1. Chapter 26
The Urinary System

2. Learning Objectives
Identify the components and functions of the urinary system
Describe the location and structural features of the kidneys
Describe the structure of a nephron, and outline the processes involved in the formation of urine
List and describe the factors that influence filtration pressure and the rate of filtrate formation

3. SECTION 26-1 An Overview of the Urinary System

4. Functions of the urinary system
Excretion
The removal of organic waste products from body fluids
Elimination
The discharge of waste products into the environment
Homeostatic regulation of blood plasma
Regulating blood volume and pressure
Regulating plasma ion concentrations
Stabilizing blood pH
Conserving nutrients

5. Urinary system includes:
The kidneys
Produce urine
The ureters
The urinary bladder
Stores urine
The urethra

6. Figure 26.1 An introduction to the Urinary System

7. SECTION The Kidneys

8. The kidneys Left kidney extends slightly more superiorly than right
Both kidneys and adrenal glands are retroperitoneal
Hilus
Entry for renal artery and renal nerves
Exit for renal veins and ureter

9. Figure 26.2 The Position of the Kidneys
Figure 26.2a, b

10. Figure 26.3 The Urinary System in Gross Dissection

11. Sectional anatomy of the kidneys
Superficial outer cortex and inner medulla
The medulla consists of 6-18 renal pyramids
The cortex is composed of roughly 1.25 million nephrons
Major and minor calyces along with the pelvis drain urine to the ureters

12. Figure 26.4 The Structure of the Kidney
Figure 26.4a, b

13. Blood supply and innervation of the kidneys
Renal arteries branch repeated
Renal artery
Segmental artery
Interlobar artery
Arcuate artery
Interlobular artery
Afferent arterioles
Renal venules follow similar opposing pattern ending with renal veins

14. Figure 26.5 The Blood Supply to the Kidneys
Figure 26.5a, b

15. Figure 26.5 The Blood Supply to the Kidneys
Figure 26.5c, d

16. The nephron consists of a renal corpuscle and renal tubule
The renal corpuscle is composed of
Bowman’s capsule and the glomerulus
The renal tubule consists of
Proximal convoluted tubule (PCT)
Loop of Henle
Distal convoluted tubule (DCT)

17. Filtrate is produced at the renal corpuscle
Nephron empties tubular fluid into collecting system
Collecting ducts and papillary ducts form the collecting system

18. Figure 26.6 A Representative Nephron

19. Nephron functions include:
Production of filtrate
Reabsorption of organic nutrients
Reabsorption of water and ions
Secretion of waste products into tubular fluid

20. Two types of nephron Cortical nephrons ~85% of all nephrons
Located in the cortex
Juxtamedullary nephrons
Closer to renal medulla
Loops of Henle extend deep into renal pyramids
Responsible for greatest amount of water reabsorbed

21. Figure 26.7 Cortical and Juxtamedullary Nephrons
Figure 26.7a

22. Figure 26.7 Cortical and Juxtamedullary Nephrons
Figure 26.7b, c

23. Renal tubule and blood flow
Blood travels from efferent arteriole to peritubular capillaries
Vasa recta
Renal tubule begins at renal corpuscle
Includes glomerulus and Bowman’s capsule
Blood leaves the nephron via the efferent arteriole

24. Glomerulus anatomy Podocytes cover lamina densa of capillaries
Project into the capsular space
Pedicels of podocytes separated by filtration slits

25. Figure 26.8 The Renal Corpuscle
Figure 26.8a, b

26. Figure 26.8 The Renal Corpuscle
Figure 26.8c, d

27. Functional anatomy of the nephron
Proximal convoluted tubule (PCT)
Actively reabsorbs nutrients, plasma proteins and ions from filtrate
Released into peritubular fluid
Loop of Henle
Descending limb
Ascending limb
Each limb has a thick and thin section
PLAY
Animation: Urinary System Anatomy

28. Functional anatomy of the nephron
Distal convoluted tubule (DCT)
Actively secretes ions, toxins, drugs
Reabsorbs sodium ions from tubular fluid
PLAY
Animation: Urinary System Dissection and Flythrough

29. SECTION 26-3 Principles of Renal Physiology

30. Urine production maintains homeostasis
Regulating blood volume and composition
Excreting waste products
Urea
Creatinine
Uric acid

31. Basic processes of urine formation
Filtration
Blood pressure
Water and solutes across glomerular capillaries
Reabsorption
The removal of water and solutes from the filtrate
Secretion
Transport of solutes from the peritubular fluid into the tubular fluid

32. Carrier Mediated Transport
Filtration in the kidneys modified by carrier mediated transport
Facilitated diffusion
Active transport
Cotransport
Countertransport
Carrier proteins have a transport maximum (Tm)
Determines renal threshold

33. Reabsorption and secretion
Accomplished via diffusion, osmosis, and carrier-mediated transport
Tm determines renal threshold for reabsorption of substances in tubular fluid

34. Renal function
Most regions of the nephron perform a combination of functions
General functions can be identified
Filtration in the renal corpuscle
Nutrient reabsorption along the PCT
Active secretion at PCT and DCT
Loops of Henle regulate final volume and solute concentration

35. Figure 26.9 An Overview of Urine Formation

36. SECTION 26-4 Renal Physiology: Filtration and the Glomerulus

37. Filtration pressures - Glomerular filtration
Occurs as fluids move across the glomerulus
In response to glomerular hydrostatic pressure (GHP) and blood pressure in the glomerular capillaries
Capsular hydrostatic pressure (CsHP) opposes GHP
Blood colloid osmotic pressure (BCOP) opposes GHP
Net hydrostatic pressure (NHP) = GHP – CsHP
Filtration (FP) = NHP – BCOP

38. Figure 26.10 Glomerular Filtration

39. Figure 26.10 Glomerular Filtration
Figure 26.10a, b

40. Glomerular filtration rate (GFR)
Amount of filtrate produced in the kidneys each minute
Factors that alter filtration pressure change GFR

41. SECTION 26-5 Renal Physiology: Reabsorption and Secretion

42. Reabsorption and secretion at the PCT
Glomerular filtration produces fluid similar to plasma without proteins
The PCT reabsorbs 60-70% of the filtrate produced
Reabsorption of most organic nutrients
Active and passive reabsorption of sodium and other ions
Reabsorption of water
Secretion also occurs in the PCT
PLAY
Animation: Early Filtrate Processing
PLAY
Animation: Glomerular filtration

43. Figure 26.12 Transport Activities at the PCT
PLAY
Animation: Proximal Convoluted Tubule
Figure 26.12

44. The loop of Henle and countercurrent multiplication
Between ascending and descending limbs of loop
Creates osmotic gradient in medulla
Facilitates reabsorption of water and solutes before the DCT
Permits passive reabsorption of water from tubular fluid

45. Figure 26.13 Countercurrent Multiplication and Concentration of Urine
Figure 26.13a

46. Figure 26.13 Countercurrent Multiplication and Concentration of Urine
Figure 26.13b

47. Figure 26.13 Countercurrent Multiplication and Concentration of Urine