digestive 2 Flashcards
the digestive secretions and contractions must be controlled such that they provide optimal conditions for
digestion and absorption
the GI control systems regulate conditions
in the lumen of the tract (rather than in the ECF)
the GI control reflexes are governed by
volume and composition of contents of the lumen (rather than the nutritional state of the body)
most of the receptors (that initiate GI reflexes) are located
in the wall of the GI tract itself
the receptors located in the wall of the GI tract respond to:
distention of the lumen wall, the osmolarity or acidity or the chyme, or the products of digestion (amino acids, fatty acids, monosaccharides, etc)
the reflexes (from receptors located in the wall of the GI tract) are triggered by the activation of these mechano-, osmo-, and chemoreceptors in the lumen wall, and influence:
the muscles in the GI tract wall and the exocrine glands that secrete into its lumen
the GI tract reflexes, like any negative feeback reflex, prevent large changes in the variables that initiate them. this prevention of change maintains the optimal luminal conditions for
digestion and absorption
GI tract has its own local nervous system, the ____ nervous system, in the form of the ____ and ____ nerve plexuses
enteric
myenteric and submucosal
sympathetic neurons are mainly
postganglionic
parasympathetic neurons are mainly
preganglionic
the neruons of the myenteric plexus and submucosal plexus synapse with each other, with the GI tract muscles, glands, and epithelial cells, so that stimulation at one point can
lead to impulses that go both up and down the tract
neural reflexes within the tract can act ____ of the CNS
independently
sympathetic and parasympathetic neurons synpase with neurons of both plexuses, allowing
CNA influence on GI tract motility and secretions
transmitters released by enteric neurons include
norepinephrine, acetylcholine, nitric oxide, ATP and several neuropeptides
a few reflexes are initiated by stimuli (such as ____ , ____ or the ____ or ____ of food) that are outside the GI tract
hunger, emotions, sight or smell
the hormone-secreting cells of the GI tract are cells scattered throughout
the tracts mucosal epithelium (rather than beging clustered into discreted organs)
the luminal surface of hormone-secreting cells of the GI tract are exposed to and stimluated by
some chemical in the chyme, causing hormone release into the blood from the cell’s other surface
the released hormone diffuses into blood capillaries, thus these hormones reach their target cells mainly via the
circulation
hormones secreted from the GI tract that participate in homronal regulation of GI control reflexes include ____ from the stomach, and ____ and ____ from the SI
gastrin
secretin and cholecystokinin
function of cholecystokinin (CKK)
keeps fat content of duodenum as close to zero as possible
chewing (mastication) occurs via ____ muscles and is regulated by ____ neurons
skeletal
somatic motor
the pressure of food against the palate, tongue, and gums reflexively activates
rhythmic contractions (and inhibits the muscles holding the jaw closed)
sailva is secreted by
parotid glands (x2)
submandibular glands (x2)
sublingual glands (x2)
unlike with most organs, both ____ and ____ input to the salivary glands ____ secretion, with ____ input being more potent
sympathetic and parasympathetic
stimulate
parasympathetic
the control reflex for saliva secretion are initiated by various stimuli including
sight of food, smell of food, mechanoreceptors in the mouth that detect pressure, and chemo/taste receptors in the mouth, especially ones that detect acids
salivary reflexes can be modified by input from other brain regions (e.g. appetite area of the ____ ) to the ____ ____ in the brainstem
hypothalamus
salivatory nuclei
salivary secretion flowchart:
eyes, smell receptors, taste buds, mouth mechanoreceptors → sensory neurons in ____ nerves from receptors to brain → ____ ____ in brainstem → ____ neurons in facial and ____ nerves → increased saliva secretion from salivary glands
eyes, smell receptors, taste buds, mouth mechanoreceptors → sensory neurons in cranial nerves from receptors to brain → salivatory nuclei in brainstem → parasympathetic neurons in facial and glossopharyngeal nerves → increased saliva secretion from salivary glands
pressure receptors in the pharynx wall are stimulated by food forced into the pharynx/posterior oral cavity, and sends sensory impulses to the swallowing center in the
medulla oblongata
swallowing center’s output:
- includes both impulses in somatic neurons to ____ muscles and in autonomic neurons to ____ muscles
- inhibits respirations and closes the ____ ( which is further protected when food pushes the ____ back to cover the glottis) ; these actions are very temporary
- elevates the soft palate to prevent food from:
- relaxes the
- causes ____ waves of the muscle contraction (skeletal muscles in the upper 1/3 and smooth muscle in the lower 2/3 of the esophagus) that force food toward the stomach
- opens the
- skeletal smooth
- glottis epiglottis
- entering the nose
- upper esophageal sphincter
- peristaltic
- lower esophageal spincter
if a food bolus does not reach the stomach, the resulting distension of the esophageal wall stimulates
sensory receptors that initiate reflexes resulting in repeated contractile waves called secondary peristalsis
if the lowe esophageal spincter is unable to prevent stomach contents from splashing into the esophagus, what happens
gastroesophageal reflux (“heart burn”)
the mucosal epithelium in the stomach, is a single cell layer that invaginates into the mucosa to form many tubular glands, they are:
gastric (oxyntic) glands
pyloric glands
gastic (oxyntic) glands secrete
- hydrochloric acid and intrinsic factor (from parietal, or oxyntic cells)
- pepsinogen (from chief cells or peptic cells)
- mucus (from mucous neck cells)
a parietal cell contains
invaginations of the luminal membrane called canaliculi
pyloric glands secrete
- mucus (for protection)
- gastrin (is secreted into the blood)
HCl secretion from gastric (oxyntic) glands:
on the luminal border:
- H+ (derived from the breakdown of water) is pumped:
- the K+ then leaks:
on the basolateral border:
- Cl- is exchanged for:
- the Cl- then diffuses:
on the luminal border:
- out of the cell and into the stomach lumen by an ATP-using active transport carrier (which is a countertransporter that pumps H+ out and K+ into the cells)
- back into the lumen through ion channels
on the basolateral border:
- biocarbonate ions (with Cl- moving into the cell and HCO3- out) by a non-energy using countertransporter
- out of the parietal cell and into the stomach lumen via ion channels
acid secretion into the stomach lumen is increased by messengers ( ____ , ____ , and the paracrine ____ ) that act on parietal cells to stimulate the insertion, into the luminal membrane, of additional H+/K+ energy-using cotransporter proteins
acetylcholine, gastrin, and histamine
acid secretion is decreased by the messenger ____ , a paracrine acting on the parietal cells
somatostatin
histiine is released from ____ cells and in addition to its own direct actions on parietal cells to stimulate acid secretion, it potentiates the actions on parietal cells of ____ and ____
enterochromaffin-like (ECL)
acetylcholine and gastrin
