Chapter 26 Notes Continued
Urinary System

Renal Physiology

7. Glomerular filtration -  PLASMA to FILTRATE
                                           GLOMERULI to BOWMAN'S CAPSULE

• controls blood solute concentration
• removes toxic wastes from blood
• blood cells and proteins do NOT LEAVE the blood
• the nephron is adapted for filtration
  - large surface area of glomeruli
  - podocytes leaky and form the filtration membrane
  - efferent arteriole small diameter raises glomerular hydrostatic pressure

1. glomerular hydrostatic pressure = 55 mmHg
    - forces fluid from glomerulus into Bowman’s capsule

2. capsular hydrostatic pressure = 15 mmHg
    - pressure of fluids present in the capsule
    - opposes hydrostatic pressure

3. blood colloid osmotic pressure = 30 mmHg
    - osmotic pressure due to proteins in blood plasma
    - opposes hydrostatic pressure

4. NFP:  NET FILTRATION PRESSURE =

• 125 MLS OF PLASMA FLOW INTO BOWMAN’S CAPSULE PER MINUTE
• after you are eighty, many of your glomeruli are twisted or missing

8. Problems with glomerular filtration

• GLOMERULARNEPHRITIS
  - glomeruli leak proteins
  - BCOP drops
  - albuminuria
  - NFP increases
  
• HEMORRHAGE
  - blood pressure drops
  - hydrostatic pressure drops
  - NFP decreases
  
• NOREPINEPHRINE
  - constricts afferent arteriole
  - hydrostatic pressure drops
  - NFP decreases

9. Tubular reabsorption - FILTRATE to PLASMA
                                           PROXIMAL CONVOLUTED TUBULE to
                                           PERITUBULAR CAPILLARIES

• the kidneys control blood solute concentration
• PCT returns solutes and water to plasma by reabsorption of filtrate
• filtrate consists of  H₂O, glucose, amino acids, urea, Na⁺, K⁺, Ca⁺⁺,
  Cl^-, HCO₃ ^-, HPO₄ ^-, uric acid, and creatinine

(circle the ones that remain in the filtrate to become the solutes in urine)

10. Tubular secretion - ADDITIONS TO FILTRATE

• amino acid deamination by hepatic cells produces urea
• urea and ammonia are secreted by cells of the PCT
• HCO₃ ^- enters the peritubular capillaries
• major role in electrolyte balance and maintaining blood pH at 7.35
• Na ⁺ and HCO₃ ^- are conserved and excess H ⁺ and K ⁺ enter the filtrate
• kidneys responsible for maintaining normal plasma HCO₃ ^-
• lactic acid, ketone bodies, fatty acids deplete this bicarbonate ion
  
• Metabolic Acidosis

- HCO₃ ^- down
- pH down
- from renal failure, diabetes mellitus, diarrhea HCO₃ ^- loss,
- starvation and strenuous exercise
- compensation by Respiratory System: hyperventilation
        1. pH up
        2. HCO₃ ^- down
        3. pCO₂ down

• Metabolic Alkalosis

- HCO₃ ^- up
- pH up
- vomiting, antacid ingestion, compensation for metabolic acidosis
- compensation by Respiratory System: hypoventilation
        1. pH down
        2. HCO₃ ^- up
        3. pCO₂ up

11. Secretion of  K ⁺

• in DCT and collecting duct
• hormone from adrenal cortex : Aldosterone
• NA ⁺ is reabsorbed into the blood and K ⁺ is secreted into filtrate

Hormone regulation

12. Renin-Angiotensin Pathway

• regulates fluid volume and blood pressure
• monitored by juxtaglomerular cells adjacent to afferent arteriole
• renin is secreted by juxtaglomerular cells when BP (Na ⁺)
  is low and blood flow through the kidneys is reduced
• renin acts on angiotensinogen, a polypeptide with no physiological activity
• angiotensinogen in converted to Angiotensin I
• Angiotensin I is converted to Angiotensin II by ACE (angiotensin converting enzyme)
• angiotensin II

- a powerful vasoconstrictor
- causes the adrenal cortex to secrete aldosterone
-  increases reabsorption of Na ⁺ and Cl ^- and water follows
- causes the posterior pituitary to release ADH, water retention by kidney

• pathway online

13. Hormones affecting kidneys

      Aldosterone

• hormone from adrenal cortex
• increases K+ secretion by kidneys and Na+ retention

    Antidiuretic Hormone

• regulates blood volume
• secreted by posterior pituitary gland
• adjusts osmolarity of urine - from hypotoinic to hypertonic
• determines water reabsorption in distal convoluted tubules and collecting ducts
• causes increased permeability of tubular cells and water flows into peritubular capillaries
• ADH secretion is blocked by caffeine, alcohol, norepinephrine, ANP and diuretics

    Atrial Natriuretic Peptide

15. Clinical Notes