Download Urinary System

Collin County Community College
BIOL. 2402
Anatomy & Physiology
WEEK 12
Urinary System
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INTRODUCTION
Main functions of the kidneys are
• regulate blood volume , water content
• regulate blood composition e..g. Na, Cl, K, pH
• remove waste products and toxins
Kidneys are the guardians of the internal environment
They receive 25 % of cardiac output. Thus blood is
filtered every 4 minutes !
190 liters of fluid (plasma) is filtered daily to produce 1 liter of urine
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Urinary System Organization
• The kidneys
– Produce urine
• The ureters
• The urinary bladder
– Stores urine
• The urethra
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Urinary System Organization
• 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
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Urinary System Organization
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Kidney Anatomy
Pyramid
• Outer capsule
• Under capsule is an
• outer cortex area
• inner medulla
• Medulla contains pyramids.
• They contain the functional units of
the kidneys = nephrons
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Kidney Anatomy
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Kidney Anatomy
• The medulla consists of 6-18 renal pyramids
• The cortex is composed of roughly 1.25 million nephrons
• Nephrons perform 3 basic functions that result in urine
formation
• filtration of blood
• re-absorption of essential elements back into the blood
• secretion of additional elements from blood into the
forming urine
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Nephron Anatomy
Bowman’s Capsule
• always located in cortex
Proximal Convoluted Tubule
• always located in cortex
Loop of Henle (dips into medulla)
• Descending limb
• Ascending limb
Distal Convoluted Tubule
• located in cortex again
Collecting Tubules and duct
• dips back into medulla
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Nephron Anatomy/Function
•
•
•
•
Production of filtrate
Reabsorption of organic nutrients
Reabsorption of water and ions
Secretion of waste products into tubular fluid
This function of the nephron is correlated with the
lining of the tubules; they are lined with simple
epithelials.
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Nephron Anatomy/Function
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Nephron Anatomy/Function
What the nephrons excrete is equals to what is filtered out of
the blood plus what is secreted from the blood minus what is
reabsorbed back into the blood.
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Nephron Anatomy/Function
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Nephron Anatomy/Function
There are 2 kinds of nephrons
• cortical nephrons :
the loop of Henle barely
reaches into the medulla
• juxta medullary nephrons :
the loop of Henle dips deep
into the medulla
15 % of nephrons are juxta
medullary nephrons ; these are
very important in water reabsorption
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Renal Blood Supply
Since the nephrons are the filters of the blood, blood needs to be
carried to the nephrons.
• A Renal artery feeds the kidney. It then shows repeated branches
– Segmental artery
– Interlobar artery
– Arcuate artery
– Interlobular artery
– Afferent arterioles
• Renal venules follow similar opposing pattern ending with renal
vein
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Renal Blood Supply
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Renal Blood Supply
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Renal Blood Supply
Bowman’s capsule of each
nephron is the filtering part and
located in the cortex area.
Blood enters the Bowman’s
capsule via the afferent arteriole.
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Nephron Blood Supply
Afferent arteriole
• enters Bowman’s capsule
Glomerulus
• capillary network
within Bowman’s
capsule
Efferent arteriole
• leaves Bowman’s capsule
Peritubular capillaries
• surround the Proximal and Distal tubules
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Nephron Blood Supply
Vasa Recta
• peritubular capillaries that surround and follow the loop of Henle in
juxta medullary nephrons
Thus we have 2 capillary beds associated with the nephrons
• First one helps to produce the filtrate inside the lumen of
the nephron (glomerulus)
• Second one functions in re-absorption and secretion aspect
of urine filtration (peritubular capillaries)
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Nephron Blood Supply
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Diagram of nephron with associated electron microscope pictures. Note
that all along the nephron, the cell layer of the tubules is only one cell layer
thick ( indicates importance of diffusion, secretion, absorption).
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Vacular Resistance in Kidneys
Controls of Resistance are located at entrance and exit of glomerulus; this
allows for a steady pressure within the glomerulus ( which is important for
homeostasis of filtering process)
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RENAL PHYSIOLOGY
• Main function of the kidneys is to regulate blood
volume and composition
• It does so by involving a process of excretion of
waste products such as
– Urea
– Creatinine
– Uric acid
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RENAL PHYSIOLOGY
Three basic mechanisms are involved :
• 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
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RENAL PHYSIOLOGY
• Filtration occurs in the Bowmans Capsule at the
Glomerulus
• Filtration is very non-specific. Filtration is modified by carrier
mediated transport, resulting in re-absorbption and/or
additonal secretion into the filtrate.
– Facilitated diffusion
– Active transport
– Cotransport
– Countertransport
• Carrier proteins have a transport maximum (Tm)
– Determines renal threshold
• Diffusion and osmosis aid in kidney function.
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RENAL PHYSIOLOGY
• 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
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RENAL PHYSIOLOGY
• Most regions of the nephron
perform a combination of
functions
• General functions can be
identified
– Filtration in the renal
corpuscle
– Nutrient re-absorption
along the PCT
– Active secretion at PCT
and DCT
– Loops of Henle regulate
final volume and solute
concentration
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RENAL PHYSIOLOGY
Glomerular Filtration
• Filtration process that occurs in Bowman’s Capsule
• Blood is filtered and the filtrate ends up in the tubule
system of the nephron
What creates the filter system ?
Combination of the membrane systems of the
capillaries and Bowman’s capsule cells
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Microscopic Anatomy of Bowman’s Capsule
Special cells, called Podocytes, cover the capillaries
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Microscopic Anatomy of Bowman’s Capsule
Pedicels of podocytes (feet extensions) create filtration slits
Podocyte in Bowman’s capsule
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Microscopic Anatomy of Bowman’s Capsule
Scanning electron microscope picture of the
fingerlike filtration slits of the podocytes !
Compare this with the diagram on left side
and previous slide !
This system provides a filtering
mechanism roughly similar to a
coffee filter, but much more refined !
It houses 3 filtering mechanisms !
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Microscopic Anatomy of Bowman’s Capsule
Filtration System in Bowman’s capsule Capillary endothelial cells
have many pores
• let everything through except
blood cells and large proteins
Basement membrane or
Basal Lamina
• Is negatively charged and
repels most smaller proteins
Foot process of the
Podocytes
• Form additional filtration slits
that only let small molecules
through
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Filtration System in Bowman’s capsule
What are the forces involved the filter system ?
• Similar forces that are involved in capillary fluid
exchange in the tissues !
• Hydrostatic pressure from the blood ( = blood
pressure )
• Hydrostatic pressure in capsule from the filtrate
• Osmotic (oncotic) pressure from the blood
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Filtration System in Bowman’s capsule
• Filtration occurs as fluids move across the glomerulus
• The positive filtration pressure is the glomerular hydrostatic
pressure due to blood pressure in the glomerular capillaries
(GHP)
– Capsular hydrostatic pressure opposes (CsHP)
– Blood colloid osmotic pressure opposes (BCOP)
• Net hydrostatic pressure (NHP) = GHP – CsHP
• Filtration (FP) = GHP - CsHP - BCOP = NHP – BCOP
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Filtration System in Bowman’s capsule
Net filtration pressure is thus a modest 10 mm Hg
Net filtration pressure is determined by the 3 forces
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Bowman’s capsule
Net Filtration pressure (NFP)
• Pressure force that drives fluid out of the blood
(out of the glomerulus) and into Bowman’s
capsule
• Due to the characteristics of the ‘filter’, the filtrate
that passes into the tubule system of the nephron
equals blood minus formed elements and minus
proteins
• Since proteins do not leave the blood stream, but
water does, the efferent arteriole will have a higher
concentration of proteins and blood cells ( will be
more viscous
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Bowman’s capsule
Glomerular Filtration Rate (GFR)
Total amount of filtrate formed per minute by the kidneys.
Depends on :
• NFP
• what happens when NFP = 0 ?
• what happens to NFP when BP increases ?
• what happens when afferent blood osmolarity
increases ? ( use next slide )
• Total filtration area ( what happens with a unilateral
nephrectomy ? )
• Filtration membrane permeability ( what happens
when some Glomeruli get clogged up ? )
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Bowman’s capsule
Blood proteins changes
affect this force
Blood pressure changes
affect this force
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Regulation of GFR
Regulation of the GFR is an important homeostatic process.
• If GFR is too high, we would produce a high rate of filtrate
and re-absorption of essential elements would not be
efficient.
• If GFR is too low, we would not be able to secrete
important waste products fast enough
Regulation of the GFR occurs via 3 mechanisms
• Renal Auto-regulation
• Neural regulation
• Renin-Angiotensin Feedback
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Regulation of GFR
1. Renal Auto-regulation
a. Juxta Glomerular Apparatus (JGA) feedback
• Distal Convoluted tubule makes contact with afferent
and efferent arteriole
• This region is called the JGA
• Contains 2 groups of cells that are important in
kidney function
• Juxta glomerular cells : are part of the afferent
arteriole wall and act as mechano-receptors and
endocrine cells
• Macula Densa cells : are part of the DCT and
they act as chemoreceptors/endocrine cells.
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Regulation of GFR
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Regulation of GFR
1. Renal Auto-regulation
b. Myogenic Effect
• When blood vessels and smooth muscles are stretched they tend to
contract
• Increased blood pressure will
cause vasoconstriction in the
afferent arteriole and
counteract a possible
increase in NFP.
• Overall effect of autoregulation is that GFR does
not change much when a
person experiences acute
blood pressure changes.
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Regulation of GFR
2. Neural Regulation
• Mostly a sympathetic effect
• Produces powerful vasoconstriction of afferent arteriole
• Decreases GFR and slows production of filtrate
• Important for example during blood-loss ; prevents body from
excreting more urine ( fluid)
• Changes the regional pattern of blood flow
• Alters GFR
• Also Stimulates release of renin by JGA
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Regulation of GFR
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Regulation of GFR
3. Renin-Angiotensin Feedback
The following will result in a Renin release by the
Juxtaglomerular cells in JGA apparatus
• Drop in Blood pressure (reduced stretch in afferent arteriole)
• Reduced release of the vasoconstrictor from the Macula Densa
cells ( thus, reduced Na+ flow in the DCT)
• Direct stimulation of JG cells by sympathetic stimuli
• All these stimuli release Renin, resulting in Angiotensin II production
• Efferent arterioles have more Ang II receptors than Afferent
arterioles ; thus this will increase the Pressure in the glomerulus (why ? )
• Ang. II also results in release of Aldosterone and ADH
( what do they do ? )
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Regulation of GFR
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Regulation of GFR
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Regulation of GFR
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