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The Human Body in Health and Illness, 4 th edition Barbara Herlihy Chapter 24: Urinary System 1

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Page 1: Chapter 024

The Human Body in Health and Illness, 4th edition

Barbara Herlihy

Chapter 24:Urinary System

1

Page 2: Chapter 024

Lesson 24-1 Objectives

• List four organs of excretion.• Describe the major organs of the urinary

system.• Describe the location, structure, blood supply,

nerve supply, and functions of the kidneys.• Explain the role of the nephron unit in the

formation of urine.

Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights

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Lesson 24-1 Objectives (cont’d.)

• Explain the three processes involved in the formation of urinefiltration, reabsorption, and secretion.

• Describe the hormonal control of water and electrolytes by the kidneys.

• List the normal constituents of urine.• Describe the structure and function of the

ureters, urinary bladder, and urethra.

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Organs of Excretion

• Kidneys

• Skin (sweat glands)

• Lungs

• Intestines

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Organs of the Urinary System

• Kidneys (2)

• Ureters (2)

• Urinary bladder (1)

• Urethra (1)

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Kidneys

• Regions – Renal cortex– Renal columns – Renal medulla– Renal pyramids– Renal pelvis

• Renal capsule• Blood supply

– Renal artery– Renal vein

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Kidneys: Functions

• Regulate blood volume and electrolytes• Regulate acid-base balance • Excrete nitrogenous waste• Regulate blood pressure • Regulate RBC production

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Urine Making: The Nephron Unit

• Nephron unit: Functional unit of the kidney

• Composed of two parts– Renal tubules– Renal blood vessels

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Nephron Unit: Tubular Structures

Bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct

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Nephron Unit: Blood Vessels

• Renal artery• Afferent arteriole• Glomerulus• Efferent arteriole • Peritubular capillaries• Renal vein

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Three Steps of Urine Formation

• Glomerular filtration

• Tubular reabsorption

• Tubular secretion

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Urine Formation: Glomerular Filtration

• Water and dissolved solute filter across glomeruli into Bowman’s capsule.

• Large molecules (albumin and RBCs) are not filtered.

• Unfiltered blood goes to peritubular capillaries.

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Glomerular Filtration Rate (GFR)

• Rate at which water and solute are filtered• Blood pressure determines GFR• Normal GFR

– 180 liters water/24 hours– 125 mL water/minute

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Urine Formation: Tubular Reabsorption

• Returns filtrate from the tubules to the blood of peritubular capillaries

• Most reabsorption takes place in the proximal tubule

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Tubular Reabsorption (cont’d.)

What is reabsorbed?Sodium

Water

Glucose

Urea

Creatinine

How much?>99%

>99%

100%

50%

O %

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Mechanisms: Tubular Reabsorption

• ActiveExample: Na+ pumped

from tubule into peritubular capillary

• PassiveExample: H2O and Cl-

passively follow Na+ into peritubular capillary

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Urine Formation: Tubular Secretion

• Moves very small amounts of select substances from the peritubular capillaries into the tubules

• Secreted substances: Potassium ions (K+), hydrogen ions (H+), uric acid, ammonium ions, and drugs

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Aldosterone and Urine Formation

• Works on distal tubule• The “salt-retaining”

hormone• Effects

Na+, H2O reabsorption

(expands blood volume)– K+ excretion (kaliuresis)

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Getting Aldosterone to the Kidney

Renin-angiotensin-aldosterone system

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Renin-Angiotensin-Aldosterone

Renin (released from kidney because of low BP)

Angiotensinogen (inactive form circulating in blood)

Angiotensin I (lungs release converting enzyme)

Angiotensin II

Aldosterone (released by adrenal cortex)

Distal tubule (kidney reabsorbs Na+ and H20 and excretes K+)Copyright © 2011, 2007 by Saunders,

an imprint of Elsevier Inc. All rights reserved.

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Antidiuretic Hormone (ADH)

• Released by posterior pituitary in response to low blood volume or high concentration

• H2O moves out of collecting duct into tissue spaces and then into peritubular capillaries

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Characteristics of Urine

• Volume: Average 1500 mL/24 hours– Oliguria, <400 mL/24 hours– Polyuria, >1500 mL/24 hours

• pH: Average 6.0 (range, 5.0-8.0)• Specific gravity: Slightly heavier than water

(1.001-1.035)• Color: Amber or straw-colored

– Deep yellow in dehydration– Pale yellow with overhydration

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Some Abnormal Constituents of Urine

• Albuminuria: Increased glomerular permeability• Glucosuria: Diabetes mellitus• Hematuria: Inflammation, trauma, disease• Hemoglobinuria: Hemolysis• Pyuria: Infection, indicated by WBCs • Ketonuria: Diabetes mellitus • Bilirubinuria: Disease of liver or biliary tree,

hemolysis

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No Urine: What’s That About?

Urinary Retention

• Kidneys produce urine

• Bladder won’t empty

• Treatment: Catheterization or drugs

Renal Suppression

• Kidneys don’t produce urine

• Patient develops uremia

• Treatment: dialysis

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Renal Dialysis

• Uremia: “Urine in the blood” resulting from renal failure

• Dialysis removes waste from blood Artificial kidney Peritoneal dialysis

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After the Nephron Unit: Then What?

• Your plumbing Calyx Renal pelvis Ureters Urinary bladder Urethra

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Urinary Bladder: Micturition Reflex

• Bladder fills, stimulates stretch receptors

• Sensory signal to spinal cord

• Motor signal to bladder• Contraction of bladder,

relaxation of internal sphincter

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reserved.27