HH Dept of Physiology Lec12 Objectives List the functions of kidney Describe the morphology of the typical nephron and its blood supply Describe the concept of clearance What is excretion ID: 785024
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Slide1
Renal system
Dr.
Zainab
H.H
Dept. of Physiology
Lec.1,2
Slide2Objectives
List
the functions of
kidney
Describe the morphology of the typical
nephron
and its blood supply
.
Describe the concept of clearance
Slide3What is excretion?
Throwing
out of waste product is known as excretion
.
The organs
through which excretion occurs.
1. Kidneys: Excrete water and water soluble waste products.
2. Lungs: Excrete carbon dioxide, water
vapour
and other volatile substances such
as acetone
.
3. Skin: Excretes water and salts mainly in the form of sweat.
4. Gastrointestinal tract: Excretes undigested food.
Slide4The Role of the Kidneys in the Body
Includes:
Regulation of the volume and composition of the ECF, by maintaining a balance between intake and output of water and electrolytes in the body.
Excretion and elimination of waste products of metabolism, such as the excretion of urea,
creatinine
and uric acids; as well as the excretion of various toxins such as drugs and food additives.
The kidneys act as endocrine glands producing hormones, such as “erythropoietin hormone” and
renin
.
Slide5Playing a dominant role in the long-term and short-term regulation of arterial blood pressure.
Kidneys along with the respiratory system contribute to acid-base regulation.
Finally, kidneys synthesize glucose from
amino acids
and other precursors
Slide6Metabolic waste products excreted by kidneys are: Urea from protein.
Uric acid from nucleic acid
.
Creatinine
from muscle
creatine.
End products of
haemoglobin
breakdown.
Slide7STRUCTURE OF NEPHRON
Nephron
is a structural and functional unit of the kidney.
Each
nephron
is capable
of forming
urine.
There
are
two types
of
nephrons
:
1.
Cortical
nephrons
.
Glomeruli
are present near the surface of the kidneys.
These
nephrons
constitute about 86% of total
nephrons
.
The
main function of
cortical
nephrons
is
absorption of sodium
.
Slide82. Juxtamedullary
nephrons
.
Glomeruli
lie at the junction of cortex and medulla of the kidney.
These constitute 14% of the
nephrons
.
The main role of
juxtamedullary
nephron
is to
increase concentration of
medullary
interstitial fluid.
Slide9Slide10Two kidneys together have two millions nephrons
.
Nephron
consists of two major parts:
Glomerulus
.
A long renal
tubule.
1.
Glomerulus
.
It is made up of tuft of capillaries which connect
afferent arteriole with
an
efferent
arteriole.
Capillaries
have single layer of endothelial cells attached to
a basement
membrane
.
Slide11Bowman’s capsule encloses the glomerulus and is formed of two layers:
inner layer which covers the
glomerular
capillaries is called visceral layer,
outer layer is called parietal layer.
Space between visceral and parietal layers is continued as the lumen of the tubular portion.
Slide12fluid-filled space, Bowman’s space, is formed within the capsule.
Blood of capillary and fluid of Bowman’s space are separated by the
glomerular
membrane.
From the Bowman’s capsule, tubule of the
nephron
extends, the lumen of which is continuous with the Bowman’s space.
Slide13Slide142. Renal tubule.
It is mainly formed of three parts:
(a)
Proximal convoluted tubule
.
(b)
Loop of
Henle
consisting of:
Thin segment :
walls of descending limb and lower end of ascending limb are very thin. Therefore, they are termed thin segment.
Hair pin bend
.
Thick ascending limb
or segment
Slide15Slide16(c) Distal convoluted tubules.
open into initial arched collecting ducts called
cortical collecting ducts
present in renal
cortex.
Seven to ten such ducts form straight collecting duct which passes into medulla forming
medullary
collecting ducts.
Slide17In the inner zone of medulla they form
papillary ducts
or ducts of Bellini.
These open into papilla of
minor calyces
.
Three or four minor calyces
unite to form
one
major calyx
.
The major calyces open into
pelvis of
ureter
.
The
pelvis
is an expanded portion present in renal sinus and it
continues as
ureter
Slide18Slide19Slide20BLOOD FLOW TO KIDNEYS
Rate of blood flow to kidneys is 1200 ml/min.
This is quite high as compared to their size.
State peculiarities of renal circulation.
1.Very high blood supply
, about 21% of cardiac output.
2.Two sets of capillaries.
The
glomerular
capillaries
.
These combine to form efferent arteriole which in turn breaks into
peritubular
capillary network around the tubules of cortical
nephrons
.
Slide21vasa
recta
which are loop-shaped vessels in
juxtamedullary
nephrons
the efferent arterioles continue as these loops dip into the
medullary
pyramids alongside the loops of
Henle
3.Glomerular capillary bed
has a high hydrostatic pressure because efferent arteriole is of a smaller diameter than afferent arteriole which offers considerable resistance to blood flow.
Slide22Slide234. Peritubular
capillary bed
is a low pressure bed.
5. Only 1 to 2% of blood flows through
vasa
recta
. The flow is very sluggish.
6. Renal blood flow shows remarkable constancy
in face of blood pressure changes due to
autoregulation
Slide24The kidneys regulate the hydrostatic pressure in both capillary beds (
glomerular
&
peitubular
) , by adjusting resistance of the afferent and efferent arterioles.
High hydrostatic pressure in
GC
(60 mmHg) causes
rapid fluid filtration
; whereas a much lower pressure in the
peritubular
capillaries
(13 mmHg) permits
rapid fluid
reabsorption
.
Slide25The afferent arteriole is a short, straight branch of the interlobular artery.
The
efferent arteriole
, that drains the GC, has a
relatively high resistance
than the
afferent arteriole.
Slide26The Process of Urine Formation:
Urine formation begins with the
Filtration of plasma through the GC
into the Bowman’s space.
As the filtered fluid flows through the remaining portions of the tubule, its composition is altered as a result of two main processes:
Tubular
reabsorption
.
Tubular secretion
.
and both processes will produce the final product,
urine
.
Concept of Clearance:
The renal clearance of a substance is the volume of plasma that is completely cleared or cleaned of that substance by the kidney per unit of time. (usually expressed as
mL
/ minute).
However, renal clearance provides a useful way of quantifying renal excretory functions.
It can be used to quantify the rate at which blood flows through the kidneys, as well as to measure the basic kidney functions such as GFR.
Slide28Concept of Clearance (continues):
Renal clearance of a substance (S) is calculated by dividing the urinary excretion rate of (S) (U
S
×
V
•
) by its plasma concentration (P
S
), as expressed below
:
U
S
× V
•
C
S
=
P
S
Where: U
S
= urine concentration of S.
V
•
= urine flow rate/ minute = (0.9
mL
/ minute).
P
S
= plasma concentration of S.
Slide29Clearance
of any
substance
depends on the
behavior of the tubular cell
towards that substance:
If a substance like
inulin
, which is freely filtered at the
glomerulus
level and is neither reabsorbed nor secreted by the renal tubule, then its
clearance
equals
to
GFR.
On the other hand, if a substance is
reabsorbed by the renal tubule
, its
clearance
is
lower
than the
GFR
.
Finally, if a substance that is in addition to filtration is
secreted by the renal tubule
, then its
clearance
is
higher than the GFR.
Slide30THANK YOU