Kidney: Structure, Function and Related Diseases

What is a Kidney?

Kidneys are organs of utmost importance to the human body for generating blood-filtering, clearing waste, and other homeostatic functions. They lie on either side of the vertebral column at the rib cage and are approximately fist-sized. Only by studying the structure and function of the kidneys is it possible to fully appreciate their contribution to health and the effects of kidney-related diseases.

Structure of the Kidney

The structure of the kidney includes:

External Anatomy

The kidneys are two bean-shaped organs that have a convex border and a concave border. On the inner concave side, there is a notch called the hilum where the renal artery enters, and the renal vein and ureter leave. The outermost layer of the kidney is a tough capsule.

Internal Anatomy

It distinguishes between an outer renal cortex from an inner renal medulla within the interior of the kidney. Extensions from the hilum extend into a funnel-like space, called renal pelvis, which has projections called calyces. Divided plies of medullary pyramids project into the calyces, and the cortex extends between these pyramids as a renal column, also called Columns of Bertini. The functional units of the kidney are the millions of nephrons that compose the organ. Each nephron is made up of the glomerulus and Bowman's capsule, the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule.

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Function of the Kidney

The functions of the kidney include:

Filtration of Blood

Each kidney filtrates blood to produce urine. Filtration takes place in the glomerulus under sufficiently high blood pressure, which forces water and solutes to pass through a membrane.

Reabsorption and Secretion

Reabsorption into the bloodstream of what is needed from the filtrate occurs in the kidneys, with simultaneous secretion of waste products directly into the urine. Mostly occurs in the PCT and loop of Henle, as well as the DCT.

Blood Pressure Regulation

The kidneys maintain the blood pressure through the renin-angiotensin-aldosterone system, whereby they alter the level of blood volume and the degree of constriction of the blood vessels.

Electrolyte Balance

The levels of electrolytes in the body are maintained by the kidneys through the reabsorption or excretion of ions such as sodium, potassium, and calcium.

Excretion of Metabolic Wastes

Kidneys clear metabolic wastes like urea and creatinine from the blood.

Production of Hormones

Kidneys produce hormones like erythropoietin, which stimulates red blood cell production, or calcitriol, which works to help in calcium absorption.

Disorders of Kidney

The common disorders related to kidneys are:

Chronic Kidney Disease (CKD)

Progressive loss of kidney function characterises CKD. Diabetes, hypertension, or another cause can be the basis for this situation. It can present with fatigue, swelling, and a change in urination. It may be treated with medication, lifestyle modifications, and eventually dialysis or transplantation.

Acute Kidney Injury (AKI)

AKI is a sudden decrease in kidney function, generally due to trauma, infection, or medicine. It requires immediate medical attention and can be reversible if treated promptly.

Kidney Stones

kidney stones are made up of mineral salts and deposits that form inside the kidneys. They may cause severe pain, nausea, and problems related to urinary flow. Treatment comprises medication, increased fluid intake, and sometimes even surgery or lithotripsy.

Glomerulonephritis

This is the inflammation of the glomeruli. It produces pink urine, swelling, and an increase in blood pressure. Treatment differs according to cause and severity.

Polycystic Kidney Disease

It is a genetic disorder wherein cysts form inside the kidneys. It can cause renal failure and therefore needs management by medication and alteration in lifestyle.

Urinary Tract Infections (UTIs) and Pyelonephritis

UTIs can spread up to the kidneys and cause pyelonephritis. The symptoms are fever, backache and urinary complaints. It is treated with antibiotics.

Methods of Diagnosis and Treatment

The diagnostic methods for kidney disease include:

Laboratory Investigations

• Urinalysis

• Blood tests

• Imaging techniques: ultrasound, CT scan, MRI

• Renal biopsy

Treatment Modalities

• Symptomatic and progression-retarding drugs

• Mainly hemodialysis and peritoneal dialysis are done for the blood filtration process

• Kidney transplant in cases of end-stage kidney failure

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