salivary and gastric secretion

Question 1

What are the functions of secretions in the body?

Answer 1

Secretions lubricate, protect, and aid digestion.

Question 2

What are examples of exocrine glands?

Answer 2

Salivary glands and gastric glands are examples of exocrine glands.

Question 3

What are the characteristics of exocrine glands?

Answer 3

Exocrine glands have ducts through which their secretions are transported.

Question 4

What are examples of endocrine glands?

Answer 4

Enteroendocrine cells in the stomach and small intestine are examples of endocrine glands.

Question 5

What are the characteristics of endocrine glands?

Answer 5

Endocrine glands do not have ducts and release their secretions directly into the bloodstream.

Question 6

What are the roles of salivary secretions?

Answer 6

Salivary secretions play a role in lubrication, protection (oral hygiene/antimicrobial agents), and initiating chemical digestion.

Question 7

What are the major salivary glands?

Answer 7

The major salivary glands include the parotid gland, submandibular gland, and sublingual gland.

Question 8

Where are dispersed salivary glands located?

Answer 8

Dispersed salivary glands are found in the mucosa of the mouth and tongue, including the labial, buccal, palatal, and lingual glands.

Question 9

What happens when a solution is hypotonic?

Answer 9

In a hypotonic solution, there is a lower concentration of solutes and a higher concentration of water than inside the cell, causing water to move into the cell.

Question 10

What happens when a solution is hypertonic?

Answer 10

In a hypertonic solution, there is a higher concentration of solutes and a lower concentration of water than inside the cell, causing water to move out of the cell.

Question 11

What is the function of the parotid glands?

Answer 11

The parotid glands, comprising approximately 25% of the major salivary glands, produce serous, watery secretions containing salivary amylase for starch digestion.

Question 12

What is the function of the submandibular glands?

Answer 12

The submandibular glands, accounting for approximately 70% of the major salivary glands, produce mixed serous and mucus secretions.

Question 13

: What is the function of the sublingual glands?

Answer 13

The sublingual glands, making up approximately 5% of the major salivary glands, produce mucus-dominant secretions that are thicker and primarily for lubrication.

Question 14

What is the function of water in saliva composition?

Answer 14

Water, making up approximately 99.5% of saliva, acts as a solvent that dissolves food components. It aids in taste perception, swallowing, initiation of digestion, and oral hygiene.

Question 15

What are the electrolytes found in saliva and their functions?

Answer 15

Saliva contains electrolytes such as K+, HCO3-, Na+, and Cl-. They function as a buffer for acidic food contents, helping to maintain the pH balance in the mouth.

Question 16

What enzymes are present in saliva and their respective functions?

Answer 16

a-amylase: Hydrolyzes a-1,4 glycosidic bonds in starch, breaking them down into disaccharide maltose, trisaccharide maltotriose, and a-dextrin.
Lysozyme: Hydrolyzes peptidoglycans in the cell wall of gram-negative bacteria.
Lingual lipase [dispersed salivary glands of the tongue]: Hydrolyzes lipid triglycerides into fatty acids and diglycerides, with optimal activity in an acidic pH.
Lactoferrin: Chelates iron to prevent microbial multiplication and exhibits antibacterial properties.

Question 17

What is the role of secretory IgA in saliva composition?

Answer 17

Secretory IgA in saliva prevents microbial attachment to the epithelium, helping to inhibit the growth and colonization of bacteria.

Question 18

What are the organic components found in saliva and their functions?

Answer 18

Saliva contains organic compounds such as urea and uric acid, which aid in the removal of waste products for excretion.

Question 19

What is the acinar structure of the salivary glands?

Answer 19

The salivary glands have an acinar structure, consisting of acinar cells that form clusters or acini. These cells are responsible for secreting saliva.

Question 20

: How is hypotonic saliva formed in two stages?

Answer 20

The formation of hypotonic saliva occurs in two stages. The saliva is rich in K+ and HCO3- ions and poor in Na+ and Cl-. The first stage involves the secretion of water and ions through the NKCC1 co-transporter, which prevents water from moving out. The second stage involves changes in composition based on the flow rate of saliva.

Question 21

Why is the NKCC1 co-transporter important for saliva secretion?

Answer 21

The NKCC1 co-transporter plays a crucial role in the secretion of water and ions in saliva. It prevents water from moving out of the acinar cells, aiding in the production of hypotonic saliva.

Question 22

How does the composition of saliva change with flow rate?

Answer 22

The composition of saliva changes with the flow rate. At a low rate of secretion, maximum reabsorption of electrolytes occurs, resulting in hypotonic saliva with lower concentrations of osmotically active electrolytes. At a high flow rate, there is reduced reabsorption of electrolytes, leading to saliva with higher osmolality, closer to the primary isotonic solution produced by the acini.

Question 23

Why is the flow of saliva important for digestion and oral hygiene?

Answer 23

The flow of saliva is essential for digestion and oral hygiene. It helps in the lubrication of food, initiation of digestion, and oral cleansing by washing away food particles and bacteria. Saliva contains enzymes and antimicrobial components that aid in the digestive process and maintain oral health.

Question 24

How does the electrolyte composition of saliva differ from plasma?

Answer 24

Electrolytes in saliva are hypotonic compared to plasma. The concentrations of Na+ and Cl- are lower in saliva, while HCO3- and K+ are higher than in plasma.

Question 25

How is the salivary secretion rate controlled by the autonomic nervous system?

Answer 25

Parasympathetic stimulation is responsible for increasing the salivary secretion rate. Sensory stimuli related to food stimulate the salivary nuclei in the brainstem via cranial nerves VII (facial nerve for sublingual and submandibular glands) and IX (glossopharyngeal nerve for the parotid gland). This leads to an increase in the production of amylase, mucin, and serous saliva, as well as vasodilation.

Question 26

What is the role of parasympathetic stimulation in salivary secretion?

Answer 26

Parasympathetic stimulation, triggered by sensory stimuli associated with food, activates salivary nuclei in the brainstem. This results in an increase in the production of amylase, mucin, and serous saliva. Parasympathetic stimulation also promotes vasodilation, increasing blood flow to the salivary glands.

Question 27

: How is sympathetic stimulation involved in salivary secretion?

Answer 27

Sympathetic stimulation, facilitated through the superior cervical ganglion and sympathetic postganglionic nerves, leads to vasoconstriction and reduced salivary production. This can result in a dry mouth sensation.

Question 28

What may be reported when there is sympathetic stimulation of salivary glands?

Answer 28

Sympathetic stimulation of salivary glands can cause a dry mouth sensation to be reported due to the vasoconstriction and decreased saliva production.

Question 29

What is Sjögren’s syndrome?

Answer 29

Sjögren’s syndrome is an autoimmune disease that causes destruction of the exocrine glands, commonly affecting tear and saliva production. It leads to dry eyes and a dry mouth, collectively known as sicca symptoms.

Question 30

What are the sicca symptoms associated with Sjögren’s syndrome?

Answer 30

The sicca symptoms associated with Sjögren’s syndrome include dry eyes and a dry mouth. “Sicca” is derived from the Latin word “siccus,” meaning dry.

Question 31

What is xerostomia?

Answer 31

Xerostomia refers to the condition of having a dry mouth. In Sjögren’s syndrome, patients experience xerostomia due to a lack of adequate saliva production.

Question 32

What are the common issues associated with xerostomia?

Answer 32

Common issues associated with xerostomia include tooth decay and halitosis (bad breath) due to bacterial overgrowth. Additionally, inadequate lubrication from reduced saliva production may result in difficulties speaking or swallowing solid food.

Question 33

What is Schirmer’s test used for?

Answer 33

chirmer’s test is employed to determine if an individual produces enough tears to keep their eyes moist and healthy. It involves placing a filter paper in the eye for 5 minutes before assessing the result. This test is commonly used to assess for problems of dry eyes, including Sjögren’s syndrome.

Question 34

What are the types of exocrine gland cells found in gastric glands?

Answer 34

Mucous neck cells: These cells secrete thin mucus.
Parietal cells: These cells secrete hydrochloric acid (HCl) and intrinsic factor.
Chief cells: These cells secrete pepsinogen and gastric lipase.

Question 35

What are the types of endocrine cells found in gastric glands?

Answer 35

G cells: These cells secrete the hormone gastrin.
D cells: These cells secrete the hormone somatostatin (GHIH).
Enterochromaffin-like (ECL) cells: These cells secrete histamine.

Question 36

What is the function of gastrin secretion in gastric digestion?

Answer 36

Gastrin secretion plays a role in promoting gastric digestion by initiating several processes:

Parietal cell secretion of HCl: Gastrin stimulates parietal cells to secrete hydrochloric acid, which aids in the breakdown of food.
Chief cell secretion of pepsinogen: Gastrin stimulates chief cells to secrete pepsinogen, an inactive form of the enzyme pepsin, which is involved in protein digestion.
Lower esophageal sphincter contraction: Gastrin promotes the contraction of the lower esophageal sphincter, preventing the reflux of stomach contents into the esophagus.
Increased motility of the stomach: Gastrin enhances stomach motility, helping to mix and churn the food.
Relaxation of the pyloric sphincter: Gastrin relaxes the pyloric sphincter, allowing the passage of partially digested food from the stomach to the small intestine.

Question 37

What are the components of gastric juice?

Answer 37

Water and electrolytes: Provide a medium for the action of acid and enzymes, facilitating the digestion of organic substances.

Question 38

What substance is secreted by mucus neck cells in the gastric glands?

Answer 38

Mucus is secreted by mucus neck cells. Mucus, which contains the glycoprotein mucin, helps decrease bacterial interaction and protects the gastric lining.

Question 39

What are the substances secreted by chief cells in the gastric glands?

Answer 39

Pepsinogen: Chief cells secrete pepsinogen, which is a pro-enzyme. Pepsinogen is converted into pepsin, an enzyme responsible for breaking down proteins into smaller peptides.
Gastric lipase: Chief cells also secrete gastric lipase, an enzyme involved in the digestion of triglycerides.
Rennin (Chymosin): In young individuals, chief cells secrete rennin, which coagulates milk to enhance its absorption. It is related to pepsin and aids in the digestion of milk proteins.

Question 40

: What is the function of parietal cells in gastric juice secretion?

Answer 40

Parietal cells secrete two important substances:

Hydrochloric acid (HCl): Parietal cells produce HCl, which helps convert the inactive pepsinogen into its active form, pepsin. HCl also denatures (breaks down) proteins, assists in killing microorganisms present in food, and provides an acidic environment for optimal digestion.
Intrinsic factor (IF): Parietal cells secrete intrinsic factor, which is essential for the absorption of vitamin B12 in the ileum. Intrinsic factor also plays a role in erythropoiesis (red blood cell production) in the bone marrow and is crucial for preventing pernicious anemia.

Question 41

How is gastric acid secretion stimulated?

Answer 41

Gastric acid secretion is stimulated by the following factors:

Acetylcholine (ACh): Acetylcholine is released from the vagus nerve, leading to the stimulation of acid secretion by parietal cells.
Gastrin: Gastrin, released from G cells, stimulates gastric acid secretion.
Histamine: Histamine, released from enterochromaffin-like (ECL) cells, plays a role in stimulating gastric acid secretion.

Question 42

What inhibits gastric acid secretion?

Answer 42

Gastric acid secretion can be inhibited by the following factors:

Somatostatin: Somatostatin, released from D cells, acts as a paracrine and endocrine inhibitor by inhibiting adenylate cyclase (AC), thereby reducing acid secretion.
Mucosal prostaglandin: Prostaglandins produced in the gastric mucosa act as antagonists for H2 receptors, which can inhibit gastric acid secretion.
NSAIDs: Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit prostaglandin formation, leading to increased gastric acid secretion.

Question 43

How are parietal cells adapted for acid secretion?

Answer 43

Parietal cells are adapted for acid secretion through the following characteristics:

Tubulovesicles: In the resting state, parietal cells contain tubulovesicles, which store components necessary for acid production.
Microvilli: Upon stimulation, these tubulovesicles fuse with the canalicular membrane, which is lined with microvilli, increasing the surface area for acid secretion.
H+/K+-ATPase and carbonic anhydrase: Parietal cells contain these enzymes, which are crucial for the production and secretion of hydrogen ions (H+) to form gastric acid.

Question 44

What are the pharmacological inhibitors of gastric acid secretion?

Answer 44

Proton pump inhibitor (PPI), such as omeprazole: PPIs inactivate the H+/K+-ATPase enzyme, also known as the proton pump, which is responsible for acid secretion in parietal cells. By inhibiting this enzyme, PPIs reduce gastric acid production.
H2 receptor antagonist, such as cimetidine: H2 receptor antagonists block the action of histamine on parietal cells, which normally stimulates acid secretion. By inhibiting this stimulus, H2 receptor antagonists decrease gastric acid secretion.
Atropine: Atropine inhibits muscarinic receptors, which are activated by acetylcholine and mediate vagal stimulation of acid secretion. By blocking these receptors, atropine reduces the stimulation of acid secretion.

Question 45

What are the three phases of gastric secretion?

Answer 45

Cephalic phase: This phase is initiated by sensory stimuli related to the thought, sight, smell, or taste of food. The vagus nerve innervates the parietal cells, chief cells, and G cells, leading to the secretion of gastric juices, including acid and gastrin.
Gastric phase: This phase occurs when food enters the stomach. It involves direct stimulation of parietal cells, chief cells, and mucus secretion. G cells release gastrin, which directly stimulates parietal cells and indirectly stimulates them via histamine release from enterochromaffin-like (ECL) cells.
Intestinal phase: This phase is further divided into an excitatory phase and an inhibitory phase:
Excitatory phase: Chyme with a pH greater than 3 and the presence of peptides stimulate gastric secretions. This stimulation occurs via vagal innervation and the release of gastrin.
Inhibitory phase: Chyme with a pH below 2, protein breakdown products, or changes in osmolarity inhibit gastric secretions. This inhibition is mediated by the hormones cholecystokinin (CCK) and gastric inhibitory polypeptide (GIP).

Question 46

What is the cephalic phase of gastric secretion?

Answer 46

The cephalic phase, also known as the “get started” phase, is initiated by the taste, smell, or thought of food. These sensory stimuli stimulate the vagal center in the medulla oblongata. Vagal signals are then sent to endocrine cells within the gastrointestinal (GI) system, resulting in the secretion of gastrin, a hormone involved in gastric secretion.

Question 47

What is the gastric phase of gastric secretion?

Answer 47

The gastric phase, also known as the “go for it” phase, occurs when the stomach is distended in preparation for the entry of food bolus. It is during this phase that the greatest volume of gastric juice is produced. The distention of the stomach triggers the release of various substances, including gastric juices, to aid in the digestion process.

Question 48

What is the intestinal phase of gastric secretion?

Answer 48

The intestinal phase, also known as the “slow down” phase, plays a role in regulating the further production of gastric juices and controlling the rate at which stomach contents enter the duodenum. This phase can either promote or inhibit the secretion of gastric juices, depending on factors such as the pH, presence of certain substances (e.g., peptides), and hormonal signals like cholecystokinin (CCK) and gastric inhibitory polypeptide (GIP).

Question 49

Why is the gastric mucosa not damaged by the acidic environment of the stomach?

Answer 49

The gastric mucosa is protected from damage by several mechanisms:

Surface mucous glands: These glands secrete a viscous mucus layer that forms a protective barrier on the surface of the gastric mucosa. The mucus acts as a physical barrier, preventing direct contact between the acidic gastric juice and the underlying tissue.
Mucin with basic side chains: Mucin, the main component of mucus, contains basic side chains in its chemical structure. These side chains prevent the neutralization of mucin by gastric acid, allowing it to maintain its protective function.
HCO3- secretion: Surface epithelial cells secrete bicarbonate ions (HCO3-) into the gastric mucosa. HCO3- helps to neutralize any H+ ions that come into contact with the mucosa, maintaining a more neutral pH in the immediate vicinity of the surface epithelial cells.
Tight junctions: Tight junctions between epithelial cells form a barrier that prevents the passage of gastric acid into the underlying tissue. This helps to maintain the integrity of the gastric mucosa.
Unstirred layer: The presence of an unstirred layer, with a pH closer to neutral (around pH 7), helps to prevent the activation of pepsinogen, an inactive precursor of the enzyme pepsin. By keeping pepsinogen inactive, enzymatic and chemical damage to the gastric mucosa is minimized.

Question 50

What is gastritis and what are its common causes?

Answer 50

Gastritis refers to the inflammation of the gastric mucosa. It can be caused by various factors, including:

Infection by the bacteria Helicobacter pylori: This is the most common cause of gastritis, accounting for approximately 50% of cases. H. pylori infection is prevalent in the population.
Cigarette smoking: Smoking tobacco can irritate the gastric mucosa and contribute to the development of gastritis.
Alcohol consumption: Excessive alcohol intake can cause inflammation and damage to the gastric mucosa, leading to gastritis.
Nonsteroidal anti-inflammatory drugs (NSAIDs): Prolonged use of NSAIDs, such as aspirin or ibuprofen, can irritate the stomach lining and result in gastritis. It is important to note that this list is not exhaustive, and there may be other causes of gastritis as well.

Question 51

How does the gastric mucosa regenerate following acute damage?

Answer 51

Following acute damage to the gastric mucosa, rapid regeneration occurs through a process called restitution. Restitution involves the rapid division of stem cells located in the neck region of the gastric glands. These stem cells differentiate and migrate to replace the damaged or lost epithelial cells, allowing for the regeneration of the gastric mucosa.

Question 52

What is known about the epidemiology of Helicobacter pylori infection?

Answer 52

The epidemiology of Helicobacter pylori infection is still not fully understood. However, it is known that H. pylori infection is highly prevalent in the population, with approximately 50% of people having experienced it. Economic and social conditions may play a role in the spread and prevalence of H. pylori, but the exact factors contributing to its epidemiology are still being investigated.