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Digestive System

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Cheryl Stover

on 13 August 2012

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Transcript of Digestive System

Cardioesophageal sphincter Mucosa
Surface epithelium
Small amount of connective tissue
Small smooth muscle layer
Just beneath the mucosa
Soft connective tissue with blood vessels, nerve endings, and lymphatics
Muscularis externa—smooth muscle
Inner circular layer
Outer longitudinal layer
Serosa—outermost layer of the wall contains fluid-producing cells
Visceral peritoneum—outermost layer that is continuous with the innermost layer
Parietal peritoneum—innermost layer that lines the abdominopelvic cavity Mucosa Submucosa Muscularis externa Longitudinal layer Circular layer LAYERS OF ALIMENTARY CANAL ORGANS  Alimentary canal (gastrointestinal or GI tract)—continuous coiled hollow tube
Accessory digestive organs ORGANS OF THE DIGESTIVE SYSTEM  Mucosa is epithelium
 Mucous neck cells—produce a sticky alkaline mucus
 Gastric glands—situated in gastric pits and secrete gastric juice
 Chief cells—produce protein-digesting enzymes (pepsinogens)
 Parietal cells—produce hydrochloric acid
 Enteroendocrine cells—produce gastrin Structure of the Stomach Mucosa Enteroendocrine Chief Cells Mucous
Cells Three structural modifications that increase surface area
Microvilli—tiny projections of the plasma membrane (create a brush border appearance)
Villi—fingerlike structures formed by the mucosa
Circular folds (plicae circulares)—deep folds of mucosa and submucosa Small Intestine Anatomy Circular folds Circular folds Circular folds Villi Villi Villi Villi Villi Capillaries Capillaries Lacteal Microvilli Located on the left side of the abdominal cavity
Food enters at the cardioesophageal sphincter
Food empties into the small intestine at the pyloric sphincter (valve)
Regions of the stomach
Fundus—expanded portion lateral to the cardiac region
Pylorus—funnel-shaped terminal end
Rugae—internal folds of the mucosa Stomach Anatomy Fundus Body Rugae Rugae Rugae Rugae Rugae Pyloric Sphincter Pyloris Pyloric Sphincter Large Intestine Anatomy Cecum—saclike first part of the large intestine
Accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis)
Hangs from the cecum
Ascending—travels up right side of abdomen
Transverse—travels across the abdominal cavity
Descending—travels down the left side
Sigmoid—enters the pelvis
Rectum and anal canal—also in pelvis
Anus—opening of the large intestine
External anal sphincter—formed by skeletal muscle and under voluntary control
Internal involuntary sphincter—formed by smooth muscle
These sphincters are normally closed except during defecation Cecum Appendix Ascending Colon Transverse Colon Descending Colon Sigmoid Colon Rectum Anal Canal External
Anal Sphincter Liver Pancreas Gall
Bladder Duodenum R. Hepatic Duct L. Hepatic Duct Hepatic Duct Cystic Duct Common
Bile Duct Common Duct Pancreatic
Duct Acessory Organs Subdivisions of Small Intestine Duodenum
Attached to the stomach
Curves around the head of the pancreas
Attaches anteriorly to the duodenum
Extends from jejunum to large intestine Salivary Glands (3 pr) Tongue Esophagus Liver Gall Bladder Stomach Pancreas Large Intestine Small Intestine Rectum Rectum DIGESTION THE DIGESTIVE SYSTEM FUNCTIONS
Ingestion—getting food into the mouth
Propulsion—moving foods from one region of the digestive system to another
Peristalsis—alternating waves of contraction and relaxation that squeezes food along the GI tract
Segmentation—moving materials back and forth to aid with mixing in the small intestine
Food breakdown as mechanical digestion
Mixing food in the mouth by the tongue
Churning food in the stomach
Segmentation in the small intestine
Mechanical digestion prepares food for further degradation by enzymes
Food breakdown as chemical digestion
Enzymes break down food molecules into their building blocks
Each major food group uses different enzymes
Carbohydrates are broken to simple sugars
Proteins are broken to amino acids
Fats are broken to fatty acids and alcohols
End products of digestion are absorbed in the blood or lymph
Food must enter mucosal cells and then into blood or lymph capillaries
Elimination of indigestible substances from the GI tract in the form of feces Chemical Digestion of Stomach Cardioesophageal sphincter Stomach Fundus Body Rugae Rugae Rugae Rugae Rugae Pyloric Sphincter Pyloris Pyloric Sphincter Liver Pancreas Gall
Bladder Duodenum R. Hepatic Duct L. Hepatic Duct Hepatic Duct Cystic Duct Common
Bile Duct Common Duct Pancreatic
Duct Acessory Organs Mastication (chewing) of food
Mixing masticated food with saliva
Initiation of swallowing by the tongue
Allows for the sense of taste
Mechanical breakdown
Food is physically broken down by chewing Chemical digestion
Food is mixed with saliva
Starch is broken down into maltose by salivary amylase
Three pairs of salivary glands empty secretions into the mouth
Parotid glands
Submandibular glands
Sublingual glands
Mixture of mucus and serous fluids
Helps to form a food bolus
Contains salivary amylase to begin starch digestion
Dissolves chemicals so they can be tasted Parotid Sublingual Submandibular Serves as a passageway for air and food
Food is propelled to the esophagus by two muscle layers
Longitudinal inner layer
Circular outer layer
Food movement is by alternating contractions of the muscle layers (peristalsis) Conducts food by peristalsis (slow rhythmic squeezing)
Passageway for food only (respiratory system branches off after the pharynx) Digestion and Absorption in the Stomach
Protein digestion enzymes (chemical digestion)
Pepsin—an active protein-digesting enzyme
Rennin—works on digesting milk protein in infants, not adults
Alcohol and aspirin are the only items absorbed in the stomach Gastric juice is regulated by neural and hormonal factors
Presence of food or rising pH causes the release of the hormone gastrin
Gastrin causes stomach glands to produce
Protein-digesting enzymes
Hydrochloric acid
Hydrochloric acid makes the stomach contents very acidic
Activates pepsinogen to pepsin for protein digestion
Provides a hostile environment for microorganisms Propulsion in Stomach Food must first be well mixed
Rippling peristalsis occurs in the lower stomach
The pylorus meters out chyme into the small intestine (30 mL at a time)
The stomach empties in 4–6 hours Pancreatic enzymes play the major digestive function
Help complete digestion of starch (pancreatic amylase)
Carry out about half of all protein digestion
Digest fats using lipases from the pancreas
Digest nucleic acids using nucleases
Alkaline content neutralizes acidic chime
Bile, formed by the liver, enters via the bile duct Absorption in the Small Intestine
Water is absorbed along the length of the small intestine
Most substances are absorbed by active transport through cell membranes
Lipids are absorbed by diffusion
Substances are transported to the liver to be processed

Propulsion in the Small Intestine
Peristalsis is the major means of moving food
Segmental movements
Mix chyme with digestive juices
Aid in propelling food
Segmentation Pancreas
Produces a wide spectrum of digestive enzymes that break down all categories of food
Enzymes are secreted into the duodenum
Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from stomach
Hormones produced by the pancreas
-Glucagon Liver
Largest gland in the body
Produces bile —emulsify fats by physically breaking large fat globules into smaller ones
Processes nutrients
Produces plasma proteins
Detoxifies Sac found in hollow fossa of liver
When no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder
When digestion of fatty food is occurring, bile is introduced into the duodenum from the gallbladder Release of pancreatic juice into the duodenum is stimulated by
Vagus nerve
Local hormones
Cholecystokinin (CCK)
Hormones travel the blood to stimulate the pancreas to release enzyme- and bicarbonate-rich product
Secretin causes the liver to increase bile output
CCK causes the gallbladder to release stored bile
Bile is necessary for fat absorption and absorption of fat-soluble vitamins Stomach Small Intestine Acessory Organs Oral Cavity Pharynx Esophagus Pancreatic Juice Secretion Large
Intestine Food Breakdown and Absorption in the Large Intestine
No digestive enzymes are produced
Resident bacteria digest remaining nutrients
Produce some vitamin K and B
Release gases
Water and vitamins K and B are absorbed
Remaining materials are eliminated via feces
Feces contains
Undigested food residues

Propulsion in the Large Intestine
Sluggish peristalsis
Mass movements
Slow, powerful movements
Occur three to four times per day
Presence of feces in the rectum causes a defecation reflex
Internal anal sphincter is relaxed
Defecation occurs with relaxation of the voluntary (external) anal sphincter Stomach Digestion The Digestive Process Digestive System Digestive Enzymes Bizarre but accurate
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