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Human Physiology Y3 > Secretion in Upper Digestive Tract > Flashcards

Secretion in Upper Digestive Tract Flashcards

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1
Q

How much saliva do we produce per day?

A

1 - 1.5 L

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2
Q

What secretes saliva?

A

Salivary glands have high rate of metabolism and blood flow

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3
Q

Describe the blood flow of salivary glands

A

Blood flow is 10x that supplied to actively contracting skeletal msucle

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4
Q

What are the symptoms of lacking functional salivary glands?

A

Dry mouth
Dental caries
Infection of buccal mucosa
Background secretion is important

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5
Q

How do infection of buccal mucosa prevent functioning of salivary glands?

A

Infections of the buccal mucosa, such as bacterial or viral infections, can potentially lead to inflammation and swelling of the mucosal tissues. While the infection primarily affects the mucosa, it can indirectly impact the functioning of salivary glands due to the inflammatory response and associated swelling

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6
Q

How does the parasympathetic nervous system mediate salivary secretion?

A

Be release of ACh that
Binds muscarinic receptors = watery saliva is secreted

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7
Q

How does the sympathetic nervous system mediate salivary secretion?

A

Release of norepinepthrine
Binds alpha and beta adrenergic receptors = thicker saliva secreted

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8
Q

What organic constituents of saliva are found in large amounts?

A

Mucin = glycoprotein
Alpha-amylase = active pH 4-11

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9
Q

What is the role of mucin?

A

Lubricate food

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10
Q

Name organic constituents of saliva present in small amounts

A

RNAase & DNAase
Lingual lipase
Lactoferrin
Secretory IgA
Lysozyme

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11
Q

Name some functions of saliva

A

Antifungal, antibacterial and antifungal
Wound healing
Buffer
Teeth mineralization
Food digestion
Coating & lubrication

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12
Q

Role of Parietal cells

A

Secrete HCl = kills most ingested bacteria
Except helicobacter pylori

Secrete intrinsic factor

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13
Q

What is intrinsic factor?

A

Glycoproteins produced by the parietal cells of the gastric glands in the stomach.

These factors play a crucial role in the absorption of vitamin B12 (cobalamin) in the small intestine

They are the only gastric secretion requried for life

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14
Q

Role of Chief cells

A

Secrete pepsinogens
Pepsinogens are cleaved to pepsin by the acidic effects of HCl

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15
Q

What hormone is secreted in stomach?

A

Gastrin = regulates gastric acid secretion

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16
Q

Role of mucus secreted by gastric gland

A

Protect gastric mucosa from mechanical and chemical destruction

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17
Q

What enzymes are secreted in infancy and diminish as we become adults?

A

Renin and gastric lipase

Gastric lipase activity is more significant in newborns and infants, contributing to the digestion of milk fats (especially in breast milk), its activity diminishes in adults

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18
Q

What is the composition of gastric juice?

A

99.5% water
0.5% solids = organic and inorganic substances

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19
Q

Describe the conc of K+ in gastric juice

A

K+ conc is always higher in gastri juice than plasma

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20
Q

What happens to ion conc in prolonged vomiting?

A

Hypokalemia

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21
Q

What does ionic composition of gastric juice depend on?

A

Rate of secretion of H+ ions
As secretory rate increases so do H+ and Cl- conc in gastric juice = because of co-traport by parietal cells
Na+ decreases in concentration
K+ stays relatively the same conc

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22
Q

Is the rate of gastric acid secretion the same in everyone?

A

No, it varies among individuals partly due to variation in number of acid secreting cells

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23
Q

What is the basal rate of gastric acid secretion?

A

1-5 mM per hour

Basal rate = unstimulated

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24
Q

What is the rate of gastric acid secretion at maximum stimulation?

A

6-40 mM per hour

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25
What is the rate of gastric acid secretion in a gastric ulcer patient?
Hyposecretion of acid The increased acidity in the stomach due to the presence of ulcers can activate negative feedback mechanisms to inhibit further acid secretion. One such mechanism involves the release of somatostatin, a hormone that inhibits the secretion of gastric acid. Somatostatin is released by various cells in the stomach lining, including D cells and enterochromaffin-like (ECL) cells. They don't produce acid because of the feedback mechanism So antacid drugs won't help
26
What is the rate of gastric acid secretion in a duodenal ulcer patient?
Hypersecretion of acid Basal rate = higher than 5mM per hour Acid is leaking out from stomach But when there is food in the stomach this is not a problem because pH increases
27
What is the rate of gastric acid secretion in a pernicious anemia patient?
Hyposecretion of acid
28
What is pernicious anemia?
Pernicious anemia is a type of anemia characterized by a deficiency of vitamin B12 (cobalamin) due to impaired absorption in the gastrointestinal tract, typically resulting from the lack of intrinsic factor (IF) secretion by the gastric parietal cells. Intrinsic factor is a glycoprotein produced by parietal cells of the gastric mucosa, and it is essential for the absorption of vitamin B12 in the small intestine
29
What are the major stimulators of HCl secretion?
Secondary messengers = Ca2+ and cAMP Transmit message from blood to lumen
30
Name the inhibitors of HCl secretion
Substituted benximidazoles Prostaglandin E = block cAMP via GCPR H2-antagonist Anticholinergics Gastrin antagonists
31
What is the function of gastrin?
Stimulate HCl secretion Increase gastric and intestinal motility Increase pancreatic secretion Proper growth of GI mucosa
32
How does gastrin cause its effects?
Enters bloodstream then goes back to stomach affectin gparietal cells
33
How does gastrin stimulate HCl secretion?
Gastrin receptor is coupled to GPCR Activation of PLC = PIP2 >>> IP3 + DAG IP3 = increases intracellular calcium releasing from ER store DAG activates PKC Calcium and PKC increase the H+/K+ ATPase pumps These proton pumps actively transport hydrogen ions (H+) from the cytoplasm into the gastric lumen in exchange for potassium ions (K+).
34
How does gastrin increase pancreatic secretion?
GPCR activates PLC Elevated intracellular calcium levels trigger the exocytosis of zymogen granules within pancreatic acinar cells. These granules contain digestive enzymes such as amylase, lipase, and proteases (e.g., trypsin, chymotrypsin), as well as bicarbonate ions (HCO3-), which are essential for pancreatic enzyme function and neutralizing acidic chyme in the duodenum.
35
Describe the conversion of pepsinogen into pepsin at low pH
Autocatlytic = more rapid conversion at low pH
36
What is pepsin's optimal pH?
Less than 3
37
Where is pepsin inactivated irreversible?
In duodenum pH = 7
38
What does pepsin digest?
10-20% of total dietary protein
39
What is intrinsic factor, where it is secreted and what is its function?
Glycoprotein Secreted by parietal cells in fundus =
40
What is the fundus?
The "fundus" refers to the upper portion of the stomach, which is located above the body of the stomach and below the esophagus. It is the part of the stomach that expands and contracts as food is swallowed and enters the stomach. `The fundus is a relatively thin-walled region that can accommodate swallowed food and gastric juices.
41
How does intrinsic factor help with Vit B12 absorption?
Forms complex with B12 which is highly resistant to digestion Complex is absorbed at terminal ileum Binds to cubilin receptors, the vitamin B12-intrinsic factor complex is endocytosed into the ileal enterocytes Vitamin B12 then binds to another protein called transcobalamin II (TC-II), which protects it from degradation and facilitates its transport within the bloodstream to various tissues and organs throughout the body Within cells, vitamin B12 plays essential roles in various cellular processes, including DNA synthesis, red blood cell production (erythropoiesis), and neurological function. Deficiency of vitamin B12 can lead to anemia, neurological disorders, and other health problems
42
What stimulates intrinsic factor secretion?
Gastrin stimulates IF and HCl secretion But their secretion is NOT linked So omeprezole has no effect on IF secretion
43
Where is mucin found, and what is its function?
Mucin = main constituent of gastric mucus Function = coat and lubricate mucosa surface
44
Mucin properties?
Large molecules with CHO side chains Insoluble in acid pH Destroyed by pepsin
45
How is mucin regulated?
Regulated by ACh Stimulated by food
46
What does ACh do to HCl secretion?
Enhances its secretion
47
What effect do prostaglandins have on other gastric mucosal cells?
Paracrine effect = the ability of prostaglandins to act locally within the gastric mucosa to influence the function of neighbouring cells. Prostaglandins are lipid compounds that are synthesized and released by various cells, including epithelial cells, in response to different stimuli.
48
What is the function of prostaglandins?
Direct inhibition of parietal cell secretion = as part of the stomach's defence mechanism to protect the gastric mucosa from damage caused by excessive acid production. Mediate mucosal defence by: Stimulation of mucus, phospholipid, and HCO3- secretion Enhancement of mucosal blood flow Stimulation of mucosal cell turnover
49
What happens when someone has a prostaglandin deficiency?
Predisposes them to gastric mucosal injury
50
What drugs cause gastric mucosal injuries?
COX inhibitors = aspirin & NSAIDs
51
What does the gastric mucosal barrier consist of?
Thick mucous layer = 1mm Consists of mucins and HCO3-
52
What is the function of gastric mucosal barrier and how does it work?
Protect against abrasions, HCl & pepsin The unstirred layer slows the inward diffusion of H+ and outward diffusion of HCO3-
53
How is the mucus and HCO3- secretion regulated in the gastric mucosal barrier?
Calcium and cholinergic agonists stimulate HCO3- secretion Adrenergic agonists decrease HCO3- secretion Aspirin and NSAIDs inhibit mucus and HCO3- secretion
54
What is the maximum HCO3- secretion?
10% of HCl secretion
55
What does decrease in HCO3- secretion cause?
Too much acid = leading to ulcers
56
Describe the gastric mucosal barrier turnover rate?
High gastric mucosa turnover rate = entire mucosa is replaced in 1-3 days
57
What is used as ulcer therapy?
Antacids = neutralize HCl Omeprazol = prevent acid release Antibiotic = helicobacter pyori bacillus Misoprostrol = prostaglandin agonist
58
What enzyme breaks down carbohydrates?
Salivary alpha-amylase Denatured at low pH
59
Describe fat digestion in stomach
Minimal fat digestion
60
How does high acidity affect fat digestion?
Inhibits fats from emulsifying into small droplets This means they stay insoluble
61
What substances are absorbed in the stomach?
Nutrients Very little absorption takes place
62
For gastric absorption, what properties do the substances have to have?
Highly lipid-soluble substances = ethanol
63
What is gastritis?
Inflammation of the lining of the stomach
64
What is heartburn?
Painful or burning sensation in the chest
65
What mechanisms causes heartburn?
Increase in gastric acid secretion Backflush of acidic chyme into esophagus
66
What factors cause heartburn?
Overeating, fatty foods Smoking, alcohol, coffee Lying down immediately after a meal Tight clothing

Human Physiology Y3 (14 decks)

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