Digestion and Absorption

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Digestion and Absorption

• Dr Gouree Francis
• MBBS

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objectives

1. Digestive system
2. Organs
3. function
4. Digestive process
5. Mechanical process
6. Chemical process

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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.

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Digestive system
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Functions of the digestive system

• Receipt, maceration and transport of ingested
  substances and waste products
• Secretion of acid, mucus, digestive enzymes, bile
  and other materials
• Digestion of ingested foodstuffs
• Absorption of materials
• Storage of waste products
• Excretion
• Ancillary functions

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Organs of the digestive system

• Main organs

• Other organs

• Mouth tongue, teeth
• Esophagus
• Stomach
• Small intestine
• Large intestines
• Rectum
• Anus

• Salivary glands
• Gallbladder
• Liver
• Pancreas

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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

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Mechanical digestion

• Mechanical digestion is the physical break down
  of food into smaller pieces.
• 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.

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• Peristalsis
• successive contractions of muscles in the
  alimentary canal which form a wave of
  constriction that moves food along.
• 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

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Chemical digestion

• Chemical digestion, is the chemical break down of
  foods into smaller pieces.
• Enzyme action
• salivary amylase is found in our saliva which
  acts to break down starch into simpler forms.
• HCl acid in the stomach helps to break down food
  and destroy any micro-organisms that accompanied
  the food.

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Absorption

• Passage of digested end products in to blood or
  lymph

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What happens to ingested food inside the
digestive system?

• Digestive process

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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

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• 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

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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

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• 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

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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

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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.

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• 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.

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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.

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Role of pancreas

• The pancreas supplies enzymes to digest proteins,
  fats, and carbohydrates.
• Trypsin
• Chymotrypsin
• Carboxypeptidase
• Lipase
• Amylase
• In addition, the pancreas produces and secretes
  buffers that help neutralize the stomach acids
  found in chyme.

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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
• Disaccharidases maltase, lactase, sucrase
• Peptidases

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• 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

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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.

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In rectum

• Temporary storage of formed faeces.
• Further absorption of water
• Undigested portion will be eliminated via anus
  during defecation.