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26-1
Anatomy and Physiology, Sixth Edition
Rod R. SeeleyIdaho State UniversityTrent D. StephensIdaho State UniversityPhilip TatePhoenix College
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
*See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.
Chapter 26Chapter 26
Lecture OutlineLecture Outline**
26-3
Urinary System Functions
• Filtering of blood
• Regulation of – blood volume– concentration of blood solutes– pH of extracellular fluid– blood cell synthesis
• Synthesis of Vitamin D
26-5
Location and External Anatomyof Kidneys
• Location– Lie behind peritoneum
on posterior abdominal wall on either side of vertebral column
– Lumbar vertebrae and rib cage partially protect
– Right kidney slightly lower than left
• External Anatomy– Renal capsule
• Surrounds each kidney
– Perirenal fat• Engulfs renal capsule and acts
as cushioning
– Renal fascia• Anchors kidneys to abdominal
wall
– Hilum• Renal artery and nerves enter
and renal vein and ureter exit kidneys
26-6
Internal Anatomy of Kidneys
• Cortex: Outer area– Renal columns
• Medulla: Inner area– Renal pyramids
• Calyces– Major: Converge to form
pelvis
– Minor: Papillae extend
• Nephron: Functional unit of kidney– Juxtamedullary
– Cortical
26-9
Internal Anatomy of Kidneys
• Renal corpuscle– Bowman’s capsule
• Parietal layer• Visceral layer
– Glomerulus• Network of capillaries
• Arterioles– Afferent
• Blood to glomerulus
– Efferent• Drains
• Tubules– Proximal (convoluted)
tubule– Loops of Henle
• Descending limb• Ascending limb
– Distal (convoluted) tubules
• Collecting ducts
26-12
Ureters and Urinary Bladder
• Ureters– Tubes through which
urine flows from kidneys to urinary bladder
• Urinary bladder– Stores urine
• Urethra– Transports urine from
bladder to outside of body
– Difference in length between males and females
– Sphincters• Internal urinary
• External urinary
26-15
Filtration
• Filtration– Renal filtrate
• Plasma minus blood cells and blood proteins
• Most (99%) reabsorbed
• Filtration membrane– Fenestrated
endothelium, basement membrane and pores formed by podocytes
• Filtration pressure– Responsible for filtrate
formation– Glomerular capillary
pressure (GCP) minus capsule pressure (CP) minus colloid osmotic pressure (COP)
– Changes caused by glomerular capillary pressure
26-17
Tubular Reabsorption
• Reabsorption– Passive transport
– Active transport
– Cotransport
• Specialization of tubule segments
• Substances transported– Active transport moves
Na+ across nephron wall
– Other ions and molecules moved by cotransport
– Passive transport moves water, urea, lipid-soluble, nonpolar compounds
26-21
Tubular Secretion
• Substances enter proximal or distal tubules and collecting ducts
• H+, K+ and some substances not produced in body are secreted by countertransport mechanisms
26-23
Urine Production
• In Proximal tubules– Na+ and other substances
removed– Water follows passively– Filtrate volume reduced
• In descending limb of loop of Henle– Water exits passively,
solute enters– Filtrate volume reduced
15%
• In ascending limb of loop of Henle– Na+, Cl-, K+ transported out of
filtrate– Water remains
• In distal tubules and collecting ducts– Water movement out
regulated by ADH• If absent, water not
reabsorbed and dilute urine produced
• If ADH present, water moves out, concentrated urine produced
26-26
Urine Concentration Mechanism
• When large volume of water consumed– Eliminate excess
without losing large amounts of electrolytes
– Response is kidneys produce large volume of dilute urine
• When drinking water not available– Kidneys produce small
volume of concentrated urine
– Removes waste and prevents rapid dehydration
26-28
Hormonal Mechanisms• ADH
– Secreted by posterior pituitary
– Increases water permeability in distal tubules and collecting ducts
• Aldosterone– Produced in adrenal cortex
– Affects Na+ and Cl- transport in nephron and collecting ducts
• Renin– Produced by kidneys,
causes production of angiotensin II
• Atrial natriuretic hormone– Produced by heart when
blood pressure increases• Inhibits ADH production
• Reduces ability of kidney to concentrate urine
26-31
Autoregulation and Sympathetic Stimulation
• Autoregulation– Involves changes in
degree of constriction in afferent arterioles
– As systemic BP increased, afferent arterioles constrict and prevent increase in renal blood flow
• Sympathetic stimulation– Constricts small arteries
and afferent arterioles
– Decreases renal blood flow
26-32
Clearance and Tubular Load
• Plasma clearance– Volume of plasma
cleared of a specific substance each minute
– Used to estimate GFR
– Used to calculate renal plasma flow
– Used to determine which drugs or other substances excreted by kidney
• Tubular load– Total amount of
substance that passes through filtration membrane into nephrons each minute
– Normally glucose is almost completed reabsorbed
26-33
Tubular Maximum
• Tubular maximum– Maximum rate at
which a substance can be actively absorbed
– Each substance has its own tubular maximum
26-34
Urine Flow and Micturition Reflex
• Urine flow– Hydrostatic pressure
forces urine through nephron
– Peristalsis moves urine through ureters
• Micturition reflex– Stretch of urinary
bladder stimulates reflex causing bladder to contract, inhibiting urinary sphincters
– Higher brain centers can stimulate or inhibit reflex
26-36
Effects of Aging on Kidneys
• Gradual decrease in size of kidney– Decrease in kidney size leads to decrease in
renal blood flow
• Decrease in number of functional nephrons• Decrease in renin secretion and vitamin D
synthesis• Decline in ability of nephron to secrete and
absorb