CHAPTER

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26The Urinary System

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Learning Outcomes

26.1 Describe the structure, location, and functions of the kidney.

26.2 Define the term nephron and describe its structure.

26.3 Explain how nephrons filter blood and form urine.

26.4 List substances normally found in urine.

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Learning Outcomes (cont.)

26.5 Describe the locations, structures, and functions of the ureters, bladder, and urethra.

26.6 Explain how urination is controlled.

26.7 Describe the causes, signs and symptoms, and treatments of various diseases and disorders of the urinary system.

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Introduction

• System functions to remove waste products from the blood

• Main functional units of the kidneys are the nephrons• Nephrons filter the blood and form the urine

KidneysKidneys

UretersUreters

BladderBladder

UrethraUrethra

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The Kidneys

Functions

Remove metabolic waste products from the blood Secrete the hormone erythropoietin, which stimulates

bone marrow to produce red blood cells Secrete the hormone renin, which helps regulate blood pressure

Description

The kidneys are bean-shaped organs that lie behind the peritoneal cavity (retroperitoneal) on either side of the vertebral column.

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The Kidneys (cont.)

• Renal sinus – concave depression of the surface of the kidney

• Hilum – point of entry for the renal artery, renal vein, and ureter

• Renal pelvis – expansion of the ureter that further divides into calyces

Kidney

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The Kidneys (cont.)

• Renal cortex – outermost portion of the kidney that covers the pyramids and dips down between them

• Renal medulla – middle portion that also divides into renal pyramids

• Renal column – portion of the cortex between pyramids

Kidney

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Nephrons• Removes waste products from the blood• Each kidney contains about 1 million nephrons• Made of a renal corpuscle and a renal tubule

Renal Corpuscles

Composed of a group of capillaries called a glomerulus Glomerulus is surrounded by Bowman’s capsule Blood filtration occurs in corpuscle

Extend from the Bowman’s capsule of a nephron Consist of three parts:

Proximal convoluted tubule Loop of Henle Distal convoluted tubule

Renal Tubules

Glomerulus

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Nephrons (cont.)

Veins of the Kidney

Afferent Arteriole

Glomerulus

Efferent Arteriole

Peritubular Capillaries

Afferent arterioles deliver blood to the glomeruli

Efferent arterioles carry blood from the glomeruli to peritubular capillaries

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Apply Your Knowledge

What are the functions of the kidney?

ANSWER: The kidney removes metabolic waste products from the blood, secretes erythropoietin to help regulate RBC production, and secretes renin to help regulate the BP.

Correct!

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Urine Formation

• Glomerular Filtration– First process occurs in

renal corpuscles

– Fluid part of the blood is forced from glomerulus into Bowman’s capsule• Becomes glomerular

filtrate Glomerulus

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Urine Formation (cont.)

• Factors affecting glomerular filtration– Filtration pressure – amount of

pressure that forces filtrate from the glomerulus into Bowman’s capsule

• Determined by blood pressure

– Rate of filtration – sympathetic nervous system control

• Constriction of afferent arterioles decreases filtration pressure

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Tubular Reabsorption

• Second process in urine formation• Glomerular filtrate proximal convoluted tubule

– Nutrients, water, and ions pass through the walls of the renal tubule into the peritubular capillaries

• Water reabsorption depends on hormones– Antidiuretic hormone (ADH)– Aldosterone– Both increase water reabsorption, which decreases

urine production

Tubular Reabsorption

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Tubular Secretion

• Third process of urine formation

• Substances move from blood in the peritubular capillaries into the renal tubules

• Secreted substances

– Drugs

– Hydrogen ions

– Waste products

Tubular Secretion

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Urine Formation (cont.)

• Urine composition– Mostly water– Urea and uric acid

• Formed by the breakdown of proteins and nucleic acids

– Trace amounts of amino acids and various ions

• Secretion of waste products helps maintain the acid-base balance

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Apply Your Knowledge

Match the following:

___ Second process in urine formation A. Glomerular filtration

___ Substances move from blood into renal tubules B. Tubular reabsorption

___ Depends on filtration pressure C. Tubular secretion

___ Third process of urine formation

___ First process of urine formation

___ Filtrate flows into the proximal convoluted tubule

C

C

B

A

A

B

ANSWER:

Nice Job!

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Urinary Bladder

• Expandable muscular organ – Stores up to 600 ml urine on average

• Detrusor muscle – smooth muscle in wall of bladder

• Trigone – triangle on internal floor of bladder formed by urethra and ureters

• Micturation– Process of urination– Stretching of bladder triggers process

• Approximately 150cc of urineBladder

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Previous

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Impulses to contract urethra; inhibit micturition impulse until ready to urinate

Urination

– External urethral sphincter relaxes

– Micturition reflex – impulses from pons and hypothalamus

– Detrusor muscle contracts

– Urine expelledBladderdistends

Stretch receptors

Spinal cord

Parasympathetic nerves stimulate detrusor muscle

Brain stemand

cerebralcortex

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Urethra

• Tube that moves urine from the bladder to the outside world

• Shorter in females – patient education– Urinate when urge occurs– Drink adequate clear fluids– Wipe front to back– Urinate after intercourse

Urethra

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True or False:

___ Ureters move urine by peristalsis.

___ The detrusor is formed by the openings of the ureters and urethra.

___ The process of micturition is triggered when the bladder contains

about 150 ml urine.

___ The urethra move urine from the kidney to the bladder.

___ The urethra is longer in females.

___ Contraction of the detrusor muscle pushes urine from the bladder.

Apply Your Knowledge

F

F

T

F

T

trigone

males

ureters

T

ANSWER:

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Diseases and Disorders of the Urinary System

Disease/Disorder Description

Acute renal failure Sudden loss of kidney function; may be reversible with treatment

Chronic renal failure Kidneys slowly lose ability to function; not reversible

Cystitis Urinary bladder infection; more common in females

Glomerulonephritis Inflammation of the glomeruli of the kidney; one cause of chronic renal failure

Incontinence Inability to control urination

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Diseases and Disorders of the Urinary System

Disease/Disorder Description

Polycystic kidney disease

Enlargement of kidneys because of the presence of many cysts within them; slow, progressive disease

Pyelonephritis Complicated urinary tract infection; starts with a bladder infection and spreads to both kidneys; can be acute or chronic

Renal calculi Kidney stones; can become lodged in ducts within kidneys or ureters

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Apply Your Knowledge

Matching:

___ Complicated urinary tract infection A. Pyelonephritis

___ Inability to control urination B. Glomerulonephritis

___ Kidney stones C. Incontinence

___ Slow loss of kidney function D. Chronic renal failure

___ Bladder infection E. Renal calculi

___ Inflammation of the glomeruli F. Cystitis

___ Kidney enlargement due to cysts G. Acute renal failure

___ Sudden loss of kidney function H. Polycystic kidney disease

H

G

F

E

D

C

B

A

ANSWER:GOOD JOB!

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In Summary

26.1 The retroperitoneal kidneys are composed of the outer renal cortex and inner renal medulla. Their function is to remove metabolic waste from the body.

26.2 A nephron is a single kidney cell. It is composed of a renal corpuscle containing the glomerulus and Bowman’s capsule and the three sections of the renal tubule: proximal convoluted tubule, loop of Henle, and distal convoluted tubule.

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In Summary (cont.)

26.3 The nephrons filter blood and form urine through three processes: glomerular filtration, tubular reabsorption, and tubular secretion.

26.4 Some of the components of urine include water, urea, uric acid, trace amounts of amino acids, and various ions.

26.5 The two ureters are long tubes extending from each renal pelvis that bring urine to the bladder for storage. The urethra is the muscular tube extending from the bladder that allows urine to be expelled from the body.

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In Summary (cont.)

26.6 Urination is controlled by a variety of factors including bladder distention, parasympathetic nerve stimulation, brain impulses affecting urethral sphincters, and contractions of the detrusor muscles of the bladder.

26.7 The diseases and disorders of the urinary system include infections of the bladder and kidneys, bladder control, and the different types of renal (kidney) failure and disease. These are discussed in more detail in the Pathophysiology section of this chapter.

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End of Chapter 26

This too shall pass—just like a kidney stone.

~H. Madson