3. The Nephron Is the Functional Unit
of the Kidney
• Each kidney in the
about 1 million
capable of forming
urine. The kidney
Therefore, with renal
injury, disease, or
normal aging, there
is a gradual
decrease in nephron
4. Function of Kidney
• Regulation of extracellular fluid volume. The
kidneys work to ensure an adequate quantity of
plasma to keep blood flowing to vital organs.
• Regulation of osmolarity.
• Regulation of ion concentrations.
• Regulation of pH.
• Excretion of wastes and toxins.
• Production of hormones.
6. Nephron Is the Functional Unit
of the Kidney
• Nephron is the basic functional unit of kidneys that consists of a
glomerulus and its associated tubules through which the glomerular
filtrate passes before it emerges as urine”
9. • Each nephron
contains (1) a
of fluid are
filtered from the
blood, and (2) a
long tubule in
filtered fluid is
urine on its way
to the pelvis of
11. Types of Nephron
• Types of Nephron
• There are two types of nephron:
• Cortical nephron
• These are the nephrons present within the
cortex. These are short and comprise about 80%
of the total nephrons.
• Juxtamedullary nephron
• These have long loops of Henle and extend into
the medulla. These are about 20%.
12. • The renal corpuscle is the site of the filtration of blood plasma. The renal corpuscle
consists of the glomerulus, and the glomerular capsule or Bowman's capsule.
• The glomerulus is the network of filtering capillaries tuft, located at the vascular pole
of the renal corpuscle in Bowman's capsule. Each glomerulus receives its blood
supply from an afferent arteriole of the renal circulation. The glomerular blood
pressure provides the driving force for water and solutes to be filtered out of the blood
plasma, and into the interior of Bowman's capsule.
• The Bowman's capsule, also called the glomerular capsule, surrounds the
glomerulus. It is composed of a visceral inner layer formed by specialized cells called
podocytes, and a parietal outer layer composed of simple squamous epithelium.
Fluids from blood in the glomerulus are ultrafiltered through several layers, resulting
in what is known as the filtrate.
• The filtrate next moves to the renal tubule, where it is further processed to form urine.
The different stages of this fluid are collectively known as the tubular fluid.
13. Renal tubule
• The renal tubule is the portion of the nephron containing the tubular fluid filtered through the
glomerulus. After passing through the renal tubule, the filtrate continues to the collecting duct
• The components of the renal tubule are:
• Proximal convoluted tubule (lies in cortex and lined by simple cuboidal epithelium with brush
borders which help to increase the area of absorption greatly.)
• Loop of Henle (hair-pin like, i.e. U-shaped, and lies in medulla)
– Descending limb of loop of Henle
– Ascending limb of loop of Henle
• The ascending limb of loop of Henle is divided into 2 segments: Lower end of ascending
limb is very thin and is lined by simple squamous epithelium. The distal portion of
ascending limb is thick and is lined by simple cuboidal epithelium.
• Thin ascending limb of loop of Henle
• Thick ascending limb of loop of Henle (enters cortex and becomes - distal convoluted
• Distal convoluted tubule
• Connecting tubule
14. • Urine formation begins
with filtration from the
into Bowman's capsule
of a large amount of fluid
that is virtually free of
• Most substances in the
plasma, except for
proteins, are freely
filtered so that their
concentrations in the
glomerular filtrate in
Bowman's capsule are
almost the same as in
Glomerular capillary membrane
16. Glomerular Capillary Membrane
• The glomerular capillary membrane is similar to
that of other capillaries, except that it has three
(instead of the usual two) major layers:
• (1) the endothelium of the capillary,
• (2) a basement membrane, and
• (3) a layer of epithelial cells (podocytes)
surrounding the outer surface of the capillary
• Together, these layers make up the filtration
barrier that, despite the three layers, filters
several hundred times as much water and
solutes as the usual capillary membrane.
17. The juxtaglomerular
apparatus is a
formed by the distal
convoluted tubule and
the glomerular afferent
arteriole. It is located
near the vascular pole
of the glomerulus and
its main function is to
regulate blood pressure
and the filtration rate of
18. • The macula densa plays an important role in
controlling nephron function. Beyond the macula
densa, fluid enters the distal tubule that, like the
proximal tubule, lies in the renal cortex.
19. • Glomerular filtration is the process by which the kidneys filter the
blood, removing excess wastes and fluids.
• Glomerular filtration rate (GFR) is the volume of fluid filtered from
the all nephrons of both kidney per minute. The GFR is typically
recorded in units of volume per time, e.g., milliliters per minute
• The normal range of Kidney Glomerular Filtration Rate is 100 to
130 mL/min/1.73m2 in men and 90 to 120mL/min/1.73m2 in women
below the age of 40. GFR decreases progressively after the age of
21. Renal clearance
• Renal clearance describes the volume of
plasma completely cleared of a substance by the
kidneys per unit time. A higher renal clearance
suggests the substance may be cleared almost
completely in one pass through the kidneys
while a low value describes a substance that
may not be eliminated by the kidneys at all.
22. Significance of Renal clearance
• Renal clearance uses to determine renal
function. The practical aspect of the clearance
principle is that by applying it to select
compounds, one can estimate glomerular
filtration rate and renal plasma flow.
• To measure GFR.
• It is useful for renal handling of different
23. • Creatinine clearance (CrCl) is the volume of
blood plasma cleared of creatinine per unit
time. It is a rapid and cost-effective method for
the measurement of renal function. Both CrCl
and GFR can be measured using the
comparative values of creatinine in blood and
• Normal creatinine clearance is 88–128 mL/min
for healthy women and 97–137 mL/min for
24. Renal threshold
• the renal threshold is the concentration of a substance
dissolved in the blood above which the kidneys begin to
remove it into the urine. When the renal threshold of a
substance is exceeded, reabsorption of the substance by
the proximal convoluted tubule is incomplete.
• When the blood glucose level exceeds about
160–180 mg/dL (8.9-10 mmol/L), the proximal
tubule becomes overwhelmed and begins to
excrete glucose in the urine. This point is called
the renal threshold for glucose
25. PHYSIOLOGIC CONTROL OF GLOMERULAR
FILTRATION AND RENAL BLOOD FLOW
• The determinants of GFR
that are most variable and
subject to physiologic control
include the glomerular
hydrostatic pressure and the
glomerular capillary colloid
• These variables, in turn, are
influenced by the sympathetic
nervous system, hormones
and autacoids (vasoactive
substances that are released
in the kidneys and act
locally), and other feedback
controls that are intrinsic to
28. URINE FORMATION
• The rates at which different substances are excreted in
the urine represent the sum of three renal processes, (1)
glomerular filtration, (2) reabsorption of substances from
the renal tubules into the blood, and (3) secretion of
substances from the blood into the renal tubules.
• Expressed mathematically,
• Urinary excretion rate = Filtration rate
• - Reabsorption rate + Secretion rate
32. Mechanism of glucose reabsorption
• the glucose in the proximal tubule is co-transported with
sodium ions into the proximal convoluted tubule walls via
the SGLT2 and SGLT1 cotransporters. Some (typically
smaller) amino acids are also transported in this way.
Once in the tubule wall, the glucose and amino acids
diffuse directly into the blood capillaries along a
concentration gradient. This blood is flowing, so the
gradient is maintained. Lastly, sodium/potassium ion
active transport pumps remove sodium from the tubule
wall and the sodium is put back into the blood. This
maintains a sodium concentration gradient in the
proximal tubule lining, so the first step continues to
34. Why Are Large Amounts of Solutes Filtered
and Then Reabsorbed by the Kidneys?
• One advantage of a high GFR is that it allows the
kidneys to rapidly remove waste products from the body
that depend primarily on glomerular filtration for their
excretion. Most waste products are poorly reabsorbed by
the tubules and, therefore, depend on a high GFR for
effective removal from the body.
• A second advantage of a high GFR is that it allows all
the body fluids to be filtered and processed by the kidney
many times each day. Because the entire plasma
volume is only about 3 liters, whereas the GFR is about
180 L/day, the entire plasma can be filtered and
processed about 60 times each day. This high GFR
allows the kidneys to precisely and rapidly control the
volume and composition of the body fluids.
• The final part of
membrane is a
layer of epithelial
that encircle the
outer surface of
• The foot
gaps called slit
which also have
filtration of plasma
36. Filtration, Reabsorption, and
Secretion of Different Substances
• In general, tubular, reabsorption is quantitatively more
important than tubular secretion in the formation of urine,
but secretion plays an important role in determining the
amounts of potassium and hydrogen ions and a few
other substances that are excreted in the urine.
• Most substances that must be cleared from the blood,
especially the end products of metabolism such as urea,
creatinine, uric acid, and urates, are poorly reabsorbed
and are, therefore, excreted in large amounts in the
• Certain foreign substances and drugs are also poorly
reabsorbed but, in addition, are secreted from the blood
into the tubules, so that their excretion rates are high.
38. Filtration, Reabsorption, and
Secretion of Different Substances
• Nutritional substances, such as amino
acids and glucose, are completely
reabsorbed from the tubules and do not
appear in the urine even though large
amounts are filtered by the glomerular
capillaries. Each of the processes -
glomerular filtration, tubular reabsorption,
and tubular secretion - is regulated
according to the needs of the body.