Digestion

Nutrition

The process by which organisms obtain and use food

Digestion

The physical and chemical breakdown of food into small soluble particles that can be absorbed into the blood

Absorption

The movement of digested food from the digestive system into the blood

Ingestion

The taking of food into the alimentary canal

Egestion

The removal of undigested and unabsorbed material as faeces

Autotrophs

Organisms that make their own food (e.g. plants by photosynthesis)

Heterotrophs

Organisms that cannot make their own food and must obtain food from other organisms

Herbivores

Animals that are adapted to feed only on plants (rabbit)

Carnivores

Animals that feed only on other animals (sparrow hawk)

Omnivores

Animals that are adapted to feed on both plants and animals (badger)

Alimentary canal

A long tube from mouth to anus through which food passes

Peristalsis

Wave-like contractions of circular and longitudinal muscles that move food along the alimentary canal

Physical digestion

The breakdown of food into smaller pieces without changing its chemical nature

Chemical digestion

The breakdown of food by enzymes into smaller soluble molecules

Function of incisors

Cutting and slicing food

Function of canines

Tearing food

Function of premolars and molars

Crushing and grinding food

Saliva

Moistens food and contains amylase

Salivary amylase

Breaks down starch into maltose

pH of saliva

Approximately pH 8 (alkaline)

Gastric juice

Produced in the stomach and contains Hydrochloric acid, pepsin and mucus. Pepsin is secreted as pepsinogen and converted to active pepsin by stomach acid.

Hydrochloric acid (HCl)

Kills bacteria and provides acidic conditions for pepsin to work at optimum rate

Pepsin

Protease enzyme that breaks proteins into peptides

Pepsinogen

Inactive form of pepsin

Why pepsin is secreted inactive

To prevent digestion of the stomach lining

Role of mucus in stomach

Protects stomach lining from acid and enzymes

Chyme

Liquid mixture of food and gastric juices in the stomach

Sphincter muscles

Circular muscles that control movement of food between organs

Small intestine

Where most digestion and absorption occur

Parts of small intestine

Duodenum, jejunum and ileum

Length of small intestine

Approximately 7 metres

Duodenum

Main site of chemical digestion, where pancreatic enzymes that were produced in the pancreas are digested into the duodenum

Secretions entering duodenum

Bile, pancreatic juice and intestinal juice

Exocrine function of pancreas

Starch-pancreatic amylase-maltose

Lipids-pancreatic lipase-fatty acids

Proteins-trypsin-peptides

Bile

Produced in the liver and stored in the gall bladder

Functions of bile

Neutralises stomach acid using sodium bicarbonate and emulsifies fats

Emulsification

Breaking fats into small droplets to increase surface area for lipase

Pancreas

Produces pancreatic juice containing enzymes and sodium bicarbonate

Function of sodium bicarbonate

Neutralises acidic chyme from the stomach

Pancreatic amylase

Breaks starch into maltose

Pancreatic lipase

Breaks lipids into fatty acids and glycerol

Trypsin

Protease that breaks proteins into peptides

Ileum

Main function is absorption

Villi

Finger-like projections that increase surface area

Microvilli

Further increase surface area on villi

Thin epithelium

Allows faster diffusion during absorption

Mitochondria in villi

Provide energy for active transport

Capillary bed in villi

Allows rapid transport of absorbed nutrients

Adaptions of Villi

1. Large surface area

2. Network of blood capillaries and lacteal from lymph system

Lacteal

Lymph vessel that absorbs fats

Absorption of sugars and amino acids..

Into blood capillaries

Absorption of fats..

Into lacteals as fatty acids and glycerol

Hepatic portal vein

Carries absorbed nutrients from intestine to liver

Large intestine

Absorbs water and forms faeces

Symbiotic bacteria

Bacteria that live in the gut and provide benefits

Role of symbiotic bacteria

Produce vitamins B and K and protect against pathogens

Fibre

Indigestible plant material

Role of fibre

Retains water, aids peristalsis and reduces constipation

Liver

Located in upper right side of abdominal cavity

Homeostasis function of liver

Produces heat and regulates blood composition

Deamination

Removal of amino group from excess amino acids, products are excreted into the kidney

Urea

Formed in liver from ammonia and excreted by kidneys

Excretion by liver

Removal of bile pigments and excess cholesterol

Detoxification

Removal of toxins such as alcohol and nicotine

Storage function of liver

Stores glycogen, iron and fat-soluble vitamins (A, D, E, K)

Assimilation

Sorting and use of absorbed food by the body

Portal system

Blood pathway that begins and ends in capillaries

Balanced diet

A diet containing all essential nutrients in correct proportions

Stages of human nutrition

Ingestion, digestion, absorption, egestion

Obesity

Unhealthy excess body fat

Anorexia

Unhealthy low body weight due to fear of weight gain