CH. 20 The Gastrointestinal System Flashcards
How is the gastrointestinal system divided? and what belongs to each division?
- Gastrointestinal tract: mouth - pharynx - esophagus - stomach - small intestine - colon - rectum - anus
- Accessory glands: several glands outside the GI tract that secrete fluids and enzymes into the lumen of the GI tract
What are the 4 walls of the GI tract?
- Mucosa: lining of the lumen
- Submucosa: connective tissue
- Muscularis externa: smooth muscle
- Serosa: connective tissue
What are the 3 layers of the mucosa?
- Mucous membrane: separates GI lumen from internal environment
- Lamina propria: connective tissue
- Muscularis mucosae: thin layer of smooth muscle functions in mixing lumenal contents
What are the three different types of enterocytes?
- absorptive cells
- exocrine cells
- endocrine cells
What are the two layers of smooth muscle of the muscularis externa and how do they function?
- inner circular layer: changes diameter
2. outer longitudinal layer: changes length
What are the two parts of the enteric nervous system?
- submucosal plexus (Meissner’s plexus): from submucosa layer
- myenteric plexus (Auerbach’s plexus): from muscularis externa
What kind of tissue is the inner layer of the serosa vs. the outer layer?
Inner layer: connective tissue
Outer layer: epithelial tissue (mesothelium)
What does digestion begin with and what is secreted to aid this process?
Begins with mastication in the mouth.
- saliva is secreted that contains salivary amylase to breakdown cell walls and digest starch and glycogen (carbs)
What is the function of the pharynx?
common passageway for air and food and where respiratory and digestive system meet
How is the esophagus broken down?
tube from pharynx to stomach
- upper esophageal sphincter: skeletal muscle between pharynx and esophagus
- lower esophageal sphincter: smooth muscle between esophagus and stomach
How does the stomach function?
stores food after it is swallowed and secretes gastric juice to help break it down
- then releases food as chime into small intestine
What are the secretory products of the gastric pits and what are they secreted by?
- pepsinogen: secreted by chief cells
- hydrogen ions: secreted by parietal cells
- intrinsic factor: secreted by parietal cells
- gastrin: secreted from G cells
- mucus: secreted from neck cells
What purpose does the acidic environment of the stomach serve?
- necessary for activating pepsinogen
- denatures proteins
- kills bacteria
What acts as a protective barrier in relation to the acidic environment of the stomach?
gastric mucosal barrier
What is the primary site of digestion and absorption and how is it divided?
small intestine
- duodenum
- jejunum
- ileum
What two secretions enter the duodenum?
- pancreatic juice: contains digestive enzymes and bicarbonate that helps to neutralize acidic chyme
- bile: secreted from liver and contains bile salts that aid in fat digestion
Where is absorption completed in the small intestine?
within the first 20% of the small intestine
What is the function of the villi and microvilli of the small intestine wall?
Villi: increase surface area of epithelium
- contain blood vessels and lacteal for absorption of nutrients
Microvilli: increase surface area of epithelial cells
- form brush border
What is the function of the Crypts of Lieberkuhn?
epithelial cells in crypts secrete bicarbonate-rich fluid
- secreted in proximal small intestine
- absorbed in distal small intestine
What is the role of the liver in absorption?
absorbs nutrients traveling in the blood to the liver before entering the general circulation
- detoxify substances and processes certain nutrients
What is the hepatic portal system?
vasculature that delivers absorbed nutrients to the liver before nutrients enter the general circulation
What is the large intestine comprised of?
consists of cecum, colon, and rectum
- ileocecal sphincter is between ileum and colon
What are the functions of the colon?
- concentration of wastes into feces
- absorption of most water
- storage of feces until defecation
What are the four sections of the colon?
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
What muscle comprises the internal and external anal sphincters?
internal anal sphincter: smooth muscle
external anal sphincter: skeletal muscle
What are the four types of glands of the GI tract and how are its products secreted?
- salivary glands: saliva
- pancreas: pancreatic juice
- acini
- liver: secretes bile
secreted via ducts into the lumen of the GI tract
What are the characteristics of saliva?
- rich in bicarbonate ions
- contains mucus
- enzymes present: salivary amylase and lysozyme
What is produced by the exocrine portion of the pancreas?
pancreatic juice
- rich in bicarbonate
- relative to weight, secretes more protein than any other tissue in body
- enzymes present: pancreatic amylase, lipases, proteases, and nucleases
What are the functions of the liver?
- secretes bile into gallbladder
- processes nutrients
- glucose into glycogen
- amino acids into fatty acids
- triglycerides and cholesterol synthesis
- lipoprotein synthesis - removal of old red blood cells: generates bilirubin
- synthesis of plasma proteins
- secretion and modification of hormones
What is the function of the Sphincter of Oddi?
regulates flow from pancreas and gallbladder to duodenum
What are the enzymes of digestion and where are they located?
- dextrinase: limit dextrins -> glucose
- glucoamylase: polysaccharides -> glucose
- sucrase: sucrose -> fructose + glucose
- lactase: lactose -> galactose + glucose
- maltase: maltose -> 2 glucose
location of enzymes: brush border of small intestine
What are the two ways in which glucose and galactose are absorbed?
- secondary active transport across apical membrane
2. facilitated diffusion across basolateral membrane
How is fructose absorbed?
facilitated diffusion across both membranes
What are the products of protein digestion?
- amino acids
- dipeptides
- tripeptides
What are the three kinds of proteases?
- Endopeptidases: split polypeptides at interior peptide bonds into small peptide fragments
- Exopeptidases: cleave amino acids from one end of polypeptide
- Zymogens: inactive storage form of proteases
Where does protein digestion begin?
in the stomach
Where does protein digestion begin?
in the stomach
What kind of transport is used in the absorption of amino acids?
- sodium-linked secondary active transport or facilitated diffusion to cross the apical membrane
- facilitated diffusion to cross the basolateral membrane
What kind of transport is used in the absorption of dipeptides and tripeptides?
- cross the apical membrane by active transport
2. when broken into amino acids, cross the basolateral membrane by facilitated diffusion
What problems do lipids face in digestion and absorption?
- not water soluble
- do not mix with stomach or intestinal contents
- form fat droplets
How do bile salts aid in lipid digestion?
increase the surface area of droplets by breaking each large droplet into several small droplets (emulsification)
What are the criteria in which fat-soluble vitamins can be absorbed?
- absorbed with lipids
2. dissolve in lipid droplets, micelles, and chylomicrons
How is sodium absorbed?
solvent drag with water reabsorption
- actively absorbed in jejunum, ileum, and colon
How is chloride absorbed?
passively follows sodium absorption
How is potassium absorbed?
passively absorbed
- secreted when lumenal concentrations are very low
How is bicarbonate absorbed and secreted in the jejunum, ileum. and colon?
jejunum: bicarbonate ions are passively absorbed
ileum and colon: bicarbonate are secreted in exchange for chloride ions
How is water absorbed?
water absorption is passive
- water follows absorption of solutes by osmosis
What are the 4 gastrointestinal hormones?
- gastrin
- cholecystokinin
- secretin
- glucose-dependent insulinotropic peptide
What are the 3 phases of the gastrointestinal control and where do their stimuli originate?
- cephalic phase: stimulate originate in head
- gastric phase: stimuli originate in stomach
- intestinal phase: stimuli originate in small intestine
What is leptin?
a hormone released from adipose cells when calories exceed demands
What are the stimuli of cephalic phase secretion?
- sight of food
- taste
- small
- chewing
- swallowing
What are the stimuli of gastric phase secretion?
- proteins, peptides, and amino acids
2. distension of stomach
What inhibits secretion in the gastric phase?
- exit of food removes stimuli for secretion
- increased acidity inhibits gastrin release
What inhibits secretion in the intestinal phase?
- food entry into the duodenum
- long and short reflex pathways
What is the function of GI motility?
mix and propel GI tract contents
What is the bolus?
chewed food + saliva
What is the integration center for swallowing?
swallowing center of medulla oblongata
What are the stimuli for vomitting?
1. illness 2, emotions 3. pain 4. distension in GI tract 5. rotation of head 6. ingestion of certain substances (emetics)
