3/24/08 digestive system chapter 22 – day 1. 3/24/08 digestive system respiratory system...
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3/24/08
Digestive System
Chapter 22 – Day 1
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Digestive systemRespiratory System
♦Brings O2 to the body
Cardiovascular System♦Brings O2 to the cells
In tissues O2 is used for cellular respiration, BUT…
O2 is only one of the ingredients – you also need♦Glucose
Digestive System♦Brings glucose to the body♦Other sources of nutrients♦And other building blocks to make cells
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Digestive systemFood is broken down & processedNutrients are absorbedWaste products are eliminated
All of this happens in the digestive tractA.K.A. alimentary canal or GI tract
The digestive tracts is a long, continuous muscular tube starting at the esophagus
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Digestive system
Fig. 21.11
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Digestive system - ProcessesIn order for nutrients to reach cells the digestive
system carries out several processes♦Ingestion = food in the mouth
♦Mechanical processing = physically breaking food into bits
♦Digestion = enzymes and hormones
♦Absorption = organic molecules enter interstitial fluid
♦Excretion = elimination of unwanted materials
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Fig. 22.3
Digestive system – Cell/Tissue layersThe digestive system has a distinct system of tissue
layersThere is an “open” surface inside the GI tract –
epithelial tissue covering on outside4 layers – from inside to outside
♦These are there ALL ALONG the GI tract♦Mucosa
•innermost layer♦Submucosa♦Muscularis externa♦Serosa
•outermost layer
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Cell/Tissue layers - MUCOSA Digestive epithelium Connective tissue – lamina propria (smooth) muscle tissue – muscularis mucosa Type of epithelium varies along the GI tract
♦Pharynx & esophagus handle large masses of food = stratified epithelium
♦In the stomach – food becomes liquid & passes to intestines♦A great deal of absorption happens in the intestines
•Simple columnar epithelium•Secrete mucous•Highly folded epithelial surface (small intestine)
Lamina propria – areolar connective tissue right below basement membrane of epithelium
Contains blood vessels, nerves, mucous glands (in the intestines this is where you find the Peyer’s patches)
Muscularis mucosa = smooth muscle – helps movement in the GI tract
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Cell/Tissue layers - SUBMUCOSADense connective tissueNerve network
♦Submucosal plexus
Communication with the nervous system – helps muscle movement
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Cell/Tissue layers – MUSCULARIS EXTERNA
Smooth Muscle TissueNerve network
♦Mysenteric plexus
More forceful contractions for movement2 layers of muscle
♦Longitudinal♦Circular
Allows 2 types of movement♦Rocking motion♦Forward movement
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Cell/Tissue layers – SEROSAFibrous tissue on outsideProtective covering which helps in attachment to
abdominal wall
Fig. 22.3
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Other important general featuresMembranes
♦Perotineal cavity•2 membrane layers
♦Encloses abdominal portion of digestive tract♦Serosa = visceral peritoneum (inner layer)♦Parietal peritoneum = lines abdominal wall (outer layer)
♦Additional serous membrane connects serosa/visceral to parietal peritoneum
♦The space between the 2 layers if filled with fluid•Peritoneal fluid
•Secreted by cells of the peritoneum
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Other important general featuresMesenteries
♦Sheets of serous membrane allow blood vessels, nerves, and lymph vessels to pass through & network
♦Stabilize the position of the GI tract•Prevents “flopping around”
♦OMENTUS – associated with the stomach (Fig. 22-12)•Lesser omentum & greater omentum
•Contains adipose tissue (fat around the belly)
♦Mesentery proper•Within small intestine, between loops
♦Mesocolon•Stabilizes large intestine
♦Areas without mesentaries = pancreas & duodenum – which are attached to the abdominal wall for stability
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SecretionsWithin the digestive tract – secretions are evident
throughout♦Mucus
•To lubricate food & “walls”
♦Digestive enzymes•Break chemical bonds
♦Electrolytes•Buffers pH
•Cofactor for enzymes
Parts of digestive system & direction of food…Explore important structures, secretions, absorption,
digestion process, movement of food
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Alvioli – Capillary Interface
Fig. 21.11
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Movement of BolusForward movement
♦Waves of contraction in muscularis externa♦Along length of tube♦Process of peristalsis♦Circular muscles contract behind bolus♦Longitudinal muscles contract at cardiac sphincter♦Wave of relaxation opens entrance to stomach
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Movement of Food (bolus)
Fig. 22.4
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Movement of BolusForward movement
♦Waves of contraction in muscularis externa♦Along length of tube♦Process of peristalsis♦Circular muscles contract behind bolus♦Longitudinal muscles contract at cardiac sphincter♦Wave of relaxation opens entrance to stomach
Side to side movement♦No set direction♦Helps to mix bolus with mucus for more lubrication♦Contraction in muscles → segmentation♦Mostly in large & small intestine – helps to fragment bolus
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Stomach AnatomyShapeSphincters
♦Cardiac♦Pyloric
Folds = rugae♦Deep muscular folds
Mucosa
Fig. 22.12
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Stomach AnatomyMucosa
♦Gastric pits with gastric glands♦Secretory cells
4 types of secretory cells:
Cell SecretionChief cells → PepsinogenParietal cells → HCl (acid)Mucus cells → MucusEnteroendocrine cells → Gastrin (hormone)
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Stomach Processes What happens to food when it enters the stomach? Digestion & Secretion – almost no absorption
3 phases of secretion in the stomach
1. Cephalic♦Begins at the sight of food♦Gastrin is secreted♦Stimulates HCl & pepsinogen
Food enters the stomach
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Phases of Gastric Secretion in Stomach2. Gastric Phase
Secretion Mucus is secreted to protect stomach lining More gastrin, more pepsinogen Acidic environment – pH drops (pepsinogen →
pepsin at low pH) Secretions stop when pH reaches 2.0
Digestion Proteins in food →pepsin →amino acids Milk proteins →gastric lipase → amino acids & renin
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Phases of Gastric Secretion in Stomach2. Intestinal PhaseMixing Rugae become stretched – stomach is distended Muscular contractions mix food for several hours Food becomes watery mixture
♦Chyme (acidic)
After several hours of mixing waves of contractions (peristalsis) reach the lower end/base of the stomach – near the pyloric sphincter
Sphincter opens & closes with each wave Squirts chyme into the duodenum The Duodenum secretes enteric gastrin
♦starts next phase
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Phases of Gastric Secretion in Stomach2. Gastric PhaseMixing Rugae become stretched – stomach is distended Muscular contractions mix food for several hours Food becomes watery mixture
♦Chyme (acidic)
After several hours of mixing waves of contractions (peristalsis) reach the lower end/base of the stomach – near the pyloric sphincter
Sphincter opens & closes with each wave Squirts chyme into the duodenum The Duodenum secretes enteric gastrin
♦starts next phase