Brief Introduction to the Kidneys: Functions and Diseases

What are the kidneys?

The kidneys are a pair of red, bean shaped organs located on either side of our spine, below the rib cage. In a healthy adult, each kidney is 10-12 cm long, 5-7 cm wide and 2-3 cm thick. The right kidney is positioned a little lower in comparison to the left kidney, as it is compressed by the liver. 

A long tube called the ureter connects each kidney to our bladder, which is located in the pubic region. Urine is temporarily stored in the bladder and expelled through the urethra through voluntary contractions. 

Each kidney has around 1 million filtering units called nephrons and each nephron includes a filter, called the glomerulus, and a tubule. The nephrons work through a two-step process: first the glomerulus filters our blood, and then the tubule returns necessary substances to the blood system and removes waste.

What are the functions of the kidneys?

The kidneys are one of the most important organs in our body and they are commonly known for their excretory functions as mentioned above. However, our kidneys have other functions such as:

• Excretion: Every day, our two kidneys filter 200 litres of blood – that’s more than 120mL of blood per minute! However, they only produce 2 litres of urine every 24 hours. 
• Waste & toxin removal: Along with water, our urine is filled with unwanted toxins and waste products such as urea, creatinine, and ammonia.
• Metabolise medications: Many medications such as morphine and paracetamol are metabolised in the kidneys so that they can be expelled from the body.
• Maintain bone health: The kidneys have an enzyme that activates the vitamin D in our diet. Once activated, vitamin D enhances calcium uptake in the small intestine. Calcium is a key element that makes up our bones and it could not be adequately absorbed from our diet without the help of activated vitamin D. 
• Regulate blood pressure: The kidneys can regulate our blood pressure by decreasing or increasing the amount of urine produced. In the event of increased blood pressure, the kidneys will reduce the amount of urine produced. 
• Regulate electrolyte balance: Ions such as sodium, potassium, and calcium play an essential role in our cardiovascular and nervous systems. Thus, their concentrations have to be maintained within a certain range. 
• Hormone synthesis: The kidneys synthesise multiple hormones that are key to our health. For example, erythropoietin is an enzyme secreted by the kidneys that functions in the formation of red blood cells. 

Kidney Diseases

In the event of kidney diseases, key functions will be compromised which in turn will affect our health negatively. Let’s have a look at some common kidney diseases.

Acute kidney injury 

Acute kidney injury (AKI) is also known as acute renal failure, it is a sudden episode of kidney failure or damage that happens within a few hours to a week. Symptoms can include low blood pressure, shortness of breath, confusion, nausea, fatigue, and swelling in legs, ankles and around the eyes. However, in some patients, AKI can be asymptomatic. 

In a survey conducted in 2016, the death rate of AKI patients was 36.9% in Eastern Asia, 13.8% in Southern Asia, and 23.6% in Western Asia.  

AKI is commonly caused by direct kidney damage (bacterial infection, medication, kidney cancer) or a blockage of the urinary tract (kidney stones, bladder/prostate/cervical cancer). 

Chronic kidney disease 

Chronic kidney disease (CKD) occurs when a patient’s kidney is damaged over a long period of time. Typically, patients do not experience symptoms until advanced stages, when the majority of the kidney function has been compromised. In Asia, this disease affects more than 14% of the population. 

Symptoms of advanced CKD include chest pain, dry skin, headaches, loss of appetite, nausea, muscle cramps, and weight loss. 

Diabetes, high blood pressure, heart disease, smoking, and a family history of kidney diseases all predispose an individual to having CKD. CKD is likely to occur at a later stage in life. 

Kidney cancer

The most common type of kidney cancer is renal cell carcinoma (RCC), with an occurrence of over 90% of all kidney cancer instances. Among Asian countries, the five countries with the highest standardised incidence rates of RCC were:

1. Republic of Korea with 8 per 100000
2. Turkey with 5.6 per 100000
3. Japan with 5.3 per 100000
4. Singapore with 5.2 per 100000
5. Korea, Democratic People’s Republic with 4.3 per 100000

Common symptoms include blood in urine, pain in the affected  side or lower back without muscle injury, lump in the abdomen, or a fever. Kidney cancer is usually predisposed by long term exposure to smoke or toxic chemicals, high blood pressure, advanced kidney disease, or a family history of kidney cancer.

How to maintain kidney health?

As one of the important organs in our body, the kidneys play a fundamental role in maintaining our health. So what can we do to keep the kidneys healthy?

• Keep active and fit
• Control blood sugar
• Monitor blood pressure
• Monitor weight and eat a healthy diet
• Do not smoke or quit smoking immediately
• Keep up fluid intake