Renal Physiology: Glomerular Filtration and Tubular Reabsorption

Practice flashcards covering the mechanisms of glomerular filtration, GFR regulation, and the processes of tubular reabsorption and secretion based on the lecture material.

What is the specific capillary bed where blood filtration takes place within the renal corpuscle?

The glomerulus.

Which three structures together form the filtration membrane that acts as a barrier to substances transitioning from the blood to the capsular space?

The fenestrated endothelial cells of the capillaries, the basement membrane, and the pedicels of the podocytes.

What is the approximate diameter of the filtration pores in the glomerular endothelial cells?

$70$ to $90\,nm$.

Why are platelets, which measure about $1.5$ to $4\,\mu m$, unable to pass through the filtration membrane?

Because they are in the micrometer size range, they are significantly larger than the nanometer-sized filtration pores ($70$ to $90\,nm$).

What composition of the basement membrane creates a meshwork and carries negative charges to repel certain molecules?

A gel of proteoglycans.

Why does albumin, which is about $7\,nm$ in size, not typically cross the filtration membrane?

It is negatively charged and is repelled by the negative charges on the proteoglycan gel of the basement membrane.

What is the average Glomerular Filtration Rate (GFR) for an average adult male and female?

$125\,ml/min$ for males and $105\,ml/min$ for females.

What is the normal net filtration pressure (NFP) calculated from the opposing forces in the renal corpuscle?

$10\,mmHg$.

In the myogenic mechanism of GFR autoregulation, how does the afferent arteriole respond to an increase in systemic blood pressure?

The smooth muscle cells in the tunica media of the afferent arteriole are stretched and respond by contracting (vasoconstriction) to reduce blood flow into the glomerulus.

Which specialized cells in the juxtaglomerular apparatus detect high levels of sodium chloride ($NaCl$) in the filtrate to help regulate GFR?

Macula densa cells.

Which chemical messenger is converted by mesangial cells from ATP to signal granular cells to constrict the afferent arteriole?

Adenosine.

What enzyme do granular cells release into circulation in response to a substantial drop in systemic blood pressure?

Renin.

Which hormone is produced when Angiotensin Converting Enzyme (ACE) acts on angiotensin I in the lungs?

Angiotensin II.

How does Angiotensin II specifically affect the efferent arteriole to sustain kidney activity during low systemic blood pressure?

It constricts the efferent arteriole, which increases the hydrostatic pressure within the glomerulus and raises the GFR.

What hormone is secreted by the heart's atria in response to dangerously high systemic blood pressure to increase GFR and reduce blood volume?

Atrial natriuretic peptide (ANP).

Which mode of transport moves two different substances in the same direction across a plasma membrane?

Symporters.

Which mode of transport moves molecules in opposite directions, such as the sodium-potassium pump?

Antiporters.

What term describes the transport of substances in between the cells of the renal tubule following a concentration gradient?

Paracellular route.

What percentage of the filtrate is typically reabsorbed by the proximal convoluted tubule (PCT)?

$65\%$.

How does the proximal convoluted tubule (PCT) achieve high rates of reabsorption structurally?

It contains a brush border of microvilli that increases the surface area of the plasma membrane, allowing for more transport proteins.

In a healthy individual, what percentage of glucose, amino acids, and lactate is reabsorbed by the proximal convoluted tubule?

$100\%$.

What condition occurs when the concentration of glucose in the blood exceeds the transport maximum ($T_{m}$) of the symporters?

Glycosuria (glucose in the urine), commonly seen in diabetes mellitus.

What is the term for the water reabsorption in the PCT that happens because aquaporins are present at all times?

Obligatory water reabsorption.

Contrast the permeability of the descending and ascending limbs of the nephron loop.

The descending limb is permeable to water but not salt; the ascending limb is impermeable to water but actively reabsorbs salt ($Na^+$, $K^+$, and $Cl^-$).

Which hormone, secreted by the adrenal cortex, is known as the sodium retention hormone?

Aldosterone.

How does antidiuretic hormone (ADH) facilitate water retention in the distal convoluted tubule and collecting duct?

It stimulates the addition of aquaporins into the plasma membranes of the tubule cells.

Why does drinking alcohol cause the production of more dilute urine and lead to dehydration?

Alcohol inhibits the secretion of antidiuretic hormone (ADH), preventing the kidneys from reabsorbing water.