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