Chapter 27 - Digestive System

Nutrition

The way in which organisms get chemicals and energy from their environment

Ingestion

Taking of food into the digestive system

Digestion

The breakdown of food chemically and mechanically

Absorption

Digested food passes from the intestine into the blood

Assimilation

The movement if products of digestion into your cells

Egestion

The removal of unabsorbed waste from the digestive system

Where does digestion occur

Mouth, stomach, duodenum

Why is digestion important

Necessary for food particles to be absorbed and transported

Difference between mechanical and chemical digestion

Mechanical is the physical breakdown of food, chemical is the breakdown of food using enzymes

2 Example of mechanical digestion

Chewing or grinding of food, churning of food in the stomach

Why is mechanical digestion important

Increases the surface area of food particles allowing enzymes to work better

Example of chemical digestion

Enzyme Amylase breaking down starch into maltose

What is a gland

Produces and secretes a substance

Function & Shape of incisors

Cut and slice, chisel shaped

Function & Shape of canines

Grip and tear, fang-like teeth

Function & Shape of Pre molars

Crush, grind and chew, flat surfaced

Function & Shape of Molars

Crush, grind and chew, large teeth with cusps

Salivary glands produce saliva. What is saliva made up of?

Mucus, buffers, salts, water,

2 enzymes - lysozyme to break down bacteria, amylase

Ball of food is also known as….

Bolus

epiglottis

A flap of tissue that closes over the trachea when food is swallowed to ensure food e tears the oesophagus

Function of oesophagus

Carry food from the mouth to the stomach

Peristalsis

An involuntary wave of muscular contraction that moves food through the GI tract

3 roles of dietary fibre

1. Reduces the risk of constipation - fibre in our intestines absorb water causing it to swell resulting in the intestines becoming stimulated so that peristalsis occurs.

2. Fibre is a source of food for the bacteria that live in our large intestine

3. Reduces the risk of colon cancer - fibre causes wastes to move through our intestines rapidly reducing the risk of carcinogens affecting intestinal cells.

2 main functions of the stomach

Digestion and storage

2 functions of HCL in the stomach

1. Kills most bacteria

2. Allows protein-digesting enzymes called proteases e.g. pepsin to break down proteins

What is chyme

a soupy liquid formed as a result of churning of food in the stomach

What does storage in regards to digestion mean

Food remains in the stomach between 2 to 6 hours allowing time for bacteria to be killed and for digestion

What is the name of the top and bottom muscles of the stomach that prevent food from leaving

Cardiac sphincter (top), Pyloric sphincter (bottom)

2 parts of the small intestine

Duodenum, ileum

Function of duodenum

Digestion

What and why does the pancreas produce

Produces sodium bicarbonate which neutralises chyme coming from the stomach. This leaves the pH of the small intestine between 7 and 8

What passes through the pancreatic duct

Enzymes - into the duodenum

What hormone does pancreas produce

Insulin

4 functions of the Liver

1. Converting glucose to glycogen for storage

2. Storing of vitamins and minerals

3. Producing heat to warm the body

4. Forming bile

Bile

a yellow/green liquid made of water, bile salts and bile pigments stored in the gallbladder

3 functions of bile

1. Bile salts emulsify lipids - form of mechanical digestion. Droplets can be more easily digested by enzymes in the duodenum as this creates a larger surface area

2. Bile neutralises the acidic chyme - bile contains sodium bicarbonate which is an alkaline

3. Bile excretes pigments made from damaged red blood cells

Function if ileum

Absorption - digested products pass from the ileum into the blood

Why is Villi and Microvilli important for absorption

Increase the surface area for absorption

Water-soluble nutrients absorbed by the ileum

Amino acids, glucose, vitamins B and C, minerals

Hepatic portal vein

Carries absorbed nutrients from the ileum to the liver to be sorted

Adaptations of the ileum and villi for absorption

• there are large numbers of villi giving a large surface area

• The lining of the villi is only one cell thick to allow for fast diffusion

• The villi have a rich bloody supply so that nutrients that can be absorbed into the blood stream

Function of large intestine

Reabsorb water

Where does most reabsorption happen in the large intestine

Colon

Give 2 importances of gut microbiome

1. Feed on our waste and produce vitamins B and K

2. Fight pathogenic bacteria

What is the relationship in the colon called

Mutual symbiotic relationship

Constipation

Unabsorbed waste waste moves too slowly through the colon due to too much water being reabsorbed

Diarrhoea

Waste travels too quickly through the colon due to too little water being reabsorbed. Waste had too much liquid