T3 L1: Introduction to kidney and renal function

• What are the two major functions of the renal system?

  excretion (removal of organic waste products from body fluids)

  elimination (discharge of waste products into environment)
• What does the renal system consist of?

  urinary system

  genitourinary system

  
• What does the renal system consist of?

  kidney: produces urine

  ureter: transports urine towards urinary bladder

  urinary bladder: temporarily stores urine prior to elimination

  urethra: conducts urine to exterior
• What are the essential renal functions?

  Excretion: excretion of endogenous waste products and drugs & their metabolites

  Homeostasis: water and electrolyte balance, acid-base balance

  Regulation: production of hormones, eg erythropoietin, renin
• What are the effects of renal dysfunction (failure) on essential renal functions?

  • Reduction in renal excretory function, Uraemia, azotaemia
  • Reduction in renal excretory function, eg drug toxicity
  • Inability to maintain salt and water balance, ie metabolic consequences eg oedema, acidosis
  • Compromised hormone function eg anaemia, hypertension
• What is azotaemia?

  build up of secondary waste products in blood, eg nitrogenous products and creatinine
• How is renal failure distributed?

  • Acute kidney injury (AKI): 10%, rapid; hours or days
  • Chronic kidney disease (CKD) 90%, slower; months to years
• What are the ultimate treatments for renal dysfunction?

  renal function must be supplemented artificially:

  • regular dialysis
  • transplanted kidney
• Where are the kidneys situated anatomically?

  posterior wall of abdomen

  behind peritoneum

  on either side of vertebral column

  joined at medial side to renal artery and vein, nerves and ureter
• How is the Organisation of the Kidney?

  Two major outer layers/areas:

  • Cortex (outer layer): composed of ~ 1.25 million nephrons
  • Medulla (inner areas): pyramids drain into pelvis which drain into ureters
• What is a nephron?

  A nephron is the “functional unit” of the kidney responsible for urine formation and composition

  Approximately 1.25 million nephrons per human kidney...but numbers (and therefore renal function) decline with age

  
• What are the five distinct sections of nephron?

  • Glomerulus (Renal corpuscle)
  • Proximal tubule (PT)
  • Loop of Henle (LOH)
  • Distal tubule (DT)
  • Collecting duct (CD

  
• What are the two types of nephron?

  Cortical nephron

  juxtamedullary nephron

  
• What are cortical nephrons?

  70-80% of all nephrons in human kidneys

  Located in the cortex

  Short loop of Henle into medulla

  Some may not enter medulla

  
• What are juxtamedullary nephrons?

  20-30% of all nephrons in human kidneys

  Situated closer to medulla

  Loop of Henle extends deep into renal pyramids

  
• How is the blood supply to the kidney?

  Kidneys receive 20% of total cardiac output

  Required for energy-consuming transport processes

  
• What is the name of the blood supply for cortical nephron (loop of Henle)?

  peritubular capillaries

  
• What is the name of Blood Supply to juxtamedullary nephron (loop of Henle)?

  Vasa recta

  
• How is the Sympathetic Nervous Supply to the Kidney?

  postganglionic fibres from sympathetic chain

  fibres from coeliac ganglion

  effects:

  • supplies arteries, afferent and efferent arterioles and granular cells (granular cells release renin which modifies blood pressure)
  • reduces blood supply to kidney during stress
• How is the Parasympathetic Nervous Supply to the Kidney?

  efferent supply from vagus nerve - ganglion in hilum

  effects:

  • may control tone of renal arteries and efferent arterioles
  • may modify renal blood flow (RBF) and glomerular filtration rate (GFR)THIS IS CONTROVERSIAL
• What are the three major functions of the nephron?

  • FILTRATION of blood to produce a filtrate - glomerular filtrate
  • REABSORPTION of water, ions and organic nutrients from filtrate (tubular fluid)
  • SECRETION of waste products into tubular fluid

  
• How does glomerular filtration work?

  Filtration occurs at the glomerulus

  It is the initial step in urine formation

  • All small molecules are filtered: Electrolytes, Amino acids, Glucose, Metabolic waste, Some drugs, metabolites
  • Cells and large molecules remain in the blood: Red blood cells, Lipids, Proteins, Large sized or protein-bound drugs and larger sized metabolites

  
• How does Tubular Reabsorption work?

  can be:

  • co-transport (eg glucose & Na+)
  • down concentration/electrochemical gradient (eg Na+)
  • Water follows passively along the osmotic gradient created by solute(Na+) reuptake via aquaporins
  • Reabsorption of solutes requires ATP which drive Na+ reabsorption via the Na+ K+ ATPase transporter

  
• How does tubular secretion work?

  Specialised pumps in the PT can transport compounds that can't be filtered at glomerulus from the plasma into the tubular fluid for excretion

  2 kinds of “pumps”:

  • For organic acids or acidic drugs(e.g. uric acid, diuretics, antibiotics – e.g. penicillin)
  • For organic bases or alkaline drugs(e.g. creatinine, procainamide)

  
• Environmental Physiology – Renal Function

  changes in physiology due to environmental occurrences worldwide, eg heat

  • increased cases of renal failure in places with extreme heat due to dehydration
  • extreme heat at work doubling the risk of stillbirth for women working out in the fields in India