36

Proteases are a group of enzymes that break down proteins into amino acids.

Question 37

What is pepsin?

Answer 37

Pepsin is an enzyme made in the stomach which breaks down proteins into smaller polypeptide chains.

Question 38

What do Proteases made in the pancreas and small intestine do?

Answer 38

Proteases made in the pancreas and small intestine break the peptides into amino acids.

Question 39

What are lipases, where are they produced and secreted?

Answer 39

Lipases are enzymes that break down lipids (fats) to glycerol and fatty acids. Lipase enzymes are produced in the pancreas and secreted into the small intestine

Question 40

What is bile and where is it stored?

Answer 40

Bile is an alkaline substance produced by cells in the liver
Before being released into the small intestine bile is stored in the gallbladder

Question 41

How does bile emulsify fats?

Answer 41

Bile contains bile salts, it is these molecules which emulsify the fats.

Question 42

What are the two main roles of bile and what is the purpose for this?

Answer 42

Bile has two main roles:
Neutralising the hydrochloric acid from the stomach and Breaking apart large drops of fat into smaller ones (and so increasing their surface area).

The more alkaline conditions and larger surface area allows lipase to chemically break down the fat (lipids) molecules into glycerol and fatty acids at a faster rate.

Question 43

How does bile neutralise the hydrochloric acid from the stomach and why is it essential?

Answer 43

The alkaline properties of bile allow for this to occur.
This neutralisation is essential as enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach.

Question 44

What is emulsification (as a role of bile)?

Answer 44

Breaking apart large drops of fat into smaller ones (and so increasing their surface area).

Question 45

What helps lipase to chemically break down the fat (lipids) molecules into glycerol and fatty acids at a faster rate?

Answer 45

The more alkaline conditions and larger surface area allows lipase to chemically break down the fat (lipids) molecules into glycerol and fatty acids at a faster rate.

Question 46

What sort of digestion is emulsification and why?

Answer 46

Mechanical direction as breaking something into smaller pieces does not break bonds or change the chemical structure of the molecules which make it up.

Question 47

What are the stages of food breakdown?

Answer 47

Ingestion
Mechanical digestion
Chemical digestion
Absorption
Assimilation
Egestion

Question 48

What is absorption?

Answer 48

Absorption is the movement of small digested food molecules from the digestive system into the blood (glucose and amino acids) and lymph (fatty acids and glycerol).

Question 49

How does the absorption of small molecules occur?

Answer 49

Absorption of small soluble molecules occurs through diffusion and sometimes active transport.

Question 50

How is water absorbed in the digestive system?

Answer 50

Water is absorbed (by osmosis) primarily in the small intestine, but also in the colon.

Question 51

What occurs after absorption?

Answer 51

After absorption, assimilation and egestion occurs

Question 52

What is assimilation?

Answer 52

Assimilation is the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells

Question 53

What is egestion?

Answer 53

Egestion is the passing out of food that has not been digested or absorbed (as faeces) through the anus.

Question 54

Describe how the small intestine adapted for absorption.

Answer 54

The small intestine is adapted for absorption as it is very long and has a highly folded surface with millions of villi (tiny, finger-like projections). These adaptations massively increase the surface area of the small intestine, allowing absorption to take place faster and more efficiently

Question 55

What specific adaptation does the villi of the small intestine have which allows for the rapid absorption of substances?

Answer 55

A large surface area, A short diffusion distance, and finally A steep concentration gradient

Question 56

Describe the large surface area crucial for the rapid absorption of substances in the villi of the small intestine?

Answer 56

Microvilli on the surface of the villus further increase the surface available for absorption.

Question 57

Describe the short diffusion distance in the villi of the small intestine.

Answer 57

The wall of a villus is only one cell thick.

Question 58

Explain the process of the steep concentration gradient in the villi of the small intestine.

Answer 58

The villi are well supplied with a network of blood capillaries that transport glucose and amino acids away from the small intestine in the blood. A lacteal (lymph vessel) runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph
Enzymes produced in the walls of the villi assist with chemical digestion
The movement of villi helps to move food along and mix it with the enzymes present.
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