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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?