Renal Structure and Function 1

Kidneys Paired Paired Retroperitoneal Retroperitoneal Partially protected by the 11 th and 12 th ribs Partially protected by the 11 th and 12 th ribs Right slightly lower due to liver Right slightly lower due to liver Surrounded by renal capsule Surrounded by renal capsule Adipose capsule Adipose capsule Renal fascia Renal fascia 2

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Anatomy Hilum (hilus) Hilum (hilus) Renal artery and vein Renal artery and vein Cortex Cortex Medulla Medulla Renal pyramids and renal papillae Renal pyramids and renal papillae Major and minor calyces Major and minor calyces Renal Pelvis Renal Pelvis Ureters Ureters 5

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Ureters connect kidneys to urinary bladder Ureters connect kidneys to urinary bladder Urethra leads from bladder outside the body Urethra leads from bladder outside the body 7

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Kidneys make up 1 % of body mass, but receive about 25% of cardiac output. Kidneys make up 1 % of body mass, but receive about 25% of cardiac output. Kidney has two major functions: Kidney has two major functions: 1. Filtration of blood Removes metabolic wastes from the body, esp. those containing nitrogen Removes metabolic wastes from the body, esp. those containing nitrogen 9

2. Regulation: Blood volume and composition Electrolytes Blood pH Blood pressure 10

Nephron Functional unit of the kidney Functional unit of the kidney Filtration, tubular reabsorption, tubular secretion Filtration, tubular reabsorption, tubular secretion Renal corpuscle: Renal corpuscle: –Glomerulus – capillaries –Glomerular or Bowman’s capsule 11

Bowman’s capsule Bowman’s capsule –Receives filtrate Proximal convoluted tubule Proximal convoluted tubule –Reabsorption of water and solutes Nephron loop or Loop of Henle Nephron loop or Loop of Henle –Regulates concentration of urine Distal convoluted tubule and Collecting duct Distal convoluted tubule and Collecting duct Reabsorption of water and electrolytes Reabsorption of water and electrolytes –ADH, aldosterone, ANP –Tubular secretion 12

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Filtration Renal corpuscle Renal corpuscle Filtration membrane Filtration membrane –Fenestrated endothelium of capillaries –Basement membrane of glomerulus –Slit membrane between pedicels of podocytes 17

Forces that influence filtration Glomerular blood hydrostatic pressure Glomerular blood hydrostatic pressure Opposing forces: Opposing forces: –Plasma colloid osmotic pressure –Capsular hydrostatic pressure 18

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Glomerular Filtration Rate Volume of plasma filtered / unit time Volume of plasma filtered / unit time Approx. 180 L /day Approx. 180 L /day Urine output is about 1- 2 L /day Urine output is about 1- 2 L /day About 99% of filtrate is reabsorbed About 99% of filtrate is reabsorbed 20

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GFR influenced by: Blood pressure and blood flow Blood pressure and blood flow Obstruction to urine outflow Obstruction to urine outflow Loss of protein-free fluid Loss of protein-free fluid Hormonal regulation Hormonal regulation –Renin – angiotensin –Aldosterone –ADH –ANP 22

Juxtaglomerular apparatus Juxtaglomerular cells lie in the wall of afferent arteriole Juxtaglomerular cells lie in the wall of afferent arteriole Macula densa in final portion of loop of Henle – monitor Na + and Cl - conc. and water Macula densa in final portion of loop of Henle – monitor Na + and Cl - conc. and water Control blood flow into the glomerulus Control blood flow into the glomerulus Control glomerular filtration Control glomerular filtration 23

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Tubular reabsorption Water, glucose, amino acids, urea, ions Water, glucose, amino acids, urea, ions Sodium diffuses into cell; actively pumped out – drawing water with it Sodium diffuses into cell; actively pumped out – drawing water with it 26

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In addition to reabsorption, also have tubular secretion – substances move from peritubular capillaries into tubules – a second chance to remove substances from blood. In addition to reabsorption, also have tubular secretion – substances move from peritubular capillaries into tubules – a second chance to remove substances from blood. 29

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By end of proximal tubule have reabsorbed: By end of proximal tubule have reabsorbed: % of water and sodium % of water and sodium about 100% of glucose and amino acids about 100% of glucose and amino acids 90 % of K+, bicarb, Ca++, uric acid 90 % of K+, bicarb, Ca++, uric acid Transport maximum – maximum amount of a substance that can be absorbed per unit time Transport maximum – maximum amount of a substance that can be absorbed per unit time Renal threshold – plasma conc. of a substance at which it exceeds Tm. Renal threshold – plasma conc. of a substance at which it exceeds Tm. 31

Loop of Henle Responsible for producing a concentrated urine by forming a concentration gradient within the medulla of kidney. Responsible for producing a concentrated urine by forming a concentration gradient within the medulla of kidney. When ADH is present, water is reabsorbed and urine is concentrated. When ADH is present, water is reabsorbed and urine is concentrated. Counter-current multiplier Counter-current multiplier 32

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Distal convoluted tubule and collecting ducts What happens here depends on ADH What happens here depends on ADH Aldosterone affects Na+ and K+ Aldosterone affects Na+ and K+ ADH – facultative water reabsorption ADH – facultative water reabsorption Parathyroid hormone – increases Ca++ reabsorption Parathyroid hormone – increases Ca++ reabsorption 34

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Distal convoluted tubule and collecting ducts Tubular secretion to rid body of substances: K+, H+, urea, ammonia, creatinine and certain drugs Tubular secretion to rid body of substances: K+, H+, urea, ammonia, creatinine and certain drugs Secretion of H+ helps maintain blood pH Secretion of H+ helps maintain blood pH (can also reabsorb bicarb and generate new bicarb) 36

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Renal diagnostic procedures Urinalysis is non-invasive and inexpensive Urinalysis is non-invasive and inexpensive Normal properties are well known and easily measured Normal properties are well known and easily measured 38

pH Normally 4.8 – 8.0 Normally 4.8 – 8.0 Higher in alkalosis, lower in acidosis Higher in alkalosis, lower in acidosis Diabetes and starvation ↓ pH Diabetes and starvation ↓ pH Urinary infections ↑ pH Urinary infections ↑ pH –Proteus and pseudomonas are urea splitters 39

Specific gravity Normal values Normal values High specific gravity can cause precipitation of solutes and formation of kidney stones High specific gravity can cause precipitation of solutes and formation of kidney stones When tubules are damaged, urine specific gravity approaches that of glomerular filtrate – – remains fixed = 2/3 of nephron mass has been lost When tubules are damaged, urine specific gravity approaches that of glomerular filtrate – – remains fixed = 2/3 of nephron mass has been lost 40

Diabetes insipidus = Diabetes insipidus = Diabetes mellitus = Diabetes mellitus = Emesis or fever = Emesis or fever =

Microscopic analysis Red blood cells – should be few or none Red blood cells – should be few or none –Hematuria – large numbers of rbc’s in urine –Catheterization –Menstruation –Inflamed prostate gland –Cystitis or bladder stones 42

Casts – precipitate from cells lining the renal tubules Casts – precipitate from cells lining the renal tubules –Red cells – tubule bleeding –White cells – tubule inflammation –Epithelial cells – degeneration, necrosis of tubule cells 43

Crystals – Crystals – –Infection –Inflammation –stones 44

White blood cells White blood cells –Pyuria –Urinary tract infection Bacteria Bacteria 45

Substances not normally present in urine Acetone Acetone Bile, bilirubin Bile, bilirubin Glucose Glucose Protein – albumin Protein – albumin –Renal disease involving glomerulus 46

Blood Urea Nitrogen BUN Urea produced by breakdown of amino acids - influenced by diet, dehydration, and hemolysis Urea produced by breakdown of amino acids - influenced by diet, dehydration, and hemolysis Normal range mg/ dL Normal range mg/ dL If the GFR decreases due to renal disease or blockage, or decreased blood flow to kidney - BUN increases If the GFR decreases due to renal disease or blockage, or decreased blood flow to kidney - BUN increases General screen for abnormal renal function General screen for abnormal renal function 47

Creatinine clearance Creatinine is an end product of muscle metabolism Creatinine is an end product of muscle metabolism Muscle mass is constant; creatinine is constant Muscle mass is constant; creatinine is constant Normal 0.7 – 1.5 mg/ dL in plasma Normal 0.7 – 1.5 mg/ dL in plasma Can then be compared to creatinine in urine over 24 hour period to determine clearance Can then be compared to creatinine in urine over 24 hour period to determine clearance 48

Creatinine clearance is an indirect measure of GFR and renal blood flow Creatinine clearance is an indirect measure of GFR and renal blood flow Creatinine is neither reabsorbed nor secreted, just freely filtered. Creatinine is neither reabsorbed nor secreted, just freely filtered. Amount excreted = amount filtered Amount excreted = amount filtered Useful to monitor changes in chronic renal function Useful to monitor changes in chronic renal function Increases with trauma with massive muscle breakdown Increases with trauma with massive muscle breakdown 49

Diagnostic testing Inulin clearance - not absorbed or secreted = GFR Inulin clearance - not absorbed or secreted = GFR PAH – para-aminohippuric acid – not absorbed ; actively secreted = renal plasma flow PAH – para-aminohippuric acid – not absorbed ; actively secreted = renal plasma flow 50