The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys filter the blood to remove waste and produce urine. Approximately 1 million nephrons in each kidney filter blood and form urine. The ureters, urinary bladder, and urethra form the urinary tract to store and release urine produced by the kidneys.

3.  The urinary system consists of the kidneys, ureters,
urinary bladder, and urethra. The kidneys filter the
blood to remove wastes and produce urine. The
ureters, urinary bladder, and urethra together form the
urinary tract, which acts as a plumbing system to drain
urine from the kidneys, store it, and then release it
during urination. Besides filtering and eliminating
wastes from the body, the urinary system also
maintains the homeostasis of water, ions, pH, blood
pressure, calcium and red blood cells.

4.  Removal of waste product from the body (mainly
urea and uric acid)
 Regulation of electrolyte balance (e.g. sodium,
potassium and calcium)
 Regulation of acid-base homeostasis
 Controlling blood volume and maintaining blood
pressure

5.  Kidney
 Ureter
 Urinary bladder
 Urethra
 Two sphincter muscles
 Nerves of the bladder

6.  The kidneys are a pair of bean-shaped organs found along
the posterior wall of the abdominal cavity. The left kidney
is located slightly higher than the right kidney because the
right side of the liver is much larger than the left side. The
kidneys, unlike the other organs of the abdominal cavity,
are located posterior to the peritoneum and touch the
muscles of the back. The kidneys are surrounded by a
layer of adipose that holds them in place and protects
them from physical damage.

7.  The kidneys are retroperitoneal organs (ie located behind
the peritoneum) situated on the posterior wall of the
abdomen on each side of the vertebral column, at about
the level of the twelfth rib. The left kidney is lightly
higher in the abdomen than the right, due to the presence
of the liver pushing the right kidney down.
 The kidneys take their blood supply directly from the
aorta via the renal arteries; blood is returned to the inferior
vena cava via the renal veins

8.  This pair of purplish-brown organs is to remove liquid
waste from the blood in the form of urine; keep a stable
balance of salts and other substances in the blood; and
produce erythropoietin, a hormone that aids the formation
of red blood cells. The kidneys remove urea from the
blood through tiny filtering units called nephrons. Each
nephron consists of a ball formed of small blood
capillaries, called a glomerulus, and a small tube called a
renal tubule. Urea, together with water and other waste
substances, forms the urine as it passes through the
nephrons and down the renal tubules of the kidney.

9.  On sectioning, the kidney has a pale outer region- the
cortex- and a darker inner region- the medulla.The
medulla is divided into 8-18 conical regions, called the
renal pyramids; the base of each pyramid starts at the
corticomedullary border, and the apex ends in the renal
papilla which merges to form the renal pelvis and then on
to form the ureter. In humans, the renal pelvis is divided
into two or three spaces -the major calyces- which in turn
divide into further minor calyces. The walls of the calyces,
pelvis and ureters are lined with smooth muscle that can
contract to force urine towards the bladder by peristalisis.
 The cortex and the medulla are made up of nephrons;
these are the functional units of the kidney, and each
kidney contains about 1.3 million of them.

10.  The nephron is the unit of the kidney responsible for
ultrafiltration of the blood and reabsorption or excretion of
products in the subsequent filtrate. Each nephron is made
up of:
 A filtering unit- the glomerulus. 125ml/min of filtrate is
formed by the kidneys as blood is filtered through this
sieve-like structure. This filtration is uncontrolled.
 The proximal convoluted tubule. Controlled absorption of
glucose, sodium, and other solutes goes on in this region.

11.  The loop of Henle. This region is responsible for
concentration and dilution of urine by utilising a counter-
current multiplying mechanism- basically, it is water-
impermeable but can pump sodium out, which in turn
affects the osmolarity of the surrounding tissues and will
affect the subsequent movement of water in or out of the
water-permeable collecting duct.
 The distal convoluted tubule. This region is responsible,
along with the collecting duct that it joins, for absorbing
water back into the body- simple maths will tell you that
the kidney doesn't produce 125ml of urine every minute.
99% of the water is normally reabsorbed, leaving highly
concentrated urine to flow into the collecting duct and
then into the renal pelvis.

12. Regions of the Kidney
 Renal cortex – outer region
 Renal medulla – inside the cortex
 Renal pelvis – inner collecting tube

13. Blood Flow in the Kidneys
Figure 15.2c

15.  The nephron is the functional unit of the kidney,
responsible for the actual purification and filtration of the
blood.
 About one million nephrons are in the cortex of each

16.  Filtering unit of kidney
 Process blood plasma
 Form urine
 1.25 million per kidney
 Looks like a funnel with a
long, winding stem

17. Components
1. renal corpuscle
2. PCT
3. loop of Henle
4. DCT
5. Collecting tubule & duct

18. RENAL CORPUSCLE-
in the cortex
1. Bowman’s capsule
 Cup-shaped mouth
of nephron
2. Glomerulus
 capillaries in BC
 Pores (fenestrations)
 Basement membrane

20. PROXIMAL
TUBULE- in
cortex
 Closest to BC
(“proximal”)
 Aka PCT
(proximal
convoluted
tubule)
 Brush border
(microvilli) face
lumen- increase

21. LOOP OF HENLE (LOH)
 Renal tubule beyond the
PCT
 Descending limb (thin)
 Sharp turn
 Ascending limb (thick)
 Dips into medulla
cortex
medulla

22. DISTAL TUBULE
 Aka DCT (distal
convoluted tubule)
 Beyond LOH
(“distal”)
 Juxtaglomerular
apparatus

23. COLLECTING
DUCT
 Straight tubule
joined by distal
tubules of several
nephrons
 Fuse to form
papillary ducts
which deliver urine
to the calyces

24.  Superiorly
 Continuous with the renal pelvis
 Inferiorly
 Pass through the abdominal cavity,
behind the peritoneum, infront of
the psoas muscle, into the pelvic
cavity ehere they enter the
posterior wall of the bladder
 25-30 cm in length
24

25. Ureters
 Carry urine from kidneys to urinary bladder via peristalsis
 Rhythmic contraction of smooth muscle
 Enter bladder from below
 Pressure from full bladder compresses ureters and
prevents backflow
Ureters
 Small diameter
 Easily obstructed or injured by kidney stones (renal
calculi)

26.  3 layers of tissue
 Outer layer
 Fibrous tissue
 Middle layer
 Muscle
 Inner layer
 Epithelium
26

27. Urinary bladder
 Muscular sac
 Wrinkles termed rugae
 Openings of ureters common site for bladder infection

28. 28

29.  3 layers
 Outer layer
 Loose connective tissue
 Middle layer
 Smooth muscle and elastic
fibres
 Inner layer
 Lined with transitional
epithelium
29

30. Urinary Bladder
 Trigone – three openings
Two from the ureters
One to the urethrea

31. Urinary Bladder Wall
 Three layers of smooth muscle (detrusor
muscle)
 Mucosa made of transitional epithelium
 Walls are thick and folded in an empty
bladder
 Bladder can expand significantly without
increasing internal pressure

32. Urethra
 Thin-walled tube that carries urine from the
bladder to the outside of the body by
peristalsis
 Release of urine is controlled by two
sphincters
Internal urethral sphincter (involuntary)
External urethral sphincter (voluntary)

33. Urethra Gender Differences
 Length
Females – 3–4 cm (1 inch)
Males – 20 cm (8 inches)
 Location
Females – along wall of the vagina
Males – through the prostate and penis

34. Urethra Gender Differences
 Function
Females – only carries urine
Males – carries urine and is a passageway for
sperm cells

35. Urethra
 ~18 cm long in males
 Prostatic urethra
~2.5 cm long, urinary bladder  prostate
 Membranous urethra
~0.5 cm, passes through floor of pelvic
cavity
 Penile urethra
~15 cm long, passes through penis

37.  Muscle layer
 Submucosa layer
 Mucosa
37

38. Urination (micturition)
 ~200 ml of urine held
 Distension initiates desire to void
 Internal sphincter relaxes involuntarily
 Smooth muscle
 External sphincter voluntarily relaxes
 Skeletal muscle
 Poor control in infants
 Bladder muscle contracts
 Urine forces through urethra

39. Micturition (Voiding)
 Both sphincter muscles must open to allow
voiding
The internal urethral sphincter is relaxed after
stretching of the bladder
Activation is from an impulse sent to the spinal
cord and then back via the pelvic splanchnic
nerves
The external urethral sphincter must be
voluntarily relaxed