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Human Physiology Y3 > Secretion in Upper Digestive Tract > Flashcards

Secretion in Upper Digestive Tract Flashcards

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
Q

What is the rate of gastric acid secretion in a gastric ulcer patient?

A

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

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26
Q

What is the rate of gastric acid secretion in a duodenal ulcer patient?

A

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

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27
Q

What is the rate of gastric acid secretion in a pernicious anemia patient?

A

Hyposecretion of acid

28
Q

What is pernicious anemia?

A

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
Q

What are the major stimulators of HCl secretion?

A

Secondary messengers = Ca2+ and cAMP
Transmit message from blood to lumen

30
Q

Name the inhibitors of HCl secretion

A

Substituted benximidazoles
Prostaglandin E = block cAMP via GCPR
H2-antagonist
Anticholinergics
Gastrin antagonists

31
Q

What is the function of gastrin?

A

Stimulate HCl secretion
Increase gastric and intestinal motility
Increase pancreatic secretion
Proper growth of GI mucosa

32
Q

How does gastrin cause its effects?

A

Enters bloodstream then goes back to stomach affectin gparietal cells

33
Q

How does gastrin stimulate HCl secretion?

A

Gastrin receptor is coupled to GPCR
Activation of PLC = PIP2&raquo_space;> 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
Q

How does gastrin increase pancreatic secretion?

A

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
Q

Describe the conversion of pepsinogen into pepsin at low pH

A

Autocatlytic = more rapid conversion at low pH

36
Q

What is pepsin’s optimal pH?

A

Less than 3

37
Q

Where is pepsin inactivated irreversible?

A

In duodenum pH = 7

38
Q

What does pepsin digest?

A

10-20% of total dietary protein

39
Q

What is intrinsic factor, where it is secreted and what is its function?

A

Glycoprotein
Secreted by parietal cells in fundus =

40
Q

What is the fundus?

A

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
Q

How does intrinsic factor help with Vit B12 absorption?

A

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
Q

What stimulates intrinsic factor secretion?

A

Gastrin stimulates IF and HCl secretion
But their secretion is NOT linked
So omeprezole has no effect on IF secretion

43
Q

Where is mucin found, and what is its function?

A

Mucin = main constituent of gastric mucus
Function = coat and lubricate mucosa surface

44
Q

Mucin properties?

A

Large molecules with CHO side chains
Insoluble in acid pH
Destroyed by pepsin

45
Q

How is mucin regulated?

A

Regulated by ACh
Stimulated by food

46
Q

What does ACh do to HCl secretion?

A

Enhances its secretion

47
Q

What effect do prostaglandins have on other gastric mucosal cells?

A

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
Q

What is the function of prostaglandins?

A

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
Q

What happens when someone has a prostaglandin deficiency?

A

Predisposes them to gastric mucosal injury

50
Q

What drugs cause gastric mucosal injuries?

A

COX inhibitors = aspirin & NSAIDs

51
Q

What does the gastric mucosal barrier consist of?

A

Thick mucous layer = 1mm
Consists of mucins and HCO3-

52
Q

What is the function of gastric mucosal barrier and how does it work?

A

Protect against abrasions, HCl & pepsin

The unstirred layer slows the inward diffusion of H+ and outward diffusion of HCO3-

53
Q

How is the mucus and HCO3- secretion regulated in the gastric mucosal barrier?

A

Calcium and cholinergic agonists stimulate HCO3- secretion

Adrenergic agonists decrease HCO3- secretion

Aspirin and NSAIDs inhibit mucus and HCO3- secretion

54
Q

What is the maximum HCO3- secretion?

A

10% of HCl secretion

55
Q

What does decrease in HCO3- secretion cause?

A

Too much acid = leading to ulcers

56
Q

Describe the gastric mucosal barrier turnover rate?

A

High gastric mucosa turnover rate = entire mucosa is replaced in 1-3 days

57
Q

What is used as ulcer therapy?

A

Antacids = neutralize HCl
Omeprazol = prevent acid release
Antibiotic = helicobacter pyori bacillus
Misoprostrol = prostaglandin agonist

58
Q

What enzyme breaks down carbohydrates?

A

Salivary alpha-amylase
Denatured at low pH

59
Q

Describe fat digestion in stomach

A

Minimal fat digestion

60
Q

How does high acidity affect fat digestion?

A

Inhibits fats from emulsifying into small droplets

This means they stay insoluble

61
Q

What substances are absorbed in the stomach?

A

Nutrients
Very little absorption takes place

62
Q

For gastric absorption, what properties do the substances have to have?

A

Highly lipid-soluble substances = ethanol

63
Q

What is gastritis?

A

Inflammation of the lining of the stomach

64
Q

What is heartburn?

A

Painful or burning sensation in the chest

65
Q

What mechanisms causes heartburn?

A

Increase in gastric acid secretion
Backflush of acidic chyme into esophagus

66
Q

What factors cause heartburn?

A

Overeating, fatty foods
Smoking, alcohol, coffee
Lying down immediately after a meal
Tight clothing

Human Physiology Y3 (14 decks)

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