Exam 4- Intro to GI and Swallowing Flashcards
What are the 4 functions of the GI tract?
Boundary (between external and internal environments), musculature, digestion, and absorption
Absorption in the GI tract occurs via what 3 processes?
Diffusion, carrier transport, endocytosis
Oral and anal events are regulated by what portion of the nervous system?
Somatic nerves via skeletal muscle
The mid-esophagus to internal anal sphincter are controlled by what portion of the NS?
ANS via visceral smooth muscle (enteric nervous system)
In addition to absorption of nutrients, what must also be reabsorpted to prevent imbalances?
7-8 L of GI secretions
What 6 processes move food through the GI tract (start to finish)?
Ingestion, mechanical digestion, propulsion, chemical digestion, absorption, defecation
What are the layers of the GI tract from serosal to luminal side?
Serosa, longitudinal muscle, myenteric plexus, circular muscle, submucosa, submucosal plexus, mucosa
What are the 3 layers of the mucosa from outside to inside?
Muscularis mucosae, lamina propria, epithelium
What is the outer most layer of the GI tract that continues to the mesentery?
Serosa
What 2 layers of the GI tract are part of the enteric nervous system (ENS)?
Submucosal plexus and myenteric plexus
What layer of the GI tract is composed of collagen, elastin, glands, and blood vessels?
Submucosa
Auerbach’s is aka?
Meissner’s is aka?
Auerbach’s = Myenteric plexus
Meissner’s = Submucosal plexus
What layer of the mucosa changes the shape of the epithelial layer?
Muscularis mucosae
Which layer of the mucosa is mostly connective tissue but also contains some blood and lymph vessels?
Lamina propria
Which layer of the mucosa is responsible for absorptive and secretory functions?
Epithelial cells
What effect does venous drainage from the GI tract into the portal vein have on the liver?
Perfuses the liver
Venous drainage from the pancreas stomach, sm & lg. intestine empties into where?
Portal vein
What does parallel organization of splanchnic circulation allow for?
Regulation of flow to individual organs
What does series organization of splanchnic circulation allow for?
Liver is exposed to all absorbed substances
What is the pathway of nerve transmission in the GI tract? (4 steps)
Chemo/ mechanoreceptors → afferent nerves → submucosal/ myenteric plexuses → CNS (via ANS)
The ENS does NOT require what in order to carry out most functions?
ANS input (it is self-contained)
What does the myenteric (Auerbach’s) plexus innervate?
Longitudinal and circular smooth muscle layers
Which plexus if primarily concerned with control of gut movements?
Myenteric (Auerbach’s) plexus
What does the submucosal (Meissner’s) plexus intervate? (3)
Glandular epithelium, intestinal endocrine cells, and submucosal blood vessel
What plexus is primarily concerned w/ control of intestinal secretion?
Submucosal plexus
SNS stimulation via what nerves innervates from the esophagus to the proximal colon?
Celiac ganglia
SNS stimulation via what nerves innervates the distal colon and rectum?
Superior and inferior mesenteric ganglia
PNS stimualtion via what nerve innervates from the esophagus to the proximal colon?
Vagus nerve
PNS stimulation via what nerves innervates the distal colon and rectum?
Sacral → pelvic nerve
What effect does SNS release of NE on intramural plexuses, vascular smooth muscle, and secretory cells have?
Inhibitory effect
What are the differences between SNS and PNS innervation of the gut?
SNS ouput synapse @ ganglia → POSTsynaptic → GI plexuses vs PNS output (pre-synaptic) → GI plexuses
What is the largest endocrine organ in the body?
GI tract (15+ hormone secreting cells)
What do GI peptides regulate? (3)
Smooth muscle, secretion of fluid/enzymes, growth of GI cells
GI peptides fall into what 3 categories?
Hormones, paracrines, neurocrines
Where are GI hormones released from?
Endocrine cells (disperesed throughout GI tract)
What are the 4 known GI hormones?
Gastrin, Cholecystokinin (CCK), Secretin, Gastric inhibitory peptide
What cells release gastrin?
Gastric G cells
What cells release CCK?
Duodenal and jejunal I cells
What cells release secretin?
Duodenal S cells
What cells release gastric inhibitory peptide (GIP)?
Duodenal and jejunal K cells
What stimulate secretion of gastin? (3)
Small peptides/ AAs, stomach distension, vagal stimulation
What stimulate secretion of CCK? (2)
Small peptides and AA, fatty acids
What stimulate secretion of secretin? (2)
H+ in the duodenum, fatty acids in duodenum
What stimulate secretion of GIP? (3)
Fatty acids, AAs, oral glucose
What hormone ↑ gastric H+ secretion and stimulates growth of gastric mucosa?
Gastrin
What 2 hormones ↑ pancreatic HCO3- secretion?
CCK and Secretin
What 2 hormones ↓ gastic H+ secretion?
Secretin and GIP
What hormone stimulates contraction of the gallbladder and relaxation of the sphincter of Oddi?
CCK
What hormones increases insulin secretion from pancreatice B cells?
GIP (why we are able to reactive so quickly to oral glucose)
What hormones inhibits trophic effects of gastrin on gastric mucosa?
Secretin
What hormone ↑ biliary HCO3- secretion?
Secretin
What hormones inhibit gastric emptying?
CCK, secretin, GIP
What hormone stimulates growth of the exocrine pancreas and gallbladder?
CCK
Paracrine are carried via what to target cells? (2)
Capillaries or diffusion
What are the 2 GI paracrines?
Somatostatin and histamine
What hormone is released from D cells and inhibits release of all gut hormones?
Somatostatin
What hormone is a non-peptide paracrine?
Histamine
Neurocrines are synthesized in neurons and released in response to what?
Action potential
What are the main GI neurocrines? (4)
Acetylcholine, norepinephrine, vasoactive intestinal peptide (VIP), gastrin-releasing peptide (GRP) (others: enkephalins, neuropeptide Y, substance P)
What neurocrine increases salivary, gastric and pancreatic secretions, relaxes sphincters, and increases contraction of wall smooth muscle?
Acetylcholine (PNS - cholinergic neurons)
What neurocrine causes increased salivary secretion, sphincter contraction and relaxation of wall smooth muscle?
Norepinephrine (SNS - adrenergic neurons)
What neurocrine caues relaxation of smooth muscle and increases GI secretions (intestinal and pancreatic)?
Vasoactive intestinal peptide (VIP) (PNS, ENS - neurons of enteric NS)
What neurocrine increases gastrin secretion?
Gastrin-releasing peptide (GRP) (PNS)
Does NO released from the neurons of the enteric NS result in relaxation or contraction of smooth muscle?
Relaxation
GRP is released from what neurons?
Vagal neurons of the gastric mucosa
What is the structure of visceral smooth muscle cells w/in the GI tract? How are the organized?
Long and slender. Organized in packed bundles (functional unit) separated by connective tissue
How are visceral smooth muscle cells connected and what does this allow for?
Connected by low resistance gap junctions, allows for electrical propagation between adjacent fibers
What do VSMC exhibit of the resting membrane potential due to variations in Ca2+ and K+ conductances?
Spontaneous oscillations (slow waves/ basic electrical rhythm)
What happens if slow waves of VSMC reach depolarization threshold?
Action potential will superimpose on slow wave resulting in strong contraction of smooth muscle
What cells initiate BER via long branched processes into the VSMC?
Interstitial cells of Cajal/ stellate pacemaker cells
Do ACh or NE affect BER frequency?
No
What effect does ACh have on the activity of VSMC? (3)
Increases: BER amplitude, number of spike potentials, VSMC tension
What effect does NE have on the activity of VSMC? (3)
Decreases: BER amplitude, number of spike potentials, VSMC tension
What are the 2 patterns of GI motility?
Segmentation and peristalsis
Contraction and relaxation of adjacent segments (agitation/mixing type movement) is what GI motility pattern?
Segmentation
Peristalsis requires contraction behind the bolus of food and relaxation ahead of the bolus of food. This results in what kind of movement?
Directed propulsive
What are the 3 phases of digestion?
Cephalic, gastric, early and late intestinal
During what phase are there low levels of motor, secretory and digestive activity?
Interdigestive
Towards the end of what phase will you have a sense of hunger?
Interdigestive
What is decribed by cycles of motor activity from the stomach to the ileum during the interdigestive phase?
Migrating motor complex (MMC)
What regulated the migrating motor complex (MMC)
The “candidate” hormone motilin from the upper duodenum
What is the “housekeeping” function of the MMC?
Removes undigested material from stomach (begins 2 hrs post prandial & stop when meal is taken)
What type of contractions are produced by the MMC?
Intense and slow, 90 minute intervals
What phase of digestion triggers autonomic and endocrine reflexes (prepares the GI tracts) via the anticipation of eating and 1st sensory contact w/ food?
Cephalic
The cephalic phase of digestion is due to activation of what neural response?
PNS efferents (sight, smell, gustatory afferents enhance PNS)
During the cephalic phase, PNS activity increases secretion of what things? (4)
Saliva, gastric acid, gastrin, pancreatic enzymes
What is the daily salivary output?
0.5-1/5 L/day (flow rate varies w/ chewing)
What is the site of formation of saliva?
Acinar cells in salivary glands
What are the 5 components of saliva?
- Mucus (lubricant) 2. a-amylase (starts starch digestion) 3. lingual lipase (starts fat digestion) 4. slightly alkaline solution (moistens food) 5. IgA & kallikrein
What is the role of IgA and kallikrein in saliva?
Increase bradykinin = increased BF to salivary glands
Saliva is hypo or hypertonic to plasma?
Hypo
What ions are present at a lower concentrations in saliva, compared to plasma?
Na+ and Cl-
What ions are present at a higher concentrations in saliva, compared to plasma?
K+ and HCO3-
What 2 things change as saliva secretion rates increases?
Saliva becomes isotonic compared to plasma and pH increases (increased HCO3-)
How does saliva change from isotonic to hypotonic after being release from acinar cells?
Salivary ducts are impermable to water, Na, Cl out > K, HCO3
Nervous regulation of salivary secretion is mostly via what?
PNS (SNS contributes slight/ short-lived, mostly mucus secretion)
What stimulates the salivary gland (in medulla)?
Taste and tactile stimulation in mouth (also smell)
ACh and VIP from PNS nerve endings stimulate what with regards to the salivary response? (4)
- saliva secretion 2. vasodilation 3. salivary duct dilation 4. secretion of amylase, lipase and mucus
What is the PNS pathway for saliva regulation?
PNS → CN VII, X → release ACh on M receptors → IP3, Ca → Saliva
What stimulates the PNS to increase saliva production? (3)
Operant conditioning, food/smell, nausea
Will there be increased or decreased salivary secretion during dehydration, fear and sleep?
Decreased
What area of the brain coordinates swallowing?
Medullary swallowing center (first voluntary then reflexive)
What are the 3 phases of swallowing?
Oral (buccal), pharyngeal, esophageal
During the oral phase of swallowing, what is stimulated after a bolus is formed during mastication and pushed voluntarily by the tongue toward the pharynx?
Stimulation of somatosensory receptors → involuntary swallowing reflex
How is the pharyngeal phase of swalloing controlled?
Reflexively
What process is inhibited during the entire pharyngeal phase of swallowing?
Breathing
What prevents reflux into nasopharynx during pharyngeal phase of swallowing?
Upward movement of soft palate
During the pharyngeal phase of swallowing, the epiglottis moves to cover the opening to the larynx and the larynx moves upwards against the epiglottis. What does this prevent?
Food from entering the trachea
What is reflexivley inhibited and relaxes briefly during the pharynageal phase of swallowing?
UES (perstaltic waves propels food through the open sphincter)
What causes the LES to relax during the esophageal phase of swallowing?
VIP
At what point during the esophageal phase of swallowing does the LES contract?
As bolus passes into stomach
An incomplete swallow or gastric regurgitation results in a second peristaltic wave/ secondary swallow. What is this controlled by?
ENS
What is used to measure the esophageal pressure changes during swallowing?
Esophageal manometry (used if there is dysfunction)
What disorder is caused by failure of the LES fails to relax during swallowing resulting in food accumulation/ dilation of esophagus?
Achalasia
What are the 2 potential causes of achalasia?
Degeneration of myenteric plexus, defective release of NO and VIP
During achalasia, when will food enter the stomach?
When esophageal pressure > LES pressure
What is the cause of reflux esophagitis?
Loss of LES tone (or overindulgence)
What does reflux esophagitis result in?
Acid reflux from stomach to esophagus = heartburn/ ulceration