Transcript Digestion and Absorption Mechanical process Chemical process

Digestion and Absorption
Dr Gouree Francis
MBBS
objectives
1. Digestive system
1. Organs
2. function
2. Digestive process
1. Mechanical process
2. Chemical process
Digestive system
• The Human gastrointestinal tract or digestive
system is the system by which ingested food is
processed by physical and chemical means to
provide the body with nutrients and excrete
the waste products.
• This system includes the alimentary canal
extending from the mouth to the anus, and
the hormones and enzymes assisting in
digestion.
Digestive system
Functions of the digestive system
1. Receipt, maceration and transport of ingested
substances and waste products
2. Secretion of acid, mucus, digestive enzymes,
bile and other materials
3. Digestion of ingested foodstuffs
4. Absorption of materials
5. Storage of waste products
6. Excretion
7. Ancillary functions
Organs of the digestive system
Main organs
1. Mouth – tongue, teeth
2. Esophagus
3. Stomach
4. Small intestine
5. Large intestines
6. Rectum
7. Anus
Other organs
1. Salivary glands
2. Gallbladder
3. Liver
4. Pancreas
What is digestion?
• Digestion is the mechanical and chemical
breaking down of food into smaller
components that can be absorbed into the
blood stream.
• Digestion is form of catabolism
– Breakdown of large insoluble molecules into
smaller soluble molecules
Mechanical digestion
• Mechanical digestion is the physical break down of
food into smaller pieces.
1. Mastication (chewing)
–
occurs in the mouth by the teeth, which act to cut and
grind food into smaller pieces. This makes them easier to
later digest as it increases the surface area of the food
molecules.
2. Peristalsis
– successive contractions of muscles in the alimentary
canal which form a wave of constriction that moves food
along.
3. Emulsification by Bile salts
– act to emulsify large fat globules into smaller fat droplets.
– breaks up all molecules and then puts a 'soapy' shield
around them so they cant join back together.
– This increases the surface area of the molecule of fat so
that enzymes (pancreatic lipase) can act on it and break it
down to smaller, simpler forms
Chemical digestion
• Chemical digestion, is the chemical break down
of foods into smaller pieces.
1. Enzyme action
– salivary amylase is found in our saliva which acts to
break down starch into simpler forms.
2. HCl acid in the stomach helps to break down
food and destroy any micro-organisms that
accompanied the food.
Absorption
• Passage of digested end products in to blood
or lymph
What happens to ingested food
inside the digestive system?
Digestive process
In mouth
• Digestion begins in the mouth
• Digestion inside the mouth occurs with the
help of teeth, palate, lips and tongue.
• As food is chewed, it becomes lubricated,
warmer, and easier to swallow and digest.
• The teeth and tongue work together to
convert each bite of food into a bolus that can
readily move into the esophagus
• Teeth
– chew, break and grind ingested food into small pieces.
• Tongue
–
–
–
–
mixes the food with saliva
make the food bolus with the help of palate and teeth
Propels food bolus toward pharynx when swallowing
Taste sensation – taste buds
Saliva
• Saliva is produced in and secreted from one of
the three salivary glands.
• Human saliva is composed of
– 98% water
– other 2% consists of other compounds such as
electrolytes, mucus, antibacterial compounds
(secretory IgA, lactofferin, lysozyme,peroxidase)
and various enzymes
• Saliva
– Facilitate taste sensation(A dry tongue can't taste)
– lubricates and protects the teeth, the tongue, and the
tender tissues inside the mouth
– also breaks down food caught in the teeth, protecting
them from bacteria that cause decay.
– Lubricates and moistens food and helps to break it
down, which in turn makes it easier for the tongue to
push the food to the back of the mouth for
swallowing.
– Contain salivary amylase
• Salivary amylase breaks down starch into sugar
– Contain Lingual lipase – important in children as they
have immature pancreas
In Oesophagus
• After the bolus is swallowed, it enters the
esophagus where it continues to be warmed
and lubricated as it moves toward the
stomach by peristalsis.
– Act as a conduit
In Stomach
•
•
In the stomach, there are three layers of muscle
(which is unique as the rest of the alimentary
canal only has 2). It has longitudinal, circular and
oblique muscle which together contract and
relax to form the churning motion which mixes
food around.
This aids in digestion as it slightly breaks up the
food and also increases the contact the food has
with enzymes and acids in the gastric juice.
• The acidic environment (HCl) of the stomach
and the action of gastric enzymes convert the
bolus into chyme, a liquefied mass that is
squirted from the stomach into the small
intestine.
• Carbohydrates tend to leave the stomach
rapidly and enter the small intestine
• proteins leave the stomach less rapidly and
fats linger there the longest.
Role of liver and gall bladder
• The liver produces the bile required for the
emulsification of fat, and the gallbladder
stores the bile until it is needed.
Role of pancreas
• The pancreas supplies enzymes to digest proteins, fats,
and carbohydrates.
1.
2.
3.
4.
5.
Trypsin
Chymotrypsin
Carboxypeptidase
Lipase
Amylase
•
In addition, the pancreas produces and secretes buffers
that help neutralize the stomach acids found in chyme.
In small intestine
• The small intestine is the principal site of
digestion and absorption.
• There, enzymes and secretions from the
pancreas, liver, gallbladder, and the small
intestine itself combine to break down nutrients
so that they can be absorbed.
• Intestinal cells also supply some enzymes – brush
border enzymes
1. Disaccharidases – maltase, lactase, sucrase
2. Peptidases
• The absorption of nutrients in the small intestine is
facilitated by tiny projections called villi, which provide
more surface area for absorption.
• The nutrients pass through the intestinal membranes
into the circulatory system, which transports them to
body tissues.
• Nutrients are then absorbed into the cells, where they
are used for growth, repair, and the release or storage
of energy. The overall process is called metabolism
In colon
• Undigested chyme proceeds from the small
intestine into the large intestine (colon),
where it becomes concentrated, as liquid is
absorbed in preparation for excretion.
• Bacteria cause fermentation, which facilitates
further breakdown, but absorption of
nutrients from the large intestine is minimal.
In rectum
• Temporary storage of formed faeces.
• Further absorption of water
• Undigested portion will be eliminated via anus
during defecation.