URINARY SYSTEM
Physiology 2
Presented by: Dr. Shaimaa Nasr Amin
Lecturer of Medical Physiology
General Education Program
Introduction and physiologic
anatomy of the kidney
1-Overview of Renal Function
Kidneys have both excretory and regulatory functions
that participates in homeostasis
*Excreting excess solutes ,water and rid waste
products
*Regulate volume and composition of body fluids
within very narrow range
Major regulatory functions of the kidneys
1-Regulation of water and electrolyte balance.
2-Excretion of metabolic waste products.
3-Excretion of foreign chemicals.
4-Endocrine functions .
5-Regulation of arterial blood pressure.
6-Regulation of acid base balance.
7-Gluconeogenesis.
8-Secretion of prostaglandins and bradykinin.
Physiologic anatomy of the kidneys
-Site: on the posterior wall of the abdomen ,outside the
peritoneal cavity.
-Weight= 150 gm /each kidney.
-Dimensions: Length <12cm.
Width <8cm.
-Surrounded by thin but tough capsule.
-The renal artery, vein, lymphatics, nerve supply and
ureter enter the kidney at he hilum on the medial side
Renal mass is
divided into
Outer cortex
Granular and
deeper in colour
Inner medulla
Striated and
lighter in colour
Pelvis
Major
calyces
Minor calyces
Renal papilla
Multiple renal
Pyramids
Medulla
1 . Renal Vein 2 . Renal Artery 3 . Renal Calyx 4 . Medullary
Pyramid 5 . Renal Cortex 6 . Segmental Artery 7 . Interlobar Artery 8 . Arcuate Artery 9 . Arcuate Vein 10 . Interlobar Vein 11 . Segmental Vein 12 . Renal Column 13 . Renal Papillae 14 . Renal Pelvis 15 . Ureter
Nephron as a functional unit -There are about 1.3 million
nephrons in each human kidney.
-Each is capable of forming urine
(functional unit)
Parts of the nephron
1- Glomerulus
2-Proximal convoluted tubule
3-Loop of Henle
4-Distal convoluted tubule
5-Collecting ducts
1-Glomerulus *Tuft of capillaries contained within the dilated blind
end of renal tubule (Bowman’s Capsule).
*The capillaries are supplied by afferent arteriole
and drained by efferent arteriole.
*It is high pressure capillary bed (,the hydrostatic
pressure is 60 mmHg)
2-Proximal convoluted tubules *15mm ,lie in the cortex
*Wall made of single layer of cells with apical tight
junctions.
*The luminal edges have brush borders due to
presence of many microvilli.
3- Loop of Henle U-shaped extension of PCT that dips in renal medulla.
Consists of :
a) Descending limb .
b) Ascending limb.
*The wall of the descending +lower½ of the ascending
limb= Thin Segment of loop of Henle
*Upper ½of the ascending limb = Thick segment of loop
of Henle
4-Distal Convoluted Tubule 5mm long lies in the cortex.
No distinct brush border but there are few microvilli.
5-Collecting Ducts 20mm long pass through renal cortex and medulla to
empty into the pelvis of the kidney
Collecting ducts lined by 2 types of cells:
2-Intercalated cells 1-Principal cells
2-Intercalated cells
(I cells)
1-Principal cells
(P cells)
*Found in smaller number .
*Have more microvilli,
mitochondria and
cytoplasmic vesicles.
Involved in:
Acid secretion.
Bicarbonate reabsorption.
Predominant ,relatively tall
Involved in :
Na+ reabsorption.
H2O reabsorption.
Types of Nephrons Juxtamedullary
Nephrons
Cortical Nephrons
15% 85% % of total
number
Deep in renal cortex near the
medulla
In the outer portion of renal
cortex
Glomeruli
Long &dips deeply into the
medullary pyramids
Short &,penetrate a short
distance into the medulla
Loop of Henle
Vasa recta + Peritubular
capillary
The tubule is surrounded by
peritubular capillary
Vascular
structures
supplying tubule
Play important role in urine
concentration
Special Functions
Juxta Glomerular apparatus
-Specialized tubular and vascular cells located at the
vascular pole where afferent and efferent arterioles
enter and leave the glomerulus.
-Plays important role in auto regulation of renal blood
flow and GFR during change in arterial pressure .
JGA Consists of:
1-Macula densa.
2-Juxtaglomerular
cells.
3-Lacis cells.
1-Macula densa *Modified tubular cells in the initial portion of distal
tubule that comes in contact with afferent and efferent
arterioles .
*The macula densa is in close proximity to JG cells.
*They monitor the composition of fluid in tubular lumen
at this point ( chemoreceptors that is stimulated by ↓
Nacl load ) .
2-Juxtaglomerular cells -Epithelioid granular cells located at the media of
afferent arterioles and to lesser extent the efferent arterioles as they enter the glomeruli.
*They secret renin.
*Act as baroreceptors and respond to change in perfusion pressure
*Stimulated by ↓ renal perfusion pressure or hypovolemia
3-Lacis cells
-These agranular cells located at the
junction between afferent and efferent
arterioles.
-They contain renin .
Renal blood flow The kidneys receive 21% of cardiac output
Renal Vascular arrangement:
*Aorta → Renal artery → interlobar arteries & Arcute & intralobular arteries
*Interlobular arteries → Afferent arterioles glomerular capillary → efferent arterioles→Peritubular capillaries → interlobular veins → arcute veins → interlobar veins → renal vien
capillary beds 2
associated with
each nephron
Glomerular
capillary bed
Peritubular
capillary bed
1-The glomerular capillary bed
(High pressure bed) *Receive its blood from afferent arterioles .
*The hydrostatic pressure is about 60mmHg (causes
rapid filtration of fluid).
What are the causes of this high
pressure?
*This high pressure is due to: 1-The renal arteries are direct branches of abdominal
aorta.
2-The afferent arterioles are short straight branches of
interlobular arteries .
3-The efferent arterioles have high resistance than the
afferent arterioles.
2-Peritubular capillary bed
(Low pressure bed) *The hydrostatic pressure is about 13mmHg.
*Behave like venous end of the capillaries.
*The low pressure permits fluid reabsorption
from the interstitium into the blood.
Regional blood flow *Renal cortex receives most of renal blood flow 98%
for filtration of large volume of plasma through the
glomeruli.
*while renal medulla receives 2% of renal blood flow
to form concentrated urine.
Autoregulation of renal blood flow -When the kidney is perfused at a moderate
pressure (90-220 mmHg) the renal blood flow is
relatively kept constant by change of renal
vascular resistance .
-Renal autoregulation is present in denervated and
isolated kidney (independent of nerves or
hormones)
Mechanisms of autoregulation of renal
blood flow 1- With rise of pressure:
-Stretch cause contraction of smooth muscles of
afferent arterioles ,this prevent excessive ↑ in renal
blood flow.
-Stretch of the vascular wall ↑ Ca++ influx from ECF
into the muscle fibers causing them to contract.
2-At low pressure:
Angiotensin II plays an important role by
constricting the efferent arteriole thus
maintaining the GFR.
Aim of autoregulation: To maintain constant GFR and to allow control
of renal excretion of water and solutes
despite marked changes in arterial blood
pressure.
Innervation of renal vessels and renal
tubules Sympathetic fibers supply: stimulation causes
1)Renal vessels:
V.C with ↓ in renal blood flow and GFR.
2)JGA:
↑ renin secretion by juxtaglomerular cells (mediated by B1
adrenergic receptor).
3)Renal tubule: ↑Na+ reabsorption by tubular cells by direct
action of norepinephrine on renal tubular cells.
Thank you