Unit 4: Homeostasis

Chapter 10: Excretion and the Interaction of Systems

Chapter 10: Excretion and the Interaction of Systems Overview

The excretory system Functions Organs

Urine formation in the nephron Other functions and disorders of the excretory

system Regulating water-salt balance Maintaining blood pH Disorders

Section 10.1: Overview of the Excretory System Excretion is the process of separating wastes

from body fluids, then eliminating the wastes from the body

Several body systems perform this function The respiratory system excretes carbon dioxide and

small amounts of other gases, including water vapour

The skin excretes water, salts, and some urea in perspiration

The digestive system excretes water, salts, lipids, and a variety of chemical compounds Note that the elimination of food residue (feces) is not

considered to be a process of excretion

Section 10.1: Overview of the Excretory System Most metabolic wastes are

dissolved or suspended in solution and are excreted by the excretory system (also called the urinary system)

The excretory system produces urine and conducts it outside the body

As the kidneys produce urine, they carry out four functions that contribute to homeostasis

Functions of the Excretory System Excretion of metabolic wastes

The kidneys excrete metabolic wastes, notably nitrogenous (nitrogen-containing) wastes Include ammonia, urea, and uric acid

Ammonia is highly toxic, but it converted in the liver to the less toxic compound urea

Urea makes up the majority of nitrogenous waste in the body About half of it is eliminated in urine

Uric acid is present in much lower concentrations, and is contained in urine

Functions of the Excretory System Maintenance of water-salt balance

Kidneys maintain the appropriate balance of water and salt in the blood

Blood volume is closely tied to the salt balance of the body By regulating salts in the blood, the kidneys are closely

involved in regulating blood pressure Kidneys also help maintain the appropriate level of

potassium (K+), bicarbonate (HCO3-) and calcium

(Ca2+) in the blood

Functions of the Excretory System Maintenance of acid-base balance

Kidneys monitor and help keep the blood pH at about 7.4, mainly by excreting hydrogen ions (H+) and reabsorbing bicarbonate ions (HCO3

-) as needed

Human urine usually has a pH of 6 or lower because our diet often contains acidic foods

Functions of the Excretory System Secretion of hormones

Kidneys secrete two hormones: Calcitriol

Active form of Vitamin D Promotes calcium absorption from the digestive tract

Erythropoietin Stimulates the production of red blood cells Released in response to increased oxygen demand or

reduced oxygen-carrying capacity of the blood Kidneys also secrete renin

Leads to the secretion of the hormone aldosterone from the adrenal cortex

The Organs of the Excretory System The human excretory system consists of:

Two kidneys Two ureters The urinary bladder The urethra

The Organs of the Excretory System Two fist-sized kidneys are located in the area of the lower back on each

side of the spine A large cushion of fat usually surrounds them

Offers protection Although most people have two kidneys, humans are capable of

functioning with only one If one kidney ceases to work, or one is removed due to disease, the remaining

kidney will increase in size to handle the increased workload

The Organs of the Excretory System The kidneys release urine into two muscular, 28-

cm-long tubes called ureters From the ureters, urine is moved by the peristaltic

actions of smooth muscle tissue to the muscular urinary bladder where it is temporarily stored

Drainage from the bladder is controlled by two rings of muscles called sphincters Both sphincters must relax before urine can drain from

the bladder The innermost sphincter is involuntarily controlled by

the brain During childhood we learn to voluntarily control

relaxation of the other sphincter

The Organs of the Excretory System Urine exits the bladder and the body through a tube called the

urethra In males, the urethra is approximately 20cm long and merges with the

ductus deferens of the reproductive tract to form a single passageway to the external environment

In females, the urethra is about 4 cm long and the reproductive and urinary tracts have separate openings

The Kidneys The kidneys are bean

shaped and reddish-brown in colour

The concave side of each kidney has a depression where a renal artery enters and a renal vein and a ureter exit the kidney Many branches of the

renal artery renal vein reach inside the kidney

The Kidneys A kidney has 3 regions

The renal cortex is an outer layer that dips down into an inner layer called the renal medulla

The renal medulla contains cone-shaped tissue masses

The renal pelvis is a central space, or cavity, that is continuous with the ureter

The Kidneys Embedded within the renal cortex and extending

into the renal medulla are more than a million microscopic structures called nephrons

A network of blood vessels is closely associated with these nephrons

Nephrons are responsible for filtering various substances from blood, transforming it into urine

To perform this function, each nephron is organized into 3 main regions: A filter A tubule A collecting duct

The Nephron A Filter

The filter structure at the top of each nephron is a cap-like formation called the Bowman’s capsule

Within each capsule, the renal artery enters and splits into a find network of capillaries called a glomerulus (means “little ball” in Latin)

The walls of the glomerulus act as a filtration device Impermeable to proteins, other large molecules, and red blood

cells, so these remain within the blood Water, small molecules, ions, and urea (the main waste products

of metabolism) pass through the walls and proceed further into the nephron

The filtered fluid that proceeds from the glomerulus into the Bowman’s capsule of the nephron is referred to as filtrate

The Nephron A Tubule

The Bowman’s capsule is connected is connected to a small, long, narrow tubule that is twisted back on itself to form a loop This long hairpin loop is a reabsorption device

The tubule has 3 sections: The proximal tubule The loop of Henle The distal tubule

The tubule absorbs substances that are useful to the body, such as glucose and a variety of ions, from the filtrate passing through it

Also secretes substances into the tissues surrounding it

The Nephron A Duct

The tubule empties into a larger pipe-like channel called a collecting duct Functions as a water-conservation device, reclaiming

water from the filtrate passing through it so that very little water is lost from the body

The filtrate that remains in the collecting duct is a suspension of water and various solutes and particles It is now called urine Its composition is distinctly different from the fluid that

entered the Bowman’s capsule The solutes and water reclaimed during

reabsorption are returned to the body via the renal vein

Section 10.2: Urine Formation in the Nephron Nephrons are surrounded by the tissues of the

renal cortex and the renal medulla Also closely associated with a network of

blood vessels that spreads throughout the surrounding tissue

Thus, any substances secreted by the nephrons enter the surrounding tissue of the kidney Most of these substances return to the

bloodstream through the network of blood vessels The remainder leave the body in the form of urine

How Urine Forms 4 processes are crucial to the formation of urine Glomerular filtration

Moves water and solutes, except proteins, from blood plasma into the nephron (recall this filtered fluid is called filtrate)

Tubular reabsorption Removes useful substances such as sodium from the filtrate

and returns them into the blood for reuse by body systems Tubular secretion

Moves additional wastes and excess substances from the blood into the filtrate

Water reabsorption Removes water from the filtrate and returns it to the blood for

reuse by body systems

Glomerular Filtration Filters Blood The formation of urine starts with glomerular

filtration This process forces some of the water and

dissolved substances in blood plasma from the glomerulus into the Bowman’s capsule

This occurs in millions of nephrons at the same time

Glomerular Filtration Filters Blood Two factors contribute to filtration The first factor is the permeability of the capillaries of the

glomerulus Capillaries of the glomerulus have many pores in their tissue

walls The pores are large enough to allow water and most dissolved

substances in the blood plasma to pass easily through the capillaries and into the Bowman’s capsule

The pores are small enough to prevent proteins and blood cells from entering

The second factor is blood pressure Blood pressure within the glomerulus is about 4X greater than

it is in capillaries elsewhere in the body The great rush of blood through the golmerulus provides the

force for filtration

Glomerular Filtration Filters Blood Each day, 1600L – 2000L of blood pass

through the kidneys, producing about 180L of glomerular filtrate

This filtrate is almost chemically identical to blood plasma, minus proteins and blood cells

If the composition of urine were the same as that of glomerular filtrate, the body would continually lose water, salts, and nutrients Therefore, the composition of the filtrate must

change as this fluid passes through the remainder of the tubule

Tubular Reabsorption: Recovery of Substances in the Proximal Tubule About 65% of the filtrate that passes through the

entire length of the proximal tubule (including the loop of Henle) is reabsorbed and returned to the body

This process of reabsorption involves both active and passive transport mechanisms The cells of the proximal tubule contain many

mitochondria, which use the energy-releasing power of ATP to drive the active transport of sodium ions, glucose, and other solutes back into the blood

Negatively charged ions tag along passively, attracted by the electrical charge on the transported substances

Water follows the ions by osmosis, so it, too, is reabsorbed into the blood flowing through the capillaries

Tubular Reabsorption: Recovery of Substances in the Proximal Tubule

Focusing on the Loop of Henle in the Proximal Tubule The function of the loop of Henle is to reabsorb water

and ions from the glomerular filtrate As the descending limb of the loop of Henle plunges

deeper into the medulla region, it encounters an increasingly salty environment

The cells of the descending limb are permeable to water and only slightly permeable to ions

As a result of the salty environment of the medulla, and the permeability of the descending limb, water diffuses from the filtrate to the capillaries by osmosis

As water moving through the descending limb leaves the filtrate, the concentration of sodium ions inside the tubule increases, reaching its maximum concentration at the bottom of the loop

Focusing on the Loop of Henle in the Proximal Tubule

Focusing on the Loop of Henle in the Proximal Tubule As the filtrate continues around the bend of

the loop of Henle and into the ascending limb, the permeability of the nephron tubule changes

Near the bend, the thin portion of the ascending tubule is now impermeable to water and slightly permeable to solutes

Sodium ions diffuse from the filtrate along their concentration gradient and pass into nearby blood vessels

Focusing on the Loop of Henle in the Proximal Tubule

Focusing on the Loop of Henle in the Proximal Tubule At the thick-walled portion of the ascending limb of

the loop of Henle, sodium ions are moved out of the filtrate by active transport

This transport of Na+ out of the filtrate has 2 consequences: It helps replenish the salty environment of the medulla,

which aids in the absorption of water from filtrate in the descending limb

The removal of sodium ions from the filtrate in the thick-walled portion of the tubule makes the filtrate less concentrated than the tissues and blood in the surrounding cortex tissue

By now, about two thirds of the Na+ and water from the filtrate has been reabsorbed

Focusing on the Loop of Henle in the Proximal Tubule

Tubular Reabsorption and Secretion in the Distal Tubule The active reabsorption of sodium ions from the filtrate into

the capillaries depends on the needs of the body Passive reabsorption of negative ions such as chloride

occurs by electrical attraction The reabsorption of ions decreases the concentration of the

filtrate, which causes water to be reabsorbed by osmosis

Tubular Reabsorption and Secretion in the Distal Tubule Potassium ions (K+) are actively secreted into

the distal tubule from the bloodstream in the capillaries

Hydrogen ions (H+) are also actively secreted from the blood into the distal tubule as necessary in order to maintain the pH of the blood

Other substances that are not normally part of the body, such as penicillin and other medications, are secreted from the blood into the distal tubule

Reabsorption and secretion in the distal tubule are under the control of hormones, as you will see in the next section

Reabsorption from the Collecting Duct The filtrate entering the collecting duct still

contains a lot of water Because the collecting duct extends deep into

the medulla, the concentration of ions along its length increases This concentration of ions is the result of active

transport of ions from the ascending limb of the loop of Henle

This causes the passive reabsorption of water from the filtrate in the collecting duct by osmosis

Reabsorption from the Collecting Duct If blood plasma is too concentrated (for example, if

a person is dehydrated) the permeability to water in the distal tubule and the collecting duct is increased This causes more water to be reabsorbed into the

surrounding capillaries in order to conserve water in the body

In the collecting duct, as in the distal tubule, hormones control reabsorption and secretion

The reabsorption of water in the collecting duct causes the filtrate to become about 4X as concentrated by the time it exits the duct This filtrate, which is approximately 1% of the original

filtrate volume, is now called urine

Section 10.3: Other Functions and Disorders of the Excretory System Kidneys not only filter wastes from the blood,

but also carry out several other important homeostatic functions including: Maintaining the water-salt balance of the blood Regulating blood pH Secreting some hormones

Kidneys also play an important role in maintaining blood pressure They can be damaged if blood pressure gets too

high Blood pressure tests, blood tests, and urinalysis

are used to determine whether the kidneys are functioning properly

Regulating Water-Salt BalanceReabsorption of water The force generated as water moves by

osmosis is called osmotic pressure Osmotic pressure affects many cellular activities,

especially the exchange of materials between cells and blood

Osmoreceptors are cells that are sensitive to osmotic pressure Most are located in the hypothalamus Recall from Chap 8 that the hypothalamus

regulates mechanisms that enable the body to maintain homeostasis Ex: Hunger, thirst, blood pressure, body temperature,

fluid balance, and salt balance

Regulating Water-Salt Balance When blood plasma becomes too concentrated (ex: if

you are dehydrated), osmotic pressure increases Osmoreceptors in the hypothalamus send impulses to

the pituitary gland which causes the release of antidiuretic hormone (ADH) “Anti” means “against” or “opposed to” and “diuresis” means

“increased excretion of urine” So “antidiuresis” means “decreased excretion of urine” ADH travels through the blood to the kidneys

It increases the permeability of the distal tubule and the collecting duct

Allows more water to be reabsorbed into the blood This dilutes the blood and lowers osmotic pressure to

normal

Regulating Water-Salt Balance If blood plasma is too dilute (i.e. if osmotic

pressure is too low) osmoreceptors in the hypothalamus stop or prevent the release of ADH

As a result, the distal tubule and the collecting duct become less permeable to water Allows more water to be excreted in the urine,

concentrating the solutes in the blood The osmotic pressure of the plasma and tissue

fluids rises to normal

Regulating Water-Salt Balance

Regulating Water-Salt Balance In a condition called diabetes insipidus ADH

activity is insufficient Person urinates excessively (as much as 4L – 8L

per day) Thirst is intense, but water is excreted more

quickly than it’s consumed, leading to severe dehydration and ion imbalances

People who have this condition may take synthetic ADH to restore the balance of water reabsorption

Regulating Water-Salt Balance The ethanol in alcoholic beverages is a

diuretic Increases the volume of urine

Alcohol stimulates urine production partly by inhibiting the release of ADH Decreases the permeability of the tubules and

collecting ducts Because it increases water loss to urine,

drinking alcohol actually intensifies thirst and leads to dehydration

Caffeine, a substance in coffee and many carbonated drinks, is also a diuretic

Regulating Water-Salt BalanceReabsorption of salt The kidneys regulate salt balance in the blood

by controlling the excretion and reabsorption of various ions

The sodium ion (Na+) is the most abundant ion in blood plasma Its concentration can fluctuate dramatically

depending on diet and the consumption of beverages with diuretic effects

Regulating Water-Salt Balance Hormones regulate the reabsorption of sodium

at the distal tubule Recall from Chap 9 that aldosterone is a

hormone secreted by the adrenal cortex Stimulates the excretion of potassium ions (K+)

and the reabsorption of sodium ions (Na+) The release of aldosterone is set in motion by

the kidneys themselves

Regulating Water-Salt Balance When blood volume, and therefore blood pressure,

is too low to promote glomerular filtration, the kidneys secrete renin Renin, an enzyme, starts a reaction that eventually

triggers the release of aldosterone from the adrenal cortex

Aldosterone stimulates the distal tubules and collecting ducts to reabsorb Na+ The reabsorption of Na+ is followed passively by

chloride ions and water Aldosterone has the net effect of retaining both salt

and water As a result, blood volume and blood pressure increases

Maintaining Blood pH The normal pH of body fluids is about 7.4

pH at which our enzymes function optimally If homeostasis is not maintained and blood pH goes

above or below 7.4, serious medical conditions can result

Many processes can alter blood pH, such as Eating a meal Drinking liquids Metabolic processes (ex: cellular respiration)

Three mechanisms maintain blood pH at 7.4 Acid-base buffer system Respiratory center The kidneys

Acid-Base Buffer System This system buffers the blood

Prevents changes in pH by taking up excess hydrogen ions (H+) or excess hydroxide ions (OH-) that enter the blood

On of the key buffering reactions in the blood involves carbonic acid (H2CO3) and bicarbonate ions (HCO3

-) When hydrogen ions are added to the blood:

H+ + HCO3- H2CO3

When hydroxide ions are added to the blood:OH- + H2CO3 HCO3

- + H2O These reactions temporarily prevent changes in blood pH

A blood buffer can be overwhelmed unless some more permanent adjustment is made

The next adjustment to maintain blood pH occurs in the lungs

Respiratory System If the hydrogen ion concentration of the blood rises, the

respiratory center in the medulla oblongata increases the breathing rate

Increasing the breathing rate rids the body of hydrogen ions because the following reaction takes place in the lung capillaries:

H+ + HCO3- H2CO3 H2O + CO2

Blood pH decreases Blood pH increases Increased breathing rate pulls the reaction to the right to

generate CO2 more quickly When CO2 is exhaled, the number of hydrogen ions is reduced

It’s important to have the correct proportion of carbonic acid and bicarbonate ions in the blood Breathing readjusts this proportion so that this particular acid-base

buffer system can continue to absorb both H+ and OH- as needed

The Kidneys The acid-base buffer system and respiration

are aided by the more powerful actions of the kidneys to control the acid-base balance of the blood Only the kidneys can rid the body of a wide range

of acidic and basic substances The kidneys are slower acting than the other two

mechanisms, but they have a more powerful effect on pH

The Kidneys Think of the kidneys as excreting H+ and reabsorbing

HCO3- as needed to maintain normal blood pH

If the blood is too acidic, H+ is excreted and HCO3- is reabsorbed

If the blood is too basic, H+ is not excreted and HCO3- is not

reabsorbed Urine is acidic, so H+ is being excreted

The Kidneys Ammonia (NH3) provides another means of

buffering and removing the hydrogen ions in urine (NH3 + H+ NH4

+) Ammonia is produced in tubule cells by the

breakdown of amino acids The ability of the kidneys to control blood pH

is crucial to maintaining an internal environment in which cell enzymes continue to function properly

Releasing Hormones In addition to being part of the feedback loop

for aldosterone, the kidneys release two hormones of their own Erythropoietin Calcitriol

Releasing Hormones If the oxygen-carrying capacity of the blood is

reduced, or oxygen demand increases, sensors in the kidneys stimulate kidney cells to release erythropoietin Stimulates the production of red blood cells in

bone marrow As the number of red blood cells in the blood

increases, the oxygen-carrying capacity of the blood increases

When oxygen delivery to the kidneys returns to normal, the kidneys stop releasing erythropoietin

Releasing Hormones The kidneys also play a role in calcium

regulation in the blood If the level of calcium in the blood falls below

normal, parathyroid hormone (PTH) is released by the parathyroid gland Stimulates the release of calcitriol by the kidneys

Calcitriol (the active form of vitamin D) promotes calcium absorption from the digestive tract

Disorders of the Excretory System The excretory system is vital to maintaining

homeostasis When it’s affected by a disorder, the proper

functioning of other body systems may be jeopardized

Urinary Tract Infection One of the most common disorders of the

excretory system If the bladder is infected, it is called cystitis If only the urethra is infected, it is called urethritis

Urinary tract infections are more common in females than in males Primarily due to difference in anatomy In females, the urethra and anal openings are

closer together, making it easier for bacteria to enter the urinary tract

Urinary Tract Infection Symptoms include:

A painful burning sensation during urination A need to urinate frequently even when no urine is

present Bloody or brown urine The upper abdomen or lower back may be tender Chills, fever, nausea, and vomiting may occur

Have the potential to become serious Can result in permanent damage to kidneys and

possible kidney failure Treatment is usually an antibiotic

In serious cases, surgery may be needed

Kidney Stones Fairly common disorder involving the

development of crystalline formations called kidney stones

Most kidney stones form due to excess calcium in the urine About 85% of stones are made up of calcium

compounds

Kidney Stones The following factors contribute to kidney stone

formation: Recurrent urinary tract infections Insufficient water consumption Low activity levels

Treatment varies depending on the size of the stones Many stones pass through the urinary tract on their own Depending on the cause of the stone formation,

medications may be able to break down the crystals If the stones are less then 20mm in diameter, ultrasound

shock waves can be used to disintegrate the stones so they can be passed naturally in the urine

For larger stones, surgery may be needed to remove them

Renal Insufficiency Renal insufficiency describes the state in which the kidneys

cannot maintain homeostasis due to damage to their nephrons Some causes of nephron damage include:

Kidney infection High blood pressure Diabetes mellitus Polycystic kidney disease (PKD)

A genetic disorder in which cysts grow in the kidneys, impairing proper functioning)

Trauma from a blow to the lower back or constant vibration from machinery

Poisoning (either from skin contact, inhalation of fumes, or ingestion of contaminated food) by heavy metals such as mercury and lead or solvents such as paint thinners

Atherosclerosis (which reduces blood flow to the kidneys) Blockage of the tubules

Renal Insufficiency Nephrons can regenerate and restore kidney

function after short-term injuries Even when some of the nephrons are irreversibly

damaged, others can compensate for their lost function

A person can survive on as little as one third of one kidney

If 75% or more of the nephrons are destroyed, however, urine output is inadequate to maintain homeostasis Under these circumstances, a person requires a

means for replacing kidney function This is achieved either with a kidney transplanted

from a donor, is one is available, or with an artificial kidney that performs a blood-cleansing process called dialysis

Hemodialysis and Peritoneal Dialysis The diffusion of dissolved substances through a

semipermeable membrane is referred to as dialysis These substances more across a membrane from the area

of high concentration to one of low concentration Substances more concentrated in blood diffuse into the

dialysis solution, called the dialysate Substances more concentrated in the dialysate diffuse

into the blood Other substances can be added to the blood

following this same principle Ex: If the acid-base balance of the blood is off and the

blood is too acidic, bicarbonate ions can be added to the dialysate where they will diffuse into the blood and reduce its acidity

Hemodialysis and Peritoneal Dialysis There are two main types of renal (kidney)

dialysis Hemodialysis

Utilizes an artificial membrane in an external device (essentially an artificial kidney) that is connected to an artery and a vein in person’s arm

Peritoneal dialysis Utilizes the lining of the intestines, called the

peritoneum, as the dialysis membrane Dialysate is introduced to the abdominal cavity,

where the large surface area and rich supply of capillaries of the peritoneum slowly filter the blood

Kidney Transplants Dialysis enables people with kidney disease to

continue many of their daily activities, such as going to a job or attending school Dialysis is not a cure, and it’s not intended to be a

long-term solution to the problem of kidney disease

Individuals with 10% or less kidney function will eventually have a replace their kidneys The need for kidneys is much greater than the

available supply 75% of people waiting for in Canada are waiting

for kidneys

Kidney Transplants The success rate of organ transplantation,

particularly of kidneys, is fairly high Success rate of 95%-98%

Surgical techniques, such as the laproscopic surgery are constantly being improved

New medicines to prevent rejection of the new organ are constantly being developed and improved

The Kidney-Coronary Connection High blood pressure is one of the main reasons that kidneys

begin to fail When blood pressure is high for a prolonged period of time, the heart

must pump a greater volume of blood, and blood vessels can be damaged

The blood vessels in the kidneys are very sensitive to changes in blood pressure If they become damaged by high blood pressure the amount of waste

and extra fluid that can be filtered from the blood will be reduced As the extra fluid accumulates in the body, it will increase the blood

volume even more and cause the blood pressure to rise further This cycle can continue until the kidney function is so reduced that

symptoms become obvious Unfortunately, both high blood pressure and kidney

impairment don’t have obvious symptoms until the damage is well underway

The Kidney-Coronary Connection Maintaining a healthy lifestyle supports the overall

health of all your body systems None of these systems functions in isolation, so any

activity that affects one of your systems will affect other systems as well For example, ensuring that you have adequate physical

exercise can help make your heart and circulatory system stronger and healthier

A stronger heart can pump more blood throughout the body with less effort

Reduced effort translates to less force on the arteries, keeping blood pressure low

High blood pressure has such an impact on kidney function that exercise to reduce blood pressure ultimately reduces the likelihood of kidney damage

Evaluating Kidney Function The composition of urine reflects the amounts of water

and solutes that the kidneys must remove from or retain in the body to maintain homeostasis

Analyzing the physical and chemical composition of urine enables physicians to make reasoned inferences and hypotheses about a person’s health and kidney function

In fact, physicians have been using urinalysis as a tool for thousands of years Examining the characteristics of urine, including colour, odour,

and taste, gave clues as to the internal conditions of the person’s body

Ex: If the urine smelled sweet or fruity, it was usually a sign of diabetes (the overabundance of sugar in the blood led to an overabundance of sugar in the urine as your body attempted to expel the excess)

Urinalysis This table provides values

for selected tests that are performed in a modern day urinalysis

These values are consistent with those of urine from a healthy adult

However, urine composition varies greatly over the course of a day due to factors such as: Dietary intake Physical activity Emotional stress Fatigue

Urine Test Accepted Healthy Value

Acetone and ketones

0

Albumin (protein)

0-trace

Bilirubin (a breakdown product of hemoglobin)

0

Calcium <150 mg/dayColour and clarity

Pale yellow to light amber; transparent

Glucose 0pH 4.5-8.0Urea 25-35 g/dayUric acid 0.5-1/0 g/day

Urinalysis Unhealthy constituents of urine may not

necessarily indicate illness or disease The presence of glucose in urine may result from a

sugary meal Proteins may appear in urine following vigorous

exercise Ketones (acids that result from the digestion of

fats when the body lacks sufficient stores of carbohydrates) may result from a short-term fast or a specifically designed low-carbohydrate diet

Because so many factors can influence the presence and amounts of substances in urine, trained professionals must consider a wide variety of variable when evaluating a sample of urine

Blood Tests Blood tests can also reveal information about kidney

function For example, health professionals may screen the blood

to measure the amount of urea nitrogen it contains If levels are higher than normal, it can indicate that the

kidneys are not working properly When kidneys are functioning properly, urea is filtered from

the blood Another measurement that may be measured is the

amount of creatinine in the blood Creatinine is waste produced by muscles during metabolic

processes A high level indicates that the kidneys are not filtering it

properly