Digestive System Flashcards
What is the main function(s) of the digestive system?
-break down foods
-release the nutrients
-absorb the nutrients
Where does the GI tract begin/end?
begins at the mouth and ends at the anus
True or false: food/waste within the alimentary canal is considered to be outside the body.
True
How are mechanical and chemical digestion begun in the mouth?
Teeth and tongue begin mechanical, salivary glands begin chemical.
What are the four main tissues that comprise the alimentary tract?
Mucosa, Submucosa, Muscularis, Serosa
What is the mucosa comprised of?
-Epithelium (in contact with digested food)
-Lamina propria (layer of connective tissue)
-Muscularis mucosa (thin smooth muscle layer)
What is the predominant epithelium in the mouth, pharynx, esophagus, and anal canal?
Non-keratinized stratified squamous
What is the predominant epithelium in the stomach and intestines?
Simple columnar epithelium
What other two cells are found among the epithelium and what are their functions?
-Goblet cells: secreting mucus and fluid into the lumen
-Enteroendocrine cells: secreting hormones into the interstitial spaces between cells
What does the lamina propria consist of, and what does it do?
-Loose connective tissue
-Numerous blood and lymphatic vessels that transport nutrients
-Serves as an immune function by housing clusters of lymphocytes (makes up the mucosa-associated lymphoid tissue, aka MALT)
What are Peyer’s Patches?
Lymphocyte clusters in the distal ileum that protect the body from foodborne bacteria/other foreign matter
What is the submucosa?
-Immediately beneath the mucosa
-Dense connective tissue
-Connects the mucosa to the muscularis
-Includes blood/lymphatic vessels and submucosal glands that release digestive secretions
What is the muscularis externa?
-Third layer of the alimentary canal
-Double layer of smooth muscle: inner circular layer + outer longitudinal layer
-Contracts to move food (peristalsis)
What is the serosa?
-Superficial to the muscularis
-Present only within the abdominal cavity
-Consists of a layer of visceral peritoneum + a layer of loose connective tissue
-Holds the alimentary canal near the ventral surface of the vertebral column
What is the peritoneum?
-Holds digestive organs within the abdominal cavity
-Broad serous membrane made up of squamous tissue surrounded by connective tissue
-Parietal peritoneum lines the abdominal wall
-Visceral peritoneum envelops the abdominal organs
What is the function of the mouth?
-Chewing & mixing food
-Begins chemical and mechanical breakdown of food
-Moistens and dissolves
-Cleans & lubricates the teeth/oral cavity
-Some antimicrobial activity
What is the function of the pharynx?
-Propels food from oral cavity to esophagus
-Lubricates food & passageways
What is the function of the esophagus?
-Propels food to the stomach via peristalsis
-Lubricates food & passageways
What is the function of the stomach?
-Mixes food to form chyme
-Chemical breakdown of proteins (HCl)
-Low pH is antimicrobial
-Secretes intrinsic factor required for vitamin B12 absorption in small intestine
What is the function of the small intestine?
-Mixes chyme with digestive juices
-Propels food slowly for digestion & absorption
-Absorbs broken down carbs, proteins, lipids, nucleic acids, vitamins/minerals, & water
What is the function of the large intestine?
-Further food breakdown
-Absorbs most residual water, electrolytes, & vitamins produced by enteric bacteria
-Propels feces to rectum
-Eliminates feces
What is segmentation?
Smooth muscle contractions in intestines that moves food back and forth
What are the accessory organs to the digestive system?
Liver, gallbladder, pancreas
What are the six activities of digestive processes?
- Ingestion
- Propulsion
- Mechanical/physical digestion
- Chemical digestion
- Absorption
- Defecation
What are the three major salivary glands?
-Submandibular glands
-Sublingual glands
-Parotid glands
What is saliva?
-95.5% water
-Contains salivary amylase for digestion
-Initiates carbohydrate breakdown
-Contains lingual lipase
Where are the major salivary glands located?
Outside the oral mucosa and deliver saliva through ducts
What does the stomach mucosa epithelial lining consist of, and what does it do?
Surface mucous cells that secrete protective alkaline mucous
What are gastric pits/glands?
-Gastric pits dot the surface of the stomach epithelium
-They lead to gastric glands which secrete gastric juice
What protects the stomach from pathogens?
-MALT (mucosa associated lymphoid tissue)
-Peyer’s patches
What are parietal cells?
Produce HCl and intrinsic factor (allows SI to absorb vitamins)
What is the purpose of HCl in the stomach?
The high acidity (pH 1.5-3.5) and is needed to activate pepsinogen into pepsin
What are chief cells?
Secrete pepsinogen, an inactive proenzyme form of pepsin
Where does the most absorption occur in the digestive system?
Small intestine
Why is the large surface area of the small intestine necessary?
For complex processes of digestion and absorption
What are the three sections of the small intestine?
- Duodenum
- Jejunum
- Ileum
What differentiates the mucosa/submucosa of the small intestine from other mucosae?
-Circular folds
-Villi
-Microvilli (brush border)
What is the purpose of villi//microvilli in the small intestine?
Increasing the surface area more than 600X
Describe chemical digestion in the small intestine:
-Completion of the digestion of proteins and carbohydrates that began in the stomach
-Lipids arrive mostly undigested, so they are focused on with bile and the enzyme pancreatic juice
-Intestinal juice combines with pancreatic juice
-Most water is absorbed by osmosis
What are the four major organic compounds?
-Carbohydrates
-Proteins
-Fats
-Nucleic acid
What are the four main regions of the large intestine?
-Cecum
-Colon
-Rectum
-Anus
Describe the histology of the large intestine:
-Few enzyme-secreting cells
-No circular folds or villi
-Mucosa is simple columnar epithelium made mostly of enterocytes and goblet cells
-Goblet cells secrete mucus to ease the movement of feces
-Enterocytes absorb water and salts as well as vitamins produced by intestinal bacteria
Which vitamins are absorbed in the large intestine due to bacterial activity?
B & K
What are most bacteria that enter the alimentary canal killed by?
-Lysozyme
-Defensins
-HCl
-Protein-digesting enzymes
What is referred to as bacterial flora?
Trillions of bacteria living within the large intestine
What do many bacterial flora do?
-Facilitate chemical digestion and absorption
-Synthesize certain vitamins: mainly biotin, pantothenic acid, vitamin K
What is the largest gland in the body?
The liver-inferior to the diaphragm in the right upper quadrant of the abdominal cavity, protected by the ribs
What is the porta hepatis?
-“Gate to the liver”
-Where the hepatic artery and hepatic portal vein enter the liver
What does the hepatic portal vein do?
-Delivers partially deoxygenated blood containing nutrients absorbed from the small intestine
-Supplies more oxygen to the liver than the smaller hepatic arteries
What type of capillary is common in the liver?
Sinusoids
What are the three main components of the liver?
-Hepatocytes
-Bile canaliculi
-Hepatic sinusoids
What are hepatic laminae?
Plates of hepatocytes that radiate outward from the portal vein in each hepatic lobule
What happens to the bile produced by hepatocytes?
-Small ducts accumulate the bile
-Flows first into bile ductules then bile ducts
-Bile ducts unite to form the right and left hepatic ducts
-R & L hepatic ducts merge & exit the liver as the common hepatic duct
-This joins with the cystic duct from the gallbladder forming the common bile duct that brings the bile to the small intestine
What is the purpose of bile?
-Lipids are hydrophobic
-Must be broken down before the watery small intestine
-Bile emulsifies lipids into smaller globules
What is the pancreas?
-Lies transversely in the retroperitoneum behind the stomach
-Head nestles into the curvature of the duodenum
-Body extends to the left about 15cm
-Mix of endocrine and exocrine
What is pancreatic juice?
-Pancreas produces over a liter per day
-Clear and mostly water, & some salts, Na bicarbonate, digestive enzymes
-Slightly alkaline (pH 7.1-8.2) to buffer acidic gastric juice
-Inactivates pepsin
-Pancreatic enzymes active in digestion of sugars, proteins, and fats
What are pancreatic enzymes?
-Pancreas produces protein-digesting enzymes in inactive forms (zymogen)
-Enzymes activated in the duodenum
What does enteropeptidase do and what is the result?
-Stimulates the activation of trypsin from trypsinogen
-This in turn changes procarboxypeptidase and chymotrypsinogen into carboxypeptidase and chymotrypsin
What is the gallbladder?
-8-10cm long
-Nested in a shallow area on the posterior aspect of the right lobe of the liver
-Stores, concentrates, and propels the bile into the duodenum via the common bile duct
What is chemical digestion?
-Large food molecules must be broken down into subunits that are small enough to be absorbed
-This is accomplished by enzymes through hydrolysis
What are the three most readily absorbed monosaccharides?
Glucose, galactose, fructose
What carbohydrates can the digestive system break down?
Sucrose, lactose, maltose, glycogen, starch
What enzyme does most of the starch and carbohydrate digestion in the small intestine?
Pancreatic amylase
What do sucrase, maltase, and lactase do?
Sucrase: splits sucrose into 1 fructose and 1 glucose
Maltase: splits maltose into 2 glucose
Lactase: splits lactose into 1 glucose and 1 galactose
What are proteins?
Polymers composed of amino acids linked by peptide bonds to form long chains
How does digestion of protein begin?
In the stomach where HCl and pepsin break them into smaller polypeptides
How are proteins digested in the small intestine?
Pancreatic enzymes including chymotrypsin and trypsin, which act on specific bonds
How are cells of the brush border involved in protein digestion?
Secrete enzymes like aminopeptidase and dipeptidase, which make the peptide chains small enough to enter the blood stream
What are the most common dietary lipids?
Triglycerides, a glycerol molecule bound to three fatty acid chains
What three lipases are responsible for lipid digestion?
Lingual lipase, gastric lipase, pancreatic lipase
What three lipases are responsible for lipid digestion?
Lingual lipase, gastric lipase, pancreatic lipase
Where does virtually all lipid digestion occur?
Small intestine
What is the only consequential source of lipase?
Pancreas
What does pancreatic lipase do to each triglyceride?
Breaks it down into two free fatty acids and a monoglyceride
What two types of pancreatic nuclease are responsible for digesting nucleic acids?
Deoxyribonuclease
Ribonuclease
What are nucleotides further broken down into and by what brush border enzymes?
Broken down into pentoses, phosphates, and nitrogenous bases by nucleosidase and phosphatase
Roughly how much water enters the small intestine daily, and how much is from foods/beverages?
9 liters, 2.3 liters from food/beverages
What is water absorption driven by?
The concentration gradient of water: higher concentration in chyme than in epithelial cells
What does the combining form an/o mean?
Anus
What does the combining form append/o and appendic/o mean?
Appendix
What does the combining form cholecyst/o mean?
Gallbladder
What does the combining form col/o and colon/o mean?
Colon
What does the combining form duoden/o mean?
Duodenum
What does the combining form esophag/o mean?
Esophagus
What does the combining form gastr/o mean?
Stomach
What does the combining form hepat/o mean?
Liver
What does the combining form ile/o mean?
Ileum
What does the combining form jejun/o mean?
Jejunum
What does the combining form or/o mean?
Mouth
What does the combining form pancreat/o mean?
Pancreas
What does the combining form pharyng/o mean?
Pharynx
What does the combining form proct/o mean?
Anus + rectum
What does the combining form rect/o mean?
Rectum
What does the combining form sigmoid/o mean?
Sigmoid colon
What does the combining form stomat/o mean?
mouth
What is cholelithiasis?
Abnormal condition of gallstones
What is cirrhosis?
Chronic disease of the liver with degeneration of liver cells
What is colonic polyposis?
Condition in which polyps protrude from the mucous membrane lining the colon
What is diverticulosis?
Abnormal condition of diverticula in the wall of the intestine (often the colon)
What is diverticulitis?
Inflammation and infection within diverticula
What is gastroesophageal reflux disease?
GERD is a condition in which contents of the stomach flow back into the esophagus
What is hepatitis?
Inflammation of the liver
What is inflammatory bowel disease?
IBD is the inflammation of the terminal portion of the ileum (crohn disease) or inflammation of the colon (ulcerative colitis)
What is irritable bowel syndrome?
IBS is a collection of symptoms that include: cramping, abdominal bloating, constipation, and diarrhea. Cause is unknown
What is hepatocellular carcinoma?
Liver cancer
What is jaundice?
Yellow colouration of the skin and other tissues caused by high levels of bilirubin in the bloodstream (hyperbilirubinemia)
What is abdominal computed tomography?
CT scan of the abdominal organs
What is abdominal magnetic resonance imaging?
MRI scan of the abdominal organs
What is abdominal ultrasonography?
Ultrasound of the abdomen
What is a barium enema?
Barium is injected into the anus and rectum, and x-ray images are taken
What is an upper GI series?
A barium swallow is barium ingested by mouth and x-ray images are taken of the esophagus, stomach, and small intestine
What is a cholangiography?
X-ray examination of the bile ducts after the injection of contrast material through the liver or a catheter from the mouth, esophagus, and stomach into the bile ducts
What is a gastrointestinal endoscopy?
Visual examination of the gastrointestinal tract with an endoscope
What is a hemoccult test?
Feces are placed on paper containing the chemical guaiac which reacts with hidden (occult) blood. Screening test for colon cancer
What is a liver function test?
Measurements of liver enzymes and other substances in the blood, high levels indicate liver damage
What is a stool culture?
Feces are placed in a growth medium to test for microorganisms
What is a virtual colonoscopy?
CT and MRI scans to produce 2 & 3D images of the colon
What is anastomosis?
Surgical creation of an opening between two gastrointestinal organs
What is a colostomy?
Surgical creating of a new opening of the colon to the outside of the body
What is an ileostomy?
Surgical creation of a new opening of the ileum to the outside of the body
What does ALT/AST stand for?
Alanine Transaminase and Aspartate Transaminase (Liver enzymes)
What does BE stand for?
Barium Enema
What does ERCP stand for?
Endoscopic Retrograde CholangioPancreatography
What does GB stand for?
GallBladder
What does GERD stand for?
GastroEsophageal Reflux Disease
What does GI stand for?
GastroIntestinal
What does IBD stand for?
Inflammatory Bowel Disease
What does IBS stand for?
Irritable Bowel Syndrome
What does LFT stand for?
Liver Function Test
What does NPO mean?
Nil Per Os (nothing by mouth)
What does TPN stand for?
Total Parenteral Nutrition
What part of the GI tract is this and what epithelial tissue lines the lumen of this part?
Esophagus-lined with non-keratinized stratified squamous epithelial tissue
Identify the organ depicted in this image, the function of the encircled structures, and the type of epithelial tissue lining these structures:
-Stomach wall
-Gastric pits + glands
-Simple columnar epithelium
What does this image depict?
Duodenum section of the small intestine
What does this image depict?
Jejunum section of the small intestine
What does this image depict?
Ileum section of the small intestine
What organ is depicted in this image, and what are the three layers shown in the image?
-Colon
-Mucosa (darkest purple)
-Submucosa (middle layer)
-Muscularis (lighter purple)
What is depicted in this image and what is structure indicated by the circle?
-Rectum
-Anal column
