The urinary system is made up of the following structures:
• 2 kidneys, which secrete urine
• 2 ureters, transports urine from the kidneys to the bladder
• The urinary bladder: stores urine temporarily
• The urethra: expels urine from the bladder to the exterior
It is also the main excretory system in the body as it produces urine, ensuring that the body gets rid of unwanted and potentially harmful substances. Filtering blood plays a vital part in maintaining homeostasis of water and electrolyte concentrations within the body.
The primary role of the kidneys is to maintain a healthy balance of water, minerals and electrolytes.The kidneys form urine, which consists of consists of 96% ...view middle of the document...
The glomerular capsule and glomerulus walls consist of a layer of flattened epithelial cells, which are more permeable than other capillaries. A single layer of highly specialised cells forms the rest of the nephron and collecting tubule. The nerve supply of the kidney is made up of sympathetic and parasympathetic nerves, which permits control of renal blood vessel diameter and renal blood flow independently of autoregulation.
Urine is formed in three stages:
Simple filtration occurs in through the semi permeable walls in the glomerulus and the glomerular capsule. Water and small molecules are able to pass through, although some are reabsorbed later on. The difference between the blood pressure in the glomerulus and the pressure of the filtrate in the glomerular capsule assist filtration. Almost all of the filtrate is reabsorbed with less that 1.5 litres excreted as urine, the volume and concentration difference is due to selective reabsorption of some constituents of the filtrate, and tubular secretion of others.
Selective Reabsorption is the process by which the composition and volume of the glomerular filtrate change during the journey through the convoluted tubules, medullary loop and collecting tubule. Certain constituents ae needed by the body to maintain the balance of electrolytes and fluid, so this is reabsorbed into the body. The renal threshold of some substances varies according to the body’s need for them at a specific time. Reabsorption can also be regulated by certain hormones.
Secretion occurs when blood flows through the glomerulus. Foreign materials and substances, such as drugs, which are not required, may not be removed through filtration as it hasn’t spent the required time in the glomerulus for this to occur. These are then removed by the action of secretion into the convoluted tubules and excreted from the body in the urine, tubular secretion...