1. Chapter 14 The Urinary System
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

2. Kidneys Overview of kidney functions Maintain H2O balance in the body
Maintain proper osmolarity of body fluids, primarily through regulating H2O balance
Regulate the quantity and concentration of most ECF ions
Maintain proper plasma volume
Help maintain proper acid-base balance in the body
Excreting (eliminating) the end products (wastes) of bodily metabolism
Excreting many foreign compounds
Producing erythropoietin
Producing renin
Converting vitamin D into its active form
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

3. Urinary System Know organs and functions
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

4. Nephron Functional unit of the kidney
Smallest unit that can perform all the functions of the kidney
Approximately 1 million nephrons/kidney
Each nephron has two components
Vascular component
Tubular component
Arrangement of nephrons within kidney gives rise to two distinct regions
Outer region
Renal cortex (granular in appearance)
Inner region
Renal medulla
Made up of striated triangles called renal pyramids
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

5. Nephron Two types of nephrons
Distinguished by location and length of their structures
Juxtamedullary nephrons
Cortical nephrons
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

6. Nephron
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

7. Glomerular filtration
Basic Renal Processes
Glomerular filtration
Tubular reabsorption
Tubular secretion
Urine results from these three processes.
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

8. Glomerular Filtration
Fluid filtered from the glomerulus into Bowman’s capsule pass through three layers of the glomerular membrane
Glomerular capillary wall
Single layer of endothelial cells
More permeable to water and solutes than capillaries elsewhere in the body
Basement membrane
Acellular gelatinous layer
Composed of collagen and glycoproteins
Inner layer of Bowman’s capsule
Consists of podocytes that encircle the glomerulus tuft
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

9. Glomerular Filtration and Layers of Glomerular Membrane
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

10. Forces Involved in Glomerular Filtration
Three physical forces involved
Glomerular capillary blood pressure
Plasma-colloid osmotic pressure
Bowman’s capsule hydrostatic pressure
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

11. Glomerular Filtration Rate
Unregulated influences on the GFR
Pathologically plasma-colloid osmotic pressure and Bowman’s capsule hydrostatic pressure can change
Plasma-colloid osmotic pressure
Severely burned patient ↑ GFR
Dehydrating diarrhea ↓ GFR
Bowman’s capsule hydrostatic pressure
Obstructions such as kidney stone of enlarged prostate can decrease filtration and elevate capsular hydrostatic pressure
Controlled adjustments in GFR
Glomerular capillary blood pressure can be controlled to adjust GFR to suit the body’s needs
Two major control mechanisms
Autoregulation (aimed at preventing spontaneous changes in GFR)
Myogenic mechanism
Tubuloglomerular feedback (TGF)
Extrinsic sympathetic control (aimed at long-term regulation of arterial blood pressure)
Mediated by sympathetic nervous system input to afferent arterioles
Baroreceptor reflex
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

12. Adjustments of Afferent Arteriole Caliber to Alter The GFR
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

13. Glomerular Filtration Rate
Influenced by changes in filtration coefficient
This coefficient is not constant but is subject to physiological control.
The coefficient depends on surface area and the permeability of the glomerular membranes. Both can be modified by contractile activity within the membrane.
The kidneys receive 20 to 25 percent of the cardiac output
The total blood flow through the kidneys average 1,140 ml per minute. If the cardiac output is 5 liters, this figure is 22 % of the cardiac output.
This kidneys need to receive this large blood flow to monitor and control the ECF
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

14. Basic Renal Processes Tubular reabsorption
Glomerular filtration
Tubular reabsorption
Tubular secretion
Urine results from these three processes.
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

15. Reabsorption Transepithelial Transport
Passive reabsorption
No energy is required for the substance’s net movement
Occurs down electrochemical or osmotic gradients
Active reabsorption
Occurs if any one of the steps in transepithelial transport of a substance requires energy
Movement occurs against electrochemical gradient
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

16. Na+ Reabsorption Tubule area % of Na+ reabsorbed
An active Na+ - K+ ATPase pump in basolateral membrane is essential for Na+ reabsorption
Of total energy spent by kidneys, 80% is used for Na+ transport
Na+ is not reabsorbed in the descending limb of the loop of Henle
Water follows reabsorbed sodium by osmosis which has a main effect on blood volume and blood pressure
Na+ Reabsorption
Tubule area
% of Na+
reabsorbed
Role of Na+ reabsorption
Proximal tubule
67%
Plays role in reabsorbing glucose, amino acids, H2O, Cl-, and urea
Ascending limb of the loop of Henle
25%
Plays critical role in kidneys’ ability to produce urine of varying concentrations
Distal and collecting tubules 8%
Variable and subject to hormonal control; plays role in regulating ECF volume
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

17. Sodium Reabsorption
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

18. RAAS Renin-angiotensin-aldosterone system
Most import and best known hormonal system involved in regulating Na+
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

19. Passive Reabsorption of Urea at the End of the Proximal Tubule
Glucose and amino acids are reabsorbed by sodium-dependent, secondary active transport.
Electrolytes other than Na+ that are reabsorbed by the tubules have their own independently functioning carrier systems within the proximal tubule
The reabsorption of water in the proximal tubule increases the concentration of urea in the tubule, as water is lost from the tubule. This produces a concentration gradient for urea from the tubule into the interstitial fluid.
Generally, unwanted waste products are not reabsorbed
Passive Reabsorption of Urea
at the End of the Proximal
Tubule
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

20. Basic Renal Processes Tubular secretion Glomerular filtration
Tubular reabsorption
Tubular secretion
Transfer of substances from peritubular capillaries into the tubular lumen
Involves transepithelial transport (steps are reversed)
Kidney tubules can selectively add some substances to the substances already filtered
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

21. Tubular Secretion Most important secretory systems are for H+ K+
Important in regulating acid-base balance
Secreted in proximal, distal, and collecting tubules K+
Keeps plasma K+ concentration at appropriate level to maintain normal membrane excitability in muscles and nerves
Secreted only in the distal and collecting tubules under control of aldosterone
Organic ions
Accomplish more efficient elimination of foreign organic compounds from the body
Secreted only in the proximal tubule
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

22. Plasma Clearance
Volume of plasma cleared of a particular substance per minute (not the amount of the substance removed)
Varies for different substances, depending on how the kidneys handle each substance
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

23. Urine Excretion
Depending on the body’s state of hydration, the kidneys secrete urine of varying concentrations.
Too much water in the ECF establishes a hypotonic ECF (result = dilute urine)
A water deficit establishes a hypertonic ECF (result = conc. urine)
A large, vertical osmotic gradient is established in the interstitial fluid of the medulla (from 100 to 1200 mosm/liter to 1200 mosm/liter). This increase follows the hairpin loop of Henle deeper and deeper into the medulla.
This osmotic gradient exists between the tubular lumen and the surrounding interstitial fluid.
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

24. Countercurrent Multiplication
The medullary vertical osmotic gradient is established by countercurrent multiplication
Comparing the descending and ascending limbs of the loop of Henle:
The descending ling is highly permeable to water but does not extrude sodium for reabsorption.
The ascending limb actively transports NaCl out of the tubular lumen into the surrounding interstitial fluid. It is impermeable to water. Therefore, water does not follow the salt by osmosis.
There is a countercurrent flow produced by the close proximity of the two limbs.
The ascending limb produces an interstitial fluid that becomes hypertonic to the ascending limb. It does this by pumping out sodium ions. Water does not follow. This interstitial fluid faces against the flow of fluid (countercurrent) in the descending limb, attracting the water by osmosis for reabsorption
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

25. Role of Vasopressin
Vasopressin-controlled, variable water reabsorption occurs in the final tubular segments.
65 percent of water reabsorption is obligatory in the proximal tubule. In the distal tubule and collecting duct it is variable, based on the secretion of ADH.
The secretion of vasopressin increases the permeability of the tubule cells to water. An osmotic gradient exists outside the tubules for the transport of water by osmosis.
Vasopressin is produced in the hypothalamus and stored in the posterior pituitary. The release of this substance signals the distal tubule and collecting duct, facilitating the reabsorption of water.
Vasopressin works on tubule cells through a cyclic AMP mechanism.
During a water deficit, the secretion of vasopressin increases. This increases water reabsorption.
During an excess of water, the secretion of vasopressin decreases. Less water is reabsorbed. More is eliminated.
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

26. Nephron Vascular component Dominant part is the glomerulus
Ball-like tuft of capillaries
Water and solutes are filtered through glomerulus as blood passes through it
Filtered fluid then passes through nephron’s tubular component
From renal artery, inflowing blood passes through afferent arterioles which deliver blood to glomerulus
Efferent arteriole transports blood from glomerulus
Efferent arteriole breaks down into peritubular capillaries which surround tubular part of nephron
Peritubular capillaries join into venules which transport blood into the renal vein
Tubular component
Hollow, fluid-filled tube formed by a single layer of epithelial cells
Components
Bowman’s capsule
Proximal tubule
Loop of Henle
Descending limb
Ascending limb
Juxtaglomerular apparatus
Distal tubule
Collecting duct or tubule
Chapter 14 The Urinary System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

27. Countercurrent

28. Renal Anatomy

29. Renal Processes 1

30. Renal Processes 2

31. Urine Concentration

32. Remaining class periods 4/13, 4/16, 4/20, 4/23 and 5/2 for students not graduating.
Exam 4
Exam IV (9, 12 14) will be available 4/17 at 12:00 PM until 4/18 at 5:00  PM.  I will not reset this exam after 4/17 at 5:00 PM
Lab exam 3 ECG and Endocrinology 4/20
Endocrinology lectures 4/20 and 4/23
Last Exam (18,19) cumulative material will be available 4/26 at 12:00 PM until 4/27 at 5:00 PM.  I will not reset this exam after 4/26 at 12:00 PM
5/2 review final exam and determine final grades.