APHY 102 Digestive System
Gastric phase
lasts 3-4 hours and provides 2/3 of total gastric juice released; the more protein in a meal, the more gastric juice released to digest it
What is the fat-digesting enzyme?
lipase
What connects the esophagus to the stomach?
lower esophageal sphincter
Does pepsin operate best in higher or lower pH?
lower; best in pH's 1.5-2.5
What do the acini do?
manufacture the digestive enzymes
What provokes the enteric nervous system?
mechanical and chemical receptors in the walls of tract organs
What are segmental contractions?
segments of intestine alternately contract and relax; churns and mixes contents to facilitate absorption
What is a migrating motor complex pattern?
series of contractions in between meals that "sweeps" food remains and bacteria into large intestine
Where are lipids broken down?
small intestine
Where does most absorption take place?
small intestine
What is the job of the large intestine?
to absorb any remaining water from the indigestible food
What is the purpose of GI hormones?
to either excite or inhibit gastric motility and/or secretion
What are the types of motility?
tonic and phasic contractions, migrating motor complex patterns, and segmental contractions
true or false: bacteria coexists without harming the host unless they migrate from colon to other locations
true
true or false: digestive controls are intrinsic and extrinsic
true
How much time does indigestible material spend in the colon?
12-24 hours
How many times a day do the powerful mass movement waves move over the colon?
3-4 times daily
What is the continuous tube through which food travels during digestion?
Alimentary canal
What are proteins broken down too?
Amino acids
Are nerve plexuses or hormone-producing cells within the GI tract itself intrinsic or extrinsic?
Intrinsic
What cells release insulin and glucagon to regulate blood sugar?
Islets of Langerhans
Segmentation
Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward. Food mixing and slow food propulsion occur.
Long reflexes
any reflex integrated (processed) in the CNS; can originate in ENS or CNS
true or false: Some proteins remain in the blood to provide building blocks for production of new digestive enzymes
True
What is chemical digestion?
action of enzymes breaking large molecules into smaller molecules that can be absorbed across epithelia
Salivary secretion is under what type of control?
autonomic
What does the gallbladder store and release?
bile
What does the pancreatic duct fuse with?
bile duct
lactase
breaks down lactose
maltase
breaks down maltose
sucrase
breaks down sucrose
What are the phases of digestion?
cephalic phase (mouth), gastric phase (stomach), intestinal phase (small intestine)
What do changes in solute and pH activate?
chemoreceptors
What is mechanical digestion?
chewing, churning to expose more food surface area for enzyme action
What happens at the beginning of the intestinal phase?
chyme enters the duodenum and mixes with pancreatic secretions containing digestive enzymes
Acini
clusters of secretory cells surrounding pancreatic ducts
Phasic contractions
contraction/relaxation cycles only last a few seconds
What are secreted from salivary glands, pancreas, and epithelial cells of stomach and small intestine?
digestive enztmes
Where do the pancreatic juice and bile empty into?
duodenum
What does bile do?
emulsifies fat, reducing attraction between fat droplets so they can be more widely dispersed; not an enzyme
Are CNS centers or autonomic nerves outside the GI tract intrinsic or extrinsic?
extrinsic
Intestinal phase
gastric juice secretion declines, chyme enters duodenum in short contractile waves through pyloric valve
digestion in the stomach
gastrin stimulates parietal cells to secrete HCl, acid activates pepsin secreted by chief cells
What are the roles of the bacteria in the colon?
help metabolize some of the molecules, release acids and gases, synthesize vitamins
What is the purpose of mucus in the digestive tract?
helps lubricate GI tract to move substances through and creates protective coating over GI epithelia
Bicarbonate from the pancreas
helps neutralize acidic chyme received from the stomach
Gastrin
hormone secreted by stomach, stimulates gastric acid secretion
Where does protein digestion begin?
in the stomach with pepsin
What does stretching by food activate?
mechanoreceptors
What do each individual epithelial cell of villi bear?
microvilli
What are villi?
mucosal extensions to increase surface area and maximize nutrient absorption
Where is mucus secreted in the digestive system?
mucous cells in stomach and salivary glands and goblet cells in intestine
Esophagus
muscular tube surrounded by smooth muscle to facilitate peristalsis, enters cardiac regain of the stomach
Cephalic phase
occurs before food even enters, results from sight, smell or thought of food (stomach growls, salivation)
Short reflexes
originate within ENS without any outside input or processing from the CNS (in house)
What resides in the colon?
over 10 million different kinds of bacteria
Where is the only source of lipase?
pancreas
What breaks down the carbs that have remained after stomach mixing?
pancreatic amylase
Where does the pancreatic juice empty through?
pancreatic duct
What does the pancreas secrete?
pancreatic juice
What is peristalsis?
phasic contractions that create motion that moves food through GI tract
What promotes defection?
powerful mass movement waves
microvilli
projections of plasma membrane that contain digestive enzymes and increase surface area
What does the pancreas secrete into small intestine to continue protein digestion?
proteases
Storage in the stomach
releases chyme in small quantities to small intestine
CCK
secreted by small intestine, stimulates pancreatic enzyme secretion, inhibits gastric emptying and acid secretion
What are the four major processes of the digestive system?
secretion, digestion, absorption and motility
What is the purpose of saliva?
softens and lubricates food, chemical digestion begins (amylase and some lipase), also has a protective function
What are the three functions of the stomach?
storage, digestion and defense
Brush Border
surface of intestinal epithelial cells covered in microvilli to increase surface area
Tonic contractions
sustained contractions lasting several minutes to several hours; sphincters
defense in stomach
swallowed pathogens are destroyed by extremely acidic environment
Deglutition
the act of swallowing; tip of tongue presses against palate and contracts, forcing bolus into pharynx
enteric nervous system
the nervous system of the digestive tract
What are cephalic reflexes?
type of long reflex that originate in the brain; sight, smell, sound or thought of food preps digestive system for eating