Chapter 9 - Digestive System

Question 1

What is the digestive system?

Answer 1

Digestive system is the body system which extracts nutrients from food eaten and absorbs them into the body for use by the cells.

Question 2

What is the alimentary canal?

Answer 2

The alimentary canal is the continuous tube that runs from the mouth to the anus.

Together with associated organs such as the pancreas, gall bladder and liver, the alimentary canal makes up the digestive system.

It’s surface is lined with a differentially permeable lining which absorbs the nutrients.

Question 3

What is digestion

Answer 3

Body cells requires simple sugars, amino acids, vitamins, minerals and fatty acids to function normally.

Small molecules; vitamins, minerals and water pass through differentially permeable membrane surrounding each cell.

Simple sugars fatty acids and amino acids are large so they need to be broken down first into smaller units before absorbed by the cells.

The process in which carbohydrates, proteins and fat molecules get broken down to products small enough to be absorbed into the blood and into cells is called digestion.

Question 4

The organs of the digestive system are structured and arranged so they can carry six basic activities. What are they?

Answer 4

1. Ingestion of food and water
2. Mechanical digestion of food
3. Chemical digestion of food
4. Movement of food along the alimentary canal
5. Absorption of digested food and water into the blood and lymph
6. Elimination of material not absorbed

Question 5

What is the pharynx

Answer 5

Pharynx is the back of the mouth, which moves up and backwards.

The tongue pushes food into the pharynx after swallowing

Question 6

What is salivary glands

Answer 6

The salivary glands are three pairs of glands which produce saliva and dissolves food so it can be tasted.

The saliva contains mucus so that lubricates mouth and food and hold food in a lumo for swallowing.

It also contains the enzyme salivary amylase, which begins starch breakdown

Question 7

What does the liver do

Answer 7

The liver produces bile, which is stored and concentrated in the gall bladder.

Bike emulsifies lipids in the small intestine

Question 8

What is the gall bladder

Answer 8

The gall bladder stores bile and release it into the small intestine, where the bile emulsifies lipids

Question 9

What is the pyloric sphincter.

Answer 9

It is a band of circular muscle that regulates flow of material from stomach to duodenum

Question 10

Duodenum

Answer 10

First part of the small intestine

Question 11

Large intestine

Answer 11

Includes of the ascending colon ( from small intestine and up), transverse colon (horizontal) and the descending colon (to anus)

Question 12

Pancreas

Answer 12

Produces pancreatic juice contains enzymes for digesting proteins, lipids, and nucleic acid

Question 13

Caecum

Answer 13

First part of large instestine

Question 14

Rectum

Answer 14

Final part of large intestine which faces are formed

Question 14

Anus

Answer 14

Opening surrounded by the anal sphincter, muscle that can voluntarily controlled = close and open

Question 14

What happens in the mouth?

Answer 14

Ingestion which is the intake of food occurs

• mouth and jaw begin mechanical digestion where food is broken down up into smaller pieces
• as food is chewed it is mixed with saliva
• saliva is a fluid secreted from the salivary glands (3 pairs) which contains mucus and a digestive enzyme, salivary amalayse which begins the chemical digestion and breakdown of large starch molecules into smaller molecules .

Question 14

Explain the type of teeth and the mechanical digestion it part takes in.

Answer 14

4 types of teeth (adult = 32)

• 4x incisors - chisel shaped used for biting, cutting
• 2x canines - one on each side of incisors , conical shaped for tearing
• 4x premolars - two on each side begin crushing of food
• 6x molars (three on each side) have broad crowns for crushing and grinding of food

Question 15

What does the oesophagus do?

Answer 15

Like the rest of the alimentary canal has a double layer of muscle made up of circular muscle, with fibres arranged in a circle around the alimentary canal and longitudinal muscles, with fibres arranged along the length of the canal.

A lump of food enters the pharynx and oesophagus, the circular muscle behind it contracts to form a construction.

By contraction of successive bands of circular muscle the construction moves in a wave along the oesophagus, pushing the food in front of it. The constriction is called peristalsis.

Movement of food along the oesophagus is lubricated by the secretion of mucus from the inner lining of the oesophagus

Question 16

What happens in the stomach?

Answer 16

The stomach lining is specialised for secretion of GASTRIC JUICE which contains HCL, mucus and digestive enzymes.

Mechanical digestion in stomach occurs by waves of muscular contraction that move along the stomach wall.

• The stomach has an oblique muscle wall layer, circular and longitudinal muscle layer
• the stomach contracts in a variety of ways to churn food and mix it with gastric juice
• the food is converted to a thick soupy liquid called CHYME

Chemical digestion occurs through enzymes in the gastric juice.

• enzyme pepsin or gastric protease breaks the bonds between certain long chains of amino acids proteins into smaller ones chains called POLYPEPTIDES
• pepsin works in acidic conditions (reason for HCL - allows the pepsin to act and kill of bacteria )

The LINING OF THE STOMACH
* mucosa is specialised for the secretion of Gastric Juice
*gastric juice is secreted by gastric glands which are located in narrow, tube-like structures called gastric pits
*each HCL, digestive enzyme and mucus is secreted by different pit
* only some alcohol, drugs and aspirin are absorbed in stomach
* the pyloric sphincter is a thick circular muscle controlling the opening to the duodenum, pushed to small intestine via peristalsis
2-8hrs in stomach

Stomach Pepsin breaks down proteins o polypeptides

Question 17

What happens in small intestine?

Answer 17

• 6m long (longest part)
• duodenum is the first part (25cm)

Muscular contractions churn food, Bile is mechanical digestion as it is not an enzyme but a salt which Emulsifies fats, breaking them into tiny droplets
Bile increases surface area where lipase can act on to bring about chemical breakdown of fat

Digestion continues under the influence of

• intestinal juice secreted by glands in lining
• pancreatic juice secreted by pancreas
• bile secreted by liver stored in gall bladder

Pancreatic juice enters the duodenum to help neutralise the acid from stomach

• ribonuclease or dexoynuclease which are enzymes that digest RNA and DNA
• pancreatic amylase breaks down starch to disaccharides
• pancreatic protease breaks down proteins to polypeptides
• pancreatic lipase breaks down lipids into fatty acids and glycerol

Intestinal juices contain many different enzymes

• intestinal amylase to break down disaccharides into simple sugars
• intestinal protease (peptidases) break down peptides to AA’s
• intestinal lipase to break done lipids to fatty acids and glycerol

The small intestines absorbs simple sugars, AA’s, glycerol and vitamin,s minerals nutrients and water.

Question 18

Why is Small intestine good for absorption

Answer 18

• long 6m
• inner lining known as mucosa has folds that extend into interiors
• mucosa has finger like projections called villi that extend from folded surface (more SA)
• outsides of vili have microscopic projections called microvili

Question 19

Vili

Answer 19

Suited for nutrient absorption
1mm long
Inside is lymph capillary called a lacteal which is surrounded by a network of blood capillaries. Absorption is helped by muscular movements of intestinal wall that keep vili moving

Simple sugars such as glucose are absorbed via active transport - pass though cells on the outside of vili and into blood capillaries
Water and water soluble vitamins are absorbed into blood capillaries by diffusion

Fatty acids and glycerol are absorbed by simple diffusion
* in cells of vili the fatty acids and glycerol recombine to form fats - tiny droplets enter lacteal

Amino acids are absorbed by active transport into blood capillaries

Question 20

Long intestine

Answer 20

Caecum is a ouch (6cm long), where small instejne joins large intestine ( appendix is small tube attached to it with no function other than bacteria collection)

Lining secrets large amount of mucus 
Slow movement (18-24)hours 
The colon is the longest part and is an inverted U shake 

The rectum is last part - semi solid material left in colon after water absorption is pushed into the rectum by peristalsis
As walls of rectum stretch they trigger a response known as DEFAECAtion. The muscle around the anus relaxes and the faeces passes out

The anus is the external opening at end of rectum
Anal sphincter is a circular muscle around it which controllers opening and closing

Faces is expelled - water, undigested food, plant cellulose, bacteria, bile pigments (giving them colour)

Absorbs water and vitamins, stores faces and defaecation

Question 21

Diet affects aliamnetary canal

Answer 21

High fat and protein meals = slow movement
Alcohol and caffeine stimulate movement of stomach = fast
Large meals stretched out stomached - sends to small intestine after than intended

Question 22

Constipation

Answer 22

If movement of type large instestines are reduced and contents remain their for long periods oc time
Elimatiion becomes hurtful
As much water is absorbed - facaes become harder and drier
- lakc of roughage in diets Eg plant cellulose, lack of exercise or emotional problems

Question 23

Diahorrea

Answer 23

Frequent watery defacifcation
Irrigation to small or large intenstine incraesing peristalsis - bacteria or viral infection
Inadequate water absorption
Eg cholera

Question 24

Bowel cancer

Answer 24

Colorectal cancer is the uncontrolled growth kfcells in the all of the large intestine

• linked to diet, high alcohol consumption and smoking
• diet with red meat, low fibre (fruit and veg) have increased risk
• overnight or obsession and physical inactive are risk factor

Question 25

Imprortanve of fibre

Answer 25

• insoluble and soluble found in plants
  Soluble, - pectins, Gums and mucliage
• Lowr cholesterols levels, decreased risk of heart disease and cancer. Beneficially Effects on blood glucose levels
  Trap fats by soluble fibre they by help pens gn lower blood choker girl level
  Oat barley, veg soy , bran

Question 26

Coeliac disease

Answer 26

Unable to digest protein Gluten found in rye, wheat and barley
Immune system response by damaging or destroying vili in small instejne
Without healthy vili absorption cannot occur
Become malnourished no matter how much you eat

Symptoms vary - muscles cranks, joint pain, tingling in legs
Inherited no cure
Only treatment to follow gluten free diet.