GIT Flashcards
Which of the following statements is correct in relation to gastric emptying?
A Is slowed down with metoclopramide
B Occurs in approximately 2 hours
C Is independent of pH in the duodenum
D Depends on osmotic pressure of materials in the duodenum
D
Explanation
Gastric emptying occurs in approximately 2 hours, starting with carbohydrates, and then proteins followed by fats.
Note: This value of 2hours may be correct. However, some sources say different. Option A (Depends on osmotic pressure of materials in the duodenum) is definitely correct, so I chosen this as the right answer. If option B read “Depends on the osmotic pressure in the duodenum”-then it may be wrong. Gastric emptying depends on the actual osmotic pressure of the MATERIALS entering the duodenum rather than the duodenum’s pressure”. In this case, I would go with option A.
The rate of emptying also depends on the osmotic pressure of the material entering the duodenum. Hyperosmolality of the duodenal contents is sensed by the duodenal osmoreceptors that initiate a decrease in gastric emptying. Metoclopramide is a prokinetic. Gastric emptying is dependent on the duodenum having an alkaline pH as an acidic pH delays gastric emptying.
Extra:
From Ganong Physiology: REGULATION OF GASTRIC MOTILITY & EMPTYING The rate at which the stomach empties into the duodenum de-pends on the type of food ingested. Food rich in carbohydrate leaves the stomach in a few hours. Protein-rich food leaves more slowly, and emptying is slowest after a meal containing fat. The rate of emptying also depends on the osmotic pressure of the material entering the duodenum. Hyperosmolality of the duodenal contents is sensed by “duodenal osmoreceptors” that initiate a decrease in gastric emptying which is probably neural in origin. Fats, carbohydrates, and acid in the duodenum inhibit gastric acid and pepsin secretion and gastric motility via neural and hormonal mechanisms. The hormone involved is probably peptide YY. CCK has also been implicated as an inhibitor of gastric emptying.
Regarding bile composition, which of the following substances makes up the largest proportion?
A Lecithin
B Bile pigments
C Cholesterol
D Bile salts
D
Explanation
Water makes up the greatest composition-97%
bile salts-0.7%
bile pigments-0.2%
cholesterol 0.06%
lecithin 0.1%
The pH of pancreatic secretions is around?
A 6
B 7
C 7.5
D 6.5
C
Explanation
The value is around 7.5-8.0
Note: Pancreatic secretions is alkaline. This alkaline solution is designed to help neutralize stomach acid, so that the pancreatic digestive enzymes can work more effectively. The pH is 7.5- 8.0.
Extra:
Pancreatic juice is alkaline and has a high HCO3 content. About 1500ml of pancreatic juice is secreted per day. Bile and intestinal juices are also neutral or alkaline, and these three secretions neutralise gastric acid, raising the pH of the duodenal contents to 6.0-7.0. By the time the chyme reaches the jejunum, its pH is nearly neutral.
Composition of normal human pancreatic juice
Cations: Na, K, Ca, Mg (pH approximately 8.0)
Anions: HCO3-, Cl, SO4, HPO4
Digestive enzymes
Other proteins
Note: the stems do not include a pH of 8. I think it may be an older questions, so I have left it as is.
Which cells secrete intrinsic factor?
A Parietal
B G cells
C S cells
D Chief cells
A
Explanation
Chief cell of the stomach secrete pepsinogen and rennin. S cells secrete secretin from the jejunum and the duodenum. G cell secretes gastrin. Parietal Cells secrete gastric acid and intrinsic factor
Which of the following gastrointestinal hormones does not stimulate gastric acid secretion?
A Acetylcholine
B VIP
C Histamine
D Gastrin
B
Explanation
Gastrin, ACH and histamine all stimulate gastric acid secretion.
VIP and Prostaglandins (group E) inhibit gastric acid secretion
Which hormone stimulates an increase in the volume of pancreatic juice but not the enzyme content?
A ACH
B Vagus nerve
C CCK
D Secretin
D
Explanation
Secretin acts on the pancreatic ducts to cause copious secretion of a very alkaline pancreatic juice that is rich in HCO3 and volume but poor in enzymes.
Cholecystokinin (CCK) acts on the acinar cells to cause the release of zymogengranules and production of pancreatic juice rich in enzymes but poor in volume.
ACH and stimulation of the vagi nerves stimulate pancreatic juice rich in enzymes but poor in volume in the same way as CCK
Blood borne factors that stimulate gastrin secretion are?
A Epinephrine
B Glucagon
C Secretin
D Calcitonin
A
Explanation
Blood borne factors inhibiting gastrin secretion
- Secretin, GIP, VIP, glucagon and calcitonin
Blood borne factors stimulating gastrin secretion
- Calcium and epinephrine
Luminal factors inhibiting gastrin secretion
- Acid and somatostatin
Luminal factors stimulating gastrin secretion
- Peptides and amino acids
- Distension
The correct type of component as a percentage of solid stool is?
A Cellulose and other indigestible fiber 20%
B Inorganic material 35%
C Fat and fat derivatives 15%
D Bacteria 30%
D
Explanation
Component Percentage of total weight
Water 75
Solids 25
Percentage of total solids
Cellulose and other indigestible fiber =variable
Bacteria= 30
Inorganic material (mostly calcium and phosphates)= 15
Fat and fat derivatives= 5
Also desquamated mucosal cells, and small amounts of digestive enzymes
The role of secretin?
A It has a half life of 25min
B Increases the secretion of bicarbonate by the pancreas
C Its secretion is triggered by fatty food.
D Increases gastric acid secretionYour
B
Explanation
Secretin is secreted by the S cells that are located deep in the glands of the mucosa of the upper portion of the small intestine. Secretin decreases gastric acid secretion and causes pylorus sphincter contraction. Secretin increases the secretion of HCO3 by the duct cells of the pancreas and biliary tract. It thus causes the secretion of a watery alkaline pancreatic juice. It augments the action of CCK in producing pancreatic secretion of digestive enzymes. Its secretion is triggered by products of protein digestion and by acid bathing in the mucosa of the upper small intestine. It has a half life of 5 minutes and little is known about its metabolism.
Which of the following statements regarding defecation is INCORRECT?
A Stimulation of the gastrocolic reflex may initiate a desire to defecate
B The first urge to defecate occurs at a rectal pressure above 55mmHg
C Defecation is a spinal reflex
D Voluntary defecation can occur by contraction of the abdominal muscles and relaxation of the puborectalis muscle
B
Explanation
Defecation is a spinal reflex. Distension of the rectum with faeces initiates reflex contraction of its musculature and the desire to defecate. The sympathetic nerve supply to the internal (involuntary) sphincter is excitatory and parasympathetic supply is inhibitory. The pudendal nerve supplies the external anal sphincter. The urge to defecate occurs at a rectal pressure of 18mmHg. At 55mmHg, the external and internal sphincter relaxes and there is reflex expulsion of the contents. This is why reflex evacuation of the rectum can occur even with a spinal injury. Voluntary defecation occurs by contracting the abdominal muscles and relaxing the puborectalis muscle. The anorectal angle is reduced to <15 degrees and combined with relaxation of the external anal sphincter, defecation occurs. Distension of the stomach or ileum with food initiates contraction of the colon and the desire to defecate. The so-called gastrocolic and ileocolic reflexes. These reflexes as well as contraction of the abdominal muscles fill the rectum with colonic contents. This distension also stimulates the puborectalis muscle and further enhances the desire to defecate. This is the rule for children after a meal but for adults habitual and cultural factors play a large role in determining when defecation occurs
Which is true regarding swallowing?
A Oesophageal content is swept down the oesophagus at a speed of 3cm/s
B Inhibition of respiration and glottis closure is a voluntary response
C Swallowing is an initial voluntary response followed by reflex action
D Swallowing is a reflex response triggered by afferent impulses in the trigeminal, hypoglossal and vagus nerves
C
Explanation
Swallowing is a reflex response triggered by afferent impulses in the trigeminal, glossopharyngeal and vagus nerves. These impulses are integrated in the nucleus of the tractus solitarius and ambigiuus. Efferent fibres pass to the pharyngeal musculature and the tongue via the trigeminal, facial and hypoglossal nerves. Swallowing is initiated by the voluntary collection of food on the tongue and propelling the food backward into the pharynx. This starts a wave of involuntary contraction of the pharyngeal muscles that push the material into the oesophagus. Inhibition of respiration and glottis closure are part of this response. A peristaltic ring contraction of the oesophageal muscle forms behind the material, which is swept down the oesophagus at a speed of 4cm/s. In an upright position gravity causes the material to enter into the lower oesophagus ahead of the peristaltic wave. However, if supine or standing upside down, a second peristaltic wave occurs propelling the food into the stomach.
Extra:
To further elaborate on the innervation of swallowing, from the prescribed textbook Ganong Physiology: Swallowing (deglutition) is a reflex response that is triggered by afferent impulses in the trigeminal, glossopharyngeal, and vagus nerves. These impulses are integrated in the nucleus of the tractus solitarius and the nucleus ambiguus. The efferent fibers pass to the pharyngeal musculature and the tongue via the trigeminal, facial, and hypoglossal nerves.
Where is most iron absorbed in the GI tract?
A Colon
B Duodenum
C Ileum
D Stomach
B
Explanation
Iron absorption primarily occurs in the duodenum, facilitated by ferric reductase
