Structure & Functions of the Kidney
Kidneys are a pair of bean-shaped organs located in the ‘back-side’ ( retro-peritoneum) of the abdomen.
Each kidney is broadly divided into a filtering part (nephrons and tubules) and a collecting part (collecting ducts). Collecting ducts join together and open in the ‘pelvis’ of each kidney. Pelvis continues as ‘ureter’ and each ureter opens into the bladder. The bladder empties outside through the ‘urethra’.
In males, a prostate gland ‘sits’ at the beginning of the urethra, just under the bladder.
The smallest functioning unit of the kidney is called the ‘nephron’. Each nephron is made up of a glomerulus ( the filter) and a series of intricate tubules ( proximal tubule, loop of henle and distal tubule). Distal tubule opens into the collecting duct.
Glomerulus is formed by capillaries coming from the afferent arteriole, an eventual branch of the main renal artery.
Glomerulus filters plasma into the proximal tubule. The tubules then reabsorb a large part of water and all the necessary substances. Only the waste products reach the collecting system and are eventually thrown out as urine.
Functions of Kidney
Functions can be largely divided as ‘excretory’, ‘synthetic’ and ‘regulatory’.
Excretory Functions of Kidney
- Throwing out waste products like Urea, creatinine, excess potassium, acids etc.
- Removing excess water from the body.
- Excrete drugs and toxins.
Synthetic Functions of Kidney
- Produce Erythropoeitin, the hormone for Red Blood Cells (RBC) survival.
- Produce Vitamin D, essential for bone health and calcium absorption.
- Produce sugar ( gluconeogenesis) in times of starvation.
Regulatory Functions of Kidney
- Regulate Blood Pressure.
- Regulate blood volume via sodium absorption or excretion.
When Kidneys fail, all the above functions go wrong and manifest as the following
- Urea, creatinine accumulate and levels rise in the blood above the normal range.
- Water accumulates in tissues giving rise to swelling under the eyes and over the feet.
- Erythropoeitin is not produced and therefore anemia develops.
- Vitamin D is not produced and therefore bones become weak ( Renal Osteodystrophy).
- Blood pressure becomes abnormally high ( Hypertension).