Chapter 26: The Urinary System
BIO 211 Lab
Instructor: Dr. Gollwitzer
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• Today in class we will:
– Identify the major function of the urinary system
– Identify the major components of the urinary system
and their functions
– Trace the path of filtrate/urine through the urinary
system
– Begin our discussion on the organs and anatomical
structures of the urinary system:
• Kidneys
–
–
–
–
–
Gross anatomy
Position
Sectional anatomy
Renal flow
Blood supply and blood flow
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Introduction
• Major function:
– To excrete waste products
• 2 major components:
– Kidneys:
• Produce urine =
– Fluid containing water, ions, small soluble compounds and toxic substances
– Urinary tract:
• Transports and stores urine prior to elimination
• Consists of:
– Ureters – paired tubes from the kidney to the bladder
– Urinary bladder – muscular sac for temporary storage of urine
– Urethra – from bladder to exterior
• Kidneys  urine  ureters  urinary bladder 
urethra  exterior
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Figure 26-1
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Figure 26-3
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Kidneys: Gross Anatomy
• Paired organs on either side of vertebral
column; left slightly superior to right
• Reddish-brown, kidney-bean shaped
• Adrenal glands on superior surface
• Approximate size of hand
• Hilum = depression where blood vessels (renal
artery and vein) and lymphatic vessels, nerves,
and ureter pass into/out of kidney
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Figure 26-2a
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Kidneys: Position
• Retroperitoneal (“behind”):
– Between muscles of dorsal body wall and parietal
peritoneum
– Behind parietal peritoneum of abdominal cavity in
retroperitoneal space; separated by parietal
peritoneum
• Position in abdominal cavity maintained by:
– Overlying peritoneum
– Contact with adjacent visceral organs
– 3 concentric layers of supportive CT
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Figure 26-2b
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Kidney: CT layers
• Renal capsule – tough layer of collagen fibers,
covers outer surface of kidney
• Adipose capsule – thick middle layer, surrounds
renal capsule; cushions kidney
• Renal fascia – dense, fibrous outer layer (also
surrounds adrenal gland)
– Anchors kidney to surrounding structures
– Fuses with deep fascia (surrounding muscles of body
wall) and peritoneum
– When renal fascia torn  floating kidney
• Dangerous because of potential twisting/kinking of ureters
and blood vessels
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Kidney: Sectional Anatomy
• Renal cortex – outer layer in contact with renal
capsule; appears grainy
• Renal columns – bands of cortical tissue that extend
into renal medulla and separate renal pyramids
• Renal medulla:
– Inner layer adjacent to renal cortex; looks like strands of
combed hair
– Consists of 6 – 18 renal pyramids (triangular structures)
• Base of each pyramid in contact with cortex
• Tip forms renal papilla
• Striations = loops of Henle and collecting ducts of nephrons
(functional units of kidney)
• Ducts discharge urine in to cup-shaped minor calyx
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Kidney
Figure 26-4, a,b
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Kidney: Sectional Anatomy
• Renal lobe:
– Functional component where urine
production occurs
– Consists of:
•
•
•
•
Renal pyramid +
Overlying renal cortex +
Adjacent renal columns
Note: Think 3D – visualize handful of waffle cones
= Kidney
– Ice cream = cortex
– Cone = medulla
– Paper around each cone = renal columns
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Kidney: Renal Flow
• Renal papillae from several renal pyramids
discharge into a minor calyx
• 4-5 minor calyces discharge into a major calyx
• 2-3 major calyces form the renal pelvis =
– Large funnel-shaped chamber that fills most of
renal sinus and connects to ureter
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Kidney
• Renal sinus = internal cavity lined by
inner surface of renal capsule
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Nephrons
• Microscopic, tubular structures in cortex of
renal lobe
• Functional/filtration unit of kidney = where
urine production begins
• Approx. 1.25 million/kidney
• Consists of:
– Renal corpuscle = filtering body
– Renal tubule (equivalent to 85 miles) = urine
collecting and concentrating tube
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Figure 26-6, 7th edition
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Kidney: Renal Corpuscle
• Round structure consisting of:
– Glomerulus
– Bowman’s capsule
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Kidney: Renal Corpuscle
• Glomerulus
– Ball of intertwined fenestrated capillaries (approx.
50)
– Parietal and visceral epithelia separated by
capsular space
– Visceral epithelium
• Covers glomerular capillaries
• Consists of podocytes (= large simple squamous cells)
with “feet” = pedicels
• Narrow gaps between adjacent pedicels = filtration
slits – allow filtrates to enter Bowman’s capsule
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Kidney: Renal Corpuscle
• Bowman’s capsule
– Cup-shaped body
– Encircles glomerular capillaries
– Collects filtrate forced out of capillaries in
capsular space
– Connected to initial segment of renal tubule
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Kidney: Renal Corpuscle
• Blood arrives at renal corpuscle via afferent
arteriole and leaves via efferent arteriole
• In renal corpuscle, BP forces fluid and
dissolved solutes out of glomerular capillaries
(fenestrated) into capsular space (between
glomerulus and capsule) = filtration 
protein-free solution (filtrate)
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Figure 26-8
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Kidney: Renal Tubule
• Filtrate (tubular fluid) leaves renal corpuscle and
enters renal tubule
• Has 3 sections:
– 2 coiled/twisted segments (located in the cortex)
– Separated by a U-shaped tubule (located partially or
completely in the medulla)
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Kidney: Renal Tubule
• Proximal convoluted tubule (PCT):
– First segment that exits Bowman’s capsule in
– Entrance opposite afferent/efferent arterioles
• Loop of Henle:
– Descending limb (turns toward renal medulla)
– Ascending limb (turns toward cortex)
• Distal convoluted tubule (DCT):
– Passes between afferent and efferent arterioles
– Empties into collecting duct in cortex
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Figure 26-6, 7th edition
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Kidney: Renal Tubule
• Tubular fluid changes in composition as it travels
through each segment of the nephron
• Reabsorption of:
– Useful organic compounds (glucose, fatty acids, amino
acids, vitamins etc)
– Ions (Na, K)
– Water (>90%) from tubular fluid and release them into
the peritubular fluid –
• Secretion of waste products missed by filtration
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Kidney:
Juxtaglomerular Apparatus (JGA)
• Located where DCT and afferent arteriole are in
close contact with each other and the renal
corpuscle
• Formed by:
– JG cells
– Macula densa
• An endocrine structure that secretes:
– Hormone erythropoietin
• In response to low O2
• Primary function
– Enzyme renin:
• Elevates BP and Na retention
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Figure 26-8
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Kidney: Types of Nephrons
• Nephrons from different locations differ in structure
• Cortical nephrons (85%) – in superficial cortex:
– Short loop of Henle; descends only slightly into renal
medulla
– Efferent arteriole delivers blood to peritubular capillaries
which surround entire renal tubule and drain into small
venules  interlobular veins
• Juxtamedullary nephrons (15%) – near medulla:
– Long loop of Henle extends deep into medulla
– Peritubular capillaries connected to vasa recta = long,
straight capillaries that parallel the loop of Henle
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Figure 26-7
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Figure 26–7
Kidney: Collecting System
• Collecting duct:
– Receives tubular fluid from DCT of several
nephrons
– Begins in cortex and ends in medulla (at papillary
duct)
• Papillary duct:
– Receives fluid from several collecting ducts
– Drains into minor calyx
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Blood Supply to Kidneys
• Major function of kidneys is to filter blood
• Therefore, large volumes of blood delivered to kidneys
(almost 20 gallons/hr!)
• Blood flow:
– Abdominal aorta  renal artery  segmental artery 
interlobar artery  arcuate artery  interlobular artery 
afferent arteriole  renal corpuscle glomerulus  efferent
arteriole 
– For cortical nephrons:
•  peritubular capillary  venule  interlobular vein
– For juxtamedullary nephrons:
•  peritubular capillary  vasa recta  venule  interlobular vein
– Interlobular vein  arcuate vein  interlobar vein 
segmental vein  renal vein
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Figure 26-5
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• Today in class we will:
– Continue our discussion on the organs and
anatomical structures of the urinary system:
• Urinary tract
– Ureters
– Urinary bladder
– Urethra
» Female
» Male
– Renal flow
– Blood supply
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Urinary Tract
• Consists of: paired ureters, urinary bladder, urethra
• Responsible for urine transport, storage, and
elimination
• Ureters:
– Pair of muscular tubes from kidney renal pelvis to urinary
bladder
– Penetrate posterior, inferior wall of bladder
– Ureteral openings are slits to prevent backflow of urine when
bladder contracts
– Every 30 seconds peristaltic contraction begins at renal pelvis
and moves along ureter, forcing urine toward urinary bladder
– Different pathways in males and females:
• Due to variations in nature, size, position of reproductive organs
• Males – base lies between rectum and pubic symphysis
• Females – base sits inferior to uterus and anterior to vagina
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Urinary Tract
• Urinary bladder:
– Hollow muscular organ/sac for temporary storage of urine; urine flows in
until bladder distended and pressure closes urethral openings
– Can contain approximately 1 L (stretch receptors triggered at approx 200 mL)
– Held in place by umbilical ligaments
– Internal surface:
• Covered by transitional epithelium (“modified” columnar epithelium)
• Has has rugae (folds) that disappear as bladder fills
– Trigone
• Triangular base (area bounded by ureteral openings and entrance of urethra)
• Funnels urine into urethra as bladder contracts
– Neck (surrounds urethral opening)
• Contains internal urethral sphincter = smooth muscle  involuntary control over
discharge of urine from bladder
– Smooth muscle layers of bladder wall form detrusor muscle – contraction
compresses urinary bladder and expels contents into urethra
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Urinary Tract
• Urethra:
– Extends from neck of urinary bladder to exterior of
body
– Drains urine from bladder to exterior opening of
body (external urethral meatus/orifice)
– Females and males differ in length and function
• Female urethra:
– Very short (1-2 in. long)
– From bladder to vestibule
– External urethral orifice/meatus = opening to
outside between vagina and clitoris
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Urinary Tract
• Male urethra:
– Extends from neck of bladder to tip of penis (6-8 in.
long)
– 3 sections:
• Prostatic urethra - passes through prostate gland
• Membranous urethra
– Penetrates urogenital diaphragm (floor of pelvic cavity)
– Surrounded by external urethral sphincter (in males and
females)
» = band of skeletal muscle
» Acts as a valve - at rest, contracted; must be voluntarily
relaxed to urinate
• Penile (spongy) urethra – passes through penis:
– From urogenital diaphragm
– To external urethral orifice/meatus (opening to outside)
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Figure 26-18
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