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1. 27-1
Human Anatomy, First Edition
McKinley & O'Loughlin
Urinary
System

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. 27-6
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

7. 27-7
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

8. 27-8
Kidneys: Gross and Sectional
Anatomy
 Sectioned on a coronal plane:
 Renal Cortex - outer
 Renal Medulla - inner

Divided into renal pyramids and columns

8 to 15 per kidney

9. 9

10. 27-10
Blood Supply to the Kidney
 About 20 to 25% of cardiac output to
kidneys

11. 27-11
Blood Supply to the Kidney
 Blood plasma is filtered across the
glomerulus into the glomerular space.

12. 27-12
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.

13. 27-13
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

14. 27-14
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.

15. 27-15
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.

16. 27-16
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.

17. 27-17
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.

18. 18

19. 27-19
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.

20. 27-20
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.

21. 27-21
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”

22. 27-22
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.

23. 23

24. 27-24
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

25. 25

26. Components of Urine
• Urine = 1-2 l /day
• 95% water
• + urea, creatinine, K+
, ammonia, uric acid,
Na+
, Cl-
, Mg2+
, sulfate, phosphate & Ca2+
• Depends on diet and state of health

27. 27-27
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.

28. Aging
 Kidneys shrink- decrease in capacity
 Thirst decreases  dehydration
  urinary tract infections
 Males: prostate enlargement frequent
urination & slow flow
 Females: more prone to leakage of
external sphincter (incontinence)
 Both: nocturia