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PHSL233 Cellular, GI and Renal > Gastrointestinal Systems (Digestive Processes) > Flashcards

Gastrointestinal Systems (Digestive Processes) Flashcards

1
Q

Where are exocrine and endocrine secretions produced?

A

Exocrine secretions are produced by epithelial cells lining the GI tract and accessory organs.

Endocrine secretions are produced by endocrine organs/glands.

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2
Q

How do exocrine secretions prepare food for digestion?

A

By diluting it to the osmolarity of the plasma and altering the pH for optimal digestion

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3
Q

What cells secrete exocrine secretions?

A

Acini cells

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4
Q

What cells secrete endocrine secretions?

A

Pancreatic islet cells

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5
Q

What do acini cells secrete?

A

Enzymes/fluid into the GI tract and out of the body

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6
Q

What do pancreatic islet cells release?

A

Hormones into the body

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7
Q

Does the pancreas produce exocrine or endocrine secretions?

A

Both

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8
Q

What is the main cation and anion in plasma?

A

Na+ and Cl-

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9
Q

What is the main cation and anion in salvia?

A

Na+ and HCO3-

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10
Q

What is the main cation and anion in the stomach?

A

Na+ and Cl- (there is no HCO3- in the stomach)

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11
Q

What is the main cation and anion in the pancreas secretions?

A

Na+ and HCO3-

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12
Q

What is the main cation and anion in the liver and small intestine?

A

Na+ and Cl-

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13
Q

What secretions have the most acidic pH?

A

Stomach (all others are slightly alkaline 7.4-7.8)

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14
Q

What is the total volume of secretions in L/day?

A

8 (majority being from plasma and stomach)

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15
Q

What is the function of saliva?

A

Oral hyglene, aids in talking, aids in chewing and swallowing by mositening and dissolving food, assists in rendering food isosmotic, pH modulation and contains amylase for starch digestion.

Without saliva you would develop xerostomia which causes dental caries and orla lesions.

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16
Q

What does saliva contain that aids in starch digestion?

A

Amylase

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17
Q

What is the carrier in vape fluid?

A

Propylene glycol (PG)

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18
Q

What do the breakdown products of PG include and what is their effect on the mouth?

A

acetic acid, lactic acid and propionaldehyde which are all toxic to tooth enamel and soft tissue

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19
Q

PG is hygroscopic - what does this mean?

A

Means water moelcuels in saliva and oral tissue bind to the PG molecules leading to the tissues drying out = results in dry mouth (xerostomia) = less dilution of food from saliva.

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20
Q

What is xerostomia?

A

Dry mouth

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21
Q

What can a sample of saliva be used to analyse?

A

DNA
Cancer proteins
Heart attack related proteins
Infection (HIV, COVID, Flu)

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22
Q

What are the three main pairs of salivary glands?

A

Parotid
Submandibular
Sublingual

*but there is also minor bucca glands in the mouth, pharynx and oesophagus.

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23
Q

What is the main fluid composition of parotid, submandibular and sublingual salivary glands?

A

Parotid is mainly serous fluid

Submandibular is mixed mucous and serous

Sublingual is mainly mucous rich fluid

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24
Q

What is the primary cite for secretion from salivary glands?

A

Acinus

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25
Q

What is the cite of modification in salivary glands?

A

Ducts

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26
Q

What does the isotonic NaCl solution and ensymes of serous acinar cells secretion contain?

A

Zymogen granules for exocytosis of enzymes

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27
Q

What do intercalated ducts drain from?

A

Acini

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28
Q

What drains into the mouth?

A

Striated ducts

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29
Q

What is the function of ducts?

A

Reabsorption of ions from primary fluid to dilute saliva to be more hypotonic

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30
Q

How much saliva is secreted per day?

A

1.5L

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31
Q

What is the basal rate of saliva secretion (mL.min)?

A

0.5 mL.min-1

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32
Q

What can increase the raate of saliva secretion 10-fold?

A

Stimulation

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33
Q

What is the composition of saliva?

A

Mucus
Digestive enzymes
NaCl/NaHCO3 solution (aka serous fluid)

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34
Q

What is serous fluid?

A

NaCl / NaHCO3 solution

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35
Q

Where is mucus secreted from?

A

Sublingual, submandibular and minor buccal glands.

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36
Q

What digestive enzymes are in saliva?

A

Amylase
Lingual lipase

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37
Q

Where is amylase secreted from?

A

Parotid gland

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38
Q

Where is lingual lipase secretd from?

A

Minor salviary glands of the tongue

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39
Q

Where is serous fluid primarily secreted from?

A

Parotid glands

Lesser extent submandibular

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40
Q

What type of solution is serous fluid?

A

Hypoosomotic solution of NaCl with slightly elevated K+ and HCO3-.

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41
Q

Is the composition of serous fluid fixed?

A

No - it varies with rate of secretion.

42
Q

How do striated and execretory ducts modify fluid?

A

By the reabsorption of Na+ and Cl-

43
Q

Striated and excretory duct reabsorption of Na+ and Cl- is without the movement of what?

A

Without the movement of water

44
Q

What do ducts secrete a limited amount of?

A

K+ and HCO3-

45
Q

What makes saliva always hypo-osmotic?

A

Na+ and Cl- concentration being less than plasma

K+ concentration being higher than plasma

HCO3- concentration being higher than plasma

46
Q

Why does osmolarity increase as the rate of secretion increases?

A

Because there is less reabsorption

47
Q

How does ion transport in the ducts change?

A

It doesn’t change - but flow rate does.

More secretion in acini = higher flow rate through the ducts

48
Q

How does NaCl reabsoprtion change with high and low flow rate?

A

Low flow rates = greater NaCl reabsorption and more hypotonic saliva

High flow rates = less NaCl reabsorption and more isotonic

49
Q

Draw the cellular model for secretion in the acini:

A

Na+/K+ ATPase and the a basolateral K+ channel generate a gradient for Na+ to enter the cell

Cl- uptake via basolateral NKCC1 increases intracellular Cl- above electrochemical equilibrium = secondary active transport (K+ against gradient)

Paracelluar Na+ movement is driven by Cl- and H2O by an osmotic gradient

CFTR allows Cl- to move across the apical membrane

50
Q

What is the modifications to the cellular model that occur in the ducts enabling reabsorption?

A

Na+ enters via an apical Na+ channel (ENaC) and exits the basolateral membrane via Na+/K+ ATPase

K+ enters the basolateral membrane via Na+/K+ ATPase and exits via an apical K+ channel

HCO3- and H+ are made bby carbonic anhydrase. HCO3- exits the apical membrane in exchange for Cl- (Cl- recycled via CFTR). H+ exits the apical membrane in exchnage for Na+.

Beause this is a tight eppithelial, water cannot follow the ions / solutes so the solutions ebcomes hypotonic

51
Q

What is saliva secreted in response to?

A

Thought of food
Approach of food
Food in the mouth
Things we associate with food

(Autonomic nervous system)

52
Q

What two reflexes are potentially involved in the regulation of saliva secretion?

A

Unconditional reflex
Conditional reflex

53
Q

What is the conditional reflex?

A

An autonomic repsonse due to sight, presence of food in the mouth and repsonse to taste receptors etc

54
Q

What is the conditional reflex?

A

A learned repsonse in which a previously neutral stimulus becomes associated with an unconditional stimulus

55
Q

What stimulates intestinal Cl- secretion?

A

Secondary messengers: cAMP stimulation of CFTR activity and Ca2+ stimulation of K+ channel activity.

56
Q

What ligands are involved in cAMP stimulation of CFTR activity?

A

VIP (ENS) and prostaglandins

57
Q

How does Ca2+ stimulate K+ channel activity?

A

Increased driving force for NKCC and Cl- to exit via CFTR = transient secretoryt repsonse

58
Q

What ligands are involved in Ca2+ stimualtion of K+ channel activity?

A

ACh (ENS) and histamine

59
Q

Is the PSNS or SNS the primary pathway in the regulation of saliva secretion?

A

PSNS

60
Q

What is the ionic compositon of saliva dependent on?

A

Flow rate through the ducts

61
Q

What are the key components of gastric secretions?

A

Acid
Pepsin
Intrinsic factor
Mucus

62
Q

What is the function of acid as a gastric secretion?

A

Protective role
Denatures proteins
Provides optimum pH for digestive enzymes in the stomach
Renders fluid isosmotic

63
Q

What is the function of pepsin as a gastric secretion?

A

Protein digestion

64
Q

What is the function of intrinsic factor as a gastric secretion?

A

Vitamin B12 absorption (DNA, RBC, Pernicious anemia)

65
Q

What is the function of mucus as a gastric secretion?

A

Protection - protects against acid and mechanical forces in the stomach

66
Q

Is the secretory roles of the stomach the same in all regions?

A

No - different regions of the stomach have different secretory roles.

67
Q

What are the luminal secretions and function of the LES and cardia region of the stomach?

A

Mucus and HCO3- therefore protective role

68
Q

What are the luminal secretions and functions of the fundus and body of the stomach?

A

Secretes everything so have majority of functions

69
Q

What is the primary function of the antrum and pyloris of the stomach?

A

protection because it secretes mucus and HCO3-.

70
Q

What is the site of acid secretion?

A

Gastric glands in the body of the stomach

71
Q

What are the key cells in the stomach lumen?

A

Mucous cells
Parietal cells
ECL cells
Chief cells
Enteroendocrine cells

72
Q

What do parietal cells secrete?

A

Acid and intrinsic factor

73
Q

What does outflow from glands prevent?

A

Infection

74
Q

What do chief cells secrete?

A

Pepsinogen

75
Q

What do ECL cells secrete?

A

Histamine (hormone like function not the allergy repsonse)

76
Q

What does the volume/composition of gastric secretions depend on?

A

Whether you are eating or fasting

77
Q

Approx how much gastric secretions are there per day?

A

2-3 L

78
Q

What is fasting?

A

The time between meals

79
Q

Is there gastric secretions during fasting?

A

Yes - mostly by surface cells

80
Q

What is the osmolarity of gastric secretions during feeding?

A

Isosmotic - HCl solution produced bby parietal cells.

81
Q

What is the approx final gastric secretion osmoalrity ?

A

200 mOsmol/L

82
Q

Are parietal cells scereting at rest?

A

No

83
Q

What is the tubulovesicular membrane?

A

Highly folded membrane within parietal cells that holds the components for acid secretion).

84
Q

How does the structure of a parietal cell change from being at rest to active?

A

Disapperance of the tubulovescular system –> it is converted into an extensive intracellular cancliculi

Appearance of large apical microvilli

Increase in surface area of apical membrane

85
Q

How much does the SA of parietal cells apical membrane increase from at rest to active form?

A

50-100 fold

86
Q

What percentage of the protein in the tubulovesicular membrane is H+,K+ ATPase?

A

80%

87
Q

What does the conversion of tubulovesicular membrane to canaliculiu allow for?

A

The insertion (via exocytosis) of the H+,K+ ATPase into the apical membrane - which is the primary active transport responsible for acid secretion.

88
Q

What does the H+, K+ ATPase do?

A

It uses ATP to actively transport H+ out of the cell in exchange for K+ into the cell

89
Q

What are the transport mechanisms in the un-stimulated parietal cell?

A

Na/K-ATPase (generates the membrane potential and mainatains K+ in cell above equilibrium)

K+ channel in basolateral membrane (recycles K+ and helps generate the membrane potential)

Na+/H+ and Cl-/HCO3- exchanger (pH homeostasis and maintenance of Cl- above equilibirum due to minimum carbonic anhydrase activity).

= essentially there is low activity and not a huge driving force

90
Q

What are the transport mechanisms in a stimulated parietal cell?

A

Additional of the H+/K+ ATPase in apical membrane to secrete H+ in exchange for K+.

K+ channel in apical membrane to recycle K+ ions in the lumen to maintain H+ secretion/

Carbonic anhydrase (produces H+ and HCO3- from CO2 and H2O).

Inactivity of the Na+/H+ exchanger in the basolateral membrane

H2O moving via paracellular pathway

91
Q

What results in a layer of alkaline mucus that protects the stomach from abrasion and acid pH?

A

The mucus secreted by mucus neck cells in glands and surface cells (HCO3- rich)

92
Q

What dpes intrinsic factor bind to and what is the effect?

A

vitamin B12 - allows for absroption in the ilium

93
Q

What does histamine act as?

A

paracrine hormone

94
Q

How is mucus and HCO3- mucins released from surface epithelial cells?

A

exocytosis

95
Q

What is pepsinogin secreted from chief cells activated by?

A

HCl

96
Q

What pH is pepsinogin most active?

A

1-2.5

97
Q

What pH is pepsinogin inactiavted at?

A

6

98
Q

What pH is pepsinogin irreversibly denatured at?

A

8

99
Q

What is an endopeptidase?

A

Means it curs protien in the middle as opposed to the ends

100
Q

What hormone is classed as an endopeptidase?

A

Pepsinogin

101
Q

What type of protein is intrinsic factor?

A

Glycoprotein

102
Q

Why does intrinsic factor need to bind to Vitamin B12?

A

In order to be absorbed in the small intestine

PHSL233 Cellular, GI and Renal (13 decks)

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