Quiz5 14Gastrointestinal Physiology and Liver Function Review

100 flashcards covering GI tract anatomy, electrical activity, neural/hormonal control, movements, secretions, and liver functions based on the BMS 595 lecture.

What are the five essential requirements provided by the alimentary tract?

(1) Movement of food, (2) secretion and digestion, (3) absorption of water/nutrients, (4) circulation of blood to carry substances, and (5) control by local, nervous, and hormonal systems.

Where does churning predominantly occur as a form of mechanical digestion?

In the stomach.

What is the primary site for the absorption of water, electrolytes, and vitamins?

The small intestine, while the large intestine mainly absorbs water and electrolytes to form feces.

Name the four layers of the alimentary tract wall from innermost to outermost.

Mucosa, Submucosa, Muscularis, and Serosa.

Which layer of the gut wall contains circular and longitudinal muscle?

The Muscularis layer.

What are the two types of intrinsic electrical waves in gastrointestinal smooth muscle?

(1) Slow waves ($SW$) and (2) Spikes ($true action potentials$).

What is the role of slow waves ($SW$) in the GIT?

They stimulate the appearance of intermittent spike potentials, which in turn stimulate muscle contraction.

What are the three major factors responsible for regulating digestive activities?

(1) Neural mechanisms, (2) hormonal mechanisms, and (3) local mechanisms.

Which local factors influence the regulation of digestive activities?

$pH$, physical stimulation, and chemical stimulation.

What does the enteric nervous system comprise?

A linear chain of interconnecting neurons extending the entire length of the GIT, including the myenteric and submucosal plexuses.

What is the alternative name for the Myenteric plexus, and where is it located?

Auerbach's plexus; it is located between the circular muscle layer and the longitudinal muscle layer.

What is the alternative name for the Submucosal plexus, and what is its primary function?

Meissner's plexus; it primarily controls gastrointestinal secretion and local blood flow.

How do Meissner's and Auerbach's nerve bundles differ in size?

The nerve bundles of Meissner's (submucous) plexus are finer than those of the Auerbach's (myenteric) plexus.

How does parasympathetic stimulation generally affect the enteric nervous system?

It causes a general increase in activity of the entire enteric nervous system and enhances most GIT functions.

In what two ways does sympathetic stimulation inhibit gastrointestinal activity?

(1) Direct effect of secreted Norepinephrine ($NE$) to inhibit smooth muscle and (2) inhibitory effect of $NE$ on the neurons of the entire enteric nervous system.

What functions are integrated within the local gastrointestinal reflexes of the gut wall?

GIT secretion, peristalsis, mixing contractions, and local inhibitory effects.

Which reflex involves stomach activity leading to increased mass movements in the colon?

The Gastrocolic (Gastroileal) reflex.

What is the trigger for the Enterogastric reflex and its primary effect?

Triggered by fat or protein chyme in the duodenum; it inhibits stomach motility and secretion to delay emptying.

What is the function of the Colonoileal reflex?

Reflexes from the colon that inhibit the emptying of ileal contents into the colon.

What occurs during the Ileogastric reflex?

Distension of the ileum inhibits gastric motility to prevent more chyme from entering the intestine.

What is the purpose of the Vagovagal reflex?

Reflexes from the stomach and duodenum to the brainstem and back to control gastric motor and secretory activity.

Where do defecation reflexes travel from and to?

They travel from the colon and rectum to the spinal cord and back to produce powerful colonic and abdominal contractions.

Which neurotransmitter in the enteric nervous system most often excites gastrointestinal activity?

Acetylcholine ($ACh$).

Which neurotransmitter in the enteric nervous system almost always inhibits gastrointestinal activity?

Norepinephrine ($NE$).

Where are G cells located, and what do they secrete?

In the antrum of the stomach, duodenum, and jejunum; they secrete Gastrin.

What are the primary stimuli for Gastrin secretion?

Protein, distention, and nerve stimulation (acid inhibits its release).

What are the primary functions of Gastrin?

Stimulates gastric acid secretion and mucosal growth.

Where are I cells located and what hormone do they secrete?

In the duodenum, jejunum, and ileum; they secrete Cholecystokinin ($CCK$).

What actions does Cholecystokinin ($CCK$) perform in the digestive system?

Stimulates pancreatic enzyme and bicarbonate secretion, gallbladder contraction, and growth of exocrine pancreas; inhibits gastric emptying.

Where are S cells located, and what is the primary stimulus for their secretion?

In the duodenum, jejunum, and ileum; they are primarily stimulated by acid and fat.

What does Secretin inhibit?

Gastric acid secretion.

What is the alternative name for Gastric Inhibitory Peptide (GIP)?

Glucose-dependent insulinotropic peptide.

What is the primary action of Gastric Inhibitory Peptide ($GIP$)?

Stimulates insulin release.

What defines the propulsive movement known as peristalsis?

A contractile ring appears around the gut and moves forward, pushing material in front of it.

What is the usual stimulus for intestinal peristalsis?

Distention of the gut.

Which plexus is essential for efficient peristalsis?

The myenteric plexus.

Define the 'law of the gut.'

The combination of the peristaltic reflex and the anal direction of motion.

What is 'receptive relaxation' in the context of peristalsis?

The gut relaxes downstream toward the anus to allow food to be propelled more easily.

What is the splanchnic circulation?

The blood flow through the gut, spleen, and pancreas, which then flows into the liver via the portal vein.

Where do hepatic cells absorb and store nutrients like carbohydrates and proteins?

In the liver sinusoids.

What percentage of blood oxygen can be bypassed in the villus due to countercurrent arrangement?

As much as $80\%$.

How much can blood flow in the villi increase during active nutrient absorption?

Up to eightfold.

What are two kinins that act as powerful vasodilators for the GI glands?

Kallidin and bradykinin.

How does decreased oxygen concentration in the gut wall affect blood flow?

It can increase intestinal blood flow by $50 - 100\%$.

What is 'autoregulatory escape' in gastrointestinal blood flow?

The mechanism where local metabolic vasodilators override sympathetic vasoconstriction to return flow toward normal.

What is the difference between hunger and appetite?

Hunger is an intrinsic desire for food; appetite is a preference for specific types of food.

Which cranial nerve supplies the muscles of mastication?

The mandibular division of Cranial Nerve V ($trigeminal$).

Where are the centers for mastication located?

In the medulla and cerebral cortex.

List the three stages of swallowing ($deglutition$).

(1) Voluntary stage, (2) involuntary pharyngeal stage, and (3) involuntary esophageal stage.

Where is the swallowing center located?

In the medulla and lower pons.

How long does the involuntary pharyngeal stage of swallowing typically last?

Less than $6\,seconds$.

What is the role of the Upper Esophageal Sphincter ($UES$)?

It briefly opens during swallowing to initiate primary peristalsis.

What triggers secondary peristalsis in the esophagus?

Esophageal distention.

What is the resting tonic contraction pressure of the Lower Esophageal Sphincter ($LES$)?

$15 - 40\,mm\,Hg$.

What is the primary function of the stomach's vagovagal reflex during food intake?

To reduce tone in the muscular wall of the stomach body to accommodate between $0.8 - 1.5\,liters$ of food.

What are 'mixing waves' and how often do they occur?

Weak peristaltic constrictor waves in the stomach wall that move toward the antrum once every $15 - 20\,seconds$.

When do hunger contractions typically begin?

$12 - 24\,hours$ after the last ingestion of food.

At what point do hunger contractions reach their greatest intensity?

After $3 - 4\,days$ of starvation.

Which hormone has an excitatory effect on stomach peristalsis?

Gastrin.

What are the two types of movements in the small intestine?

Mixing contractions ($segmentation$) and propulsive contractions ($peristalsis$).

What is the maximum frequency of segmentation contractions in the duodenum and proximal jejunum?

$12/min$.

What is the frequency of segmentation contractions in the terminal ileum?

$8 - 9/min$.

What is the average net movement speed of chyme in the small intestine?

$1\,cm/min$.

How long does it typically take for chyme to pass from the pylorus to the ileocecal valve?

$3 - 5\,hours$.

Which hormones inhibit small intestine motility?

Secretin and glucagon.

What is a 'peristaltic rush'?

Powerful and rapid peristalsis caused by intense irritation of the mucosa, sweeping contents into the colon within minutes.

How much chyme typically empties into the cecum each day?

$1500 - 2000\,mL$.

What are the two primary functions of the large intestine?

(1) Absorption of water and electrolytes and (2) storage of fecal matter.

What are 'haustrations' in the large intestine?

Baglike sacs formed by combined contractions of circular muscle and the teniae coli.

What are the teniae coli?

Three longitudinal strips of muscle in the colon.

Which reflex results from irritation of the peritoneum and can cause intestinal paralysis?

The peritoneointestinal reflex.

What are the two primary functions of gastrointestinal secretory glands?

(1) Secretion of digestive enzymes and (2) secretion of mucus for lubrication and protection.

What is the total daily volume of gastrointestinal secretions?

$6700\,mL$.

Which secretion has the highest daily volume and what is its pH?

Small intestine secretion ($1800\,mL$) with a pH of $7.5 - 8.0$.

Stimulation of which nerves increases secretion in the upper GIT (salivary, gastric, pancreas)?

Glossopharyngeal and vagus nerves.

What are the three main pairs of salivary glands?

Parotid, submandibular (submaxillary), and sublingual glands.

What is the daily secretion range of saliva?

$800$ to $1500\,mL$.

What major enzyme is found in the serous secretion of saliva?

Ptyalin (an $\alpha$-amylase).

Which salivary glands provide both serous and mucus secretions?

Submandibular and sublingual glands.

What do parietal (oxyntic) cells in the gastric pits secrete?

Hydrochloric acid ($HCl$) and intrinsic factor.

What is the function of intrinsic factor?

Binds with vitamin $B_{12}$ to aid its absorption, which is necessary for RBC maturation.

What do peptic (chief) cells secrete?

Pepsinogen.

What is the main driving force for $HCl$ secretion by parietal cells?

The $H^+-K^+\,ATPase$ pump.

In the parietal cell, which ion is exchanged for $HCO_3^-$?

Chloride ($Cl^-$).

How does gastric acid ($HCl$) assist in protein digestion?

It denatures proteins and helps convert pepsinogen to pepsin.

List the three stimulants of gastric secretion.

Acetylcholine ($ACh$), Gastrin, and Histamine.

How many hours does it take for a fatty meal to pass through the stomach?

$5 - 6\,hours$.

What are Peyer's patches?

Lymph nodules located in the ileum.

What enzymes are bound to the membranes of absorptive cells in the small intestine?

Disaccharidases, peptidases, and nucleases.

What stimulates Brunner's glands?

Vagus nerve, secretin, and chemical or tactile irritation.

Which bacteria-produced vitamins are absorbed in the large intestine?

Vitamin $K$ and $B_{12}$.

What enzyme activates trypsinogen to trypsin?

Enterokinase ($from the duodenal mucosa$).

What is the daily volume of pancreatic secretion?

About $1\,liter$.

What are the five general functions of the liver?

(1) Filtration/storage of blood, (2) metabolism (carbs, proteins, fats, hormones), (3) formation of bile, (4) storage of vitamins/iron, and (5) formation of coagulation factors.

What percentage of total body blood flow does the liver receive?

Approximately $28\%$.

What is the functional unit of the liver?

The liver lobule.

What constitutes a portal triad?

A bile duct, a portal vein branch, and a hepatic artery branch.

Name the protein synthesized by the liver responsible for oncotic pressure.

Albumin.

What is the role of Kupffer cells?

Phagocytic macrophages that line hepatic venous sinuses and cleanse blood of bacteria.

Which minerals are stored in the liver?

Copper, Zinc, Magnesium, and Iron.