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NME Emma copy and edit > Salt and Water transport in the GI tract > Flashcards

Salt and Water transport in the GI tract Flashcards

1
Q

What does osmolality mean?

A
  • concentration of dissolved particles of chemicals and minerals within a solution
  • high osmolality = high concentration of the substance dissolved
  • very salty water = high osmolality of salt
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2
Q

What is a hypotonic solution?

A
  • high concentration of solute inside cell
  • H2O enter the cell to dilute solute and cell swells
  • osmolality is lower than plasma
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3
Q

What is a hypertonic solution?

A
  • low concentration of solute inside cell
  • H2O leaves the cell to dilute solute outside of cell and it shrinks
  • osmolality is higher than plasma
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4
Q

What is an isotonic solution?

A
  • solute concentration is equal inside and outside of the cell
  • no net movement of H2O
  • osmolality is the same as plasma
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5
Q

Maintenance of bodily fluids comes under the regulation of 3 systems, what are these?

A

1 - enteric nervous system

2 - immune system

3 - endocrine system (hormones)

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6
Q

Where does fluid reabsorbtion take place in the GIT?

A
  • throughout the GIT
  • most in colon
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7
Q

Roughly how many litres of fluid enters the GIT through diet and secretions from the GIT, and how much of this gets reabsorbed?

A
  • 9L enters the GIT
  • 8.9L is reabsorbed
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8
Q

Although the majority of fluid secreted into the GIT is reabsorbed, where is fluid lost in the GIT?

A
  • faeces
  • aprox 100ml/day
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9
Q

Why is it important that the GIT reabsorbs the majority of liquid secreted into the GIT?

A
  • maintains homeostasis
  • allows secretions into GIT (enzymes etc..)
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10
Q

If liquids in the GIT tract either cannot be absorbed sufficiently or too much is absrobed or caused by dehydration, what can this cause?

A
  • too much reabsorbed or dehydration = constipation
  • too little reabsorbed = diarrhea
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11
Q

What does electrolyte mean?

A
  • a substance that is capable of carrying an electrically charge
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12
Q

If sodium chloride (NaCl) was dissolved in a liquid what would this dissacociate into?

A
  • Na+
  • Cl-
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13
Q

What are the dominant intra and extracellular ions?

A
  • inter = K+
  • extra = Na+
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14
Q

What is the dominant extracellular anion?

A
  • Cl-
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15
Q

Why is it important for the concentration of Na+, K+ and Cl- to be different intracellularly and extracelluarly?

A
  • gives us the electrochemical gradient
  • important for metabolic processes
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16
Q

What is the normal intra and extracellular concentration of Na+?

A
  • intra = 10 mEq/L
  • extra = 142 mEq/L
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17
Q

What is the normal intra and extracellular concentration of K+?

A
  • intra = 140 mEq/L
  • extra = 4 mEq/L
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18
Q

What is the normal intra and extracellular concentration of K+?

A
  • intra = 4 mEq/L
  • extra = 103 mEq/L
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19
Q

Cell membranes in the body are semi-permeable. What does this mean?

A
  • certain things are able to cross but others are not
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20
Q

What is endocytosis and exocytosis?

A
  • endocytosis = substance/molecule is brought into the cell
  • exocytosis = substance/molecule leaves the cell
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21
Q

Molecules that are unable to cross semi-permeable membranes use what to transfer across membranes?

A
  • transmembrane proteins
  • Na/ATPas for example
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22
Q

What is able to freely move cross the semi-permeable membranes?

A
  • non-polar, hydrophobic molecules (O2, CO2)
  • small uncharged molecules (i.e. water, urea, ethanol)
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23
Q

What is not able to freely move cross the semi-permeable membranes?

A
  • large and charged molecules (ions, glucose)
24
Q

What are the 3 main broad types of membrane proteins?

A

1 - protein pump (Na+/K+ ATPase)

2 - protein carrier mediated (Na+/glucose symporter)

3 - protein channel mediated (K+, Cl- channels)

25
Q

Protein pumps are a type of membrane protein. How do they transport things?

A
  • active transport meaning they need energy
  • generally against concentration gradient
26
Q

Protein carrier mediated is a type of membrane protein. How do they transport things?

A
  • secondary active transport, so energy is required
  • one molecule moves across membrane against concentration gradient using ATP, likley to be something like Na+/K+ ATPase
  • second molecule piggy back on this opening of the channel like glucose
27
Q

Protein channel mediated is a type of membrane protein. How do they transport things?

A
  • facilitated diffusion of ions
  • no energy required
  • K+ and aquaporin (water channels) are examples
28
Q

In terms of the epithelium in the GIT, what is the apical and basal surfaces?

A
  • apical = facing the lumen
  • basal = facing mucousal membrane
29
Q

What are enterocytes?

A
  • cells lining the GIT
30
Q

What is present inbetween endocytes that stops fluid and molecules from moving freely between the cells?

A
  • tight junctions
31
Q

What does paracellular refer to?

A
  • transport of substances across an epithelium by passing through the intercellular space between the cells
32
Q

Does paracellular require ATP?

A
  • no
33
Q

What does transcellular refer to?

A
  • transportation of solutes by a cell through a cell
  • glucose movement from the intestinal lumen to extracellular fluid by epithelial cells is an example
34
Q

Does transcellular transfer solutes against or with concentration gradients?

A
  • can be against
  • if against it uses ATP
35
Q

Passive transport can move via transcellular through ion channels or paracellularly through permeable tight junctions. Do these require energy?

A
  • no energy required
  • involves moving down concentration gradients
36
Q

Solvent drag is a form of enterocyte transport, what is solvent drag?

A
  • H2O moves to reach osmotic equilibrium
  • drags with it ions (Na+, K+, Cl-)
  • important in proximal small intestine- where tight junctions more permeable
37
Q

Active transport is a form of enterocyte transport, what is active transport?

A
  • requiring ATP to transport ions against concentration gradients
  • Na+/K+ ATPase pump depletes cellular Na and draws Na across apical membrane via channel or cotransporter
38
Q

In the image below denoting the villi and crypts present in the small intestines, does the majority of adbsorption take place in the villi or the crypt?

A
  • villi
39
Q

In the image below denoting the villi and crypts present in the small intestines, does the majority of secretion take place in the villi or the crypt?

A
  • crypt
40
Q

What are the crypts of Lieberkuhn?

A
  • the lowest point of the epithelium, below villia
  • often just referred to as crypts
41
Q

Are villi present in the large intestines?

A
  • no
42
Q

Is permeability higher in the villi or the crypt?

A
  • higher in crypts
43
Q

In the oral cavity and the stomach the majority of the chyme will be H2O. However, once it reaches the duodenum it will contain all the secretions in the duodenum including electrolytes Na+, K+, Cl- and HCO3-. In the duodenum the aim is to create an isotonic chyme. How is the isontonic chyme achieved in the duodenum?

A
  • solvent drag where H2O drags Na+ and Cl- through enterocytes
  • facilitated by paracellular pathway through permeable tight junctions
44
Q

Electrolytes Na+ and K+ are absorbed throughout the GIT. However, which electrolytes are absorbed in the jejunem?

A
  • reabsorbs Na+, K+, Cl- and H2O
45
Q

Electrolytes Na+ and K+ are absorbed throughout the GIT. However, which electrolytes are secreted by the ileum?

A
  • HCO3-
46
Q

What electrolytes are reabsorbed in the large intestines, and which electrolytes are secreted in the large intestines?

A
  • reabsorbs Na+, Cl- and H2O
  • secretes K+ and HCO3- that leave in faeces
47
Q

Which ion is the primary driver of other ions and organics in the small intestines?

A
  • Na+
48
Q

Na+ is the primary driver of other ions and organics in the small intestines. What pump facilitates this movement?

A
  • Na+ / K+ ATPase pump
  • present on the basolateral side of the enterocytes
49
Q

The Na+/K+ ATPas pump based at the basolateral surface of the enterocytes is able to create an electrochemical charge due to the movement of 3 Na+ out and 2 K+ into the enterocytes. How does this facilitate Na+, Cl- and H2O to enter the enterocytes?

A
  • Na+ is moved out of the enterocyte and into the plasma, so will be low concentration gradient inside the enterocyte
  • Na+ moves down the concentration gradient from lumen into enterocyte
  • Cl- is drawn into enterocyte by + electrical gradient paracelluarly
  • H2O enters the cell via osmosis
50
Q

In addition to Cl- moving down the electronegative gradiant paracelluarly, Cl- is able to move into the cell using another method through the enzyme carbonic anyhdrase. How does this enzyme facilites the movement of Cl-?

A
  • carbonic anyhdrase converts CO2 and H2O into HCO3- and H+
  • HCO3- / Cl- exchanger moves Cl- into enterocytes and HCO3- out
51
Q

In the large intestine which ion is the driver of absorption of electrolyes?

A
  • Na+
  • via the Na+ / K+ ATPase pump on basolateral surface
52
Q

In addition to creating an electronegative charge that facilitates the reabsorption of Na+, Cl- and H2O, what steroid hormone secreted by the supraadrenal (adrenal) gland also encourages the retention of Na+ and H2O?

A
  • aldosterone
53
Q

When is K+ secreted into the lumen of the large intestines?

A
  • when K+ levels are low
54
Q

Bacteria in the large intestines are able to produce acids which can lower the pH and could be dangerous. What is secreted with the assistance of carbonic anhydrase to raise buffer the production of acids by bacteria?

A
  • Cl- is reabsorbed
  • HCO3- is secreted
55
Q

Are the tight junctions inbetween enterocytes in the large intestines as permeable as those in the small intestines?

A
  • no
  • mainly only re-absorb H2O so no need to be
56
Q

How is H2O reabsorbed in the GIT?

A
  • H2O absorption is dependent on solutes, specifically Na+
  • NaCl will increase paracelluarly between enterocytes
  • H2O will follow Na+ due to osmotic gradient

NME Emma copy and edit (61 decks)

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