Kidney

• Isotonic solution means that the relative salt concentration of fluid is equal to that in the cell so there is no net water movement
• Hypotonic solution means that the relative salt concentration of fluid is less than to that in the cell so there is net water movement into the cell
• Hypertonic solution means that the relative salt concentration of fluid is greater than that in the cell so there is net water movement out of the cell
• Total Body Water volume is formed of intracellular fluid (67%) and extracellular fluid: made up of interstitial fluid (25%) and plasma fluid (8%)
• Osmolality is the measure of osmotically active particles in one kilo of water. It is preferred clinically because it is independent of temperature and density, and all particles have the same effect
• The kidneys secrete erythropoietin hormone which regulates RBC production. It also controls anti-apoptosis, enhances immune response, induces angiogenesis (the production of new capillary networks) and is anti-inflammatory.
• The kidney regulates the production of vitamin D, with calcitriol made in the proximal tubules
• Kidneys contribute to glucose homeostasis by filtering and reabsorbing glucose (sodium-glucose co-transporter 2 (SGLT2) expressed in the proximal tubules)
• Detectable renal dysfunction indicates a loss of approximately 67-75% of functional nephrons as the healthy kidney has far more nephrons than are necessary to maintain normal homeostasis. Nephrons are irreplaceable.
• the adrenal gland sits medial to the kidneys and are crossed by the phrenicoabdominal veins
• although nephrons are capable of some repair after damage, new nephrons cannot be formed after the early postnatal stages
• the renal corpuscle is formed of the glomerulus and bowman's capsule
• Each kidney lobe is composed of an outer cortex and inner medullary pyramids. Each medullary pyramid drains into a minor calyx, converging into a major calyx and then the renal pelvis. The renal pelvis is surrounded by the renal sinus (fatty tissue filling the U shaped convergences between pyramids). The renal pelvis drains into the ureter.
• Each kidney lobe is composed of an outer cortex and inner medullary pyramids. Each medullary pyramid drains into a minor calyx, converging into a major calyx and then the renal pelvis. The renal pelvis is surrounded by the renal sinus (fatty tissue filling the U shaped convergences between pyramids). The renal pelvis drains into the ureter.
• The Renal artery supplies the kidneys. It diverges into Segmental then Interlobular then Arcuate arteries. Arcuate arteries supply individual glomeruli. The afferent arteriole enters the glomerulus and the efferent arteriole leaves it.
• The efferent arteriole gives rise to the Peritubular Capillary Network (feeds the medulla with oxygen and nutrients) and the Vasa Recta (supplies oxygen and nutrients and helps in the removal of water and solutes from the medullary interstitium)
• Up to a third of total cardiac output can pass through the renal arteries to be filtered by the kidneys. Obstructions in renal arteries (stenoses) can cause poorly controlled high blood pressure, congestive heart failure and kidney failure
• Multipyramidal kidneys have 18-25 lobes per kidney, giving them a lumpy, broken-up appearance. They are found in large ruminant species
• Human and pig kidneys are multipyramidal internally but have a smooth, fused cortex
• Cats and rodents have a complete fusion of their medullary pyramids (basically one giant medulla) and have blood vessels on the outside of the capsule
• Dogs, horses and sheep have a fused cortex and medulla, forming a common renal crest which may be ridged. These are Modified Unipyramidal. Horse kidneys are loveheart shaped
• Histologically, the cortex appears granular, containing renal corpuscles and convoluted tubules. The medulla appears striated containing the collecting ducts, loops of henle and vasa recta.
• The glomerulus is a network of anastomosing capillaries; fed by an afferent arteriole and drained by an efferent arteriole. Supported by specialised connective tissue called the glomerular mesangium. The glomerulus is surrounded by Bowman’s capsule- a simple squamous epithelium (a single layer of cells on basement membrane).
• The Bowman’s capsule has two layers: Parietal layer constituting the capsule; visceral layer surrounds the glomerular capillaries by podocytes (specialised epithelia with foot process called pedicles which form filtration slits)
• the juxtaglomerular apparatus is formed of the afferent arteriole and DCT of the same nephron. They regulate the renal blood flow under action of baroreceptors and chemoreceptors
• The Macula Densa is a modified DCT which sits on top of the glomerular blood supply. It is taller and denser than the surrounding cells, with larger nuclei
• The renal tubule extends from bowman’s capsule to the collecting duct and selectively reabsorbs water, inorganic ions and other molecules. It is composed of four zones:

  • Proximal convoluted tubule (PCT)
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting tubules
• The proximal convoluted tubule is lined by simple cuboidal epithelium with a prominent brush border which increase surface area for absorption. The PCT is the longest and most convoluted part of the nephron, composing much of the renal cortex. It is surrounded by a rich capillary network and returns absorbed molecules to the circulation
• The thick ascending and descending limbs of the loop of henle are lined by cuboidal epithelium with no brush border. By contrast, the thin portions of the LOH are lined by simple squamous epithelium
• The DCT is a shorter and comparatively straighter tubule than the PCT. It also lacks a brush border. It has a larger lumen and more nuclei in transverse section
• the collecting ducts merge in the medulla to form larger Ducts of Bellini
• The ureter is a muscular tube lined by folded urothelium in relaxed state
• the urinary bladder is made up of three loosely arranged layers of smooth muscle and elastic fibres with overlying lamina propria and submucosa. It's luminal surface is covered in urinary epithelium which can accommodate stretch
• The male urethra is lined by urinary epithelium up to the level of the prostate. Beyond that, the male urethra is lined by pseudostratified columnar epithelium

   

  The female urethra is predominantly lined by urinary epithelium but near the external urethral orifice there is a change to stratified squamous epithelium
• Birds use arginine instead of vasopressin as their antidiuretic hormone
• normally, in birds venous return from the pelvic limbs passes through the kidneys before reaching the caudal vena cava, with the portal valves closed. under stress or the effect of adrenaline those valves open and blood bypasses the kidneys
• Plasma Na+ should be much higher than ICF
• ICF K+ values should be higher than plasma
• ICF Ca2+ is virtually zero
• vascular endothelium separates fluids in interstitial space and intravascular space. cell membrane separates fluid inside cells from the interstitium and is the membrane over which electrochemical gradient is generated