Inquiry into LifeTwelfth Edition

Chapter 16

Lecture PowerPoint to accompany

Sylvia S. Mader

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16.1 Urinary System

• Functions of the Urinary System– Excretion of Metabolic Wastes

• Urea, Creatinine, Uric acid

– Maintenance of Water-Salt Balance• NaCl, K+, HCO3

-, Ca2+

– Maintenance of Acid-Base Balance• Excretion of H+, reabsorption of HCO3

-

– Secretion of Hormones• Renin, Erythropoietin

The Urinary System

16.1 Urinary System

• Organs of the Urinary System– Kidneys

• Located in lumbar region• Behind peritoneum• Covered by tough capsule of fibrous connective tissue• Concave side has a depression called a hilum

– Location of renal artery and vein

– Ureters• Conduct urine from kidney to bladder• Three-layered wall

– Mucosa, smooth muscle, outer connective tissue• Conveys urine by peristalsis

16.1 Urinary System

• Organs of the Urinary System– Urinary Bladder

• Stores urine

• Has three openings– Two for the ureters, one for the urethra

• The bladder wall is expandable

• Two sphincter muscles control the release of urine into the

urethra

16.1 Urinary System

• Organs of the Urinary System

– Urethra

• A small tube that leads from the urinary bladder to an

external opening

• It’s function is to remove urine from the body

• The urethra is longer males than females

• The urethra also transports semen in males

16.1 Urinary System

• Urination– Stretch receptors in

wall of bladder• Send impulses when

bladder fills to 250 ml• Motor impulses from

spinal cord– Bladder contraction– Micturition occurs

16.2 Anatomy of the Kidney and Excretion

• There are three regions to a kidney– The renal cortex– The renal medulla– The renal pelvis

• Nephrons are the functional units of the kidney– Each kidney has over one million nephrons

Gross Anatomy of the Kidney

Nephron Anatomy

16.2 Anatomy of the Kidney and Excretion

• Anatomy of a Nephron– A nephron is composed of a system of tubules

– Each nephron has its own blood supply• From renal artery, afferent arteriole leads into the glomerulus

• Blood leaves the glomerulus via an efferent arteriole

• Efferent arteriole takes blood to peritubular capillaries– These surround rest of the nephron

– Blood then goes to renal vein

16.2 Anatomy of the Kidney and Excretion

• Parts of a Nephron– Glomerular capsule (Bowman’s capsule)

• Cuplike structure• Inner layer has podocytes

– Form pores for passage of small molecules

– Proximal convoluted tubule (PCT)• Cuboidal epithelial cells with microvilli

– Increased surface area for absorption

16.2 Anatomy of the Kidney and Excretion

• Parts of a Nephron– Loop of Henle

• U-shaped tube

• Simple squamous epithelium

– Distal Convoluted tubule (DCT)

• Lack microvilli

• Designed for tubular excretion rather than reabsorption

– Collecting Ducts

Processes in Urine Formation

16.2 Anatomy of the Kidney and Excretion

• Urine Formation– Glomerular Filtration

• Blood enters the afferent arteriole and glomerulus • Blood pressure forces water and small molecules into the

glomerular capsule (filtration)• Large molecules and formed elements cannot leave the

capillaries

• Remaining processes must reabsorb desirable substances and allow wastes to pass

16.2 Anatomy of the Kidney and Excretion

• Urine Formation– Glomerular Filtration

Filterable Blood Components

Nonfilterable Blood Components

Water Blood cells and platelets

Nitrogenous wastes Plasma proteins

Nutrients

Salts

16.2 Anatomy of the Kidney and Excretion

• Urine Formation– Tubular Reabsorption

• Molecules are reabsorbed both actively and passively– Sodium reabsorbed by active transport– Chloride follows passively– Water absorbed by osmosis

• Only molecules recognized by carrier proteins are actively reabsorbed

– Glucose is an example– There is a limited number of carrier proteins– Excess glucose ends up being excreted

16.2 Anatomy of the Kidney and Excretion

• Urine Formation– Tubular Reabsorption

Reabsorbed Filtrate Components

Nonreabsorbed Filtrate Components

Most water Some water

Nutrients Much nitrogenous wastes

Required salts (ions) Excess salts (ions)

16.2 Anatomy of the Kidney and Excretion

• Urine Formation– Tubular Secretion

• Hydrogen ions, potassium, creatinine, many drugs

• Actively transported from the blood

– Urine Contains• Filtered substances that have not been reabsorbed

• Substances that have been actively secreted

16.3 Regulatory Functions of the Kidneys

• Reabsorption of Water– Excretion of hypertonic urine depends on

reabsorption of water from the loops of the nephrons and the collecting ducts

– Reabsorption of water requires• Reabsorption of salt• Establishment of solute gradient• Reabsorption of water

16.3 Regulatory Functions of the Kidneys

• Reabsorption of Water

– Reabsorption of Salt• Regulated by the absorption and excretion of ions

– Na+, K+, HCO3-, Mg2+

• More than 99% of Na+ filtered at the glomerulus is returned to the blood

– 67% is reabsorbed at the proximal tubule– 25% is reabsorbed at the ascending limb of the nephron loop– The rest is reabsorbed from the distal convoluted tubule and

the collecting duct

16.3 Regulatory Functions of the Kidneys

• Reabsorption of Water

– Reabsorption of Salt• Hormonal Regulation at the Distal Convoluted Tubule

– Occurs when blood pressure at the glomerulus is low» Juxtaglomerular Apparatus secretes renin» Renin is an enzyme that changes angiotensinogen into

Angiotensin I» Angiotensin I is then converted into Angiotensin II» Angiotensin II stimulates the adrenal cortex to release aldosterone» Aldosterone promotes the excretion of K+ and the reabsorption of

Na+

» The reabsorption of Na+ is followed by the reabsorption of H2O» Blood volume and blood pressure increase

16.3 Regulatory Functions of the Kidneys

• Reabsorption of Water

– Reabsorption of Salt• Hormonal Regulation at the Distal Convoluted Tubule

– Atrial naturietic hormone (ANH)» Another hormone regulating sodium» Secreted by right atrium of heart in response to stretching» Indicates increased blood volume» Inhibits renin secretion by juxtaglomerular apparatus» Inhibits aldosterone release» Promotes sodium excretion - natriuresis

Juxtaglomerular Apparatus

16.3 Regulatory Functions of the Kidneys

• Establishment of Solute Gradient

– A long loop of nephron has two parts• Descending limb and ascending limb

– Salt diffuses out of lower part of ascending limb– Upper part of ascending limb actively transports more salt out– This creates high osmotic pressure (high solute concentration)

within the tissues of the renal medulla– Urea contributes to high solute concentration in medulla– Leaks from lower collecting duct– This results in a concentration gradient favoring reabsorption of

water

Reabsorption of Water

16.3 Regulatory Functions of the Kidneys

• Reabsorption of Water– Water leaves distal convoluted tubule because of the

osmotic gradient– Water also leaves descending limb of loop of the

nephron• Countercurrent multiplier

– As filtrate enters collecting duct it is hypotonic to cells of renal cortex

– Permeability of collecting duct under hormonal control

16.3 Regulatory Functions of the Kidneys

• Reabsorption of Water– Permeability of collecting duct is under hormonal

control• Antidiuretic hormone (ADH) is produced by the posterior

pituitary gland– In the absence of ADH, a dilute urine is produced– In the presence of ADH, the collecting duct become more

permeable to water and a concentrated urine is produced

16.3 Regulatory Functions of the Kidneys

• Diuretics– Increase flow of urine– Alcohol

• Shuts off ADH• Dehydration causes hangover

– Caffeine• Increases glomerular filtration rate• Decreases tubular reabsorption of sodium

– Diuretic drugs• Many inhibit active transport of sodium at loop of the nephron or the

distal convoluted tubule

16.3 Regulatory Functions of the Kidneys

• Acid-Base Balance

– Normal pH for most body fluids is 7.4– Alkalosis: pH is greater than 7.4– Acidosis: pH is less than 7.4

– Several Mechanisms Maintain a pH of ~ 7.4• Acid-Base buffer system• Respiratory Center• The Kidneys

16.3 Regulatory Functions of the Kidneys

• Acid-Base Balance– Acid-Base Buffer Systems

• Chemical or combination of chemicals• Can take up excess H+ or OH-

• Prevents large changes in pH

• When H+ added to blood the following occurs

H+ + HCO3- H2CO3

• When OH- added to blood the following occurs

OH- + H2CO3 HCO3- + H2O

16.3 Regulatory Functions of the Kidneys

• Acid-Base Balance– Respiratory Center

• Increasing breathing rate removes CO2

– Removes hydrogen ions– Forces reaction to the right

H+ + HCO3- H2CO3 H2O + CO2

• Respiratory system adjusts proportion of bicarbonate and carbonic acid

16.3 Regulatory Functions of the Kidneys

• Acid-Base Balance– The Kidneys

• Only kidneys can remove many acids and bases• Slower acting than respiratory system but more powerful• Reabsorbs bicarbonate ions• Excretes hydrogen ions• In urine ammonia can absorb hydrogen ions• Phosphate provides another means of buffering hydrogen

ions in urine

Acid-Base Balance

16.4 Disorders of the Urinary System

• Disorders of the Kidneys– Pyelonephritis: Infections of the kidneys

• Kidney infections usually result from bladder infections• Most are curable with antibiotics if diagnosed in time• Some infections can cause severe damage

– Kidney Stones• Hard granules that form in the renal pelvis• Composed of substances such as calcium, phosphate, uric acid and

protein• Excess animal protein in the diet, imbalanced urinary pH, and

urinary tract infections may be contributing factors• May pass unnoticed in the urine,large stones can be very painful

– The presence of albumin or blood cells in the urine are early signs of kidney damage

16.4 Disorders of the Urinary System

• Disorders of the Kidneys– Hemodialysis

• Artificial kidney machine or continuous ambulatory peritoneal dialysis (CAPD)

• Dialysis– Diffusion of dissolved molecules through a membrane– Selective permeability– Blood is cleansed– pH is adjusted– Water and salt balance maintained

• In CAPD the peritoneum is the dialysis membrane

An Artificial Kidney Machine

16.4 Disorders of the Urinary System

• Disorders of the Bladder and Urethra– Bladder Infections

• Urine leaving the bladder is usually bacteria-free• The urethra is normally colonized with bacteria• Sometimes bacteria make their way to the bladder

– Usually treatable with antibiotics– Bladder Stones

• Occur as a result of bladder infections or prostate enlargement• May actually be kidney stones that were carried to the bladder• Can be removed surgically or broken apart by lithotripsy

– Bladder Cancer• Smoking greatly increases the risk• Some types are very malignant necessitating removal of the

bladder.