Chapter 26: The Urinary System

BIO 211 LabInstructor: 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 4

Figure 26-3 5

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 7

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 9

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 12

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 17

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 22

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 25

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 28

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 26–7Figure 26-7 30

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 33

• 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 39