the urinary system chapter 26 functions of the urinary system 1.removal of metabolic wastes...
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The Urinary System
Chapter 26
Functions of the Urinary System
1. Removal of metabolic wastes (especially nitrogenous wastes e.g. urea & uric acid).
2. Water balance (and therefore blood pressure).
3. Control of electrolyte balance.
4. Control of pH.
5. Removal of toxins.
Anatomy of the Urinary System
• The Kidneys: the functional heart of the urinary system.
• The Ureters: pipeline from the kidneys to the bladder.
• The Urinary Bladder: holding tank of urine.
• The Urethra: avenue of relief
(word of the day “micturition” = voiding the bladder)
UrinarySystem
Components
The Kidneys
• Location: retroperitoneal against the dorsal wall of the abdominal cavity. The right kidney is slightly lower than the left.
• Size & weight: approximately 150 grams (about 5 ounces) each and 12 cm x 10 cm x 4 cm.
• Shaped like a bean (or are beans shaped like kidneys?)
The Position of
the Kidneys
Figure 26–2
Gross Anatomy
of the
Urinary System
Figure 26–3
The Structure of the Kidney
Figure 26–4
Blood Supply to Kidneys
• Kidneys receive 20–25% of total cardiac output
• 1200 - 1500 ml of blood flows through kidneys each minute
• Kidney receives blood through renal artery
Blood Supply to
the Kidneys
Figure 26–5
A slice of kidney
Medulla
Cortex
Glomeruli
Capsule
The Nephron: functional unit of the kidney
Afferent Arteriole
Glomeruli
Interlobular artery
Functional Anatomy
of Nephron
and Collecting System
Figure 26–6
Renal Corpuscle
The Nephron
and Collecting System
Table 26–1
Filtrate & Urine
flow
Cortical and Juxtamedullary Nephrons Figure 26–7
The renal corpuscle and the Juxtaglomerular apparatus
The renal filtration membrane:Podocytes and fenestrated capillaries
Filtration slits Pedicles
The filtration membrane
An Overview of Urine
Formation
Figure 26–9 (Navigator)
Blood pressure drops due to peripheral resistance
Filtration pressures: NFP must be positive for U2P
GFRGFR is “Glomerular Filtration Rate”.• It is directly proportional to NFP.• It is a measurement of FLOW in milliliters
per minute (ml/min).• If NFP drops more than 15% below 10
mmHg, GFR goes to 0.• If NFP goes up less than 30% above
normal, the kidneys can handle it without major compensatory mechanisms kicking in.
Creatinine Clearance Test
• Is used to estimate GFR
• A more accurate GFR test uses inulin:– which is not metabolized
Response to Reduction in
GFR
Figure 26–11
Tubular reabsorption
•Reabsorption of filtered solutes occurs in the Proximal Convoluted Tubules.•Most solutes are reabsorbed by secondary active transport with Na+. Does this look familiar?
4 Types of Carrier-Mediated Transport
1. Facilitated diffusion
2. Active transport
3. Cotransport
4. Countertransport
The Transport Maximum (Tm)• If nutrient concentrations rise in tubular
fluid:– reabsorption rates increase until carrier
proteins are saturated
• Concentration higher than transport maximum:– exceeds reabsorptive abilities of nephron– some material will remain in the tubular fluid
and appear in the urine
• Determines the renal threshold
Transport Activities
at the PCT
Figure 26–12 (Navigator)
Reabsorptionof sodium
Reabsorption of glucose
Reabsorption of electrolytes
and water
Reabsorption of ions in the Loop
of Henle
Reabsorption
• 60–70% of filtrate volume produced at glomerulus:– is reabsorbed before tubular fluid reaches
loop of Henle
The Loop of Henle
• Reabsorbs about 1/2 of water, and 2/3 of sodium and chloride ions remaining in tubular fluid by the process of countercurrent exchange
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 cortex
Multiplication
• Refers to effect of exchange:– increases as movement of fluid continues
Parallel Segments of Loop of Henle
• Are very close together, separated only by peritubular fluid
• Have very different permeability characteristics
Formation of dilute
urine
Countercurrent Multiplication and Concentration of Urine
Figure 26–13a (Navigator)
Countercurrent Multiplication and Concentration of Urine Figure 26–13b, c
Na+—K+/2 Cl— Transporter
• Each cycle of pump carries ions into tubular cell:– 1 sodium ion– 1 potassium ion– 2 chloride ions
Tubular Fluid at DCT
• Arrives with osmotic concentration of 100 mOsm/L:– 1/3 concentration of peritubular fluid of renal
cortex
• Rate of ion transport across thick ascending limb:– is proportional to ion’s concentration in tubular
fluid
Regional Differences
• More Na+ and Cl— are pumped into medulla:– at start of thick ascending limb– than near cortex
• Regional difference in ion transport rate:– causes concentration gradient within medulla
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
Urea and the Concentration Gradient (1 of 2)
• Thick ascending limb of loop of Henle, DCT, and collecting ducts:– are impermeable to urea
• As water is reabsorbed:– concentration of urea rises
Urea and the Concentration Gradient (2 of 2)
• Tubular fluid reaching papillary duct:– contains 450 mOsm/L urea
• Papillary ducts are permeable to urea:– concentration in medulla averages 450
mOsm/L
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
In the collecting
duct
Reabsorption in the Distal Convoluted Tubule & Collecting
Duct
Differences between
Solute Composition
in Urine and Plasma
Table 26–2
Summary of tubular
reabsorption/excretion
Renal autoregulation
Compensatory Mechanisms to maintain
GFR
A Pyelogram
Figure 26–17
After the Kidneys:
the bladder
& urethra
Male Figure 26–18a
Female Figure 26–18c
The HumanBladder:It can hold
a maximum of 800 –
1000 ml!
Histology
Physical characteristics of Urine
• Color - Clear to deep yellow, almost rusty, depending on concentration.
• Odor - Fresh urine is slightly aromatic, stale urine smells like downtown Tacoma on a Sunday morning.
• pH – range of 4.5 – 8 depending on diet. High protein leads to low pH (acid ash diet), vegetarian (alkaline ash) diet leads to high pH. Heavy vomiting and bacterial infection can also lead to alkaline urine.
• Specific gravity – Normal range is 1.001 – 1.030. Distilled water has a s.g. of 1.000. Anything solutes cause the specific gravity of a liquid to go up. Concentrated urine has a higher s.g. than dilute urine.
General Characteristics of Normal UrineTable 26–5
Typical Values
Obtained from
Standard Urinalysis
Table 26–6
Composition of UrineNormalUreaUric acidCreatinineNaKPhosphatesSulfatesBicarbonateCaMg
AbnormalGlucose “glycosuria”Proteins “proteinuria” or
“albuminuria”Ketones “ketonuria”Hemoglobin
“hemoglobinuria”Erythrocytes “hematuria”Bile pigments “bilirubinura”Leukocytes “pyruia”
Abnormally low output = oliguriaNo output = anuriaAbnormally high output = polyuriaDiuresis = increased urine outputDiuretic = substance that leads to diuresis
A Summary of Renal Function
Figure 26–16a
A Summary of Renal Function
Figure 26–16b
The Micturition ReflexFigure 26–20 (Navigator)
Incontinence
• Is the inability to control urination voluntarily
• May be caused by trauma to internal or external urethral sphincter
Age-Related Changes in Urinary System
• Decline in number of functional nephrons
• Reduction in GFR
• Reduced sensitivity to ADH
• Problems with micturition reflex
Stages of Renal Disease
• Stage 1: signs of kidney damage w/ GFR ≥ 90.
• Stage 2: signs of kidney damage w/ GFR 60 – 89.
• Stage 3: GFR 30 – 59.
• Stage 4: GFR 15 – 29.
• Stage 5: < 15
Renal ClearanceThe volume of plasma that is cleared of a particular substance in a given time (usually one minute).
RC = UV/PU = concentration of the substance in urine (mg/ml)V = flow rate of formation (ml/min)P = concentration of the substance in the plasma (mg/ml)High renal clearance values means that the substance is being effectively cleared, low values means that more is being reabsorbed. For some solutes low is good (glucose should be 0). For others, high RC would be expected (creatinine should be complete, urea should be about 80%).
The Excretory System
• Includes all systems with excretory functions that affect body fluids composition:– urinary system– integumentary system– respiratory system– digestive system
Kidney stonesRenal Calculi
“Well Mr. Osborne, I
don’t think that it’s kidney
stone after all”