Physiology of kidney
Irfan Idris
Physiology Department, Medical
Faculty, UNHAS
Objectives
With the end of this session you are be able
to :
• have knowledge of physiologic anatomy of the
kidneys
• understand how kidney creates urine
• understand filtration & tubular transport process
• have knowledge about role of tubuloglomerular
feedback
Physiologic anatomy of the kidneys
Blood Supply
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Interlobular vein
Interlobular artery
Renal pelvis
Renal artery
Renal vein
Ureter
Cortex
Medulla
Arcuate vein
Arcuate artery
• Renal artery  interlobar
artery  arcuate artery 
interlobular artery 
afferent arteriole 
glomerulus  efferent
arteriole  peritubular
artery  vasa recta  vv.
peritubular  arcuate
vein  interlobar vein 
renal vein
NEPHRON
Nephron is a functional unit of kidney. Each kidney consists of about
one million nephrons. The tubule is made up of a number of sections,
the proximal tubule, the medullary loop (loop of Henle), and the distal
tubule which finally empties into the collecting duct.
URINE FORMATION
Filtration and tubular transport
• Filtration : a fluid that resembles plasma is filtered
through the glomerular capillaries into the renal tubules
– Molecules with a radius of r <1.8 nm (molecular mass < 10 000
Da) freely pass through the filter,
– While those with a radius of r > 4.4nm (molecular mass >80
000DA, e.g., globulins) normally cannot pass through.
– Only a portion of molecules where 1.8 nm < r < 4.4nm applies
are able to pass through the filter.
– Negatively charged particles (e.g., albumin: r = 3.4 nm) are less
permeable than neutral substances of equal radius because
negative charges on the wall of the glomerular filter repel the
ions.
• The GFR in an average-sized normal man
is approximately 125 mL/min
• GFR = Kf x (pG – pB – G + B)
Transport of Substances Through
the Cell Membrane
Transport of Substances Through
the Cell Membrane
• Active Transport
• Passive Transport
Active transport
• Primary active transport
– Ion Pump
• Secondary active transport
– Co transport
– Counter transport
Passive Transport
• Simple diffusion
• Facilitated diffusion
SGLT-2
SGLT-1
PepT2
PepT1/2
Role of Tubuloglomerular Feedback
• The tubuloglomerular feedback
(1) an afferent arteriolar
feedback mechanism and (2)
an efferent arteriolar feedback
mechanism  arrangements
of the juxtaglomerular complex
• The juxtaglomerular complex
consists of macula densa cells
in the initial portion of the distal
tubule and juxtaglomerular
cells in the walls of the afferent
and efferent arterioles.
Acid base
• The lungs and kidneys work together to produce
a normal extracellular fluid and arterial pH of
7.35-7.45.
• The kidney excretes fixed acid and performs
three functions to achieve this 1)Tubular
secretion of acid 2) Glomerular filtration of
buffers which combine with H+ 3) Ammonia is
produced enzymatically from glutamine and
other amino acids, and is secreted in the tubules
Excretion of waste products
• Filtration occurs as blood flows through
the glomerulus. Some substances not
required by the body, and some foreign
materials (e.g. drugs) may not be cleared
by filtration through the glomerulus. Such
substances are cleared by secretion into
the tubule and excreted from the body in
the urine
Hormones and the Kidney
• Renin (see above) increases the production of
angiotensin II which is released when there is a
fall in intravascular volume e.g. haemorrhage
and dehydration.
• Aldosterone promotes sodium ion and water
reabsorption in the distal tubule and collecting
duct where Na+ is exchanged for potassium
(K+) and hydrogen ions by a specific cellular
pump.
• Atrial Natruretic Peptide(ANP) is
released when atrial pressure is increased
e.g. in heart failure or fluid overload. It
promotes loss of sodium and chloride ions
and water chiefly by increasing GFR.
• Antidiuretic Hormone (ADH) increases
the water permeability of the distal tubule
and collecting duct, thus increasing the
concentration of urine.
• The hormones
interact when blood
loss or dehydration
occurs to maintain
intravascular volume.
The flow diagram
(left) illustrates this
Other Substances Produced by
the kidney
• 1,25 dihydroxy vitamin D (the most active
form vitamin D) which promotes calcium
absorption from the gut.
• Erythropoietin which stimulates red cell
production
Micturition
• Process by which the urinary bladder empties
when it becomes filled
– First, the bladder fills progressively until the tension in
its walls rises above a threshold level
– this elicits the second step, which is a nervous reflex
called the micturition reflex that empties the bladder
or, if this fails, at least causes a conscious desire to
urinate.
• Although the micturition reflex is an autonomic
spinal cord reflex, it can also be inhibited or
facilitated by centers in the cerebral cortex or
brain stem
Blood vessels and have little to do with bladder contraction.
Some sensory nerve fibers also pass by way of
the sympathetic nerves and may be important in the
sensation of fullness and, in some instances, pain.
The sensory fibers : degree of stretch in the bladder wall, reflexes that cause bladder
emptying.
The motoric fibers : innervate wall of the ballder and the detrusor muscle. Also Most important are
the skeletal motor fibers transmitted through the pudendal nerve to the external bladder
sphincter. These are somatic nerve fibers that innervate
and control the voluntary skeletal muscle of the sphincter
As a summary  Functions of the Kidney
• Regulation of the water and electrolyte
content of the body.
• Retention of substances vital to the body
such as protein and glucose
• Maintenance of acid/base balance.
• Excretion of waste products, water soluble
toxic substances and drugs.
• Endocrine functions.
Recommended references
• Textbook of Medical Physiology, 11th
edition, Guyton & Hall, Elsevier Saunders,
2006
• Review of Medical Physiology,, 21th
edition, WF. Ganong, McGraw-Hill
Company, 2003