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Physiology of the digestive system
• There are Four Stages of Food Processing:
• Ingestion—the taking in of food
• Digestion—the breakdown of food
• Absorption—the taking up of nutrients
• Elimination—the removal of waste materials
from the body
The digestive system
 Digestion is when food undergoes physical and chemical
changes that transforms complex food molecules into
simple nutrients allowing us to use the energy
 Mechanical digestion physically breaks up food into
smaller particles increasing the surface area facilitating
chemical digestion (breakdown by chemicals).
The Mouth ( oral cavity)
 Contains :
 teeth -mechanically break down food.
 a tongue- tastes and manipulates food.
 the uvula, the flap hanging down at the back of the
throat (closes the nasal cavity when swallowing, gag
reflex)
 salivary glands that produce saliva that lubricate food
and start digestion
teeth
tongue
uvula
The Pharynx
 Area at the back of the throat.
 It is the area where the air and food pass.
 A flap called the epiglottis closes the airway when
food is swallowed.
pharynx
epiglottis
The Esophagus
 Muscular tube
 Connects pharynx to stomach.
 Moves food by means of peristalsis (sequential
contractions of muscles e.g. in the esophagus)
The Stomach
 Muscular bag
 Grinds food and mixes
it with hydrochloric acid
and enzymes into what
is called chyme (partially
digested food with the
consistency of cottage cheese).
 The stomach is lined with a mucus membrane that
resists the acid.
 Two sphincters (muscular rings) control entrance
and exit of food.
Small Intestine
 7 m long
 It is where digestion and absorption of nutrients
and vitamins
•Walls are covered in folds which are covered with villi (fingerlike projections) which are intern covered with microvilli (hairlike structures on the villi)
•This increases the surface area
folds
VILLI
Large Intestines
 Also called the colon.
 1.5m long (6.5 cm across)
 absorbs most of the water
 Has a smooth mucus lining to facilitate
the passage of waste.
 Rectum- storage of waste
 Anus- opening for elimination
Digestive Glands
 A gland is an organ or group of cells that
produces secretions.
 Secretions are chemical substances (hormones)
or liquids (sweat, mothers milk) that have
different functions in the body.
 The Salivary glands:
 found in the mouth.
 secret about1-1.5L
of saliva daily.
 The saliva lubricates the “bolus”
(mashed food) and is involved in the
breaking down of carbohydrates
 The liver:
 It produces bile (breaks down fats) daily
 Some of the bile is stored in the gall bladder.
 The pancreas:
 This gland secretes pancreatic juices
(digestive juices)
 Also secretes insulin
( a hormone for the
metabolism of sugar)
 Gastric glands:
 found over the entire internal surface of the
stomach
 Secretes gastric juices that digest only protein
(contains HCl and pepsin)
The Digestive tract
Pharynx
Epiglottis
Uvula
Oral Cavity
Tongue
Salivary Glands
Esophagus
Liver
Gall Bladder
Duodenum
Transverse Colon
Ascending Colon
Cecum
Appendix
Anus
Stomach
Pancreas
Jejunum
Descending Colon
Rectum