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
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