Biochemistry LE 4: Renal Metabolism, Water, Sodium, and Potassium

What is the primary source of energy for the renal medulla?

Oxidation of FFAs

Where is gluconeogenesis primarily located in the kidneys?

Renal cortex

What percentage of glucose production during fasting is attributed to the kidneys?

20%-25%

What is the role of phosphofructokinase in the kidneys?

Glycolysis

What is the function of glucose 6-phosphatase in the renal cortex?

Synthesis of glucose

What is the effect of meals on renal gluconeogenesis?

It increases by 2-fold

What are the preferential gluconeogenic precursors in the kidneys?

Glutamine and lactate

Where is hexokinase primarily located in the kidneys?

Renal medulla

What is the rate of gluconeogenesis dependent on in the kidneys?

Biochemistry

What triggers the release of renin in the juxtaglomerular apparatus?

Decreased renal perfusion pressure

What is the substrate for the enzyme renin?

Circulating angiotensinogen

What type of protein is angiotensinogen?

Glycoprotein

What is the primary function of the Renin-Angiotensin-Aldosterone System (RAAS)?

Regulation of body sodium

Which hormone increases sodium reabsorption in the kidneys?

Cortisol

What is the location of angiotensinogen synthesis?

Liver

What stimulates the secretion of renin?

Prostaglandin E2 and norepinephrine

What is the effect of prostaglandins and kinins on sodium reabsorption?

Decreases sodium reabsorption

What is the role of adenylate cyclase in renin regulation?

Regulates renin secretion through pathways involving PKA and cAMP-responsive binding protein (CREB)

What is the primary driving force behind sodium reabsorption in the tubular cells?

Electrochemical gradient generated by the Na+/K+-ATPase

In the proximal tubule, sodium enters the tubular cells via which of the following mechanisms?

Na-H exchanger and glucose cotransporter

What percentage of filtered sodium is reabsorbed in the ascending limb of the loop of Henle?

25%

Which of the following diuretics acts on the proximal tubule?

Acetazolamide

What is the mechanism of action of loop diuretics, such as furosemide?

Block Na+K+2Cl cotransporter

In the collecting duct, sodium is reabsorbed via which of the following channels?

Amiloride-sensitive epithelial Na channels

What is the effect of spironolactone on sodium reabsorption and potassium secretion?

Decrease sodium reabsorption and potassium secretion

What is the result of inhibiting NaHCO3 cotransporter in the proximal tubule?

Decrease sodium and HCO3 reabsorption

What is the effect of natriuretic hormones on sodium reabsorption and glomerular filtration rate?

Decrease sodium reabsorption and increase GFR

What is a characteristic of an ideal marker of GFR?

Must be freely filterable

Why are new markers not widely available?

They are more expensive than creatinine

What is the function of NGAL in tissue remodeling?

It promotes heterodimerization with metalloproteinase 9

In which cells is NGAL produced?

In various epithelial cells and myelocytes

What happens to NGAL after tissue damage?

Its synthesis and secretion into the bloodstream is immediately released

What is the molecular weight of NGAL?

25 kD

What is the function of NGAL in innate immunity?

It plays a role

What happens to NGAL in the proximal tubules?

It is freely filtered and reabsorbed

What is the relationship between cellular stress and NGAL excretion?

There is a quantitative link

What is the most likely explanation for glucosuria?

Exceeds maximal reabsorptive capacity for glucose

Where does sodium reabsorption not occur in the renal tubules?

Thin ascending limb

Which hormone inhibits renal gluconeogenesis?

Insulin

Which part of the kidney has the highest ATP consumption?

Proximal

Who has the highest amount of total body water relative to sex?

Males

What is the function of the proximal tubule in the kidney?

All of the above

What is the primary function of the thick ascending limb?

Sodium reabsorption

Which of the following is NOT a site of sodium reabsorption?