Transcript PPT Lecture - Annmarie Kotarba

Chapter 26:
The Urinary System
Primary sources for figures and content:
Marieb, E. N. Human Anatomy & Physiology. 6th ed. San Francisco: Pearson Benjamin Cummings, 2004.
Martini, F. H. Fundamentals of Anatomy & Physiology. 6 th ed. San Francisco: Pearson Benjamin Cummings,
2004.
Urinary System
• Components
– Kidneys
– Urinary Tract
• Ureters
• Urinary
Bladder
• Urethra
Figure 26–1
Functions of the Urinary System
1. Excretion by the Kidneys:
– removal of organic wastes from body fluids
2. Elimination by the Urinary Tract:
– discharge of waste products
3. Homeostatic regulation of plasma volume and
solute concentrations by the kidneys:
– Blood volume, BP
– Concentration of ions
– Stabilize blood pH
– Conserve nutrients
– Assist liver: deamination, detoxification
Functions of the Urinary System
4. Other kidney functions:
– Gluconeogenesis during starvation
– Produce renin to regulate BP
– Produce erythropoietin for RBC production
– Convert Vitamin D to calcitriol for calcium
absorption in the GI tract
The location and structures of
the kidneys.
Gross Anatomy of
the Urinary System
Figure 26–3
Kidneys
•
•
•
•
1% body weight
Retroperitoneal, posterior abdominal wall
Adrenal gland anchored superior
3 layers CT anchor kidneys
1. Renal capsule:
- collagen fibers covering organ
2. Adipose capsule:
- adipose cushion around the renal capsule
3. Renal fascia:
- collagen fibers fused to renal capsule and
deep fascia of body wall and peritoneum
Kidneys
• Renal ptosis = floating kidney
– Cause  Starvation or injury
– Result  Kidney becomes loose from body
wall
• Kidney could twist blood vessels or
ureters
The Structure of the Kidney
Figure 26–4
Kidney
• Hilum (Hilus):
– Point of entry for renal artery and renal nerves
– Ureters enter and exit
• Hilus opens to renal sinus
• Renal sinus lined with renal capsule that is
contiguous with outside
Kidney
• Kidney has two layers
1. Cortex = superficial
• Contact renal capsule
• Houses filtration structures = nephrons
2. Medulla = 6-18 renal pyramids
• Parallel bundles of collection tubules
• Apex = papilla, points toward renal sinus
• Kidney divided into sections: renal lobes
• Renal lobe =
– renal pyramid + surrounding cortex called renal
columns
– Lobe is site for urine production
Urine Production
• Nephron (cortex)  collecting ducts (medulla) 
papilla  minor calyx major calyx  renal
pelvis
• Renal pelvis
– Fills majority of real sinus
– Funnels urine into ureters
• Pyelonephritis
– Inflammation of kidney
– Infection usually enters from ureter and
spreads up through ducts to nephron
Blood Supply to the Kidneys
Figure 26–5
Blood Supply and Innervation to Kidney
• Receives 20-25% cardiac output
• Highly vascularized, many capillaries involved in
filtration (nephrons)
• Innervation from Renal Plexus controlled by ANS
• Most is sympathetic to
1. Adjust rate of urine formation
- Change BP and flow at nephron
2. Stimulate release of renin
- Restricts water and sodium loss at nephron
Blood Supply and Innervation to Kidney
• Two important capillary beds associated with
each nephron
1. Glomerulus = filtration
2. Peritubular capillaries:
- reclaim filtrate, concentrate urine
• Both connected to arterioles only (not for oxygen
exchange)
• Afferent arteriole  capillary  efferent
arteriole
Glomerulus
• Consists of 50 intertwining capillaries
• Blood delivered via afferent arteriole
• Blood leaves in efferent arteriole:
– flows into peritubular capillaries
– which drain into small venules
– and return blood to venous system
The Nephron and Collecting System
Figure 26–6
Nephron
• Two types of nephrons
– Cortical nephron = Majority
• In cortex, short loop of Henle
– Juxtamedullary nephrons = 15%
• At cortex/medulla interface
• Long loops of Henle
• Important for water conservation and
concentrated urine
Cortical and
Juxtamedullary Nephrons
Figure 26–7
Renal Corpuscle
• Site of filtration
• 2 parts
1. Glomerular capsule
• Thin parietal epithelium, forms capsule around
glomerulus
2. Glomerulus
• Fenestrated capillaries covered by podocytes
• Podocytes are on the visceral epithelium
– Wrapped around the capillaries, to create
filtration slits on surface of capillaries
– Slits smaller than fenestrations in glomerular
capillaries to restrict filtration of large
molecules
The Renal Corpuscle
Figure 26–8
Renal Corpuscle
• Golmerulonephritis
– Inflammation of glomeruli
– Prevents filtration
– Can be result of antigen/Ab complexes
trapped in filtration slits following
allergy or blood infection
The Nephron and Collecting System
Figure 26–6
Renal Tubule
• Reabsorption to process raw filtrate into urine
• 3 parts
1. PCT (proximal convoluted tubules)
• Simple cuboidal epithelium with microvilli
• Reabsorbs organic nutrients, ions, water, small
plasma proteins from filtrate exiting glomerular
capsule
2. Loop of Henle
• Simple squamous epithelium
• Reabsorbs Na+, Cl-, H2O form filtrate
• Important to regulate volume and solute
concentration of urine
• Descending and ascending limbs
Renal Tubule
3. DCT (distal convoluted tubules)
• Simple cuboidal epithelium
• Flat surface
• Four important functions
1. Secretion
2. Reabsorb Na+ and Ca++ from filtrate
3. Optional H2O reabsorption from filtrate under
hormonal control
4. Contribute to formation of Juxtaglomerular
Apparatus
Table 26–1
Juxtaglomerular Apparatus (JGA)
• Consists of two cell types
1. Endocrine cells of DCT = macula densa
2. Granular cells of apparent arteriole =
Juxtaglomerular cells
• Together cells monitor blood and produce
1. Renin: Enzyme, restricts Na+ and H2O at
nephron
2. Erythropoietin: hormone, stimulates RBC
production
Collecting System
• Collecting ducts + papillary ducts = nephrons  1
collecting duct (renal pyramid)  Many collecting
ducts  1 papillary duct
• Final osmotic concentration of filtrate adjusted
by collecting duct, after this urine is complete
and exits kidney:
– Papillary ducts (renal papilla)  minor calyx 
major calyx  renal pelvis  ureter
• Polycystic Kidney Disease
– Genetic, cysts form that cause swelling of
kidney tubules, compression reduces function
KEY CONCEPT
• Kidneys remove waste products from
blood
• Nephrons are primary functional units
of kidneys
• Kidneys help regulate:
– blood volume and pressure
– ion levels
– blood pH
Which portion of the nephron is
NOT in the renal cortex?
A.
B.
C.
D.
proximal convoluted tubule
distal convoluted tubule
collecting duct
loop of Henle
Why don’t plasma proteins pass
into the capsular space under
normal circumstances?
A. glomerular capillary pores are too
small
B. glomerular blood pressure is too low
C. glomerular filtration rate is too low
D. glomerular blood flow is too slow
Damage to which part of the nephron
would interfere with the control of
blood pressure?
A.
B.
C.
D.
juxtaglomerular apparatus
Bowman’s capsule
PCT
loop of Henle
Renal Physiology
Renal Physiology
• Urinary system functions to regulate blood
volume and concentration
– Removes wastes and produce urine
• Filtrate =
– Everything in blood plasma except large
proteins and cells
• Urine = metabolic waste, 1% filtrate
Common Wastes
1. Urea: from catabolism of amino acids
2. Creatinine: from catabolism or damage of skeletal
muscle tissue
– Creatine phosphate is energy storage of muscle
3. Uric acid: from recycling of RNA
4. Urobilin: from breakdown of hemoglobin (yellow
color)
• All wastes excreted as solution in water
• Loss of filtering  toxic waste buildup
– death in a few days
• Dialysis  blood filtering machine used for patients
with kidney failure
Urine Formation
1. Glomerular Filtrations
– Blood hydrostatic pressure forces water and
solutes through glomerular wall
2. Tubular Reabsorption
– Selective uptake of water and solutes from
filtrate
3. Tubular Secretion
– Transport of wastes from capillaries to
tubules
An Overview of Urine Formation
Figure 26–9 (Navigator)
1. Glomerular Filtration
• Occurs through filtration membrane
1. Fenestrated endothelium of glomerular
capillaries
-
Restricts cells
2. Podocytes (visceral epithelium of capsule)
-
Filtration slits restrict solutes protein sized
and larger
3. Fused basal lamina for both
1. Glomerular Filtration
• Filtrations depends on
1. Large surface area
2. High glomerular blood pressure
3. Good permeability
• Glomerular Filtration Rate (GFR)
– Amount of filtrate kidneys produce/minute
– ~125 ml/min  180L/day
– 99% reabsorbed, 1% lost as urine
– Drop in blood pressure = decrease GFR
• Decrease 15% BP = 0 GFR
Glomerular Filtration
• Filtration is passive
but all small solutes
escape e.g. glucose,
amino acids, etc.
Figure 26–10
Regulation of Filtrations
3 Levels of GFR Control
1. Autoregulation (local level)
2. Hormonal regulation (initiated by
kidneys)
3. Autonomic regulation (by sympathetic
division of ANS)
1. Autoregulation of GFR
• Functions to maintain constant GFR with normal blood
pressure fluctuations in systemic arteriole pressure
A. Reduced blood flow/BP triggers
• Dilation of afferent arteriole and glomerular capillaries
• Constriction of efferent arteriole
• All functions to INCREASE PRESSURE at the glomerulus
to INCREASE GFR
B. High blood flow/BP triggers
• Constriction of afferent arteriole and glomerular
capillaries
• Dilation of efferent arteriole
• All functions to DECREASE PRESSURE at the glomerulus
to DECREASE GFR
2. Hormonal Regulation
• Extrinsic regulation aimed at maintaining systemic
blood pressure
A. Renin = Enzyme released by juxtaglomerular
apparatus in response to:
1. Decline in BP in kidney
2. Decline in osmotic concentration of filtrate
3. Direct sympathetic stimulation
2. Hormonal Regulation
A. Renin =
• Renin activates angiotensin in blood to form
Angiotensin II which triggers
1. Arteriole constriction to elevate BP
2. Secretion of aldosterone from adrenal glands
» Aldosterone promotes sodium reabsorption in
kidney tubules
3. Thirst
4. Release of ADH from pituitary (ADH promotes
water uptake in tubules)
• Effect =
– Increase blood volume
– Decrease urine production
2. Hormonal Regulation
B. Natriuretic Peptide =
• Hormone released in response to stretching in
heart or aorta (increase blood volume)
• Triggers
1. Dilation of afferent arteriole
2. Constriction of efferent arteriole
• Effect =
– Increase GFR
– Increase Urine Production
– Decrease blood volume
3. Autonomic Nervous System
Regulation
• Sympathetic causes vasoconstriction
– Decrease GFR
– Decrease Urine Production
– Prolonged sympathetic stimulation can cause
hypoxia of kidneys and waste accumulation in
blood
Response
to Reduction
in GFR
Figure 26–11
KEY CONCEPT
• Glomeruli produce about 180 L of
filtrate per day (70 times plasma
volume)
• Almost all fluid volume must be
reabsorbed to avoid fatal dehydration
What nephron structures are
involved in filtration?
A. glomerular capillaries, lamina
densa, and filtration slits of the
podocytes
B. filtration slits of the podocytes, PCT
C. PCT, lamina densa, descending loop
of Henle
D. glomerular capillaries, PCT
What occurs when the plasma
concentration of a substance
exceeds its tubular maximum?
A.
B.
C.
D.
glomerular blood pressure increases
filtration shuts down
excess is excreted in urine
glomerular osmotic pressure
decreases
How would a decrease in blood
pressure affect the GFR?
A.
B.
C.
D.
increase
decrease
cause random fluctuations
no effect due to glomerular
compensation
2. Reabsorption and 3. Secretion
• Reabsorption:
– recovers useful materials from filtrate
• Secretion:
– ejects waste products, toxins, and other
undesirable solutes
2. Tubular Reabsorption
• Transport proteins in renal tubule cells
• Return substances from filtrate to plasma
• When carrier proteins are saturated by the
substance they carry  the renal threshold for
that substance has been reached. All additional
amounts of that substance will be lost in urine
– E.g. Glycosuria = glucose in urine
• Glucose levels in blood/filtrate exceed renal
threshold
2. Tubular Reabsorption
• PCT reabsorption
– PCT reabsorbs 60-70% of filtrate
1. Reabsorption of 99% of organic nutrients by
facilitated diffusion and cotransport
2. Passive reabsorption of ions by diffusion
3. Selective reabsorption of ions by active
transport
- Ion pumps controlled by hormones
4. Reabsorption of water by osmosis
- Water follows ions
2. Tubular Reabsorption
• Loop of Henle reabsorption
– Functions to concentrate filtrate
– Reabsorbs half remaining water and 2/3 Na+ and Clby countercurrent multiplications
• Ascending limb pumps ions from filtrate to
medulla
• High ion concentration then causes water to
move by osmosis out of descending limb
Countercurrent Multiplication
• Is exchange that occurs between 2 parallel segments of
loop of Henle:
– the thin, descending limb
– the thick, ascending limb
• Countercurrent = Refers to exchange between tubular
fluids moving in opposite directions:
– fluid in descending limb flows toward renal pelvis
– fluid in ascending limb flows toward medulla/cortex
• Multiplication = Refers to effect of exchange:
– increases as movement of fluid continues
Countercurrent Multiplication
and Concentration of Urine
Figure 26–13a (Navigator)
Countercurrent Multiplication
and Concentration of Urine
The Thin Descending Limb
• Is permeable to water, impermeable to solutes
• As tubular fluid flows along thin descending limb:
– osmosis moves water into peritubular fluid
– leaving solutes behind
– osmotic concentration of tubular fluid increases
• Normal Maximum Solute Concentration
– Of peritubular fluid near turn of loop of Henle: 1200
mOsm/L
• The Concentration Gradient of the Medulla
– 2/3 (750 mOsm/L) from Na+ and Cl—: pumped out of
ascending limb
• Remainder from urea
2 Benefits of
Countercurrent Multiplication
1. Efficiently reabsorbs solutes and
water:
–
before tubular fluid reaches DCT and
collecting system
2. Establishes concentration gradient:
–
that permits passive reabsorption of
water from tubular fluid in collecting
system
2. Tubular Reabsorption
• DCT reabsorption
– Aldosterone promotes Na+ uptake and K+ loss via
sodium potassium pump
– Parathyroid hormone and calcitriol promote Ca++
uptake
– ADH stimulates water uptake
3. Tubular Secretion
• Selectively removes solutes from blood  delivers
them to filtrate
1. Dispose of drugs and wastes that were not filtered
2. Eliminate wastes that were reabsorbed
3. Rid body of excess K+
4. Control blood pH: Remove H+
• CO2 + H2O  H2CO3  H+ + HCO3**Bicarbonate ions used to buffer blood pH but H+
must be secreted into filtrate
• Secretion carried out mostly by DCT, but some also
occurs in collecting ducts
KEY CONCEPT
• Reabsorption involves diffusion, osmosis, channelmediated diffusion, and active transport
• Many processes are independently regulated by
local or hormonal mechanisms
• The primary mechanism governing water
reabsorption is “water follows salt”
• Secretion is a selective, carrier mediated process
What effect would increased amounts
of aldosterone have on the K+
concentration of urine?
A.
B.
C.
D.
increase
decrease
no effect
impossible to predict
What effect would a decrease in the
Na+ concentration of filtrate have on
the pH of tubular fluid?
A.
B.
C.
D.
higher
lower
no effect
impossible to predict
How would the lack of juxtamedullary
nephrons affect the volume and
osmotic concentration of urine?
A.
B.
C.
D.
increase volume; decrease osmotic concentration
decrease volume; decrease osmotic concentration
increase volume; increase osmotic concentration
decrease volume; increase osmotic concentration
Why does a decrease in the amount of
Na+ in the distal convoluted tubule lead
to an increase in blood pressure?
A.
B.
C.
D.
Because it increases renin production.
Because it decreases water content in blood.
Because it increases filtration rate.
Because it increases water loss through
kidneys.
Control of Water Volume
• Control of Water Volume
– Obligatory water reabsorption occurs by osmosis in
PCT and descending loop of Henle
• Cannot be prevented
– Facultative water reabsorption can occur in DCT and
collecting ducts
• Usually impermeable
– ADH causes formation of water channels by
triggering insertion of aquaporin proteins in cell
membrane of DCT and collecting ducts
– Aquaporins allow more osmosis to concentrate urine
and conserve water
The Effects of ADH on the
DCT and Collecting Duct
Figure 26–15 (Navigator)
Control of Water Volume
• Control of Water Volume
1. Diuretics = Substance that cause water loss
• Osmostic diuretics
– Substances that cannot be reabsorbed and thus
take water with then
• Hypertension and edema meds
– Prevent Na+ uptake
– Water follows salt
• Alcohol
– Inhibits ADH preventing facultative water
reabsorption
Control of Water Volume
• Control of Water Volume
2. Diabetes insipidus = not enough ADH
• Produce large quantities of dilute urine
• Up to 24 L/day, normal = 1.2 L/day
3. Anuria = low urinary output
• Less than 150 ml/day
• Usually due to events that block filtration
– Nephritis
– Immune reactions
– Crushing injuries
Urine Transport, Storage, Elimination
• Urine Transport, Storage and Elimination
– Urine production and modification
• Renal tubules and collecting system
– Once in renal pelvis  Urine Complete  excreted
via ureters, bladder, urethra
– Nephrolithiasis = Blockage of urinary passage
• E.g. Calculi (kidney stones)
– Crystallized deposits of calcium, magnesium, or
uric acid
– Form in renal pelvis, can become lodged in
ureters
– Large ones may need disruption by a lithotripter
Ureters
• Ureters
– Connect renal pelvis to urinary bladder
– Wall layers
1. Mucosa, with transitional epithelium
2. Muscularis, with two layers of smooth muscle
3. Adventitia, attaches to posterior body wall
– Contractions occur every 30 sec to force urine
toward bladder
Urinary Bladder
• Urinary Bladder
– Wall folded into rugae when empty – expands
– Wall layers
• Mucosa with transitional epithelium
• Muscularis with 3 layers of smooth muscle =
detrusor muscle
1. Contraction causes expulsion of urine from
bladder
2. Detrusor muscle thickened around urethral
opening to create the internal urethral sphincter
» Provides involuntary control over release of
urine
3. Adventitia = Fibrous, Anchors bladder to pelvic
floor
Urethra
• Urethra
– Single tube, connects bladder to environment
– Lined with pseudostratified columnar epithelium
– Passes through band of skeletal muscle that forms
external urethral sphincter
• under voluntary control
• relaxation results in micturition
Micturition Reflex
• When bladder contains ~ 200ml urine
1. Stretch receptors triggered
2. Signal conscious awareness of pressure
3. Stimulates contraction of detrusor muscle
• Voluntary maintenance of contracted external urethral
sphincter prevents urination
1. Detrusor will relax
2. Opening will open internal urethral sphincter
3. Urination will occur
• Continued increase in urinary volume will repeatedly
trigger reflex
Micturition Reflex
• If volume exceeds ~500 ml
– Forced relaxation of internal and external urethral
sphincters will result in non-voluntary
urination/micturition
• Incontinence
– Inability to voluntarily control urine excretion
– Due to:
• loss of muscle tone
• Damage to sphincters
• Damage to nerves or control centers in brain
The Micturition Reflex
Figure 26–20 (Navigator)
Age Related Changes
1. Decline in functional nephrons
2. Reduction in GFR
– Damage or decrease blood flow
3. Reduced sensitivity to ADH = dilute urine
4. Problems with micturition
– Incontinence
– Urinary retention, enlarged prostate
What effect would a high-protein diet
have on the composition of urine?
A.
B.
C.
D.
increased urea
increased potassium
increased fluid volume
A and C are correct
An obstruction of a ureter by a kidney
stone would interfere with the flow of
urine between which two points?
A.
B.
C.
D.
ureter and urethra
renal medulla and renal pelvis
renal medulla and urethra
renal pelvis and urinary bladder
The ability to control the micturition
reflex depends on your ability to
control which muscle?
A.
B.
C.
D.
urogenital diaphragm
internal urinary sphincter
external urinary sphincter
coccygeus
Urinalysis
• Is the analysis of a urine sample:
– an important diagnostic tool
• Includes color and appearance of urine
General Characteristics
of Normal Urine
Table 26–5
Typical Values Obtained from Standard Urinalysis
Table 26–6
A Summary of Renal Function
Figure 26–16a
A Summary of Renal Function
Figure 26–16b
Step 1: Glomerulus
• Filtrate produced at renal corpuscle
has the same composition as blood
plasma:
– without plasma proteins
Step 2: Proximal
Convoluted Tubule (PCT)
• Active removal of ions and organic
substrates:
– produces osmotic water flow out of
tubular fluid
– reduces volume of filtrate
– keeps solutions inside and outside tubule
isotonic
Step 3: PCT and
Descending Limb
• Water moves into peritubular fluids,
leaving highly concentrated tubular
fluid
• Reduction in volume occurs by
obligatory water reabsorption
Step 4: Thick Ascending Limb
• Tubular cells actively transport Na+ and
Cl— out of tubule
• Urea becomes higher proportion of
total osmotic concentration
Step 5: DCT and Collecting Ducts
• Final adjustments in composition of
tubular fluid
• Osmotic concentration is adjusted
through active transport (reabsorption
or secretion)
Step 6: DCT and Collecting Ducts
• Final adjustments in volume and
osmotic concentration of tubular fluid
• Exposure to ADH determines final urine
concentration
Organs for the Conduction
and Storage of Urine
Figure 26–18a
Organs for the Conduction
and Storage of Urine
Figure 26–18b
Organs for the Conduction
and Storage of Urine
Figure 26–18c
Organs that Collect
and Transport Urine
Figure 26–19
SUMMARY
• Urinary system functions:
– excretion
– Elimination
• Kidneys
• Urine
• Urination (micturition)
• Nephron
• Renal corpuscle
• Renal tubule
• Filtrate
• Tubular fluid
• Collecting system
• Loop of Henle
SUMMARY
•
•
•
•
•
•
•
•
•
•
Urine formation
Filtration
Reabsorption
Secretion
Glomerulus filtration
Countercurrent multiplication
Ureters
Urinary bladder
Urethra
Micturition reflex