The urinary system includes the kidneys, ureters, urinary bladder, and urethra. The kidneys filter waste from the bloodstream and produce urine, which is transported via the ureters to the bladder for storage. When full, the bladder empties through the urethra. The primary functions of the urinary system are to remove waste from the blood, regulate fluid and electrolyte balance, and excrete urine.

1. 27-1
Urinary System
DR MAKENZIH

2. 27-2
General Structure and Functions
of the Urinary System
 General Concept:
 Waste products accumulate in blood
 Are toxic
 Must be removed to maintain
homeostasis
 Urinary System organs
 remove waste products from the blood
 then from the body
 Major homeostatic system

3. 27-3
General Structure and Functions
of the Urinary System
 Organs of the Urinary System:
 Kidneys
 Ureters
 Urinary Bladder
 Urethra
 Primary organs: kidneys
 filter waste products from the bloodstream
 convert the filtrate into urine.
 The Urinary Tract:
 Includes:
 ureters
 urinary bladder
 urethra
 Because they transport the urine out of the body.

4. 4

5. 5

6. 6

7. 27-7
Functions of the Urinary System
 Removing waste products from the bloodstream.
 Storage of urine.
 the urinary bladder is an expandable, muscular sac that can
store as much as 1 liter of urine
 Excretion of urine.
 Blood volume regulation.
 the kidneys control the volume of interstitial fluid and blood
under the direction of certain hormones
 Regulation of erythrocyte production.
 as the kidneys filter the blood, they are also indirectly
measuring the oxygen level in the blood
 Erythropoietin (EPO): hormone produced by kidney
 Released if blood oxygen levels fall
 Stimulates RBC production in red bone marrow

8. 27-8
Kidneys: Gross and Sectional
Anatomy
 Retroperitoneal
 Anterior surface covered with peritoneum
 Posterior surface against posterior
abdominal wall
 Superior pole: T-12
 Inferior pole: L-3
 Right kidney ~ 2cm lower than left
 Adrenal gland on superior pole

9. 9

10. 27-10
Kidneys: Gross and Sectional
Anatomy
 Hilum: concave medial border
 Renal sinus: internal space
 Houses blood vessels, lymphatic vessels,
nerves
 Houses renal pelvis, renal calyces
 Also fat

11. 27-11
Kidneys: Gross and Sectional
Anatomy
 Surrounding tissues, from deep to superficial:
 Fibrous capsule (renal capsule)
 Dense irregular CT
 Covers outer surface
 Perinephric fat (adipose capsule)
 Also called perirenal fat
 Completely surrounds kidney
 Cushioning and insulation
 Renal fascia
 Dense irregular CT
 Anchors kidney to posterior wall and peritoneum
 Paranephric fat
 Between renal fascia and peritoneum

12. 12

13. 27-13
Kidneys: Gross and Sectional
Anatomy
 Sectioned on a coronal plane:
 Renal Cortex
 Renal arches
 Renal columns
 Renal Medulla
 Divided into renal pyramids
 8 to 15 per kidney
 Base against cortex
 Apex called renal papilla

14. 27-14
Kidneys: Gross and Sectional
Anatomy
 Minor calyx:
 Funnel shaped
 Receives renal papilla
 8 to 15 per kidney, one per pyramid
 Major calyx
 Fusion of minor calyces
 2 to 3 per kidney
 Major calyces merge to form renal pelvis
 Renal Lobe
 Pyramid plus some cortical tissue
 8 to 15 per kidney

15. 15

16. 16

17. 27-17
Blood Supply to the Kidney
 About 20 to 25% of cardiac output to
kidneys
 Path:
 Renal artery to segmental arteries to
interlobar arteries to arcuate arteries to
interlobular arteries to:
 Afferent arteriole to glomerulus to efferent
arteriole to peritubular capilaries and vasa
recta

18. 18

19. 27-19
Blood Supply to the Kidney
 Blood plasma is filtered across the glomerulus
into the glomerular space.
 Once the blood plasma is filtered
 blood leaves the glomerulus
 enters an efferent arteriole.
 efferent arteriole is still carrying oxygenated
blood
 a gas and nutrient exchange with the kidney
tissues has not yet occurred.

20. 27-20
Blood Supply to the Kidney
 The efferent arterioles branch into one of two
types of capillary networks:
 peritubular capillaries
 vasa recta
 these capillary networks are responsible for
the actual exchange of gases and nutrients
 Peritubular capillaries: primarily in cortex
 Vasa recta: surround the thin tubes that
project into the medulla.

21. 27-21
Blood Supply to the Kidney
 Path for veins:
 Interlobar veins to arcuate veins to
interlobar veins to the renal vein

22. 22

23. 27-23
Nephrons
 The functional filtration unit in the kidney.
 Consists of the following:
 Renal corpuscle
 Glomerulus
 Glomerular capsule (Bowman’s capsule)
 Proximal convoluted tubule (PCT)
 Nephron loop (loop of Henle)
 Ascending loop of Henle
 Descending loop of Henle
 Distal convoluted tubule (DCT)
 collectively called the renal tubule
 In both kidneys: approximately 2.5 million nephrons.
 Are microscopic: measure about 5 centimeters in
length.

24. 27-24
Nephrons
 Cortical Nephrons
 Near peripheral edge of cortex
 Short nephron loops
 Have peritubular capillaries
 Juxtamedullary nephrons
 Near corticomedullary border
 Long nephron loops
 Have vasa recta

25. 25

26. 27-26
Urine Formation
 Three processes
 Filtration
 Renal corpuscle: forms filtrate
 From blood to tubule
 Reabsorption
 Mostly PCT
 Water and salt: rest of nephron
 From tubule to blood
 Secretion
 From blood to tubule

27. 27-27
Renal Corpuscle
 Vascular pole
 Afferent and efferent arterioles
 Tubular pole
 Connects to PCT
 Two structures:
 Glomerulus and glomerular capsule
 Glomerulus
 Capillary bed
 High pressure
 fenestrations

28. 27-28
Renal Corpuscle
 Glomerular Capsule
 Parietal layer
 Simple squamous epithelium
 Visceral layer
 Podocytes
 Pedicels
 Filtration slits
 Capsular space (Bowman’s capsule): location of
filtrate
 Filtration membrane
 Fenestrations
 Filtration slits

29. 29

30. 30

31. 27-31
Proximal Convoluted Tubule
 Begins at tubular pole of the renal corpuscle.
 Cells: simple cuboidal epithelium
 actively reabsorb from the filtrate:
 almost all nutrients (glucose and amino acids)
 electrolytes
 plasma proteins
 Osmosis: reabsorption of 60% to 65% of the
water in filtrate.
 Have microvilli
 Solutes and water:
 moved into blood plasma
 via the peritubular capillaries.

32. 27-32
Nephron Loop (loop of Henle)
 originates at end of proximal convoluted tubule
 projects toward and/or into the medulla.
 Each loop has two limbs.
 descending limb:
 from cortex toward and/or into the medulla
 ascending limb:
 returns back to the renal cortex

33. 33

34. 34

35. 27-35
Distal Convoluted Tubule
 begins at the end of the thick ascending limb of the
nephron loop
 adjacent to the afferent arteriole (important physiologically)
 Juxtaglomerular apparatus.
 primary function:
 Secretion
 From blood plasma to filtrate.
 secretes ions
 potassium (K+)
 acid (H+)
 Reabsorption of water also occurs:
 influenced by two hormones
 Aldosterone
 antidiuretic hormone (ADH).

36. 27-36
Collecting Collecting Ducts
 Function in a well hydrated person:
 transport the tubular fluid into the papillary duct and then
into the minor calyx.
 Function in a dehydrated person:
 water conservation
 more-concentrated urine is produced.
 ADH can act on the collecting duct epithelium
 Cells become permeable to water
 Water moves from filtrate into blood plasma
 Involves vasa recta.

37. 27-37
Innervation of the Kidney
 innervated by a mass of autonomic nervous system
fibers
 called the renal plexus.
 The renal plexus
 accompanies each renal artery
 enters the kidney through the hilum.

38. 27-38
Urinary Tract : Ureters
 long, fibromuscular tubes
 conduct urine from the kidneys to the urinary
bladder.
 average 25 centimeters in length
 retroperitoneal.
 ureters originate at the renal pelvis
 extend inferiorly to enter the posterolateral wall of
the base of the urinary bladder.
 wall is composed of three concentric tunics.
 mucosa
 muscularis
 adventitia.

39. 27-39
Urinary Tract – Urinary Bladder
 The urinary bladder:
 expandable, muscular container
 serves as a reservoir for urine
 positioned immediately superior and posterior to the pubic
symphysis.
 in females
 the urinary bladder is in contact with the uterus posterosuperiorly
and with the vagina posteroinferiorly.
 in males
 it is in contact with the rectum posterosuperiorly and is
immediately superior to the prostate gland.
 is a retroperitoneal organ.
 when empty exhibits an upside-down pyramidal shape.
 Filling with urine distends it superiorly until it assumes an oval
shape.

40. 27-40
Urinary Tract – Urinary Bladder
 Trigone
 posteroinferior triangular area of the urinary bladder wall
 formed by imaginary lines
 connect the two posterior ureteral openings
 and the anterior urethral opening.
 The trigone remains immovable as the urinary
bladder fills and evacuates.
 It functions as a funnel
 directs urine into the urethra as the bladder wall contracts
 four tunics
 mucosa
 submucosa
 Muscularis: called the detrusor muscle
 adventitia.
 Internal urethral sphincter (smooth muscle)

41. 41

42. 42

43. 43

44. 27-44
Micturition (Urination)
 The expulsion of urine from the bladder.
 Initiated by a complex sequence of events called the
micturition reflex.
 The bladder is supplied by both parasympathetic and
sympathetic nerve fibers of the autonomic nervous
system.

45. 27-45
Urethra
 Fibromuscular tube
 exits the urinary bladder through the urethral opening
 at anteroinferior surface
 conducts urine to the exterior of the body.
 Tunica mucosa: is a protective mucous membrane
 houses clusters of mucin-producing cells called urethral
glands.
 Tunica muscularis: primarily smooth muscle fibers
 help propel urine to the outside of the body.
 Two urethral sphincters:
 Internal urethral sphincter
 restrict the release of urine until the pressure within the urinary
bladder is high enough
 External urethral sphincter
 and voluntary activities needed to release the urine are
activated.

46. 27-46
Urethra
 The internal urethral sphincter
 involuntary (smooth muscle)
 superior sphincter surrounding the neck of the bladder,
where the urethra originates.
 a circular thickening of the detrusor muscle
 controlled by the autonomic nervous system
 The external urethral sphincter
 inferior to the internal urethral sphincter
 formed by skeletal muscle fibers of the urogenital
diaphragm.
 a voluntary sphincter
 controlled by the somatic nervous system
 this is the muscle children learn to control when they
become “toilet-trained”

47. 27-47
Female Urethra
 Has a single function:
 to transport urine from the urinary bladder to the vestibule,
an external space immediately internal to the labia minora
 3 to 5 centimeters long, and opens to the outside of
the body at the external urethral orifice located in the
female perineum.

48. 48

49. 27-49
Male Urethra
 Urinary and reproductive functions:
 passageway for both urine and semen
 Approximately 18 to 20 centimeters long.
 Partitioned into three segments:
 prostatic urethra is approximately 3 to 4 centimeters long and is the
most dilatable portion of the urethra
 extends through the prostate gland, immediately inferior to the male
bladder, where multiple small prostatic ducts enter it
 membranous urethra is the shortest and least dilatable portion
 extends from the inferior surface of the prostate gland through the
urogenital diaphragm
 spongy urethra is the longest part (15 centimeters)
 encased within a cylinder of erectile tissue in the penis called the
corpus spongiosum
 extends to the external urethral orifice

50. 50

51. 27-51
Aging and the Urinary System
 Changes in the size and functioning of the kidneys begin at 30.
 Gradual reduction in kidney size.
 Reduced blood flow to the kidneys.
 Decrease in the number of functional nephrons.
 Reabsorption and secretion are reduced.
 Diminished ability to filter and cleanse the blood.
 Less aldosterone or antidiuretic hormone.
 Ability to control blood volume and blood pressure is reduced.
 Bladder decreases in size.
 More frequent urination.
 Control of the urethral sphincters—and micturition—may be lost.

52. 52