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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