Human Nutrition Part 2

The StomachMuscular bag to store

and digest food

Food enters through cardiac sphincter muscle

Can hold 1 litre of food for 4 hours

The Stomach Lining of stomach is heavily

folded forming millions of gastric glands

These produce gastric juices

1. Mucous is made by goblet cells it prevents self digestion

2. Pepsinogen is made by zymogen cells it is an inactive enzyme made active in the stomach it breaks proteins into peptides

3. Hydrochloric acid is made by oxyntic cells

Hydrochloric acid

This gives stomach a pH of 1 to 2! Very acidic This acidity kills many bacteria, loosens fibrous and

cellular foods, activates pepsinogen and denatures amylase from saliva

Too much acid in the stomach leads to heartburn – can be neutralised with alkalis such as alka seltzers or Rennies

Chyme

When the stomach is churning it turns food + gastric juices into a thick soupy mixture called Chyme

This leaves stomach in small amounts when the Pyloric Sphincter opens Gastric juice could digest the stomach wall – this is prevented by mucous

lining the stomach, mucous is alakaline, Pepsin is released as inactive pepsinogen, tightly packed cells line the stomach that can be replaced rapidly

If gastric juice does manage to digest the stomach wall ulcers can result

If ulcer becomes perforated bacteria could get into body and cause death

Small Intestine6 meter long tube!

First 25 cm is called the Duodenum (where most of the digestion takes place)

Remainder is Jejunum and Ileum these are the regions where absorption of digested food takes place

Small Intestine

Main function of duodenum is digestion

Cells that line the duodenum produce many enzymes

Products of the Liver and Pancreas also enter the duodenum

•.

The Pancreas

Secretes hormone insulin and digestive materials which form pancreatic juice

Pancreatic juice contains sodium bicarbonate salt to neutralise chyme from the stomach

Enzymes such as amylase and lipases are also present The pancreatic duct leads from the pancreas to the duodenum

Liver – Complex organ

Function Makes Bile Detoxifies the body – breaks down

poisons such as alcohol and drugs Breaks down excess amino acids to

form urea Converts glucose to glycogen for

storage Converts excess carbohydrate to fat Stores vitamins (eg vit D) Stores minerals (eg Iron) Makes plasma proteins Makes cholesterol for hormones Produces heat to warm the blood and

the body

Bile

Partly formed from remains of red blood cells Consists of water salts and bile pigments (NO ENZYMES) Made in the liver and stored in gall bladder Gallstones in bile duct stop the release of bile Functions

1. Emulsifies lipids – increases surface area (shake oil in a test tube to get emulsion)

2. Helps neutralise Chyme3. Excretes pigments biliverdin and bilirubin made from dead red blood cells

Jejunum and Ileum

Food entering here is almost fully digested it is here that they will finally be absorbed into the body

Lining contains many villi to increase the surface area The walls are only one cell thick and they have a rich

blood supply to absorb the glucose, amino acids, vitamins and minerals

The capillaries carry the nutrients to the hepatic portal vein which takes them to the liver

The Liver acts like a giant warehouse allowing some nutrients out and storing others

Amino acids cannot be stored in the body so any that are not needed are broken down in a process called Deamination

This forms urea which is excreted in urine Urea leaves through the Hepatic vein along with other wastes and goes to

the kidneys

VilliLining of small

intestine contains many foldings called villi (singular villus)

Each villus has approx 600 microvilli!

This increases surface area for digestion and absorption

Intestinal glands between the villi produce intestinal juice

Inside each villus is a Lacteal containing lymph

Fatty acids and glycerol enter here are transported to the subclavian veins and distributed around the body

Large Intestine

1.5 metres long Food stays here for between 10 hours

and a few days Caecum and Appendix are Vestigial

organs in humans - they have lost their function

Sometimes bacteria gather and grow in the apendix, bacterial waste builds up and causes pain if appendix ruptures it can be very serious

The Colon

This part of the large intestine reabsorbs water from the waste forming Faeces

Diarrhoea occurs if not enough water is reabsorbed Constipation occurs if too much water is reabsorbed Symbiotic bacteria in the colon produce vitamins while

others digest cellulose

Rectum

Stores Faeces

A Balanced Diet

Seven components1. Carbohydrate2. Lipid3. Protein4. Minerals5. Vitamins6. Fibre7. Water

The amount of food a person requires depends on age, activity, gender and health

Four food groups are:1. Cereals breads and potatoes2. Fruit and Vegetables3. Milk cheese and yoghurt4. Meat, fish and poultry

A Balanced Diet

Eating DisordersAnorexia Nervosa and

Bulimia NervosaCause is unknown

excessive desire to be thinBulimia involves binge

eating and self – induced vomiting it is easier to disguise than anorexia

Both are extremely serious