Chapter 19a

The Kidneys

About this Chapter

• Anatomy of the urinary system• Overview of kidney function• Homeostasis• pH• Electrolytes• fluid• Filtration• Reabsorption• Secretion• Excretion

• Micturition

Functions of the Kidneys

• Regulation of extracellular fluid volume and blood pressure

• Regulation of osmolarity• Maintenance of ion balance• Homeostatic regulation of pH• Excretion of wastes• Production of hormones

Figure 19-1a

Kidney

Ureter

Urinary bladder

Urethra

(a) The urinary system

THE URINARY SYSTEMAnatomy: The Urinary System

Figure 19-1b

Ureter

Diaphragm

Aorta

Inferior vena cava

Right kidney Left kidney

Renal artery

Renal vein

(b) The kidneys are located retroperitoneallyat the level of the lower ribs.

Urinarybladder

Peritoneum(cut)

Rectum(cut)

Left adrenal gland Anatomy: The Urinary System

Figure 19-1c

Cortex

Medulla

Renal pelvis

Ureter

Capsule

(c) The kidney, in cross section.

Nephrons

Anatomy: The Urinary System

Polycystic kidney

Figure 19-1i

Cortex

Medulla

Arterioles

Nephrons

(i) Some nephrons dip deepinto the medulla.

Anatomy: The Urinary System

Figure 19-1g–h

Glomerulus(capillaries)

Peritubularcapillaries

Juxtaglomerularapparatus

(g) One nephron has two arteriolesand two sets of capillaries.

Efferent arteriole

Afferentarteriole

(h) Juxtamedullary nephronwith vasa recta

Glomerulus

Peritubularcapillaries

Vasa recta

Loop ofHenle

Collectingduct

Anatomy: The Urinary System

Figure 19-1d–e

Anatomy: The Urinary System

Figure 19-1f

(f) The capillaries of the glomerulus form aball-like mass.

Cut edge ofnephron tubule

STRUCTURE OF THE NEPHRON

Glomerulus

Anatomy: The Urinary System

Figure 19-1j

Bowman’scapsule

Distal tubuleProximal tubule

Collectingduct

Ascendinglimb

Descendinglimb

Loop ofHenle

(j) Parts of a nephron

Descendinglimb of loop

begins

Ascendinglimb of loopends

To bladder

Anatomy: The Urinary System

Figure 19-2

Collectingduct

Distal tubule

Afferentarteriole

Loopof

Henle

Efferentarteriole

Glomerulus

Peritubular capillaries

ProximaltubuleBowman’s

capsule

To renalvein

To bladder andexternal environment

KEY

= Filtration: blood to lumen

= Reabsorption: lumen to blood

= Secretion: blood to lumen

= Excretion: lumen to externalenvironment

Kidney Function

• Filtration, reabsorption, secretion, and excretion

Table 19-1

Kidney Function

Figure 19-3

– + =

Efferentarteriole

Afferentarteriole

Glomerulus

Bowman’scapsule

Peritubularcapillaries To renal vein

To bladder andexternal environment

amount of soluteexcreted

Amountfiltered

Amountreabsorbed

Amountsecreted

Tubule

Kidney Function

• The urinary excretion of substance depends on its filtration, reabsorption, and secretion

Figure 19-4

>19% of fluidis reabsorbed.

Plasma volumeentering afferentarteriole = 100%

<1% ofvolume isexcreted toexternalenvironment.

Remainderof nephron

Bowman’scapsule

Glomerulus

>99% of plasmaentering kidneyreturns to systemiccirculation.

Efferent arteriole Peritubularcapillaries

Afferentarteriole

20% ofvolumefilters.

80%

1

2 3

4

5

The Filtration Fraction

Figure 19-5a

Bowman’scapsule

Capsularepithelium

Podocyte

GlomerularcapillaryLumen ofBowman’scapsule

Proximaltubule

Efferentarteriole

Afferentarteriole

Thickascending

limb ofloop ofHenle

(a) The epithelium around glomerularcapillaries is modified into podocytes.

The Renal Corpuscle

Figure 19-5d

Filtration slit

Basal lamina

Filteredmaterial

(d) Filtered substances passthrough endothelial poresand filtration slits.

Foot processof podocyte

Lumen ofBowman’scapsule

Capillarylumen

Pores inendothelium

The Renal Corpuscle

Figure 19-5c

(c) Podocyte foot processes surround eachcapillary, leaving slits through which filtrationtakes place.

Lumen ofBowman’s

capsule

Podocytefoot

processes

Glomerularcapillary

Podocyte

Mesangialcell

Capillaryendothelium

The Renal Corpuscle

Forces that Influence Filtration

• Hydrostatic pressure (blood pressure)• Colloid osmotic pressure• Fluid pressure created by fluid in Bowman’s

capsule

Figure 19-6

Filtration

• Filtration pressure in the renal corpuscle depends on hydrostatic pressure, and is opposed by colloid osmotic pressure and capsule fluid pressure

Afferentarteriole Glomerulus

Bowman’scapsule

PH = Hydrostatic pressure (blood pressure) = Colloid osmotic pressure gradientdue to proteins in plasma but notin Bowman’s capsulePfluid = Fluid pressure created by fluid inBowman’s capsule

PH – – = net filtration pressure

55 30– – = 10mm Hg15

KEY

Efferentarteriole 15 mm Hg

30 mm Hg

55 mm HgPH

Pfluid

Net filtrationpressure =10 mm Hg

Pfluid

Figure 19-7

Filtration

• Autoregulation of glomerular filtration rate takes place over a wide range of blood pressures

Figure 19-8a

Filtration

• Resistance changes in renal arterioles alter renal blood flow and GFR

Figure 19-8b

Filtration

Figure 19-8c

Filtration

GFR Regulation

• Myogenic response• Similar to autoregulation in other systemic

arterioles• Tubuloglomerular feedback• Paracrine control by macula densa

• Hormones and autonomic neurons• By changing resistance in arterioles• By altering the filtration coefficient

• Surface area

Figure 19-9

Juxtaglomerular Apparatus

Bowman’s capsule

Proximal tubule

Granular cells

Efferent arteriole

Afferent arteriole Endothelium

Ascendinglimb of loop

of Henle

Glomerulus

Macula densa cells

(a) (b)

Figure 19-10, steps 1–5 (4 of 4)

Tubuloglomerular FeedbackGFR increases.

Flow through tubule increases.

Flow past macula densa increases.

Paracrine from maculadensa to afferent arteriole

Afferent arteriole constricts.

Resistance in afferentarteriole increases.

Hydrostatic pressurein glomerulus decreases.

GFR decreases.

Efferent arteriole

Granular cells

Afferent arteriole

Bowman’s capsule

Glomerulus

Macula densa

Distal tubule

Collectingduct

Loopof

Henle

Proximaltubule

1

2

3

4

5

1

23

45