chapter 30 structure and function of the kidney

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 30Structure and Function

of the Kidney


Structure and Locations of the Kidneys• Structure

– Paired, bean-shaped organs– Multilobular structure, composed of up to 18 lobes– Each lobule is composed of nephrons, the functional units

of the kidney.• Location

– Outside the peritoneal cavity in the back of the upper abdomen

– One on each side of the vertebral column at the level of the 12th thoracic to 3rd lumbar vertebrae


Capillary Systems Supplying the Nephron• Glomerulus capillary system

– A unique, high-pressure capillary filtration system located between the afferent and the efferent arterioles

– Selectively dilates or constricts to regulate glomerular capillary pressure

• Peritubular capillary system– A low-pressure reabsorptive system that originates

from the efferent arteriole


Function of the Nephron• Glomerular filtration

– Three layers of filtration• Reabsorbs water, electrolytes, and other substances

needed to maintain the constancy of the internal environment into the bloodstream

• Secretes unneeded compounds into the tubular filtrate for elimination


Factors Affecting the Glomerular Filtration Rate • Glomerular capillary hydrostatic pressure• Glomerular capillary osmotic pressure• Hydrostatic and osmotic pressures in Bowman’s capsule


Four Segments of the Nephron Tubule• Proximal convoluted tubule

– A highly coiled segment; drains Bowman’s capsule• Loop of Henle

– A thin, looped structure• Distal convoluted tubule

– A distal coiled portion • Collecting tubule

– Joins with several tubules to collect the filtrate


Na+ Transport as the Driving Force• Na+/K+ ATPase maintains concentration gradient• Symport• Antiport• Exchange


Question• Which of the following best describes the function of the

nephron?a. The detoxification of bloodb. The retention of important organic materials found in

the filtratec. The resorption of water, electrolytes, and other

substances from the bloodstreamd. The synthesis and storage of urine


Answer

a. The detoxification of bloodb. The retention of important organic materials found in

the filtratec. The resorption of water, electrolytes, and other

substances from the bloodstreamd. The synthesis and storage of urine


Tubular Filtration• Urine filtrate flows through the tubular component of the

nephron• As the filtrate flows through the tubule, the concentration

of water and electrolytes in the filtrate changes due to: – Reabsorption of water and solutes by tubular cells

into the peritubular capillary blood– Secretion from the blood into the tubular lumen


Regulation of Urine Concentration• Response to changes in interstitial osmolarity

– 1200 mOsm normal• Antidiuretic hormone changes the permeability of the

tubules of the collecting duct.


Elimination Functions of the Kidney• Renal clearance• Regulation of sodium• Potassium elimination• pH-dependent elimination of organic ions• Uric acid elimination• Urea elimination• Drug elimination


Endocrine Functions of the Kidney• Juxtaglomerular complex • The renin-angiotensin-aldosterone mechanism

– Plays an important part in regulation of blood pressure• Erythropoietin

– Regulates the differentiation of red blood cells in bone marrow

• Vitamin D– Increases calcium absorption from the gastrointestinal tract– Helps regulate calcium deposition in bone


Question• Which of the following hormones is produced in the

kidney?a. Antidiuretic hormoneb. Erythropoietinc. Aldosteroned. Angiotensin


Answer

a. ADHb. Erythropoietin: Erythropoietin is formed in the kidney in

response to decreased blood oxygenation.c. Aldosteroned. Angiotensin


Action of Diuretics• Loop diuretics

– Exert their effect in the thick ascending loop of Henle • Thiazide diuretics

– Prevent the reabsorption of NaCl in the distal convoluted tubule


Action of Diuretics (cont.)• Aldosterone antagonists (potassium-sparing diuretics)

– Reduce sodium reabsorption and increase potassium secretion in the late distal tubule and cortical collecting tubule site regulated by aldosterone


Renal Clearance• Definition

– The volume of plasma that is completely cleared each minute of any substance in the urine

• Determining factors– The ability of the substance to be filtered by the

glomeruli– The capacity of the renal tubules to reabsorb or

secrete the substance


Characteristics of Normal Urine• Clear, amber-colored fluid • Approximately 95% water and 5% dissolved solids• The kidneys normally produce approximately 1.5 L of

urine each day.• Contains metabolic wastes and few or no plasma

proteins, blood cells, or glucose molecules


Tests for Renal Function• Urinalysis• Glomerular filtration rate• Blood tests

– Serum creatinine– Blood urea nitrogen

• Cystoscopy• Ultrasonography• Radiologic and other image studies


Question• Normal urine should be_______________.a. Cloudyb. Have a pH of 7.0 or greaterc. Should have a specific gravity of 1.0d. Sterile


Answer

a. Cloudyb. Have a pH of 7.0 or greaterc. Should have a specific gravity of 1.0d. Sterile: There will be no bacteria present in a healthy

urinary tract.

chapter 30 structure and function of the kidney

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