Renal Physiology 1

Question 1

Basic Functions of Kidney

Answer 1

Regulation of water and electrolyte balance

Excretion or clearance of metabolic wastes

Excretion or clearence of foreign products

Regulation of arterial blood pressure

Regulation of Acid/Base balance

Regulation of erythrocyte production

Regulation of Vitamin D metabolism

Gluconeogenesis

Question 2

What metabolic waste products do the kidneys excrete?

Answer 2

urea from protein metabolism

uric acid from nucleic acid metabolism

creatinine from muscle metabolism

end products from hemoglobin breakdown (bilirubin)

Hormonal metabolites

Question 3

How do the kidneys maintain Arterial Blood Pressure?

Answer 3

Maintain water (volume) balance

Maintain sodium balance

Contributes to the maintenance of cardiac output by regulation of ECF

Endocrine release of hormones and autacoids. ex: renin-angiotensin system, prostaglandins

Question 4

Effects of increasing sodium intake 10-fold on urinary sodium excretion and extracellular fluid volume

Answer 4

2-3 days after raising sodium intake, renal excretion also increases, so that a balance between intake and output is re-established.

However, during the 2 to 3 days of renal adaptation to high sodium intake, there is a modest accumulation os sodium that raises extracellular fluid volume slight and triggers hormonal changes and other compensatory responses that signal the kidneys to increase their sodium excretion

Question 5

How do the kidneys regulate acid/base balance?

Answer 5

Excretion of hydrogen ion/bicarbonate

reabsorption of filtered bicarbonate

generation of new bicarbonate

regulation of body fluid buffer systems

Question 6

Regulation of Erythrocyte Production

Answer 6

Stimulated by reduction in oxygen delivery to renal tissue

This can occur due to:

anemia

hypoxia

low renal blood flow

Renal disease can lead to reduction of erythropoitin secretion and subsequent anemia or reduced activation of the bone marrow

Question 7

Regulation of Vitamin D

Answer 7

Production of the active form of Vitamin D, 1,25 dihydroxy vitamin D (calcitrol)

Vitamin D is important for regulation of calcium metabolism, calcium deposition in bone, calcium reabsorption by the gut and in the regulation of calcium and phosphate balance

Question 8

Gluconeogenesis in Kidneys

Answer 8

During periods of starvation or prolonged fasting, the kidneys are able to synthesize glucose from amino acids and other precursors

kidney gluconeogenesis capability is comparable to that of the liver

Question 9

Characteristics of Proximal Tubules

Answer 9

Receives 125 ml/min of initial volume from Bowmans Space

Absorbs ~60-70% of filtered load

125 ml/min - ~88 ml/min reabsorbed = 37 ml/min exits PT

Reabsorbs plasma constituents like water, sodium, potassium, chloride, bicarbonate, glucose, amino acids etc.

Glomerular tubular balance

Secretion of toxic materials like organic acids, drug metabolites, etc.

Question 10

Characteristics of the Thin Descending Loop of Henle

Answer 10

Impermeable to solute

Highly permeable to water

Concentrates tubular fluid as water is extracted from the tubular fluid while the solute is left behind

Limited permeability to urea

Question 11

Characteristics of Thin Ascending Loop of Henle

Diluting Segment

Answer 11

Receives volume from thin loop of Henle

Impermeable to water

Has a lot of electrolyte transporters that selectively remove sodium, potassium, and chloride from the tubular fluid

reabsorbs 20-25% of the NaCl filtered load

Selective solute removal reduces solute concentration and renders tubular fluid concentration more dilute than in the thin loop segment

**Subject to influence of loop diuretics–reducing sodium reabsorption

Question 12

Characteristics of Juxtaglomerular Apparatus

Answer 12

Macula densa cells monitor tubular fluid composition and flow

transmit signals to adjust glomerular filtration rate by adjusting preglomerular resistance

May regulate renin secretion from the juxtaglomerular cells

Question 13

Characteristics of Distal Tubule

Final electrolyte regulatory site

Answer 13

This is where aldosterone acts–promotes sodium reabsorption

site of hydrogen ion secretion regulation

constitutes the most highly regulated portion of sodium reabsorption

subject to some diuretic actions

Question 14

Characteristics of the collecting duct

Final water regulatory site

Answer 14

250 very large collecting ducts in each kidney; collects from 4000 nephrons

ADH acts here, on the collecting duct

most important segment for urea reasbsorption

Question 15

Glomerular Filtration

Answer 15

the process of protein-free plasma passing from the glomerular capillary lumen, across the glomerular filtration barrier and into Bowmans space

Question 16

Tubular reabsorption

Answer 16

movement of substances from the tubular lumen to the blood of the peritubular capillaries and vasa recta

Question 17

Tubular secretion

Answer 17

movement of substances from the peritubular capillary plasma to the tubular lumen.

secondary route of delivery of plasma constituents to the tubular fluid

electrolytes (K+, H+)

organic and inorganic acids

forgein metabolites

Question 18

Urinary excretion rate

Answer 18

urinary excretion rate = filtration rate - reabsorption rate + secretion rate

excretion rate is different for different solutes and different for water