Download Digestive System part 1

Digestive System Includes:
GI tract
(gastrointestinal (digestive) tract
alimentary canal)
Accessory organs:
teeth,
salivary glands,
liver,
gallbladder,
pancreas
Digestion Involves Many Processes:
INGESTION- process of taking food and liquid into mouth
(eating)
SECRETION (water, acid, buffers, enzymes) -7L/day
DIGESTION (chemical, mechanical)
Extracellular process, occurs within the gut
Digestion Involves Many Processes:
MOTILITY (peristalsis) Mixing and propulsion – alternating
contraction and relaxation of smooth muscle in walls of GI
tract mix food and secretions and move them toward the anus
(motility)
ABSORPTION: the passage of digested nutrients from the gut
lumen into the blood or lymph, which distributes them
through the body.
ELIMINATION: the expulsion of indigestible residues from the
body. (Defecation)
SALIVARY GLANDS
Saliva
Moistens and lubricates food
Components:
water (99%)
mucus:
salivary amylase
lysozyme
bicarbonate
Once food has been chewed, it is called a bolus
UNIT B Chapter 9: Digestive System
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Section 9.1
UNIT B Chapter 9: Digestive System
Section 9.1
The Pharynx
The pharynx is a passageway that
receives air from the nasal cavities
and food from the mouth.
Swallowing (a reflex action) occurs in the pharynx.
• The soft palate moves back to close off the nasopharynx
• The trachea moves up under the epiglottis to cover the
glottis (the opening to the larynx (voice box))
• During swallowing, food enters the esophagus because the
air passages are blocked
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UNIT B Chapter 9: Digestive System
The Esophagus
The esophagus is a long muscular
tube that moves food from the mouth
to the stomach by peristalsis.
Functions
• transport of food to the stomach
• secrete mucus (lubricates food
and allows easy passage)
NO digestive or absorptive function
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Section 9.1
Peristalsis
Peristalsis (rhythmic
muscular contractions)
pushes food along the
esophagus and through
the digestive tract to the
stomach.
UNIT B Chapter 9: Digestive System
Section 9.1
The Stomach
The stomach is an organ that receives food from the
esophagus, mechanically and chemically digests food, and
moves food into the small intestine.
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Stomach Structure
Four regions:
Cardia
Fundus
Body
Pyloric part
Structure of Stomach
Three muscle layers:
Circular,
Longitudinal,
Oblique
Rugae – folds
2 sphincters:
lower esophageal sphincter  prevents esophageal reflux
pyloric sphincter  regulates movement of stomach contents
into the intestines
4 Main Functions of Stomach
1. Storage of a meal
4 Main Functions of Stomach
2. Mechanical Digestion
4 Main Functions of Stomach
3. Chemical Digestion
4 Main Functions of Stomach
4. Protection against Germs
What about Absorption?
Absorption in the stomach is limited because:
– thick layer of mucus
– epithelial cells lack specialized transport
mechanisms
– most nutrients are not fully digested
What can be absorbed?
Water, some ions, some glucose, amino acids, lipid soluble
substances
Drugs
Alcohol
Some lipid soluble; diffuses through mucous membrane and cell
membranes
Most Food is not absorbed here
UNIT B Chapter 9: Digestive System
• When food leaves the stomach, it is a thick, soupy
liquid called chyme.
o Chyme enters the small intestine by way of the
pyloric sphincter.
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Section 9.1
Gastric Secretions
pepsinogen-an inactive enzyme that is converted to pepsin once
released into the stomach (breaks down proteins) by chief cells
hydrochloric acid (HCl)- converts pepsinogen to pepsin; kills
microorganisms. Secreted by parietal cells.
intrinsic factor- required for the absorption of vitamin B12 for
RBC production. (parietal cells)
mucus- protects the stomach wall from gastric acid
gastrin - hormone that stimulates:
(1) HCl and pepsinogen release,
(2) gastric motility, (increase stomach movements)
(3) relaxes the pyloric sphincter
Peptic Ulcer
open sore
usually found in the
lining of the stomach, esophagus,
or upper small intestine.
gastric ulcers occur in stomach,
duodenal ulcers in duodenum.
UNIT B Chapter 9: Digestive System
The Small Intestine
The small intestine receives chyme from the stomach and
completes the digestion of food. Macromolecules are broken
down into nutrients, which are absorbed in the small intestine
and pass into the blood.
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Section 9.1
Secretions into duodenum
Secretions into the duodenum
1. Bile from liver & gall bladder
2. Pancreatic juice from pancreas
3. Digestive enzymes that finish the digestion of protein and
starch (from interstitial glands within duodenum itself)
4. Mucus from goblet cells
5. Hormones from endocrine cells --> regulate stomach
emptying, pancreatic secretions, gallbladder contraction,
satiety, etc.
Small Intestine Enzymes
MALTASE digest maltose to glucose
SUCRASE digest sucrose to glucose and fructose.
LACTASE digest lactose to glucose and galactose.
LIPASE digest fats to fatty acids.
PEPTIDASE digest small peptides to single amino acids.
Enterogastric Reflex inhibits gastric motility and the secretion
of gastric acid
Peristalsis - the longitudinal muscles within the small intestine
wall contract, and then the circular muscles contract, pushing the
food down the tract.
Segmentation –localized contraction of circular smooth muscles
that constrict the intestine into segments mixing chyme and
increasing contact with intestinal wall
Key Functions of Small Intestine
– mechanical digestion (segmentation)
– completion of chemical digestion, requires
• enzymes from the pancreas and intestinal epithelial
cells (complete nutrient digestion)
• bile (digestion of fats)
• alkaline pH (for enzyme function)
– 90% of nutrient absorption
ABSORPTION takes place across the
wall of each villus
UNIT B Chapter 9: Digestive System
Section 9.1
Structure
The wall of the small intestine contains plicae (circular
folds) and villi (finger-like projections), which increase the
surface area to improve the absorption of nutrients.
o Microvilli increase the surface area of the villus for
the absorption of nutrients
o Each villus contains blood capillaries and a small
lymphatic capillary called a lacteal
o Nutrients are absorbed into the blood capillaries and
the lacteals, which carry them to body cells
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CELIAC DISEASE
an inherited, autoimmune disease
antibodies attack the intestinal lining following the consumption
of gluten (protein in wheat, rye and barley).
inflammation leads to the atrophy (flattening) of villi
impaired absorption  weight loss, malnutrition, anemia, fatty
stools, fatigue
Lactose Intolerance
• results from a deficiency in lactase
• unabsorbed lactose provides fuel for bacteria in the colon 
gas production
Gastrointestinal Hormones
Gastrin
–Origin: Stomach
–Stimulus: Food in stomach
–Function: stimulate gastric glands secretion.
–Stimulates HCl & pepsinogen secretion, increases stomach
motility
Gastrointestinal Hormones
Secretin
• Origin: Duodenum
• Stimulus: Acid chyme from stomach
• Function: stimulate pancreatic juice secretion.
Gastrointestinal Hormones
Cholecystokinin (CCK)
• Origin: Duodenum
• Stimulus: Fat & protein in duodenum
• Function: stimulate pancreatic secretion & gallbladder
contraction.
Gastrointestinal Hormones
Gastric Inhibitory Protein (GIP)
–Origin: Duodenum
–Stimulus: Fats and bile
–Function: Inhibit stomach motility and secretion of
acid and enzymes
UNIT B Chapter 9: Digestive System
Section 9.1
The Large Intestine
The large intestine absorbs water, salts, and some vitamins. It
also stores indigestible material until it is eliminated as feces.
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UNIT B Chapter 9: Digestive System
Section 9.1
Structure and Function of the Large Intestine
• Colon: includes the ascending, transverse, descending, and
sigmoid colon
• Rectum: the last part of the large intestine; opens at the anus
• Anus: rectum opening; site of defecation (expulsion of feces)
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Colon
Function of Large Intestine
1.
2.
3.
4.
Absorption of water
Bacteria produce vitamin K, B vitamins.
Secretion of mucus (lubrication of feces)
Contractions move feces along large intestine and rectum, to
be expelled out of the anal canal
• No digestion occurs in the large intestine.