3. Objectives
At the end of this session students will be able to:
Define the Urinary System.
List the organs of Urinary system
Understand the functions of the urinary system
Explain how kidney contributes to homeostasis
Describe the location of the kidney.
Describe the :
gross structure of kidney
microscopic structure of kidney.
4. Objectives
Discuss the role of each component of nephron in
terms of :
Filtration
selective reabsorption &
secretion involved in the formation of urine.
Briefly discuss the role of kidney in maintaining
water and electrolyte balance.
Discuss the structure and functions of
Ureters
Urinary bladder
Urthera
Briefly the process of micturition
5. Urinary System
The urinary system plays a vital part in
maintaining homeostasis of water and
electrolyte concentrations within the body.
The kidneys produce urine that contains
metabolic waste products, including the
nitrogenous compounds urea and uric acid,
excess ions and some drugs.
7. Organs of Urinary System
The urinary system is the main excretory system and
consists of the following structures:
2 kidneys, which secrete urine
2 ureters, which convey the urine from the kidneys
to the urinary bladder
The urinary bladder where urine collects and is
temporarily stored
The urethra through which the urine passes from the
urinary bladder to the exterior.
8.
9. Functions of Urinary System (FRS)
1. Filtration of the blood by removing toxins or
waste.
2. Reabsorption of vital nutrients, ions and
water by conserving important materials
3. Secretion of excess materials by preventing a
build-up of certain materials in the body such
as drugs, waste, etc.
10. Functions…
Activation of Vitamin D
Active Vitamin D (D3) assists homeostasis by increasing
calcium absorption from the digestive tract
Release of Erythropoietin by the kidney
New RBCs assist homeostasis by ensuring adequate
Oxygen and Carbon Dioxide transport
Release of Renin by the kidney
• Renin stimulates the formation of a powerful
vasoconstrictor called Angiotensin II
• Angiotensin II assists homeostasis by causing
vasoconstriction which increases blood pressure
11. Secretion of H (+1) and reabsorption of HCO3
(-1)
Eliminates excess hydrogen ions and conserves
buffer material such as bicarbonate hence controlling
acid/base conditions in body fluids
13. Location of Kidney
• Kidney lie on the posterior abdominal wall one on each
side of the vertebral column behind the peritoneum and
below the diaphragm.
• They extend from the level of 12th thoracic vertebrae to
the third lumber vertebrae receiving some protection
from lower rib cage
• Right kidney is slightly lower then the left because of
considerable space occupied by the liver.
14.
15. Structure of Kidney
Bean shaped organ, weighs 150g
Length 11cm Width 6cm Thickness 3cm
Three layers of tissue surrounds each kidney
Renal capsule (innermost)
Adipose capsule
Renal Fascia (outermost)
These layers protect, maintains shape, and anchors
kidney with the posterior abdominal wall
19. Gross Structure of Kidney
Fibrous capsule: Surrounds the kidney
Cortex: Reddish brown layer of tissue immediately
below the capsule. Portion of cortex b/w pyramids
called renal column.
Medulla: They are 8-18 in number . It forms the
inner most layer consisting of pale conical shape
structure called renal pyramids have an apex & base.
Renal papilla: It is the apex of pyramids
Renal lobe: Consists of renal pyramid, its overlaying
area of renal cortex and one half of each adjacent
renal column.
20. Hilum: The concave medial border of the kidney
where the renal blood and lymph vessels, the ureter and
nerve enter. The hilum expand into a cavity called renal
sinus
Renal pelvis: Funnel shaped structure which receive
urine formed by the kidney is called pelvis. It has a
number of distal branches called calyces.
Minor calyx: It is the region after the papilla.
Major Calyx: Minor calyx joins to form major calyx
Each kidney has 8-18 minor calyces and 2-3 major
calyces.
24. Microscopic structure of kidney
Each kidney is composed of about 1–2 million
functional units, the nephrons, and a smaller
number of collecting ducts.
Each nephron consists of:
1. Renal corpuscles (close end)
2. Renal tubules (open end)
25.
26. Renal Corpuscles
• The two components of renal corpuscles are:
glomerulus (capillary network)
glomerular (Bowman) capsule.
Note the difference in
the diameters of the
afferent and the
efferent arteriole
27. Renal Tubules
Renal tubule consists of the three parts:
Proximal convoluted tubule
It is attached to the glomerular capsule, it is tightly coiled
rather then straight
Loop of Henle
It the proximal and distal convoluted tubule. Its first part
called descending limb of LOH, dips into the renal medulla,
it then make turn and return to renal cortex as a ascending
limb of LOH
Distal convoluted tubule
This part away from glomerular capsule
28. Cortical and Juxtamedullary Nephrons
Cortical nephron
They are 80-85%. Their renal corpuscle lie in the
cortex and they have short LOH that lie mainly
in the cortex and penetrate only in the outer
region of medulla
Juxtamedullary nephron:
They are 15-20%.The renal corpuscle of these
nephron lie deep in the cortex near medulla and
they have long LOH that extend into the deeper
region of the medulla.
29.
30. Histology of Nephron:
Glomerular capsule consists of visceral and parietal
layer.
Visceral layer consists of modified simple squamous
epithelial cells called Podocytes. Many foot like
projection of these cells (pedicels) wrap around the
single layer of endothelium of the glomerular
capillaries.
32. Parietal Layer
The parietal layer of glomerular capsule consists
of simple squamous epithelium and form the
outer wall of the capsule.
Fluid filter in the glomerular capillaries enter
into the capsular space and then to the renal
tubules.
33.
34. Juxtaglomerular Apparatus
It consists of:
• Specialized macula densa cells
• Specialized granular juxtaglomerular (JG) cells
Macula Densa Cells:
The ascending limb of LOH make contact with
afferent arteriole, here the columnar tubule cells
become crowded which are known as macula
densa.
Juxtaglomerular cells
Along side the macula densa the wall of afferent
arteriole contains modified smooth muscle fibers
called juxtaglomerular cells.