Functions of the Urinary SystemFunctions of the Urinary System

Rinal diseas =09i8d Nitrogenous wastes

Toxins

Drugs

Blood Flow in the KidneysBlood Flow in the Kidneys

Figure 15.2c

The structural and functional units of the kidneys

Responsible for forming urine

Main structures of the nephrons

A specialized capillary bed

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

arteriole

Narrow efferent arteriole Figure 15.3c

GlomerulusGlomerulus

Capillaries are covered with podocytes from the renal tubule

The glomerulus sits within a glomerular (Bowman’s) capsule (the first part of the renal tubule) Figure 15.3c

Renal TubuleRenal Tubule

Figure 15.3b

Types of NephronsTypes of Nephrons

Located entirely in the cortex

Includes most nephrons

Figure 15.3a

Types of NephronsTypes of Nephrons

Found at the boundary of the cortex and

medulla (loop of Henle dips into medulla)

Figure 15.3a

Glomerular CapillariesGlomerular Capillaries Afferent arteriole feeds glomerular capillary bed

Efferent arteriole drains glomerular capillary bed

Arterioles are high resistance vessels

Afferent diameter is greater than Efferent diameter, so blood pressure in glomerulus is extremely high

The high BP forces fluids and solutes out of the blood and into the glomerular capsule that drains into the collecting tubule

Peritubular CapillariesPeritubular Capillaries

Arise from efferent arteriole of the glomerulus

Normal, low pressure capillaries

Attached to a venule

Cling close to the renal tubule

Reabsorb (reclaim) some substances from collecting tubes

Urine Formation ProcessesUrine Formation Processes

Figure 15.4

FiltrationFiltration

Water and solutes smaller than proteins are forced through capillary walls

Blood cells cannot pass out to the capillaries

Filtrate is collected in the glomerular capsule and leaves via the renal tubule

ReabsorptionReabsorption

Some water

Glucose

Amino acids

Ions

Some reabsorption is passive, most is active

Most reabsorption occurs in the proximal convoluted tubule (PCT)

Materials Not ReabsorbedMaterials Not Reabsorbed

Nitrogenous waste products Urea

Uric acid

Creatinine

Excess water

Secretion – Reabsorption in Secretion – Reabsorption in ReverseReverse

Some materials move from the peritubular capillaries into the renal tubules

Hydrogen and potassium ions

Creatinine

Materials left in the renal tubule move toward the ureter

Formation of UrineFormation of Urine

Figure 15.5

Characteristics of Urine Used for Characteristics of Urine Used for Medical DiagnosisMedical Diagnosis

Colored somewhat yellow (straw) due to the pigment urochrome (from the destruction of hemoglobin) and solutes

Sterile

Slightly aromatic

Normal pH of around 6

Specific gravity of 1.001 to 1.035

Characteristics of Urine Used for Characteristics of Urine Used for Medical Diagnosis (Dip Stick)Medical Diagnosis (Dip Stick)

= excessive sugar intake, diabetes mellitus

= physical activity, pregnancy, glomerulonephritis, hypertension

= urinary tract infection

= bleeding (kidney stone, infection)

= transfusion reaction, hemolytic anemia

= hepatitis

UretersUreters

Continuous with the renal pelvis

Enter the posterior aspect of the bladder

Runs behind the peritoneum

Peristalsis aids gravity in urine transport

Urinary BladderUrinary Bladder Smooth, collapsible, muscular sac

Temporarily stores urine

Retroperitoneal, behind pubic symphysis

Figure 15.6

Urinary BladderUrinary Bladder

– three openings

Two from the ureters

One to the urethrea

Figure 15.6

Urinary Bladder WallUrinary Bladder Wall Three layers of smooth muscle (

)

Mucosa made of transitional epithelium

Walls are thick and folded in an empty bladder

In males the prostate gland surrounds the neck of the bladder where it empties into urethra

UrethraUrethra

Thin-walled tube that carries urine from the bladder to the outside of the body by peristalsis

Release of urine is controlled by two sphincters

Urethra Gender DifferencesUrethra Gender Differences

Length

Females – 3–4 cm (1.5 inches)

Males – 20 cm (8 inches)

Location

Females – along wall of the vagina, opening anterior to vaginal opening

Males – through the prostate and penis

Urethra Gender DifferencesUrethra Gender Differences

Function

Females –

Males –

3 parts of urethra in males

– through prostate

– through membraneous tissue between prostatic and penile

– through penis

Both sphincter muscles must open to

allow voiding

The internal urethral sphincter is relaxed after stretching of the bladder

Activation is from an impulse sent to the spinal cord and then back to bladder via the pelvic splanchnic nerves causing contractions

This sends urine past internal sphincter, and causes the sensation of having to void

The external urethral sphincter must be voluntarily relaxed

Fluid, Elecrolyte, & Acid-Base BalanceFluid, Elecrolyte, & Acid-Base Balance Blood composition depends on:

Diet, cellular metabolism, & urine output

In 24 hours the kidneys filter 150 – 180 liters of blood plasma, but only 1 – 1.8 liters of urine is produced

Filtrate is same as blood plasma, and as it moves along CD the kidney reabsorbs the good stuff (water, nutrients, ions), and secretes more of the bad stuff (nitrogenous wastes, and unneeded substances)

The left over filtrate is Urine

Fluid, Elecrolyte, & Acid-Base BalanceFluid, Elecrolyte, & Acid-Base Balance

Kidney’s role in blood composition:

1)

2)

3)

4)

Maintaining Water BalanceMaintaining Water Balance

Normal amount of water in the human body

Young adult females – 50% (F>fat, F<musles)

Young adult males – 60%

Babies – 75% (low fat, low bone mass)

Old age – 45%

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

Distribution of Body Fluid (Fluid Distribution of Body Fluid (Fluid Compartments)Compartments)

Interstitial fluid

Blood plasma

CSF, lymph, serous, eye humors, etc.

Figure 15.7

The Link Between Water and SaltThe Link Between Water and Salt

Changes in electrolyte balance (solute concentrations in/between compartments) causes water to move from one compartment to another

Alters blood volume and blood pressure

Can impair the activity of cells

Maintaining Water BalanceMaintaining Water Balance Sources for water intake

Ingested foods and fluids

Water produced from metabolic processes

Cellular metabolism (small amount)

Sources for water output Vaporization out of the lungs Lost in perspiration Leaves the body in the feces Urine production (will vary w/ kidney control)

Maintaining Water BalanceMaintaining Water Balance

Dilute urine is produced if water intake is excessive

Less urine (concentrated) is produced if large amounts of water are lost

Likewise, proper concentrations of various electrolytes must be present

Regulation of Water and Electrolyte Regulation of Water and Electrolyte ReabsorptionReabsorption

Regulation is primarily by hormones prevents

excessive water loss in urine

regulates sodium ion content of extracellular fluid

Triggered by the rennin-angiotensin mechanism

Cells in the kidneys and hypothalamus are active monitors

Maintaining Water and Electrolyte Maintaining Water and Electrolyte BalanceBalance

Figure 15.9

Maintaining Acid-Base Balance in Maintaining Acid-Base Balance in BloodBlood

Blood pH must remain between 7.35 and 7.45 to maintain homeostasis

Most (hydrogen) ions originate as byproducts of cellular metabolism

Maintaining Acid-Base Balance in Maintaining Acid-Base Balance in BloodBlood

Most acid-base balance is maintained by the kidneys

Other acid-base controlling systems

Blood buffers

Respiration (blow of CO2, Carbonic Acid)

Blood BuffersBlood Buffers 1st line of defense, because quick to act

Molecules react to prevent dramatic changes in hydrogen ion (H+) concentrations Bind to H+ when pH drops

Release H+ when pH rises

Three major chemical buffer systems

Acid-Base ReveiwAcid-Base Reveiw Acid – proton (H+) donor, decreases pH

Strong Acid – dissociate completely and give up a lot of H+, decreases pH significantly

Weak Acid – dissociate partially and gives up a few H+, lowering pH only slightly (ex: carbonic acid)

Weak acids get stronger (release more H+) as pH rises

Buffer system

Acid-Base ReveiwAcid-Base Reveiw Base – proton (H+) acceptor, increases

pH Strong Base – dissociate completely and

tie up a lot of H+, raising pH significantly

Weak Base – dissociate partially and tie up a few H+, raising pH only slightly (ex: bicarbonate ion, ammonia)

Weak bases get stronger (tie up more H+) as pH decreases

Buffer system

The Bicarbonate Buffer SystemThe Bicarbonate Buffer System Mixture of carbonic acid (H2CO3, weak acid)

and sodium bicarbonate (NaHCO3, weak base)

Bicarbonate ions (HCO3–) react with strong

acids (HCl) to change them to weak acids and salt

Carbonic acid dissociates in the presence of a strong base to form a weak base and water

Weak bases/acids do not cause fluctuations in pH, thus allowing us to maintain a narrow range of 7.35-7.45

Respiratory System Controls of Respiratory System Controls of Acid-Base BalanceAcid-Base Balance

Carbon dioxide in the blood is converted to bicarbonate ion and transported in the plasma

Increases in hydrogen ion concentration produces more carbonic acid

Excess hydrogen ion can be blown off with the release of carbon dioxide from the lungs

Respiratory rate can rise and fall depending on changing blood pH (stim. Chemoreceptors in respiratory centers in brain)

Renal Mechanisms of Acid-Base Renal Mechanisms of Acid-Base BalanceBalance

Slow processes, takes hours to days

1)

2)

Urine pH varies from 4.5 to 8.0

Developmental Aspects of the Developmental Aspects of the Urinary SystemUrinary System

Functional kidneys are developed by the third month

Urinary system of a newborn

Bladder is small

Urine cannot be concentrated

Developmental Aspects of the Developmental Aspects of the Urinary SystemUrinary System

Control of the voluntary urethral sphincter does not start until age 18 months

Urinary infections are the only common problems before old age

Aging and the Urinary SystemAging and the Urinary System

There is a progressive decline in urinary function

The bladder shrinks with aging

Urinary retention is common in males