renal physiology

• what are the 4 main parts of the renal system?

  Kidneys, ureters, bladder, urethra
• what is the brief role of the kidney?

  Filters blood and removes waste (makes urine) + Controls red blood cell production and controls blood pressure.
• what is the cardiac output of the kidneys?

  ~10%
• functions of the kidney include...

  Removal of waste products from blood

  Respond to hormones.

  Make hormones.
• which hormones do the kidneys respond to?

  ADH, PTH and aldosterone
• what hormones do the kidneys make?

  Renin, vitamin D and erythropoietin
• describe the gross anatomy of the kidney;

  Capsule - covers the whole kidney

  Cortex - outer layer

  Medulla - inner layer

  Renal pelvis - drains to the ureter

  Nephron - functional unit
• what is the function of the renal capsule?

  Help support the kidney mass and protect the vital tissue from injury.

  It's fibrous and is the fat layer on top. Lowers the risk of trauma to the kidney (also ribs).
• the nephron crosses between layers;

  glomeruli and proximal + distal tubule are in the cortex

  loop of Henle and collecting duct are in the medulla
• function of nephrons;

  to form urine
• urine -> renal pelvis -> ureter -> bladder
• glomerulus;

  • Blood supplied by capillaries at high pressure
  • Contains a Bowman capsule
  • Made of tubular epithelium
  • located in the cortex
• what does the hydrostatic pressure in the glomerulus allow for?

  The high pressure forces water, ions and small molecules into the Bowman capsule (ultrafiltration). Anything large won't be filtered to the capsule. Molecular sieve: < 50 kDa
• proximal convoluted tubule;

  • Columnar epithelium lining
  • Have microvilli (which face the lumen of the nephron) - increases surface area so allows for high permeability for the reabsorption of nutrients
  • Have lots of mitochondria
• why does the PCT have lots of mitochondria?

  Needs a lot of energy for active transport
• what are the 2 main functions of the PCT?

  Source of most re-absorption and Site of tubular secretion into the urine.
• PCT - the source of most reabsorption;

  Passive and active reabsorption.

  Approx 60% of water reabsorption.

  Nutrients like glucose and amino acids are also reabsorbed.

  Reabsorption of Na, K, Ca and phosphate and drugs too.
• PCT - site of tubular secretion into the urine;

  Secretion of:

  • H+ and NH+ (to maintain the pH homeostasis of the blood)
  • Waste products off metabolism (e.g. creatinine, indoxyl sulfate)
  • Drugs via ABC and SLC transporters
• what are the biological mechanisms occurring in the PCT for the movement of substances?

  • Passive permeability/diffusion across membrane
  • Transporters [SLC, ABC](e.g. Na+/K+ ATPase)
  • Ion channels (e.g. K+)
  • Endocytosis (low molecular weight proteins)
• loop of Henle;

  Creates osmotic gradient.

  Split into two sections:

  • Descending limb - water permeable
  • Ascending limb - wear impermeable
• what is the function of the descending limb?

  Permeable to water. Water absorption occurs passively via aquaporin-1 channels. Secretion of urea occurs too (as a part of urea recycling). Water reabsorption is driven by the counter current multiplier system set up by the active reabsorption of sodium in the thick ascending limb.
• what is the function of the ascending limb?

  The thick ascending limb is the primary site of sodium reabsorption. 10-20% of sodium is reabsorbed here. The driver of the reabsorption is the Na+/K+ ATPase on the basolateral membrane which actively pumps 3 Na+ out of the cell and 2 K+ into the cell. This creates a concentration gradient that allows sodium to be brought in via the Na+/K+/2Cl- ATPase that is on the luminal membrane. This contributes to the dilution of the tubular fluid and helps establish the osmotic gradient in the renal medulla.
• distal convoluted tubule;

  Hormone controlled.

  Responds to parathyroid hormone (PTH) - reabsorbs calcium

  Responds to aldosterone - reabsorbs Na+ and secretes K+
• collecting duct;

  Concentrates urine.

  Reabsorbs water - anti-diuretic hormone can affect function by promoting water reabsorption.

  The medulla is salty (due to Na+ gradient) and so water leaves by osmosis passively.
• what is one thing ADH is inhibited by?

  alcohol
• renal physiological functions;

  Removal of waste products from blood - without losing water and nutrients

  Blood acid-base (pH) and osmolarity homeostasis.

  Respond to hormones and make hormones.
• renin;

  Produced by the juxtaglomerular apparatus.

  Released in response to low sodium.

  Renin leads to the formation of angiotensin II - which acts on the nephron and promotes sodium retention (in the blood) and is also a potent vasoconstrictor (helps regulate blood pressure)
• erythropoietin;

  Made by fibroblasts in response to low oxygen concentrations (hypoxia) in blood. Promotes red blood cell formation in bone marrow.
• vitamin D;

  Steroid hormone. It gets metabolised in the kidney to 1,25-dihydroxy cholecalciferol. Promotes Ca and K absorption from the gut.
• pharmacology

  A) loop diuretic

  B) thiazides

  C) potassium-sparring

  
• ureters;

  Tubes - one from each kidney

  Transport urine - from renal pelvis to bladder

  Muscular tubes - peristalsis, smooth muscle and line with epithelium (which can stretch - transitional)
• urinary bladder;

  Receives urine via two ureters.

  Hollow

  Made of smooth muscle. Transitional epithelium allows it to stretch to 1000mL

  After a few 100 mL - reflex is activated
• what happens after the reflex in the urinary bladder is activated?

  Smooth muscle contracts release to the urethra. Controlled by urinary sphincters. (Internal = involuntary and external = voluntary)