The Urinary System
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Urinary System Functions
 3 main functions:
 Excretion – _____________________________________________________________________
 Elimination – ___________________________________________________________________
 ______________________________________________________________________________
 4 other essential homeostatic functions:
 Regulating blood volume and pressure
 Helping to stabilize blood pH
 Conserving valuable nutrients
Parts/Path of the Urinary Tract
 _______________ produce urine
 Urine travels though the _______________ to the urinary bladder
 The _______________
_______________ stores urine until you are ready for excretion
 Urine leaves the urinary bladder through the _______________ and exits the body
The Kidneys
 The right kidney sits slightly lower than the left
 Each kidney is covered by a fibrous capsule and is packed is a cushion of adipose tissue (fat)
 Typically reddish-brown in color and about 4in long
 Indentation along the medial side called the _______________ that is the site of exit for the ureter and
renal vein and the site of entrance for the renal artery and nerve
 Sectional anatomy
 ______________________________
 ______________________________
 Contains 6-18 renal pyramids (______________________________________________)
 The tip of each pyramid is the renal papilla
 Urine is discharged into the minor calyx from the renal papilla
 4-5 minor calyces join to form the 2 major calyces
 The 2 major calyces join to form the renal pelvis (connected to the ureter)
The Kidneys – The Nephron
 _____________________________________________________________________________________
 ______________________________________________________________________________
 2 types: cortical (in the cortex) and juxtamedullary (near the medulla)
 Begins at the renal corpuscle – a round structure consisting of the glomerular (______________) capsule
and a capillary network (_______________) within separated by capsular space
 Blood pressure forces fluid and dissolved solutes out of the capillaries and into the surrounding
capsular space. _________________________________________________________________
 The advantage of filtration is that it is passive, so it requires no energy expense.
However, its large pores allow needed ions and nutrients to escape
 Filtrate then enters the renal tubule
 3 parts: ________________________________________________________________________
 As filtrate travels through it changes composition and becomes tubular fluid
 The job of the renal tubule is to reabsorb all of the useful organic molecules from filtrate,
_______________________________________________, and secrete waste products that
were missed by the filtration process
 ________________________________________________________________________
Finally empties into the collecting system
 Many nephrons release tubular fluid into a collecting duct and then several collecting ducts
merge to form a papillary duct, which deliver urine to a minor calyx
Blood supply to the kidneys
 Every minute about _______________ of the cardiac output of blood flows through the kidneys
Urine Formation
 _____________________________________________________________________________________
 The excretion of urea, creatinine, and uric acid is especially important in this process
 The kidneys must concentrate urine to avoid large amounts of water loss
 To do this the kidneys must perform 3 processes:
 _______________ – blood pressure forces water across the filtration membrane in the
renal corpuscle. Solute molecules small enough to pass through the membrane are
carried into the filtrate with water
 _______________ – this is the removal of water and solute molecules from the filtrate
and their reentry into the circulation at the peritubular capillaries
 _______________ – the transport of solutes from the paratubular capillaries, across the
tubular epithelium, and into the filtrate
Summary of Kidney Function & Urine Formation
 Step 1 - ______________________________________________________________________________
 Step 2 - In the PCT 60-70% of the water and almost all of the dissolved nutrients are reabsorbed
 Step 3 - From the PCT going towards the loop of Henle, water moves into surrounding interstitial fluid
and then into the peritubular capillaries, leaving a small volume of highly concentrated tubular fluid
 Step 4 - Going from the loop to the DCT, tubular cells actively pump sodium and chloride ions out of
tubular fluid
 Step 5 - Final concentration and composition of tubular fluid is determined in the DCT
 Step 6 - Concentration of urine is determined
 Step 7 - ______________________________________________________________________________
Glomerular Filtration Rate (GFR)
 _____________________________________________________________________________________
 GFR is regulated in 3 ways:
1. Local, automatic adjustments in glomerular pressures
 ________________________________________________________________________
2. Activities of the sympathetic division of the ANS
 Primarily shift blood flow away from the kidneys, lowering the GFR and slowing the
production of filtrate
3. The effects of various hormones (long-term adjustments)
 4 main hormones:
 _________________________________
o Vasoconstriction in capillary beds, constriction of efferent arterioles in
the nephron, triggers release of ADH, and stimulates secretion of
aldosterone
 _________________________________
o Increases water permeability in the DCT and collecting duct
o Induces sensation of thirst
 _________________________________
o Stimulates reabsorption of sodium ion and secretion of potassium ion
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 _________________________________
o Decreases sodium ion reabsorption, increasing sodium ion loss in urine
o Dilation of glomerular capillaries, increasing urinary water loss
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The Ureters
 _____________________________________________________________________________________
 Begins at the renal pelvis and ends at the posterior wall of the bladder
 Ureteral openings are slit-like to prevent the backflow of urine into the ureters or kidneys when
the bladder contracts
The Urinary Bladder
 _____________________________________________________________________________________
 Can hold up to a liter or urine
 Trigone
 Smooth triangular area outlined by the openings for the ureters and the urethra
 ______________________________________________________________________________
 Collapses when empty; rague will appear
 Bladder neck is surrounded by internal urethral sphincter which provides involuntary control over
discharge of urine from the bladder
 Contraction of the _________________ compresses the bladder and expels its contents into the urethra
The Urethra
 Extends from the neck of the urinary bladder to the exterior (________________________) of the body
 Where the urethra passes through the floor of the pelvic cavity, a band of skeletal muscle forms the
external urethral sphincter (_______________________________)
 The micturition (_____________________) reflex
 Stretch receptors are stimulated as the bladder fills with urine and these impulses are carried to
the sacral spinal cord
 These sensations are then relayed to the cerebral cortex and we become aware of pressure
within our urinary bladder
 ______________________________________________________________________________
 ______________________________________________________________________________
 If volume reaches 500mL, sphincters are forced open
Fluid, Electrolyte, and Acid-Base Balance
 Treatment of any serious illness affecting the nervous, cardiovascular, respiratory, urinary, or digestive
system must always include steps to restore normal fluid , electrolyte, and acid-base balance
 Water is essential for life; if water content in the body declines too far, cellular activities are jeopardized
 ______________________________________________________________________________
______________________________________________________________________________
 Homeostasis of fluid volumes, solute concentrations, and pH involves 3 interrelated factors:
 ____________________ – involves regulating water in the ECF and ICF
 ____________________ – gained in food/water & lost through urine, sweat, and feces
 ____________________ – exists when the pH of body fluids is within normal limits
Fluid Balance
 Water moves out of plasma and into interstitial spaces via capillary beds and moves back and forth
across epithelial surfaces
 Fluid shifts – __________________________________________________________________________
 Occur relatively rapidly, reaching equilibrium within minutes/hours
 ______________________________________________________________________________
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Electrolyte Balance
 Electrolyte balance is important because:
 A gain/loss of electrolytes can cause a gain/loss of water
 The concentration of individual electrolytes affects a variety of cell functions
 Na+ and K+ are major contributors to osmotic concentrations and directly affect normal functioning cells
 ______________________________________________________________________________
 ______________________________________________________________________________
Acid-Base Balance
 The pH of your body fluids represents a balance among the acids, bases, and salts in solution (pH of the
ECF is between 7.35-7.45)
 ______________________________________________________________________________
 ______________________________________________________________________________
 Acids in the body
 Carbonic acid (H2CO3) is important in the body, it gets broken down into CO2 and H2O
 In peripheral tissues, the CO2 interacts with H2O again to form H2CO3 which then
dissociates into H+ and HCO3 ________________________________________________________________________
 This reaction occurs spontaneously but can be rapid in the presence of carbonic _________ (an enzyme)
 Because of how this reaction proceeds, ___________________________________________ (PCO2 is the
most important factor affecting pH in body tissues)
Buffers and buffer systems
 _____________________________________________________________________________________
 The body has 3 major buffer systems:
 Protein buffer systems – __________________________________________________________
 Depend on amino acid side groups(either –COOH or –NH2) to give/receive hydrogen ions
 Carbonic acid-bicarbonate buffer systems – ___________________________________________
 Primary role is to prevent pH changes caused by metabolic acids
 Phosphate buffer systems – _______________________________________________________
 Consists of an anion, __________________________________ (H2PO4-), which is a weak
acid that dissociates into a hydrogen ion and ____________________________ (HPO42-)
Maintaining acid-base balance
 Because buffer systems do not eliminate the excess hydrogen ions, they provide only a temporary
solution. For homeostasis to maintain balance, the captured hydrogen ions must be removed. The
problem is that buffer supply is low
 _____________________________________________________________________________________
 Respiratory and renal mechanisms support buffer systems by:
 ________________________________________________________________________
 ________________________________________________________________________
 ________________________________________________________________________
 Respiratory contributions to pH regulation
 ______________________________________________________________________________
 Occurs when pH exceeds normal limit
 Has a direct effect on the carbonic acid-bicarbonate buffer system
 Renal contributions to pH regulation
 ______________________________________________________________________________
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