5. Human Digestive System

Question 1

Digestion

Definition

Answer 1

Digestion is the process that breaks down complex food substances into simple, soluble molecules that are small enough to be absorbed into body cells.

Question 2

Physical Digestion

Definition + Examples

Answer 2

Physical digestion is the mechanical breakdown of food into smaller particles to increase the surface area to volume ratio, for a faster rate of chemical digestion by digestive enzymes.

Examples: Chewing in mouth, churning action in stomach, emulsification of fats in duodenum

Question 3

Chemical Digestion

Definition

Answer 3

Chemical digestion is the breakdown of large food molecules into small soluble molecules, catalysed by digestive enzymes through hydrolytic reactions.

Question 4

Ingestion

Definition

Answer 4

Ingestion is the act of taking food into the mouth.

Question 5

Digestion in the mouth

Types of digestion that take place + What happens after

Answer 5

Physical digestion: Chewing
Chemical digestion: Salivary amylase

Afterwards, the thoroughly chewed food is rolled into a bolus by the tongue. The bolus is then swallowed and enters the oesophagus.

Question 6

Saliva

Where it is produced + What it contains + Function

Answer 6

• Produced by salivary glands in the mouth
• Contains salivary amylase which digests starch into maltose
• Help to soften and moisten food

Saliva has a pH of 6.5 - 7.5

Question 7

Salivary Amylase

What it is + Where it is found + Function + Optimum pH

Answer 7

• Salivary amylase is an enzyme found in saliva
• Digests starch into maltose
• Optimum pH of 6.5 to 7.5

Question 8

Peristalsis

Definition + Function + State of muscles

Answer 8

Peristalsis is the rhythmic, wave-like, muscular contractions of the wall of the alimentary canal.

It functions to mix and propel food down the alimentary canel.

Behind the food:

• Longitudinal muscles are relaxed
• Circular muscles are contracted

The alimentary canel is the digestive tract from the mouth to the anus

Question 9

Stomach

What it is

Answer 9

An elastic, muscular bag with thick muscular walls.

Stomach has pH 2

Question 10

Gastric Juice

Where it is produced + What it contains

Answer 10

• Secreted by gastric glands in the stomach when the bolus enters the stomach
• Contains mainly hydrochloric acid, pepsin & rennin

Question 11

Hydrochloric acid in the stomach

Function

Answer 11

1. Provides an acidic medium suitable for the action of enzymes in the stomach
2. Kills bacteria
3. Changes inactive forms of enzymes to active forms: converts pepsinogen to pepsin

Question 12

Pepsin

What it is + Where it is found + Function + Optimum pH

Answer 12

• Pepsin is an enzyme found in gastric juice
• Digests proteins into polypeptides
• Optimum pH of 2

Polypeptides are long chains of amino acids

Question 13

Rennin

What it is + Where it is found + Function

Answer 13

• Rennin is an enzyme found in gastric juice
• Converts soluble milk protein caseinogen into insoluble caesin, causing coagulation of milk

Coagulation: process of a liquid changing to a solid/semi-solid state

Question 14

Digestion in the stomach

Types of digestion that take place + What happens after

Answer 14

Physical digestion: Churning
Chemical digestion: Pepsin

After a few hours, the partly digeted food will become liquified, forming chyme, which passes into the duodenum in small amounts.

Question 15

Churning

What it is + Function

Answer 15

Churning is a form of physical digestion in the stomach.

Function is to:

1. Mix food with gastric juice
2. Break down food into smaller particles to increase the surface area to volume ratio, for a faster rate of chemical digestion by digestive enzymes

Question 16

What are the 3 sections of the small intestine?

Answer 16

Duodenum, jejunum & ileum (highly coiled)

Question 17

Digestion in the small intestine

Types of digestion that take place

Answer 17

Physical digestion: Emulsification of fats by bile
Chemical digestion: 8 types of digestive enzymes

Question 18

Bile

What it is + Where it is produced + Function

Answer 18

What it is:

• Bile is a thick, yellowish-green fluid
• Contains bile salts and bile pigments
• Alkaline - neutralises chyme from the stomach

Where it is produced:

• Produced by liver, stored in gall bladder temporarily, secreted into the duodenum via the bile duct

Function:

• Functions to emulsify fats, to physically break down large fat droplets into tiny fat droplets to increase surface area to volume ratio for a higher rate of chemical digestion by lipases
• Creates an alkaline environment suitable for the action of enzymes by reducing the acidity of chyme

Question 19

Enzymes secreted by the pancreas via the pancreatic duct

Names + Functions

Answer 19

• Pancreatic amylase - digests starch into maltose
• Trypsin - digests proteins into polypeptides
• Pancreatic lipase - digests fats into fatty acids + glycerol

Question 20

Enzymes secreted by intestinal glands

Names + Functions

Answer 20

• Maltase - digests maltose into glucose
• Sucrase - digests sucrose into glucose + fructose
• Lactase - digests lactose into glucose + galactose
• Peptidase - digests polypeptides into amino acids
• Intestinal lipase - digests fats into fatty acids + glycerol

Question 21

Gall bladder

Function

Answer 21

• Stores bile produced by the liver temporarily
• Secretes bile into the duodenum via the bile duct

Question 22

Components of Undigested and Unabsorbed Matter in the Large Intestine

Answer 22

• Mainly cellulose
• Water
• Bile pigments
• Dead cells from intestinal lining
• Dead & live bacteria

Question 23

Large Intestine

Function

Answer 23

Large intestine functions to absorb water (by osmosis) and mineral salts (by facilitated diffusion or active transport) from undigested matter into the blood stream.

Question 24

Egestion / Defecation

Definition

Answer 24

Egestion/defacation is the elimination of undigested material from the alimentary canal.

Question 25

4 adaptations of the small intestine

Answer 25

1. Small intestine is long: To provide sufficient time for absorption of nutrients to take place 2. Inner walls of the small intestine have many transverse folds bearing many finger-like projections called villi. Each villus possesses numerous microvilli: To increase the surface area to volume ratio *for faster absorption of digested food substances by diffusion* 3. The epithelium of the villus is 1 cell thick: To reduce the distance for digested products to diffuse into the cappilaries and lacteal, *for faster absorption of digested food substances by diffusion* 4. The small intestine consists of a dense network of blood capillaries and lacteal within the villi: The continuous transport of digested food substances away from the small intestine maintains a steep concentration gratident, *for faster absorption of digested food substances by diffusion*

Question 26

Products of Digestion

Answer 26

- Monosaccharides (glucose, fructose, galactose) - Amino acids - Fatty acids - Glycerol - Water The products of digestion are absorbed throughout the small intestine, especialy in the highly coiled ileum.

Question 27

Glucose and amino acids in the small intestine | How they are absorbed + How they are transported away

Answer 27

Glucose and amino acids are absorbed by facilitated diffusion or active transport (depending on the concentration gradient between the intestinal lumen and blood capillaries) into the blood capillaries of the villi. Blood capillaries join to form venules which then join to form the hepatic portal vein. The hepatic portal vein carries blood rich in glucose and amino acids to the liver to be processed.

Question 28

Fatty acids and glycerol in the small intestine | How they are absorbed + How they are transported away

Answer 28

Fatty acids and glycerol are absorbed by simple diffusion into the epithelial cells of the villi, where they recombine to form minute fat globules, which then diffuse into the lacteal. Fat globules are transported away from the small intestine by the lacteal.

Question 29

Assimilation | Definition

Answer 29

Assimilation is the utilisation of absorbed nutrients and how the body deals with excess nutrients.

Question 30

Assimilation of Glucose | Utilisation + How the body deals with excess

Answer 30

Utilisation: - Glucose is a substrate for respiration to release energy for cellular activities. How the body deals with excess (high blood glucose concentration): - Excess glucose is converted into glycogen by the liver cells and stored. - This is stimulated by insulin, a hormone produced by islets of Langerhans in the pancreas. When there is low blood glucose concentration: - When blood glucose is low, glycogen is converted into glucose by the liver cells. - This is stimulated by glucagon, a hormone produced by islets of Langerhans in the pancreas.

Question 31

Assimilation of Amino Acids | Utilisation + How the body deals with excess

Answer 31

Utilisation: - Used in the synthesis of new cells, for growth and repair of worn out cells. - To synthesise important proteins: enzymes, hormones, antibodies, transport & structural proteins. How the body deals with excess: - Excess amino acids are deaminated in the liver. - Their amino group is removed and converted into urea. - The remaining carbon residue is converted into glucose.

Question 32

Assimilation of Lipids | Utilisation + How the body deals with excess

Answer 32

Utilisation: - Required to maintain cell membranes (phospholipid bilayer). - Required to produce steroid hormones. - Required to protect vital organs. - When there is inadequate supply of glucose and glycogen, fats will be broken down in the liver to provide energy. How the body deals with excess: - Excess lipids are stored in adipose tissues under the skin. - In adipose cells, fat droplets can collect in the cytoplasm and increase in size and number to form one large globule of fat in the middle of the cell, pushing the cytoplasm into a thin layer and nucleus to one side. - Groups of adipose cells form adipose tissue.

Question 33

Liver | 6 main functions

Answer 33

1. Bile production (plays a role in digestion of fats) 2. Regulation of blood glucose (homeostasis) 3. Protein synthesis of proteins in blood (e.g. fibrinogen) 4. Deamination of excess amino acids 5. Breakdown of red blood cells 6. Detoxification

Question 34

Breakdown of red blood cells by the liver

Answer 34

The liver breaks down haemoglobin in red blood cells and stores the released iron.

Question 35

Detoxification of blood by liver

Answer 35

The liver converts harmful substances into harmless ones. Enzymes (alcohol dehydrogenase) break down alcohol into acetaldehyde, which can be futher broken down into glucose. Catalase breaks down hydrogen peroxide (toxic by-product of celluar activities) into water and oxygen.

Question 36

Effects of excessive alcohol consumption

Answer 36

Alcohol is a depressant (slows down brain and nervous system) that when consumed in excess, results in: - reduced self-control - longer reaction times / slower reflex action - cirrhosis of the liver