The document provides an overview of the urinary system and kidney anatomy and histology. It describes the key functions and components of the kidneys, including the cortex and medulla. It explains the nephron is the functional unit of the kidney, consisting of the renal corpuscle and uriniferous tubule. The renal corpuscle contains the glomerulus and Bowman's capsule. Filtration occurs across the glomerular capillary endothelium, glomerular basement membrane, and podocytes within Bowman's capsule.

1. Histology of the kidney
part 1
Maha Hammady Hemdan
MBBCh, Demonstrator at Medical Histology & Cell Biology
Department,
Faculty of Medicine Alexandria university

2. OVERVIEW OF THE URINARY SYSTEM
The urinary system consists of the
paired kidneys; paired ureters, which
lead from the kidneys to the urinary
bladder; and the urethra, which
leads from the bladder to the
exterior of the body.

3. OVERVIEW OF THE URINARY SYSTEM
• functions of the kidneys:
A.excresion:
-Excretion of excess water and electrolytes
-bioactive drugs metabolic wastes
B.metabolic
-Gluconeogenesis
C.homeostasis
-Regulation of the acid-base balance
D.hormonal
-Secretion of renin (regulation of blood pressure )
-Secretion of erythropoietin
-Conversion of the steroid prohormone vitamin D to
the active form (1,25-dihydroxyvitamin D3 or calcitriol)

4. OVERVIEW OF THE URINARY SYSTEM
Anatomy
• The kidneys are large, reddish, bean-shaped organs
located on either side of the spinal column in the
retroperitoneal space of the posterior abdominal cavity.
the right kidney positioned slightly lower. Each kidney
measures approximately 10 cm long X 6.5 cm wide X 3 cm
thick. On the upper pole of each kidney, embedded within
the renal fascia and a thick protective layer of perirenal
adipose tissue, lies an adrenal gland. The medial border
of the kidney is concave and contains a deep vertical
fissure, called the hilum, through which the renal vessels
and nerves pass and the expanded, funnel-shaped origin
of the ureter, called the renal pelvis, exits. A section
through the kidney shows the relationship of these
structures

5. Histological features
1)Stroma :
a-Capsule
The kidney surface is covered by a connective
tissue capsule consists of two distinct layers:
1-an outer layer of fibroblasts and collagen
fibers (OLC )
2-an inner layer (ILC ) with a cellular
component of myofibroblasts that may aid in
resisting volume and pressure variations that
can accompany variations in kidney function.
The capsule passes inward at the hilum,
where it forms the connective tissue covering
of the sinus and becomes continuous with the
connective tissue forming the walls of the
calyces and renal pelvis .
photomicrograph of a Mallory-
Azan–stained section

6. 1)Stroma :
B)interstium
The renal interstitium is a scant amount of loose connective tissue housing three types of
cells:
1-fibroblasts
2-macrophage
3-Interstitial cells are most numerous between straight collecting ducts. Interstitial cells
have elongated nuclei and numerous lipid droplets. It is believed that these cells
synthesize medullipin I, a substance that is converted in the liver to medullipin II, a
potent vasodilator that lowers blood pressure
C)reticular fibers

7. OVERVIEW OF THE URINARY SYSTEM
2) parenchyma
• Examination with the naked eye of
the cut face of a fresh, unfixed,
hemisected kidney reveals that its
substance can be divided into two
distinct regions(reflects the
distribution of blood in the organ):
• Cortex, the outer reddish-brown
part (90% to 95% of the blood
passing through the kidney is in
the Cortex)
• Medulla, the much lighter
colored inner part (5% to 10% of
the blood is in the medulla)

8. OVERVIEW OF THE URINARY SYSTEM
2) parenchyma
A The cortex is characterized by renal
corpuscles and their associated tubules(
convoluted tubules and straight
tubules,connecting tubules, collecting ducts)
and an extensive vascular supply
-vertical striations.(medullary rays )collecting
ducts.
-The regions between medullary rays(cortical
labyrinths. ) contain the renal corpuscles, the
convoluted tubules of the nephrons, and the
connecting tubules.

9. OVERVIEW OF THE URINARY SYSTEM
2) parenchyma
A The cortex is characterized by renal
corpuscles and their associated tubules(
convoluted tubules and straight
tubules,connecting tubules, collecting ducts)
and an extensive vascular supply
-vertical striations.(medullary rays )collecting
ducts.
-The regions between medullary rays(cortical
labyrinths. ) contain the renal corpuscles, the
convoluted tubules of the nephrons, and the
connecting tubules.

10. OVERVIEW OF THE URINARY SYSTEM
2) parenchyma
A The cortex is characterized by renal
corpuscles and their associated tubules(
convoluted tubules and straight
tubules,connecting tubules, collecting ducts)
and an extensive vascular supply
-vertical striations.(medullary rays )collecting
ducts.
-The regions between medullary rays(cortical
labyrinths. ) contain the renal corpuscles, the
convoluted tubules of the nephrons, and the
connecting tubules.

11. OVERVIEW OF THE URINARY SYSTEM
2) parenchyma
BThe medulla is characterized by collecting
ducts, and a special capillary network, the vasa
recta.,that runs in parallel with the various
tubules.
The tubules in the medulla, because of their
arrangement and differences in length,
collectively form a number of conical structures
called pyramids . Usually ( 8 to 12) .
The apical portion of each pyramid, which is
known as the papilla, projects into a minor
calyx. The tip of the papilla, also known as the
area cribrosa, is perforated by the openings of
the collecting ducts.

12. OVERVIEW OF THE URINARY SYSTEM

13. OVERVIEW OF THE URINARY SYSTEM
2) parenchyma
cThe renal columns represent cortical tissue
contained within the medulla. Although renal
columns contain the same components as the
rest of the cortical tissue, they are regarded as
part of the medulla.

14. OVERVIEW OF THE URINARY SYSTEM
3)Kidney Lobes and Lobules
Each medullary pyramid and the
associated cortical tissue at its base and
sides (one half of each adjacent renal
column) constitute a lobe of the kidney.
Each lobe is reflcted as a convexity on the
outer surface of the organ, but they usually
disappear after birth. Each human kidney
contains 8 to 18 lobes
The lobes of the kidney are further
subdivided into lobules consisting of a
central medullary ray and surrounding
cortical material.
boundaries between adjacent lobules are
not demarcated from one another by
connective tissue septa.

15. OVERVIEW OF THE URINARY SYSTEM
3)Kidney Lobes and Lobules
Each medullary pyramid and the
associated cortical tissue at its base and
sides (one half of each adjacent renal
column) constitute a lobe of the kidney.
Each lobe is reflcted as a convexity on the
outer surface of the organ, but they usually
disappear after birth. Each human kidney
contains 8 to 18 lobes
The lobes of the kidney are further
subdivided into lobules consisting of a
central medullary ray and surrounding
cortical material.
boundaries between adjacent lobules are
not demarcated from one another by
connective tissue septa.

16. OVERVIEW OF THE URINARY SYSTEM
multilobed kidney

17. The Uriniferous Tubule
The Uriniferous Tubule
the nephron
renal corpuscle tubule system
PCT Loop of henle DCT
the collecting tubules and duct

18. The Uriniferous Tubule

19. The Nephron
midcortical nephrons

20. The Nephron

21. The Nephron

22. The Nephron

23. The Nephron
-the renal corpuscle(Malpighian) :represents the beginning of the nephron. The renal
corpuscle is spherical ,consists of :
1-the glomerulus, a tuft of capillaries composed of 10 to 20 capillary loops, supplied by an
afferent arteriole and are drained by an efferent arteriole  vascular pole
2- Bowman’s capsule :a double-layered epithelial cup(visceral and parietal epithelial layers of
and space an between them : the bowman's space) -urinary pole

24. The Nephron
-the renal corpuscle(Malpighian) :represents the beginning of the nephron. The
renal corpuscle is spherical ,consists of :
1-the glomerulus:
2- Bowman’s capsule
3- mesangium :The mesangial cells are enclosed by the GBM .These cells and their
extracellular matrix constitute the mesangium.The mesangial cells are not
confined entirely to the renal corpuscle; some are located outside the corpuscle
along the vascular pole, where they form part of what is called the
juxtaglomerular apparatus

25. The Nephron
Filtration Apparatus of the Kidney (glomerular filtration barrier)
1)Endothelium of the glomerular capillaries :
larger, more numerous, and more irregular in outline than fenestrations in
other capillaries , without diaphragm , contain aquaporin-1 (AQP-1) water
channels .

26. The Nephron
Filtration Apparatus of the Kidney (glomerular filtration barrier)
1)Endothelium of the glomerular capillaries
2) Glomerular basement membrane (GBM), a thick (300 to 370 nm) basal
lamina that is the joint product of the endothelium and the podocytes.
GBM can also be visualized employing immunofluorescence techniques
using antibodies directed to type IV collagen

27. The Nephron
Filtration Apparatus of the Kidney (glomerular filtration barrier)
1)Endothelium of the glomerular capillaries
2) Glomerular basement membrane (GBM)
3)Visceral layer of Bowman’s capsule, which contains specialized cells called
podocytes or visceral epithelial cells.

28. The Nephron
Filtration Apparatus of the Kidney (glomerular filtration barrier)
1)Endothelium of the glomerular capillaries
2) Glomerular basement membrane (GBM)
3)Visceral layer of Bowman’s capsule, which contains specialized cells called
podocytes or visceral epithelial cells.