Nutrition & Digestive System

• Nutrition is the process of taking in food, breaking it down, absorbing it and using it for energy, growth and repair.
• Food is both the body's fuel (for energy) and its building material (for new and repaired cells).
• Digestion is the breaking of large, complex food molecules into small, simple, soluble molecules the blood can absorb.
• Soluble means the molecules can dissolve in watery blood and be carried everywhere.
• Autotrophs (green plants) make their own food by photosynthesis; heterotrophs (animals, humans) must eat others.
• Humans are heterotrophs and cannot make their own food.
• Autotroph — Self-feeding (makes food) — Green plants
• Heterotroph — Feeds on others — Animals, humans

Nutrition is the process of taking in food, breaking it down, absorbing it and using it for energy, growth and repair.

Food is both the body's fuel (for energy) and its building material (for new and repaired cells).

Digestion is the breaking of large, complex food molecules into small, simple, soluble molecules the blood can absorb.

Soluble means the molecules can dissolve in watery blood and be carried everywhere.

Autotrophs (green plants) make their own food by photosynthesis; heterotrophs (animals, humans) must eat others.

Humans are heterotrophs and cannot make their own food.

• There are six classes of nutrients: carbohydrates, proteins, fats, vitamins, minerals and water.
• Carbohydrates are the main quick-energy food (rice, wheat, sugar, potato); broken down to glucose.
• Proteins are building material for muscles and tissues (dals, eggs, fish, milk); broken to amino acids.
• Fats (lipids) store energy and give over double the energy of carbohydrates per gram.
• Vitamins and minerals are needed in tiny amounts; their lack causes deficiency diseases.
• Water carries everything and runs every reaction, but gives zero calories.
• Legumes (pulses) are highly nutritious because they are rich in proteins.
• Carbohydrate — Glucose — Rice, wheat, sugar
• Protein — Amino acids — Dals, eggs, fish
• Fat — Fatty acids + glycerol — Oils, butter, nuts

There are six classes of nutrients: carbohydrates, proteins, fats, vitamins, minerals and water.

Carbohydrates are the main quick-energy food (rice, wheat, sugar, potato); broken down to glucose.

Proteins are building material for muscles and tissues (dals, eggs, fish, milk); broken to amino acids.

Fats (lipids) store energy and give over double the energy of carbohydrates per gram.

Vitamins and minerals are needed in tiny amounts; their lack causes deficiency diseases.

Water carries everything and runs every reaction, but gives zero calories.

Legumes (pulses) are highly nutritious because they are rich in proteins.

• Extra glucose is stored in the liver and muscles as glycogen, nicknamed 'animal starch'.
• Glycogen is the body's ready energy savings account.
• Milk is almost a 'complete food' but lacks vitamin C and is low in iron.
• Milk is rich in calcium, protein, fat and vitamin A.
• A glass of water gives 0 calories (no energy value).
• Calcium, protein — Vitamin C
• Fat, vitamin A — Iron

Extra glucose is stored in the liver and muscles as glycogen, nicknamed 'animal starch'.

Glycogen is the body's ready energy savings account.

Milk is almost a 'complete food' but lacks vitamin C and is low in iron.

• Most vitamins are NOT synthesised in the human body and must come from diet.
• Vitamin K is essential for blood clotting (coagulation).
• Vitamin A is essential for normal vision (its lack causes night blindness).
• Vitamin C deficiency causes scurvy; its richest source is amla (Indian gooseberry).
• Vitamin B2 (riboflavin) deficiency causes cheilosis / ariboflavinosis.
• Vitamin B12 is the anti-anaemic factor; vitamin D prevents rickets.
• A — Vision / Night blindness — Carrot, milk
• B2 (Riboflavin) — Cheilosis — Cod-liver oil
• C — Scurvy — Amla, citrus
• D — Rickets — Sunlight, fish
• E — Antioxidant — Wheat germ
• K — Blood clotting — Green leaves

Vitamin K is essential for blood clotting (coagulation).

Vitamin A is essential for normal vision (its lack causes night blindness).

Vitamin C deficiency causes scurvy; its richest source is amla (Indian gooseberry).

Vitamin B2 (riboflavin) deficiency causes cheilosis / ariboflavinosis.

Vitamin B12 is the anti-anaemic factor; vitamin D prevents rickets.

• An enzyme is a biological catalyst that speeds up a reaction without being used up.
• Almost all enzymes are proteins; a few RNA molecules called ribozymes also act as enzymes.
• Each enzyme has an active site that fits one substrate like a key fits one lock.
• Enzymes are denatured (destroyed) by high heat and stop working above about 40°C.
• Some enzymes need a helper called a cofactor (metal ion, prosthetic group or coenzyme).
• Many coenzymes are made from vitamins (e.g. NAD and NADP contain niacin).
• All true cells have enzymes; the exception is a virus, which has no enzymes or metabolism of its own.

An enzyme is a biological catalyst that speeds up a reaction without being used up.

Almost all enzymes are proteins; a few RNA molecules called ribozymes also act as enzymes.

Each enzyme has an active site that fits one substrate like a key fits one lock.

Enzymes are denatured (destroyed) by high heat and stop working above about 40°C.

Some enzymes need a helper called a cofactor (metal ion, prosthetic group or coenzyme).

Many coenzymes are made from vitamins (e.g. NAD and NADP contain niacin).

All true cells have enzymes; the exception is a virus, which has no enzymes or metabolism of its own.

• The system has two parts: the alimentary canal and the digestive glands.
• The alimentary canal is one food tube about 9 metres long, from mouth to anus.
• Order: mouth → pharynx → oesophagus → stomach → small intestine → large intestine → rectum → anus.
• The three accessory glands are the salivary glands, liver (with gall bladder) and pancreas.
• Starch digestion starts in the mouth, protein in the stomach, and all food is finally digested in the small intestine.
• Digestion is a relay, passed from organ to organ along the canal.
• Mouth — Starch digestion begins
• Stomach — Protein digestion begins
• Small intestine — All food fully digested + absorbed
• Large intestine — Water absorption

The system has two parts: the alimentary canal and the digestive glands.

The alimentary canal is one food tube about 9 metres long, from mouth to anus.

Starch digestion starts in the mouth, protein in the stomach, and all food is finally digested in the small intestine.

Digestion is a relay, passed from organ to organ along the canal.

• Digestion begins in the mouth; teeth chew (mastication) and the tongue mixes food with saliva.
• Food rolled into a soft, slippery ball is called a bolus.
• Teeth set in sockets in the jaw is called thecodont; two sets of teeth in life is diphyodont.
• Saliva contains salivary amylase (ptyalin) and the germ-killing enzyme lysozyme.
• Salivary amylase digests starch into maltose – the first chemical step of digestion.
• This is why plain bread or rice slowly tastes sweet when kept in the mouth.
• Swallowing the bolus is called deglutition.
• Incisors — Cutting, biting
• Canines — Tearing
• Premolars — Grinding
• Molars — Grinding, crushing

Digestion begins in the mouth; teeth chew (mastication) and the tongue mixes food with saliva.

Food rolled into a soft, slippery ball is called a bolus.

Teeth set in sockets in the jaw is called thecodont; two sets of teeth in life is diphyodont.

Saliva contains salivary amylase (ptyalin) and the germ-killing enzyme lysozyme.

This is why plain bread or rice slowly tastes sweet when kept in the mouth.

Swallowing the bolus is called deglutition.

• The oesophagus (food pipe) is a muscular tube carrying the bolus to the stomach.
• The oesophagus does NOT digest food – it is only a passage.
• Food moves by peristalsis: wave-like contractions of the muscular wall.
• Peristalsis squeezes food downward and occurs all along the alimentary canal.
• These muscular waves let food move even against gravity.

The oesophagus (food pipe) is a muscular tube carrying the bolus to the stomach.

The oesophagus does NOT digest food – it is only a passage.

Food moves by peristalsis: wave-like contractions of the muscular wall.

Peristalsis squeezes food downward and occurs all along the alimentary canal.

These muscular waves let food move even against gravity.

• Protein digestion begins in the stomach.
• The stomach secretes hydrochloric acid (HCl), which kills germs and gives an acidic medium.
• The enzyme pepsin digests proteins into smaller peptides.
• Trypsin and chymotrypsin are pancreatic enzymes, NOT secreted by the stomach.
• The acid plus enzymes turn food into a semi-liquid paste called chyme.
• A layer of mucus protects the stomach wall from its own acid.
• HCl — Kills germs, acidic medium
• Pepsin — Digests protein
• Mucus — Protects stomach lining

The stomach secretes hydrochloric acid (HCl), which kills germs and gives an acidic medium.

The enzyme pepsin digests proteins into smaller peptides.

Trypsin and chymotrypsin are pancreatic enzymes, NOT secreted by the stomach.

The acid plus enzymes turn food into a semi-liquid paste called chyme.

A layer of mucus protects the stomach wall from its own acid.

• The liver is the largest gland; it makes bile, stored in the gall bladder.
• Bile is received by the small intestine (duodenum) from the liver.
• Bile emulsifies fats (breaks large fat drops into tiny ones) but contains no enzymes.
• Gallstones in the gall bladder block bile and affect fat digestion.
• The pancreas secretes pancreatic juice with trypsin, lipase and amylase.
• The liver also stores glycogen, iron and some vitamins.
• Liver — Bile — Fats (emulsify)
• Pancreas — Trypsin — Proteins
• Pancreas — Lipase — Fats

The liver is the largest gland; it makes bile, stored in the gall bladder.

Bile emulsifies fats (breaks large fat drops into tiny ones) but contains no enzymes.

Gallstones in the gall bladder block bile and affect fat digestion.

The pancreas secretes pancreatic juice with trypsin, lipase and amylase.

• The small intestine is where ALL food is finally and fully digested.
• It receives bile from the liver and pancreatic juice in its first part, the duodenum.
• Carbohydrates become glucose, proteins become amino acids, fats become fatty acids and glycerol.
• Its inner wall has tiny finger-like villi that hugely increase absorbing surface area.
• Absorption of digested food into the blood happens mainly here.
• The human body cannot digest cellulose (roughage/fibre), as it lacks the enzyme to break it.

The small intestine is where ALL food is finally and fully digested.

It receives bile from the liver and pancreatic juice in its first part, the duodenum.

Carbohydrates become glucose, proteins become amino acids, fats become fatty acids and glycerol.

Its inner wall has tiny finger-like villi that hugely increase absorbing surface area.

Absorption of digested food into the blood happens mainly here.

The human body cannot digest cellulose (roughage/fibre), as it lacks the enzyme to break it.

• The large intestine absorbs mostly water from undigested food.
• Undigested matter forms faeces, stored in the rectum.
• Removal of faeces through the anus is called egestion (defaecation).
• Cellulose (fibre) is not digested by humans but adds essential roughage.
• Roughage helps the smooth movement of food and prevents constipation.

The large intestine absorbs mostly water from undigested food.

Undigested matter forms faeces, stored in the rectum.

Removal of faeces through the anus is called egestion (defaecation).

Cellulose (fibre) is not digested by humans but adds essential roughage.

Roughage helps the smooth movement of food and prevents constipation.