Digestive System Flashcards
What are the main functions of the digestive system?
- Take in food
- Break down into nutrient molecules
- Absorb molecules into the bloodstream
- Get rid of waste
What are the two groups of the digestive system?
- Alimentary canal (gastrointestinal/GI/gut)
- Accessory digestive organs
What constitutes the alimentary canal?
Mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus
What constitutes the accessory digestive organs?
Teeth, tongue, gallbladder, digestive glands, salivary glands, liver and pancreas
What is propulsion and what does it involve?
- Movement of food through the alimentary canal including:
- swallowing
- Peristalsis: altering waves of contraction and relaxation
What is a mesentery and what does it do?
A double layer of peritoneum- a sheet of two serous membranes fused back to back that extends to the digestive organs from the body wall.
- Provide routes for blood vessels, lymphatics, and nerves to reach the digestive viscera
- Hold organs in place
- Store fat
What is segmentation?
- The process of mechanical breakdown; chewing, mixing food with saliva, and churning food in stomach.
Digestion is a series of _______ steps that involve enzymes that break down complex food molecules into chemical building blocks
Catabolic
What does absorption mean?
Passage of digested fragments from lumen of GI tract into blood or lymph
What does defecation mean?
Elimination of indigestible substances via anus in form of feces
What are the four basic layers of all digestive organs?
Tunics:
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
What does the mucosa or mucous membrane do?
- Secrete mucus, digestive enzymes and hormones
- Absorb the end products of digestion into the blood
- Protect against infectious disease
Simple columnar epithelium
What does MALT (the mucosa-associated lymphoid tissue) do?
Help defend against bacteria and other pathogens
What type of cells secrete mucous?
Mucous neck cells
What do parietal cells do?
Secrete HCL which activates pepsin and kills many bacteria and intrinsic factor needed for B12 absorption
What do chief cells secrete?
Pepsinogen and lipases
What do enteroendocrine cells secrete?
Paracrine chemicals e.g. serotonin and histamine into lamina propria, and hormones somatostatin and gastrin?
What two hormones/chemicals increase release of HCL?
Gastrin and histamine
What hormone decreases HCL secretion?
Somatostatin
What hormone increases gastric motility (the ability of an organism to move independently, using metabolic energy)?
Serotonin
What are the processes carried out by stomach?
- Carries out breakdown of food
- Serves as holding area for food
- Delivers chyme to small intestine
- Denatures proteins by HCI
- Pepsin carries out enzymatic digestion of proteins
- Lipid-soluble alcohol and aspirin are absorbed into blood
- Only stomach function essential to life is secretion of intrinsic factor for vitamin B12 absorption
What enzyme carries out digestion of protein in the stomach?
Pepsin
What are absorbed into blood in the stomach?
Lipid-soluble alcohol and aspirin
What is the only stomach function that is essential to life?
Secretion of intrinsic factor for vitamin B12 absorption
- Needed for red blood cells to mature
- Lack of intrinsic causes pernicious anemia
Liver, gallbladder and pancreas are accessory organs associated with ______?
Small intestine
What is the function of liver and what is it for?
Production of bile for detoxification
What is the function of gallbladder?
Storage and concentration of bile released through cystic duct
What is the exocrine function of pancreas?
Production of enzymes needed to digest chyme and bicarbonate to neutralize stomach acid (found in pancreatic juice)
What is the endocrine function of pancreas?
Secretion of insulin and glucagon hormones by Langerhans islets
What does pancreatic juice compose of?
- Alkaline solution to neutralize acidic chyme
- Electrolytes
- Digestive enzymes e.g. proteases, amylase, lipases, and nucleases
What are the four digestive enzymes in pancreatic juice?
- Proteases (protein)
- Amylase (carbs)
- Lipases (lipids)
- Nucleases (nucleic acids)
What is cholecystokinin (CKK) release stimulated by?
Proteins and fats in chyme
What is secretin release stimulated by?
Acidic chyme
What does chyme from stomach contain?
Partially digested carbs, proteins and undigested fats
What are the sources of enzymes for digestion?
Bile, bicarbonate, digestive enzymes are imported from liver and pancreas
What performs the final digestion of chyme?
The brush border enzyme bound to plasma membrane
What happens in the large intestine?
- No food breakdown except enteric bacteria digestion
- Vitamins, water and electrolytes are reclaimed
- Major function: propulsion of feces to anus and defecation
What process allow the breakdown of macromolecules small enough for absorption during digestion?
Catabolic process which makes molecules small enough to be absorbed across wall of small intestine
What is absorption?
A process of moving substances from lumen of gut into body
What ensures the molecules passes through epithelial cells rather than between them?
Tight junctions. Enters cells through apical membrane and exit through basolateral membrane
Lipid molecules can be absorbed through membrane via ______ transport
Passive
Polar molecules are absorbed by ______ transport
Active
When are most nutrients absorbed?
Before they reach ileum
What type of carbs can only be absorbed?
Monosaccharides. Starch and disaccharides are broken down to oligosaccharides, disaccharides, and monosaccharides
What are the types of monosaccharides?
Glucose, fructose, and galactose
What starts the breakdown of starches and disaccharides?
Salivary amylase in the mouth, then the pancreatic amylase in the pancreas
What are monosaccharides further broken down into?
Lactose, maltose, and sucrose
How is glucose and galactose absorbed in the small intestine?
Via the cotransport (secondary active transport) with Potassium
How are monosaccharides absorbed in the intestine to the blood?
- Pancreatic amylase breaks down starch and glycogen into oligosaccharides and disaccharides
- Brush border enzymes break oligosaccharides and disaccharides into monosaccharides
- Monosaccharides are cotransported across the apical membrane of the absorptive epithelial cell. This active transport uses the Na concentration gradient established by the Na K ATPase pump in the basolateral membrane
- Monosaccharides exit across the basolateral membrane by facilitated diffusion and enter the capillary via intercellular clefts.
How are fructose pass through the small intestine?
Via facilitated diffusion
What are the brush border enzymes in small intestine that break down oligosaccharides and disaccharides?
Dextranase, glucoamylase, lactase, maltase, and sucrase
People who have lactose intolerance have deficient amount of _____?
Lactase
What are proteins broken down into?
- Large polypeptides
- Small polypeptides and small peptides
- Finally into amino acid monomers, with some dipeptides and tripeptides
Where does protein digestion begin?
In the stomach where pepsinogen is converted to pepsin at ph 1.5-2.5 in presence of HCI; protein in broken down to large polypeptides
What are the pancreatic proteases that break large polypeptides into small polypeptides and small peptides in the small intestine?
Trypsin, chymotrypsin, and carboxypeptidase
What are the brush border enzymes that break small polypeptides and small peptides into amino acids?
Aminopeptidase, carboxypeptidase, and dipeptidase
What does trypsin and chymotrypsin do?
Cleave protein into smaller peptides
What does carboxypeptidase do?
Takes off one amino acid at a time from end
What are the steps of lipid digestion in intestine?
- Emulsification
- Digestion
- Micelle formation
- Diffusion
What happens during emulsification?
Triglycerides and their breakdown products are insoluble in water; bile salts break large fat globules into smaller ones, increasing the surface area available to lipase enzymes
What happens during digestion of lipids?
Pancreatic lipases hydrolyze triglycerides, yielding monoglycerides and free fatty acids
What happens during the micelle formation?
Micelles (fatty acids, monoglycerides, and bile salts) ferry their contents to epithelial cells
What happens during the diffusion phase of the lipid digestion?
Fatty acids and monoglycerides diffuse from micelles into epithelial cells
What process do lipid products that diffuse inside epithelial cells undergo?
- Chylomicron formation
- Chylomicron transportation
What happens during the chylomicron formation phase of lipids digestion?
Fatty acids an monoglycerides are recombined and packaged with other fatty subtances and proteins to form chylomicrons
What happens during the chylomicron transport phase of lipids digestion?
Chylomicrons are extruded from the epithelial cells by exocytosis, enter lacteals, and are carried away from the intestine in lymph
What happens to chylomicrons once they’re in the blood?
- Broken into free fatty acids and glycerol by lipoprotein lipase so they can be used by cells
- Short chain fatty acids can diffuse directly into blood
