A&P Chapter 24: The digestive system
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What 2 organs are primarily responsible for water absorption?
- 1. Small intestines
- 2. Large intestines
What are the main functions of the stomach
- 1. Store ingested food
- 2. Disruption of chemical bonds in food through the action of acid and enzymes
- 3. Mechanical breakdown of food
- 4. Production of intrinsic factor needed for absorption of vitamin B12
What are the 3 types of cells found in the stomach and what substances do they secrete?
- 1. G cells: Gastrin (reduces pH of gastric juice and stimulates motility)
- 2. Chief cells: pepsinogen (converts to pepsin in acidic environment of stomach to break apart peptide bonds in proteins)
- 3. Parietal cells: intrinsic factor and HCl (H2CO3 dissociates, HCO3- is transported out/Cl- transported in, Cl- diffuses across cell membrane and H+ is transported out, results in HCl inside the stomach)
Where is the hormone cholecystokinin (CCK) found and what does it do?
- 1. Produced by enteroendocrine cells in the duodenum
- 2. Secreted when chyme arrives in the duodenum (especially lipids and partially digested proteins)
- 3. Increases the secretion of pancreatic enzymes
- 4. Relaxes hepatopancreatic sphincter, contracts gallbladder to eject bile and pancreatic juice into the duodenum
Where is the hormone gastrin found and what does it do?
- 1. Secreted by G cells in the stomach and duodenum when exposed to incompletely digested proteins
- 2. Increases stomach motility
- 3. Stimulates production of gastric acids and enzymes
Where is the hormone secretin found and what does it do?
- 1. Released in the duodenum when chyme is present
- 2. Increases the secretion of bile and buffers that act to increase the pH of the chyme
- 3. Reduces gastric motility and secretory rates
Where is the hormone gastric inhibitory peptide (GIP) and what does it do?
- 1. Secreted in the duodenum when fats and carbs (glucose) enter the small intestines
- 2. Inhibits gastric activity and stimulates the release of insulin
- 3. Stimulates duodenal gland activity, synthesis of adipose tissue and increases glucose use by skeletal muscles
Where is the hormone vasoactive intestinal peptide (VIP) and what does it do?
- 1. Secreted in the duodenum
- 2. Stimulates the secretion of intestinal glands, dilates regional capillaries, and inhibits acid production in the stomach
- 3. Dilation provides an efficient mechanism for removing absorbed nutrients in the intestinal tract
Where is the hormone enterocrinin found and what does it do?
- 1. Secreted in the duodenum when chyme enters
- 2. Stimulates mucin production by the submucosal glands
What are the 3 phases of gastric secretion?
- 1. Cephalic phase
- 2. Gastric phase
- 3. Intestinal phase
What happens during the cephalic phase of gastric secretion?
- 1. Prepares stomach for the arrival of food
- 2. Begins when you see, smell, taste or think of food
- 3. Generally lasts only a couple minutes
What happens during the gastric phase of gastric secretion?
- 1. Stomach secretes juice and mixes food into chyme
- 2. Initiated by distension of the stomach, increased pH of gastric contents and presence of undigested material
- 3. Generally lasts 3 to 4 hours
What happens during the intestinal phase of gastric secretion?
- 1. Stomach empties and decreases secretions
- 2. Controls the rate of gastric emptying to ensure that secretory, digestive and absorptive function of the small intestine can proceed efficiently
What are the 2 central gastric reflexes?
- 1. Gastroenteric reflex: stimulates motility and secretion along the entire small intestine
- 2. Gastroileal reflex: triggers the opening of the ileocecal valve, allowing materials to pass from the small intestine to the large intestine
What is rugae and what is its function in the stomach?
- 1. Prominent folds in the mucosa
- 2. Allows the gastric lumen to expand when you eat
- 3. Stomach can stretch up to 50x its empty size
- 4. As stomach fills, rugae flatten out until they almost disappear at maximum distension
What is the function of the pyloric sphincter and where is it located?
- 1. Located at the distal end of the pylorus separating the stomach from the duodenum
- 2. Regulates gastric emptying into the duodenum
What is the duodenal ampulla and where is it located?
- 1. Chamber located about halfway along the length of the duodenum
- 2. Receives bile from liver and pancreatic secretions through the pancreatic duct and the common bile duct
What are the endocrine and exocrine portions of the pancreas?
- 1. Endocrine: Pancreatic islets, release insulin or glucagon into the blood
- 2. Exocrine: Pancreatic acini, secrete pancreatic juice into small intestines (alkaline mixture of water, ions and digestive enzymes)
Which part of the small intestine is most likely to develop a gastric ulcer from exposure to gastric juice?
- 1. DUODENUM
- 2. Because it receives chyme with a pH of 1-2
HCl in the stomach is neutralized by what in the small intestine?
Sodium bicarbonate in the pancreas
What is pancreatic juice and what does it do?
- 1. An alkaline mixture of digestive enzymes, water and ions
- 2. Released into the small intestines through the pancreatic duct
- 3. Breaks down carbohydrates, lipids and proteins
What are the pancreatic enzymes?
- 1. Pancreatic alpha amylase (carbohydrase): breaks down starches similar to salivary amylase
- 2. Pancreatic lipase: break down certain complex lipids, releases products that can be easily absorbed
- 3. Nucleases: break down RNA and DNA
- 4. Proteolytic enzymes: break apart certain proteins, includes proteases for large complex proteins and peptidases for small peptide chains
What are the multiple characteristics of serosa of the intestinal wall?
- 1. Contributes to the mesentery of the small intestine
- 2. Part of the visceral peritoneum
- 3. Composed of simple squamous epithelia
What are the 3 distinctive physical characteristics of the colon?
- 1. Haustra: pouches that allow the colon to expand and elongate
- 2. Taeniae Coli: 3 longitudinal bands of smooth muscle, muscle tone in the taeniae coli create the haustra
- 3. Epiploic (fatty) appendages: teardrop sacs of fat lining the serosa
What is the digestive function of lacteals?
- 1. Lymphatic vessels
- 2. Transport products of fat digestion
What is the absorptive state of digestion?
- 1. The period following a meal when nutrient absorption is underway
- 2. Liver cells form glycogen
- 3. Absorbed nutrients are used for growth, maintenance, and energy reserves
What is the post absorptive state of digestion?
- 1. The period when nutrient absorption is not underway
- 2. The body relies on internal energy reserves for energy demands
- 3. Liver cells conserve glucose and break down lipids and amino acids
- 4. Lipid and amino acid catabolism generates acetyl-CoA
- 5. Increased concentration of acetyl-CoA results in the formation of ketone bodies
What happens in your body as a result of starvation?
- 1. Muscle proteins and lipids are used as energy sources
- 2. Lipid and amino acid catabolism generates acetyl-CoA which forms ketone bodies
- 3. Ketone bodies dissociate in solution releasing hydrogen ions
- 4. results in ketonemia
What are ketonemia and what complications does it cause?
- 1. The appearance of ketone bodies in the blood
- 2. Lowers blood pH and causes ketoacidosis
- 3. Blood pH can fall to as low as 7.05 resulting in coma, cardiac arrhythmias and death
What is ketonuria?
The presence of ketone bodies in the urine
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