CHAPTER 26  URINARY SYSTEM

I. Introduction

          A. The kidney as a regulatory organ:

                    1. Regulates body fluid osmolality and volume

                    2. Regulates electrolyte balance

                    3. Regulates acid-base balance

                    4. Excretion of metabolic products and foreign substances

                    5. Production and secretion of hormones

                              a. erythropoietin

                              b. renin

                              c. activates vitamin D

 

 

          B. The organs of the urinary system are the

             kidneys, ureters, urinary bladder, and urethra.

 

 

                    DRAW THE URINARY SYSTEM.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

II. Anatomy of the kidneys

  A. External anatomy

          1. The kidneys are retroperitoneal organs attached to the posterior wall in the lumbar region of the abdominopelvic  cavity.

          2. The right kidney is positioned more inferior than the left.

          3. Three layers of tissue surround each kidney:

                    a. innermost - renal capsule

                    b. middle - adipose capsule

                    c. outer - renal fascia

          4. The hilus is a notch in the concave medial border through which the ureter, blood vessels, lymphatic vessels, and nerves enter or exit.

 

 

  B. Internal anatomy

          1. medulla

          2. cortex

          3. pyramid

          4. minor calyx

          5. major calyx

          6. renal pelvis

          7. renal column

          8. papilla

          9. capsule

          10.nephron

          11.renal artery

          12.renal vein

          13.ureter                

 

 

 C. Nephron

          1. Functional unit of the kidney

          2. Approximately 1.5 million per kidney

          3. Each forms urine

          4. Composed of a glomerulus and a renal tubule

          5. Urine formation pathway:

(G) glomerulus->Bowman's capsule->(PT) proximal tubule-> (DTL)descending thin limb of the loop of Henle-> (ATL) ascending thin limb-> (TAL) thick ascending limb-> (DT) distal tubule-> (CT) collecting tubule-> (CD) collecting duct->minor calyx->major calyx -> renal pelvis->ureter->bladder->urethra

          6. Two types characterized by location

               *a. Cortical nephrons

                    1. glomerulus more superficial area of cortex

                              2. short thin segments in loop of Henle

                                 which extend to outer medulla

               *b. Juxtamedullary nephrons

                              1. glomerulus in deep cortex near medulla

                              2. long loops of Henle through medulla 

 

DRAW A NEPHRON AND LABEL EACH SECTION OF THE TUBULE.

SHOW THE DIFFERENCE BETWEEN *a AND *b.

 

 

 

 

 

D. Glomerulus

                    1. a network of capillaries

                    2. surrounded by Bowman's capsule (beginning of renal tubule)

          E. Blood enters the glomerulus through the AFFERENT ARTERIOLE

          F. Blood exits the glomerulus ate the EFFERENT ARTERIOLE

          G. Blood from the eferent arterial enters the peritubular capillary network which

surrounds the Proximal, distal and collecting renal tubules.

          H. The vasa recta are long capillary loops from the peritubular network which

extend into the medulla and lie near the thin limbs of the juxtaglomerular

nephrons.

 

III. Renal Blood Flow

  A. From renal artery:

           1. segmental arteries

           2. interlobar artery

           3. arcuate artery

           4. interlobular artery                   

           5. afferent arteriole

           6. glomerulus

           7. efferent arteriole

           8. peritubular capillaries

              (vasa recta)

           9. cortical venules

          10. interlobular vein

          11. arcuate vein

          12. interlobar vein

          13. segmental vein

          14. renal vein

 

  B. 1200 ml/min rate of blood flow through both kidneys

                   

 

  C. Afferent arterioles

          1. Cortical nephrons

                    a. thick muscle walls

                    b. sympathetic vasoconstrictor influence

                    c. have a juxtaglomerular apparatus component

                    d. larger diameter than efferent

                    e. low resistance to blood flow at rest

         

          2. Juxtamedullary nephrons

                    a. thin muscle walls

                    b. not very sensitive to sympathetic vasoconstrictor activity

                    c. no juxtaglomerular apparatus

                    d. have high resistance to blood flow

                    e. larger diameter than efferent

 

  D. Efferent arterioles

          1. most have thick muscle walls

          2. sensitive to sympathetic vasoconstrictor activity and angiotensin II

 

  E. Juxtaglomerular Apparatus (JGA)

 

          1. Macula densa cells of the distal convoluted tubule and juxtaglomerular cells of the afferent arteriole of the

          juxtaglomerular nephron

          2. Renin secreted to convert angiotensinogen to angiotensin

          3. Angiotensin II may act to

                    a. conserve water/NaCl (to increase BP) via ADH

                    b. maintain a steady filtration rate at the glomerulus (GFR)

                    c. potent vasoconstrictor

 

DRAW THE AFFERENT AND EFFERENT ARTERIOLE,GLOMERULUS,AND INDICATE THE LOCATION OF THE MACULA DENSA CELLS AND JUXTAGLOMERULAR CELLS.

 

 

 

 

 

 

 

F. Renal capillaries

          1. Glomerular capillary bed

                    a. receives blood from afferent arteriole

                    b. resistance offered at efferent arteriole

          2. Peritubular capillary bed

                    a. receives blood from efferent arteriole

                    b. low pressure bed

 

 

IV. Renal Function

  A. Processes occurring at the renal tubule

          1. filtration - pressure

 

          2. reabsorption

 

          3. secretion

 

                              filtration                         reabsorption    

    GLOMERULUS                  TUBULES                   PERITUBULAR CAPILLARY

                                                                  secretion

 

 

 

 


  B. Glomerular filtration

          1. Ultrafiltrate enters Bowman's capsule

                    a. similar to interstial fluid but no protein

          2. Urine flow rate

                              0.5 ml/min to 20 ml/min

          3. Renal Clearance

                    a. volume of plasma cleared of a substance per unit time(1 min)

         

 

          4. GFR- glomerular filtration rate

                    a. sum of filtrate formed each minute

                    b. index of renal function

                    c. substance measured must:

                              1. reach stable plasma concentration

                              2. be freely filtered at the glomerulus

                              3. not be reabsorbed, secreted, or metabolized by the kidney

                              4. Inulin meets criteria

                                        filtered inulin= excreted inulin

                                       

                                        GFR= Uin x V/Pin

                             

                              5. Endogenous creatinine used to measure GFR

                                        a) creatine phosphate as energy

                                                  source in skeletal muscle

 

                    d. 125 ml/min is normal GFR (from inulin)

                              1)in 1 minute the kidney clears all inulin in 125  ml plasma

                    e. GFR=0

                              1) substance completely reabsorbed

                    f. GFR>125

                              1) substance secreted

 

          5. Regulation of glomerular filtration

                    a. autoregulation

                              1) intrinsic control

                                        a. substances secreted?

                                        b. metabolites?

                                        c. myogenic mechanism?

                                                  1. smooth muscle response

                              2) tubuloglomerular feedback

                                        a. macula densa cells of JA -renin

 

                    b. sympathetic nervous system

                              1) constriction of afferent arterioto inhibit filtration when norepinephrine binds to alpha receptors

                              2) also stimulates release of renin to increase BP

 

          C. Tubular Reabsorption

                    1. reclamation beginning in Proximal tubule

                    2. act to maintain normal plasma levels

                    3. active processes

                              a. ATP dependent

                              b. glucose - PT

                              c. amino acids -PT

                              d. lactate-PT

                              e. vitamins-PT

                              f. ions

                                        1) Na - all areas

                                        2) bicarbonate - PT CT

                                        3) H - CT

                              g. most cotransported with sodium

                                        1) Na most abundant in filtrate

                              h. fructose, galactose, and glucose

                                        use same carrier

                    4. passive processes

                              a. diffusion, facilitated diffusion, osmosis

                              b. driven by electrochemical gradient resultin

                                 from active transport of sodium

                              c. chloride (- charge) goes with Na+ at all

                                 areas of tubule

                              d. osmotic gradient established by sodium

                                 and pulls water

                              e. obligatory water reabsorption

                                        1) where sodium goes water follows      

                                        2) by osmosis at all sites

                              f. urea - diffusion PT and CT

                    5. nonreabsorption

                              a. lack carriers

                              b. too large to pass through tubular cells

                              c. not lipid soluble

                              d. urea

                              e. creatinine

                              f. uric acid

                    6. different regions of tubules absorb different substances

 

          D. Tubular Secretion

                    1. move from blood in peritubular capillaries

                    2. into tubule to filtrate

                    3. urine contains sum of filtered substances and

                       secreted substances

                    4. K (CT)

                    5. creatinine

                    6. ammonia

                    7. drugs - penicillin, phenobarbital (PT)

                    8. H - control pH  (PT,CT)

                    9. bicarbonate ions can be secreted  CT

                                       

V. Regulation of Urine

          A. osmolarity

                    1. number of solute particles in one liter of water

                    that causes water to move by osmosis (higher osmolarity water moves by osmosis to the higher osmolarity area)

                    2. kidney acts to keep body fluids at 300mosm/L        

          B. countercurrent mechanism

                    1. establish a concentration gradient of solutes so

                    that water will move

                    2. in the interstitium near LH- NaCl and CT- urea are ransported to establish gradient in the interstitium

          C. fitrate has similar osmolarity as blood

                    1. water is reabsorbed and filtrate gets concentrated

                              in PT and descending loop of Henle

                    2. NaCl is reabsorbed to decrease osmolarity in ascending LH which is impermeable to water

          D. blood in vasa recta osmolarity changes with its position

                    in the medulla by exchange of NaCl or water

          E. aldosterone

                    1. reabsorption of water in DT

          F. antidiuretic hormone

                    1. reabsorption of water in DT and CT

                    2. facultative water reabsorption

                              a. depends on presence of ADH

                    3. ADH released as plasma osmolarity increases

          G. Characteristics of urine

                    1. color

                              a. urochrome

                                        1) yellow pigment from bilirubin

                              b. more concentrated darker color

                              c. riboflavin - yellow color

                    2. odor

                              a. ammonia odor due to bacteria

                    3. pH =4.5-8 (6)

          H. Bladder

                    1. trigon

                              a) base of bladder

                              b) triangular region about the openings of

                                        2 ureters, and urethra openings

                    2. three layers

                              a) mucosa with transitional epithelium

                              b) muscular

                                        1) detrusor muscle

                              c) adventitia

          I. Micturition

                    1. urination

                    2. incontinence