Digestive System Disorders Flashcards
What are the five continuous layers of the gut?
Inner layer mucosa - contains mucus-producing cells
Submucosal layer - Connective tissue, including blood vessels, nerves, lymphatics and secretory glands
Circular smooth muscle fibers
Longitudinal smooth muscle fibers
Outer layer visceral peritoneum or serosa
Peritoneum
A large serous membrane in the abdominal cavity
Parietal covers the abdominal wall and superior surface of the urinary bladder and uterus
Visceral encases the organs such as the stomach and intestine
Peritoneal cavity
The potential space between the parietal and visceral peritoneum. Contains serous fluid.. Numerous lymphatic channels drain excessive fluid from the cavity.
Characteristics of serous membranes
Thin, somewhat permeable, highly vascular.
Mesentery
Double layer of peritoneum that supports the intestines and conveys blood vessels and nerves to supply the wall of the intestine
Attaches the jejunum and ileum to the posterior (dorsal) abdominal wall
Greater omentum
A layer of fatty peritoneum that hangs from the stomach like an apron over the anterior surface surface of the transverse colon and the small intestine.
Lesser omentum
Part of the peritoneum that suspends the stomach and duodenum from the liver.
Adhesions
Inflammation of the omentum and peritoneum may lead to scar tissue that causes the structures to adhere. Ex. loops of intestine, restricting mobility.
Retroperitoneal organs
The kidneys and pancreas are located posterior to the stomach against the abdominal wall and behind the parietal peritoneum, they are covered with peritoneum only on the anterior surface and are therefore retroperitoneal organs.
Where do salivary secretions come from?
Parotid, sublingual and submandibular glands.
What do salivary secretions contain?
Mucus and the enzyme amylase which begins the digestion of carbohydrate in the mouth.
Nerves responsible for swallowing?
Trigeminal and glossopharangeal nerves - relay information to the swallowing center in the medulla.
Actions required to move food or fluid into the stomach
Cranial nerves V, IX, X, and XII Soft palate is pulled upward Vocal cords are approximated Epiglottis covers the larynx Respiration ceases Bolus is seized by constricted pharynx Bollus moves into esophagus, peristalsis initiated Lower esophageal (gastroesophageal or cardiac) sphincter relaxes allowing it to move into the stomach
Salivary amylase
Parotid gland - splits starch and glycogen into disaccharides
Pepsin
Gastric chief cells - initiates splitting of proteins
Pancreatic amylase
Pancreas - Splits starch and glycogen into disaccharides
Pancreatic Lipase
Pancreas - splits triglycerides into fatty acids and monoglycerides
Trypsin, chymotrypsin, carboxypeptidase
Pancreas - Splits proteins into peptides
Pancreatic nucleases
Pancreas - splits nucleic acids into nucleotides
Intestinal peptidase
Intestinal mucosa - converts peptides into amino acids
Intestinal lipase
Intestinal mucosa - converts fats into fatty acids and glycerol
Intestinal sucrase, maltase, lactase
Intestinal muscosa - converts disaccharides into monosaccharides
How much can the stomach hold?
1L to 1.5L
Rugae
Folds of the stomach wall
Composition of stomach wall
Three smooth muscle layers, longitudinal, circular and oblique, plus mucosa (contains numerous glands) and submucosa.
Chyme
Stomach contents with added secretions.
What do the gastric glands do?
Contain parietal cells that secrete hydrochloric acid (highly acidic, ph 2) and chief cells that secrete pepsinogen (converts into active form, pepsin by activation by hydrochloric acid)
Parietal cells produce Intrinsic factor which is required for the absorption of Vit B12 in the ileum.
Gastrin - stimulates the parietal and chief cells
What secretions are added to the chyme in the duodenum?
Secretions from the liver and the exocrine pancreas through the ampulla of Vater and duodenal papilla.
Liver
Upper right quadrant under the diaphragm. Covered by fibrous capsule.
Metabolic center
Hepatocytes
Arranged in lobules, each lobule has plates of cells radiating from central veins, eventually drain blood back into the general circulation through the hepatic veins and inferior vena cava.
Sinusoids
Filled with blood from two sources pass between the plates of hepatocytes. Blood entering sinusoid comes from branches of the hepatic artery, carrying oxygen to the liver cells, venous blood from the portal vein, which transports nutrients absorbed from the stomach and intestines (hepatic portal circulation) as well as from the pancrease and spleen. Arterial and venous blood mix and flow slowly through the sinusoids, permitting the hepatocytes to do their jobs.
Kupffer cells
Line the sinusoids. Remove and phagocytose any foreign material and bacteria from the digestive tract before blood enters the general circulation.
What does the liver do?
As blood flows through sinusoids, absorbed nutrients are taken up by the hepatocytes to be stored (iron, copper, A, B6, B12, D and K and folic acid). Releases nutrients and glucose into blood as they need to be replaced.
Converts one amino acid into another as needed.
Synthesis and control of blood levels of other materials such as plasma proteins, clotting factors or lipoproteins
Synthesis of cholesterol - for use in the production of steroid hormones such as cortisol and bile salts.
Hormones such as aldosterone and estrogen are inactivated and prepared for excretion.
Ammonia ( a nitrogen waste resulting from protein metabolism) is removed from blood and converted to urea so it can be excreted by kidneys.
Drugs and alcohol are detoxified - increases solubility to facilitate excretion.
Removes damaged or old erythrocytes to facilitate recycling of iron and protein from hemoglobin.
Serves as a blood reservoir.
How does the liver work with insulin?
The liver responds to high levels of blood glucose by glycogenesis, converting glucose to glycogen which is stored in the liver. Hepatocytes break down glycogen and release glucose into the blood when glucose levels drop and glucagon secretion increases.
Gluconeogenesis - conversion of protein and fat into glucose may take place when glucose drops under influence of cortisol or epinephrine.
Main function of hepatocytes
Constantly produce bile (water, bile salts, bile pigment - conjugated bilirubin), cholesterol, and electrolytes). Bile is vital for digestion- serves as a vehicle for removal of bilirubin and excess cholesterol from body.
Bile salts
Formed from cholesterol - essential for emulsification of fats and fat-soluble vitamins (A, D, E and K) before they can be absorbed from the intestine.
Bicarbonate ions in bile assist in neutralizing gastric acid, increasing the pH of the small intestine so intestinal and pancreatic enzymes can function.
How does bile reach the intestines?
Flows though small canaliculi in the liver and drains into larger ducts until it reaches the right or left hepatic duct then the common bile duct. Will either go to gallbladder for storage or to the duodenum.
Pancreas
Posterior to stomach
Cells arranged in lobules, secrete digestive enzymes, electrolytes and water into tiny ducts, which drain into main pancreatic duct, joins the common bile duct and drains into the duodenum.
Composition of pancreatic secretions
Proteolytic enzymes - trypsin, chymorypsin, carboxypeptidase, ribonuclease.
Pancreatic amylase - digestion of carbohydrates
Lipase - digestion of fats
Enzymes are inactive until the reach the duodenum
Bicarbonate ion - neutralizes HCl in duodenum
Sections of small intestine
Duodenum - enzymes are added and alkaline pH obtained, jejunum, ileum - major site of nutrient absorption
Plicae circularies
Transverse folds of the small intestine mucosa covered with villi and microvilli
Composition of a villus
Capillary network, nerves, and a lacteal (terminal lymphatic vessel, essential for absorption of lipids).
Intestinal crypts
Deep pockets at base of villi where new epithelial cells arise. Produce fluid of pH 7, enzymes such as enterokinase, cholecystokinin, peptidases, nucleosidases, lipase, sucrase, maltase, and lactase.
Juncture between small and large intestine
ileocecal valve
Cecum
At the juncture between small and large intestine, pouch, from with the appendix extends
Passage of food along the intestines
Duodenum, jejunum, ileum, ileocecal valve, cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anal canal.
Function of the colon
Absorption of water and large amounts of electrolytes, helps maintain fluid and acid-base balances in the body (ex sodium, bicarbonate). General digestion and absorption ceases in the colon. Resident bacteria assist in further breakdown of certain food materials and convert belirubin to urobilinogen (brown feces).
Peyer’s patches
Large masses of lymphoid tissue in the ileum, limit the spread of bacteria into the small intestine.
Example of a beneficial bacteria
Bacteria that synthesize Vit K which is required for clotting factors in the liver.
Mass movements
Happen in the transverse and descending colon, strong peristaltic contractions that occur several times daily.
Haustra
Large pouches in the colon wall that allow for expansion as more solid material collects.
Composition of feces
Fiber, other indigestible material, sloughed mucosal cells, bacteria.
Function of fiber
Increased bulk increases intestinal motility and rate of passage, larger fecal mass and more frequent defecation.
Function of parasympathetic nervous system to digestion
Through the vagus nerve, increased motility (peristalsis) increased secretions.
Nerves that stimulate saliva production
Facial nerve (VII) and Glossopharyngeal (IX)
How long does it take the stomach to empty?
2-6 hours
Enterogastric reflux
The presence of food in the intestine stimulates intestinal activity but inhibits gastric activity to prevent overloading of the duodenum and sufficient time for intestinal digestion and absorption.
What reflex happens after you eat?
Increase in peristalsis around the ileocecal valve, moves ileal contents into the cecum and colon.
Gastrocolic reflex
Stimulates a mass movement of the contents from the colon into the rectum when food enters the stomach
Gastrin
Secreted by mucosal cells in the pyloric antrum of the stomach in response to distention of the stomach. Gastrin enters the blood, circulates, then returns to stimulate the gastric cells to increase secretions, increase gastric motility, relax pyloric and ileocecal sphincters and promote stomach emptying.
What hormones are released by mucosal cells in the duodenum?
Secretin - decreases gastric secretions and increases bicarbonate ion content of pancreatic secretions and bile when chyme is highly acidic
Cholecystokinin (CCK) - inhibits gastric emptying, stimulates pancreatic secretions with increased digestive enzymes, stimulates contraction of gallbladder to increase bile flow into the duodenum.
Gastrin
Released by gastric cells in response to food in stomach, protein, caffeine, or high pH of chyme - increased gastric secretions and motility and gastric emptying
Cholecystokinin
Released by Intestinal mucosal cells, in response to protein and fat in the duodenum.
Increases gastric secretions and motility, stimulates pancreatic enzyme secretion, stimulates gallbladder contractions and release of bile
Secretin
Released by intestinal mucosal cells, in response to acidic chyme in the duodenum. Stimulates bile and pancreatic secretions with high bicarbonate content
How do nutrients go from the intestines to the liver?
Nutrients are absorbed along with electrolytes and water into the blood and transported to the liver through the hepatic portal system.
How are carbohydrates digested?
Digested first in the mouth, then in the intestine, broken by enzymes into simple sugars (monosaccharides) that are absorbed by the intestine (primarily jejunum and ileum)
How are proteins digested?
First split into peptides in the stomach and intestine and then broken down by peptidases into amino acides, many of which are absorbed by a sodium co-transport system in the small intestine.
How are lipids digested?
Must first be emulsified by bile in the small intestine, enzymes then act on the fats forming monoglycerides and free fatty acids, which then diffuse across the membrane.
Chylomicrons
After fats cross the membrane, they often recombine to form triglycerides again and then bind to protein to form chylomicrons, most of which diffuse into the lacteals or lymph circulation, which then go to the liver or adipose tissue.
Short-chain fatty acids may diffuse directly into the blood.
How are fat-soluble vitamins digested?
A, D, E and K, do not require digestion, absorbed with the fats.
What activates the vomiting center in the medulla?
Distension of irritation of the digestive tract
Stimuli from various parts of the brain in response to unpleasant sights or smells, or ischemia
Pain or stress
Vestibular apparatus of the inner ear
Increased intracranial pressure
Stimulation of the chemoreceptor trigger zone in the medulla by drugs, toxins, and chemicals.
Drugs- by irritation of the digestive mucosa.
Increased risks of aspiration
When person is supine or unconscious or when vomiting reflex is depressed by drugs, the barriers to the respiratory tract may not be completely closed off or the vomit may not be completely expelled, cough reflex may also be expelled. post surgery.
Hematemesis
Brown, granular material resulting from partial digestion in the stomach of protein in the blood (coffee grounds).
Yellow-greenish vomit
Bile from the duodenum
Deep brown vomit
May indicate content from the lower intestine, typical of recurrent vomiting in persons with intestinal obstruction
Characteristics of bulimia
Damage to teeth from HCl, anorexia, tears of esophagus, constipation, diarrhea, electrolyte / nutritional imbalances and deficiencies.
Enterocolitis
Diarrheal diseases
Different types of diarrhea
Large-volume - often related to infections with short transit time. Common cause is lactose intolerance
Small-volume - often in inflammatory bowel disease, may contain blood, mucus or pus, cramps, urgency.
Steatorrhea - “fatty diarrhea” frequent bulky, greasy, loose stools, foul odor. Characteristic of malabsorption syndromes such as celiac or cystic fibrosis. Abdomen often distended.
Frank blood
Red, often from lesions in rectum or anal canal, has not been digested
Occult blood
Small, hidden amounts of blood, not visible to the eye, detectable on tests, may be from small bleeding ulcers in stomach or small intestine
Melena
Dark coloured (tarry) stool, results from significant bleeding that has occurred higher in the digestive tract
Causes of constipation
Increased age and weakness of the smooth muscle in intestines
Inadequate dietary fiber
Inadequate fluid intake
Failure to respond to defecation reflex because of pain or bad timing
Muscle weakness or inactivity
Neurologic disorders, such as multiple sclerosis or spinal cord trauma
Drugs like opiates and other central nervous system depressants or anticholinergics
Some antacids, iron meds, bulk laxatives with insufficient fluid intake
Obstruction (delay passage and cause excessive reabsorption)
What is the result of dehydration / hypovolemia from vomiting?
Electrolytes such as sodium are lost
Diarrhea leads to significant loss of potassium ion
Acid-base imbalances - vomiting leads to loss of hydrochloric acid, resulting in metabolic alkalosis and hypochloremia with increased serum bicarbonate levels
Metabolic acidosis
If vomiting is severe, duodenal secretions containing large quantities of bicarbonate ion are lost, ketoacidosis develops from glucose deficit, lactic acide accumulates from hypovolemia and impaired tissue perfusion, as well as increased muscle activity. Dehydration can limit ability of kidneys to respond to acidosis.
