urinary system part two - linn-benton community college
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Review 1. Name the 4 regions of the renal tubules
2. The structural and functional regions that form urine are the __________.
3. Micturition is controlled by the ____________ nervous system.
4. How is filtrate different that urine? (2 sentences)
Part 2
Urine Formation Filtrate
Blood plasma minus most proteins
Urine <1% of total filtrate
Contains metabolic wastes and unneeded substances
Urine Formation 1. Glomerular filtration
2. Tubular reabsorption Returns components to blood
Glucose amino acids, water and salt
3. Tubular secretion Reverse of reabsorption
Selective addition to urine
4. Water conservation
Figure 25.10
Cortical
radiate
artery
Afferent arteriole
Glomerular capillaries
Efferent arteriole
Glomerular capsule
Rest of renal tubule
containing filtrate
Peritubular
capillary
To cortical radiate vein
Urine
Glomerular filtration
Tubular reabsorption
Tubular secretion
Three major
renal processes:
Glomerular Filtration Occurs at renal corpuscle
Passive process driven by hydrostatic pressure
Glomerulus is a very efficient filter
Permeable membrane
Water and small solutes pushed through filter
Large surface area
Higher blood pressure
Figure 25.8
Glomerulus
Glomerular capsule
Afferent arteriole
Efferent arteriole
Red blood cell
Podocyte cell body (visceral layer)
Foot processes of podocytes Parietal layer
of glomerular capsule
Proximal tubule cell
Lumens of glomerular capillaries
Endothelial cell of glomerular capillary
Efferent arteriole
• Macula densa cells
of the ascending limb of loop of Henle
• Granular cells
• Extraglomerular
mesangial cells
Afferent arteriole
Capsular space
Renal corpuscle Juxtaglomerular
apparatus
Mesangial cells between capillaries
Juxtaglomerular
apparatus
(c) Three parts of the filtration membrane
Fenestration
(pore)
Filtrate in
capsular
space
Foot processes
of podocyte
Filtration
slit
Slit
diaphragm
• Basement membrane • Capillary endothelium
Capillary
Filtration membrane
• Foot processes of podocyte
of glomerular capsule
Plasma
(b) Filtration slits between the podocyte foot processes
Foot
processes
Filtration slits
Podocyte
cell body
Figure 25.9a
Glomerular capillary
covered by podocyte-
containing visceral
layer of glomerular
capsule
Glomerular capillary
endothelium (podocyte
covering and basement
membrane removed)
Proximal
convoluted
tubule
Parietal layer
of glomerular
capsule
Afferent
arteriole
Glomerular capsular space
Fenestrations
(pores)
Efferent
arteriole
Podocyte
cell body
Foot processes
of podocyte
Filtration slits
Cytoplasmic extensions
of podocytes
(a) Glomerular capillaries
and the visceral layer of
the glomerular capsule
Glomerular Filtration Filtration membrane
Allows passage of water and small solutes
Fenestrations prevent filtration of blood cells
Negatively charged basement membrane repels large anions
Glomerular Filtration Net Filtration Pressure (NFP)
Glomerular hydrostatic pressure (HPg)
Capsular hydrostatic pressure (HPc)
Blood osmotic pressure (OPg)
Glomerular Filtration Net Filtration Pressure (NFP)
The pressure responsible for filtrate formation
NFP = HPg – (OPg + HPc)
Figure 25.11
Glomerular
capsule
Afferent
arteriole
10
mm
Hg
Net
filtration
pressure
Glomerular (blood) hydrostatic pressure
(HPg = 55 mm Hg)
Blood colloid osmotic pressure
(Opg = 30 mm Hg)
Capsular hydrostatic pressure
(HPc = 15 mm Hg)
Net Filtration Pressure
NFP = HPG – (OPG + HPC)
= 55 mm Hg – (30 mmHg + 15 mmHg)
= 10 mmHg
Glomerular Filtration Glomerular Filtration Rate (GFR)
125 ml/min
1800 liters of blood through kidneys/day
= 1200 ml/min = about 180 liters filtrate/day
Glomerular Filtration Factors affecting GFR
Kidney disease
↓ blood osmotic pressure, ↑ capsular osmotic pressure
Hemorrhage
↓ glomerular blood hydrostatic pressure
Hypotension
Glomerular blood hydrostatic pressure = capsule hydrostatic and blood osmotic pressure = filtration stops!
Renal suppression
Glomerular Filtration GFR is tightly controlled by two types of mechanisms
Intrinsic controls (renal autoregulation)
Act locally within the kidney
Extrinsic controls
Nervous and endocrine mechanisms that maintain blood pressure and affect kidneys
Glomerular Filtration Intrinsic controls
Maintain a nearly constant GFR when MAP is in the range of 80–180 mm Hg
Renal autoregulation
Mechanisms that cause vasoconstriction of afferent arterioles in response to increased BP
Extrinsic Controls Sympathetic nervous system
At rest
Renal blood vessels are dilated
Renal autoregulation mechanisms prevail
GFR maintained
Extreme stress
Norepinephrine and epinephrine released
Both cause constriction of afferent arterioles
Inhibits filtration
Shunts blood to other vital organs
Tubular Reabsorption 125 ml/min of filtrate produced
Most of this fluid is reabsorbed
A selective transepithelial process
Includes active and passive process
Most occurs in PCT
Figure 25.10
Cortical
radiate
artery
Afferent arteriole
Glomerular capillaries
Efferent arteriole
Glomerular capsule
Rest of renal tubule
containing filtrate
Peritubular
capillary
To cortical radiate vein
Urine
Glomerular filtration
Tubular reabsorption
Tubular secretion
Three major
renal processes:
Tubular Reabsorption PCT
Site of most reabsorption
65% of Na+ and water
All nutrients
Ions
Small proteins
Tubular Reabsorption Transcellular route
Luminal membranes of tubule cells → cytosol of tubule
cells → basolateral membranes of tubule cells →
endothelium of peritubular capillaries
Figure 25.13
Active transport
Passive transport
Peri- tubular
capillary
2
4
4
3
3 1
1 2 4 3
Filtrate in tubule lumen
Transcellular
Paracellular
Paracellular
Tight junction Lateral intercellular space
Capillary endothelial cell
Luminal membrane
Solutes
H2O
Tubule cell Interstitial fluid
Transcellular
Basolateral membranes
1 Transport across the luminal membrane.
2 Diffusion through the cytosol.
4 Movement through the interstitial fluid and into the capillary.
3 Transport across the basolateral membrane. (Often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces.)
Movement via the
transcellular route involves:
The paracellular route
involves:
• Movement through leaky tight junctions, particularly in the PCT.
Tubular Reabsorption Paracellular route
Between cells
Limited to water movement and reabsorption of Ca2+, Mg2+, K+, and some Na+ in the PCT where tight junctions are leaky
Figure 25.13
Active transport
Passive transport
Peri- tubular
capillary
2
4
4
3
3 1
1 2 4 3
Filtrate in tubule lumen
Transcellular
Paracellular
Paracellular
Tight junction Lateral intercellular space
Capillary endothelial cell
Luminal membrane
Solutes
H2O
Tubule cell Interstitial fluid
Transcellular
Basolateral membranes
1 Transport across the luminal membrane.
2 Diffusion through the cytosol.
4 Movement through the interstitial fluid and into the capillary.
3 Transport across the basolateral membrane. (Often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces.)
Movement via the
transcellular route involves:
The paracellular route
involves:
• Movement through leaky tight junctions, particularly in the PCT.
Tubular Reabsorption Sodium
Most abundant cation in filtrate
Primary active transport out of the tubule cell by Na+-K+ ATPase in the basolateral membrane
Na+ passes in through the luminal membrane by secondary active transport or facilitated diffusion mechanisms
Figure 25.14
1 At the basolateral membrane,
Na+ is pumped into the
interstitial space by the Na+-K+
ATPase. Active Na+ transport
creates concentration gradients
that drive: 2 “Downhill” Na+ entry at the
luminal membrane.
4 Reabsorption of water by
osmosis. Water reabsorption
increases the concentration of
the solutes that are left
behind. These solutes can
then be reabsorbed as
they move down their
concentration gradients:
3 Reabsorption of organic
nutrients and certain ions by
cotransport at the luminal
membrane.
5 Lipid-soluble
substances diffuse by the
transcellular route.
6 Cl– (and other anions),
K+, and urea diffuse by the
paracellular route.
Filtrate
in tubule
lumen
Glucose
Amino
acids
Some
ions
Vitamins
Lipid-soluble
substances
Nucleus
Tubule cell
Paracellular
route
Interstitial
fluid Peri-
tubular
capillary
Tight junction
Primary active transport
Passive transport (diffusion)
Secondary active transport
Transport protein
Ion channel or aquaporin
Cl–, Ca2+, K+
and other
ions, urea
Cl–
3Na+
2K+
3Na+
2K+
K+
H2O
Na+
6
5
4
3
2
1
Tubular Reabsorption Sodium
Low hydrostatic pressure and high osmotic pressure in the peritubular capillaries
Promotes bulk flow of water and solutes (including Na+)
Tubular Maximum Transport maximum (Tm) reflects the number of
carriers in the renal tubules available
When the carriers are saturated, excess of that substance is excreted
Example: too much glucose in the blood entering glomerulus will cause glucosuria
Tubular Reabsorption Reabsorption of nutrients, water, and ions
Blood becomes hypertonic to filtrate
Water is reabsorbed by osmosis
Cations and fat-soluble substances follow by diffusion
Figure 25.14
1 At the basolateral membrane,
Na+ is pumped into the
interstitial space by the Na+-K+
ATPase. Active Na+ transport
creates concentration gradients
that drive: 2 “Downhill” Na+ entry at the
luminal membrane.
4 Reabsorption of water by
osmosis. Water reabsorption
increases the concentration of
the solutes that are left
behind. These solutes can
then be reabsorbed as
they move down their
concentration gradients:
3 Reabsorption of organic
nutrients and certain ions by
cotransport at the luminal
membrane.
5 Lipid-soluble
substances diffuse by the
transcellular route.
6 Cl– (and other anions),
K+, and urea diffuse by the
paracellular route.
Filtrate
in tubule
lumen
Glucose
Amino
acids
Some
ions
Vitamins
Lipid-soluble
substances
Nucleus
Tubule cell
Paracellular
route
Interstitial
fluid Peri-
tubular
capillary
Tight junction
Primary active transport
Passive transport (diffusion)
Secondary active transport
Transport protein
Ion channel or aquaporin
Cl–, Ca2+, K+
and other
ions, urea
Cl–
3Na+
2K+
3Na+
2K+
K+
H2O
Na+
6
5
4
3
2
1
Figure 25.10
Cortical
radiate
artery
Afferent arteriole
Glomerular capillaries
Efferent arteriole
Glomerular capsule
Rest of renal tubule
containing filtrate
Peritubular
capillary
To cortical radiate vein
Urine
Glomerular filtration
Tubular reabsorption
Tubular secretion
Three major
renal processes:
Tubular Secretion Reabsorption in reverse
K+, H+, NH4+, creatinine, and organic acids move from
peritubular capillaries or tubule cells into filtrate
Involves active transport since no concentration gradients in this case
Figure 25.18a
Cortex
Outer
medulla
Inner
medulla
(a)
(b)
(c)
(e)
(d)
Na+ (65%)
Glucose
Amino acids
H2O (65%) and
many ions (e.g.
Cl– and K+)
300
Milliosmols
600
1200
Blood pH regulation
H+,
NH4+
HCO3–
Some
drugs
Active transport
(primary or
secondary) Passive transport
(a) Proximal convoluted tubule:
• 65% of filtrate volume reabsorbed
• Na+, glucose, amino acids, and other nutrients actively
transported; H2O and many ions follow passively
• H+ and NH4+ secretion and HCO3
– reabsorption to
maintain blood pH (see Chapter 26)
• Some drugs are secreted
Tubular Secretion Principle effects
Rids body of
Foreign substances (penicillin and other drugs)
Nitrogenous wastes
Excess K+
Controls blood pH:
Altering amounts of H+ or HCO3– in urine
Review continued… 5. Name the 4 steps to urine formation
6. Dilute urine = _________ urine
7. Concentrated urine = ___________ urine
Questions?