Renal

• The kidneys are part of the excretory system, but specifically they are in the URINARY SYSTEM

  
• Excretory System


  • Water-soluble wastes are through the sweat (minimal amount) and the urinary system
  • Lipid-soluble wastes excreted through the GIT
  • Gas (excess) are excreted through the Respiratory System
• To form urine


  1. Excretion of Excessive Waste Products

  2. Regulation of Water and Electrolyte
• Waste Products Excreted


  • Urea – from amino acids
  • Creatinine – from muscle creatine
  • Uric Acid – from nucleic acid (purine)
  • Bilirubin – from end product of hemoglobin breakdown
• Regulation of Water and Electrolyte

  Most of the water and electrolytes in the body are excreted through the kidneys. This may be a basis for administration of IV Fluid: 3L/day

  
• Regulation of body fluid osmolality and electrolyte concentration

  As it regulates the water and electrolyte balances, the plasma osmolality is also regulated
• Starling's Forces


  • Inside the Capillary: Capillary Hydrostatic Pressure – drives away fluid, Capillary Osmotic (Oncotic/Colloid) Pressure of Plasma Protein – attracts fluid in

  Outside the Capillary: Interstitium or Tissue Hydrostatic Pressure, Interstitium or Tissue Oncotic Pressure of Plasma Protein
• Filtration


  Capillary Hydrostatic Pressure + Interstitial Osmotic Pressure
• Reabsorption


  Capillary Osmotic Pressure + Interstitial Hydrostatic Pressure
• Regulation of Arterial Pressure

  Plays a dominant role in long term regulation of arterial pressure by excreting variable amounts of Sodium and Water

  Intermediate regulation of blood pressure: Renal-Fluid Shift → ↑ BP = ↓ Urine Output, ↓ BP = ↑ Urine Output

  Short term regulation by secreting hormones and vasoactive factors or substances (Renin) that lead to formation of vasoactive products (Angiotensin II)
• Regulation of Acid-Base Balance


  1st: Intra/Extracellular buffers (Ex. Bicarbonates, Hemoglobin, Calcium, Phosphates, Phosphoric Acids)

  2nd: Respiratory System

  3rd: Recruit the Kidney → The kidney can only acidify up to the pH 5.0 and alkalinize until pH 8.0 (Urine pH: 5.0 – 8.0)
• Regulation of Erythrocyte Production

  Erythropoietin – for erythropoiesis (primarily stimulated by tissue hypoxia)
• Secretion, Metabolism, and Excretion of Hormones

  • Renin, Erythropoietin, Vitamin D/1,25-dihydroxyvitamin D/Calcitriol (Final Activation)
• Gluconeogenesis


  Kidneys synthesize glucose from AA and other precursors in cases of severe hypoglycemia

  During extreme conditions, it helps Glucagon, Cortisol, Epi/Norepinephrine, Catecholamines, Thyroid Hormone, and Growth Hormones (in children) to increase blood sugar levels
• Macroscopic Anatomy of the Kidney

  • There are 2 Kidneys in the body: Right and Left

  Located at the upper abdomen, posterior, and retroperitoneal

  Approximately the size of a closed fist

  On the average: Length: 10cm, Wide: 6cm, Thick: 3cm, Weight: 115 – 170g (Average: 150g each kidney)

  At the medial portion of the kidney, there is an indentation called the Renal Hilum

  Covered by a non-distensible structure called the Renal Capsule

  
• Structures at the Renal Hilum

  • Renal Vein
  • Renal Artery
  • Renal Pelvis
  • Renal Nerve
  • Renal Lymphatic

  
• Renal Cortex


  Outer portion of the kidney

  
• Renal Medulla


  Inner portion of the kidney, contains about 7 to 8 conical structure called the Renal Papilla

  
• Renal Pyramids


  • Triangular structure in the Renal Medulla, the base is near the cortex and the apex towards the Renal pelvis

  
• Urine Formation


  Minor Calyces will join together to form Major Calyces

  Major Calyces will form the Renal Pelvis

  Urine will now pass through the renal pelvis to the Ureters and will be collected in the Urinary Bladder

  
• Composition of Renal Cortex

  • Glomerulus
  • Bowman's Capsule
  • PCT and DCT
  • Cortical Collecting Duct

  
• Composition of Renal Medulla

  • Loop and Henle
  • Medullary Collecting Duct

  
• Renal Cortex


  Isotonic concentration
• Renal Medulla


  Hypertonic concentration
• Urethra


  • Female: 5cm (2in) – more prone to UTI

  Male: 20cm (10in) - 3 Sections: Prostatic (hidden), Membranous (hidden), Penile Urethra - (+) Glands of Littre, releases antibacterial secretions = less prone to UTI
• The right kidney has 3 Minor Calyces while in the left it only has 2 Minor Calyces

  
• Micturition


  Both involuntary and voluntary

  1st Voluntary: the bladder fills progressively until the tension in its wall rises above a threshold level

  2nd Involuntary/Micturition Reflex: a nervous reflex that empties the bladder

  Can be regulated on certain amounts/volume - Depending on the height, the capacity of the urinary bladder is around 700 mL (<5ft); 1L (>5ft) - >700 mL or 1L = Reflex Micturition - 150-300 mL → urge to urinate
• Renal Blood Flow


  • Blood supply of the kidneys comes from the renal arteries. Renal artery is direct branch of aorta.

  Each kidney weighs only 150 grams and yet they receive 20%-25% of the CO (1200-1250 mL/min)

  Normal hydrostatic pressure = 25-35 mmHg, decreases as it bifurcates into several branches, reaches 60 mmHg in the glomerular capillaries, and decreases to 18 mmHg when the blood passes through the efferent arteriole

  
• Comparison of the Distribution of Blood Flow to the Different Organs

  • Kidney: 4.0 mL/g/min

  Heart: 0.9 mL/g/min

  Brain: 0.6 mL/g/min

  Liver: 0.2 mL/g/min

  Resting Muscle: 0.1 mL/g/min

  
• True Capillary is between an arteriole and venule → Peritubular Capillary
• Special Circulation: Glomerular Capillary


  • In between 2 arterioles
• Pressure Drop in Renal Vessels

  • Renal Artery: 100 mmHg - 100 mmHg (0% drop)

  Interlobar, Arcuate, Interlobular Arteries: 100 mmHg - 85 mmHg (16% drop)

  Afferent Arteriole: 85 mmHg - 60 mmHg (26% drop)

  Glomerular Capillaries: 60 mmHg - 59 mmHg (1% drop)

  Efferent Arteriole: 59 mmHg - 18 mmHg (43% drop)

  Peritubular Capillaries: 18 mmHg - 8 mmHg (10% drop)

  Interlobar, Arcuate, Interlobular Veins: 4 mmHg - 4 mmHg (0% drop)
• Glomerular Capillaries


  • High Pressure Capillary, in between and Afferent and Efferent Arteriole, Favors Filtration
• Peritubular Capillaries


  • Low Pressure Capillary, in between and Efferent Arteriole and a Venule, Favors Reabsorption and Secretion
• Nephron


  • Characteristic cells of the Kidney, Basic unit of Renal Structure and Function, 1.2 million in each kidney, You can actually survive with just 50%
• Components of Nephron


  • Glomerulus
  • Renal Tubule

  
• Glomerulus


  • Formed by the Glomerular Capillaries enclosed by a Bowman's Capsule, Primary Function: Fluid Filtration

  
• Bowman's Capsule


  • Parietal/Visceral Layers lined with Simple Squamous (podoctyes with pedicel), Bowman's Space – space between the Parietal and Visceral Layer
• Glomerular Capillaries


  • Fenestrated without diaphragm, Forms the Filtration Barrier – size, shape, and charge selective
• Structures of Renal Tubule

  • Proximal Convoluted Tubule (Pars Convoluta)

  Proximal Straight (Pars Recta)

  Thin Descending Loop of Henle

  Hairpin Loop

  Thin Ascending

  Thick Ascending

  Distal Tubule (Early Distal Tubule, Late)

  Connecting Tubule

  Collecting Duct (Cortical, Medullary)