GI tract gastrointestinal digestive tract alimentary canal Accessory organs teeth salivary glands liver gallbladder pancreas Digestion Involves Many Processes INGESTION ID: 631442
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Slide1
Digestive System Includes:
GI tract(gastrointestinal (digestive) tractalimentary canal)Accessory organs:teeth, salivary glands, liver, gallbladder, pancreasSlide2
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 Slide3
Slide4
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)Slide5Slide6Slide7
salivary glands
Slide8
Saliva
Moistens and lubricates foodComponents: water (99%) mucus: salivary amylase lysozyme bicarbonate Once food has been chewed, it is called a bolusSlide9
UNIT B
Chapter 9: Digestive System
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Section 9.1Slide10
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
UNIT B
Chapter 9: Digestive System
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Section 9.1Slide11
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
UNIT B
Chapter 9: Digestive System
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Section 9.1Slide12
Peristalsis
Peristalsis (rhythmic muscular contractions) pushes food along the esophagus and through the digestive tract to the stomach.Slide13
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.
UNIT B
Chapter 9: Digestive System
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Section 9.1Slide14
Stomach Structure
Four regions: Cardia Fundus Body Pyloric part Slide15
Structure of Stomach
Three muscle layers: Circular, Longitudinal, ObliqueRugae – folds2 sphincters: lower esophageal sphincter prevents esophageal reflux
pyloric sphincter
regulates movement of stomach contents into the intestinesSlide16
4 Main Functions of Stomach
1. Storage of a mealSlide17
4 Main Functions of Stomach2. Mechanical Digestion Slide18
4 Main Functions of Stomach3. Chemical
DigestionSlide19
4 Main Functions of Stomach4. Protection against Germs Slide20
What about Absorption?
Absorption in the stomach is limited because:thick layer of mucus epithelial cells lack specialized transport mechanismsmost nutrients are not fully digestedSlide21
What can be absorbed?
Water, some ions, some glucose, amino acids, lipid soluble substancesDrugsAlcohol Some lipid soluble; diffuses through mucous membrane and cell membranesMost Food is not absorbed hereSlide22
When food leaves the stomach, it is a thick, soupy liquid called
chyme.Chyme enters the small intestine by way of the pyloric sphincter.
UNIT B
Chapter 9: Digestive System
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Section 9.1Slide23Slide24
Gastric Secretions
pepsinogen-an inactive enzyme that is converted to pepsin once released into the stomach (breaks down proteins) by chief cellshydrochloric 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 acidgastrin - hormone that stimulates: (1) HCl and pepsinogen release,
(2) gastric motility, (
increase
stomach movements)
(3) relaxes the pyloric sphincterSlide25
Slide26
Peptic Ulcer
open soreusually found in the lining of the stomach, esophagus, or upper small intestine. gastric ulcers occur in stomach, duodenal ulcers in duodenum.Slide27
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.
UNIT B
Chapter 9: Digestive System
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Section 9.1Slide28
Secretions into duodenumSlide29
Secretions into the duodenum
Bile from liver & gall bladder Pancreatic juice from pancreas Digestive enzymes that finish the digestion of protein and starch (from interstitial glands within duodenum itself) Mucus from goblet
cells
Hormones from endocrine
cells
-->
regulate
stomach emptying, pancreatic
secretions
, gallbladder contraction, satiety, etc.Slide30
Small Intestine Enzymes
MALTASE digest maltose to glucoseSUCRASE 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.Slide31
Enterogastric
Reflex inhibits gastric motility and the secretion of gastric acidPeristalsis - 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 wallSlide32
Key Functions of Small Intestine
mechanical digestion (segmentation)completion of chemical digestion, requiresenzymes from the pancreas and intestinal epithelial cells (complete nutrient digestion)bile (digestion of fats)alkaline pH (for enzyme function) 90% of
nutrient
absorptionSlide33
absorption takes place across the wall of each villusSlide34
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.Microvilli increase the surface area of the villus for the absorption of nutrientsEach villus contains blood capillaries and a small lymphatic capillary called a lacteal
Nutrients are absorbed into the blood capillaries and the lacteals, which carry them to body cells
UNIT B
Chapter 9: Digestive System
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Section 9.1Slide35
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 villiimpaired absorption weight loss, malnutrition, anemia, fatty stools, fatigueSlide36
Lactose Intolerance
results from a deficiency in lactaseunabsorbed lactose provides fuel for bacteria in the colon gas productionSlide37
Slide38
Gastrointestinal Hormones
Gastrin –Origin: Stomach–Stimulus: Food in stomach–Function: stimulate gastric glands secretion.–Stimulates HCl & pepsinogen secretion, increases stomach motilitySlide39
Gastrointestinal HormonesSecretin
Origin: DuodenumStimulus: Acid chyme from stomachFunction: stimulate pancreatic juice secretion.Slide40
Gastrointestinal HormonesCholecystokinin (CCK)
Origin: DuodenumStimulus: Fat & protein in duodenumFunction: stimulate pancreatic secretion & gallbladder contraction.Slide41
Gastrointestinal HormonesGastric Inhibitory Protein (GIP)
–Origin: Duodenum–Stimulus: Fats and bile–Function: Inhibit stomach motility and secretion of acid and enzymesSlide42
The Large Intestine
The large intestine absorbs water, salts, and some vitamins. It also stores indigestible material until it is eliminated as feces.
UNIT B
Chapter 9: Digestive System
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Section 9.1Slide43
Structure and Function of the Large Intestine
Colon: includes the ascending, transverse, descending, and sigmoid colonRectum: the last part of the large intestine; opens at the anusAnus: rectum opening; site of defecation (expulsion of feces)
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Chapter 9: Digestive System
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Section 9.1Slide44
Fig. 12.8Slide45
ColonSlide46
Function of Large Intestine
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 canalNo digestion occurs in the large intestine.