The document summarizes the histology of the urinary system. It describes the structures and cell types found in the kidney, nephron, ureter, bladder, and urethra. In the kidney, nephrons contain glomeruli and Bowman's capsules for blood filtration. The ureter transports urine from the kidney to the bladder via smooth muscle layers. The bladder stores urine in transitional epithelium before exiting the body through the urethra, lined with stratified squamous epithelium in males and females. Clinical correlates of urinary structures include incontinence and overactive bladder.

1. HISTOLOGY OF THE URINARY
SYSTEM

2. Contents
 Kidney
* Parts of nephron and structures
juxtaglomerular apparatus
Functional aspects
Blood circulation
 Ureter and urinary bladder
• General features
 Urinary epithelium Urethra
* Structure of male and female urethra

3. Kidney
 Main organ of the excretory system
 Kidney is built of billions of little tubes called the
nephrons.
 At the beginning of each nephron, a web of capillaries
releases much water and other molecules into the
nephron.
 The urine is collected in the urinary bladder and, when it
fills up, it is excreted via urethra into the outside
environment.

4. Kidney's Internal Structure
 Cortex -- the outer part of the kidney;
 Medulla -- the inner portion of the kidney;
 Pyramids -- the triangular-shaped divisions of the
medulla of the kidney;
 Papilla -- narrow, innermost tip of the pyramid;
 Pelvis -- the kidney or renal pelvis is an extension of
the upper end of the ureter (the tube that drains
urine into the bladder);
 Calyx -- each calyx is a division of the renal pelvis;
opening into each calyx is the papilla of a pyramid.

7. Nephron
 basic structural and functional unit of the
kidney.
 Its chief function is to regulate the
concentration of water and soluble
substances like sodium salts by filtering the
blood, reabsorbing what is needed and
excreting the rest as urine.

8. Nephron
 A nephron eliminates wastes from the body,
regulates blood volume and blood pressure,
controls levels of electrolytes and metabolites,
and regulates blood pH. Its functions are vital to
life and are regulated by the endocrine system by
hormones such as antidiuretic hormone,
aldosterone, and parathyroid hormone.

10.  microscopic units of a kidney, have 2 main parts,
1. renal corpuscle (Bowman's capsule with glomerulus)
2. renal tubule.

11. RENAL CORPUSCLERENAL CORPUSCLE
 glomeruli surrounded by Bowman's capsules.
 Bowman's capsule -- the cup-shaped top of a nephron.
It is the sack-like Bowmans's capsule that surrounds the
glomerulus.
 Glomerulus -- a network of blood capillaries tucked
into Bowman's capsule.

13. Juxtaglomerular apparatus
 The juxtaglomerular apparatus is a microscopic structure
in the kidney, which regulates the function of each
nephron.
 There are three cellular components of the apparatus
which are the;
1. macula densa,
2. extraglomerular mesangial cells,
3. juxtaglomerular cells (also known as granular cells).

14. RENAL TUBULE
 Proximal convoluted tubule -- the first segment of a renal
tubule, called proximal because it lies nearest the tubule's
origin from Bowman's capsule, and convoluted because it has
several bends in it.
 Loop of Henle -- the extension of the proximal tubule;
observe that the loop of Henle consists of a straight
descending (directed downward) limb, a loop, and a straight
ascending limb (directed upwards).

15. Cont.
 Distal convoluted tubule -- the part of the tubule distal to
the ascending limb of Henle. It is the extension of the
ascending limb of Henle.
 Collecting tubule -- a straight (not convoluted) part of a
renal tubule; distal tubules of several nephrons join to
form a single collecting tubule

16. Histology Bowman's capsule
 Cells of the outer or parietal layer of Bowman's capsule form a simple squamous
epithelium.
 Cells of the inner layer, podocytes in the visceral layer, are extremely complex in
shape. Small foot-like processes, pedicles, of their cytoplasm form a fenestrated
epithelium around the fenestrated capillaries of the glomerulus.
 The openings between the pedicles are called filtration slits.They are spanned by a
thin membrane, the filtration slit membrane. Between the podocytes and the
endothelial cells of the capillaries a comparatively thick basal lamina, which can be
subdivided into an outer lamina externa, a middle lamina densa and an inner lamina
interna.
 The basal lamina and the slit membranes form the glomerular filtration barrier,
which prevents some large molecules from entering the capsular space between
the outer and inner epithelial layers of Bowman's capsule.
 Mesangial cells in the glomerulus form the connective tissue that gives structural
support to podocytes and vessels.

17. Histo: proximal tubule
 walls - low columnar epithelium.
 The eosinophilic cells of the epithelium have a wide brush
border and are active in endocytosis.

18. Histo of Loop of Henle

It is 'U' shaped and has descending and ascending
segments.

Thin descending segment has flattened
epithelium( squamous). It is permeable to water but not
solutes.

19. Histo: Distal convoluted tubule
 straight part of the DCT is formed by the low cuboidal
cells without a brush border.The diameter of the tubule
gradually expands to about 35 microns.
 convoluted part and comes in contact with the
Glomerulus forming the Macula Densa.

23. Nephron structure characteristic
Renal corpusle Capillary ball covered by podocyte &
surrounded by simple squamous epithelial
capsule, capsular space.
Proximal convulated Lined with simple cubodial epithelium &
prominent brush border
Loop of Henle Tubule that form a loop, there are thick &
thin ascending & desecnding portion; the
most distal part of the loop often extends
into the medulla.
Thick limb are lined with simple
squamous/ cuboidal epithelium
Thin limb are lined with simple squamous
epithelium
Distal convulated Lined with simple cuboidal with only
sparse brush border; cytoplasm of cells
tend to be paler than that of proximal
convulated

24. Ureter
The wall of the ureter is made 3 layers. From inside
outwards they are :
1. Mucosa- which is made up of epithelium &
lamina propria
2. Muscular coat – made of smooth muscles
3. Fibrosa – made of fibrous connective tissue
Mucosa- is thrown into folds and thus gives the
appearance of star shaped lumen.

25. 1. Transitional epithelium. 3-5 layers thickness.
2. Lamina propria- dense, irregular layer of
fibroelastic connective tissue

The epithelium is separated from the lamina propria by a
basal lamina.

26. 
Muscular layer – Upper 2/3 of the ureter is made of
two layers of smooth muscle cells.

Inner longitudinal and outer circular layer( in contrast to the
wall of GIT which has inner circular & outer longitudinal !).

Lower 1/3 of the ureter has a third outer layer of longitudinal
muscles( inner longitudinal, middle circular, outer
loingitudinal ).
Fibrous coat – is made up of fibrous connective tissue

29. The urethra:
 Female: relatively short, exits just anterior to the vagina
 Male: longer, divided into three sections the prostatic,
membranous and spongy urethra. The prostatic urethra
is enclosed in the prostate gland. The membranous
urethra is a short section that penetrates the urogenital
diaphragm. The spongy urethra or penile urethra extends
from the membranous urethra to the external urethral
orifice (meatus).

30.  Histology: In both male and females the urethra starts
out as transitional cell but quickly becomes stratified
squamous in the female.
 The male urethra is more variable but ends up stratified
squamous as well.

32. Histology of the bladder
mucosa of transitional epithelium, Submucosa, and thick
muscular layer know as the detrusor muscle

35. Clinical correlates
 Urinary incontinence
 Childbirth and other events can injure the scaffolding that helps
support the bladder in women. Pelvic floor muscles, the vagina, and
ligaments support your bladder.
 Overactive bladder
Specifically, the symptoms of overactive bladder include
urinary frequency—bothersome urination eight or more times a day
or two or more times at night
urinary urgency—the sudden, strong need to urinate immediately
urge incontinence—leakage or gushing of urine that follows a sudden,
strong urge
nocturia—awaking at night to urinate