Salivary and Pancreatic Secretion Quiz

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Questions and Answers

Which type of saliva is secreted by the parotid glands?

Mucus

Serous (correct)

Mixed (serous and mucus)

Viscous

Approximately what percentage of total saliva volume is contributed by the submandibular glands?

70% (correct)

95%

25%

Which of the following best describes the secretion type of the submandibular glands?

Primarily mucus

Exclusively serous

Mixed (serous and mucus) (correct)

Exclusively serous with enzymatic additives

If a patient exhibits a significant decrease in serous saliva production, which glands are most likely affected?

Parotid glands Signup and view all the answers

Which combination of glands contributes approximately 95% of the total saliva volume?

Parotid and submandibular Signup and view all the answers

What is the initial event in the proposed mechanism of secretion described?

Active transport of $Cl^-$ across the basal membrane. Signup and view all the answers

Why does the active transport of $Cl^-$ cause the membrane's potential to become more negative?

The movement of negative ions into the cell. Signup and view all the answers

Following the active transport of $Cl^-$, which ion is subsequently attracted?

$Na^+$ Signup and view all the answers

What drives the attraction of $Na^+$ according to the proposed mechanism?

The increased negative electrical potential across the membrane. Signup and view all the answers

Where does the active transport of $Cl^-$ occur that initiates the secretions?

The basal membrane. Signup and view all the answers

Which enzyme is directly responsible for activating chymotrypsinogen?

Trypsin Signup and view all the answers

What is the primary function of pancreatic amylase?

Converting polysaccharides into disaccharides Signup and view all the answers

Which of the following enzymes functions as an exopeptidase?

Carboxypeptidase Signup and view all the answers

In what form is pancreatic amylase secreted?

In an active form to start polysaccharide breakdown Signup and view all the answers

What type of cells are arranged in layers inside the lobule?

Hepatocytes Signup and view all the answers

What is the role of trypsin in the activation of carboxypeptidase?

Trypsin converts carboxypeptidase into its active state Signup and view all the answers

How thick are the layers of hepatocytes within the liver lobule?

Two cells thick Signup and view all the answers

Sinusoids facilitate the flow of blood derived from which two vessels inside the liver lobule?

Portal vein and hepatic artery Signup and view all the answers

In which direction does the blood flow within the sinusoids of the liver lobule?

From the hepatic artery and portal vein towards the central vein Signup and view all the answers

What is the main structural arrangement of hepatocytes within a liver lobule designed to optimize?

Efficient blood filtration and detoxification Signup and view all the answers

What is the primary function of cholesterol ester hydroxylase?

To hydrolyze cholesterol esters, facilitating cholesterol absorption Signup and view all the answers

What is a key observable indicator of pancreatic insufficiency related to fat digestion?

Steatorrhea, characterized by yellowish, fatty stools Signup and view all the answers

Which cells are primarily responsible for secreting water and bicarbonate in the digestive system?

Duct cells Signup and view all the answers

What is the primary function of bile in relation to bilirubin?

To facilitate the excretion of bilirubin. Signup and view all the answers

What is the role of glucuronide, sulfate, and other substances in the context of bilirubin secretion?

They conjugate with bilirubin to facilitate its secretion. Signup and view all the answers

If a patient presents with steatorrhea, which of the following enzyme deficiencies might be suspected?

Cholesterol ester hydroxylase Signup and view all the answers

What is the primary role of bicarbonate secretion in the digestive process?

To neutralize acidic chyme entering the small intestine Signup and view all the answers

What is the direct precursor to bilirubin in the catabolism of heme?

Biliverdin Signup and view all the answers

What is the initial event in the formation of bilirubin from hemoglobin?

Decomposition into heme and globin Signup and view all the answers

Why does a high concentration of bilirubin in the skin cause jaundice?

Bilirubin deposition in the skin due to increased levels causing yellow discoloration. Signup and view all the answers

Study Notes

Gastrointestinal Secretion

Secretions in the GI tract are a response to food, varying by food type
Secretions digest food and protect the mucosa
Secretion involves organic materials synthesized and stored in secretory cells, and release of water and electrolytes from blood vessels.

Types of Secretory Glands

Single-cell glands (e.g., goblet cells)
Pits (invaginations)
Crypts of Lieberkühn (small intestine)
Tubular glands (stomach)
Complex glands (e.g., mucus glands in lower esophagus)
Organs (outside tubular GI structure)
Salivary glands
Pancreas
Liver

Regulation of Glandular Secretion

Presence of food stimulates glandular secretions
Mechanical and chemical stimulation triggers secretory reflexes -leading to increased secretions.

Role of ANS in Glandular Secretion

Parasympathetic stimulation increases glandular secretion rates.
Sympathetic stimulation moderately increases secretion via enhanced vesicle transport and reduces water and electrolyte secretion by decreasing blood flow.

Hormonal Regulation of Glandular Secretion

Hormones are secreted in response to food in digestive organs, stimulating glands to increase secretions.

Salivary Glands Secretion

Defined as the movement of water, electrolytes, proteins (e.g., amylase, glycoproteins) into the salivary duct.
Acinar cells secrete water and electrolytes from extracellular fluid.

Proposed Steps of Salivary Secretion

Basal membrane active Cl⁻ transport increases membrane negativity
Increased membrane negativity attracts Na⁺ ions

Osmotic Pressure and Apical Membrane Rupture

Increased osmotic pressure draws water into acinar cells, increasing hydrostatic pressure
This increased pressure causes small ruptures in the apical membrane, flushing water, electrolytes, and organic materials into the lumen.

Synthesis and Secretion of Protein Components

Proteins (e.g., ptyalin, lingual lipase, mucin) are synthesized in the endoplasmic reticulum of acinar cells
These proteins are transported to the apical membrane and secreted via exocytosis.
Mitochondria provide energy for transport and protein synthesis.

Primary Secretion by Acinar Cells

Acinar cells secrete a primary solution containing ptyalin, mucin, and electrolytes
The water and electrolyte concentration equals that of extracellular fluid.

Role of Duct Cells in Saliva Composition

Saliva composition modifies as it passes through ducts via Sodium Reabsorption and Potassium secretion

Final Saliva Composition

The final saliva is hypotonic
Reabsorption of Na⁺ and Cl⁻ exceeds K⁺ and HCO₃⁻ secretion
Net Ionic Changes
Na⁺ and Cl⁻ concentration are reduced to 1/10th plasma concentrations
K⁺ concentration increases 7-fold
HCO₃⁻ concentration increases 2-3-fold

Salivary Glands Contribution and Secretion Types

Parotid glands (25%): secrete serous (watery) saliva
Submandibular glands (70%): secrete mixed (serous and mucous) saliva
Sublingual glands (5%): secrete mucous saliva

pH of Saliva

Resting secretion: ~7.0
Active secretion: approaches ~8.0

Changes in Saliva During Stimulation

Maximal stimulation increases primary saliva production up to 20-fold.
Increased duct flow reduces reabsorptive and secretory duct cell activity.

Impact on Secondary (Final) Saliva Composition

Higher concentrations of Na⁺ and Cl⁻
Lower concentrations of K⁺ compared to lower flow rates.

Control of Salivary Secretion

1. Unconditioned Salivary Reflex: triggered by chemo- or pressure receptors (e.g., eating), using afferent fibers to salivary centers in the medulla which send stimulatory signals to increase salivation through autonomic nerves.
1. Conditioned Salivary Reflex: learned responses such as thinking about, seeing, or smelling food to increase salivation.
1. Nervous regulation:
Both sympathetic and parasympathetic systems stimulate salivation but via different mechanisms.
High sympathetic activity can reduce salivation due to vasoconstrictive effects on blood supply.

Functions of Saliva

Carbohydrate digestion: Salivary amylase breaks down polysaccharides into maltose.
Swallowing: Moistens food and lubricates or reduces friction during swallowing.

Antibacterial Actions

Lysozyme destroys bacteria
Continuous saliva flow removes food residues & foreign particles
Immunoglobulin A contributes to bacterial destruction.

Taste Facilitation and Speech Aid

Saliva acts as a solvent for taste stimuli.
Enables smooth movements of lips and tongue for speech.

Neutralization of Acids

Bicarbonate helps neutralize acidic food and bacterial acids, thus preventing dental caries.

Esophageal Secretion

Simple mucus glands secrete mucoid substances: lubrication and protection from damage during swallowing.
Compound mucus glands (near esophageal-gastric junction) secrete alkaline mucus neutralizing acidic contents from the stomach.

Gastric Secretion

Mucus-secreting cells line the entire stomach surface for lubrication and protection against mechanical injury.
Mucus protects against proteolytic enzymes and neutralizing hydrochloric acid (HCl).

Tubular (Oxyntic) Glands

Secrete HCl, intrinsic factor, and mucus.
Mucus Neck cells: mucus and pepsinogen
Peptic cells: large quantities of pepsinogen
Parietal cells: secrete HCl and intrinsic factor

Mechanism of HCl Secretion

Cl⁻ active transport creates a negative potential for K⁺ and Na⁺ (primarily K⁺) diffusion.
H⁺ formation from carbonic anhydrase reaction on water and carbon dioxide
HCO₃⁻ is transported from the cell and exchanged for Cl⁻
H⁺ is pumped into the canaliculus via the H⁺/K⁺ pump
Water enters canaliculus by osmosis

Net Reaction

Water, carbon dioxide, and sodium chloride react to produce sodium bicarbonate and hydrochloric acid

Importance of HCI

Activates pepsinogen to pepsin
Decomposes connective tissue
Kills microorganisms

Pepsinogen Secretion

Secreted by chief (peptic) and mucus cells in an inactive form
Becomes pepsin in acidic environments (pH 1.8–3.5)
Breaks down long polypeptides into smaller peptides.

Intrinsic Factor Secretion

Secreted by parietal cells
Essential for vitamin B12 absorption
Lack of intrinsic factor can lead to pernicious anemia.

Pyloric Glands

Mucus cells similar to gastric glands
G cells secrete gastrin.

Gastrin

Released into the blood and acts on the stomach to increase HCl and pepsinogen secretion.
Maintains gastric mucosal growth.

Regulation of HCI Secretion: Neural Control

The enteric nervous system directly stimulates parietal and peptic cells
Parasympathetic vagal activation during cephalic and gastric phases activates enteric neurons, releasing ACh and stimulating enterochromaffin-like cells to secrete histamine and GRP for G-cell activation

Regulation of HCI Secretion: Hormonal Control

Gastrin is secreted by G cells into the blood and acts on parietal cells to increase HCl secretion
The release is stimulated by gastric distention and presence of proteins (in chyme), and by vagal stimulation.

Regulation of HCI Secretion: Paracrine Control

Histamine is secreted by enterochromaffin-like cells in response to vagal stimulation and local inflammation, activating parietal cells via H2 receptors.

Regulation of HCI Secretion: Somatostatin

Somatostatin is secreted by paracrine cells in the mucosa
It acts on parietal cells to decrease cAMP.

Regulation of Pepsinogen Secretion

HCl acts indirectly by activating enteric reflexes to increase pepsinogen secretion by peptic cells.

Phases of Gastric Secretion

Cephalic phase: initiated by thinking about, smelling, tasting, and chewing food, activating the vagus nerve.
Gastric phase: food reaching the stomach causing maximal stimulation of gastric secretion, stimulated by local reflexes, and enhanced by proteins presence.
Intestinal phase: -Excitatory: duodenum distension slightly stimulating gastric secretions through gastrin release.
Inhibitory: chyme presence in the intestine inhibits gastric secretion by initiating, neural reflexes and release of hormones ( GIP, CCK, secretin, enterogastrone).

Intestinal Secretion

Tubular glands in duodenum submucosa secrete mucus, water, electrolytes.
Local neural mechanisms activate secretions, mediated by Ach and VIP

Colonic Secretion

Mostly mucus and a small amount of rich in K+ and HCO₃⁻ serous secretion.

Pancreatic Secretion

Endocrine portion (Islets of Langerhans): secretes insulin, glucagon, somatostatin, pancreatic polypeptide into the blood.
Exocrine portion (acinar cells): secretes enzymes for nutrient digestion, and duct cells secrete water and bicarbonate
Pancreatic secretion is high in enzymes, hypotonic, and alkaline

Mechanism of Pancreatic Secretion

Enzymes are synthesized by acinar cells and stored in inactive zymogen granules
Proteolytic enzymes are activated in the duodenum, including trypsinogen to trypsin, chymotrypsinogen to chymotrypsin, and procarboxypeptidases to carboxypeptidases.
Pancreatic amylase converts polysaccharides into disaccharides.
Lipolytic enzymes break down lipids, requiring lipase, bile salts, and colipase.

Pancreatic Water and Bicarbonate Secretion

-Water and bicarbonate are secreted by duct cells of the pancreas -Bicarbonate neutralizes the acidic chyme in the duodenum, creating optimal pH for enzyme function

Control of Pancreatic Secretion

Neural (Parasympathetic): Vagal stimulation (excitatory) via enteric nervous system innervating acinar cells.
Hormonal:
- Secretin: major stimulant of water and HCO₃⁻ secretion, secreted by duodenal mucosa into the blood.
- Cholecystokinin (CCK): major stimulant of enzyme secretion, released by duodenal mucosal cells, stimulated by breakdown products of fat and proteins (in chyme), and increases enzymatic secretion directly.

Liver Secretions

Largest and most important metabolic organ, essential for digestive processes, metabolism, detoxification, and blood component synthesis.
Functions include metabolic processes, detoxification, protein synthesis, glycogen storage, and excretion of cholesterol and bilirubin.

Bile Production and Composition

Hepatocytes produce bile, which flows to the bile canaliculi.
Bile flows into the bile duct and to the duodenum.
Bile is composed of bile salts, water, bilirubin, cholesterol, and electrolytes.
Bile salts are synthesized by the liver from cholesterol.

Bile Storage and Release

Bile is stored in the gallbladder between meals.
Presence of fats and proteins in chyme in the duodenum trigger the release of CCK and relaxation of the sphincter of Oddi, allowing bile to enter the lumen.

Bile Salt Recycling

About 20% of bile salts are lost daily in feces
The liver synthesizes new bile salts to replace lost ones during enterohepatic circulation.

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Description

Test your knowledge on the types of saliva secreted by various glands and the mechanisms behind pancreatic secretions. This quiz covers the functioning of major salivary and digestive enzymes, emphasizing their roles and interactions. Ideal for students of physiology and anatomy.