3/28/0 Movement of Bolus Forward 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
Movement of Bolus. Forward 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 - PowerPoint PPT Presentation
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3/28/08
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
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
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Phases of Gastric Secretion in Stomach2. Gastric Phase
General info/reminders After 2-6 hours, the stomach is emptied Some macromolecules move faster through the
stomach: ♦Carbohydrates♦Proteins♦Then fats
Remember NO absorption in the stomach except for EtOH, H2O, aspirin (alcohol is absorbed fast – gets to brain fast)
On to next phase = intestinal phase
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Phases of Gastric Secretion in Stomach3. Intestinal Phase
Food moves to intestine = gastric emptying Small intestine secretes 2 hormones: Cholecystokinin (CCK)
♦Is released when proteins & fat are in the chyme♦Inhibits gastric secretions♦Triggers pancreas secretion
Secretin♦Released when pH in duodenum drops below 4.5♦Stimulates bicarbonate release from pancreas
•Deactivates pepsin
•Inhibits stomach secretions
•Stimulates bile secretion from liver
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Accessory Structures Digestion in small intestine depends on secretions
from pancreas & liver - Take a closer look at these accessory structures
Pancreas♦Elongated organ posterior to stomach♦Contains pancreatic islets & acini♦Acini – very important for digestive system
•Secretes pancreatic juice when cholecystokinin is secreted in duodenum
♦Pancreatic Juice •Contains: water, bicarbonate ions
•It alters the pH of the chyme to 7.1-8.2
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Accessory Structures: Pancreas Enzymes produced by Pancreas = 6
♦Pancreatic α-amylase•Carbohydrate digestion
♦Pacreatic lipase•Fat digestion
♦Nucleases•Nucleic acid digestion
♦Trypsin♦Chymotrypsin♦Carboxypeptidase
These enzymes are secreted by the acinar cells ♦Are carried to the duodenum in 2 major ducts
proteins
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Accessory Structures: Pancreas
Fig. 22.18
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Accessory Structures: Pancreas These enzymes are secreted by the acinar cells
♦Are carried to the duodenum in 2 major ducts
Pancreatic Duct/Duct of Wirsung♦Joins the common bile duct to enter the duodenum
•At the hepatic pancreatic ampulla
Accessory Duct/Duct of Santorini♦Enters the duodenum above the ampulla
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Accessory Structures: Liver Important synthesis and recycling center in the body Nutrients are absorbed and go to the liver first External anatomy:
♦Left & Right Lobes•Held together by Falciform ligament
♦Posterior surface of the liver - 2 other lobes•Caudate – near superior vena cava•Quadrate – near gall bladder
Important vessels♦Hepatic vein & Hepatic portal vein
•Drain blood into vena cava♦Hepatic Artery
•Brings blood in♦Common bile duct
•Brings bile out of liver Fig. 22.19
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Accessory Structures: Liver Internal anatomy – histology Network of vessels among cells – see Fig. 22.20 Cells:
♦Hepatocytes•Square cells/plates of cells
•Vein branches run between cells = sinusoids
•Lead to a central vein – to the hepatic vein
♦Sinusoid walls are lined with epithelium♦Contain phagocytes = Kupffer Cells
•Break down old RBCs, WBCs, toxins, & bacteria
Liver recycles, but also produces & secretes:♦Hepatocytes – secrete total of approx. 1 L of bile every day♦Bile enters bile caniculli also dispersed among
hepatocytes
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Accessory Structures: Liver - Gallbladder
Fig. 22.20
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Accessory Structures: Liver - Gallbladder Bile canaliculi merge with hepatic ducts – bile is
taken to the gall bladder for storage At release bile leaves via the cystic duct This merges with the common hepatic duct to form
the common bile duct which goes to the duodenum♦The liver also releases bilirubin into the duodenum for
waste excretion♦Stimulated by the vagus nerve & secretin stimulation
In the gall bladder♦Bile is concentrated, water is absorbed♦The common bile duct enters the duodenum at the same
entrance as the pancreatic duct
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Accessory Structures: Liver - Gallbladder Release is controlled by the hepatopancreatic
sphincter Contraction of sphincter is stimulated by CCK Secretin increases the rate of production In the intestines – bile breaks down fats =
emulsification
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Small Intestine Long tube = 20 feet in length Divided into 3 regions
♦Duodenum•Shortest region – follows stomach
•Approx. 10 inches long
♦Jejunum •8 feet
♦Ileum•12 feet
Activities in the small intestine:♦Secretion & Absorption
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Small Intestine – Secretions Summary Hormones in duodenum
Small Intestine – Anatomy Within the tube = 4 layers Mucosa
♦Contains waves of ridges•Plicae – these are like rugae, but they don’t stretch
♦Contains small projections•Villi – these are absorptive cells
Within each villus – single layer epithelial tissue♦There are hair like extensions on the cell – “brush border”♦Below the epithelium = capillaries for absorption
•There is also a lymph vessel = lacteal •Other larger molecules are not transferred through the blood •Will enter the lacteal
♦Goblet cells•Produce alkaline mucus•Neutralize pH, thus protecting the intestine from acid
Submucosa – below villi♦Contains “Peyer’s patches” = lymph nodules – these help in fat
absorption
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Small Intestine – Digestion Duodenum
♦Main job = secretion
Summary of secretions:♦Maltase, sucrase, & lactase
All 4 types of macromolecules can be digested in the S.I.
Chyme is mixed with secretions – needs segmentation & peristalsis
There are parasympathetic controls
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Small Intestine – DigestionDigestion of Macromolecules Carbohydrates: