Biology Chapter: Kidney Function and Filtration

The functional unit of the kidney, responsible for filtering blood and producing urine.

A network of capillaries within Bowman's capsule that filters blood.

A cup-shaped structure surrounding the glomerulus, collecting the filtered fluid from blood.

The process of removing waste products and excess fluids from the blood and into the nephron.

The process of returning essential nutrients, water and electrolytes from the nephron back into the bloodstream.

The process of removing waste products and excess fluids from the nephron into the collecting duct.

A tube that collects urine from the nephron and transports it to the renal pelvis

A funnel-shaped structure that collects urine from the collecting ducts and transports it to the ureter.

The efferent arteriole is the blood vessel that carries blood away from the glomerulus, the filtering unit of the kidney.

Glomerular filtration is the first step in urine formation, where blood plasma is filtered from the glomerulus into Bowman's capsule.

The proximal convoluted tubule (PCT) is the first part of the renal tubule, where most of the filtered substances are reabsorbed back into the bloodstream.

Transepithelial transport is the movement of substances across the epithelial cells that line the renal tubule, allowing for reabsorption and secretion.

Active transport is the movement of substances across the cell membrane against their concentration gradient, requiring energy.

Sodium (Na+) is transported into the luminal cells against its concentration gradient using the Na+/K+ pump.

Glucose and amino acids are co-transported into luminal cells alongside sodium, using the energy of the sodium gradient created by the Na+/K+ pump.

The passive movement of water follows the osmotic gradient created by reabsorbed solutes, such as sodium, in the proximal tubule.

The active transport of ions, particularly sodium, creates the osmotic gradient that drives water reabsorption.

The loop of Henle, particularly in juxtamedullary nephrons, establishes a vertical osmotic gradient in the interstitial fluid, with higher concentration in the medulla. This gradient allows for regulated water reabsorption in the proximal convoluted tubule and collecting ducts.

Osmoreceptors in the hypothalamus detect an increase in blood osmolarity, signaling dehydration.

ADH (antidiuretic hormone) binds to V2 receptors on the distal convoluted tubule (DCT) and collecting duct (CD).

ADH stimulates the insertion of aquaporin-2 (AQP-2) water channels into the luminal membrane of the DCT and CD.

Water diffuses into the cells of the DCT and CD via AQP-2 and then exiting into the bloodstream through AQP-3 or AQP-4.

The amount of ADH released determines the extent of AQP-2 insertion, controlling how much water is reabsorbed and the concentration of urine.

The descending limb of the loop of Henle is highly permeable to water due to the presence of aquaporin-1 channels, allowing water to move out of the tubule and into the surrounding interstitial fluid, increasing the concentration of solutes in the tubule.

The ascending limb of the loop of Henle is impermeable to water. However, it actively reabsorbs sodium, potassium, and chloride ions using the Na+/K+ ATPase pump and the NKCC2 transporter, creating a concentration gradient.

The countercurrent multiplication system is created by the opposing flow of fluid in the descending and ascending limbs of the loop of Henle. This flow pattern establishes a concentration gradient, allowing for efficient reabsorption of water and solutes.

The vasa recta, a network of blood vessels surrounding the loop of Henle, maintains the osmotic gradient by acting as a countercurrent exchanger. The blood in the vasa recta flows in the same direction as the fluid in the loop of Henle, allowing for selective reabsorption and preventing diffusion of solutes out of the medulla.

The distal convoluted tubule and collecting duct are the final segments of the nephron, where fine-tuning of urine concentration takes place under hormonal control. They reabsorb water and solutes according to hormonal regulation.

About 80% of filtered water is reabsorbed before reaching the distal convoluted tubule and collecting duct. The remaining 20% is regulated by hormones.

Vasopressin (Antidiuretic Hormone - ADH) is a hormone released by the posterior pituitary gland. It increases the permeability of the distal convoluted tubule and collecting duct to water, allowing for water reabsorption and concentrated urine.

ADH acts on the kidneys by binding to receptors on the cells of the distal convoluted tubule and collecting duct. This binding triggers a series of events that increase water permeability and allow for water reabsorption.

The loop of Henle is crucial for concentrating urine, but the urine isn't actually concentrated within the loop itself. It's the overall process that leads to concentrated urine.

Countercurrent flow in the loop of Henle creates the osmotic gradient, which is essential for water reabsorption and urine concentration.