phth 211 urinary system2

8/9/2019 PHTH 211 Urinary System2

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Copyright 2009, John Wiley & Sons, Inc.

Chapter 26: Introduction to the

Urinary System


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Overview of kidney functions

Regulation of blood ionic composition

Regulation of blood pH

Regulation of blood volume

Regulation of blood pressure Maintenance of blood osmolarity

Production of hormones (erythropoietin)

Regulation of blood glucose level

Excretion of wastes from metabolic reactions andforeign substances (drugs or toxins)


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Gross anatomy of the urinary system

1. Left and right Kidneys

2. Left and right Ureter

3. Bladder

4. Urethra


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Gross anatomy of the kidney


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External anatomy of the kidney

Renal hilium indent where ureter emerges along

with blood vessels, lymphatic vessels and nerves

Surrounded by layers of adipose tissue and fatthat protect it and from external trauma 3


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Internal anatomy of the kidneysSuperficial - Renal cortex ; inner region renal medulla


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Blood and nerve supply of the kidneys

kidneys are 0.5% of total body mass BUT they receive20-25% of resting cardiac output Left and right renal artery enters kidney

Each nephron receives one afferent arteriole which divides into a

capillary ball called a glomerulus which then forms the efferentarteriole (!)

Divide to form peritubular capillaries, peritubular venule,interlobar vein and renal vein exits kidney

Renal nerves are part of the sympathetic autonomic nervoussystem

Most are vasomotor nerves regulating blood flow


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Blood supply of the kidneys


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Anatomy of the kidneys

Nephron = microscopic functional units ofkidney

involved in urine formation

Urine formed by nephron drains into

Renal pelvis

Ureter

Urinary bladder


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Structures and functions of a nephron

Renal corpuscle Renal tubule and collecting duct

Peritubular capillaries

Urine

(contains

excreted

substances)

Blood

(contains

reabsorbed

substances)

Fluid in

renal tubule

Afferent

arteriole

Filtration from blood

plasma into nephron

Efferent

arteriole

Glomerular

capsule

1



Urine

(contains

excreted

substances)

Blood

(contains

reabsorbed

substances)

Tubular reabsorption

from fluid into blood

Fluid in

renal tubule

Afferent

arteriole


plasma into nephron

Efferent

arteriole

Glomerular

capsule

1

2



Urine

(contains

excreted

substances)

Blood

(contains

reabsorbed

substances)

Tubular secretion

from blood into fluid



Fluid in

renal tubule

Afferent

arteriole


plasma into nephron

Efferent

arteriole

Glomerular

capsule

1

2 3


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The nephron functional unit of

kidney

2 parts

Renal corpuscle filters blood plasma to

produce fluid

Glomerulus capillary network

Glomerular (Bowmans) capsule double-walled

cup surrounding glomerulus

Filtered fluid passes into renal tubule and

then into collecting duct


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The structure of nephrons and associated

blood vessels


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Overview of renal physiology1. Glomerular filtration

Water and most solutes in blood plasma move across the wall ofthe glomerular capillaries into glomerular capsule and then renaltubule

2. Tubular reabsorption As filtered fluid moves along tubule and through collecting duct,

about 99% of water and many useful solutes reabsorbed

returned to blood3. Tubular secretion

As filtered fluid moves along tubule and through collecting duct,other material secreted into fluid such as wastes, drugs, andexcess ions removes substances from blood

Solutes in the fluid that drains into the renal pelvis remain in thefluid and are excreted

Excretion of any solute = glomerular filtration + secretion - reabsorption


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Structures and functions of a nephron



Urine

(contains

excreted

substances)

Blood

(contains

reabsorbed

substances)

Fluid in

renal tubule

Afferent

arteriole


plasma into nephron

Efferent

arteriole

Glomerular

capsule

1



Urine

(contains

excreted

substances)

Blood

(contains

reabsorbed

substances)



Fluid in

renal tubule

Afferent

arteriole


plasma into nephron

Efferent

arteriole

Glomerular

capsule

1

2



Urine

(contains

excreted

substances)

Blood

(contains

reabsorbed

substances)

Tubular secretion

from blood into fluid



Fluid in

renal tubule

Afferent

arteriole


plasma into nephron

Efferent

arteriole

Glomerular

capsule

1

2 3


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Glomerular filtration rate

Glomerular filtration rate (GFR) amount of filtrate formed in all the renal corpuscles of bothkidneys each minute - needs to be maintained

constant (homeostasis) Too high substances pass too quickly and

are not reabsorbed

Too low nearly all reabsorbed and some

waste products not adequately excreted


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Glomerular filtration rate

GFR can be increased or decreased by increasing

(vasodilatation) or decreasing (vasoconstriction) the blood

flow in the afferent arteriole. This can be regulated by

1. Sympathetic NS activation decreases GFR

2. Hormonal regulation

Angiotensin II (circulating) reduces GFR

Atrial natriuretic peptide (from heart) increases

GFR


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Tubular reabsorption and tubular secretion

Reabsorption return of most of the filteredwater and many solutes to the bloodstream About 99% of filtered water reabsorbed

Both active and passive processes Secretion transfer of material from blood

into tubular fluid Helps control blood pH

Helps eliminate substances from the body


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Hormonal regulation of tubular reabsorption

and secretion

When blood volume and blood pressure decrease,Angiotension II

and aldosterone (from adrenal gland) stimulate increased

reabsorption of salt and water in the renal tubule. These help to

support blood pressure and volume.


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Summary of regulation of Sodium and

Water BalanceThree major hormones are involved in regulating sodium and waterbalance in the body at the level of the kidney.

1. ADH (antidiuretic hormone) from the posterior pituitary acts on the

kidney to promote water reabsorption, thus preventing its loss in

the urine.

2. Aldosterone from the adrenal gland acts on the kidney to promote

sodium reabsorption, thus preventing its loss in the urine.

3. ANH (atrial natriuretic hormone) from the atrium of the heart acts

on the kidney to promote sodium excretion so that it is excreted in

the urine



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Production of dilute and concentrated

urine Even though your fluid intake can be highly

variable, total fluid volume in your bodyremains stable

Depends in large part on the kidneys toregulate the rate of water loss in urine

ADH controls whether dilute or concentratedurine is formed

Absent or low ADH = dilute urine

Higher levels = more concentrated urine throughincreased water reabsorption


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Evaluation of kidney function

Urinalysis

Analysis of the volume and physical, chemical and

microscopic properties of urine

Water accounts for 95% of total urine volume

Typical solutes are filtered and secreted

substances that are not reabsorbed

If disease alters metabolism orkidney function,

traces of substances normally not present or

normal constituents in abnormal amounts may

appear


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Evaluation of kidney function

Blood tests Blood urea nitrogen (BUN) measures blood nitrogen that

is part of the urea resulting from catabolism anddeamination of amino acids

Plasma creatinine results from catabolism of creatinephosphate in skeletal muscle and it is removed from thebody only by the kidneys measure of renal function

Renal plasma clearance More useful in diagnosis ofkidney problems than above

Volume of blood cleared of a substance per unit time

High renal plasma clearance indicates efficient excretion ofa substance into urine


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Urine transportation, storage, and

elimination Ureters

Each of 2 ureters transports urine from renal

pelvis of one kidney to the bladder

Peristaltic waves, hydrostatic pressure and gravitymove urine

No anatomical valve at the opening of the ureter

into bladder when bladder fills it compresses the

opening and prevents backflow


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Ureters, urinary bladder, and urethra in a

female The bladder is astretchymuscular bag

that collects and

stores urine.

It is located in the

pelvis at the

lowest point in

the abdomen,immediately

behind the pubic

bone


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Urinary bladder and urethra Urinary bladder

Hollow, distensible muscular organ; Capacity 700-800mL

Micturition discharge of urine from bladder

Combination of voluntary and involuntary muscle contractions

When volume increases stretch receptors send signals to

micturition center in spinal cord triggering spinal reflex

micturition reflex. In early childhood we learn to initiate and stop it

voluntarily

Urethra

Small tube leading from internal urethral orifice in floor of bladder to

exterior of the body


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Urinary Incontinence

Urinary incontinence is the unintentional passing of

urine. It is a very common problem that is thought to

affect about three million people in the UK.

Anyone can experience urinary incontinence, although it

is more common in older people. The condition affects

far more women than men, and it is thought to occur in

one in five women who are over 40 years of age.



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Types of Urinary Incontinence

Two main types Stress incontinence occurs when the pelvic floor muscles are

too weak to prevent urination.

Urge incontinence is thought to occur as a result of incorrect

signals being sent between the brain and the bladder.

These two types of urinary incontinence are responsible

for 90% of all cases of the condition. It is also possible to

have a mixture of both types.



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Symptoms of Stress Incontinence

Most common type particularly among women who havehad children or been through the menopause.

Not related to feeling stressed

Occurs when your bladder is put under an extra amount

of sudden pressure. Symptoms include urine leakage during physical

activities such as: Coughing, Sneezing, Laughing, Heavy

lifting, Exercise.

The amount of urine that is passed is usually small, butstress incontinence can also cause you to pass larger

amounts, particularly if your bladder is very full.



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Symptoms of Urge Incontinence

It is the second most common type of urinary incontinence.

Urge incontinence is where you have an unstable, oroveractive

bladder.

Symptoms include: sudden and very intense need to pass urine

before quickly releasing large amounts of urine. There is often only a

few seconds between the need to urinate and the release of urine.

Your need to pass urine may be triggered by a sudden change of

position, or even by the sound of running water.

If you have urge incontinence you may need to pass urine very

frequently. You may need to get up several times during the night.



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Treatment of Incontinence Depend on the type of incontinence you have and the severity of

your symptoms. If caused by an underlying condition, such as an enlarged prostate

gland (in men), you will receive treatment for this first.

Lifestyle changes

Your GP may suggest that you make some simple changes to yourlifestyle in order to reduce your incontinence. These changes can

help improve your condition regardless of the type of urinary

incontinence that you have.

For example, your GP may recommend:

Reducing your caffeine intake. Changing the amount you drink, that is reducing it if it is too

much, or increasing it if it is too little.

Losing weight if you are overweight or obese.

. Copyright 2009, John Wiley & Sons, Inc.


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Initial treatment for stress incontinence involves making

simple lifestyle changes, such as those described above,

and doing exercises in order to strengthen your pelvic

floor muscles.

If lifestyle changes and pelvic floor exercises prove to be

unsuccessful in treating your stress incontinence,

surgery may be recommended.


Treatment of Incontinence


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End of Chapter 26

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phth 211 urinary system2

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