Human Kidneys And their Function

The human body is a complex and intricate system, with each organ playing a vital role in maintaining balance and harmony. Among these unsung heroes, the kidneys stand out as remarkable filters that silently perform crucial functions to keep us healthy.

In this blog post, we embark on a journey to explore the fascinating world of human kidneys and  their function.

Human Kidneys Structure (Anatomy)

The kidneys are two bean-shaped organs, each about the size of a fist. They are located just below the ribcage on either side of the spine.

Healthy kidneys filter about a half cup of blood every minute

The kidneys, vital organs in the human body, exhibit a complex yet highly organized structure designed to facilitate their diverse functions.

Let’s delve into the key structural components of the kidneys:

1. Renal Cortex:
   • The outermost layer of the kidney.
   • Rich in blood vessels and contains structures like renal corpuscles and renal tubules.
2. Renal Medulla:
   • Lies beneath the renal cortex.
   • Composed of renal pyramids, each containing tubules that collect urine.
3. Renal Pelvis:
   • A funnel-shaped structure at the center of the kidney.
   • Collects urine from the renal pyramids and directs it to the ureter.

4. Nephrons 

• • Functional units of the kidney.
  • Consists of renal corpuscles (Bowman’s capsule and glomerulus) and renal tubules (proximal convoluted tubule, loop of Henle, and distal convoluted tubule).
  • Responsible for filtering blood and producing urine

5. Renal Arteries and Veins:

• • • Renal arteries supply blood to the kidneys, branching into smaller vessels within the renal cortex.
    • Renal veins carry filtered blood away from the kidneys.

6. Ureters:

• Tubes connecting the renal pelvis to the bladder.
• Transport urine from the kidneys to the bladder

7. Renal Capsule:

• Fibrous, transparent covering that surrounds each kidney.
• Provides support and protection.

8. Collecting Ducts:

• Tubules that receive urine from multiple nephrons.
• Merge to form papillary ducts that transport urine to the renal pelvis.

Healthy kidneys filter about a half cup of blood every minute, removing wastes and extra water to make urine. The urine flows from the kidneys to the bladder through two thin tubes of muscle called ureters, one on each side of your bladder. Your bladder stores urine. Your kidneys, ureters, and bladder are part of your urinary tract.

How Do human Kidneys Work? (Renal Physiology)

Each of our kidneys is made up of about a million filtering units called nephrons. Each nephron includes a filter, called the glomerulus, and a tubule. The nephrons work through a two-step process: the glomerulus filters your blood, and the tubule returns needed substances to your blood and removes wastes.

The functioning of human kidneys involves a complex process of filtration, reabsorption, and secretion. Here’s a simplified overview of how kidneys work:

1. Filtration:

• Blood is carried to the kidneys through the renal arteries, where it enters tiny filtering units called nephrons.
• Within each nephron, blood is filtered in a structure known as the renal corpuscle, which consists of the glomerulus (a network of tiny blood vessels) and Bowman’s capsule (a capsule-like structure surrounding the glomerulus).
• Filtration allows water, dissolved salts, glucose, and waste products from the blood to pass into the renal tubules, forming a fluid called filtrate.

2. Reabsorption:

• As the filtrate travels through the renal tubules (proximal convoluted tubule, loop of Henle, and distal convoluted tubule), essential substances like glucose, water, and ions are reabsorbed back into the bloodstream.
• Reabsorption occurs selectively, ensuring that necessary components are retained while excess substances continue to move through the tubules.

3. Secretion:

• In addition to filtration, the renal tubules actively secrete certain substances (such as hydrogen ions and potassium) from the blood into the filtrate.
• This secretion process helps in maintaining the body’s acid-base balance and electrolyte levels.

4. Formation of Urine:

• The remaining filtrate, now called urine, flows through the collecting ducts, merging into larger ducts and ultimately reaching the renal pelvis.
• From the renal pelvis, urine moves into the ureters, which carry it to the bladder for storage.

5. Excretion:

• When the bladder is full, urine is expelled from the body through the urethra during the process of micturition.

Other Functions Of human Kidneys

In addition to the fundamental functions of filtration, reabsorption, and secretion, the kidneys serve several other crucial roles in maintaining overall health:

1. Blood Pressure Regulation:

• The kidneys play a key role in regulating blood pressure by adjusting the volume of blood and the concentration of salts in the bloodstream.
• The renin-angiotensin-aldosterone system, activated by the kidneys, helps control blood pressure by influencing blood vessel constriction and fluid balance.

2. Erythropoiesis Stimulation:

• The kidneys produce and release erythropoietin, a hormone that stimulates the production of red blood cells in the bone marrow.
• This function helps maintain an adequate oxygen-carrying capacity in the blood.

3. Calcium and Phosphate Balance:

• The kidneys contribute to the regulation of calcium and phosphate levels in the body by influencing their reabsorption and excretion.
• Proper balance is crucial for bone health, nerve function, and various metabolic processes.

4. Detoxification:

• The kidneys filter and eliminate various metabolic waste products (such as  creatinine,  uric acid etc), drugs, and toxins from the body.
• This detoxification function is essential for preventing the accumulation of harmful substances in the bloodstream.

5. Glucose Regulation:

• The kidneys play a role in glucose homeostasis by reabsorbing glucose back into the bloodstream.
• In conditions like diabetes, where blood glucose levels are elevated, the kidneys may excrete excess glucose into the urine.

Kidney Diseases

Common Structural Kidney Diseases:

1. Kidney Stones:
   • Solid deposits that form in the kidneys, often composed of calcium, oxalate, and other substances.
   • Can cause intense pain and may obstruct the flow of urine.
2. Renal Cell Carcinoma:
   • A type of kidney cancer that originates in the cells lining the small tubes within the kidneys.
   • Symptoms may include blood in the urine, abdominal pain, and weight loss.
3. Hydronephrosis:

• Swelling of the kidney due to the backup of urine caused by an obstruction.
• Obstruction can result from conditions like kidney stones or congenital abnormalities.

4. Renal Artery Stenosis:

• • Narrowing of the renal arteries, often due to atherosclerosis.
  • Impairs blood flow to the kidneys, impacting their function and potentially leading to hypertension.

5. Interstitial Nephritis:

1. • Inflammation of the kidney’s interstitial tissue.
   • Can be caused by infections, allergic reactions to medications, or autoimmune diseases.

Common Functional Kidney Diseases:

1. Chronic Kidney Disease (CKD):
   • A progressive condition where kidney function declines over time.
   • Common causes include diabetes, hypertension, and glomerulonephritis.
2. Acute Kidney Injury (AKI):
   • Sudden and rapid loss of kidney function.
   • Can be caused by severe infections, dehydration, or conditions that affect blood flow to the kidneys.
3. Glomerulonephritis:
   • Inflammation of the glomeruli, the filtering units of the kidneys.
   • Can result from infections, immune disorders, or other underlying conditions.
4. Polycystic Kidney Disease (PKD):
   • Genetic disorder leading to the formation of fluid-filled cysts in the kidneys.
   • Gradual enlargement of cysts can impair kidney function.