Homeostasis in urinary system is maintain by kidneys, of several important internal conditions by controlling the excretion of substances out of the body.
The urinary system is maintain and sustains homeostasis by eliminating wastes from the body, regulating blood acidity levels and controlling the levels of metabolites and electrolytes in the blood, such as sodium, potassium and calcium. The internal environment of urinary system is kept stable by assisting the osmo-regulation of blood volume and pressure.
Homeostasis in Urinary System
All systems of the body are interrelated. If there is a change in one system may affect all other systems in the body, with mild to devastating effects. A failure of urinary continence can be embarrassing and inconvenient, but is not life threatening.
The kidneys maintain the homeostasis of several important internal conditions by controlling the excretion of substances out of the body.
There are positive and negative ions in the body which the kidney is to be controlled the excretion of potassium, sodium, calcium, magnesium, phosphate, and chloride ions into urine.
When these ions reach a higher level than normal concentration, then kidneys can increase their excretion out of the body to return them to a normal level.
Conversely, the kidneys also conserve these ions when it is present in lower than normal levels, kidneys allowing the ions to be reabsorbed into the blood during filtration.
One more function of the kidneys are to monitor and regulate the levels of hydrogen ions (H+) and bicarbonate ions in the blood to control blood pH.
H+ ions are produced naturally by the metabolism of dietary proteins and which accumulate in the blood over time. The excess H+ excreted by the kidney into urine for elimination from the body.
The kidneys also conserve bicarbonate ions, which act as important buffer pH in the blood.
The cell of the body requires isotonic environment to grow properly and also in order to maintain their fluid and electrolyte balance.
The kidneys function to maintain the body’s osmotic balance by controlling the amount of water which is filtered out of the blood and excreted into urine.
When a person consumes a large amount of water, the kidneys starts to reduce their reabsorption of water and to allow the excretion of excess water through urine. This results in the production of dilute and watery urine.
When the body is being dehydrated, the kidneys reabsorb as much as water possible back into the blood to produce highly concentrated urine, which is full of excreted ions and wastes.
The changes of excess excretion of water are controlled by antidiuretic hormone (ADH). ADH is produced in the hypothalamus and released by the posterior pituitary gland to help the body retain water.
The kidneys also helps to monitor the body’s blood pressure, which maintain homeostasis.
Due to osmosis, water follows where Na+ leads. Much of the water is recover by the kidneys from the forming urine follows the reabsorption of Na+. ADH stimulation of aquaporin channels allows in regulation of water recovery in the collecting ducts.
When blood pressure is elevated, the kidneys would help to reduce blood pressure by reducing the volume of blood in the body. It start to reduce blood volume by reducing the reabsorption of water into the blood and producing watery, diluted urine.
When blood pressure becomes too low, the kidneys start to produce the enzyme renin, to constrict blood vessels and produce concentrated urine, which allows more water to remain in the blood.
When the blood pressure is low, the kidney synthesizes and releases renin. Renin converts angiotensinogen into angiotensin I, and ACE produced in the lung converts angiotensin I into biologically active angiotensin II.
The immediate and short-term effect of angiotensin II is to raise blood pressure by causing widespread vasoconstriction. Angiotensin II helps stimulates the adrenal cortex to release the steroid hormone Aldesterone, which results in renal reabsorption of Na+ and its associated osmotic recovery of water. The reabsorption of Na+ helps to raise and maintain blood pressure over a longer term.
Regulation of Osmolarity
Due to severe hypo-osmolarity the blood cell gets rupture which can cause problems widespread edema, which is due to a solute imbalance.
Inadequate solute concentration (such as protein) in the plasma results in water moving toward an area of greater solute concentration, in this case, the interstitial space and cell cytoplasm.
If the glomeruli of kidneys are damaged by an autoimmune illness,it causes losses of protein in large quantities in the urine.
It results drop in serum osmolarity which leads to widespread edema, if the condition is severe, it may lead to damaging or fatal brain swelling.
Due to severe dehydration would arise severe hypertonic conditions, which is caused by lack of water intake, severe vomiting, or uncontrolled diarrhea.
Recovery of Electrolytes
Sodium, calcium, and potassium must be closely regulated by the kidneys. Failure of K+ regulation can have serious consequences on nerve conduction, skeletal muscle function, and most significantly, on cardiac muscle contraction and rhythm.
Vitamin D Synthesis
Vitamin D is most important in the body,it become active, it must undergo a hydroxylation reaction in the kidney, that is, an –OH group must be added to calcidiol to make calcitriol (1,25-dihydroxycholecalciferol).
Activated vitamin D in the kidneys is important for absorption of Ca++ in the digestive tract, its reabsorption in the kidney, and the maintenance of normal serum concentrations of Ca++ and phosphate.
In recent research, it has been confirmed that vitamin D receptors are present in most of the body cell, if not all, reflecting the systemic importance of vitamin D. Many scientists have suggested it be referred to as a hormone rather than a vitamin.
Production of Hormones
The kidneys produce and interact with several hormones that are involved in the control of systems outside of the urinary system.
EPO is a 193-amino acid protein which stimulates the formation of red blood cells in the bone marrow. The kidney produces 85 percent of circulating EPO; and remaining 15 percent in the liver.
Erythropoietin, also known as EPO, is a hormone which is produced by the kidneys to stimulate the production of red blood cells.
The kidneys monitor the condition of the blood that passes through their capillaries, including the oxygen-carrying capacity of the blood. When the blood becomes hypoxic, which mean carrying low level of oxygen, cells lining the capillaries begin producing EPO and release it into the bloodstream.
EPO travels through the blood to the red bone marrow, where it stimulates hematopoietic cells to increase their rate of red blood cell production.
Red blood cells contain hemoglobin, which increases the blood’s oxygen-carrying capacity and which helps to ends the hypoxic conditions.
If you move to a higher altitude, the partial pressure of oxygen is lower, and because of that there is less pressure to push oxygen across the alveolar membrane and into the red blood cell.
If you start an aerobic exercise, your tissues will need more oxygen to cope with situation, and the kidney will produce more EPO. If erythrocytes are lost due to severe or prolonged bleeding, or under produced due to disease or severe malnutrition, the kidneys come to the rescue by producing more EPO.
Renal failure (loss of EPO production) is associated with anemia, which makes it difficult for the body to cope with increased oxygen demands or to supply oxygen adequately even under normal conditions. In this cases EPO supplement to be given to the person.
Calcitriol is the active form of vitamin D in the human body. It is produced by the kidneys from precursor molecules produced by UV radiation striking the skin.
Calcitriol works together with parathyroid hormone (PTH), it helps to raise the level of calcium ions in the bloodstream. When the level of calcium ions in the bloodstream drops below a threshold level, the parathyroid glands release PTH, which in turn stimulates the kidneys to release calcitriol.
Calcitriol promotes the small intestine to absorb calcium from food and deposit it into the bloodstream. It also stimulates the osteoclasts of the skeletal system to break down bone matrix to release calcium ions into the blood.
Renin is not a hormone itself, but an enzyme that the kidneys produce to start the renin-angiotensin system (RAS). The RAS increases blood volume and blood pressure in response to low blood pressure, blood loss, or dehydration.
Renin is released into the blood where it catalyzes angiotensinogen from the liver into angiotensin I. Angiotensin I is further catalyzed by another enzyme into Angiotensin II.
Angiotensin II stimulates several processes, including stimulating the adrenal cortex to produce the hormone aldosterone.
Aldosterone use changes the function of the kidneys to increase the reabsorption of water and sodium ions into the blood, increasing blood volume and raising blood pressure.
Negative feedback from increased blood pressure finally turns off the RAS to maintain healthy blood pressure levels.