The Kidney in Health and Disease: Basic Facts for Africans

 

By: Adebowale Bello, Freelance Health Writer. With medical review and editorial support by the Datelinehealth Africa Team

Illustration showing the kidneys lying below the rib cage in the back area of the upper abdomen.

 

Key Takeaway

• The kidneys are a pair of bean-shaped organs located below the rib cage in the back region of the upper abdomen.

• The main function of the kidney is to remove waste products from the body as urine.

• The kidney can be affected by different diseases which are treatable. 

• You can protect your kidneys by drinking enough water daily, eating and living healthy, as well as exercising regularly.

 

Introduction

Your kidneys are amazing organs, though you may not consciously attach much significance to them. However, this pair of bean-shaped organs are crucial to your overall well-being and this is because they serve as a natural filtration system that eliminates toxic waste from the bloodstream through the urine.

Apart from the removal of waste, the kidneys regulate the blood pressure and maintain the body's internal fluid and chemical balance, known as homeostasis. 

As World Kidney Day was marked recently, this article aims to raise awareness and educate Africans, especially about the kidney; what it does, how it may be damaged, and how you can take care of your kidneys to live a healthy life.

 

Structure of the kidney

The kidneys are a pair of bean-shaped organs located just below the rib cage and to the left and right of your spine. They are linked to the bladder through two thin tubes of muscle called ureters, one on each side of your bladder. The urine formed in the kidneys passes through the ureters and is stored in the bladder. Your kidneys, ureters, and bladder are part of your urinary tract. (see fig 1)

Fig. 1: Illustration of the human urinary tract. Photo credit, NIDDK. Click image to enlarge.

 

On the top of each kidney is the adrenal gland, which is responsible for the production of several hormones, such as the stress hormone cortisol, aldosterone and adrenaline. The adrenal glands have no direct role in the functions of the kidneys.

The kidney can be segmented into an outer layer known as the renal cortex and an inner layer known as the renal medulla. (see fig. 2)

Fig. 2: An illustration of a cross section of the gross kidney showing an outer cortex and inner medulla. Click image to enlarge.

 

The renal cortex consists largely of renal corpuscles, which are specialised structures involved in the blood filtration process. The renal corpuscles are made up of the glomeruli which form from a meshwork of blood vessels and the two layered Bowman's capsule. It  opens into a tubular system. The initial stage of filtration of blood for waste and excess fluid occurs in the cortex of the kidney as the blood passes through the glomeruli in the renal corpuscles (see Fig. 3)

Fig.3: Illustration of the composition of the nephron in the cortex and medulla of the kidney

 

The renal medulla contains the renal pyramids, which are cone-shaped structures that appear striped. However, it is the nephron that partitions each renal pyramid, giving it the striped appearance. The renal medulla regulates the amount of water to be reabsorbed from urine, thereby concentrating the urine before it leaves the kidneys. (see figure 3)  

 

How Does The Kidney Filter Waste?

The kidneys play a crucial role in filtering waste products and excess substances from the blood to maintain proper balance within the body. Here's how the process works:

 

• Filtration: Blood enters the kidneys through the renal arteries, where it flows into tiny structures called nephrons, which are the functional units of the kidney. Within each nephron, there is a cluster of capillaries known as the glomerulus.

Blood pressure forces fluid, waste products, electrolytes and water out of the blood and into the surrounding Bowman's capsule, a structure that encases the glomerulus.

 

• Reabsorption: As the filtrate passes through, essential substances such as glucose, amino acids and electrolytes are reabsorbed back into the bloodstream. This process ensures that vital nutrients and electrolytes are retained in the body.

 

• Secretion: At this stage, some waste products like urea and drugs still persist, hence they are actively secreted or removed from the blood into the renal tubules.

 

• Concentration and Dilution: After the kidneys clean the blood, the leftover liquid goes through more changes in the kidneys' tubes where hormones like antidiuretic hormone (ADH) and aldosterone help control how much water and minerals are reabsorbed into the body or excreted as urine.

 

• Excretion: At this stage, the urine moves through the collecting ducts, the ureters and then to the bladder, where it is stored until it is expelled from the body through urination.

 

The Functions of the Kidney

Although the main function of the kidney is to remove waste products, such as uric acid, creatinine and excess fluid and electrolytes (salts), it also performs several additional functions that include:

• Regulation of body fluid and electrolytes.

• Production of important hormones necessary for red blood cell production.

• Regulation of blood pressure.

• Removal of toxic drugs from the body.

• Regulation of the body's acid-base balance (pH)

• Fine regulation of calcium excretion and vitamin D levels in blood.

 

Some Common Kidney Diseases

Just like every other organ, different diseases affect the kidney and they could either be short-term (acute) or long-term (chronic).

Here are four of the most common kidney diseases.
 

1. Chronic Kidney Disease (CKD)

Chronic kidney disease (CKD) is a kidney disease that begins slowly and progresses over a long time. The kidney is therefore unable to properly filter the body's waste and this waste accumulates gradually, which can lead to several other health problems. In 2017, an estimated 850 million people lived with CKD and with the increase in its risk factors, these numbers are steadily on the rise.

To differentiate CKD from other kidney diseases, a test known as the Estimated Glomerular Filtration Rate (eGFR) is carried out to check your kidney function and if the test results are low for 90 days, it confirms CKD.

Risk Factors For Chronic Kidney Disease 

There are several medical conditions which may increase your risk of developing chronic kidney disease and some of these risk factors include:

• Diabetes 

• Heart disease 

• Obesity 

• Smoking

• Hypertension

Symptoms Of Chronic Kidney Disease

The progressive nature of chronic kidney disease means you may likely not notice any symptoms out of the ordinary but as the disease progresses, you might begin to experience symptoms like

• Nausea

• Fatigue

• Muscle cramps

• Shortness of breaths

• Loss of appetite.

 

2. Kidney Stones

Minerals in the body can form solid masses, which may be tiny or huge. These masses are known as kidney stones or renal calculi (see fig. 4) and if you do have them, you may pass out the smaller stones while urinating. However, the bigger kidney stones may block the urinary tract, also known as the ureter.

The presence of the larger urinary stones in the ureter makes it extremely difficult to pass out urine, thereby causing severe pain. According to the National Kidney Foundation, 1 out of 10 people will have a kidney stone in their lifetime, thereby showing how common this condition is.

Causes Of Kidney Stones

Some likely causes of kidney stones include:

• Obesity.

• Not drinking enough water.

• Consumption of excess fructose (found in fruits and table sugar).

Symptoms Of Kidney Stones

Kidney stones are majorly characterised by abdominal pain, which may either be dull or sharp and this pain can occur in one side of your belly or feel like it's all over. 

Other symptoms of kidney stones include:

• Painful urination.

• Inability to urinate.

• Bloody urine.

• Foul-smelling urine

• Nausea

Types of Kidney Stones

There are 4 types of kidney stones and this is because of different compounds that form them (see fig. 4).

Figure 4: Showing varieties of kidney stones. Courtesy: Kumar A. 

Click image to enlarge.

 

The different types of kidney stones include;

1. Uric acid stones

This makes up at least 10% of all kidney stones. The stones form when the uric acid levels in the urine are high. These high levels are due to increased consumption of foods that contain purine, such as fish, beef and poultry.
 

2. Struvite stones

A struvite stone is formed when bacteria leads to an upper urinary tract infection. These stones grow fast and can become large enough to block the urinary tract. In most cases, the stone is broken down and removed surgically.
 

3. Calcium oxalate stones

This is the most common type of kidney stones and it occurs when there is too much of the naturally occurring compound known as oxalate. This substance can be found in fruits, grains and nuts, while your body also produces it as a waste product. However, when you don't drink enough water, oxalate binds with calcium in bits until it forms a big stony mass.
 

4. Cystine stones

Cystine is an amino acid that performs different roles in the body, from aiding digestion to boosting the immune system. However, cystine stones can be formed when excess cystine is present in the urine and this is caused by cystinuria, which is a rare condition. Cystine stones might reoccur because cystinuria is a lifelong condition, however, if managed properly, formation of stones will cease.

Though rare, cystine stones are the most common inheritable cause of kidney stones worldwide and it affects more males than females.

 

3. Glomerulonephritis

Glomerulonephritis is the inflammation of the glomeruli, which are the tiny filters in the kidneys responsible for removing waste products and excess fluids from the blood to form urine. This inflammation can impair the kidney's ability to filter blood properly, leading to various symptoms and complications.

Causes of Glomerulonephritis

• Infections

• Autoimmune disorders like lupus and vasculitis can cause the immune system to mistakenly attack the glomeruli, leading to inflammation.

• Primary glomerular diseases: Some individuals develop glomerulonephritis without an identifiable cause, known as primary or idiopathic glomerulonephritis.

Symptoms of Glomerulonephritis

• Bloody urine (hematuria)

• Foamy urine, due to excess protein in the urine.

• Decreased urine output.

• High blood pressure.

• Fluid retention: Some body parts such as the feet and hand may swell due to the kidneys' inability to remove excess fluid from the body.

• Fatigue

 

4. Acute kidney injury

Acute kidney injury (AKI) is a sudden and rapid decline in kidney function, leading to the accumulation of waste products and fluids in the body. It can occur rapidly over hours or days and there is a sudden decrease in urine output and/or an increase in serum creatinine levels. 

Causes of Acute Kidney Injury

• Reduced blood flow to the kidneys.

• Kidney damage due to infections, kidney stones and medications.

• Urinary tract obstruction due to kidney stones, tumours or enlarged prostate glands.

• Sepsis, a life-threatening infection that spreads throughout the body, can cause AKI by triggering widespread inflammation and reduced blood flow to the kidneys.      

Symptoms of Acute Kidney Injury

• Decreased urine output.

• Swelling of the legs, ankles, feet, face or abdomen.

• Fatigue and weakness.

• Shortness of breath.

• Nausea and vomiting.

• Chest pain or pressure due to fluid overload and congestion in the chest.

 

Diagnostic Tests for Kidney Diseases

There are three main categories of tests which can be carried out to determine the health  of your kidneys and these tests are discussed below.

1. Urine Tests 

Urine tests are diagnostic tests that analyse the urine to provide information about various aspects of a person's health. Some common urine tests include:

• Urinalysis: This test examines the physical, chemical and microscopic properties of urine. It can detect abnormalities, such as urinary tract infections, kidney disease, diabetes, and dehydration.

• Urine culture: This test is used to identify and determine the susceptibility of bacteria or other microorganisms causing a urinary tract infection (UTI).

• Urine protein test: This test measures the amount of protein present in the urine and the test is important because elevated protein levels may indicate kidney damage or disease.

2. Blood Tests

Blood tests are diagnostic procedures that involve analysing blood samples to assess various aspects of health. These tests play a crucial role in diagnosing medical conditions, monitoring treatments and evaluating kidney function.

Some blood tests commonly used to assess kidney function include:

• Serum creatinine: Measures the level of creatinine in the blood and may indicate kidney dysfunction.

• Blood urea nitrogen (BUN): Measures the amount of urea nitrogen in the blood, another waste product.

• Estimated Glomerular Filtration Rate (eGFR): Calculated based on creatinine levels, age, gender and race. It estimates the rate at which the kidneys filter waste from the blood and a lower eGFR indicates decreased kidney function.

• Serum electrolytes: Measures the levels of electrolytes, such as sodium, potassium, chloride and bicarbonate.

• Serum albumin: Measures the level of albumin, a protein produced by the liver and low levels may indicate kidney disease.

3. Imaging Tests

These are medical procedures that depict the inside of the body. These tests are carried out to help your doctor make an accurate diagnosis of the kidneys. 

Some of the tests are;

• Ultrasound: Use of sound waves to create kidney images

• Computed Tomography (CT) scan: Used to detect kidney stones and tumours, and provides a detailed cross-sectional image of the kidney.

• Magnetic Resonance Imaging (MRI): Used to check for blood flow and tumours, while using magnetic and radio waves to do so. 

• Renal angiography: Injection of contrast dyes into the kidney blood vessels to detect any irregularities.

 

Treatments Of Common Kidney Diseases

Treatment for kidney diseases vary depending on the specific condition and its severity. Here's an overview of common treatments:

• Medications: Depending on the underlying cause of the kidney disease, medications may be prescribed to manage symptoms, control blood pressure and reduce inflammation. Drugs such as angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs) are commonly prescribed to lower blood pressure and slow the progression of kidney disease.

 

• Dietary changes: Adopting a kidney-friendly diet can help manage kidney disease. This typically involves reducing sodium, phosphorus, and potassium intake while ensuring adequate protein and calorie consumption. Some kidney-friendly African foods include yam, okra, fufu, millet porridge, green beans, spinach and cabbage.(see fig 5)

Fig. 5: Examples of kidney friendly African foods. Left: Yam, Right: spinach. Click image to enlarge.
 

• Blood pressure management: Controlling high blood pressure is crucial in slowing the progression of kidney disease. Lifestyle modifications such as dietary changes, regular exercise, weight management and limiting alcohol intake may be recommended.

 

• Dialysis: In advanced stages of kidney disease, when the kidneys are no longer able to adequately filter waste products from the blood, dialysis may be necessary.

Dialysis is a medical procedure that artificially removes waste and excess fluids from the blood and there are two types of dialysis; hemodialysis, which involves using a machine to filter blood outside the body, and peritoneal dialysis, which uses the lining of the abdomen to filter blood internally.
 

• Kidney transplant: For some patients with end-stage kidney disease, a kidney transplant may be the best treatment option. A healthy kidney from a living or deceased donor is surgically implanted to replace the diseased kidney.

Transplant recipients usually require lifelong immunosuppressive medications to prevent rejection of the donor organ.

 

How To Take Care Of Your Kidneys 

Taking care of your kidneys is important if you want to remain healthy and free from kidney disease. Here are some important tips for you:
 

• Stay hydrated

Drinking an adequate amount of water helps to keep the kidneys functioning properly by flushing out waste products from the body. This is not always easy as the urge to drink flavour filled soft drinks is always high. However, you can get a water bottle and set occasional alarms on your mobile devices to remind you to drink water.

If your circumstances permit, you can make it a goal to drink between 2.5 to 3.5 litres of water daily.
 

• Eat a healthy diet

Eating a balanced diet rich in fruits and vegetables can support kidney health. Consumption of  processed foods which contain saturated fats, sugars and salts increase your risk of high blood pressure, diabetes and obesity, which are major risk factors for kidney disease.
 

• Control your blood pressure and blood sugar

High blood pressure can damage the kidneys over time so it's important to monitor your blood pressure regularly and take steps to keep it within a healthy range. You can do this by exercising regularly, reducing salt intake and taking prescribed medications.

If you live with diabetes, follow the management plan recommended by your doctor and constantly monitor your blood sugar levels.
 

• Quit smoking

Whether you've been smoking for decades or just started, one thing is sure;

Smoking is bad for your health. 

Smoking can impair kidney function and increases your risk of kidney disease, hence quitting smoking is vital in prolonging your healthy kidneys. 

If you're finding it difficult to quit smoking, seek support from doctors , counsellors, or smoking cessation programs designed to help you quit smoking.
 

• Limit alcohol consumption 

Excessive alcohol consumption is a risk factor for many medical conditions including kidney failure. If you must drink alcohol, do so in moderation.
 

• Exercise regularly

Engaging in regular physical activity can help you to maintain a healthy weight, lower blood pressure and improve cardiovascular health, all of which support kidney health. Setting aside 30 minutes daily to perform exercises like jogging, yoga and swimming can help you meet up with the 150 minutes of moderate-intensity exercise recommended by health guidelines.

 

Conclusion

In summary, understanding the kidney and how it works is crucial as it enables you to make informed health decisions. These decisions would let you prioritise your health and wellness as well as enlighten those around you. 

 

References

1. National Institute of Diabetes and Digestive and Kidney Diseases. [Internet, June 2018] . Your Kidneys & How They Work. Accessed March 13,2024.
 

2. Cleveland Clinic. [Internet, May 2022]. Adrenal Gland. Available from https://my.clevelandclinic.org/health/body/23005-adrenal-gland. Accessed March 13,2024.
 

3. National Kidney Foundation. [Internet, n.d]. How Your Kidneys Work. Available from https://www.kidney.org/kidneydisease/howkidneyswrk. Accessed March 13, 2024.
 

4. Kovesdy CP. Epidemiology of chronic kidney disease: an update 2022. Kidney Int Suppl (2011). 2022 Apr;12(1):7-11. doi: 10.1016/j.kisu.2021.11.003. Epub 2022 Mar 18. PMID: 35529086; PMCID: PMC9073222. Accessed March 13, 2024.
 

5. Mayo Clinic. [Internet, September 2023]. Chronic kidney disease. Available from https://www.mayoclinic.org/diseases-conditions/chronic-kidney-disease/symptoms-causes/syc-20354521. Accessed March 18, 2024.
 

6. National Kidney Foundation. [Internet, n.d]. Uric acid stones. Available from https://www.kidney.org/atoz/content/uric-acid-stone. Accessed March 18, 2024.
 

7. National Kidney Foundation. [Internet, n.d]. Struvite stones. Available from https://www.kidney.org/atoz/content/struvite-stone. Accessed March 18, 2024.
 

8. National Kidney Foundation. [Internet, n.d]. Calcium oxalate stones. Available from https://www.kidney.org/atoz/content/calcium-oxalate-stone. Accessed March 18, 2024.
 

9. National Kidney Foundation. [Internet, n.d]. Cystine stones. Available from https://www.kidney.org/atoz/content/What-are-cystine-stones. Accessed March 18, 2024.
 

10. Stephen W. Leslie; Hussain Sajjad; Lama Nazzal. [Internet, May, 2023]. Cystinuria. Available from https://www.ncbi.nlm.nih.gov/books/NBK470527/#:~:text=Cystine%20stones%20are%20due%20to,to%20the%20development%20of%20stones. Accessed March 18, 2024.

11. Bello, A. K., Okpechi, I. G., Osman, M. A., Cho, Y., Htay, H., Jha, V., Wainstein, M., & Johnson, D. W. (2022). Epidemiology of haemodialysis outcomes. Nature Reviews Nephrology, 18(6), 378-395. https://doi.org/10.1038/s41581-022-00542-7. Accessed March 21, 2024

 

 

Published: March 21, 2024

© 2024. Datelinehealth Africa Inc. All rights reserved.

Permission is given to copy, use and share content for non-commercial purposes without alteration or modification and subject to attribution as to source.