Biology Ch 9. The Digestive System Flashcards
Intracellular digestion
Involves the oxidation of glucose and fatty acids to make energy, part of metabolism
Extracellular digestion
Occurs in the lumen of the alimentary canal
Alimentary canal
Location where extracellular digestion occurs, runs from mouth to anus, occurs within lumen which is technically outside the body
Mechanical digestion
The physical breakdown of large food particles into smaller food particles
Chemical digestion
The enzymatic cleavage of chemical bonds, such as the peptide bonds of proteins or the glycosidic bond of starches
Digestive pathway
Oral cavity, pharynx, Soffa guess, stomach, small intestine, large intestine, rectum
Accessory organs of digestion
The salivary glands, pancreas, liver, and gallbladder, help to provide the enzymes and lubrication necessary to aid in the digestion of food
Enteric nervous system
In the walls of the alimentary canal and controls peristalsis, its activity is up regulated by the parasympathetic nervous system (increases secretion from exocrine valves and promotes peristalsis) and down regulated by the sympathetic nervous system
Oral cavity
Mouth, where alimentary canal starts, mastication and secretion of salivary amylase and lipase occur (both physical and chemical digestion), once food formed into a bolus, it is swallowed
Anus
Where alimentary canal ends
Sphincters
Circular smooth muscles around the alimentary canal that can contract to allow compartmentalization of function
Digestion
The breakdown of food into its constitute organic molecules: starches and other carbohydrates into monosaccharides, lipids into free fatty acids in glacier all, and proteins into amino acids
Absorption
Involves the transfer the products of digestion from the digestive tract into the circulatory system for distribution to the bodies tissues and cells
Pharynx
A shared pathway for both food entering the digestive system and air entering the respiratory system, connects the month and posterior nasal cavity to the esophagus, divided into nasopharynx, oropharynx, and laryngopharynx
Esophagus
Muscular tube that transports food from pharynx to stomach using peristalsis, lower esophageal (cardiac) sphincter at end, top third is skeletal muscle (somatic motor control), bottom third is smooth muscle (autonomic control), and middle third is both
Rectum
Location with feces are stored until an appropriate time of release
Peristalsis
Rhythmic contractions of the smooth muscle throughout the gut tube, in order to move materials through the digestive system
Hormones regulating feeding behavior
Antidiuretic hormone or vasopressin, aldosterone, glucagon and ghrelin, and leptin and cholecystokinin
Antidiuretic hormone and aldosterone feeding behavior
Promote thirst, encourage fluid consumption
Glucagon and ghrelin feeding behavior
Promote hunger, glucagon from pancreas and ghrelin from stomach
Leptin and cholecystokinin feeding behavior
Promote satiety
Mastication
Chewing, starts the mechanical digestion of food in the oral cavity, the breaking up of food using the teeth, lips, and tongue, increases SA to V ratio which allows for more enzymatic digestion, also reduces obstruction risk
Salivary amylase
Starts chemical digestion of food in the oral cavity, in saliva, aka ptyalin, capable of hydrolyzing starch into smaller sugars (maltose and dextrins)
Lipase
Starts chemical digestion of food in the oral cavity, catalyses the hydrolysis of lipids
Bolus
What food is formed into prior to it being swallowed
Lower esophageal (cardiac) sphincter
Where food from the esophagus enters the stomach, relaxes to allow the passage of food
Stomach parts
Fundus, body, antrum, and pylorus
Less curvature
Internal curvature of the stomach
Greater curvature
External curvature of the stomach
Rugae
Folds of the stomach
Stomach
Has four parts, has lesser and greater curvature, is thrown into rugae, lined with numerous secretory cells, ends with pyloric sphincter, capacity of 2 L, located in the upper left quadrant of the abdominal cavity underneath the diaphragm , uses HCl and enzymes to digest food
Mucous cells
Produce bicarbonate rich mucus to protect the stomach from harshly acidic and proteolytic environment
Chief cells
Secrete pepsinogen, a protease activated in the acidic environment of the stomach
Pepsinogen
A protease activated by the acidic environment of the stomach, inactive, zymogen form of pepsin
Parietal cells
Secrete hydrochloric acid and intrinsic factor, which is needed for vitamin B 12 absorption, hydrogen ions released cleave pepsinogen to pepsin
Intrinsic factor
Secreted by the parietal cells in the stomach, needed for vitamin B 12 absorption
G cells
Secrete gastrin
Gastrin
Peptide hormone that increases hydrochloric acid secretion and gastric motility, induces parietal cells and the stomach to contract, mixing contents
Chyme
Food particles that have undergone mechanical and chemical digestion in the stomach, semifluid mixture
Pyloric sphincter
Where food leaves the stomach and enters the duodenum
Duodenum
First part of the small intestine and is primarily involved in chemical digestion, presence of chyme causes release of brush based enzymes, enteropeptidase, secretin, and CCK
Disaccharidases
Brush-border enzymes that break down maltose (maltase), isomaltose (isomaltase), lactose (lactase), and sucrose (sucrase) into monosaccharides
Brush-border enzymes
Present on the luminal surface of cells lining the duodenum and break down dimers and trimers of biomolecules into absorbable monomers, Includes dissacharidases, amino peptidase, and dipeptidases
Enteropeptidase
Activates trypsinogen and procarboxypeptidases A and B, initiating an activation cascade of other accessory organs of digestion
Secretin
Peptide hormone that stimulates the release of pancreatic juices into the digestive tract, regulates pH by reducing HCl secretion from parietal cells, can increase bicarbonate secretion from the pancreas, and is a type of enterogastrone
Cholecystokinin
CCK - Peptide hormone that stimulates bile release from the gallbladder, release of pancreatic juices, and promotes satiety in the brain
Salivary glands
Three pairs of them produce saliva in the oral cavity
Saliva
Produced by three pairs of salivary glands in oral cavity, aids in mechanical digestion by moistening and lubricating food, innervated by the parasympathetic nervous system by presence of food, contains salivary amylase and lipase
Nasopharynx
Division of the pharynx behind the nasal cavity
Oropharynx
Division of the pharynx at the back of the mouth
Laryngopharynx
Division of the pharynx above the vocal cords
Epiglottis
A cartilaginous structure that folds down to cover the laryngeal inlet during swallowing to prevent food from entering larynx
Emesis
aka vomiting, reversal of peristalsis in response to chemicals, infectious agents, physical stimulation of the posterior pharynx, or cognitive stimulation
Upper esophageal sphincter
Where swallowing in initials in the muscles of the oropharynx
Fundus
Part of the stomach, contains mostly gastric glands
Body
Part of the stomach, contains mostly gastric glands
Antrum
Part of the stomach, contains mostly pyloric glands
Pylorus
Part of the stomach, contains mostly pyloric glands
Gastric glands
Respond to signals from the vagus nerve of the PNS, have three different cell types: mucous cells, chief cells, and parietal cells
Gastric juice
Combination of secretions from chief cells and parietal cells
Pepsin
Digests proteins by cleaving peptide bonds near aromatic amino acids, resulting in short peptide fragments
Stomach hydrochloric acid
Hydrogen ions cleave pepsinogen into pepsin, kills most harmful bacteria, and helps to denature proteins
Pyloric glands
Contain G cells
Stomach absorption
Mainly digestion, only a few substances such as alcohol and aspirin that are absorbed directly from the stomach
Small intestine
Divided into three segments,
Small intestine segments
Duodenum, jejunum, and ileum
Lacking a particular disaccharidase
Bacteria in intenstines hydrolyze disaccharide producing methanols gas, osmotic effect pulling water into stool and causing diarrhea
Peptidases
Breaks down proteins
Aminopeptidase
Peptidase secreted by glands in the duodenum that remove the N terminal animal acid from a peptde
Dipeptidases
Cleaves the peptide bonds of dipeptides to release free animo acids
Trypsinogen
A pancreatic protease which is activated by enteropeptidase into trypsin
Trypsin
Initiates an activation cascade
Enterogastrone
A hormone that slows motility through the digestive tract, allows increased time for digestive enzymes (especially needed for fats)
Bile
Complex fluid composed of bile salts, pigments, and cholesterol
Bile salts
Derived from cholesterol, do not directly perform chemical digestion (they are not enzymes) but serve important role in the mechanical digestion of fats and chemical digestion of lipids
Bile salts emulsification
Emulsify fats and cholesterol into micelles using hydrophilic and hydrophobic regions, necessary so that fats dont separate out of mixture because pancreatic lipase is water-soluble, also increase surface area so lipase can act faster
Pancreatic juices
Complex mixture of sever enzymes in a bicarbonate-rich alkaline solution, helps to neutralize acidic chyme to pH where enzymes are the most active (around pH 8.5), travels to duodenum via duct system ad enter via the major and minor duodenal papillae
Acinar cells
Cells in the pancreas that produce pancreatic juices that contain bicarbonate pancreatic amylase, pancreatic peptidases (trypsinogen, chymotrypsinogen, carboxypeptidases A and B, and pancreatic lipase
Liver digestion
Located in upper right quadrant of the abdomen, synthesizes bile which is either then stored in the gallbladder or released immediately, also processes nutrients from blood draining from abdominal portion of the digestive tract through the hepatic portal vein and then sends blood to IVC, produces urea, detoxifies chemicals, activates or inactivates medications, and synthesizes albumin and clotting factors
Bile pigments
Most important bilirubin from the breakdown of hemoglobin)
Gallbladder
Stores and concentrates bile, located just beneath the liver, contracts and releases bile into binary tree upon release of CCK, common site of cholesterol or bilirubin stone formation
Accessory organs of digestion
The pancreas, liver, and gallbladder
Pancreatic amylase
Breaks down large polysaccharides into small disaccharides, responsible for carbohydrate digestion
Pancreatic peptidases
Include trypsinogen, chymotrypsinogen, and carboxypeptidases A and B, all released in zymogen form but are activated by enteropeptidase
Pancreatic lipase
Capable of breaking down fats into fatty acids and glycerol
Major and minor duodenal papillae
Where bile ducts empty pancreatic juices into the duodenum
Bile ducts
Connects the liver with both the gallbladder and small intestine
Liver glucose
Liver takes up excess sugar to create glycogen, can produce glucose using glycogenolysis and gluconeogenesis
Glycogen
Storage form of glucose
Bilirubin
A byproduct of the breakdown of hemoglobin, conjugated in the liver and secreted into the bile for excretion, if the body is unable to process or excrete bilirubin, jaundice may occur
Jaundice
Yellowing of the skin because the body is unable to process or excrete bilirubin
Albumin
Protein that maintains plasma oncotic pressure and serves as a carrier for many drugs and hormones, synthesized by the liver
Clotting factors
Synthesized by the liver, used during blood coagulation
Biliary tree
Connects gallbladder to duodenum, merges with pancreatic duct
Triacylglyercols digestive pathway
Lipase in oral cavity, lipase from pancreas, bile micelles from gallbladder
Carbohydrates digestive pathway
Amylase in oral cavity, amylase from pancreas, sucrase, lactase, maltase, and isomaltase from the small intestine (brush border)
Protein digestive pathway
Pepsin from stomach, typsin, chymotrypsin, carboxypeptidases A and B in the pancreas, dipeptidases and aminopeptidase from the small intestine (brush border)
Jejunum
Primarily involved in absorption, lined with villi
Ileum
Primarily involved in absorption, lined with villi
Villi
Lines small intestine, small fingerling projections from the epithelial lining covered in microvilli which furtherer increase the surface area for absorption, contain a capillary bed (for water soluble compounds such as monosaccharides, amino acids, water soluble vitamins, small fatty acids etc) and a lacteal (for fat soluble compounds such as cholesterol, fat soluble vitamins)
Lacteal
A vessel of the lymphatic system, transports fat soluble compounds from the small intestine, form the beginning of the lymphatic system, converge and enter the venous circulation at the thoracic duct which empties into the left subclavian vein
Microvilli
Cover villi to increase SA for absorption
Large intestine
Absorbs water and salts, forms semisolid feces, divided into the cecum, the colon, and the rectum
Cecum
An out pocketing that accepts fluid from the small intestine through the ileocecal valve and is the site of attachment of the appendix
Ilocecal valve
Transfers fluid from the small intestine to the cecum
Colon
Divided into ascending, transverse, descending, and sigmoid portions, main function to absorb water and salts
Rectum
Stores feces which contains indigestible material, water, bacteria, and certain digestive secretions that are not reabsorbed (enzymes and some bile)
Gut bacteria
Produce Vitamin K and biotin
Simple sugars and amino acid absorption
Absorbed by secondary active transport and facilitated diffusion, diffuse across epithelial cell membrane into the intestinal capillaries, because blood constantly flowing, there is always a concentration gradient, absorbed molecules head to liver via hepatic portal circulation
Short chain fatty acid absorption
Same process as carbohydrates and amino acids by diffusing directly into intestinal capillaries, are nonpolar so they can traverse across cell membrane
Larger fats, glycerol, and cholesterol absorption
Move separately into intestinal cells and then reform into triglycerides, triglycerides and cholesterol are then packaged into chylomicrons which enter the lymphatic system via lacteals
Thoracic duct
Where laterals converge and enter the venous circulation and them empty into the left subclavian vein
Chylomicrons
Packaged triglycerides and esterified cholesterol that enters the lymphatic circulation through lacteals
Fat soluble vitamins
A, D, E, K, dissolve directly into chylomicrons to enter the lymphatic system
Water soluble vitamins
B complex and C, taken up across endothelial cells passing directly into plasma
Transcellular passing
Across the cell membrane, water uses this method to reach blood along with paracellular passing
Paracellular passing
Squeezing between cells, water uses this method to reach blood along with transcellular passing
Appendix
A small fingerlike projection that was once thought to be vestigial but may play a role in warding off some bacteria infections and repopulating the large intestine with normal flora after episodes of diarrhea
Internal anal sphincter
Under involuntary/autonomic control
External anal sphincter
Under voluntary/somatic control
