1. The Urinary System
Chapter 15

2. Functions of the Urinary System Overview of the Urinary System
Outline
Functions of the Urinary System
Overview of the Urinary System
Kidney Structure
Urine Formation
Glomerular Filtration
Tubular Reabsorption
Tubular Secretion
Maintaining Water-Salt Balance
Maintaining Blood pH
Homeostasis

3. Functions of the Urinary System
Carry out excretion of metabolic wastes.
Excretion is the removal of metabolic waste products- Elimination is the removal of un-used or un-usable material from the body
Urea is the primary nitrogenous end product, but ammonium, creatinine, and uric acid are also excreted.
Maintains salt-water balance of blood and thus regulates blood volume and blood pressure.
Ions regulated include sodium (Na+), potassium (K+), and calcium (Ca2+).

4. Functions of the Urinary System (Con’t)
Maintains acid-base balance of the blood.
Regulates bicarbonate ions (HCO3-) and hydrogen ions (H+).
Performs these functions by producing urine and conducting it outside the body.
Has a hormonal function.
Produces erythropoietin.
Produces renin for the renin-angiotensin-aldosterone system.
Activates inactive form of Vitamin D

5. Overview of the Urinary System
Kidneys are primary organs of the urinary system.
The concave side of a kidney has depression called the hilum where the renal artery enters and the renal vein and ureters exit the kidney.
Urinary bladder gradually expands as urine enters.
Urethra extends from the urinary bladder to an exterior opening.

6. Figure 15.1a Organs of the urinary system.
Overview of the Urinary System
Hepatic veins (cut)
Inferior vena cava
Renal artery
Adrenal gland
Renal hilum
Aorta
Renal vein
Kidney
Iliac crest
Ureter
Rectum (cut)
Uterus (part of female reproductive system)
Urinary bladder
Urethra
(a)

7. Figure 15.1b Organs of the urinary system.
12th rib
(b)

8. Fig. 9.A

9. Kidney Structure The kidney contains three major regions:
Renal cortex.
Renal medulla.
Renal pelvis.
Additional structures of importance
Renal columns
Renal papilla
Renal pyramids
Minor & major calyces
Microscopically, the kidney is composed of over one-million nephrons that produce urine.

10. (a) Anterior view of dissection of right kidney
PATH OF URINE DRAINAGE:
Nephron
Collecting duct
Renal
hilum
Minor calyx
Renal cortex
Major calyx
Renal artery
Renal medulla
Renal pelvis
Renal vein
Renal column
Renal pyramid
in renal medulla
Renal papilla
Renal capsule
Ureter
Urinary bladder
Renal lobe
(a) Anterior view of dissection of right kidney

11. Blood Supply to the Kidney
Glomerulus
Afferent
arteriole
Peritubular
capillary
Frontal plane
Efferent
arteriole
Interlobular
vein
Vasa recta
Blood supply of nephron
Interlobular artery
Renal capsule
Arcuate artery
Interlobar artery
Renal cortex
Segmental artery
Renal artery
Renal vein
Renal pyramid
in renal medulla
Interlobar vein
Arcuate vein
Interlobular vein
(a) Frontal section of right kidney

12. Kidney Structure: The Nephron
Nephron is functional unit of the kidney.
Two types of nephrons
Coritcal: 80-85%, normal renal function
Juxtamedullary: 15-20%, involved with generation of very dilute or very concentrated urine
Each nephron has its own blood supply.
From the renal artery, afferent arteriole leads to the glomerulus, then to the efferent arteriole and then to the peritubular capillary network (or vasa recta of juxtamedullary nephrons) which surrounds the nephron.
From there blood goes into a venule that joins the renal vein.

13. Figure 15.3a Structure of the nephron.
Cortical nephron
Fibrous capsule
Renal cortex
Collecting duct
Renal medulla
Proximal convoluted tubule
Renal cortex
Renal pelvis
Glomerulus
Juxtamedullary nephron
Ureter
Distal convoluted tubule
Nephron loop
Renal medulla
(a)

14. Kidney Structure: The Nephron (Con’t)

15. Kidney Structure: The Nephron (Con’t)
Each nephron is composed of several parts.
Glomerular capsule (Bowman’s capsule).
Filtration
Proximal convoluted tubule.
Tubular reabsorption
Loop of the nephron (loop of Henle).
Tubular reabsorption and secretion
Distal convoluted tubule.
Collecting duct.

17. Figure 15.7 Glomerular capsule Glomerular space Glomerulus Blood flow
Movement of glomerular filtrate
Afferent arteriole
Efferent arteriole
a) The outer surface of several glomerular capillaries.
Podocyte
Filtrate
Proximal tubule
Capillary wall
A highly magnified view of the inner surface of a single glomerular capillary, revealing its porous sievelike structure.
Figure 15.7

18. 1 2 3 Renal corpuscle Renal tubule and collecting duct Afferent
arteriole
Glomerulus
Glomerular
capsule
Glomerular filtrate
in renal tubule
Urine
(contains
excreted
substances)
Glomerular filtration (filtration
of blood plasma by glomerulus) 1 2
Tubular reabsorption from glomerular filtrate into blood 3
Tubular secretion from blood into glomerular filtrate
Efferent
arteriole
Blood
(contains
reabsorbed
substances)
Peritubular capillaries

19. Urine Formation
Urine formation is divided into three steps.
Glomerular filtration.
Filterable blood components
water
nitrogenous wastes
nutrients
salts (ions)
Nonfilterable blood components
white and red blood cell, platelets
plasma proteins

20. Urine Formation (Con’t)
Tubular reabsorption.
Reabsorbed filtrate components
most water
nutrients
required salts (ions)
Nonreabsorbed filtrate components
some water
much nitrogenous waste
excess salts (ions)

21. Urine Formation (Con’t)
Tubular secretion.
Active removal from the blood of some compounds, such as drugs, with secretion into the distal convoluted tubule

22. Filtration and Reabsorption
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23. Maintaining Salt-Water Balance
Reabsorption of Water- Water Balance
Very dilute or very concentrated urine
Dependent upon reabsorption of water from the descending limb of loops of Henle and collecting ducts
Mostly juxtamedullary nephrons
Osmotic gradient exists within the tissues of the renal medulla.
Antidiuretic hormone (ADH) released by the posterior lobe of the pituitary (due to osmolarity of plasma) causes more water to be reabsorbed in collecting ducts and less urine to form
Diuretics increase urine flow
Alcohol- inhibits ADH release from posterior pituitary
Caffeine- inhibits reabsorption of Na+

24. Maintaining Salt-Water Balance
Reabsorption of Water- Water Balance
Osmotic gradient exists within the tissues of the renal medulla
Creation of osmotic gradient
Countercurrent multiplication- nephron tubules
Maintenance of osmotic gradient
Countercurrent exchange- vasa recta blood vessels

25. Creation of Osmotic Gradient
Vasa
recta
Maintenance of Osmotic Gradient
Loop of
Henle
Juxtamedullary nephron and its blood supply together
Glomerular (Bowman’s) capsule
H2O
Glomerulus
Na+Cl–
Afferent arteriole
Distal convoluted tubule
Blood flow
Interstitial
fluid in
renal cortex
Presence of Na+–K+–2Cl– symporters
200
Flow of tubular fluid
H2O
Efferent
arteriole
H2O
300
Proximal convoluted tubule
H2O
300
320
Collecting duct
300
300
300
H2O
100
320
H2O 3
Principal cells in collecting duct reabsorb more water when ADH is present
Interstitial fluid
in renal medulla
Na+Cl–
Na+Cl–
H2O
380
400
400
200
H2O
400
500
H2O
600 1
H2O
600
Symporters in thick ascending limb cause buildup of
Na+ and Cl– in
renal medulla
580
400
Na+Cl–
Osmotic
gradient
600
H2O
Urea recycling causes buildup of urea in renal medulla
700 4
800
800
780
600
H2O
H2O
Urea
800
H2O
900
Na+Cl–
800
1000
1000
Na+Cl–
1000 2
980
1100
Countercurrent flow through loop of Henle establishes osmotic gradient
H2O
1200
1200
Papillary duct
1200
1200
Loop of Henle
1200
Concentrated urine
(a) Reabsorption of Na+, Cl–, and water in long-loop juxtamedullary nephron
(b) Recycling of salts and urea in vasa recta

26. Maintaining Salt-Water Balance
Reabsorption of Water- Water Balance
Very dilute or very concentrated urine
Dependent upon reabsorption of water from the descending limb of loops of Henle and collecting ducts
Mostly juxtamedullary nephrons
Antidiuretic hormone (ADH) released by the posterior lobe of the pituitary (due to osmolarity of plasma) causes more water to be reabsorbed in collecting ducts and less urine to form
Diuretics increase urine flow
Alcohol- inhibits ADH release from posterior pituitary
Caffeine- inhibits reabsorption of Na+

27. Distal convoluted tubule
ADH & Making Dilute Urine
Afferent
arteriole
Glomerular (Bowman's) capsule
Glomerulus
Distal convoluted tubule
Efferent
arteriole
Interstitial fluid in renal cortex
100
300 90
Proximal
convoluted
tubule
300
300
350
350
150
350
Collecting
duct
550
550
350
550 80
Interstitial
fluid in
renal
medulla
750
750
550
750 70
Papillary
duct
900 65
Loop of Henle 65
Dilute
urine

28. ADH & Making Concentrated Urine
Vasa
recta
Loop of
Henle
Juxtamedullary nephron and its blood supply together
Glomerular (Bowman’s) capsule
H2O
Glomerulus
Na+Cl–
Afferent arteriole
Distal convoluted tubule
Blood flow
Interstitial
fluid in
renal cortex
Presence of Na+–K+–2Cl– symporters
200
Flow of tubular fluid
H2O
Efferent
arteriole
H2O
300
Proximal convoluted tubule
H2O
300
320
Collecting duct
300
300
300
H2O
100
320 3
Principal cells in collecting duct reabsorb more water when ADH is present
H2O
Interstitial fluid
in renal medulla
Na+Cl–
Na+Cl–
H2O
400
400
380
200
H2O
400
500
H2O
600 1
H2O
600
Symporters in thick ascending limb cause buildup of
Na+ and Cl– in
renal medulla
580
400
Na+Cl–
Osmotic
gradient
600
H2O
Urea recycling causes buildup of urea in renal medulla
700 4
800
800
780
600
H2O
H2O
Urea
800
H2O
900
Na+Cl–
1000
800
1000
1000 2
980
Na+Cl–
1100
Countercurrent flow through loop of Henle establishes osmotic gradient
H2O
1200
1200
Papillary duct
1200
1200
Loop of Henle
1200
Concentrated urine
(a) Reabsorption of Na+, Cl–, and water in long-loop juxtamedullary nephron
(b) Recycling of salts and urea in vasa recta

29. Maintaining Salt-Water Balance
Fluid Compartments & Fluid Balance
Intracellular fluid (ICF)- inside cells
Extracellular fluid (ECF)- outside cells
Interstitial fluid- microscopic space outside every cell of the body
Plasma
Renal processes of filtration, reabsorption, diffusion, and osmosis promote continuous exchange between the fluid compartments
Thus fluid balance is directly related to electrolyte (ions) balance
“Wherever salt goes water follows”

30. Renal effects on salt distribution will affect fluid distribution
Total body mass (female)
Total body mass (male)
Renal effects on salt distribution will affect fluid distribution
45%
Solids
40% Solids
Total body fluid
2/3
Intracellular
fluid (ICF)
Tissue
cells
55% Fluids
60% Fluids
Extracellular
fluid
80%
Interstitial
fluid
1/3
Extracellular
fluid (ECF)
20% Plasma
Blood capillary
(a) Distribution of body solids and fluids in average lean, adult female and male
(b) Exchange of water among body fluid compartments

31. Maintaining Salt-Water Balance
Reabsorption of Salt.
Kidneys regulate blood’s salt balance by controlling excretion and reabsorption of various ions, most important one being Na+
Usually more than 99% of sodium filtered at the glomerulus is returned to the blood
Hormonal control of salt reabsorption
Starts at juxtaglomerular apparatus (JGA)
Decrease in blood volume/pressure-renin from the JGA is released into blood-enzymatically cleaves angiotensinogen to angiotensin-I, angiotensin-I converted to angiotensin-II in lungs, angiotensin-II stimulates release of aldosterone from adrenal cortex, aldosterone stimulates Na+ reabsorption

32. Juxtaglomerular Apparatus
Fig. 9.9

33. Figure 15.3b Structure of the nephron.
Proximal convoluted tubule (PCT)
Peritubular capillaries
Glomerular capillaries
Distal convoluted tubule (DCT)
Glomerular (Bowman’s) capsule
Efferent arteriole
Afferent arteriole
Cells of the juxtaglomerular
apparatus
Cortical radiate artery
Arcuate artery
Arcuate vein
Cortical radiate vein
Collecting duct
Nephron loop
(b)

34. Maintaining Salt-Water Balance
Reabsorption of Salt.
Hormonal control of salt reabsorption (Cont.)
Wherever salt goes water follows, thus increase reabsorption of water
Causes of decrease blood volume- blood loss (hemorrhage), profuse sweating (includes loss of blood water/salt), profuse vomiting, profuse diarrhea
Reabsorption of water increases blood volume
Decreased blood volume means decreased blood pressure- hence increase in blood volume- increase in blood pressure
Thus direct link between salt regulation and blood pressure regulation
ADH increases to increase water reabsorption

35. Aldosterone Angiotensin II Angiotensin I
ADH
Blood volume
Increase
Set point
Save water
Decrease
Save
salt
Kidneys
Kidneys
Aldosterone
Adrenal
cortex
Angiotensin-
converting
enzyme
Renin
Lungs
Angiotensin II
Angiotensin I
Angiotensinogen
Vasoconstriction,
blood pressure
Liver
Figure 15.15

37. Maintaining Salt-Water Balance
Reabsorption of Salt.
Hormonal control of salt reabsorption (Cont.)
Starts at atria of heart
Increase in Na+ concentration in plasma- huge salt filled meal
99% of Na+ reabsorbed- wherever salt goes water follow
Water enters blood from fluid compartments- intracellular space, then interstitial space, then into plasma
Increase in blood volume
Increase stretch of atria of heart- release atrial natriuretic peptide
Causes increased salt excretion (decrease Na+ reabsorption)

38. Maintaining Salt-Water Balance
Reabsorption of Salt.
Hormonal control of salt reabsorption (Cont.)
Wherever salt goes water follows
Increase removal of water from blood- decrease in blood volume- decrease in blood pressure
Hypertension- may be a defect in atrial natriuretic peptide system
What is happening to ADH during this situation?
Increased osmolarity of blood should stimulate ADH release but that can’t happen because that would increase blood volume when you want to decrease it
Thus ADH is mostly involved when you have changes in water affecting osmolarity not salt affecting osmolarity

39. Fig

41. Fate of Some Compounds, Normal Amount of Urine
Nutrients- amino acids, glucose / all filtered from blood into urine in glomerulus / all reabsorbed in proximal / none in urine
Water and salts / most filtered from blood into urine in glomerulus / most reabsorbed in proximal and collecting duct / concentration in urine dependent on need and hormones
Metabolic wastes- urea, uric acid/ all filtered from blood into urine in glomerulus / none reabsorbed / concentration in urine higher than blood

42. Fate of Some Compounds, Low Amount of Urine- After Sleeping
Nutrients- amino acids, glucose / all filtered from blood into urine in glomerulus / all reabsorbed in proximal / none in urine
Water / most filtered from blood into urine in glomerulus / even more reabsorbed in proximal and collecting duct due to prevention of loss during sleep / ADH increases reabsorption in collecting duct
Metabolic wastes- urea, uric acid/ all filtered from blood into urine in glomerulus / none reabsorbed / concentration in urine much higher than under normal condition due to less water

43. Table 15.1

44. Fate of Some Compounds, High Amount of Urine- After McDonalds Meal
Nutrients- amino acids, glucose / all filtered from blood into urine in glomerulus / all reabsorbed in proximal / none in urine
Salt and water / most filtered from blood into urine in glomerulus / most reabsorbed in proximal and collecting duct / high salt in food, goes into blood, water follows, increase volume, increase pressure, ANH released, salt reabsorption decreased, ADH turned off, water follows salt into urine
Metabolic wastes- urea, uric acid/ all filtered from blood into urine in glomerulus / none reabsorbed / concentration in urine lower than normal due to large amount of water in urine

45. Maintaining Blood pH
Reabsorption of bicarbonate ions and secretion of hydrogen ions
Exhalation of Carbon Dioxide

46. Maintaining Blood pH
Fig. 9.10

47. Homeostasis
In conjunction with the lungs, maintenance of acid-base balance.
Maintenance of water-salt balance of blood and the overall osmolarity.
Helps regulate blood volume and pressure.
Releases-erythropoietin; increases number of red blood cells
Regulates the concentration of important ions such as calcium (Ca2+) and potassium (K+).
In conjunction with the liver, excretion of metabolic wastes.

48. Need to Know Functions of the urinary system Metabolic waste excretion
Salt-Water balance
Blood pressure regulation
Acid-base balance
Red blood cell quantity regulation
Activation of inactive Vitamin D
Kidney Structure: The Nephron
Afferent and efferent arterioles
Glomerulus
Peritubular capillary network

49. Need to Know (Cont.) Kidney Structure: The Nephron (Cont.)
Glomerular capsule
Proximal convoluted tubule
Loop of the nephron
Distal convoluted tubule
Collecting duct
Urine formation
Glomerular filtration concept
Tubular reabsorption concept
Tubular secretion concept
Must know what’s filtered and not filtered, what’s reabsorbed and not reabsorbed and what’s secreted

50. Need to Know (Cont.)
Reabsorption of salt
Juxtaglomerular apparatus
Renin-angiotensin-aldosterone system
Atria natriuretic hormone
Blood pressure regulation
Acid-Base balance
Reabsorption of bicarbonate ion
Excretion of hydrogen ion

51. Need to Know (Cont.)
Kidney Structure: Gross anatomy
Renal cortex
Renal medulla
Renal pelvis
Urinary system: General
Kidney
Ureters
Urinary bladder
Urethra