Kidney Physiology

1. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Dee Unglaub Silverthorn, Ph.D.
HUMAN PHYSIOLOGY
PowerPoint® Lecture Slide Presentation by
Dr. Howard D. Booth, Professor of Biology, Eastern Michigan University
AN INTEGRATED APPROACH
T H I R D E D I T I O N
Chapter 19
The Kidneys

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About this Chapter
• Anatomy of the excretory system
• How the kidney is organized
• How the nephron works to filter blood, recycle,
secrete, and excrete
• How filtration is regulated
• Urination reflex

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Kidney Functions
• Filter 200 liters of blood daily, allowing toxins,
metabolic wastes, and excess ions to leave the
body in urine
• Regulate volume and chemical makeup of the
blood
• Maintain the proper balance between water and
salts, and acids and bases

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Other Renal Functions
• Gluconeogenesis during prolonged fasting
• Production of renin to help regulate blood
pressure and erythropoietin to stimulate RBC
production and activation of Vitamin D
• Homeostatic regulation: ECF volume, osmolarity,
ion & pH balance
• Excretion: Metabolic wastes & foreign molecules

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Excretory System: Anatomy Review
Figure 19-1: Anatomy Summary: The Urinary System
• Kidney
• Cortex
• Medulla
• Pelvis
• Nephrons
• Ureter
• Bladder
• Urethra

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Urinary System Organs
Figure 25.1a

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Kidney Location and External Anatomy
Figure 25.2a

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Kidney Location and External Anatomy
• The bean-shaped kidneys lie in a retroperitoneal
position in the superior lumbar region and extend
from the twelfth thoracic to the third lumbar
vertebrae
• The right kidney is lower than the left because it is
crowded by the liver
• The lateral surface is convex and the medial
surface is concave, with a vertical cleft called the
renal hilus leading to the renal sinus
• Ureters, renal blood vessels, lymphatics, and
nerves enter and exit at the hilus

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Internal Anatomy
Figure 25.3b

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Other Urinary System Organs
• Urinary bladder – provides a temporary storage
reservoir for urine
• Paired ureters – transport urine from the kidneys
to the bladder
• Urethra – transports urine from the bladder out
of the body

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The Nephron
• Nephrons are the structural and functional units
that form urine, consisting of:
• Glomerulus – a tuft of capillaries associated
with a renal tubule
• Glomerular (Bowman’s) capsule – blind, cup-
shaped end of a renal tubule that completely
surrounds the glomerulus

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Kidney Functions: Overview
Figure 19-3: The excretion of a substance depends on the amount that was filtered, reabsorbed, and secreted

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Nephron Functions: Overview
Figure 19-2: Filtration, reabsorption, secretion, and excretion

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Glomerulus & Bowman's Capsule: Blood Filtration
• Capillaries
• Podocytes
• Mesanglial cells
• Bulk flow
• Solutes
• Water
• (Few proteins)
• (Not cells)

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Glomerulus & Bowman's Capsule: Blood Filtration
Figure 19-4: Structure of the renal corpuscle

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Glomerular Flow Rate (GFR)
Figure 19-6: Filtration pressure in the renal corpuscle
• Capillary
• Hydrostatic
pressure
• Colloidal
• Capsule pressure
• Back pressure
• Net Filtration p
• GFR  180L/day
(about 1% is
excreted)

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Glomerular Flow Rate (GFR)
Figure 19-5: The filtration fraction

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Regulation of GFR
• Autoregulation
• Myogenic stretch
• Tubuloglomerular feedback
• Macula densa
• J G cells
• ANS-Sympathetic
• Arteriole vasoconstriction
• Hormones/paracrines
• Angiotensin II
• Prostaglandins

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Regulation of GFR
Figure 19-9: The juxtaglomerular apparatus

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Reabsorption: 10 Active Transport
• (Passive diffusion in)
• Active Transport
• Na+ to ECF
• K+ into cell
• ATP-ase
• Uses energy
• Na+ ECF
peritubular capillaries
• Reabsorption  blood

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Reabsorption: 10 Active Transport
Figure 19-11: Sodium reabsorption in the proximal tubule

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Reabsorption: Secondary Active Transport
Figure 19-12: Sodium-linked glucose reabsorption in the
proximal tubule
• Na+ linked 20 transport
• Symport
• Glucose
• Ions
• Amino acids
• Proximal tubule, key site

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Reabsorption: Passive Transport & Trancytosis
• Passive Transport of urea
• Na+ pumped out
• H2O follows
• Passive
•  [urea]
• [urea] higher than ECF
• passive diffusion to ECF
• Trancytosis of proteins

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Reabsorption: Passive Transport & Trancytosis
Figure 19-13: Passive reabsorption of urea in the proximal tubule

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Reabsorption: Receptors can Limit
• Transport maximum
• Saturation (# of receptors)
• Competition
• Specificity
• Renal Threshold
• Example: glucosuria

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Reabsorption: Receptors can Limit
Figure 19-15: Glucose handling by the nephron

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Secretion: From Peritubular Blood vessels & ECF
Figure 19-2 : Filtration, reabsorption, secretion, and excretion

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The key difference between vasa
recta and peritubular capillaries is
that vasa recta are the special
type of peritubular capillaries
that supply oxygen and
nutrients to the medulla of the
kidney while peritubular
capillaries are the capillaries
that arise from the efferent
arteriole and feed the kidney
with oxygen and nutrients.

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Solute Clearance: Rate of removal from the Blood
Figure 19-16: Inulin clearance
• Information on
Kidney Function
• GFR
• Reabsorption
rates
• Secretion rates

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• Excess ions, H2O, molecules, toxins, "foreign
molecules"
• "nitrogenous waste": NH4
+ and excess urea
• Kidney Ureter  bladder urethra
out of body
Excretion:
All Filtration Products that are not reabsorbed

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Excretion:
All Filtration Products that are not reabsorbed
Figure 19-5: The filtration fraction

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Urination: Micturation reflex
• Bladder:
• smooth muscles
• internal sphincter
• external sphincter
• Regulation

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Urination: Micturation reflex
Figure 19-18: The micturition reflex

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Summary
• Kidney produces urine, ureter bladder
urethra
• Nephron filters, reabsorbs, secretes and excretes
• Arteriole pressure dictates GFR through
autoregulation, ANS and hormonal influences
• Most filtrate is reabsorbed & returned via
peritubular blood vessels; excess & toxic remains
are excreted
• Urination reflex uses involuntary and voluntary
paths