Module 15 Flashcards
State the overall function of the digestive system
Breaking down organic nutrients to be absorbed into the body (carbs, proteins, fats, water, vitamins, minerals)
List the anatomy of the digestive system, in order
Mouth, salivary glands, esophagus, stomach, liver, gallbladder, pancreas, small intestine, large intestine, rectum
Describe the basic function of the mouth
Break up food by chewing (mastication) and mix food with saliva
Describe the basic function of salivary glands
Produce saliva to moisten and begin digesting some food particles
Describe the basic function of the esophagus
A straight muscular tube connecting the mouth and pharynx to the stomach
Describe the basic function of the stomach
Store, mix, and digest some food and deliver food to the small intestine
Describe the basic function of the liver
Many functions, but for digestion specifically produces and stores bile
Describe the basic function of the gallbladder
Stores and concentrates bile produced by the liver
Describe the basic function of the pancreas
Secrete digestive enzymes, hormones, and bicarbonate
Describe the basic function of the small intestine
Allows digestion and absorption of most food particles
Describe the basic function of the large intestine
Stores and concentrates undigested material and absorbs salt and water
Describe the basic function of the rectum
Site where the defecation reflex is triggered
Describe secretion (digestion)
Release of digestive fluids into the lumen of the digestive tract; may include water, mucus, acid, electrolytes, enzymes, bile salts, and digestive enzymes
Define digestion
The process whereby food is broken down into smaller molecules by the digestive enzymes so they can be taken up by the body
Define absorption (digestion)
The process whereby small digested molecules are taken up by the circulatory system and distributed throughout the body
List the salivary glands
Parotid, sublingual, and submandibular
Describe saliva and its role in digestion
Mostly water with some ions and proteins
Up to 2L produced per day
Helps lubricate the bolus of food and begins digesting carbs with the enzyme amylase
Produced and secreted under control of the ANS
Describe the sequence of events involved with swallowing
Once bolus has been formed and lubricated with saliva, pushed to back of mouth by tongue to initiate swallow reflex
Uvula of soft palate closes nasopharynx
Larynx is lifted by muscles in neck, epiglottis bends over glottis, covering larynx
Bolus moves down esophagus through cardiac orifice into stomach by wave of smooth muscle contraction (peristalsis)
List the parts of the stomach
Fundus, body, antrum, cardiac orifice, pyloric sphincter, rugae
List the functions of the stomach
Liquefies, mixes, and stores bolus of food, creating chyme
Controls the release of chyme into the small intestine
Some digestion of proteins by pepsin
Absorption of alcohol and aspirin
List the secretions of the stomach
Mucus, HCl, pepsinogen, gastrin, intrinsic factor
Describe the function of mucus in the stomach and where it is secreted
Secreted by cells in body and antrum, protects lining of stomach from acidic environment
Describe the function of HCl in the stomach and where it is secreted
Secreted by cells in the stomach body, begins to denature complex protein and connective tissue molecules found in protein, kills bacteria and converts pepsinogen to pepsin
Describe the function of pepsinogen in the stomach and where it is produced
Produced by cells in the body of the stomach, when converted to pepsin by HCl begins to digest large protein molecules
Describe the function of gastrin in the stomach and where it is secreted
Secreted by cells in the antrum, it is a hormone that stimulates secretion of HCl
Describe the function of intrinsic factor in the stomach
Helps with absorption of vitamin B12
Describe the location and structure of the pancreas
Lies below the stomach, has exocrine and endocrine functions, main pancreatic duct that merges with common bile duct from liver and gallbladder before entering duodenum
Describe the function of the pancreas in digestion
Produces and secretes amylase (carbs), trypsin, chymotrypsin, and proteases (proteins) and lipase (fat), also secretes bicarbonate into duodenum to neutralize acid
List the three segments of the small intestine
Duodenum (shortest) Jejunum Ileum (longest, 50% of small intestine)
Describe the inner structure of the small intestine
Inner wall has large surface area with villi, containing capillary network and lymphatic lacteal, layer of epithelial cells covering villi, and microvilli that face into the lumen, creating a brush border
Describe the functions of the small intestine in detail
Almost all digestion and absorption (duodenum and jejunum)
Digestion of chyme using digestive enzymes (from pancreas and epithelial cells) and bile (from liver for fats)
Large surface area good for absorption and motility (moving food through digestive tract)
List the building blocks of carbohydrates
Monosaccharides (glucose, fructose, galactose) can form disaccharides (sucrose, maltose, lactose) or longer polysaccharides
Describe carbohydrate digestion
Carbs must be broken down into monosaccharides to be absorbed
Digestion in mouth by amylase (to smaller polysaccharides and maltose)
Once in stomach, carb digestion stops in acidic environment
In duodenum, amylase starts digestion again (into disaccharides)
Each disaccharide requires specific enzyme to break down into monosaccharides
Describe lactose intolerance
People who don't produce lactase, cannot break down lactose (disaccharide) into monosaccharides Causes diarrhea (from lactose in digestive tract) and gas, bloating, and cramps (from bacteria feeding on it) Treated with synthetic lactase
Describe carbohydrate absorption
Similar to glucose reabsorption in kidneys
Na+/K+ pump creates [ ] gradient, which powers Na+/glucose co-transporter (secondary active transport) on luminal side of cell, moves glucose into cell, then glucose diffuses out through basal side by facilitated diffusion
List building blocks of proteins
20 amino acids 11 nonessential (can be produced in the body) 9 essential (must come from diet)
Describe protein digestion
Must be broken down into amino acids for absorption
Digestion begins in stomach when HCl converts pepsinogen to pepsin
HCl helps uncoil long proteins so pepsin can digest into smaller polypeptide chains
In small intestine, pancreatic enzymes trypsin and chymotrypsin continue digestion
Proteases from pancreas digest proteins into amino acids (endopeptidases and exopeptidases)
Describe protein absorption
Can absorb single amino acids and small polypeptides
Uses secondary active transport, requiring Na+ [ ] gradient and Na+/amino acid co-transporter
Remaining small peptides absorbed by endocytosis
Describe the structure of fats and lipids
Triglycerides (glycerol with three fatty acid chains)
Cholesterol
Long fatty acid chains
Phospholipids (glycerol, two fatty acid chains, and phosphate group)
Not water soluble so don’t mix with water
Describe the breakdown of fatty acids
Emulsification (churning of the stomach to break up large drops of fat into small drops of fat)
Important because lipid digesting enzymes cannot work on large drops, only small ones, so need to stay emulsified
Describe where bile is produced and stored
Produced in the liver
Transported to gallbladder for storage and concentration
Describe the functions of bile
Not a digestive enzyme
Released during digestion into duodenum
Bile salts keep lipid droplets emulsified so they can’t form large droplets
Describe colipase and its function
Secreted by pancreas
Not a digestive enzyme, a protein that allows lipase to get access to lipid interior of fat droplet when surrounded by bile salt
Describe fat digestion
Fat droplets after emulsification and bile salt attachment contain different types of lipids
Pancreatic lipase removes fatty acid chains from glycerol, making droplets smaller
Droplets get small enough, become micelles (single layer of bile surrounding small lipid droplet)
Describe fat absorption
Fatty acids and monoglycerides diffuse through membrane of epithelial cells in small intestine Cholesterol is transported into cells by active transport Enter smooth ER to combine and form chylomicrons, which are packaged into secretory vesicles by golgi apparatus to leave cell Enter lacteals (lymphatic system) then drain into circulatory system
Describe the absorption of vitamins
Depends on water or lipid soluble
Lipid soluble are absorbed like fats
Water soluble are absorbed by carrier-mediated mechanisms (absorption similar to sugar and amino acids)
List amounts of water absorbed in different sections of the digestive system
Duodenum and jejunum: 44%
Ileum: 38%
Large intestine: 1.5%
Remaining excreted
Describe water absorption
Similar to in kidneys
As molecules of glucose, amino acids and lipids are absorbed, osmotic gradient builds across intestinal epithelial cells
Cells develop high solute concentration, causing water to flow in by osmosis
As solutes move out into circulation, water flows out by osmosis into blood
Describe the absorption of ions
Na+ is same as in kidney, help from Na+/K+ pump on basal lateral surface of intestinal cells, establishes [ ] gradient, then Na+ moves into cells down [ ] gradient, and along with carbs and amino acids in co-transporters
K+ absorbed passively by diffusion
List the parts of the large intestine
Ileocecal valve, cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus
Describe the functions of the large intestine
Absorb water and electrolytes
Store and concentrate feces
Na+ absorbed by active transport, water by osmosis
Most absorption in first half
Secretes mucus to protect lining from chemical and mechanical damage and to lubricate feces
Some K+ and bicarbonate secreted into colon
Little digestion of polysaccharides by bacteria, absorbed by passive diffusion and causing gas and vitamin K production
Describe the purpose enteric nervous system
Both branches of the ANS (PSYN and SYN) can influence activity of the digestive tract by altering activity of nerves in the ENS
Nerves affect smooth muscle activity, enzyme-secreting cells, endocrine cells, and blood vessels
Describe how the enteric nervous system functions
Two reflex loops
Long loop travels through CNS
Short loop travels locally within digestive system
Describe the short loop of the ENS
Begins by a mechanical distension of digestive tract or chemical change like pH or osmolarity
Changes detected by sensors of ENS that initiate reflex
Reflex activates effector organs, like secretory cells or smooth muscle, causing release of enzymes or altering motility
Describe the long loop of the ENS
Include input from higher brain centers
Stimulus could be sight or smell of food
Signals sent through PSYN to ENS to alter digestive function - enzyme release and gastric motility
Define motility (digestion)
The muscular contractions of the stomach that mix food and propel it through the digestive tract
Needs regulation to ensure digestion and absorption is completed
Describe how motility is regulated
Interstitial cells (specialized smooth muscle cells) surrounding the digestive tract act like pacemaker cells of the heart Alter their membrane potentials, producing BERs, whose frequency determines number of waves (3/min in stomach, 12/min in duodenum)
Describe how BERs regulate gastric motility
Can alter their membrane potentials, don’t cause muscle contraction often because don’t often reach threshold
Spread through gap junctions
Reaching threshold requires additional stimulus (mechanical, nervous, or hormonal) to fire action potentials and cause smooth muscle contraction
List the hormones of the intestine
Secretin, CCK, and glucose-dependent insulinotropic peptide
Describe the function of secretin in the intestine
Released in response to presence of acid in intestine
Inhibits emptying from stomach
Causes release of pancreatic bicarbonate and bile from liver
Results: bicarbonate neutralizes stomach acid so digestive enzymes in intestines can function
Describe the function of CCK in the intestine
Released in presence of fats
Slows emptying of stomach
Stimulates pancreas to release digestive enzymes
Causes gallbladder to contract and release bile
Describe the function of glucose-dependent insulinotropic peptide in the intestine
Secreted in response to glucose and amino acids
Stimulates release of insulin
May inhibit emptying of stomach
Describe the function of gastrin (hormone) in the stomach
Secreted by G cells (in antrum) in response to presence of proteins, mechanical distension, and stimulation from PSYN
Primary function: cause secretion of HCl to convert pepsinogen to pepsin
List the three phases of gastric acid secretion
Cephalic phase (brain) Gastric phase (stomach) Intestinal phase (intestine)
Describe the cephalic phase
Increased gastric acid secretion initiated in response to sight, smell, taste, or chewing food (triggers PSYN)
Anticipatory response, activates long loop reflex of ENS
Causes parietal cells to release HCl
Causes G cells to release gastrin
Stomach motility increases
Describe the gastric phase
Begins once food is swallowed
Stimulus is presence of food in stomach that distends walls (mechanical) and presence of amino acids (chemical) from protein breakdown
Triggers short loop reflex in ENS
Causes release of HCl, gastrin, and pepsinogen
Increases gastric motility
Describe the intestinal phase
Food leaves stomach and enters intestine
Carefully regulated
Stimulus is presence of glucose, fat, and acidic chyme in intestine
Decreases motility and inhibits stomach secretions
Performed by ENS and hormones secretin, CCK, and glucose-dependent insulinotropic peptide
