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Excretion

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					THE URINARY SYSTEM
Systems Involved in Excretion
(Elimination of metabolic waste)
• Urinary system
  – _____
     Urine
• Respiratory system
  – ____________
     Carbon dioxide

• Digestive system
  – _____
     Feces
• Integumentary system
  – _____
     Sweat
Functions of the Urinary System
• Excretion of metabolic wastes
• Regulation of fluid and electrolyte balance
• Regulation of blood pH
• Regulation of blood pressure by the enzyme
  renin
• Production of Erythropoietin hormone that
  stimulate RBC formation
• Activation of vitamin D to Calcitriol that
  regulate blood calcium levels
             Anatomy of the urinary system

• Kidneys filter blood and
  produce urine
• Ureters transport urine to
  urinary bladder            Kidney-----
• Urinary bladder stores
  urine until eliminated     Ureter----------
• Urethra is tube for
  elimination of urine
                         Urinary bladder----------
                         Urethra----------------------
                        Anatomy of the Kidney
• Renal capsule
  sheaths kidney
                                  Renal capsule-----
• Renal cortex is
  outer region
• Renal medulla is
  inner region with               Renal papilla------
  8-18 renal                Renal cortex-----
  pyramids                  Renal pyramid--------
• Renal papilla is
  apex or tip of            Renal column---------------
  renal pyramid
• Renal columns
  are cortical tissue
  between
  pyramids
                  Anatomy of the Kidney
                                                 • Minor calyx
                                                   receives urine
                                                   from renal papilla
                      ---------------Minor calyx • Major calyx
Major calyx---------                               collects urine from
                                                   two or more minor
Renal pelvis--------------                         calyces
                                                 • Renal pelvis
                                                   collects urine from
                                                   all major calyces
                                     ---Ureter
                                                 • Ureter carries
                                                   urine from renal
                                                   pelvis to bladder
          THE NEPHRON
• Microscopic filtering units of kidneys
  composed of renal tubules and a blood supply
• Called functional units – make most of urine
• About 1 million per kidney
• Mostly in renal cortex with some tubules
  extending into renal pyramids of medulla
                     THE NEPHRON
• Structure
   – Renal corpuscle
      • Loops of capillaries called
        glomerulus
      • Double layered Bowman’s
        capsule surrounds glomerulus
   – Renal tubules
      • Proximal convoluted tubule
        (PCT) connects to Bowman’s
        capsule
      • Loop of Henle with
        descending and ascending
        limbs
      • Distal convoluted tubule
        (DCT) is last part of nephron
      • DCT of several nephrons
        connect to a collecting duct
        (CD)
                 NEPHRON ANATOMY

  Bowman’s capsule---------------- -------------Glomerulus
  PCT------------------------------   ----------DCT
Descending limb of Henle----------------
                                           -----------Ascending limb of Henle
                                                    ---------CD
          Renal Corpuscle Anatomy

                               ---Bowman’s capsule
Afferent arteriole----------
                                -------Glomerulus
DCT-----------------

                                            -------PCT
Efferent arteriole-----
                                --------Capsular space
Physiology of the Urinary System
 •Four processes required for urine formation
   1. Filtration from the glomerulus blood into
   Bowman's capsule
   2. Tubular Reabsorption from renal tubules to blood
   3. Tubular Secretion from blood into the renal
   tubules
   4. Excretion of the final product (urine)

              1
                                   3
                                                  4. Urine
                        2
            FILTERATION
• High glomerular blood hydrostatic pressure
  of about 55 mmHg forces water and solutes
  through the filtration membrane
  – Formed by glomerular capillaries and inner
    layer of Bowman’s capsule
                FILTERATION
• Water and many different solutes pass from
  glomerulus blood into the Bowman’s capsule
• Resulting fluid in capsular space called filtrate
• Filtrate contains
   – Wastes such as urea and uric acid that must be
     eliminated in the urine
   – Useful (vital) substances such as water, organic
     nutrients and electrolytes that must be kept
           FILTERATION
• Amount of blood flow through kidneys in
  one minute = renal blood flow (RBF)
  – About 1200 mL/minute
• Amount of filtrate formed in one minute =
  glomerular filtration rate (GFR)
  – Between 105 and 125 mL/minute
• So around 10% of RBF becomes filtrate
    TUBULAR REABSORPTION
• Most of filtrate moves from the nephron tubules
  back into the blood
  – Water, organic nutrients and electrolytes are kept
• Most reabsorption in proximal convoluted tubule


 Blood of peritubular capillaries
    TUBULAR REABSORPTION
• Water reabsorbed by Osmosis
• Solutes reabsorbed by:-
- Diffusion
- Active transport
- Co-transport
- Pinocytosis
     TUBULAR SECRETION
• Some solutes move from the blood of the
  peritubular capillaries into the filtrate
  – Potassium, ammonium, hydrogen and
    bicarbonate ions are secreted into filtrate
• Helps regulate acid-base balance and
  electrolyte concentrations
              Blood of peritubular capillaries
     WATER REABSORPTION
•   Each day, between 150-180 L of filtrate
•   Each day, 1-2 L of urine
•   Each day, about 148 – 178 L reabsorbed
•   Amounts of H2O reabsorbed
    –   65% in proximal convoluted tubules
    –   15% in descending limbs of Henle
    –   None in ascending limb of Henle
    –   10% in distal convoluted tubules
    –   10% in collecting ducts
   WATER REABSORPTION
• Each day we lose about as much water as
  we gain
• If loss exceeds gain, become dehydrated
• If gain exceeds loss, become over-hydrated
• Controlled by reabsorption of varying
  amounts of water
   Types of Water Reabsorption
• Obligatory water reabsorption
  – In PCT and descending LOH
  – More constant
• Facultative water reabsorption
  – In DCT and CD
  – Variable, depending on degree of hydration
  – This reabsorption is controlled by ADH
Setting Stage for Water Reabsorption
• 65% of water is reabsorbed in the PCT
• 15% is reabsorbed in descending LOH
• No water reabsorbed by ascending LOH
• Sodium chloride is actively reabsorbed by
  ascending LOH
• Filtrate becomes about 4X as concentrated at
  bottom of LOH
 Steps in Concentration of Urine
1. As water loss exceeds gain, hypothalamus
  stimulate secretion of Antidiuretic hormone
  (ADH) from the posterior pituitary
2. ADH makes the cells of the DCT and CD
  more permeable to water
3. More water leaves the DCT and CD and
  enters concentrated interstitial fluid and
  blood at the bottom of the LOH
 Steps in Concentration of Urine
4. Concentrated interstitial fluid and blood
  take more water out of the filtrate and
  concentrate the urine
5. Aldosterone from adrenal cortex increases
  salt reabsorption from tubules and thus
  helps to concentrate urine
6. Results in less, dark & concentrated urine
Concentration of Urine-ADH Present


                                 ADH
                             DCT and CD more
                             permeable to water
                             and more water
                             reabsorbed
     Steps in Dilution of Urine
1. As water gain exceeds loss, hypothalamus
    stops secreting Antidiuretic hormone (ADH)
2. DCT and CD become less permeable to
    water and less water is reabsorbed
3. Adrenal cortex decreases aldosterone
    secretion, thus less salt is reabsorbed from
    tubules and this helps to dilute urine
4. More water stays in filtrate and urine
   resulting in more, light and dilute urine
Dilution of Urine
                    No ADH, so DCT and
                    CD less permeable to
                    water and less water
                    reabsorbed
       Urine: the final product
• Urine composition
  – 95% H2O
  – 5% solutes (solids)
     • Electrolytes
     • Nitrogenous wastes such as urea, creatinine and uric acid
        – Urea from __________________
                       protein metabolism
        – Creatinine from ________________
                           muscle metabolism
        – Uric acid from ____________________
                          nucleic acid metabolism
      Urine: the final product

• Characteristics of Urine
  – Color:- Yellowish to water clear

  – Turbidity:- Clear without turbidity

  – Specific gravity:- 1.00 to 1.03

  – pH:- Acidic
             Clinical Terms
• Nephritis:- Inflammation of the nephrons

• Renal failure:- inability to produce urine

• Hemodialysis:- blood dialysis to remove
  waste metabolites when there is renal
  failure
             Clinical Terms
• Cystitis:- inflammation of urinary bladder

• Urethritis:- inflammation of the urethra

• Calculi:- formation of kidney stones

				
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posted:10/25/2011
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