Human Nutrition

Balanced diet

consists of all the food groups in the correct proportions.

Carbohydrates

provide energy for respiration in cells. Eg. pasta, rice, potatoes

Fats

used as long term stores of energy, layer of fat underneath skin acts as insulation. Eg. cheese, fatty meats, butter

Proteins

all cells contain protein, so it is a vital substance for growth and repair of tissues. Eg. fish, meat, eggs.

Vitamin C

maintain healthy skin and gums. deficiency causes scurvy where wounds do not heal and there is excessive bleeding like in gums. Eg. citrus fruits

Vitamin D

helps the body absorb calcium, which is needed for strong bones and teeth. Deficiency causes rickets causes weak or soft bones and deformities. Eg. dairy products, fish oil, eggs

Mineral ions: Calcium

needed for strong bones and teeth, plays a role in blood clotting. Eg. milk, cheese, eggs

Mineral ions: Iron

needed to make hemoglobin present in red blood cells, helps carry oxygen around the body. Eg. read meat, green vegetables like spinach

Fibre (roughage)

helps food to move through stomach and intestines. Eg. vegetables, fruits, whole grains

Water

needed for chemical reaction to take place in cells 

Digestive system

role is to break down large insoluble molecules into smaller soluble food molecules to provide the body with nutrients
eg. the alimentary canal: mouth, esophagus, stomach, small intestine (duodenum and ileum) and large intestine (colon, rectum, anus)
asc. organs: Salivary glands, pancreas, liver, gall bladder

Ingestion

the taking of substances eg. food and drink into the body

Digestion

the breakdown of food

Absorption

the movement of nutrients from the intestines to the blood, i.e. nutrients move from digestive system to circulatory system
e.g. small intestine where nutrients are absorbed, most water is absorbed in small intestine but also in colon

Assimilation

the uptake and use of nutrients i.e. nutrients move from circulatory system to cells

Egestion

removal of undigested food from the body as feces

Physical Digestion

the breakdown of food into smaller pieces without chemical change to food molecules,
increases the surface area of food for the action of enzymes in chemical digestion,
mainly carried out by the teeth, stomach, bile in duodenum

Teeth

canines, incisors, premolars, molars

Incisors

for biting and cutting

Canines

for tearing holding and biting

Premolars

for chewing and grinding

Molars

for chewing and grinding

Structure of tooth

enamel, cement, dentine, pulp cavity, nerves, blood vessels, bone, gums

Stomach

physical digestion occurs as the stomach walls to squeeze the food to liquify it i.e. the lining of the stomach contains muscles which contract to physically squeeze and mix the food with the strong digestive juices that are present in the stomach.

Bile

alkaline mixture that neutralises the acidic mixture of food and gastric juices entering the duodenum from the stomach, to provide a suitable pH for enzyme action.
It is made by the liver, stored in the gall bladder, secreted from bile duct into the duodenum for 2 reasons.
1. Alkaline so neutralises the hydrochloric acid which comes from the stomach. 2. Breaks down large drops of fat into smaller ones, aka emulsification. 

Chemical Digestion

the breakdown of large insoluble molecules into small soluble molecules,
the role of chemical digestion is to produce small soluble molecules that can be absorbed 

Digestive enzymes

1. Amylase: starch to maltose e.g. produced in salivary glands acts in mouth, duodenum
2. Maltase: maltose to glucose e.g. produced in pancreas and acts in membranes of the epithelium lining the small intestine
3. Protease (pepsin): protein to amino acids e.g. produced and acts in stomach where acidic conditions
4.  Protease (trypsin): protein to amino acids e.g. produced in pancreas, acts in duodenum where alkaline conditions
5. Lipase: breaks down fats and oils into fatty acids and glycerol e.g. produced in pancreas, acts in duodenum

Functions in HCL in gastric juices

killing harmful microorganisms in food, provides an acidic pH for optimum enzyme e.g. pepsin activity

Villi

The ileum is adapted for absorption as it has a highly folded surface with millions of villi and microvilli, which are tiny fingerlike projections.
These greatly increase the internal surface area of the ileum, allowing absorption to take place faster and efficiently

Structure of villus

thin surface layer,
microvilli,
capillaries: absorb glucose and amino acids and carry it away from the small intestine in the blood,
blood vessels,
lacteals: absorb fatty acids and glycerol and transport them away from the small intestine in the lymph