We have two kidneys located closer to our back on either side of the spine.
Located behind the liver.
Structure
Divided into two main components: Renal Cortex and Renal Medulla.
The Nephron: The Functional Unit of the Kidney
Key Roles
Waste excretion
Maintenance of water level in the blood
Structure
Each kidney contains approximately 1 million nephrons.
Composed of a long tubule passing from the cortex into the medulla and back.
Blood Flow in the Nephron
Afferent Arteriole
Brings blood into the nephron.
Glomerulus
High pressure, porous capillary bed where filtration begins.
Surrounded by podocytes that filter the blood.
Bowman's Capsule and Space
Collects the filtrate from the glomerulus.
Filtrate includes water, small ions, glucose, and amino acids; excludes large proteins and red blood cells.
Components of the Nephron
Proximal Tubule
Function
Reabsorption of glucose, sodium, amino acids, and some water.
Utilizes active transport (ATP) to pump substances back into the blood.
Loop of Henle
Structure
Descending limb: permeable only to water.
Ascending limb: actively pumps out salts (Na+, K+, Cl-).
Function
Creates a hypertonic medulla to facilitate water reabsorption due to osmotic gradients.
Distal Convoluted Tubule
Function
Further reabsorption of calcium, sodium, and other ions.
Slight reabsorption of water.
Collecting Duct
Function
Collects the processed filtrate (now closer to urine) from multiple nephrons.
Further water reabsorption occurs due to antidiuretic hormone (ADH) making the duct walls more permeable.
Conclusion
The nephron is essential in refining the filtrate through reabsorption at various stages to ensure water and useful substances are conserved, while waste products are excreted as urine.
Key process occurs in Loop of Henle, creating an efficient system of reabsorption using energy and osmotic principles.
Final filtrate (urine) travels through the ureters to the bladder for excretion.