Chapter 23 the urinary system
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Chapter 23— The Urinary System. Ch. 23 Study Guide. Critically read 23.1 to right before the 23.7 (Urine Storage and Elimination) section (pp. 905-931) Comprehend Terminology (those in bold) Study-- Figure questions, Think About It questions, and Before You Go On (section-ending) questions

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Ch 23 study guide
Ch. 23 Study Guide

Critically read 23.1 to right before the 23.7 (Urine Storage and Elimination) section (pp. 905-931)

Comprehend Terminology (those in bold)

Study-- Figure questions, Think About It questions, and Before You Go On (section-ending) questions

Do end-of-chapter questions:

Testing Your Recall— 2-10, 12-17, 19-20

True or False– 1-9

Testing Your Comprehension-- #1-2


Major nitrogenous wastes
§ Major Nitrogenous Wastes

Ammonia: very toxic; from amino group in the a.a.

Urea: less toxic; converted from ammonia in the __________

Uric acid:

nucleic acid catabolism


creatine phosphate catabolism

Major nitrogenous wastes1
§ Major Nitrogenous Wastes

BUN (Blood Urea Nitrogen)

  • Measure the amount of ________ in your blood

  • Why is it done?

  • Disorders:

    • Azotemia: an abnormally elevated BUN is called; may indicate renal insufficiency

    • Uremia: toxic effects as wastes (urea) accumulate in the blood; patients with renal failure

      • Symptoms– vomiting, diarrhea, cardiac arrhythmia etc.

      • Treatment--Hemodialysis

Major kidney functions 1
§ Major kidney functions (1)

  • Eliminate wastes & foreign compounds

    • Major nitrogenous wastes?

    • Major foreign cpds?

  • Maintain blood volume and electrolyte (ion) concentration

    • For example, water balance during exercise

    • Another example, [K+]  and ectopic focus

Major kidney functions 2
§ Major kidney functions (2)

  • Produce hormones— two major ones?

  • Detoxifies free radicals and drugs

  • In times of starvation-- gluconeogenesis (makes glucose from amino acids or fats)

The urinary system
§ The urinary system

  • Kidneys (a pair)

    • Functions--

  • The ureter(a pair)

  • The single urinary bladder

    • A muscular sac for _________________

  • The urethra

    • Draining urine to the outside

    • In females vs. in males (length and external orifice) + proper toilet habits

      Figure 23.1

Gross anatomy of kidney
§ Gross Anatomy of Kidney

  • Renal cortex: outer 1 cm; extensions of the cortex called renal columns

  • Renal medulla: inner zone; renal columns divide the medulla into 6-10 renal pyramids (each blunt point called renal papilla)

  • The renal papilla is nestled in a cup called a minor calyx  major calyx

  • Lobe of kidney: pyramid and it’s overlying cortex

    Fig. 23.4 + a practice figure

Figure 23 5a
Figure 23.5a

§ Renal circulation--




Path of blood through kidney
Path of Blood Through Kidney

  • Renal artery: into segmental artery and then

     A--interlobararteries(up renal columns, between lobes)

     B--arcuatearteries (over pyramids)

     C--interlobulararteries (up into cortex)

     afferentarterioles

     glomerulus (cluster of capillaries)

     efferentarterioles (near medulla  vasa recta)

     peritubular capillaries

     interlobular veins  arcuate veins  interlobar veins

  • Renal vein

Chapter 23 the urinary system



Two kinds of nephrons depending upon locations
Two kinds of Nephrons, depending upon locations

  • Cortical nephrons (85%)

    • short nephron loops of Henle

    • efferent arterioles branch off into peritubular capillaries

  • Juxtamedullary nephrons (15%)

    • Where?

    • very long nephron loops--

    • Vasa Recta– Efferent arterioles descend into the medulla and give rise to Vasa Recta instead of peritubular capillaries.

    • The capillaries of the vasa recta lead into venules that empty into the interlobular and arcuate veins

The nephron 2
§ The Nephron (2)

  • How many nephrons in each kidney? Answer: ___________

  • The nephron are blood-processing units and each one of them is a functional unit of the kidneys

  • Vascular and tubular parts of the nephron

  • Vascular parts first--Figure 23.6, 23.7

Chapter 23 the urinary system

4. Efferent arteriole

3. Glomerulus

2. Afferent arteriole

1. Interlobular Artery

6. Interlobular vein

5. Peritubular capillaries

To renal pelvis

Vascular part of the nephron 3
§ Vascular part of the Nephron (3)

  • The renal artery (. . . interlobular artery)–

  • Afferent arteriole–

    • supplies each nephron and delivers blood to the glomerulus

  • The glomerulus– cluster of capillaries (1st set of capillary in each nephron);


Vascular part of the nephron 4
§ Vascular part of the Nephron (4)

  • The efferent arteriole—

    • Where the glomerular capillaries rejoin

  • The peritubular (2nd set of) capillaries--

    • Impt in exchanges between blood and ______________

  • The renal veins--

    • The major blood vessels leave the kidney


    • Tubular parts of the nephron– @Fig. 23.8

Chapter 23 the urinary system

1. Bowman’s capsule

4. Distal tubule

2. Proximal tubule


5. Collecting






3. Loop of Henle (nephron loop)

To renal pelvis

Tubular part of the nephron 5
§ Tubular part of the Nephron (5)

  • A hollow tube formed by a single layer of epithelial cells; They are, in order:

  • Bowman’s (Glomerular) capsule–

    • Cup-shaped; double-wall invagination

    • Surround each __________

  • Proximal tubule– closest to Bowman’s capsule

    • Lies entirely within the cortex

Tubular part of the nephron 6
§ Tubular part of the Nephron (6)

  • The loop of Henle (nephron loop)–

    • Forms a U-shaped loop

  • The distal tubule–

    • most distant from the capsule; lies entirely within the ____________

  • Collecting tubule/duct—

    • drains fluid from up to 8 nephrons

      Figure 23.8

Figure 23 8b
Figure 23.8b






ID parts (1-5) of the nephron.

Questions muddiest points

Questions?Muddiest points?

Three urine forming processes
§ Three urine forming processes

1.-- Glomerular filtration

  • From the glomerulus into Bowman’s (glomerular) capsule

    2A.--Tubular reabsorption

  • From the tubular lumen into ___________

    2B.--Tubular secretion

  • From the peritubular capillaries into the __________________

    3.-- Water conservation

    Figure 23.9

Chapter 23 the urinary system

Different names (fluid in renal tubules) in different areas:

1. Glomerular filtrate (in the capsular space)

2. Tubular fluid (proximal tubule to distal tubule)

3. Urine (collecting duct and beyond)

Iii urine formation 1 glomerular filtration


1 glomerular filtration
§ 1. Glomerular filtration

  • Def.– filtering blood by forcing small molecules into the Bowman’s capsule

  • What in the filtrate?

    • Small molecules can pass—

    • Large molecules cannot—

  • Mechanism? ATP?

    • What is the major force? Glomerular blood hydrostatic pressure (BHP)

1 glomerular filtration cont
§ 1. Glomerular filtration (cont.)

  • Layers of the glomerular filtration mem.

    • 1-Fenestrated endothelium of capillaries

      • Large pores (100x more permeable)

      • Molecules can pass–

    • 2-(Acellular) basement mem.

      • Collagen & glycoproteins

      • Function--

    • 3a-Filtration slits; present in inner layer of the Bowman’s capsule-- podocytes (3b) bear many foot processes (pedicles)

      Figure 23.10 (a-d)

Chapter 23 the urinary system

Afferent arteriole

Efferent arteriole




Lumen of





Lumen of








Outer layer of

Bowman’s capsule


foot process

Inner layer

of Bowman’s capsule


Proximal convoluted tubule

Chapter 23 the urinary system

3b. Podocyte

& foot process



2. Basement


1. Capillary


Chapter 23 the urinary system

1b. Endothelial


1a. Capillary


Lumen of glomerular


2. Basement


Lumen of

Bowman’s capsule (capsular space)



3b. Podocyte

foot process

Chapter 23 the urinary system




Lumen of glomerular



Lumen of

Bowman’s capsule




1 glomerular filtration cont1
§ 1. Glomerular filtration (cont.)


  • Albuminuria– also called proteinuria; presence of ________ in the urine

    • Criteria: >250 mg/day: pathological

  • Hematuria– presence of ______ in the urine

Iii urine formation 2a tubular reabsorption


2 tubular reabsorption
§ 2. Tubular reabsorption

  • Def. reclamation process to move molecules back into the blood

  • Goal: to move molecules from tubular lumen to the peritubular capillaries (or vasa recta)

    Table x & Figure y

2 tubular reabsorption cont1
§ 2.Tubular reabsorption (cont.)

  • What are reabsorbed?

    • All the glucose, vitamins, and . . .

  • How efficient?

    • Glucose— no glucose escapes

    • Water— 180 L filtrate to 1-2 L of urine/day

    • Analogy— Clean out a cluttered drawer

Iii urine formation 2a tubular reabsorption in the proximal convoluted t

III. Urine Formation; 2A. TUBULAR REABSORPTION– in the proximal convoluted T.

2 tubular reabsorption cont2
§ 2. Tubular reabsorption (cont.)

Two examples—Na+, water in proximal convoluted tubules and beyond

  • --1st example– sodium reabsorption

  • Where are sodium ions been reabsorbed? Most of the tubule

    Exception is the descending limb of the loop of Henle

  • Routes taken: both transcellular and paracellular routes

2 tubular reabsorption cont3
§ 2. Tubular reabsorption (cont.)

  • Mechanisms of sodium reabsorption—

    • A--symport proteins (channels)—

    • B--Na+-H+ antiport—

    • C--Na+-K+ pumps– basal and lateral membrane

    • D– Paracellular route--

      Figures 23.16

Chapter 23 the urinary system

2 tubular reabsorption cont4
§ 2 Tubular reabsorption (cont.)

  • --2nd example– water reabsorption Locations? All the renal tubule; however, 2/3 occurs in PCT

    • Mechanisms—

       Via water channels (aquaporins)

       Between cells

       Water moves into blood plasma

      Figures 23.16


Chapter 23 the urinary system

Reabsorption limit
§ Reabsorption Limit

  • Def.-- A limit to the amount of solute the renal tubule can reabsorb

  • Why? Limited no. of transport proteins

  • Tm= Transport maximum; example--

    • Glucose’s Tm is 320 mg/min

    • Glucose normally enters the renal tubule at 125 mg/min; will all of it be reabsorbed?

    • Threshold of glucose in the plasma– 220 mg/dL (= 220mg/100mL); begin to see glucose in the urine called glycosuria

    • Untreated diabetes mellitus patients– 400 mg/dL (plasma glucose)


Iii urine formation 2a tubular reabsorption in the nephron loop

III. Urine Formation; 2A. TUBULAR REABSORPTION– in the nephron loop

The nephron loop loop of henle
§ The nephron loop (loop of Henle)

  • Primary function— to generate a salinity gradient that enables the collecting duct to concentrate the urine and conserve water

  • Mechanism—

    • Thick segment (ascending limb) of the loop: Impermeable to water

    • Tubular fluid becomes very dilute by the time it reaches the DCT

      Fig. 23.19


Chapter 23 the urinary system



Nephron loop


Increasing Osmolarity


Iii urine formation 2a tubular reabsorption in the distal convoluted tubule and collecting duct

III. Urine Formation; 2A. TUBULAR REABSORPTION– in the distal convoluted tubule and collecting duct

Dct and collecting duct cd
§ DCT and collecting duct (CD)

  • Reabsorption regulation– by several hormones including aldosterone etc. (see following slides)

  • Cells here in DCT and CD—


    • more abundant; they have receptors for these hormones

    • Functions– involved in salt and water balance


    • fewer; functions– in acid-base balance


Aldosterone 1
§ Aldosterone (1)

  • Chemistry – peptide, steroid, or monoamine? (which one)

  • Secreted by – the adrenal cortex

  • Function-- to promote sodium retention and increase blood pressure

  • Triggered by –

    • low blood sodium concentration

    • a drop in blood pressure (via renin)

      Fig. 23.15


Aldosterone 2
§ Aldosterone (2)

  • Acts on– three areas in the kidneys

    • the thick segment of the ascending limb of the nephron loop

    • The DCT

    • The cortical portion of the collecting duct

  • Physiology Effects—

    • Retain NaCl and water

    • Maintain blood volume


Atrial natriuretic peptide 1
§ Atrial Natriuretic Peptide (1)

  • Chemistry –

  • Secreted by – atrial myocardium of the heart

  • Triggered by – high blood pressure

Atrial natriuretic peptide 2
§ Atrial Natriuretic Peptide (2)

  • Physiology Effects–

    • Promoting sodium and water loss

    • Reducing blood volume and pressure

  • Actions— on Kidney

    • Dilates the afferent arteriole and constricts the efferent arteriole

    • Inhibits renin and aldosterone secretion

    • Inhibits ADH secretion and the action of ADH on the kidney

    • Inhibits NaCl reabsorption by the collecting duct

Iii urine formation 2b tubular secretion


Tubular secretion
§ Tubular secretion

  • Process— transfer of selective molecules from the capillary blood and secrete them into the ___________

  • Locations– PCT, nephron loop, DCT

  • Purposes—

    • Waste removal—

      • For example—

    • Acid-base balance– hydrogen and bicarbonate ions

      Fig. x


Chapter 23 the urinary system

Fig.-- the nephron & molecule movements (demo)





















Tubule (from proximal

tubule to collecting duct)


Iii urine formation 3 water conservation


The principal function left to the collecting duct is to conserve water.

The collecting duct cd
§ The Collecting Duct (CD)

  • Location –

    • Begins in the cortex and passes through the medulla

  • Mission – it reabsorbs water and concentrates the urine

  • Mechanisms—

    • Osmolarity of the ECF is ______ times as high in the lower medulla as it is in the cortex

    • Medullary portion of the CD is more permeable to _______ than to NaCl

      Fig. 23.19

Figure 23 17
Figure 23.17



Which portion of the renal tubule?

Control of water loss
§ Control of water loss

How concentrated the urine becomes depends on the state of hydration

1. Dehydration– your urine becomes little & more concentrated:

  • High blood osmolarity  release ADH (more/less; circle one)

  •  renal tubule synthesize aquaporins

  •  install them in the plasma mem.

  •  CD reabsorbs more water

  • Well hydrated– opposite to the above

  • 23-67

    Countercurrent multiplier 1
    § Countercurrent Multiplier (1)

    • The ability of the collecting duct to concentrate urine depends on the salinity gradient of the renal medulla.

      • Mechanism behind this: The nephron loop acts as a countercurrent multiplier

      • Result: the nephron continues to return salts to the deep medullary tissue

      • Hence it is called multiplier b/c it multiplies the salinity deep in the __________

      • Countercurrent? Fluid flows in opposite directions. Where? Descending limb and ascending limb of the nephron loop

        Fig. 23.20


    Chapter 23 the urinary system










    Nephron loop


    Countercurrent multiplier 2
    § Countercurrent Multiplier (2)

    • How countercurrent multiplier works?

      • Medulla-- An environment of increasing salinity toward deeper part of medulla

      • Descending limb (nephron loop)– very permeable to _______ but not to NaCl

      • Ascending limb– impermeable to _____, but has pumps to transport ions

      • Keeps the osmolarity high in medulla

      • Tubular fluid: more and more diluted toward the distal tubule

    Countercurrent multiplier 3
    § Countercurrent Multiplier (3)

    • In the lower end of collecting duct (CD)– urea helps to maintain (40%) the osmotic gradient in medulla


      • Lower end of CD is permeable to urea; urea diffuses into the ECF

      • Urea enters the descending thin segment; but the thick segment of the loop and DCT is NOT permeable to urea

      • Therefore, continual recycling of urea from the CD to the medulla and back

        Fig. 23.21

    Chapter 23 the urinary system

    Next slide


    Countercurrent exchange system
    § Countercurrent Exchange System

    • Vasa recta that supply the medulla recycle the salt and urea; How?

      • Blood flows in opposite directions in adjacent parallel capillaries called countercurrent exchange system

      • It flows downward– exchanges water for salt

      • It flows back toward the cortex– exchange salt for water

      • Thus, vasa recta gives the salt back and DO NOT subtract from the osmolarity of the medulla

    Urine volume 1
    § Urine Volume (1)

    • Normally, 1-2 liters of urine per day

    • Polyuria (or diuresis)– output in excess of 2 L/day (detail next slide)

      • Causes– fluid intake, some drugs, diabetes

    • Oliguria– output of less than 500 mL/day

    • Anuria– output of 0-100 mL/day

      • Causes– kidney disease, dehydration, etc.

      • Result-- Azotemia

    Urine volume 2
    § Urine Volume (2)

    • Polyuria (details)—

      • Results from all four forms of diabetes—

        • Diabetes mellitus type I, type II, gestational diabetes (all three above are due to hyperglycemia), and diabetes insipidus (due to ADH hyposecretion)

      • Diabetes mellitus and gestational diabetes are glycosuria but NOT in diabetes insipidus patients

    Urine volume 3
    § Urine Volume (3)

    • Diuretics— def. chemicals that increase urine volume

      • Mechanisms–

        • increasing glomerular filtration rate (GFR) or

        • reducing tubular reabsorption

      • Example 1: Caffeine, dilates the afferent arteriole and increases GFR (due to A or B above; circle one)

      • Example 2: Alcohol inhibits ADH secretion (due to A or B above; circle one)

    Renal clearance
    § Renal Clearance

    • Def.– the volume of blood plasma from which a particular waste is completely removed in 1 minute; Example:

      • Urea concentration in urine = 6.0 mg/mL

      • Rate of urine output = 2 mL/min

      • Urea concentration in plasma = 0.2 mg/mL

      • Renal clearance = AB/C = (6.0 mg/mL x 2 mL/min)/0.2 mg/mL = 60 mL/min

      • This means the equivalent of 60 mL of blood plasma is completely cleared of urea per minute

    • Renal clearance of glucose? (healthy adults)

    Glomerular filtration rate gfr 1
    § Glomerular filtration rate (GFR)-(1)

    • Def.– the rate at which glomerular filtrate is formed; volume of filtrate formed each minute by all glomeruli; Example: Inulin (no tubular reabsorption, nor tubular secretion)

    • Urine concentration of inulin = 30 mg/mL

    • Urine output is = 2 mL/min

    • Plasma concentration of inulin = 0.5 mg/mL

    • GFR = AB/C = (30 x 2)/0.5 = 120 mL/min = Renal clearance of inulin (why?) (next slide)

    Glomerular filtration rate gfr 2
    § Glomerular filtration rate (GFR)-(2)

    For inulin, GFR (120 mL/min) is equal to the renal clearance. Why?

    • All inulin filtered by the glomerulus remains in the renal tubule and appears in the urine.

    • A solute that is reabsorbed by the renal tubules will have renal clearance less than the GFR; renal clearance of urea @ 60 mL/min

    • A solute that is secreted by the renal tubules will have a renal clearance greater than the GFR; renal clearance of creatinine @ 140 mL/min