Overview of Renal Handling of Plasma Substances and Renal Wrap Up

Question 1

explain how kidneys assist in maintaining homeostasis, including regulation of extracellular fluid volume and osmolarity, and electrolyte, mineral, and acid-base balance

Question 2

describe the renal handling of sodium along the nephron (4)

Answer 2

1. the filtered load of Na+ is high; is the main extracellular cation, high concentration in plasma
2. Na+ is freely filtered in the glomerulus, and there is high Na+ in the glomerular filtrate and the entire body content of Na+ is filtered in 2 hours
3. regulatory control is primarily in the distal nephron as most filtered Na+ is reabsorbed proximally; distal nephron is for fine tuning
4. Na+ is only reabsorbed, NEVER secreted

Question 3

describe the renal handling of potassium along the nephron

Answer 3

1. filtered load of K+ is relatively small; is the main intracellular cation so there is low K+ concentration in plasma
2. K+ is freely filtered by the glomerulus but there is low K+ concentration in the glomerular filtrate and only approximately 1% of body content of K+ is filtered in 2 hours
3. regulatory control is primarily in the distal nephron; most filtered K+ is reabsorbed proximally and the distal nephron is important for fine-tuning, reabsorbing or secreting based on the body’s needs

Question 4

describe the regulation of renal handling of sodium, including the effects of sympathetic nerves, angiotensin II, aldosterone, and atrial natriuretic peptide

Answer 4

3 factors promote Na+ excretion:
1. increased ECF Na+ concentration
2. increased ECF volume/pressure natriuresis: increased renal perfusion pressure triggers a decrease in tubular reabsorption of Na+
3. natriuretic peptides: atrial natriuretic peptide and brain natriuretic peptide are secreted in response to cardiac wall stretching and ECF expansion

3 factors promote Na+ retention:
1. angiotensin II
2. aldosterone
3. sympathetic stimulation: produces vasoconstriction, antinatriuresis, and antidiuresis, stimulates JGA to release renin

Question 5

describe the regulation of the renal handling of potassium, including the effects of aldosterone

Answer 5

4 factors promote the excretion of potassium:
1. hyperkalemia, which also causes aldosterone secretion
2. aldosterone
3. increased Na+ delivery to the distal nephron
4. GI hormones (released in response to ingested K+)

hypokalemia is the only factor that promotes K+ retention

Question 6

summarize the renal handling of proteins, amino acids, and glucose

Answer 6

freely filtered solutes have 3 fates: conserved (complete unreg reabsorb), balanced (reabsorb controlled by tubules), or excreted (no reabsorb, secreted)

glucose: conserved solute, 100% reabsorb by prox tubule; means glucosuria is always abnormal, need to eval blood glucose for diagnosis as osmotic diuresis can occur regardless of if hyperglycemia or normoglycemic glucosuria (indicates prox tubule disorded or SGL2 inhibitors)

amino acids: conserved solutes, 100% reabsorb by prox tubule, co-transport with Na+; defects in these cotransporters can lead to aminoaciduria, and if that’s cysteine can form crystals = ouch

proteins: either not filtered (if larger than albumin) or poorly filtered and can go either the LMW or HMW/albumin pathway