236 Questions
What is the primary function of Gut-associated lymphoid tissue (GALT)?
To protect against potential microbial pathogens
How does Peristalsis contribute to digestion?
By mixing food with digestive juices
What is the purpose of churning in the GI tract?
To mix food with digestive juices
Which type of contraction occurs in the small intestine to promote mixing movements?
Segmental contraction
How do segmentation contractions impact the digestion process?
By forming segments that chop food multiple times per minute
What is the speed range of Peristalsis in the GI tract?
$15-20$ cm/sec
What is the function of the Enteric Nervous System (ENS) in the gastrointestinal tract?
Coordinates the activity of muscular layers
Which plexus is located between the circular and longitudinal muscle layers in the GI tract?
Myenteric (Auerbach) plexus
Which nervous system is responsible for innervating epithelial cells and muscularis mucosae in the GI tract?
Enteric Nervous System (ENS)
How many neurons does the Enteric Nervous System (ENS) consist of?
~100 million neurons
Which part of the Autonomic Nervous System (ANS) modulates the Enteric Nervous System (ENS)?
Both parasympathetic and sympathetic divisions
What is the main difference between myenteric and submucosal plexuses in the GI tract?
Location within the gut layers
What is a paracrine signal?
A chemical that acts on cells in the immediate vicinity of the secreting cell
Where are the interstitial cells of Cajal located?
Throughout the GI tract from esophagus to anus
What is the function of voltage-gated Ca2+ channels in smooth muscle cells?
Depolarize the cell
What characterizes slow wave activity in GI smooth muscles?
Depolarization by voltage-gated Ca2+ channels
Which parts of the GI tract have contractile tissue that is not smooth muscle?
Pharynx and upper 1/3 esophagus
What does neurocrine refer to?
Both endocrine messengers that influence neurons and messengers released from neurons with endocrine effects
What is the main function of hepatic cells in the liver?
Absorb and store 50-75% of the nutrients except fats
Which hormones released from the mucosa of the intestinal tract play a role in vasodilation during the digestive process?
Vasoactive intestinal peptide and kinins
What happens to blood flow in the gastrointestinal tract due to sympathetic stimulation?
Vasoconstriction of arterioles leads to decreased blood flow
What is the term used for the mechanism where blood flow returns to near normal after a period of intense vasoconstriction due to sympathetic stimulation?
'Autoregulatory escape'
How does decreased O2 concentration in the tissue affect intestinal blood flow?
It increases intestinal blood flow
What effect does parasympathetic nervous system stimulation have on local blood flow in the gastrointestinal tract?
Increases local blood flow
What is the primary function of mucus in the gut?
To provide a protective coating and lubrication
Which hormone is stimulated by lipids and proteins in the small intestine?
Cholecystokinin (CCK)
What is the primary action of secretin in the body?
Inhibits acid secretion and stomach emptying
Which hormone stimulates insulin secretion from the pancreas?
Glucagon like peptide -1 (GLP-1)
What stimulates parietal cells for acid secretion?
Histamine
Which hormone inhibits gastric acid secretion?
Somatostatin
What is the function of motilin in the GI tract?
Increases gastric and intestinal smooth muscle contractions
Which hormone is released as a satiety signal after a meal?
Peptide YY
Which hormone promotes enzyme secretion from the pancreas?
Cholecystokinin (CCK)
What is the site of secretion for GIP (Gastric Inhibitory Peptide)?
Small intestine
What is the primary function of the hypoglossal nerve (CN XII) in the digestion process?
Controlling mastication by innervating chewing muscles
Why is chewing considered to have both voluntary and involuntary components?
Some chewing actions can be voluntarily initiated, but once started, chewing becomes a reflex action
What is the primary role of the trigeminal nerve (CN V) in the digestive system?
Innervating the chewing muscles for mastication
Which component of digestion involves the interplay between teeth, tongue, and chewing muscles?
Digestion in the mouth (chewing-mastication)
In what way does damage to the cranial nerves affect the swallowing mechanism?
Causes paralysis of the swallowing mechanism
What is the primary effect of impaired salivary secretion in conditions like Sjögren's syndrome?
Altered taste perception of food
What is the primary function of myoepithelial cells in the salivary glands?
Contract to eject saliva into the mouth
Which enzyme is responsible for cleaving high-molecular-weight kininogen into bradykinin in saliva?
Kallikrein
At what pH level does lingual lipase, an enzyme in saliva, exhibit optimal activity?
4-5
Which nerve innervates the acinar cells in the salivary glands to stimulate saliva secretion?
Facial nerve
What percentage of starch is hydrolyzed by alpha-amylase secreted by acinar cells?
5%
Which component in saliva is more significant for infants and patients with pancreatic deficiency?
Lingual lipase
What is the primary control system responsible for stimulating saliva secretion?
Parasympathetic nervous system
Which of the following is NOT a function of saliva as described in the text?
Initiate breakdown of proteins
Where is the swallowing (deglutition) center located in the brain?
Medulla and lower pons
During the swallowing reflex, why does the soft palate raise?
To prevent food from entering the nasal cavity
Which stage of swallowing involves the voluntary movement of food into the oropharynx?
Voluntary Stage
What is the role of peristalsis during swallowing?
To transport food from the mouth to the esophagus
Which part of the brain coordinates involuntary chewing actions in response to the pressure of food in the mouth?
Medulla
What is the primary function of salivary amylase secreted by serous cells in the salivary glands?
Starting carbohydrate digestion
Which salivary gland secretes a more viscous fluid compared to the parotid glands?
Submandibular glands
What type of nerve impulses stimulate the secretion of watery saliva when a person sees, smells, tastes, or thinks about food?
Parasympathetic nerve impulses
What are the main chemical features of saliva in terms of pH and ion concentrations?
pH 6-7, High [HCO3-]
What is the primary function of lingual lipase found in saliva?
Begin lipid digestion
What could potentially happen if the food intake regulation system fails?
Increased risk of obesity
In the experiments with the Ob/Ob strain of hyperphagic mice, what was the outcome when the Ob mouse was surgically connected to a wild-type mouse?
The Ob mouse lost weight
What is the role of leptin in food intake regulation?
Leptin decreases food intake
What happens to the Ob/Ob mouse in terms of weight loss when surgically joined with a wild-type mouse?
The Ob/Ob mouse loses weight
What is an outcome of the food intake regulation system failing?
Reduced basal metabolic rate
In the context of energy balance, what is critical for long periods of stability in the body's total mass?
Energy expenditure matching energy intake
What is the primary role of the paraventricular nuclei in the hypothalamus?
Decrease food intake
Which hypothalamic nucleus is responsible for depressing eating behavior when lesions occur?
Dorsomedial nucleus
What is the main function of the arcuate nuclei in the hypothalamus?
Regulate food intake and energy expenditure
How do hypothalamic feeding and satiety centers influence hormonal secretion?
By influencing thyroid hormone secretion
What signals does the hypothalamus receive that influence feeding behavior?
Signals from sight, smell, and taste
Which metabolic aspect does the hypothalamus primarily regulate to maintain body weight in adulthood?
Caloric intake
What happens to leptin secretion in response to starvation?
It decreases as adipocytes shrink.
Which neurotransmitter is a neuromodulator in the brain that increases food intake?
Neuropeptide Y
What is the primary function of orexigenic peptides and neurotransmitters?
Increase food intake
Which hormone is released mainly from adipose tissue and is known for suppressing appetite?
Leptin
What is the effect of decreased leptin concentration on appetite and metabolism?
It increases appetite and slows down metabolism.
Which factor contributes to the regulation of food intake by crossing the blood-brain barrier?
Peripheral stimuli and inhibitors
What happens if the ventromedial nuclei of the hypothalamus are destroyed?
Voracious eating leading to extreme obesity
Which condition is characterized by marked weight loss, muscle weakness, and decreased metabolism?
Inanition
What can be expected if the lateral nuclei of the hypothalamus are stimulated?
Voracious eating
What is the role of the ventromedial nuclei of the hypothalamus in relation to the feeding center?
It inhibits the feeding center.
Which part of the brain maintains homeostasis by regulating various visceral activities and linking the nervous and endocrine systems?
Hypothalamus
What visceral activity does the hypothalamus regulate in addition to hunger and body weight?
Control of body temperature
Which hormone is primarily secreted from the entire GI tract, especially from the ileum and colon, and affects food intake by inhibiting feeding?
Peptide YY (PYY)
What is the main mechanism through which gastrointestinal filling inhibits feeding?
Activation of vagus nerve
Which receptor in the brain receives projections from the arcuate nucleus (ARC) affecting food intake and energy expenditure?
Y1R1
What role do 'oral factors' related to feeding play as food passes through the mouth?
Trigger salivation and taste perception
Which hormone, in addition to PYY, acts on a shorter time course to affect food intake?
Cholecystokinin (CCK)
In addition to the lateral hypothalamus and brainstem, where do outputs from the ARC mediate alterations in feeding or energy expenditure?
Thalamus
Which method of temperature measurement is least affected by changes in environmental temperature?
Rectal temperature
What is the approximate temperature difference between axillary and rectal temperatures?
1.5°C higher in axillary
Which part of the body is usually warmer than its environment?
Skeletal muscles
At rest, which of the following organs generates most of the heat in the body?
Liver
Which method is used to measure radiant temperature over the temporal artery?
Infrared thermometer
Which region of the hypothalamus mediates temperature increasing mechanisms?
Posterior region
What is the primary medium for transporting heat from the body core to skin regions?
Blood
In heat regulation, what is the important structure supplied by inflow of blood from the skin capillaries?
Arteriovenous anastomoses
Which body parts receive blood supply directly from small arteries through arteriovenous anastomoses?
Hands, feet, and ears
Which system primarily controls heat conduction through the skin via vasoconstriction?
Sympathetic nervous system
What primarily influences changes in vasoconstriction of arterioles supplying blood to the venous plexus of the skin?
Body core temperature changes
What is the primary way heat moves from the skin to the environment?
Radiation
Which factor contributes the most to resting metabolism during exercise?
Muscle activity
What is the primary determinant of lost heat in the body in terms of heat transfer?
Conduction rate
Which process accounts for around half of body heat loss under normal conditions?
Radiation
What acts as a heat insulator for the body in terms of heat loss prevention?
Fat of subcutaneous tissues
What is the primary source of the energy lost during exercise?
Muscle activity
What is the primary means by which the body can rid itself of heat when the temperature of the surroundings becomes greater than that of the skin?
Evaporation
Which mechanism aids in enhancing conduction to air across the body surface?
Wind
What is the process by which water evaporates from body surfaces and removes large amounts of body heat?
Evaporation
Which heat loss method usually has a rate significantly greater when losing heat to water compared to air?
Evaporation
What contributes to the enhancement of conduction to air across the body surface?
Cool air
What is the primary way by which molecules absorb heat from the environment and escape as gas (water vapor) during evaporation?
Evaporation
What is the primary mechanism responsible for increasing heat production in the body?
Chemical thermogenesis by sympathetic stimulation
Where is the shivering center located in the brain for thermoregulation?
Posterior hypothalamus
Which factor contributes to the immediate increase in cellular metabolism in response to cold signals?
Sympathetic stimulation
What is the limited contribution of brown fat to heat production in adults?
It is not present in adult humans
How does thyroxine secretion impact cellular metabolism?
By increasing the rate of cellular metabolism
Why does a person experience a sensation of being overheated or cold discomfort when internal body temperature is disrupted?
To prompt appropriate behavioral adjustments
What is the primary function of bile in the body?
Promoting digestion and absorption of lipids
Which substances are synthesized by the liver to meet the body's metabolic demands?
Albumin, glucose, and fatty acids
What is the significance of releasing substrates into the bloodstream by the liver?
Supplying fuels for other organs
During fasting, what role do ketone bodies play in the body?
Sparing glucose for the nervous system
Why does the liver synthesize phospholipids?
For triglyceride biosynthesis
How do lipophilic chemicals get processed in the liver for excretion?
Metabolized into water-soluble substances
Which zone of the liver lobule houses the most resistant hepatocytes to circulatory compromise or nutritional deficiency?
Zone I
Where does bile enter after being secreted into the canaliculi between hepatocytes?
Canals of Hering
What characterizes the lining of interlobular bile ducts in the liver?
Cuboidal/columnar epithelium
What is the primary function of the canals of Hering in the liver lobule?
Channeling bile to terminal ductules
Which part of the liver lobule is sequentially perfused with blood that has been modified by preceding hepatocytes?
Zone III
What type of cells line the interlobular bile ducts closely surrounding portal vein branches?
Cuboidal/columnar epithelium
Which structure in the liver includes all hepatocytes drained by a single central vein and is bounded by two or more portal triads?
Hepatic lobule
How can the liver be viewed if the triad is considered the core of a portal lobule?
As a mass of hepatocytes drained by a single central vein
What is the primary defining characteristic of a portal acinus in the liver?
Zonal relationship with blood supply
What is the primary determining factor for the oxygen and solute concentrations received by hepatocytes in the liver?
Proximity to the vascular core
In the liver, what axis in the portal acinus is formed by a line between two triads?
High PO2 axis
What is the key characteristic of the portal veins in the liver?
Connection to hepatic venules
What is the role of Kupffer's cells in the liver?
Removing particulate matter from circulation
Which cells play a central role in the storage of vitamin A in the liver?
Stellate cells
What is the primary function of hepatic sinusoids in the liver?
Combining blood from portal venules and hepatic arterioles
Which of the following is true about the blood supply to the liver?
Blood from portal venules and hepatic arterioles combine in hepatic sinusoids
What can be transformed into proliferative, fibrogenic, and contractile myofibroblasts on liver injury?
Stellate cells
What is the most significant cellular component of liver parenchyma (by volume) other than hepatocytes?
Endothelial cells
What is the primary function of the hepatocyte in handling molecules?
Transporting materials across the basolateral membrane
What is the primary source of secondary bile acids in the intestinal tract?
Dehydroxylation of primary bile acids by bacteria
What causes jaundice in body tissues?
Accumulation of bilirubin in extracellular fluid
What is bilirubin primarily a degradation product of?
Hemoglobin
How are bile acids recycled in the body?
Uptake by enterocytes in the small intestine
What accounts for the majority of total bilirubin production in the body?
Heme metabolism of senescent red cells
What is the primary role of exopeptidases in peptide digestion?
Release free amino acids from peptides
Which end of the protein do carboxypeptidases act on in peptide digestion?
Carboxy-terminal end
What is the main function of aminopeptidases in the digestive process?
Act on the amino-terminal end of proteins
How are free amino acids primarily carried into cells for absorption?
Na+-dependent cotransport
Which transporter is responsible for carrying dipeptides and tripeptides into enterocytes?
PepT1 using H+-dependent cotransport
How are amino acids transported from the enterocyte into the blood for circulation?
Facilitated diffusion
How is calcium absorbed across the basolateral membrane in the duodenum?
By a Na+-Ca2+ antiporter
What is the primary transporter for ionized iron Fe2+ absorption in the enterocyte?
Divalent metal transporter 1 (DMT1)
Which hormone regulates iron uptake by causing the destruction of the ferroportin transporter?
Hepcidin
How is water primarily transported through the intestinal membrane?
Osmosis
Which type of iron is absorbed by an apical transporter on the enterocyte?
Heme iron
What factor determines the absorption of water through the intestinal mucosa?
Laws of osmosis
How are lipophilic fats like fatty acids and monoglycerides primarily absorbed in the gastrointestinal tract?
By simple diffusion
What is the fate of chylomicrons formed in the enterocytes?
They are packaged into secretory vesicles by the Golgi
Why do chylomicrons have to be absorbed into lacteals instead of directly entering the capillaries?
Due to the inability to cross the basement membrane of capillaries
Where do monoglycerides and fatty acids recombine into triglycerides after entering the enterocytes?
Smooth endoplasmic reticulum
What is the primary mechanism by which lipophilic fats move across the enterocyte membrane?
Simple diffusion
Why are pancreatic enzymes required for the digestion of phospholipids?
To hydrolyze them into simpler components
Which statement about the absorption of short- and medium-chain fatty acids is accurate?
They are absorbed directly into the portal blood without being converted into triglycerides.
What happens to nucleic acid polymers like DNA and RNA during digestion?
They are digested into nucleotides and further broken down into nitrogenous bases and monosaccharides.
What is the role of fat-soluble vitamins A, D, E, and K in the body?
They support various metabolic reactions as coenzymes or cofactors.
Why do vitamins need to be acquired from the diet rather than being synthesized in the body?
Because they are not naturally present in the body for internal production.
How are water-soluble vitamins different from fat-soluble vitamins?
Water-soluble vitamins can be excreted easily through urine, while fat-soluble vitamins are retained longer in the body.
Which process is responsible for absorbing nucleic acid bases and monosaccharides?
Secondary active transport
What is the primary role of Mg2+ in the context of parathyroid hormone secretion and response?
Promoting proper secretion and end-organ response to parathyroid hormone
Which process leads to the production of lipophilic substances like butyric acid in the colon?
Fermentation by intestinal flora
What is the primary function of butyric acid in the colon?
To serve as an energy substrate for colonocytes
Which of the following is NOT a product of bacterial activity in the colon?
Glucose
What is the consequence of a lack of vitamin K or liver disease affecting prothrombin formation?
Bleeding tendency
Which substance is absorbed by simple diffusion in the large intestine due to its lipophilic nature?
Butyric acid
What is the primary function of brush border enteropeptidase in the pancreas?
Converts inactive trypsinogen to active trypsin
Which pancreatic enzyme is responsible for splitting whole and partially digested proteins into peptides?
Trypsin
What signals trigger the release of pancreatic enzymes into the intestine?
All of the above
Which enzyme completes the digestion of some proteins to the amino acid state?
Carboxypolypeptidase
What is the primary role of NaHCO3 solution secreted by duct cells in the pancreas?
Neutralizes acidic chyme from the stomach
What initiates the cascade activation process of most pancreatic enzymes from zymogens to active forms?
Enteropeptidase activity
What is the major pancreatic secretory response stimulated by the entry of chyme into the proximal small intestine?
Release of secretin to stimulate duct cells
Which route is responsible for stimulating pancreatic secretions during the gastric phase primarily?
Vagovagal reflex by stomach distention
What is the mechanism by which gastric acid entering the duodenum stimulates a major pancreatic secretory response?
Stimulation of duodenal S cells to release secretin
What percentage of total secretion of pancreatic enzymes after a meal is accounted for by moderate amounts of enzymes secreted into the pancreatic acini?
20%-25%
Which product stimulates gastrin release from the stomach, acting as a poor agonist of CCKA receptors on acinar cells?
Peptones
What is the primary function of Secretin in regulating pancreatic secretions?
Stimulating the secretion of water and electrolytes by the pancreatic ductal epithelium
During which phase of pancreatic secretion does the cephalic phase occur?
First phase
Which two hormones regulate pancreatic secretions from the small intestine?
Cholecystokinin (CCK) and Secretin
What stimulates the acinar cells in the pancreas to produce large quantities of pancreatic digestive enzymes?
Acetylcholine
Which nerve releases acetylcholine in the pancreas during the cephalic phase of pancreatic secretion?
Vagus nerve
What is the primary stimulus for pancreatic secretion during the intestinal phase?
Secretin and CCK release
What enzyme is responsible for hydrolyzing neutral fat into fatty acids and monoglycerides in fat digestion?
Pancreatic lipase
Why is it important for proteolytic enzymes of the pancreatic juice not to become activated until after secretion into the intestine?
To avoid digestion of the pancreas
Which substance prevents the activation of trypsin inside the secretory cells and ducts of the pancreas?
Trypsin inhibitor
What enzyme causes the hydrolysis of cholesterol esters in fat digestion?
Cholesterol esterase
During carbohydrate digestion, which enzyme hydrolyzes most carbohydrates to form mostly disaccharides and a few trisaccharides?
Pancreatic amylase
What is the primary source of bicarbonate secretion into the duodenum for neutralizing stomach acid?
Pancreas
What is one hallmark of cystic fibrosis?
Secretion of Cl- and fluid ceases.
Which basic stimuli are important in causing pancreatic secretion?
Acetylcholine and cholecystokinin (CCK)
How is chloride transported in exchange for bicarbonate in the cell?
By entering the cell on a basolateral NKCC cotransporter
Which cells continue to secrete mucus in cystic fibrosis despite the defect in CFTR channel protein?
Goblet cells
What causes disruption of pancreatic enzyme secretion into the intestine in cystic fibrosis?
Clogging of small pancreatic ducts
Which molecule is secreted by the duodenal and upper jejunal mucosa to stimulate pancreatic secretion when food enters the small intestine?
Cholecystokinin (CCK)
What is the primary function of the double-layered fold of peritoneal membrane called mesentery?
To suspend the small intestine parts in the peritoneal cavity
What controls motility in the small intestine?
Segmental contractions
Which type of contractions promote the absorption of nutrients in the small intestine?
Segmental contractions
What is the percentage distribution of the jejunum and the ileum in the small intestine?
Jejunum: Two-fifths, Ileum: Three-fifths
Why must the entry of chyme into the small intestine be controlled?
To avoid overwhelming the small intestine
How are intestinal contents propelled forward in the small intestine?
By a combination of segmental and peristaltic contractions
What are the three hormones that reinforce the 'decrease motility' signal in the intestine?
Secretin, cholecystokinin (CCK), gastric inhibitory peptide (GIP)
Which hormone is released in response to the presence of acidic chyme in the duodenum?
Secretin
What triggers the release of CCK into the bloodstream?
Presence of fats in a meal
What is the primary function of gastric inhibitory peptide (GIP) in the regulation of intestinal digestion and absorption?
Slows gastric emptying
How do signals from the gut to the stomach and pancreas primarily travel?
Primarily through neural and hormonal pathways
Which substance may be broken down into its constituent components before absorption?
TAG
How does the ileocecal valve function during the passage of chyme from the ileum to the cecum?
It relaxes each time a peristaltic wave reaches it
Which function is NOT attributed to the ileocecal sphincter in the text?
Intensifies peristalsis in the ileum after a meal
What is the primary function of the colonic microflora in the large intestine?
Performs fermentation of dietary carbohydrates
What initiates regulated and controlled elimination of colonic contents in the large intestine?
Voluntary control
What is one of the functions NOT mentioned for the human large intestine in the text?
Absorption of nucleic acid bases and monosaccharides
What happens to the ileocecal sphincter immediately after a meal?
Intensifies relaxation to speed up emptying into the cecum
Which sphincter is under voluntary control?
External sphincter
What initiates the defecation reflexes?
Stretching of the rectal wall
Which muscle type is present in the internal anal sphincter?
Smooth muscle
What controls the external sphincter?
Voluntary conscious signals
What is the primary mechanism that triggers the defecation reflex?
Distension of the organ wall
Which component of the external anal sphincter is continuously constricted subconsciously?
Striated muscle
What distinguishes the motor pattern in the colon from that in the small intestine?
Distinct fasting and fed patterns of contractions
What is the role of the tenia coli in the large intestine?
Formation of bulging pockets called haustra
Which nerve mediates parasympathetic control of the descending and rectosigmoid colon?
Pelvic nerves
How does the muscularis of the large intestine differ from that of the small intestine?
It has a continuous longitudinal muscle layer
What characterizes the mucosa of the colon in comparison to that of the small intestine?
Smooth luminal surface lacking villi
Which factor contributes to creating bulging pockets known as haustra in the large intestine?
Contractions of the tenia coli
Explore the neural regulation of the gastrointestinal system, including the enteric nervous system (ENS), myenteric plexus, submucosal plexus, and the autonomic nervous system (ANS) components such as the parasympathetic and sympathetic nervous systems.
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