Lecture 3: Transport mechanisms Flashcards

1
Q

Define reabsorption:

A

The movement of a substance from the tubular fluid, back into the circulation

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2
Q

Define secretion:

A

The movement of substances from the blood into the tubular fluid via tubular cells (active transport) or intracellular spaces (passive transport)
(not via glomerulus)

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3
Q

Define excretion:

A

The removal of waste products from the blood and the net result of filtration, secretion and reabsorption of a substance

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4
Q

How are solutes transported?

A

Paracellular movement: across the tight junctions connecting the cells, down the concentration gradient
Transcellular movement: through the cell, may be down/against the concentration gradient, water also follows the movement of solutes

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5
Q

Give some examples of passive transport mechanisms:

A

Diffusion: movement of a substance down its electrochemical gradient
Facilitated diffusion: movement of a substance down its concentration gradient, relies on a carrier molecules to transport substances across the membrane (faster than diffusion)

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6
Q

What is primary active transport?

A

An energy dependent process in which substances cross the cell membrane against their concentration/electrochemical gradient
-involves hydrolysis of ATP to ADP and Pi to provide chemical energy

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7
Q

What is the most important active transporter in the kidney?

A

Na+/K+ ATPase pump found on the basolateral membrane of tubular cells (outside)
-transports 3 Na+ within cell and exchanging them with 2 K+ outside the cell so 99% of Na+ is reabsorbed (the 1% of Na+ is how we alter blood pressure)

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8
Q

Give some active transporters on the tubular cell membrane:

A

Ca2+ ATPase
H+/K+ ATPase
H+ ATPase

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9
Q

What is secondary active transport?

A

Uses energy produced from another process for transporting molecules. Carried out by specific carrier proteins embedded in cell membranes called transporters
(Na+/K+ ATPase is vital for pumping Na+ against its concentration gradient to form a driving force for other pumps)

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10
Q

What is a symporter?

A

Moving things in the same direction as the Na+ gradient from the tubule into the tubular cell e.g. Na+/glucose

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11
Q

What is an antiporter?

A

Moving things in opposite directions (other substance is moving in the opposite direction to the sodium gradient
e.g. Ca+/Na+ exchangers

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12
Q

What are ion channels?

A

Protein pores found on epithelial cell membranes, allowing rapid transport of ions into the cell

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13
Q

What ion channels do we find on the apical membrane of tubular cells?

A

Cl-
K+
Na+
(very fast, but not as many of these in comparison to other transporter types)

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