Ch. 22 Digestive System
why is lipid absorption more complex than carbohydrate or protein absorption?
lipids are non polar and clump together
how do the muscularis externa and mucosa in the esophagus differ from the tissues in most of the alimentary canal?
they do not only consist of smooth muscle
what will happen to supplemental digestive enzymes in the stomach after they're ingested
they will probably be damaged and denatured by the acid in the stomach and pepsin will begin digesting them into smaller polypeptides
how does protein digestion occur in the small intestine
trypsin and brush border enzymes break down proteins into oligopeptides and free amino acids to be absorbed
steps of defecation reflex
1) stretch receptors transmit sensation of rectal distention to the spinal cord 2) parasympathetic neurons cause smooth muscle in the sigmoid colon and rectum to contract, and the internal anal sphincter to relax 3) impulses from the cerebral cortex trigger relaxation of the external anal sphincter and contraction of the levator ani muscle, allowing feces to pass out of the body
what are the primary triggers for bile release
CCK triggers contraction of smooth muscle in the wall of the gallbladder and causes it to release bile into the cystic duct
what hormones and neural stimuli trigger the gastric phase?
ENS and vagus nerve increase acid secretion
what do parietal cells produce
HCl and intrinsic factor
what do mucous neck cells produce
acidic mucus
which cells secrete pancreatic juice and what are its components
acinar cells; consists of water, bicarbonate, and digestive enzymes
where does protein digestion begin, and with which enzyme
begins in the stomach with pepsin
where is the peritoneal cavity located?
between the visceral and parietal peritoneum
what are the 3 phases of acid secretion in the stomach
cephalic phase, gastric phase, intestinal phase
which structures form the lateral, anterior, and superior walls of the oral cavity?
cheeks, lips, and hard/soft palate
segmentation
churning movement
what hormones and neural stimuli trigger the intestinal phase
chyme in duodenum stimulates acid secretion; enterogastric reflex decreases acid
what is the role of bile salts in lipid digestion
emulsification in the small intestine
what are the mineral and non mineral components of the tooth?
enamel, dentin and cementum are mineral
which branches of the nervous system supply the digestive organs?
enteric nervous system and 2 branches of autonomic nervous system
describe parasympathetic reflex arc that stimulated salivation
facial and glossopharyngeal nerves release ACh onto acinar cells which trigger release of saliva
how are amino acids absorbed across the apical and basal enterocyte membranes
facilitated diffusion
how do glucose, galactose, and fructose cross the apical enterocyte membrane
glucose and galactose - secondary active transport Na+/glucose cotransporter fructose - facilitated diffusion
what is a portal triad
hepatic arteriole, portal venule, and bile duct
where does the blood from the abdominal digestive organs drain?
hepatic portal vein to the liver (splanchnic circulation)
what do enteroendocrine cells produce
hormones for digestion (gastrin)
would bile salts be effective if they were polar molecules instead of amphiphilic molecules? what if they were non polar molecules?
if polar, they would be unable to interact with lipids. if non polar, they would be unable to interact with water
where does lipid digestion begin and with what enzyme?
in the stomach by gastric lipase
why is the internal surface of the small intestine arranged into progressively smaller folds
increases surface area for absorption (circular folds, villi, microvilli)
what are the 6 basic processes of the digestive system
ingestion, secretion, propulsion, digestion, absorption, and defection
how do the internal and external anal sphincters differ
internal is involuntary and external is voluntary
The weight loss drug orlistat, available OTC under the name All, blocks the activity of pancreatic lipase. Predict the effects of this drug. Why might it help a person lose weight?
it blocks chemical digestion of lipids and therefore their absorption, this decreases the amount of dietary fat the body absorbs; could lead to deficiency of fat-soluble vitamins
how do CCK and secretin affect pancreatic secretion
mediate pancreatic secretion during meals
motility of small intestine between meals
migrating motor complex
what would happen to the motility of the stomach if the vagus nerve were cut
motility would decrease; the migrating motor complex in the small intestine would still function but peristalsis and segmentation would diminish
where does carbohydrate digestion take place?
mouth and small intestine
in which parts of the alimentary canal does chemical digestion take place
mouth, stomach, and small intestine
what are the four main tissue layers of the alimentary canal?
mucosa, submucosa, muscular externa, and serosa
what are the primary cell types of the gastric glands?
mucous neck cells, parietal cells, chief cells, enteroendocrine cells
primary digestive function of the pharynx? which muscles carry out this function?
muscles contract during swallowing and propel the bolus inferiorly (pharyngeal constrictor muscles)
which enzymes catalyze reactions that digest nucleic acids?
nucleases and brush border enzymes
how is water absorbed in the small and large intestines
osmosis
what are the 3 types of paired salivary glands and where are they located
parotid glands (masseter muscle), submandibular glands, sublingual glands
what do chief cells produce
pepsinogen
where is the esophagus located and what are its major functions
posterior to the trachea; waves of peristalsis massage the food inferiorly
how do the primary dentition and secondary dentition differ?
primary - 20 teeth, 6 months to 24 months secondary - 32 teeth
how do accessory organs assist digestion
produce and secrete digestive enzymes
what functions are performed by normal flora in the colon
produce vitamins, metabolize undigested materials, deter the growth of harmful bacteria, stimulate the immune system
what are the main functions of the liver
production of bile (nutrient metabolism, detoxification, excretion, production of plasma proteins, and storage of nutrients)
peristalsis
propulsive movement
what are the main functions of the gallbladder
receives and stores bile
3 functions of gastric motility
receptive function, churning function, and emptying function
which type of epithelium makes up the mucosa from the stomach to the end of the large intestine?
regenerative epithelial cells
The treatment for pancreatic cancer may require removing the pancreas. Predict the consequences of this procedure for the body's digestive functions.
removal of the pancreas would severely impact chemical digestion; supplementary digestive enzymes would need to be administered
which enzymes are involved in digesting carbohydrates
salivary amylase, pancreatic amylase, lactase, maltase, and sucrase
how does the endocrine system regulate digestive processes?
secretion of hormones
what type of movements occur in the proximal large intestine
segmentation and mass movements
motility of small intestine during eating
segmentation and peristalsis
how is sodium ion absorption achieved
sodium is absorbed by cotransport with monosaccharides and amino acids
A patient needs a medication that is normally given at a dose of 500 mg by mouth every 8 hours. However, the patient has liver disease, and the pharmacist recommends giving the drug at a dose of 250 mg every 12 hours instead. Explain why the pharmacist made this recommendation.
the liver will metabolize the drug less efficiently, prolonging the life of the drug in the blood so a lower dose is needed
are supplemental digestive enzymes likely to be useful?
they are fairly useless as the enzymes will be rendered nonfunctional in the stomach
what hormones and neural stimuli trigger the cephalic phase?
vagus nerve stimulates parietal cells, histamine and gastrin are released and somatostatin is inhibited
what are the components of saliva and what are its functions
water, mucus, salivary amylase, lysozyme, and IgA; it moistens food and assists in mechanical and chemical digestion