Kidney Structure, Function and Related Diseases

The kidneys are two bean-shaped organs located on either side of the spine, just below the rib cage. Each kidney is roughly the size of a closed fist (10–12 cm in length). Their primary role is to filter the blood and form urine, which is then passed through the ureters to the bladder.

To understand kidney structure and function better, let us look at the major external and internal features:

• Shape and Size: Bean-shaped with a convex and a concave border.

• Hilum: A notch on the concave side where the renal artery enters and the renal vein and ureter exit.

• Capsule: A tough, protective outer layer.

• Renal Cortex: The outer region of the kidney.

• Renal Medulla: The inner region is made up of medullary pyramids.

• Renal Columns: Known as Columns of Bertini, these are cortical extensions that lie between the medullary pyramids.

• Renal Pelvis: A funnel-like cavity that collects urine, continuing as the ureter. It has further cup-like projections called calyces.

Nephrons – The Functional Units

Inside every kidney, there are over a million tiny filtering units called Nephrons, which play a crucial role in urine formation. Each nephron has its structure of nephron, consisting of:

• Glomerulus: A network of capillaries where the initial filtration takes place.

• Bowman’s Capsule: Surrounds the glomerulus and collects the filtrate.

• Tubules (Proximal, Loop of Henle, Distal): Help reabsorb essential substances back into the bloodstream.

• Collecting Duct: Transports the final urine into the renal pelvis.

Key Functions of the Kidneys

1. Filtration of Blood and Urine Formation

• The kidneys filter metabolic waste products like urea and uric acid from the blood, turning these wastes into urine.

2. Excretion of Metabolic Wastes

• By removing toxins such as urea, the kidneys prevent harmful accumulation in the bloodstream.

3. Hormone and Enzyme Secretion

• Erythropoietin (EPO): Stimulates red blood cell production in response to low oxygen levels.

• Renin: Helps control blood pressure through the renin-angiotensin-aldosterone system.

• Calcitriol: Aids in calcium absorption from the intestines.

4. Acid-Base Balance

• The kidneys regulate blood pH by reabsorbing bicarbonates and excreting acids like hydrogen ions.

5. Water and Electrolyte Balance

• Working with the pituitary gland, the kidneys maintain appropriate water and salt levels, preventing dehydration or fluid overload.

Major Kidney Diseases and Their Symptoms

Certain conditions can interfere with normal kidney functions. Below are a few common diseases:

1. Uremia

• Damaged kidneys cannot eliminate urea and other toxins, causing a buildup in the bloodstream.

• Symptoms: Fatigue, itching, muscle twitching, and confusion.

• Treatment often involves evaluation and, in severe cases, dialysis.

2. Renal Calculi (Kidney Stones)

• Crystallised deposits of salts and minerals form stones in the kidneys.

• Symptoms: Severe abdominal or back pain, nausea, painful urination.

• Treatment: Medication to dissolve small stones, increased water intake, or surgical procedures if needed.

3. Glomerulonephritis

• Inflammation of the glomeruli.

• Symptoms: Pink or cola-coloured urine (due to blood), facial swelling, high blood pressure.

• Requires prompt medical attention to prevent complications.

Additional Information for Students

Keeping your kidneys healthy involves:

• Staying hydrated with water.

• Maintaining a balanced diet rich in fruits, vegetables, and moderate protein.

• Monitoring blood pressure and blood sugar levels.

• Avoiding excessive intake of painkillers and over-the-counter medications without consultation.

Quick Quiz (With Answers)

1. Which part of the nephron is mainly responsible for filtering the blood?

Answer: The glomerulus

2. Name one hormone secreted by the kidney that helps control blood pressure.

Answer: Renin

3. Which hormone is involved in red blood cell production?

Answer: Erythropoietin

4. True or False: Kidneys help in maintaining the pH level of the body.

Answer: True

Related Topics

• Urine Formation

• Regulation of Kidney Function

• Kidney Function Test

• Kidney Failure Symptoms

• Facts about Kidneys

• Difference Between Left and Right Kidney