A description of the renal system
- Features of the kidneys
- The Micro-structure of a kidney
- Regulation of the Glomerular Filtration Rate (GFR)
- The role of the loop of henle
- Regulation of water reabsorption
Kidneys are complex organs; they perform three vital, life-sustaining functions: They clean waste materials and extra fluids from the body, they also filter the blood and maintain normal body chemistry, and they regulate blood pressure and the production of red blood cells.
The kidneys are two bean shaped organs that lie on either side of the vertebral column below the diaphragm and liver. A fibrous capsule encases the kidney, this is known as the renal capsule. (Foster & Smith 2005) The renal capsule provides an impermeable barrier to infections of the kidney surface. This is the first of three protective layers around the kidneys. Outside the renal capsule is a middle layer of fat, this is called the adipose capsule. The fat tissue of the capsule helps cushion the kidney against blows. Outside the adipose capsule is the renal fascia, the fascia is composed of dense fibrous connective tissue that helps to protect the kidney whilst anchoring it to the nearby tissues. (Alcamo 1997)
Each adult kidney weighs about 160g and is about 11cms long, 5 ? 7cms wide and 2.5 cm thick. A kidney each contains about 160km of blood vessels, and more than a million separate lengths of extremely fine tube called kidney tubules, which have a combined length of approximately 60km. The indentation of the bean-shaped organ is known as the hilus. This is the point where the blood vessels, ureter, and nerves enter or exit the kidney. (Becket 1982).
[...] One afferent arteriole is distributed to each nephron, where the arteriole divides into a tangled network of around fifty fenestrated capillaries called the glomerulus. The glomerulus is surrounded by the Bowman's capsule The Bowman's capsule is the cup shaped mouth of the nephron which is made of simple squamous epithelium, which makes up the parietal (outer) epithelium. The visceral (inner) epithelium consists of podocytes, which have numerous small feet called pedicels. (Vieira Lazaroff 2004) Pedicels interdigitate, like the fingers of a clasped hand, as they wrap around the glomerular capillaries. [...]
[...] (Parker 2001) As well as reabsorption of materials from the filtrate to the blood, other materials are placed into the filtrate by a process known as secretion. Secretion plays a big part in the balance of ions in the blood. An excess amount of could cause cardiac arrest, the level is lowered by secreting it into the collecting duct. When blood gets to acidic, ions are secreted into the PCT and the collecting duct, this raises the pH to normal. [...]
[...] (Tortora & Grabowski 2001) Regulation of the Glomerular Filtration Rate (GFR) Regulation Stimulus Afferent GFR Arteriole Sympathetic Activation by Constricts Decreases nerves baroreceptor reflex or by higher brain centres Autoregulation Decreased blood Dilates No change pressure Autoregulation Increased blood Constricts No change pressure (Fox 1999) RENAL AUTOREGULATION The ability of the kidneys to maintain a constant GFR despite changes in systematic blood pressure is called renal autoregulation. INCREASING INPUT OUTPUT Increased secretion of vasoconstrictor (Tortora & Grabowski 2001) Approximately 99% of the filtrate is reabsorbed back into the blood in the peritubular capillaries. [...]