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Questions and Answers
What primarily controls salivary secretion?
What primarily controls salivary secretion?
What is the effect of parasympathetic stimulation on salivary secretion?
What is the effect of parasympathetic stimulation on salivary secretion?
Which neurotransmitter is primarily associated with sympathetic stimulation of salivary secretion?
Which neurotransmitter is primarily associated with sympathetic stimulation of salivary secretion?
During which phase of swallowing is the food transferred from the mouth to the pharynx?
During which phase of swallowing is the food transferred from the mouth to the pharynx?
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What happens to respiration during the pharyngeal phase of swallowing?
What happens to respiration during the pharyngeal phase of swallowing?
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What stimulates the secretion of aqueous components in the pancreas?
What stimulates the secretion of aqueous components in the pancreas?
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Which component is primarily responsible for stimulating the release of enzymes in the pancreas?
Which component is primarily responsible for stimulating the release of enzymes in the pancreas?
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Which of the following phases of pancreatic secretion occurs first after a meal?
Which of the following phases of pancreatic secretion occurs first after a meal?
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Which phase of pancreatic secretion is triggered by the presence of chyme in the small intestine?
Which phase of pancreatic secretion is triggered by the presence of chyme in the small intestine?
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What is the main effect of secretin on pancreatic secretion?
What is the main effect of secretin on pancreatic secretion?
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What is one of the stimulators for CCK secretion from the duodenal I cells?
What is one of the stimulators for CCK secretion from the duodenal I cells?
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Which nervous system activity is associated with the cephalic phase of pancreatic secretion?
Which nervous system activity is associated with the cephalic phase of pancreatic secretion?
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What triggers the release of CCK from the duodenal I cells?
What triggers the release of CCK from the duodenal I cells?
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What type of transport occurs through the tight junctions of the intestinal epithelium?
What type of transport occurs through the tight junctions of the intestinal epithelium?
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Which substance is known to increase water absorption in the intestine?
Which substance is known to increase water absorption in the intestine?
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How does the sympathetic nervous system influence electrolyte absorption in the intestine?
How does the sympathetic nervous system influence electrolyte absorption in the intestine?
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What type of cells are primarily affected by pathogens that induce malabsorptive diarrhea?
What type of cells are primarily affected by pathogens that induce malabsorptive diarrhea?
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What is the role of cholera toxin in intestinal function?
What is the role of cholera toxin in intestinal function?
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What is a common result of crypt cell activation by bacterial toxins?
What is a common result of crypt cell activation by bacterial toxins?
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Which hormone is primarily responsible for increasing Na+ absorption in the intestine?
Which hormone is primarily responsible for increasing Na+ absorption in the intestine?
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In which part of the intestine are tight junctions the leakest?
In which part of the intestine are tight junctions the leakest?
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What is the primary function of the proximal half of the colon?
What is the primary function of the proximal half of the colon?
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Which part of the large intestine is specialized for the storage and dehydration of feces?
Which part of the large intestine is specialized for the storage and dehydration of feces?
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What role does the ileocecal valve play in the large intestine?
What role does the ileocecal valve play in the large intestine?
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Which colon segment serves as a conduit between the transverse and sigmoid colon?
Which colon segment serves as a conduit between the transverse and sigmoid colon?
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How long does it typically take to move chyme from the ileocecal valve to the transverse colon?
How long does it typically take to move chyme from the ileocecal valve to the transverse colon?
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What is haustration in the context of colon movement?
What is haustration in the context of colon movement?
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What is the average speed of segmental propulsion in the proximal colon after eating?
What is the average speed of segmental propulsion in the proximal colon after eating?
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Which vitamin is specifically mentioned as being absorbed in the large intestine?
Which vitamin is specifically mentioned as being absorbed in the large intestine?
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What stimulates the secretion of intestinal juice?
What stimulates the secretion of intestinal juice?
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What is the primary composition of feces?
What is the primary composition of feces?
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Which statement accurately describes the role of intestinal juice?
Which statement accurately describes the role of intestinal juice?
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What will decrease the secretion of intestinal juice?
What will decrease the secretion of intestinal juice?
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What is primarily absorbed in the large intestine?
What is primarily absorbed in the large intestine?
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What initiates the defecation reflex?
What initiates the defecation reflex?
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During defecation, what action is taken by the external anal sphincter?
During defecation, what action is taken by the external anal sphincter?
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What is the primary role of sodium in water movement during absorption?
What is the primary role of sodium in water movement during absorption?
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Study Notes
Regulation of Salivary Secretion
- Primarily controlled by neural input
- Parasympathetic stimulation:
- Major, stronger, more lasting
- Secretes large volume of watery fluid (amylase, electrolytes)
- Stimulated by visual and olfactory stimuli
- Acetylcholine: Muscarinic receptor
- IP3/Ca2+ pathway promotes secretion
- Sympathetic stimulation:
- Slight increase in serous and mucous secretion (highly viscous)
- Norepinephrine:
- 𝛼 receptor: IP3/Ca2+ pathway promotes electrolyte secretion
- β receptor: cAMP pathway promotes amylase secretion
Swallowing (Deglutition)
- Oral phase:
- Voluntary initiation, reflex control
- Tongue moves bolus upward, touching hard palate
- Moves backward into the mouth
- Lowering of soft palate (epiglottis open for breathing)
- Pharyngeal phase:
- Involuntary (medulla control)
- Less than 1 second duration
- Respiration reflexly inhibited
- Contraction of palatopharyngeal muscles: Soft palate closes nasopharyngeal cavity
- Epiglottis covers the opening of the larynx
- Constriction of hypopharyngeal muscles
- Relaxation of upper esophageal sphincter
- Peristaltic wave propels food downwards
Regulation of Pancreatic Secretion
- Aqueous component:
- Stimulated by secretin
- S cells in duodenum and upper jejunum release secretin in response to acidic lumen (pH 4.5 or below)
- Secretin stimulates HCl > fat > peptide secretion; CCK stimulates peptide > fat > HCl > amino acid secretion
- Cholecystokinin (CCK) potentiates the effect of secretin
- Stimulated by secretin
- Enzyme component:
- Stimulated by CCK
- CCK secretion from mucosal I cells in duodenum and jejunum
- Stimulated by specific amino acids, peptides, and long chain fatty acids (peptide > fat > HCl > AA); releasing factors: CCK-RP, monitor peptide
- Vagus nerve (acetylcholine, GRP: gastrin releasing peptide)
Phases of Pancreatic Secretion
- Cephalic phase: (~20% of total secretion)
- Same nervous signals as cephalic phase of gastric secretion
- Vagus nerve impulses: ACh release
- Moderate enzyme secretion; low volume, high protein pancreatic juice
- Gastric phase: (5-10% of total secretion)
- Small amounts of enzymes secreted
- Intestinal phase:
- Response to chyme entering small intestine
- Large amount of pancreatic juice secreted
- Acid in duodenum and upper jejunum:
- Secretin: High volume, poor enzyme pancreatic juice (rich in HCO3-)
- Peptide, amino acid, fatty acid:
- CCK: Enzyme-rich pancreatic juice
- Hormone actions
- Vago-vagal reflex: Enhanced secretion and release of ACh, GRP, and VIP via activation of pancreatic enteric neurons
Liver
- Mechanisms of salt and water absorption by the intestine:
- Structural considerations:
- Tight junctions: Leakiest in duodenum, tighter in jejunum, ileum, and tightest in colon
- Transcellular vs paracellular transport
- Villous vs crypt cells
- Ion transport:
- Transporters, exchangers, channels, electric charge
- Control of intestinal electrolyte absorption:
- Autonomic nervous system:
- Sympathetic: Increased absorption of Na+, Cl-, and water
- Parasympathetic: Decreased net rate of ion and water absorption
- Adrenal hormones:
- Aldosterone: Increased Na+, Cl- absorption
- Glucocorticoid: Increased Na+, K+ -ATPase activity, stimulating water absorption
- Opioid peptides (enkephaline) and somatostatin: Strongly stimulate salt and water absorption
- Autonomic nervous system:
- Structural considerations:
Villous vs Crypt Cells
- Villous cells: Responsible for nutrient absorption
- Crypt cells: Responsible for electrolyte secretion and cell renewal
Intestinal Absorption and Secretion: Relevance to Diarrhea
- Pathogens damaging villous epithelium lead to malabsorptive diarrhea: PEDv, Coccidiosis, TGEv, Rotavirus
- Bacterial toxins and inflammatory stimuli elicit massive Cl-, HCO3-, and water secretion from crypt cells: e.g. E.coli, S.typhimurium
Functional Disorders of the Intestine
- Diarrhea:
- Enterotoxin: Escherichia coli, Shigella dysenteriae, Vibrio cholerae
- Cholera toxin:
- Acts on apical membrane of mucosa (jejunum and ileum)
- Stimulates adenyl cyclase activity, increasing intracellular cAMP which leads to secretion of Cl- rich intestinal juice
- Malabsorption of Nutrients:
- Regional enteritis (Crohn’s disease)
- Tropical sprue
- Celiac sprue
- Gluten-sensitive enteropathy
- Idiopathic steatorrhea
Digestion in Colon
- No significant digestion occurs, mainly absorption and water removal
Structure and Function of the Large Intestine
- Structure:
- Connected to small intestine, 6.25 cm diameter, 1.5 m length
- Cecum, colon, and rectum
- Cecum: Short pocket with appendix, located under ileocecal valve
- Colon: Ascending, transverse, descending, sigmoid
- Rectum: Located in pelvis, connected to anus
- Taeniae coli: Longitudinal muscle bands
- Function:
- Absorption of water and electrolytes (proximal half)
- Absorption of vitamins (B’s, K) produced by bacteria
- Storage of fecal matter (distal half)
- Defecation: Emptying the rectum
Part-Specific Function of the Large Intestine
- Cecum: Connection between ileum and colon
- Ileocecal valve: Prevents reflux, controls emptying
- Immune function, protects digestive bacteria
- Ascending colon: Chyme transmission from ileum
- Transverse colon: Storage and dehydration of feces
- Descending colon: Storage, movement, and discharge of feces
Movements of the Colon
- Segmental propulsion: Slow movement of chyme (5 cm/hr fasting, 10 cm/hr after eating)
- Haustration: Segmentation movement in colon, gentle non-propulsive peristalsis
- Intestinal juice:
- Isotonic solution, 60 ml/day
- High K+ and HCO3- concentration, alkaline
- Stimulated by: Distention, chemical irritation, parasympathetic stimulation
- Decreased by sympathetic stimulation
- Function: Neutralize acidic products of fecal fermentation
Absorption in the Large Intestine
- Absorption of water, electrolytes, short chain fatty acids
- Absorption of secondary bile acids
- Feces composition:
- 3/4 water
- 1/4 solid: Dead bacteria, fat, inorganic, protein, undigested
- Color: Stercobilin and urobilin
- Odor: Bacterial flora and foods (indole, scatole, mercaptans, hydrogen sulfide)
- Water movement: Absorption due to osmotic pressure difference, driven by Na+ movement via exchangers and ATPase
Defecation
- Voluntary and reflex activity
- Intrinsic reflex (myoenteric plexus) and extrinsic reflex (parasympathetic)
- Process:
- Feces enter rectum → rectal distention → stretch receptor activation → afferent pelvic splanchnic nerve carries signal to defecation center
- Defecation center (spinal cord neurons) transmits signal to pelvic nerve (efferent, parasympathetic): Spinal reflex
- Contraction of sigmoid colon and rectum, relaxation of internal anal sphincter
- External anal sphincter constricted, inhibits defecation
- Voluntary relaxation of external anal sphincter releases feces
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Description
This quiz covers the mechanisms regulating salivary secretion and the phases of swallowing (deglutition). It explores the roles of parasympathetic and sympathetic nervous systems in salivation, as well as the voluntary and involuntary processes involved in swallowing. Test your knowledge on these crucial physiological functions!
