1. The Urinary System
Chapter 15

2. Functions of the Urinary System
Elimination of waste products
Nitrogenous wastes
Toxins
Drugs
Regulate aspects of homeostasis
Water balance
Electrolytes
Acid-base balance in the blood
Blood pressure
Red blood cell production
Activation of vitamin D

3. Organs of the Urinary system
Kidneys
Ureters
Urinary bladder
Urethra

4. Location of the Kidneys
Kidney is located against dorsal body wall in the body
Kidneys extend from T12 to L3
The right kidney is slightly lower than the left

5. Features and Structure of Kidney
Is dark red kidney-bean shaped
12 cm long, 6 cm wide, 3 cm thick
Has medial indentation called Renal hilum
Several structures enter or exit the kidney (ureters, renal blood vessels, and nerves) at hilum
An adrenal gland sits atop each kidney

6. Coverings of the Kidneys
Three layers of supportive tissue surround each kidney:
Fibrous capsule
Transparent fibrous capsule surrounds each kidney
Perirenal fat capsule
Surrounds the kidney and cushions against blows
Renal fascia
Outermost capsule that helps hold the kidney in place against the muscles of the trunk wall

7. Regions of the Kidney Cortex – the light colored, outer region
Medulla – Reddish brown area
Has cone-shaped medullary (renal) pyramids separated by renal columns
Renal pelvis – Medial to the hilus
Flat basin like cavity

8. Regions of the Kidney Calyces – large branches of the renal pelvis
Collect urine draining from tips of pyramids
Empty urine into the renal pelvis
Urine flows through the renal pelvis to ureter and then to the bladder

9. Blood Flow in the Kidneys
Kidneys continuously cleanse the blood
One-quarter of the total blood supply of the body passes through the kidneys each minute
Renal artery provides each kidney with arterial blood supply
Venous blood drain from kidney takes place via Renal vein

10. Nephron
Each kidney contains more than a million tiny structures – Nephrons
Nephrons - The structural and functional units of the kidneys
Responsible for forming urine
Main structures of the nephron
Glomerulus
Renal tubule

11. Glomerulus Is a knot of capillaries
Attached to arterioles on both sides (maintains high pressure)
Large afferent arteriole
Narrow efferent arteriole

12. Glomerulus Capillaries are covered with
Octopus –like cells called podocytes
Forms porous membrane around glomerulus
Cup-shaped, First part of renal tubule surrounds the glomerulus known as Glomerular (Bowman’s) capsule

13. Nephron
Renal Tubule
Renal tubule extends from glomerular capsule and ends at the collecting duct
Proximal convoluted tubule (PCT)
Loop of Henle
Distal convoluted tubule (DCT)

14. Types of Nephrons Cortical nephrons Located entirely in the cortex
Includes most nephrons
Juxtamedullary nephrons
Found at the boundary of the cortex and medulla

15. Collecting Duct Receives urine from many nephrons
Run through the medullary pyramids
Deliver urine into the calyces and renal pelvis

16. Nephron Anatomy
Each and every Nephron is associated with two capillary beds
Glomerulus
Peritubular capillary bed

17. Glomerulus Glomerulus is fed and drained by arterioles
Afferent arteriole— arises from a cortical radiate artery and feeds the glomerulus
Efferent arteriole— receives blood that has passed through the glomerulus
Specialized for filtration
BP in glomerular capillaries is much higher than other capillaries
High pressure forces fluid and solutes (smaller than proteins) out of blood and into the glomerular capsule
Most of the filtrate from renal tubule is absorbed by peritubular capillary beds and returned to blood

18. Peritubular Capillaries
Arise from efferent arteriole of the glomerulus, which drains the glomerulus
low pressure capillaries
Adapted for absorption instead of filtration
Cling close to the renal tubule to reabsorb (reclaim) some solutes and water
Drains into the veins

19. Urine Formation Processes
Three processes:
Glomerular Filtration
Tubular Reabsorption
Tubular Secretion

20. Glomerular Filtration
Nonselective passive process
Fluid passes from blood into glomerular capsule (part of renal tubule)
Fluid (Water and solutes smaller than proteins)
are forced through capillary walls
Blood cells and proteins cannot pass out to the capillaries
Filtrate is collected in the glomerular capsule
and leaves via the renal tubule

21. Tubular Reabsorption
Besides wastes and excess ions ,Filtrate contains many useful substances, which is returned to blood via absorption
Reabsorption begins when filtrate enters proximal convoluted tubule from glomerulus
The peritubular capillaries reabsorb useful substances
Water
Glucose
Amino acids
Ions
Some reabsorption is passive, most is active
Most reabsorption occurs in the proximal convoluted tubule

22. Reabsorption Materials not reabsorbed Nitrogenous waste products
Urea— protein breakdown
Uric acid— nucleic acid breakdown
Creatinine— associated with creatine metabolism in muscles
Excreted through the urine

23. Tubular Secretion Some materials move from
the peritubular capillaries into the renal tubules filtrate to be eliminated in urine, such as
Hydrogen and potassium ions
Creatinine
Materials left in the renal tubule move toward the ureter

24. Formation of Urine

25. Characteristics of Urine
In 24 hours, about 1.0 to 1.8 liters of urine are produced
Yellow color due to the pigment urochrome (from the destruction of hemoglobin) and solutes
Sterile
Slightly aromatic
Normal pH of around 6
Specific gravity of to 1.035

26. Characteristics of Urine
Solutes normally found in urine
Sodium and potassium ions
Urea, uric acid, creatinine
Ammonia
Bicarbonate ions

27. Characteristics of Urine
Solutes NOT normally found in urine
Glucose
Blood proteins
Red blood cells
Hemoglobin
White blood cells (pus)
Bile

28. Ureters Slender tubes attaching the kidney to the bladder
Superior end of ureter is continuous with the renal pelvis
Enter the posterior aspect of the bladder
Ureters are passageways that carry urine from kidneys to bladder
Propel urine into bladder by Peristalsis aids

29. Urinary Bladder Smooth, collapsible, muscular sac
Temporarily stores urine
Trigone – three openings
Two from the ureters
One to the urethra

30. Urinary Bladder Wall
Bladder wall contains three layers of smooth muscle, collectively known as detrusor muscle
And its mucosa is made of transitional epithelium
Suited for urine storage
When bladder is empty it collapses and thrown into folds
Bladder can expand significantly without increasing internal pressure

31. Urinary Bladder Capacity
A moderately full bladder is about 5 inches long and holds about 500 mL of urine
Capable of holding twice that amount of urine

32. Urethra
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
Internal urethral sphincter
Involuntary and made of smooth muscle
External urethral sphincter
Voluntary and made of skeletal muscle

33. Urethra Gender Differences
Length
Females – 3–4 cm (1 inch)
Males – 20 cm (8 inches)
Location
Females – along wall of the vagina
Males – through the prostate and penis
Function
Females – only carries urine
Males – carries urine and is a passageway for sperm cells

34. Micturition (Voiding)
Is the act of emptying the bladder
Two sphincters, internal and external sphincter control the flow of urine
When volume of bladder reaches around 200 ml
Bladder stretches and activates stretch receptors
Then impulses transmitted to spinal cord

35. Micturition (Voiding)
And then back to bladder via Pelvic splanchnic nerves
Pelvic splanchnic nerves initiate bladder to go into reflex contractions
Urine is forced past the internal urethra sphincter and the person feels the urge to void
The external urethral sphincter must be voluntarily relaxed to void

36. Fluid, Electrolyte, and Acid-Base Balance
Kidneys have four roles in maintaining blood composition
Excretion of nitrogen-containing wastes
Maintaining water balance of the blood
Maintaining electrolyte balance of the blood
Ensuring proper blood pH

37. Distribution of Body Fluid
Normal amount of water in the human body
Young adult females – 50%
Young adult males – 60%
Babies – 75%
Old age – 45%
Intracellular fluid (inside cells) -2/3 of body fluid
Extracellular fluid (outside cells)
Interstitial fluid
Blood plasma

38. Maintaining Water Balance
Water intake must equal water output
Sources for water intake
Ingested foods and fluids
Water produced from metabolic processes
Thirst mechanism is the driving force for water intake
Sources for water output
Vaporization out of the lungs
Lost in perspiration
Leaves the body in the feces
Urine production

39. Maintaining Water Balance
Dilute urine is produced if water intake is excessive
Less urine (concentrated) is produced if large amounts of water are lost
Proper concentrations of various electrolytes must be present in both intracellular and extracellular fluids

40. The Link Between Water and Salt
Electrolytes: Na+, K+
Changes in electrolyte balance
causes water to move from one compartment to another
Alters blood volume and blood pressure
Can impair the activity of cells

41. Regulation of Water and Electrolyte Reabsorption: ADH and Aldosterone
Cells in the kidneys and hypothalamus are active monitors
When the blood pressure and volume decrease
Kidney releases renin
Renin acts on angiotansiogen
to form angiotensin I
Angiotensin I is further broken to
Angiotensin II
Angiotensin II stimulates
Vasoconstriction
Release of hormones ADH and aldosterone
Stimulates hypothalamus thirst center to drink water

42. Antidiuretic hormone (ADH) release Stimulates body to retain water
By the kidneys
Increases fluid volume
Increases blood pressure
Thus brings blood pressure and volume together
In addition it takes the help of aldosterone

43. Aldosterone regulates sodium ion content of extracellular fluid
Triggered by the rennin-angiotensin mechanism
Increases Na+ retention
Increases fluid retention
Increases blood volume

44. Maintaining Acid-Base Balance in Blood
Blood pH must remain between 7.35 and 7.45 to maintain homeostasis
Alkalosis – pH above 7.45
Acidosis – pH below 7.35

45. Maintaining Acid-Base Balance in Blood
Most acid-base balance is maintained by the kidneys
Other acid-base controlling systems
Blood buffers
Respiration

46. Blood Buffers
Molecules react to prevent dramatic changes in hydrogen ion (H+) concentrations
Bind to H+ when pH drops
Release H+ when pH rises

47. Blood Buffers Acids are proton (H+) donors
Strong acids dissociate completely and liberate all of their H+ in water
Cause large change in pH
Weak acids, such as carbonic acid, dissociate only partially
Less effect on solution`s pH
Play imp. role in buffer system
Bases are proton (H+) acceptors
Strong bases dissociate easily in water and tie up H+
Weak bases, such as bicarbonate ion and ammonia, are slower to accept H+

48. Blood Buffers Three major chemical buffer systems
Bicarbonate buffer system
Phosphate buffer system
Protein buffer system

49. Bicarbonate Buffer System
Mixture of carbonic acid (H2CO3) and sodium bicarbonate (NaHCO3)
Bicarbonate ions (HCO3–) react with strong acids to change them to weak acids
HCl NaHCO3  H2CO NaCl
strong acid weak base weak acid salt

50. Bicarbonate Buffer System
Carbonic acid dissociates in the presence of a strong base to form a weak base and water
NaOH H2CO3  NaHCO H2O
strong base weak acid weak base water

51. Respiratory System Controls of Acid-Base Balance
Carbon dioxide in the blood is converted to bicarbonate ion and transported in the plasma
Increase in carbon dioxide produces more carbonic acid
And 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 by increasing the breathing rate
CO2 + H2O H2CO H+ + HCO3-
Respiratory rate can rise and fall depending on changing blood pH

52. Renal Mechanisms of Acid-Base Balance
Excrete bicarbonate ions if needed
Conserve (reabsorb) or generate new bicarbonate ions if needed
When blood pH rises
Bicarbonate ions are excreted
Hydrogen ions are retained by kidney tubules
When blood pH falls
Bicarbonate ions are reabsorbed
Hydrogen ions are secreted
Urine pH varies from 4.5 to 8.0

53. Developmental Aspects of the Urinary System
Functional kidneys are developed by the third month
Urinary system of a newborn
Bladder is small
Urine cannot be concentrated
Control of the voluntary urethral sphincter does not start until age 18 months
Urinary infections are the only common problems before old age
There is a progressive decline in urinary function
The bladder shrinks with aging