Basic renal physiology - Ohio State University

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Basics of Renal Physiology
Beth Lee, Ph.D.
Physiology and Cell Biology
The Ohio State University
College of Medicine
Objectives
Define
Describe
At the end of this module, you will
learn to:
the major functions of the renal system.
the 2 types of nephrons and their anatomical
differences
Define
the segments of nephrons in the order in which
filtrate passes through.
Describe
the components of the renal corpuscle and the
filtration barrier.
Describe
the components of the juxtaglomerular
apparatus.
Define
the three basic renal processes.
Renal Physiology Text
 DC Eaton and JP Pooler, Vander’s Renal Physiology, 6th
or 7th edition McGraw-Hill Inc..

This is a concise, well-written book (in paperback, and
therefore inexpensive!) that was put together with the
needs of medical students in mind. It lists learning
objectives and gives sample questions. I use this as
the basis for my lectures.

For this lecture, please read Chapter 1.
Today’s Topic Outline
 Overall renal function
 Anatomy of nephrons
 Anatomy of the renal corpuscle and filtration
barrier
 Juxtaglomerular apparatus
 Basic renal processes
Overall Renal Function
 The kidneys process the plasma portion of the
blood so that whatever is not needed to maintain
homeostasis is excreted in the urine.
 This is done by a combination of plasma filtration
and subsequent alteration of the content of this
filtrate.
Renal Function
Regulation of total body water and osmolality
Regulation of electrolyte balance



Sodium, the major extracellular cation
Potassium, the major intracellular cation
Chloride, the major extracellular anion
Regulation of acid-base balance
Regulation of mineral balance


Calcium
Phosphorus
Renal Function (cont.)
 Excretion of metabolic products
 Urea, the major end product of protein catabolism
 Uric acid, a product of nucleic acid catabolism
 Creatinine, produced by skeletal muscle
 End products of hemoglobin breakdown (responsible
for the color of urine)
 Excretion of foreign substances
 Drugs
 Food additives
Renal Function (cont.)
 Production and secretion of hormones
 Erythropoietin (Epo), regulator of red blood cell
production
 Renin, regulates sodium balance and blood pressure
 1,25-Dihydroxyvitamin D3, the active form of vitamin D
 Gluconeogenesis during fasting: the kidney, along with
the liver, contributes to generation of glucose from amino
acids and triglycerols
Relationship of Nephron to Kidney
Nephrons: the Functional Units of the Kidney
Flow of Filtrate through the Nephron
The Renal Corpuscle
Bowman’s capsule
Afferent arteriole
Bowman’s space
Efferent arteriole
To nephron
tubules
Glomerular capillaries
Podocytes
Filtration Barrier of the Glomerulus
Podocytes
Scanning electron
micrograph of rat
podocytes
Podocytes
Podocyte cell body
Podocyte foot
processes
Basement membrane
Fenestrated endothelial layer
The Nephron Tubule
Proximal
convoluted
tubule
Distal convoluted
tubule
Collecting duct
Descending
thin limb of
loop of
Henlé
Ascending thick limb
of loop of Henlé
Juxtaglomerular Apparatus (JGA)
Quiz #1
 Place these nephron segments in the same order as the
direction of blood flow:






A. Loop of Henle
B. Collecting Duct
C. Glomerulus
D. Proximal Convoluted Tubule
E. Proximal Straight Tubule
F. Distal Convoluted Tubule
Give feedback for this answer
(The correct answer is C, D, E, A, F, B).
Quiz #2
 Which of these cell types are not part of the
juxtaglomerular apparatus?

A. Podocytes
B. Extraglomerular mesangial cells
C. Juxtaglomerular cells
D. Granular cells
E. Macula densa cells

(The correct answer is A.)




Give feedback for each answer:
why correct and incorrect.
Basic Renal Processes
 Glomerular filtration
 Reabsorption of filtered solutes from the tubule
to the blood stream
 Secretion of solutes from the blood stream to the
tubule
Glomerular Filtration
Blood flow (RBF) = 1.1 L/min
Plasma flow (RPF) = 605 ml/min
Bowman’s capsule
Afferent arteriole
Bowman’s space
GFR = 125 ml/min
To nephron
tubules
Glomerular capillaries
Podocytes
Efferent arteriole
Renal Blood Flow v. Renal Plasma Flow
(RBF v. RPF)
 Blood volume = 45% cells and 55% plasma
(average values)
 The RPF can be calculated as 55% of the RBF:
 1.1 L/min X 0.55 = 0.605 L/min = 605 ml/min
Reabsorption and Secretion
Blood
Tubule
lumen
Cell
R
S
Apical
Basolateral
Reabsorption is the
net movement of
solutes from the
tubule lumen to the
blood (the peritubular
capillaries and vasa
recta).
Secretion is the net
movement of solutes
from the blood to the
tubule lumen.
The Nephron, Simplified
Renal Handling of Hypothetical Solutes
Renal Handling of Common Solutes
Metabolism by Tubule Cells
 Metabolism by tubular epithelia has not traditionally been
considered a basic renal function, but it does certainly
alter the composition of plasma and urine.
 Some metabolism occurs simply for the cells’ own
nutritional needs.
 Other occurs in a specific attempt to change plasma and
urine composition (e.g. formation of H+ and HCO3- in
regulating blood acid-base balance).
Functions of Different Segments of the
Nephron
 Glomerulus: filters blood volume 60 times per
day
 Proximal tubule:




Reabsorbs most of filtered salt (NaCl) and water
Reabsorbs a fraction of other important ions
(phosphate, calcium, bicarbonate, potassium)
Reabsorbs useful organic substances (e.g. amino
acids and glucose)
Secretes metabolic waste products and drugs
Functions of Different Segments of the
Nephron (cont.)
 Loop of Henle: determines osmolarity of the
urine by reabsorbing varying levels of salt and
water
 Distal tubule (and connecting tubule): reabsorbs
a small percentage of salt and water
 Cortical collecting duct: responsive to
aldosterone and ADH to regulate salt and
potassium balance
 Medullary collecting duct: also regulates salt and
water balance; regulates urea reabsorption and
acid-base balance
Summary
References
Thank you
 Thank you for completing
this module. If you have
any questions, please
contact me.
 [email protected]
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