The document summarizes the anatomy and composition of the urinary system. It describes the key components including the kidneys, ureters, urinary bladder, and urethra. It then provides details on the internal and external anatomy of the kidneys, including the location of the kidneys and their internal structures like the cortex, medulla, renal pyramids, and nephrons. It also describes the layers, muscles, and sphincters of the ureters, urinary bladder, and urethra. Finally, it focuses on the structures and function of the nephron, including Bowman's capsule and how it filters blood to form urine.

1. URINARY SYSTEM
UROOJ TARIQ
PHARM-D, M.PHIL.

2. ■ COMPOSITION OF URINARY SYSTEM:
• The urinary system consists of
 two kidneys,
two ureters,
the urinary bladder,
the urethra

3. KIDNEYS
• Kidneys are paired, reddish, bean–shaped organs responsible for formation of urine by blood
filtration
■ Location
• Kidneys are positioned against the posterior wall of the abdominal cavity (retroperitoneal)
between the levels of the twelfth thoracic (T12) and the third lumbar vertebrae (L3)
• The right kidney is slightly lower than the left because of the space occupied by the large right
lobe of the liver above it.
• The right kidney is usually 1.5 to 2.0 cm lower than the left because of the large area
occupied by the liver on the right side.

6. EXTERNAL ANATOMY OF KIDNEYS
• Each adult kidney is a bean-shaped organ about 11.25 cm (4 in.) long, 5.5 to 7.7 cm (2–3 in.)
wide, and 2.5 cm (1 in.) thick.
• Each kidney is embedded in a fatty fibrous pouch consisting of three layers:
 The renal capsule - layer ofdense fibrous connective tissue surrounding each kidney, protects kidney
from trauma and infection and maintain its shape
 Renal adipose capsule – layer of adipose tissue surrounding the renal capsule functions as a shock
absorber, cushioning the kidneys against mechanical shock.
 Renal fascia - thin layer of connective tissue surrounding the adipose tissue, anchors the kidney to the
posterior abdominal wall
* The lateral border of each kidney is convex, whereas the medial border is strongly concave
* On the medial border is hilum, a depression through which renal artery, vein and nerves enter
and leave kidney
* The superior border of each kidney is capped by the adrenal gland

7. INTERNAL ANATOMY OF KIDNEYS
• The coronal section of the kidney show two distinct regions and a cavity.
• The outer light red coloured is called cortex, the inner dark red- brown coloured called medulla and
cavity is called as renal sinus
• The medulla has distinctive conical structures called renal pyramids
• The renal pyramids has a base and an apex. The apex is called renal papillae and they point
towards renal sinus
• The base is directed towards the cortex (outside). The base of pyramids makes border between
cortex and medulla

8. • The cortex occupies outer portion of the kidney and it inviginates deep into the medulla in
between the renal pyramids. These extensions of cortex into medulla are called renal columns
• The cavity of the kidney collects and transports urine from the kidney to the ureter. It is divided
into several portions.
1. The papilla of a renal pyramid projects into a small depression in the renal sinus called the
minor calyx.
2. Several minor calyces unite to form a major calyx. In turn, the major calyces join to form the
funnel-shaped renal pelvis.
3. The renal pelvis collects urine from the calyces and transports it to the ureter.
4. A human kidney is divided into 8 to 15 renal lobes. A renal lobe consists of a medullary
pyramid and some cortical substance from the renal columns adjacent to it on either side, as
well as the cortex external to the pyramid base.

9. • Together, the renal cortex and renal pyramids of the renal medulla constitute the
parenchyma or functional portion of the kidney.
• Within the parenchyma are the functional units of the kidney—about 1 million
microscopic structures called nephrons.
• Filtrate formed by the nephrons drains into large papillary ducts, which extend through the
renal papillae of the pyramids.
• The papillary ducts drain into cuplike structures called minor calyces which drains into
major calyces. Each kidney has 8 to 18 minor calyces and 2 or 3 major calyces.
• A minor calyx receives urine from the papillary ducts of one renal papilla and delivers it to a
major calyx.
• From the major calyces, urine drains into a single large cavity called the renal pelvis
and then out through the ureter to the urinary bladder

11. Ureters
• The ureters are long, fibromuscular tubes that conduct urine from the kidneys to the urinary
bladder.
• Each tube averages 25 centimeters in length and is retroperitoneal
• The ureters originate at the renal pelvis as it exits the hilum of the kidney, and then extend
inferiorly . At the level of base of urinary bladder they curve medially to enter the
posterolateral wall of the of the urinary bladder inferiorly.

12. • The ureter is made up of three layers or tunic:
Mucosa – innermost coat, made up of mucous membrane of
transitional epithelium and lamina propria which is made up of
areolar connective tissue. The transitional epithelium can stretch
to accommodate variable amount of urine. The goblet cells in
mucosa secretes mucous to protect the cells from urine
Muscularis - next to mucosa is muscularis. It is made up of two
layers of muscles the inner longitudinal and outer circular. The
distal one third of ureter contain another longitudinal muscular
layer. The muscularis exhibit peristaltic movement to propel the
urine through its length
Adventitia – outer most layer made up of loose connective tissue.
It anchors the ureter to posterior abdominal wall through its
extensions.

14. Urinary bladder
• The urinary bladder is a saccular organ for storage of urine
• The urinary bladder is a retroperitoneal organ, since only its superior surface is
covered with peritoneum
• The urinary bladder is positioned immediately posterior to the pubic symphysis
• The shape of the urinary bladder is determined by the volume of urine it contains. An
empty urinary bladder is pyramidal. As it fills, it becomes ovoid and bulges upward into
the abdominal cavity
• A fibrous, cordlike median umbilical ligament extends from the apex and connect it to the
umbilicus.

15. • The wall of urinary bladder is made up of four layers:
■ The mucosa –
• the innermost layer
• composed of transitional epithelium that becomes thinner as the urinary bladder
distends and the cells are stretched.
• Further distension is permitted by folds of the mucosa, called rugae, which can be
seen when the urinary bladder is empty.
• Fleshy flaps of mucosa, located where the ureters pierce the urinary bladder, act as
valves to prevent a reverse flow of urine toward the kidneys as the urinary bladder
fills.

16. ■ Submucosa -
• The second layer of the urinary bladder
• functions to support the mucosa
• Made up of dense irregular connective tissue
■ The muscularis
• consists of three interlaced smooth muscle layers collectively called the detrusor muscle.
• At the neck of the urinary bladder, the detrusor muscle is modified to form the superior (called the
internal urethral sphincter) of urethra.
• The openings of two ureters and the urethra mark a smooth-surfaced triangular area called the
Trigone
■ Adventitia
• Outermost fibrous layer

18. Urethra
• The urethra is a fibromuscular tube that originates at the neck of the urinary
bladder and conducts urine to the exterior of the body
• The male urethra is different from female urethra as male urethra also
perform reproductive function.
■ Four basic anatomic feature common in male and female urethra :
Innermost mucous membrane lining releasing mucus
Layer of smooth muscle next to mucus membrane oriented
longitudinally
Urethral glands embedded in urethral wall releasing mucus
Two muscular sphincters;

19. Female urethra
• The urethra of the female is a straight tubular organ, about 4 cm (1.5 in.) long
• empties urine through the urethral orifice into the vestibule between the labia minora.
• The external urethral orifice is positioned between the clitoris and vaginal orifice.

21. Male urethra
• About 20cm long
• It has three parts:
Prostatic part - proximal part, pass through prostate gland near the neck of urinary bladder,
receives drainage from small ducts of the prostate and two ejaculatory ducts of the
reproductive system
Membranous part – short portion about 0.5 cm , pass through the muscular floor
of the pelvic cavity.
The spongy (penile) urethra is about 15 cm and passes through the penis to the external
urethral orifice.
■ The mucosa has a transitional epithelium near the bladder, a pseudostratified epithelium for most
of its length, and finally a stratified squamous epithelium near the external urethral orifice. There
are mucous urethral glands in its wall.

27. INTRODUCTION
■ These are small structures and they form the functional units of the kidney.
■ There are approximately over 1 million nephrons per kidney, and it is in these structures
where urine is formed.
■ The nephron is divided into several sections:
•• Bowman’s capsule
•• proximal convoluted tubule
•• loop of Henle
•• distal convoluted tubule (DCT)
•• the collecting ducts.

28. Each nephron consists of two parts:
■ a renal corpuscle where blood plasma is filtered,
■ and a renal tubule into which the filtered fluid passes.
The two components of a renal corpuscle are the glomerulus (capillary network) and the
glomerular (Bowman’s) capsule, a double-walled epithelial cup that surrounds the
glomerular capillaries.
Blood plasma is filtered in the glomerular capsule, and then the filtered fluid passes into the
renal tubule.

29. BOWMANN’S CAPSULE
• Also known as the glomerular capsule
• Bowman’s capsule is a cup‐like sac and is the first portion of the nephron.
• Bowman’s capsule is part of the filtration system in the kidneys.
• When blood reaches the kidneys for filtration, it enters Bowman’s capsule first, with the
capsule separating the blood into two components:
• a filtrated blood product and a filtrate that is moved through the nephron.
• The glomerular (Bowman’s) capsule consists of visceral and parietal layers.
• The visceral layer consists of modified simple squamous epithelial cells called podocytes The
many footlike projections of these cells (pedicels) wrap around the single layer of endothelial
cells of the glomerular capillaries and form the inner wall of the capsule.
• The parietal layer of the glomerular capsule consists of simple squamous epithelium and forms
the outer wall of the capsule. Fluid filtered from the glomerular capillaries enters the capsular
(Bowman’s) space, the space between the two layers of the glomerular capsule.

30. Proximal convoluted tubule
From Bowman’s capsule, the filtrate drains into the proximal convoluted tubule
■ In the proximal convoluted tubule, the cells are simple cuboidal epithelial cells
with a prominent brush border of microvilli on their apical surface (surface facing
the lumen). These microvilli, like those of the small intestine, increase the
surface area for reabsorption and secretion

31. Loop of Henle
The proximal convoluted tubule then bends into a loop called the loop of Henle The loop of Henle is
the part of the tubule that dips or ‘loops’ from the cortex into the medulla (descending limb), and
then returns to the cortex (ascending limb).
The loop of Henle is divided into the descending and ascending loops. The ascending loop of Henle
is much thicker than the descending portion.
■ The descending limb of the loop of Henle and the first part of the ascending limb of the loop of
Henle (the thin ascending limb) are composed of simple squamous epithelium.
■ The thick ascending limb of the loop of Henle is composed of simple cuboidal to low columnar
epithelium.
■ In each nephron, the final part of the ascending limb of the loop of Henle makes contact with the
afferent arteriole serving that renal corpuscle (Figure 26.6a). Because the columnar tubule cells
in this region are crowded together, they are known as the macula densa (macula spot; densa
dense).
■ Alongside the macula densa, the wall of the afferent arteriole (and sometimes the efferent
arteriole) contains modified smooth muscle fibers called juxtaglomerular (JG) cells. Together
with the macula densa, they constitute the juxtaglomerular apparatus (JGA). As you will see
later, the JGA helps regulate blood pressure within the kidneys.

33. Distal convoluted tubule
The thick ascending portion of the loop of Henle leads into the DCT. The DCT is lined with
simple cuboidal cells, and the lumen of the DCT is larger than the proximal convoluted tubule
lumen because the proximal convoluted tubule has a brush border (microvilli).
The distal convoluted tubule (DCT) begins a short distance past the macula densa. In the last
part of the DCT and continuing into the collecting ducts, two different types of cells are present.
Most are principal cells, which have receptors for both antidiuretic hormone (ADH) and
aldosterone, two hormones that regulate their functions.
A smaller number are intercalated cells, which play a role in the homeostasis of blood pH.
(reabsorb K and secrete H+)
The collecting ducts drain into large papillary ducts, which are lined by simple columnar
epithelium.

35. Collecting ducts
The DCT then drains into the collecting ducts. Several collecting ducts converge
and drain into a larger system called the papillary ducts, which in turn empty into the minor
calyx (plural: calices). From here the filtrate, now called urine, drains into the renal pelvis.