Kidney Function, Filtration, and Reabsorption: Key Concepts for Biology

What is the primary function of the kidneys?

To maintain salt and water balance, eliminate metabolic wastes, regulate pH, secrete hormones, and perform gluconeogenesis.

What does ECF stand for and what does it consist of?

Extracellular Fluid; it consists of interstitial fluid and plasma.

What is the Glomerular Filtration Rate (GFR)?

The volume of fluid filtered into Bowman's space per unit time, typically 125 ml/min or 180 L/day.

What is the main role of the proximal tubule in the nephron?

It reabsorbs 70-80% of solutes and water and secretes H+.

What is the main function of the Loop of Henle?

To reabsorb filtered Na+ and H2O, creating a hypertonic medullary interstitial fluid.

What is the role of aldosterone in the kidneys?

It regulates Na+ reabsorption and K+ secretion in the distal tubule and collecting duct.

What is the significance of the juxtamedullary nephrons?

They are involved in establishing a hypertonic medullary interstitial fluid.

How is the filtered load of a substance calculated?

Filtered Load of substance X = [X]P * GFR.

What does renal clearance measure?

The rate of removal of a substance from the plasma compartment per unit time.

What is the equation for calculating clearance (CX)?

CX = ([X]U * V) / [X]P, where [X]U is urine concentration, V is urine flow rate, and [X]P is plasma concentration.

What is the role of ADH in the kidneys?

It regulates water reabsorption in the collecting duct.

What substances are not filtered at the glomerulus?

Red blood cells, white blood cells, proteins, and other large molecules.

What happens to the small amount of filtered protein?

It is reabsorbed by endocytosis in the proximal tubule.

What is the primary driving force for filtration at the glomerulus?

Net filtration pressure driven by bulk flow.

What is the basic renal process equation?

Excreted = Filtered + Secreted - Reabsorbed.

What is the primary function of the collecting duct?

To regulate water reabsorption and concentrate urine.

What is the composition of the extracellular fluid (ECF)?

It is composed of interstitial fluid and plasma.

What is the significance of the renal corpuscle?

It is the site of filtration where plasma-like fluid is filtered from blood.

What is the primary function of the distal tubule?

To reabsorb a small amount of solutes (mostly NaCl) without water.

What is the role of the peritubular capillaries?

They are involved in osmotic reabsorption of solutes and water.

What does the term 'bulk reabsorber' refer to?

The proximal tubule, which reabsorbs the majority of filtered solutes and water.

What is the function of the efferent arteriole?

It carries blood away from the glomerulus after filtration.

What is the primary role of the afferent arteriole?

To supply blood to the glomerulus for filtration.

What is the role of the Loop of Henle's descending segment?

It reabsorbs water.

What is the role of the Loop of Henle's ascending segment?

It reabsorbs sodium.

What is the significance of the high pressure in glomerular capillaries?

It favors filtration of plasma-like fluid into Bowman's space.

What is the primary function of the renal nephron?

To filter blood, reabsorb essential substances, and secrete wastes.

What is the formula for clearance (CX)?

CX = ([X]U * V)/[X]P

What is the filtered load equation?

Filtered load = [X]P * GFR

What does it mean if a substance is freely filtered, not reabsorbed, and not secreted?

Filtered load equals amount excreted.

What is the clearance equation for a substance (X)?

GFR = ([X]U * V)/[X]P

Which substances can be used to estimate GFR?

Inulin and creatinine.

What is the clearance of inulin equation?

GFR = Cinulin = ([inulin]U * V)/[inulin]P

What is the clearance of creatinine equation?

GFR = Ccreatinine = ([creatinine]U * V)/[creatinine]P

What is the typical GFR value?

Approximately 180 L/day or 125 mL/min.

What is the primary site of glucose reabsorption in the kidneys?

Proximal tubule.

What type of transport is used for glucose reabsorption?

Active transport via SGLT-2 and facilitated diffusion via GLUT-2.

What is the normal plasma glucose concentration range?

90-100 mg/dL.

What does the threshold for glucose reabsorption indicate?

Plasma glucose at which glucosuria begins, around 170-200 mg/dL.

What is the transport maximum for glucose?

The maximum reabsorption rate of glucose, reached at plasma glucose > 300 mg/dL.

What happens to glucose excretion when plasma glucose exceeds the transport maximum?

Glucose excretion increases as all SGLT transporters are saturated.

What is the significance of the clearance of a substance being greater than that of inulin?

The substance is undergoing net secretion.

What is the significance of the clearance of a substance being less than that of creatinine?

The substance is undergoing net reabsorption.

What occurs when the amount excreted of a substance equals the filtered load?

The substance is neither reabsorbed nor secreted.

What is the role of afferent and efferent arterioles in regulating GFR?

Constriction or dilation affects capillary pressure and GFR.

What happens to GFR if the afferent arteriole is constricted?

GFR decreases due to reduced blood flow.

What happens to GFR if the efferent arteriole is constricted?

GFR increases due to increased pressure in the glomerulus.

What is the effect of increased plasma glucose concentration on urine excretion in a diabetic individual?

Urine excretion rate increases due to glucosuria.

What is the expected change in ECF volume when plasma glucose is elevated?

ECF volume increases due to osmotic effects.

What is the expected change in ICF volume when ECF osmolarity increases?

ICF volume decreases as water moves out of cells.

What is the primary mechanism for glucose reabsorption in the proximal tubule?

Secondary active transport coupled with Na+ movement.

What are the two transporters involved in glucose reabsorption?

SGLT-2 (apical) and GLUT-2 (basolateral).

What is the significance of renal handling of substances?

It determines whether substances are reabsorbed, secreted, or excreted.

What does it mean if the amount excreted of a substance is greater than the filtered load?

The substance is being secreted by the kidneys.