Chapter 15 The Urinary System. Functions of the Urinary System Elimination of waste products Nitrogenous wastes Toxins Drugs Regulate aspects

Chapter 15The Urinary System

Functions of the Urinary SystemFunctions of the Urinary System

Elimination of waste products Nitrogenous wastes

Toxins

Drugs

Regulate aspects of homeostasis Volume and chemical makeup of

the blood

Water and electrolyte balance

Acid-base balance in the blood

Produce hormones Renin: regulates blood pressure

and kidney function

Erythropoietin: red blood cell production

Organs of the Urinary systemOrgans of the Urinary system Kidneys

Filters about 200 liters of fluid daily (47 gallons!)

Major excretory organs

Ureters Transport urine from kidneys to

bladder

Urinary bladder Temporary storage reservoir for

urine

Urethra Transports urine from bladder to

the external environment

Location of the KidneysLocation of the Kidneys Bean-shaped organ

Lies in the superior lumbar region

Extends from T12 to L3

Right kidney is slightly lower than the left

Average dimensions (about the size of a bar of soap)

12 cm long; 6 cm wide; 3 cm thick

Lateral surface is convex

Medial surface is concave

Renal hilum

The ureter, blood vessels, lymphatic vessels and nerves all join the kidney here

Atop each kidney is an adrenal gland

Regions of the KidneyRegions of the Kidney Renal cortex

Outer region

Renal medulla

Inside the cortex

Exhibit medullary pyramids

Renal columns separate the pyramids

Renal pelvis

Inner funnel-shaped tube

Continuous with the ureter leaving the hilum

Figure 15.2b

Kidney StructuresKidney Structures

Medullary pyramids

Triangular regions of tissue in the medulla

Calyces

Cup-shaped structures that collect urine from the medullary pyramids and empty it into the renal pelvis

Major calyces and minor calyces

Blood Flow in the KidneysBlood Flow in the Kidneys As each renal artery approaches a kidney, it divides into five segmental

arteries

Each segmental artery branches further to form lobar arteries and then interlobar arteries

The interlobar arteries branch into the arcuate arteries that arch over the bases of the medullary pyramids

Small interlobular arteries radiate outward from the arcuate arteries to supply the cortical tissue

Afferent arterioles branching from the interlobular arteries turn into microscopic blood vessels called the glomerulus, which is the key element of kidney function

Blood Flow in the KidneysBlood Flow in the Kidneys Veins trace the pathway of arterial supply in reverse

Blood leaving the renal cortex (efferent arteriole) drains into the interlobular veins, arcuate veins, interlobar vein and then renal vein(notice no segmental veins) and then the renal vein empties into the inferior vena cava

Blood Flow in the KidneysBlood Flow in the Kidneys

NephronsNephrons The structural and functional units of the kidneys

Kidneys contains over 1 million of these tiny blood-processing units

Responsible for forming urine

Each nephron consists of a glomerulus (capillaries) and renal tubule

The renal tubule has a cup-shaped end called the glomerular capsule or Bowman’s capsule

GlomerulusGlomerulus A specialized capillary bed

Attached to arterioles on both sides (maintains high pressure) Large afferent arteriole

Narrow efferent arteriole

Endothelium of the capillaries is very porous

This allows large amounts of solute-rich, protein free fluid to pass from the blood to the glomerular capsule

Filtrate contains everything found in blood plasma except proteins

Urine contains mostly metabolic wastes and unneeded substances

Figure 15.3c

Renal TubuleRenal Tubule Four parts to the renal tubules

Glomerular (Bowman’s) capsule

Proximal convoluted tubule (PCT)

Walls are cuboidal epithelial cells with dense microvilli

Increases the surface area to reabsorb water and solutes from the filtrate

Loop of Henle

Descending end walls are similar to PCT

Distal convoluted tubule (DCT)

Empties into a collecting duct

The length enhances its filtrate processing capabilities

Figure 15.3b

Renal TubuleRenal Tubule Collecting ducts

Receive filtrate from many nephrons

Run through the medullary pyramids

As they reach the renal pelvis, a couple fuse together and deliver urine into the minor calyces

Figure 15.3b

Nephron Capillary BedsNephron Capillary Beds

The renal tubule of every nephron is closely associated with two capillary beds

Glomerulus

Produces the filtrate

Peritubular capillaries

Reclaims most of the filtrate

Nephron Capillary BedsNephron Capillary Beds Glomerulus is specialized for

filtration

Blood pressure in glomerulus is extremely high to easily force fluids and solutes out of the blood

Afferent arteriole is feeding the glomerulus and it is larger in diameter than the efferent arteriole draining the bed

Between the blood and glomerular capsule lies a filtration membrane

Porous membrane that allows free passage of all plasma components (water and solutes) but not blood cells

Nephron Capillary BedsNephron Capillary Beds Peritubular capillaries

Arise from efferent arteriole of the glomerulus

Cling close to the renal tubule and empty into nearby venules

Normal, low pressure capillaries

Readily absorb solutes and water from collecting tubes

Most of the resulting filtrate (99%) is reabsorbed by the renal tubule and returned to the blood in the peritubular capillaries

Kidney Physiology: Urine FormationKidney Physiology: Urine Formation


The total plasma filters into the renal tubules about every 22 minutes

All of our plasma would be drained away as urine in less than 30 minutes were it not for the fact that most of the tubule contents are quickly reclaimed and returned to the blood

1. Renal artery brings blood into each kidney.

2. Blood vessels branch off the main artery until they form the glomerulus (specialized capillary bed)

3. Water and other small substances such as glucose, salts, amino acids and urea are filtered out of the glomerulus and into the Bowman’s capsule.

4. As the filtrate flows through the renal tubule (PCT, loop of Henle and DCT) most of the water and nutrients are reabsorbed back into the peritubular capillaries that wrap around the nephrons.

5. Some materials are secreted back into the tubules from the blood.

6. The cleaned blood, which has slightly less water and much less waste material, leaves each kidney in the renal vein to the inferior vena cava.

7. The yellow fluid that remains in the tubule is called urine.

8. Urine leaves each kidney through the ureter and flows into the urinary bladder, where urine is stored.


• Pathway of Urine

• Bowman’s capsule (filtrate)Proximal convoluted tubule (filtrate) loop of Henle (filtrate) distal convoluted tubule (filtrate) collecting duct (urine) minor calyces (urine) major calyces (urine) ureter (urine) bladder (urine) urethra(urine)


Kidney Physiology: Urine FormationKidney Physiology: Urine Formation Kidneys form urine in the nephrons and adjust

the blood composition with three major processes

Glomerular filtration (#1)

Dump filtrate into renal tubules

Filters about 200 L daily and only 1.5L leaves the body as urine

Tubular reabsorption (#2)

Kidneys reclaim what the body needs

Almost all the filtrate (99%)

Water, salt, glucose and amino acids

Not reabsorbed is uric acid, creatinine, urea

Anything not reabsorbed becomes urine

Tubular secretion (#3)

Fine-tuning the body’s chemical balance

Kidney Physiology: Urine FormationKidney Physiology: Urine Formation Step 1: Glomerular Filtration

Passive, nonselective process

Glomerular blood pressure is extremely high

Pressure forces fluids and solutes through a membrane

Small molecules such as water, salts, bicarbonate, hydrogen ions, urea, glucose, amino acids and some drugs

Blood cells and large molecules cannot pass through the wall

Kidney Physiology: Urine FormationKidney Physiology: Urine Formation Step 2: Tubular Reabsorption

Selective process

Begins as soon as the filtrate enters the proximal tubules

Most organic nutrients are completely reabsorbed

Hormones regulate the reabsorption of water and many ions

Depending on substances transported, the reabsorption can be passive or active

Sodium ions are the single most abundant cation in the filtrate


Reabsorptive abilities of regions of the renal tubules

Proximal convoluted tubule (PCT) Most active reabsorbing area

Sodium (Na+), bicarbonate (HCO3-),

chlorine (Cl-) and water

Loop of Henle Water is salts are reabsorbed

Vital role in kidneys ability to form dilute or concentrated urine

Distal convoluted tubule (DCT) NaCl and water

Most reabsorption at this time depends on the body’s needs


Regulated by hormones

Aldosterone

Released when blood pressure decreases or Na+ concentration drops

Antidiuretic hormone (ADH)

Reabsorption of water

Kidney Physiology: Urine FormationKidney Physiology: Urine Formation Step 3: Tubular Secretion

Substances such as H+, NH4+, creatinine, organic acids move from the

capillaries into the renal tubule

Important for disposing substances, such as drugs or poisons that can not be filtered

Eliminates undesirable substances or end products that have been reabsorbed by passive processes like urea and uric acid

Physical Characteristics of UrinePhysical Characteristics of Urine

Color

Clear to deep yellow

Yellow color is due to the pigment urochrome (from the destruction of hemoglobin)

More concentrated the urine, the deeper the yellow color

An abnormal color such as pink or brown may result from eating certain foods (beets, rhubarb), the presence of bile pigments or blood, or from some commonly prescribed drugs and vitamins

Cloudy urine may indicated a urinary tract infection

Odor

Slightly aromatic

If allowed to stand, it develops an ammonia odor as bacteria metabolize its urea solutes

Physical Characteristics of UrinePhysical Characteristics of Urine

pH

Slightly acidic (around pH 6)

Acidic diet that contains large amounts of protein and whole wheat products, diabetes mellitus and starvation produces acidic urine

Vegetarian diet, prolonged vomiting, and bacterial infection of the urinary tract all can cause the urine to become alkaline

Specific gravity

Ratio of the mass of a substance to the mass of an equal volume of distilled water

Urine is water plus solutes

Distilled water specific gravity is 1.00

Urine specific gravity ranges from 1.001 to 1.035 depending on its solutes

Chemical Composition of UrineChemical Composition of Urine Urine is 95% water and 5% solutes

Solutes

Urea (largest component)

Derived from the normal breakdown of amino acids

Uric acid

End product of nucleic acid metabolism

Creatinine

Metabolite for creatinine phosphate which stores energy for the regeneration of ATP

Normal solute concentrations in urine from high to low

Urea sodium potassium phosphate sulfate creatinine uric acid

Chemical Composition of UrineChemical Composition of Urine Abnormal Urinary Constituents

Glucose (glycosuria) Benedict’s solution and heat

Causes: diabetes mellitus

Proteins (proteinuria) Biuret’s solution

Causes: Non-pathological: excessive physical exertion, pregnancy, high-protein diet; Pathological: heart failure, severe hypertension, renal disease

Chemical Composition of UrineChemical Composition of Urine Abnormal Urinary Constituents

Hemoglobin (hemoglobinuria)

Causes: transfusion reaction, hemolytic anemia, severe burns, etc.

Bile pigments (bilirubinuria)

Causes: liver disease (hepatitis, cirrhosis)

Erythrocytes (hematuria)

Causes: bleeding (due to trauma, kidney stones, or infection)

Leukocytes (pyuria)

Causes: urinary tract infection

UretersUreters Slender tubes that carry urine from the kidneys to the bladder

Composed of transitional epithelium

Peristalsis aids gravity in urine transport

Homeostatic Imbalance

Kidney stones

Calcium, magnesium, or uric acid salts in urine may crystallize and precipitate in the renal pelvis

Most are under 5 mm in diameter and pass through the urinary tract without causing problems

Larger stones can obstruct a ureter and block urine drainage

Increasing pressure in the kidney causes excruciating pain

Treatment includes shock wave lithiotripsy a noninvasive procedure that uses ultrasonic shock waves to shatter the stone

Urinary BladderUrinary Bladder

Smooth, collapsible, muscular sac that temporarily stores urine

Located on the pelvic floor just posterior to the pubic symphysis

Interior has three openings called trigone

Two from the ureters

One to the urethra

Urinary BladderUrinary Bladder

When empty, the bladder collapses and its walls are thick and have folds (rugae)

Bladder can expand significantly

A full bladder is about 12 cm (5 inches) long and holds approximately 500 mL (1 pint) of urine, but it can hold nearly double that if necessary

Maximum capacity of the bladder is 800-1000 mL and when it is overdistended, it may burst

Urine is formed continuously by the kidneys but it is stored in the bladder until it is convenient to release

UrethraUrethra

Thin-walled muscular tube that drains urine from the bladder to the outside of the body

Release of urine (micturition or voiding)is controlled by two sphincters

Internal urethral sphincter (involuntary)

External urethral sphincter (voluntary)

Urethra Gender DifferencesUrethra Gender Differences Length and function of the urethra differ in the two sexes

Females

Length: only 3–4 cm (1.5 inches)

Function: carries only urine out of the body

Males

Length: Urethra is 20 cm (8 inches) long

Double function: carries semen and urine out of the body

Maintaining Water BalanceMaintaining Water Balance

Normal amount of water in the human body

Young adult females – 50% because more body fat

Young adult males – 60% because more muscles

Babies – 75% because of low body fat and low bone mass

Old age – 45%

Water is necessary for many body functions and levels must be maintained

Distribution of Body FluidDistribution of Body Fluid Total body water volume is 40 L or

60% of body weight

Water occupies two main fluid compartments within the body

Intracellular fluid (inside cells)

About 25 L or 40% body weight

Extracellular fluid (outside cells)

About 15 L or 20% body weight

Divided into two subcompartments

Interstitial fluid (fluid in the microscopic spaces between tissue cells)

Blood plasma (fluid portion of blodd)

Composition of Body FluidsComposition of Body Fluids Water is the universal solvent in which a variety of solutes are dissolved

Solutes can be classified into electrolytes and nonelectrolytes

Nonelectrolytes have bonds and cannot dissociate in solution

Organic molecules such as glucose, lipids, creatinine and urea

Electrolytes are chemical compounds that do dissociated into ions in water

Inorganic and organic acids and bases and some proteins

Have the greatest ability to make fluid shifts down their gradients

Most abundant solutes in body fluids

Extracellular fluids have high sodium and chloride ions

Intracellular fluids contains only small amounts of sodium and chloride ions; its most abundant cation is potassium anion is phosphate (HPO42-) as well as high amounts of proteins

Fluid Moving Among CompartmentsFluid Moving Among Compartments

Continuous exchange and mixing of fluids are regulated by osmotic and hydrostatic pressures

Water moves freely between the compartments along osmotic gradients

Solutes are unequally distributed because of their size, electrical charge, or dependence on transport proteins

Changes in electrolyte balance causes water to move from one compartment to another

Maintaining Water BalanceMaintaining Water Balance Body must remain properly hydrated water intake must equal water

output Water intake is typically about 2500 mL a day in adults

Water enters the body through ingested liquids (60%), solid foods (30%) and produced from metabolic processes (10%

Water output occurs by several routes Vaporization out of the lungs and skin (28%)

Perspiration of skin (8%)

Leaves the body in the feces (4%)

The balance (about 60%) is excreted by the kidneys in urine

Maintaining Water BalanceMaintaining Water Balance

A rise in plasma concentration causes thirst (prompts us to drink water) and release of antidiuretic hormone (ADH) which causes the kidneys to conserve water and excrete concentrated urine

A decline in plasma concentration inhibits thirst and ADH release and causes output of large volumes of dilute urine

Regulation of WaterRegulation of Water Water intake is controlled by the thirst mechanism

An increase in plasma concentrations

A dry mouth occurs

Less saliva production

Decrease in blood pressure

Water Output of certain amounts of water is unavoidable

Reason why we cannot live without drinking

Solute concentration and volume of urine excreted depend on fluid intake, diet and water loss via other avenues

Regulation is primarily by hormones Antidiuretic hormone (ADH) prevents excessive water loss in urine

Aldosterone regulates sodium ion content of extracellular fluid

Osmoreceptor cells in the kidneys are active monitors

Regulation of WaterRegulation of Water Dehydration

When water output exceeds intake over a period of time and the body is in negative fluid balance

Commonly follows hemorrhage, severe burns, prolonged vomiting or diarrhea, profuse sweating, and diuretic abuse

Signs are sticky oral mucosa, thirst, dry flushed skin, and decreased water output (oliguria)

Electrolyte BalanceElectrolyte Balance Refers to the salt balance in the body

Important in controlling fluid movements and crucial for cellular activity

Salts enter the body in foods and fluids

Salts are lost from the body in perspiration, feces and urine

Sodium holds a central position in fluid and electrolyte balance and overall body homeostasis

Water follows salt

A change in plasma sodium levels affects not only plasma volume and blood pressure but also the ICF and IF volumes

Regulation is linked to blood pressure and aldosterone

When aldosterone is high all the sodium is reabsorbed in the DCT

Water follows sodium and maintains blood pressure

When aldosterone is inhibited none of the sodium is reabsorbed

Goal of aldosterone is to decrease urinary output and increase blood volume

Acid-Base Balance Acid-Base Balance All biochemical reactions are influenced by the pH of their fluid

environment

The acid-base balance of body fluids is closely regulated

pH measures the amount of H+ ions in solution

Acids are proton donors

Blood normally ranges between pH 7.35 and pH 7.45

If the pH rises above 7.45 a person has alkalosis

If the pH drops below 7.35 a person has acidosis

H+ concentration regulation

Chemical buffers resist changes within a fraction of a second

Respiratory rate changes within 1-3 minutes

Kidneys requires hours to a day to effect changes in blood pH

Acid-Base Balance Acid-Base Balance Respiratory acidosis

Most common cause of acid-base imbalance

Caused when a person breathes shallow or when gas exchange is hampered by diseases

CO2 accumulates in the blood and causes the pH to fall

Respiratory alkalosis

Results from carbon dioxide being eliminated faster than it is produced otherwise known as hyperventilation

Metabolic acidosis

Second most common cause of acid-base imbalance

Low blood pH and HCO3- levels

Caused when a person ingests too much alcohol and excessive loss of HCO3- as a result of excessive diarrhea

Metabolic alkalosis

Rising blood pH and HCO3- levels

Caused by vomiting and intake of excess base

Acid-Base Balance Acid-Base Balance Effects of acidosis and alkalosis

Absolute blood pH limits for life are a low of 7.0 and a high of 7.8

When the pH falls below 7.0 the CNS is so depressed that the person goes into coma and death

When blood pH rises above 7.8, the nervous system is overexcited and leads to muscle spasms, extreme nervousness, and convulsions; death usually results from respiratory arrest

Documents

Chapter 15 The Urinary System. Functions of the Urinary System Elimination of waste products Nitrogenous wastes Toxins Drugs Regulate aspects