The many faces of the kidneys
What's the building block of any relationship? Communication and Partnership Mentality!
The kidneys are in a forever lasting partnership with the liver, working together to ensure we are free of toxins and waste materials 24/7. The liver shares attributes of the postman. It sorts and packages by-products of the gut before they get transported around the body. It metabolises substances, and it does the legwork for the kidneys and the bowel to remove toxins and waste materials.
THE KIDNEYS ARE HIGHLY DEPENDANT ON THE LIVER!
If the liver is overworked and/or clogged, the detoxification function suffers. As a result, the kidneys have to work harder to filter toxins and waste products.
While they are both working towards a common goal which is cleansing the blood of waste products, the kidneys receive about 20% of the cardiac output.
For this reason, they have a DENSE NETWORK OF BLOOD VESSELS!
Why are the kidneys so important?
BLOOD FILTRATION | EXCRETION OF WASTE
How do we filter blood? By microscopic tube-like filtration units, there is 1 million in each kidney. The filtration takes place in tiny capillaries that work like sieves allowing only certain materials passing through. Small molecules such as water, minerals, glucose and amino acids are reabsorbed. The waste products leave the body via urine.
WATER & ELECTROLYTE BALANCE
There must be a balance between water intake and output. The majority of the water comes from the food we eat, the fluids we drink, and some are produced through biological processes. We need a minimum of 500ml urine per day to aid the clearance of waste. That's why hydration is key! Dehydration and thirst are detected by the hypothalamus, in response to the anti-diuretic hormone (ADH) released. ADH stimulates water and sodium re-absorption which, in turn, affects blood pressure. The next paragraph covers blood pressure regulation.
BLOOD PRESSURE REGULATION
It is well known that fluid levels affect blood pressure. What is the kidney's role in regulating blood pressure?
In short: low fluid levels > low blood volume > low blood pressure. The low blood pressure triggers the kidney to release RENIN.
Renin and other hormones such as angiotensin and aldosterone stimulate a chain of biochemical processes involving also the liver and the lungs to increase the blood pressure. Chronically high blood pressure damages the blood vessels. This has a big impact on the kidneys due to the dense network of blood vessels. Damaged kidneys can lead to loss of function in the long run.
PH (ACID-BASE) BALANCE
The kidneys control the blood's PH by regulating bicarbonate and hydrogen levels. For proper physiological functioning, there must be a tight balance between the concentrations of acids and bases in the blood. The lungs also regulate these levels by expelling CO2.
BLOOD GLUCOSE REGULATION
Glucose is filtered through and re-absorbed by the kidneys before it passes back into circulation. The kidneys have a threshold of how much they can handle. Excess glucose spilt into the urine. Chronic and high intake of sugar damages the blood vessels, and consequently the kidneys.
The kidneys release a hormone called calcitriol, which is needed to utilise the active form of Vitamin D. Vitamin D is unique, in that it can be made from exposure to sunlight. It comes in two forms, D2 and D3. Vitamin D2 in our skin is converted to Vitamin D3, followed by various metabolic processes before it reaches the kidney. The first stop is in the liver, where it becomes 25-hydroxyvitamin D, 25 (OH) D. The second conversion happens in the kidneys to 1,25 dihydroxy vitamin D, 1,25(OH)2D.
There is confusion around which test to request amongst practitioners. While 1.25 (OH) D is the active form (most potent) to assess Vitamin D stores, it is more useful to consider 25 (OH ). This one is a more accurate reflection since it is not influenced by other hormones.
The kidneys also produce erythropoietin, which is involved in red blood cell production.