The document discusses the structure and function of the urinary system. It describes the key organs - kidneys, ureters, urinary bladder, and urethra. The kidneys filter waste from the bloodstream and produce urine, which is transported via the ureters and stored in the bladder before being excreted through the urethra. The functions of the urinary system include removing waste, regulating blood volume and pressure, and producing hormones like erythropoietin.

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