Chapter 14 (Digestive system)

Why do we need to eat?

The food we eat provides us with nutrients that allows our body cells to undergo respiration to release energy for cellular activities.

Types of nutrients (main 3 to focus on)

Carbohydrates, protein and fats

Examples of carbohydrates

Rice, bread, biscuits and noodles, etc.

Examples of protein

Fish, tofu and milk, etc.

Other types of nutrients that are required for body to function properly?

Vitamins, water, fibre and mineral salts

How do nutrients enter our body cells?

Higher concentration of nutrients in the blood capillaries diffuses into the body cells, where there is a lower concentration of nutrients.

How do Unicellar Organisms absorb nutrients?

Via diffusion

How do multicellular organisms absorb nutrients?

Requires a digestive system to break down large and insoluble food molecules into smaller and soluble food molecules to be absorbed into the bloodstream for the body cells to undergo respiration to release energy for various cellular activities, such as cell repair and growth

Respiration releases energy

"Not produces energy" as energy can neither be created not destroyed

What are two processes that food goes through when it moves down the digestive tract?

Physical and chemical digestion

What is physical digestion?

The process of food being broken up by the teeth into smaller pieces by physical or mechanical means such as chewing, grinding, mixing or crushing

What is chemical digestion?

The process of larger and insoluble food molecules being broken down into smaller and soluble food molecules through the action of enzymes

What are enzymes?

Enzymes are biological molecules produced by the digestive system and are highly specific as they only act on one type of substance

Function of enzymes?

To speed up the breakdown of large and insoluble food molecules into smaller and soluble food molecules.

Difference between "break up" and "break down" of food molecules?

Break up— to change in size and shape (from bigger pieces to smaller pieces)
Break down—to change in form

Types of enzymes

Carbohydrases, proteases and lipases

Function of carbohydrases

Carbohydrases—- speed up digestion of carbohydrates into simple sugars

Function of proteases

Proteases—-to speed up the digestion of proteins into amino acids

Function of lipases

Lipases—- to speed up the digestion of fatty acids ad glycerol.

end products of digestion

Simple sugars, amino acids, fatty acids and glycerol are small and soluble molecules that will be absorbed into the bloodstream via the small intestine and transported to all parts of the body.

Parts of the digestive system (in order)

Mouth, oesophagus, stomach, small intestine , large intestine, rectum and anus,

Function of digestive system

To break down large and insoluble food molecules into smaller and soluble food molecules so that they can be absorbed into the bloodstream for the body cells to undergo respiration to release energy for various cellular activities

Physical digestion in mouth

Strong teeth and jaw muscles in the mouth cut, crush and grind food into smaller pieces

Chemical digestion in mouth

Saliva containing carbohydrases partially digests starch.

Function of saliva

To soften the food in the mouth and lubricate it for easier swallowing

Where does starch digestion begin?

In the mouth

Purpose of chewing food into smaller pieces

To increase the surface area for faster partial digestion by carbohydrases

Chemical digestion in oesophagus

No presence of enzymes, digestion of starch continues, no new digestion

Function of oesophagus

Muscles for oesophagus contract and relax to help push food towards stomach

Physical digestion in stomach

Stomach churns food into smaller pieces

Chemical digestion in stomach

Stomach releases gastric juice which contains proteases that digest protein.

Where does protein digestion start?

It starts in the stomach

Functions of the stomach

To release gastric juice containing dilute hydrochloric acid, to kill harmful microorganisms and provide the right conditions for proteases to digest protein

How does stomach protect itself from dilute hydrochloric?

Stomach has a thick layer of mucus to protect its tissues from damage chased by the dilute hydrochloric acid and proteases in the gastric juice.

How does food enter and leave the stomach?

The stomach muscles contracts and relax to control the food entering and leaving the stomach

Is there physical digestion in the small intestine?

No

Chemical digestion in the small intestine

The small intestine is the main site for chemical digestion in the body. Fats are digested by lipases in the small intestine while all carbohydrases, lipases and proteases are present in the small intestine, therefore digestion of carbohydrates, proteins and fats are completed in the small intestine.

Where does fat digestion begin and end?

It begins and ends in the small intestine

Where does carbohydrate digestion begin and end?

It begins in the mouth and ends in the small intestine

Where does protein digestion begin and end?

Protein digestion begins in the stomach and ends in the small intestine

Where is digestion of food fully completed

It is fully completed in the small intestine

Where does water absorption begin?

It begins in the small intestine

Where does the absorption of digested food and water begin?

It begins in the small intestine

Function of large intestine

The function of the large intestine is to absorb water and mineral salts

Function of rectum

To store faeces

What is faeces

Faeces is the undigested food and waste

Function of anus

Faces is released through this opening

Carbohydrate digestion

Mouth: starch is partially digested by carbohydrases in the mouth
Gullet: no new starch digestion, starch from the mouth continues to be digested
Stomach: no chemical digestion takes place
Small intestine: all carbohydrates are completely digested by carbohydrases into simple sugars such as glucose

Protein digestion

Mouth: no chemical digestion takes place
Gullet: no chemical digestion takes place
Stomach: intermediate protein digestion by proteases begins here
Small intestine: all proteins are completely digested by proteases to form amino acids

Fat digestion

Mouth: no chemical digestion
Gullet: no chemical digestion
Stomach: no chemical digestion takes place
Small intestine: fat digestion by lipids begins and ends here to form fatty acids and glycerol

Function of digestive system

To break down larger and insoluble food molecules into smaller and soluble food molecules to be absorbed into the bloodstream and into our body cells to undergo respiration to release here for cellular activities

Why is the digestive system made up of different organs

Not a single organ can complete digestion on its on therefore Every organ in the digestive system works together to break down large and insoluble food molecules into smaller and soluble food molecules to be absorbed into the bloodstream quickly and completely in order for the body to use the digested food effectively.