D3.3 HL Role of the Kidney [IB Biology HL]

Understanding Homeostasis and the Role of the Kidney

Overview of Kidney Functions

• The kidneys play a crucial role in homeostasis, primarily through osmoregulation and excretion.

• Osmoregulation involves controlling osmotic concentration, which is vital for maintaining water balance and pressure within cells.

Excretion of Toxic Waste

• The kidneys are responsible for removing toxic metabolic byproducts, such as urea from protein digestion.

Anatomy of Nephrons

• Each kidney contains approximately one million nephrons, the functional filtering units that process blood.

• Blood enters the nephron via the afferent arteriole and exits through the efferent arteriole; this structure includes a glomerulus where filtration occurs.

Filtration Process in Nephrons

Ultra Filtration Mechanism

• High pressure in the glomerulus forces small molecules out into Bowman's capsule during ultrafiltration; larger molecules remain in circulation.

Selective Reabsorption

• After ultrafiltration, selective reabsorption occurs in the proximal convoluted tubule to reclaim essential substances like glucose and ions back into the bloodstream.

Structure and Function of Nephron Components

Regions of the Kidney

• The kidney consists of three main regions: cortex (outer), medulla (middle), and renal pelvis (inner).

Loop of Henle's Role

• The Loop of Henle has descending and ascending limbs with distinct functions: water reabsorption occurs in the descending limb while sodium ions are actively transported out in the ascending limb.

Hormonal Regulation of Water Reabsorption

Anti-Diuretic Hormone (ADH)

• ADH regulates water reabsorption at the collecting duct by increasing its permeability to water based on osmotic concentration monitored by the hypothalamus.

Response to Hydration Levels

• In dehydration, ADH secretion increases leading to more aquaporins being inserted into cell membranes, allowing greater water retention. Conversely, low solute concentrations inhibit ADH release.

Blood Flow Regulation to Kidneys

Variability Based on Activity Levels

• Blood flow to organs varies with activity levels; during sleep, blood flow to kidneys decreases while it increases during rest or exercise.

Impact on Urine Production

• Increased blood volume through kidneys leads to higher urine production; conversely, reduced blood flow results in less urine output.