The kidneys are bean-shaped organs present in a pair in the posterior region of the abdominal cavity. They are mainly associated with the excretion in addition to the other organs/systems like GI tract, liver, skin, and lungs which are also involved in the excretion but in a limited capacity. The kidneys aid in the removal of waste products of metabolism like excess water, and salts from the blood thereby maintaining blood pH in the normal range. The kidneys, thus, function as the filtration units of the body that purify the blood and remove toxins and undesired products through urine formation.
Thus, the primary role of the kidneys is maintenance of homeostasis, through urine formation. The unwanted products formed during various metabolic activities and excreted by kidneys are listed in the Table 1. In addition to these biochemicals, other harmful substances such as foreign chemicals, heavy metals, pesticides, etc are also excreted/eliminated by kidneys. This process helps in maintaining water and electrolyte balance as well as in establishing the acid-base balance in the body. The acid-base balance is critical to our health, since the body has a tendency of drifting towards acidosis which is prevented by the action of kidneys.
Table 1. Various process and products that are excreted through the kidneys
Kidneys also have an endocrine function (viz. hormone-secretory function) where they are known to secrete calcitriol, prostaglandin, erythropoietin, and thrombopoietin. The hematopoietic properties of erythropoietin and thrombopoietin help in the formation of cellular components of blood namely erythrocytes (red blood cells, RBCs) and thrombocytes (blood platelets) respectively. Kidneys play a crucial role in regulating the blood pressure through Renin-Angiotensin system that modulates constriction (contraction) and dilation (expansion) of the blood vessels (arteries). Kidneys activate Vitamin D to form calcitriol, which aids the intestine in absorbing calcium into the blood.
Overall, these bean shaped organs constitute to be a part of the renal/excretory system that comprises of the (i) pair of kidneys, (ii) ureters, (iii) urinary bladders and (iv) urethra. Anatomically, the kidneys receive the renal artery and the renal vein near the hilum region depression on their medial borders. The kidneys are compound tubular glands connected through the connective tissue. Histologically (figure 1), the kidney is composed of outer cortex, and inner medulla, wherein the medulla comprises of the parenchyma consisting of uriniferous tubules (column and pyramids) and lastly the renal sinus.
Meaning of scientific terms
1. Metabolism: Chemical reactions occurring in living cells that lead to the generation of energy essential to perform several life processes
2. Homeostasis: Refers to the healthy state maintained by the continuous adjustment of pathways/processes occurring inside the body
3. Hematopoietic: Involved in the formation of the blood cells
4. Anatomy: Science dealing with the structure of internal organs of the human body
5. Histology: Science involving study of microscopic structure of tissues
References
1. Chaurasia, B. D. (2004). Human anatomy (p. 53). CBS Publisher.
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About the author:
A researcher by heart, writer by the soul.
Anomitra is a post-doctoral research fellow at Indian Institute of Technology Bombay (IITB), Mumbai. Earlier, she obtained her PhD in Bioprocess Technology from Institute of Chemical Technology, Mumbai. She is a budding scientist who is exploring the art of creative writing and science blogging.