Chapter 64 - Guyton Flashcards
Glands of the GI tract.
goblet cells - mucus
pits (crypts of Lieberkühn in small intestine) - secretions
tubular glands - secretion (acid- and pepsinogen-secreting gland of the stomach)
salivary glands, pancreas, and liver - secretions for digestion or emulsification of food
What is the primary stimulus of secretions in the GI tract?
food contact with the epithelium
Parasympathetic stimulation of the gut ________ secretions.
increases
Control of secretions.
local - tactile, distention, irritation
reflex - nervous input
hormonal - GI hormones
Sympathetic stimulation of the gut _________ secretions.
increases or decreases (decreases if parasympathetic is already increasing)
What is secreted along with a substance to move it?
water and electrolytes
Mucus composition.
mainly water, electrolytes, glycoprotein
Mucus properties that make it essential for digestion.
adherent - sticks to food body - coats the walls well low resistance - provides lubrication self adherent - sticks together (form poop) resistant to digestion by GI enzymes buffering - neutralize acids
Salivation glands.
parotid, submandibular, sublingual (also smaller buccal)
Saliva contains two major types of protein secretion:
1) serous secretion that contains ptyalin (an
a-amylase), an enzyme for digesting starches
2) mucus secretion that contains mucin for lubricating and surface protective purposes
Types of secretion by gland.
parotid - serous
submandibular and sublingual - serous and mucus
buccal - mucus
90% of total secreted saliva comes from which glands?
parotid and submandibular
Two stages of formation and secretion of saliva.
acini - primary secretion similar to plasma (Cl is primary ion that is secreted actively not Na)
salivary ducts - modified as it passes through the ducts
Sodium and chloride in saliva is _____ than in plasma, while potassium and bicarbonate is _____ than in plasma.
less; greater
Saliva is always hypotonic, but its osmolarity _________ as its flow rate increases.
increases
Xerostomia
absence of saliva (dry mouth)
____________ stimulation directly increases salivation but can decrease Ach stimulated effects because of blood vessel constriction.
Sympathetic (T1-T3, superior cervical ganglion)
Parasympathetics to the salivary glands through which cranial nerves primarily?
CN IX and X (Ach)
Tubular glands of the stomach mucosa.
The oxyntic (acid-forming) glands secrete hydrochloric acid, pepsinogen, intrinsic factor, and mucus. The pyloric glands secrete mainly mucus for protection of the pyloric mucosa from the stomach acid. They also secrete the hormone gastrin.
What occurs in order for pepsinogen to be converted into its active form pepsin?
contact with HCl and pepsinogen is cleaved into pepsin
In chronic gastritis, if the parietal cells are destroyed, a person can develop achlorhydria (lack of stomach acid secretion) but often also pernicious anemia due to what?
lack of secretion of intrinsic factor by the parietal cells leads to failure to absorb B12
The _______ cells, located deep in the oxyntic glands of the main body of the stomach, are the only cells that secrete hydrochloric acid.
parietal
The rate of formation and secretion of hydrochloric acid by the parietal cells is directly related to the amount of histamine secreted by which cell?
enterochromaffin-like cells (ECL cells)
Stimulates histamine production by ECL cells:
1) gastrin
2) Ach (vagus nerve)
3) hormonal substances secreted by enteric nervous system in the stomach wall
Regulation of pepsinogen secretion by the peptic cells in the oxyntic glands:
1) Ach from the vagus nerves or gastric enteric nervous plexus
2) acid in the stomach
Phases of gastric secretion and their regulation.
Cephalic phase: 1. vagus nerve to stomach Gastric phase: 1. local nervous secretory reflexes 2. vagal reflexes 3. gastrin-histamine stimulation Intestinal phase: 1. nervous mechanisms 2. hormonal mechanisms
Hormones that inhibit gastric secretions.
secretin, GIP, VIP, somatostatin
The combined product of enzymes and sodium bicarbonate from the pancreas flows through a long pancreatic duct that joins the hepatic duct immediately before it empties into the duodenum through the papilla of _____, surrounded by the sphincter of ____.
Vater; Oddi
Secrete pancreatic digestive enzymes.
pancreatic acini
Pancreatic enzymes for digesting proteins.
trypsin, chymotrypsin, carboxypolypeptidase
Pancreatic enzyme for digesting carbohydrates.
pancreatic amylase
Pancreatic enzymes for digesting fats.
pancreatic lipase, cholesterol esterase, phospholipase
Why do the pancreatic enzymes not digest the pancreas under normal conditions?
the pancreatic acini simultaneously secrete trypsin inhibitor to prevent trypsin from forming and activating the enzymes from their inactive state
Stimuli for pancreatic secretion:
- Ach from parasympathetic vagus nerve endings and other cholinergic nerves in the enteric nervous
system - Cholecystokinin secreted by the duodenal and upper jejunal mucosa when food enters the small intestine
- Secretin secreted by the duodenal and jejunal mucosa when highly acid food enters the small intestine
Stimulates secretion of large quantities of water solution of sodium bicarbonate by the pancreatic ductal epithelium.
secretin
These two stimuli are largely responsible for the pancreatic enzyme production by acinar cells of the pancreas.
Ach and CCK (CCK is responsible for 70-80% of secretion)
Composition of bile.
bile salts, bilirubin, cholesterol, lecithin, and the usual electrolytes of plasma
The most important stimulus for gallbladder contraction.
CCK
The stimulus for cholecystokinin entry into the blood from the duodenal mucosa is mainly?
the presence of fatty foods in the duodenum
What is the primary function of bile salts?
emulsification of fats and also help with absorption by forming micelles
Causes of gallstones:
1) too much absorption of water from bile
2) too much absorption of bile acids from bile
3) too much cholesterol in bile
4) inflammation of epithelium
These glands secrete large amounts of alkaline mucus in response to (1) tactile or irritating stimuli on the duodenal mucosa; (2) vagal stimulation,
(3) gastrointestinal hormones, especially secretin.
Brunner’s glands (in the wall of the first few centimeters of the duodenum)
Located over the entire surface of the small intestine are small pits called?
crypts of Lieberkühn (goblet cells - mucous and enterocytes - water and electrolytes)
As food particles pass through the small intestine epithelium, several enzymes further break down the food. Which enzymes?
peptidases, sucrase, maltase, isomaltase, lactase, intestinal lipase
By far the most important means for regulating small intestine secretion are _______________, especially reflexes initiated by tactile or irritative stimuli from the chyme in the intestines.
local enteric nervous reflexes
The mucosa of the large intestine, like that of the small intestine, has many crypts of Lieberkühn; however, unlike the small intestine, there are no ____.
villi
