Human nutrition

What is a balanced diet?

A diet that contains all the nutrients in the right proportions relative to lifestyle

What are the nutrients that should be included in a balanced diet?

Carbohydrates

Protein

Lipids

Vitamins

Minerals

Dietary fibre

Water

Sources, functions & deficiency symptoms of carbohydrates

Sources → Bread, rice, pasta, potatoes

Functions → To provide energy

Deficiency symptoms → Lack of energy, low blood sugar levels (hypoglycemia)

Sources, functions & deficiency symptoms of protein

Sources → Meat, fish, eggs, pulses

Functions → Growth & repair, production of enzymes, hormones & anitbodies, some are used structurally for hair & nails

Deficiency symptoms → Stunted growth, kwashiorkor

Sources, functions & deficiency symptoms of lipids

Sources → Butter, oils, dairy products

Functions → Energy source, insulation, protection of organs

Deficiency symptoms → Lack of energy

Sources, functions & deficiency symptoms of vitamin A

Sources → Carrots, green vegetables

Functions → Needed for vision, helps cell growth & healthy skin

Deficiency symptoms → Night blindness

Sources, functions & deficiency symptoms of vitamin C

Sources → Citrus fruit

Functions → Keeps healthy skin, teeth & gums, helps absorb iron

Deficiency symptoms → Scurvy

Sources, functions & deficiency symptoms of vitamin D

Sources → Sunlight, dairy products, oily fish

Functions → Helps to absorb calcium

Deficiency symptoms → Rickets

Sources, functions & deficiency symptoms of calcium

Sources → Dairy products

Functions → Strengthens teeth & bones, prevents blood clotting

Deficiency symptoms → Rickets

Sources, functions & deficiency symptoms of iron

Sources → Red meat, spinach

Functions → Needed for haemoglobin

Deficiency symptoms → Anaemia

Sources, functions & deficiency symptoms of dietary fibre

Sources → Wholegrains, vegetables

Functions → Helps food move along the digestive system by efficient peristalsis

Deficiency symptoms → Bowel cancer, constipation

Sources, functions & deficiency symptoms of water

Sources → Water, fruits

Functions → Needed for cell reactions to take place, temperature control, transport

Deficiency symptoms → Dehydration, headaches

How do energy requirements vary with age?

Young children & teenagers need more energy because they are rapidly growing & developing

Adults & elderly need less energy as they have stopped developing & they often have lower activity levels

How do energy requirements vary with activity levels?

People who have high activity levels need more energy to replenish the energy they used during their activity

People who have low activity levels do not require as much energy

How do energy requirements vary with pregnancy?

Pregnant women need more energy for the growth & maintenance of the foetus

The also need more energy for the extra weight they are carrying

Label this diagram of the digestive system

Mouth

Chews up food to make it easier to swallow

This also increase the surface area, making it easier for digestive enzymes to act on it

Tongue

Helps chewed food form a ball called a bolus

Salivary gland

Releases saliva which moistens & lubricates food, making it easier to swallow

Saliva contains amylase which helps break down carbohydrates

Oesophagus

Connects the mouth to the stomach

Boluses move down it by the wave-like contractions created by circular muscles & longitudinal muscles that make a squeezing action

Stomach

Releases gastric juice which contains hydrochloric acid & pepsin

Pepsin breaks down protein & hydrochloric acid kills bacteria & provides the optimum pH (pH 2) for pepsin

Muscular movements in the stomach wall help to churn food into chyme

Liver

Produces bile

Excess glucose is removed from the blood & stored as glycogen

Excess amino acids cannot be stored so are broken down to form urea which is then passed to the kidney

Gall bladder

Bile is stored here & passed into the small intestine through the bile duct

Bile

Alkaline to neutralise the hydrochloric acid from the stomach when it enters the small intestine

Emulsifies large drops of fat into smaller droplets which increases the surface area, therefore allowing lipase enzymes to break it down faster

Pancreas

Secretes carbohydrase, protease & lipase enzymes into the small intestine

Small intestine (duodenum)

First part of the small intestine

Completes the breaking down of food using carbohydrase, protease & lipase enzymes

Small intestine (illeum)

Second part of the small intestine

Lined with villi which helps absorb digested food back into the blood

Large intestine

Absorbs water & some vitamins from indigestible food to produce faeces

Rectum

Where faeces is compacted & stored

Anus

Where faeces is egested out of the body

How is food moved through the gut by peristalsis?

Muscular tissue all throughout the alimentary canal squeezes balls of food (boluses) through the gut

These waves of circular muscle contraction that squeeze the food down is called peristalsis

Without peristalsis bits of food would clog up the gut

Carbohydrase enzymes break down ____

Starch is broken down into ____ by ____ enzymes

Maltose is broken down into ____ by ____ enzymes

1 = Carbohydrates

2 = Maltose

3 = Amylase

4 = Glucose

5 = Maltase

Protease enzymes break down ____

____ enzymes are found in the stomach & break down protein into peptides

Trpepsin also break down protein into peptides but are found in the ____

____ enzymes break down peptides into amino acids

1 = Protein

2 = Pepsin

3 = Small intestine

4 = Peptidase

Lipids are broken down by ____ enzymes into ____ & ____

1 = Lipase

2 = 3 fatty acids

3 = glycerol

How has the small intestine adapted for absorption?

- Very long which gives enough time for food to be broken down & absorbed

- Covered in millions of villi which provides a large surface area for absorption

How have villi adapted for absorption?

- Covered in microvilli which increases the surface area

- Surrounded by capillaries which provides a steep concentration gradient

- Has a single layer of permeable cells (epithelial cells) which decreases the diffusion distance

- Epithelial cells contain lots of mitochondria to provide energy for active transport

Ingestion is…

The intake of food into the body via the mouth

Digestion is…

The breaking down of large soluble food into smaller soluble molecules

Absorption is…

When small soluble food molecules are taken back into the blood through the wall of the intestine

Assimilation is…

The manufacturing of new substances in cells using the products of digestion

Egestion is…

The removal of undigested food via the anus

What is the difference between egestion & excretion?

Egestion is the removal of undigested food as faeces via the anus whereas excretion is the removal of metabolic waste products

(e.g. CO₂ via the lungs, urine via the kidney, sweat via the skin)