1. Chapter 15 The Urinary System

2. Functions of the Urinary System
1. Elimination of waste
Nitrogenous wastes
Toxins
Drugs
2. Regulates homeostasis
(kidney function)
Water balance
Electrolytes
Acid-base balance in the blood
Blood pressure
RBC blood cell production
Activation of vit. D

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

4. Urinary System Organs Kidneys are major excretory organs
Urinary bladder is the temporary storage reservoir for urine
Ureters transport urine from the kidneys to the bladder
Urethra transports urine out of the body

5. Location of the Kidneys
Retroperitoneal - against dorsal wall
T12 to L3
Right lower than left
Attached to ureters, renal blood vessels, & nerves at renal hilus
Atop kidney is adrenal gland

6. Anterior Inferior vena cava Aorta Peritoneal cavity (organs removed)
Peritoneum
Supportive
tissue layers
Renal
vein
• Renal fascia
anterior
posterior
Renal
artery
• Perirenal
fat capsule
Body of
vertebra L2
• Fibrous
capsule
Body wall
(a)
Posterior
Figure 25.2a

7. Coverings of the Kidneys
1. Renal capsule
Surrounds kidney
2. Adipose capsule
protection
keeps kidney in location

8. Regions of the Kidney Renal cortex – outer region
Renal medulla – inside the cortex
Renal pelvis – inner collecting tube

9. Kidney Structures
Medullary pyramids – triangular regions of tissue in medulla
Renal columns – extensions of cortex-like material inward
Calyces – cup-shaped structures that funnel urine towards renal pelvis

10. (a) Photograph of right kidney, frontal section (b) Diagrammatic view
Renal
hilum
Renal cortex
Renal medulla
Major calyx
Papilla of
pyramid
Renal pelvis
Minor calyx
Ureter
Renal pyramid
in renal medulla
Renal column
Fibrous capsule
(a) Photograph of right kidney, frontal section
(b) Diagrammatic view
Figure 25.3

11. Blood Flow in the Kidneys

12. Blood and Nerve Supply
Renal arteries deliver ~ 1/4 (1200 ml) of cardiac output to the kidneys each minute
Arterial flow into and venous flow out of the kidneys follow similar paths
Nerve supply is via sympathetic fibers from the renal plexus

13. Cortical radiate artery Arcuate vein Arcuate artery Interlobar vein
Cortical radiate vein
Cortical radiate artery
Arcuate vein
Arcuate artery
Interlobar vein
Interlobar artery
Segmental arteries
Renal vein
Renal artery
Renal pelvis
Ureter
Renal medulla
Renal cortex
(a) Frontal section illustrating major blood vessels
Figure 25.4a

14. Nephrons
Structural and functional units of the kidneys that forms urine
About 1 million per kidney
Main structures
a. Glomerulus
b. Renal tubule

15. Glomerulus Specialized tuft of capillaries
Arterioles on both sides (maintains high pressure)
Large afferent arteriole
Narrow efferent arteriole
Capillaries covered with podocytes from the renal tubule
Glomerulus sits within a glomerular (Bowman’s) capsule (1st part of the renal tubule)

16. Figure 25.5

17. Nephrons Renal corpuscle Glomerulus + its Bowman’s capsule
Allows filtrate to pass from plasma into the glomerular capsule

18. Renal Tubule Glomerular (Bowman’s) capsule Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule

19. Figure 25.5

20. Renal Tubule Proximal convoluted tubule (PCT)
Functions in reabsorption and secretion
Loop of Henle with descending and ascending limbs
Freely permeable to water
Distal convoluted tubule (DCT)
Function more in secretion than reabsorption

21. Types of Nephrons 1. Cortical 2. Juxtamedullary entirely in cortex
most nephrons
2. Juxtamedullary
at boundary of cortex & medulla

22. Nephrons
Cortical nephrons—85% of nephrons; almost entirely in the cortex
Juxtamedullary nephrons
Long loops of Henle deeply invade the medulla
Extensive thin segments
Important in the production of concentrated urine

23. Peritubular Capillaries
Arise from efferent arteriole
Normal, low pressure capillaries
Attached to venule
Cling to renal tubule
Reabsorb substances from collecting tubes
Urine Formation
Filtration
Reabsorption
Secretion

24. Kidney Physiology: Mechanisms of Urine Formation
The kidneys filter the body’s entire plasma volume 60 times each day
Filtrate
Blood plasma minus proteins
Urine
<1% of total filtrate
Contains metabolic wastes and unneeded substances

25. Mechanisms of Urine Formation
Glomerular filtration
Tubular reabsorption
Returns all glucose and amino acids, 99% of water, salt, and other components to the blood
Tubular secretion
Reverse of reabsoprtion: selective addition to urine

26. Glomerular capillaries
Afferent arteriole
Glomerular capillaries
Efferent arteriole
Cortical
radiate
artery
Glomerular capsule
Rest of renal tubule
containing filtrate
Peritubular
capillary
Three major
renal processes:
Glomerular filtration
To cortical radiate vein
Tubular reabsorption
Tubular secretion
Urine
Figure 25.10

27. Filtration Nonselective passive process driven by hydrostatic presure
Water and solutes smaller than proteins are forced through capillary walls (Filtrate same as blood plasma)
Blood cells cannot pass out to the capillaries
Filtrate - collected in glomerular capsule and leaves via the renal tubule

28. Afferent arteriole Glomerular capsule
Glomerular (blood) hydrostatic pressure
(HPg = 55 mm Hg) 10 mm Hg
Blood colloid osmotic pressure
(Opg = 30 mm Hg)
Net
filtration
pressure
Capsular hydrostatic pressure
(HPc = 15 mm Hg)
Figure 25.11

29. Glomerular Filtration Rate (GFR)
Volume of filtrate formed per minute by the kidneys (120–125 ml/min)

30. Reabsorption Peritubular capillaries reabsorb
- Some water, Glucose, Amino acids, Ions
Some passive, most active
Most reabsorption occurs in proximal tubule
Not Reabsorbed
Nitrogenous waste products
- Urea
- Uric acid
- Creatinine
Excess water

31. Secretion – Reabsorption in Reverse
Materials move from peritubular capillaries into renal tubules
H+ & K+
Creatinine
Materials left in renal tubule move to ureter

32. Tubular Secretion
Eliminates undesirable substances that have been passively reabsorbed (e.g., urea and uric acid)
Rids the body of excess K+
Controls blood pH by altering amounts of H+ or HCO3– in urine