1. Lecture 26: The Urinary System
Lecturer: Dr. Barjis
Room: P313
Phone: (718)

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
Describe the normal characteristics, composition, and solute concentrations of a representative urine sample

3. Learning Objectives
List and describe the factors that influence filtration pressure and the rate of filtrate formation
Identify the types of transport mechanisms found along the nephron
Describe how antidiuretic hormone and aldosterone levels influence the volume and concentration of urine

4. Functions of the urinary system
Functions of the urinary system includes:
1) Excretion
The removal of organic waste products from body fluids e.g. urea
2) Elimination
The discharge of waste products into the environment
3) Homeostatic regulation of blood plasma
Regulating blood volume and pressure
Regulating plasma ion concentrations
Stabilizing blood pH
Conserving nutrients i.e. preventing nutrient excretion by re-absorption
Detoxification

5. Organs of Urinary system includes:
1) The kidneys
Produce urine
2) The ureters
Transport urine from the kidneys to the bladder
3) The urinary bladder
Stores urine
4) The urethra
Eliminates urine

6. An introduction to the Urinary System

7. The kidneys Left kidney extends slightly more superiorly than right
Both kidneys and adrenal glands are retroperitoneal
Hilus
Point of entry and exit for renal artery, renal nerves and renal veins and ureter

8. The Urinary System in Gross Dissection

9. Sectional anatomy of the kidneys
Kidneys have two layers: An outer cortex and an inner medulla
The medulla consists of 6-18 conical shaped structures called renal pyramids
The cortex is composed of roughly 1.25 million nephrons
Major and minor calyces along with the pelvis drain urine to the renal pelvis, and renal pelvis is connected to the ureters

10. The Structure of the Kidney

11. Blood supply of the kidneys
Pathway of blood flow to the kidnes:
Renal artery – renal arteries deliver blood to the kidneys
Segmental artery – renal arteries branch to segmental arteries
Interlobar artery - Segmental arteries divide into a series of interlobar arteries
Arcuate artery - interlobar arteries supply blood to the arcuate arteries
Interlobular artery - Each arcuate artery gives rise to a number of interlobular arteries
Afferent arterioles - interlobular artery branch to numer of afferent arterioles
Glomeruli – afferent arteries deliver blood to capillaries called glomeruli.
Glomeruli is network of capilaries found in the corpuscle of nephrone
Renal venules follow similar opposing pattern ending with renal veins

12. The Blood Supply to the Kidneys

13. The Blood Supply to the Kidneys

14. The Nephron The nephron consists of :
1) Renal corpuscle – the head of the nephron
The renal corpuscle is composed of Bowman’s capsule and glomeruli
Bowman’s capsule is the cover of the corpuscle that surrounds the glomerulus
the glomerulus is the network of capillaries found inside the corpuscle
Blood arrives at glomerulus by way of an afferent arteriole and departs in an efferent arteriole
2) Renal tubule – the tubular passageway of the nephron
The renal tubule consists of
Proximal convoluted tubule (PCT)
Loop of Henle
Distal convoluted tubule (DCT)

15. Filtrate is produced at the renal corpuscle of the nephron
In renal corpuscle, blood pressure forces fluid and dissolved solutes out of the glomerular capillaries and into the capsular space. This process is called filtration
Filtration produces an essentially protein-free solution, known as a filtrate
Filtrate is similar to plasma but without proteins i.e. it contains organic substrates (e.g. glucose, fatty acids, amino acids), vitamins, water, electrolytes, waste product and other solutes
Organic substrates, most water, most electrolytes and vitamins are recaptured (re-absorbed) by the renal tubes, before filtrate leaves the kidneys
From the renal corpuscle, filtrate enters the tubular passageway of the nephron

16. The Nephron The tubular passageway of the nephron is responsible for:
1.   Reabsorbing organic substrates and vitamins
2.   Reabsorbing water and electrolytes
3.   Secreting waste products
From the tubular passageway of the nephron fluid enters into the collecting system (collecting system are tubes that carry tubular fluid away from the nephron)
Collecting ducts carry he fluid to papillary ducts
Papillary ducts carry the fluid (urine) to the minor calyx
Minor calyx carry the fluid (urine) to major calyx
Number of minor calyces join together to form a major calyx
Major calyx deliver the fluid (urine) to renal pelvis
Renal pelvis is connected to the ureter
Ureter transports the urine to the bladder

17. Summary of fluid flow from the nephron to the Ureter
Renal corpuscle - capsular space.
Tubular passageway of the nephron
PCT
Lube of Henle
DCT
3) Collecting duct
4) Papillary ducts
Minor calyx
Major calyx
Renal pelvis
Uureter

18. The Nephron

19. Nephron functions include:
The Nephron
Nephron functions include:
1) Production of filtrate – this occurs at the corpuscle of the nephron
2) Reabsorption of organic nutrients – this occurs at the tubular passageway of the nephron
3) Reabsorption of water and ions - this occurs at the tubular passageway of the nephron
4) Secretion of waste products into tubular fluid - this occurs at the tubular passageway of the nephron

20. There are two types of nephron
The Nephron
There are two types of nephron
1) Cortical nephrons
~85% of all nephrons
Located in the cortex
2) Juxtamedullary nephrons
Closer to renal medulla
Loops of Henle extend deep into renal pyramids

21. Cortical and Juxtamedullary Nephrons

22. Cortical and Juxtamedullary Nephrons

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

24. The Renal Corpuscle

25. The Renal Corpuscle

26. Functional anatomy of the nephron
Tubular passageway of the nephron:
1) Proximal convoluted tubule (PCT)
Actively reabsorbs nutrients, plasma proteins and ions from filtrate
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 (this is mostly function of DCT)

27. Transport Activities at the PCT

28. Functional anatomy of the nephron
Tubular passageway of the nephron:
2) Loop of Henle
Descending limb
Ascending limb
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

29. Countercurrent Multiplication and Concentration of Urine

30. Countercurrent Multiplication and Concentration of Urine

31. Countercurrent Multiplication and Concentration of Urine

32. Functional anatomy of the nephron
Tubular passageway of the nephron:
Distal convoluted tubule (DCT)
DCT performs final adjustment of urine
Actively secretes ions, toxins, drugs
Reabsorbs sodium ions from tubular fluid
Tubular cells actively resorb Na+ and Cl-
In exchange for potassium or hydrogen ions (secreted)

33. Tubular Secretion and Solute Reabsorption at the DCT
Animation: Distal Convoluted Tubule (see tutorial)

34. Tubular Secretion and Solute Reabsorption at the DCT

35. Urine production maintains homeostasis
Regulating blood volume and composition by excreting or reabsorbing water, sodium, hydroge and other electrolyte
Excreting waste products such as:
Urea
Creatinine
Uric acid

36. Basic processes of urine formation
1) Filtration – this is the first process, and it occurs in corpuscle of nephron
Filtration occur because blood pressure forces fluid and dissolved solutes out of the glomerular capillaries and into the capsular space
2) Reabsorption – this is the second process, and it occurs in tubular passageway of the nephron
One limitation to the filtration process is that the filtrate produced in the corpuscle contain organic substrates, vitamins and other beneficial material. Therefore the second process will reabsorb water and solutes from the filtrate
3) Secretion – this is the third process and it occurs in the tubular passageway of the nephron
Transport of solutes from the peritubular fluid into the tubular fluid

37. Filtration and Reabsorption
Filtration in the kidneys modified by carrier mediated transport
Facilitated diffusion
Active transport
Cotransport
Countertransport
Reabsorption and secretion is accomplished via:
Diffusion,
Osmosis, and
Carrier-mediated transport

38. 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

39. An Overview of Urine Formation

40. 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

41. Glomerular Filtration

42. Glomerular Filtration

43. Glomerular filtration rate (GFR)
GFR is the amount of filtrate produced by the kidneys in one minute
Factors that alter filtration pressure will change the GFR e.g. a drop in pressure will lead to a decrease in GFR

44. The Response to a Reduction in the GFR
When blood pressure is law, the amount of filtrate in the corpuscle decreases.
Law filtrate stimulates production of renin by juxtaglomerular nephron (apparatus)
Renin converts angiotensin to angiotensin I
Angiotensin I is activated to angiotensin II
Angiotensin II affects the/ or acts on:
Blood vessel
Angiotensin II stimulates constriction of blood vessels
Adrenal gland
At the adrenal gland it increases production of aldosterone. Aldosterone increases sodium retention. Higher sodium rentention means higher water retention.
Central nervous system
At the central nervous system it stimulates thirst, increases production ADH. ADH increases water reabsorption by the collecting system. Note that in the absence of ADH no reabsorption takes place in the collecting system
All of the above actions will lead to an increase in the blood pressure

45. Reabsorption and secretion along the collecting system
Water and solute loss is regulated by aldosterone and ADH
Reabsorption
Sodium ion, bicarbonate, and urea are resorbed
Secretion
pH is controlled by secretion of hydrogen or bicarbonate ions

46. The Effects of ADH on the DCT and Collecting Ducts

47. Function of the vasa recta
Removes solutes and water
Balances solute reabsorption and osmosis in the medulla

48. Composition of normal urine
Varies with the metabolic and hormonal events of the body
Reflects filtration, absorption and secretion activity of the nephrons
Urinalysis is the chemical and physical analysis of urine

49. A Summary of Renal Function

50. A Summary of Renal Function

51. Urine production ends with fluid entering the renal pelvis
Rest of urinary system transports, stores and eliminates
Ureters
Bladder
Urethra

52. A Radiographic View of the Urinary System

53. The ureters and The urinary bladder
Pair of muscular tubes
Extend from renal pelvis to the bladder
Peristaltic contractions force urine toward the urinary bladder
The urinary bladder
Hollow, muscular organ
Reservoir for the storage of urine
Contraction of detrusor muscle voids bladder

54. Organs for the Collection and storage of Urine

55. Organs for the Collection and storage of Urine

56. Organs for the Collection and storage of Urine

57. The urethra
Extends from the urinary bladder to the exterior of the body
Passes through urogenital diaphragm (external urinary sphincter)
Differs in length and function in males and females

58. The Histology of the Organs that Collect and Transport Urine

59. Micturition reflex and urination
Urination coordinated by micturition reflex
Initiated by stretch receptors in wall of bladder
Urination requires coupling micturition reflex with relaxation of external urethral sphincter

60. The Micturition Reflex

61. Changes with aging include:
Decline in the number of functional nephrons
Reduction of GFR
Reduced sensitivity to ADH
Problems with the micturition reflex

62. You should now be familiar with:
The components of the urinary system and their functions
The location and structural features of the kidneys
The structure of a nephron, and the processes involved in the formation of urine
The normal characteristics, composition, and solute concentrations of a representative urine sample

63. You should now be familiar with:
The factors that influence filtration pressure and the rate of filtrate formation
The types of transport mechanisms found along the nephron
How antidiuretic hormone and aldosterone levels influence the volume and concentration of urine