Nutrition in humans

Carbohydrates

• FUNCTION - Provides energy

• SOURCES - potatoes (starch) fruit (sugar)

Lipids

• FUNCTIONS -

  1. long term energy store,

  2. heat insulation,

  3. protection of vital organs,

     1. main component of cell membranes

        SOURCES - butter, and olive oil

Protein

• FUNCTION - growth and repair of muscles (biological cells)

• SOURCES - meat and eggs

Protein - digestive system

• breaks down nutrients from food into small pieces that can be readily absorbed

  eg. amylase, lipase, pepsin

Protein - transport

• carries oxygen in red blood cells

  eg. haemoglobin

Protein - structure

• makes hair and muscles

  eg. keratin and collagen

Protein - hormone signaling

• coordinates the activity of different body systems

  eg. insulin

Protein - defense

• protects body from foreign pathogens

  eg. antibodies

vitamin A

• FUNCTION - Improves vision, skin and hair health

• SOURCES - liver

Vitamin C

• FUNCTION - prevents scurvy

• SOURCES - Citrus fruit

Vitamin D

• FUNCTION - calcium absorption

• SOURCES - eggs

Calcium

• FUNCTION - Strong bones and teeth

• SOURCES - milk and cheese

Iron

• FUNCTION - needed to make haemoglobin

• SOURCES - Red meat

Water

• FUNCTION - always needs replacing due to water loss from breathing, urinating and sweating.

Dietary fibre

• FUNCTION - Aids the movement of food through the gut.

• SOURCES - Wholemeal bread

Mouth

• teeth chew food through mechanical digestion. Increases surface area for enzymes to work efficiently.

• digestive enzymes, released from salivary glands, break down food molecules.

Oesophagus

muscular tube that connects mouth → stomach

• waves of muscular contractions move food down oesophagus (peristalsis)

stomach

• mechanical digestion (churning)

• chemical digestion (enzymes)

adaptations of the stomach

hydrochloric acid in the stomach:

1. kills bacteria

2. provides an optimum pH (pH2) for pepsin.

Small intestine - duodenum

• movement of contents along intestine.

• this is powered by muscle contractions in intestine walls (peristalsis)

small intestine - ileum

• main region of chemical digestion

• absorption of digestion products into bloodstream

adaptations of the villi

lining of small intestine folded into finger like projections called villi.

• provide a large surface area, which increases absorption of small food molecules into bloodstream.

lacteal

• central vessel in villi responsible for absorption of fats

• transports products of fat digestion

large intestine - colon

• water remaining in waste products is absorbed back into bloodstream.

• sodium and potassium (salts) absorbed

• undigested food and bacteria left as waste

large intestine - rectum

• rectum stores faeces until removed by egestion in the anus

Pancreas

manufactures and secretes enzymes into small intestine:

• amylase - breaks down starch → maltose

• protease - breaks down proteins

• lipase - breaks down fats

Peristalsis

• wave like motion in the gut caused by the contraction and relaxation of muscles in the intestine.

• this moves the bolus through the intestines.

where is bile produced?

• produced by liver

• stored in gallbladder

• secreted into large intestine

bile

yellow/green liquid

• neutralizes stomach acid (some hydrochloric acid released into large intestine with digested food.)

• creates alkaline environment need for enzyme function in small intestine

• emulsifies fat, increasing surface area for enzymes to break down lipids

describe an experiment to determine the energy content of a food sample

1. measure water into boiling tube.

2. record temperature of the water at start.

3. weigh a small portion of food sample.

4. hold the burning food sample under the test tube, so the flame touches the tube.

5. record the increased temperature of the water.

6. calculate energy content of food sample

equation to calculate energy content of a food sample

energy transferred (Joules) =

mass of water x 4.2 x temp. increase/mass of food sample

explain the digestion of starch

1. salivary amylase breaks down starch into polysaccharide starch.

2. becomes disaccharide maltose.

3. maltase breaks down maltose into glucose.

explain the digestion of protein

1. protease breaks down proteins into amino acids

explain the digestion of lipids

1. lipase breaks down lipids into fatty acid and glycerol.

   the new products are made into new products or respired for energy.

5 stages of digestion - INGESTION

Food put into system (eating)

5 stages of digestion - DIGESTION

Food broken down into smaller pieces

5 stages of digestion - ABSORPTION

small molecules absorbed by cells

5 stages of digestion - ASSIMILATION

building molecules into useful components

5 stages of digestion - EGESTION

removal of non-digested material (poo and waste products)

Explain how the villi is adapted for the absorption of amino acids and glucose

• large SA: microvilli on the surface of the villus further increase the SA for absorption.

• short diffusion distance: the villi walls are only one cell thick.

• steep concentration gradient: villi have network of blood capillaries that transport glucose and amino acids away from the small intestine.