BIOL 1308 Chapter16_lecture

8/22/2019 BIOL 1308 Chapter16_lecture

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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.


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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


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The Urinary System


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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


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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


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16.1 Urinary System

Organs of the Urinary System

Urethra

A small tube that leads from the urinary bladder to anexternal opening

Its function is to remove urine from the body

The urethra is longer males than females

The urethra also transports semen in males


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16.1 Urinary System

Urination

Stretch receptors in

wall of bladder

Send impulses whenbladder fills to 250 ml

Motor impulses from

spinal cord

Bladder contraction

Micturition occurs


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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


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Gross Anatomy of the Kidney


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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


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Nephron Anatomy


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and Excretion

Parts of a Nephron

Glomerular capsule (Bowmans 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


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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


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Processes in Urine Formation


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and Excretion

Urine Formation

Glomerular Filtration

Blood enters the afferent arteriole and glomerulus

Blood pressure forces water and small molecules into theglomerular capsule (filtration)

Large molecules and formed elements cannot leave the

capillaries

Remaining processes must reabsorb desirable substances

and allow wastes to pass


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and Excretion

Urine Formation

Glomerular Filtration

Filterable Blood

Components

Nonfilterable Blood

Components

Water Blood cells and

platelets

Nitrogenous wastes Plasma proteins

Nutrients

Salts


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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 activelyreabsorbed

Glucose is an example

There is a limited number of carrier proteins Excess glucose ends up being excreted


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and Excretion

Urine Formation

Tubular Reabsorption

Reabsorbed Filtrate

Components

Nonreabsorbed

FiltrateComponents

Most water Some water

Nutrients Much nitrogenous

wastesRequired salts (ions) Excess salts (ions)


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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


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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


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of the Kidneys


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 returnedto 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 andthe collecting duct


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of the Kidneys


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 intoAngiotensin 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 ofNa+

The reabsorption of Na+ is followed by the reabsorption of H2O

Blood volume and blood pressure increase


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of the Kidneys


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


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Juxtaglomerular Apparatus


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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


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of the Kidneys


Water leaves distal convoluted tubule because of the

osmotic gradient

Water also leaves descending limb of loop of thenephron

Countercurrent multiplier

As filtrate enters collecting duct it is hypotonic to cells

of renal cortex

Permeability of collecting duct under hormonal control


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of the Kidneys

Reabsorption of Water Permeability of collecting duct is under hormonal

control

Antidiuretic hormone (ADH) is produced by the posteriorpituitary 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


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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 thedistal convoluted tubule


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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


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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


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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


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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


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Acid-Base Balance


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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 andprotein

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 earlysigns of kidney damage


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Disorders of the Kidneys Hemodialysis

Artificial kidney machine or continuous ambulatory peritonealdialysis (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


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An Artificial Kidney Machine


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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 thebladder.

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BIOL 1308 Chapter16_lecture