The nephron is the functional unit of filtration in the kidney.
Key components of a nephron: Bowman's capsule, glomerulus, proximal convoluted tubule, nephron loop (Loop of Henle), distal convoluted tubule, and collecting duct.
Nephrons are located in the renal pyramids, renal medulla, and renal cortex.
Kidney and Nephron Structure
Renal Cortex: Upper region of the kidney where initial filtration occurs.
Renal Medulla: Lower region where further processing of the filtrate occurs.
Renal Artery & Blood Supply: Branches into smaller vessels; blood enters the nephron through the glomerulus within the Bowman's capsule.
Filtration Process
Bowman's Capsule and Glomerulus:
Blood enters through renal artery into the glomerulus.
High pressure in the glomerulus forces fluid (plasma) into Bowman's capsule, initiating filtration.
About 20% of blood plasma is filtered; becomes "filtrate."
Reabsorption and Transport
Proximal Convoluted Tubule:
Close to Bowman's capsule.
Reabsorbs about two-thirds of filtered water and essential nutrients (sugars, vitamins) back into the blood.
Nephron Loop (Loop of Henle):
Descends into the renal medulla, which is highly salty.
Descending Limb: Water diffuses out into the blood due to osmosis.
Ascending Limb: Impermeable to water; actively transports sodium and chloride out, contributing to the medulla's high salt concentration.
Distal Convoluted Tubule:
Water Reabsorption: Regulated by the presence of ADH; water can be reabsorbed back into blood.
Collecting Duct
Collects urine from several nephrons.
Water reabsorption also regulated by ADH.
Urine travels from the collecting duct to the ureter, then to the bladder for excretion.
Hormonal Regulation
Antidiuretic Hormone (ADH):
Released by the pituitary gland.
Increases permeability of distal convoluted tubule and collecting duct to water when dehydrated, conserving water in the body.
Absence of ADH results in less water reabsorption, leading to dilute urine.
Summary
Blood enters the nephron, is filtered in the glomerulus, travels through the nephron where reabsorption and secretion regulate the composition and volume of urine.
ADH plays a critical role in water conservation through hormonal regulation of nephron reabsorption processes.
Understanding nephron function is crucial for grasping kidney physiology and the body's fluid balance management.
Recap
Filtration occurs at Bowman's capsule.
Reabsorption of water and nutrients is mainly in the proximal convoluted tubule.
Descending limb facilitates osmosis due to medulla’s saltiness; ascending limb pumps out Na+ and Cl-.
ADH determines the extent of water reabsorption in distal convoluted tubule and collecting duct.
Considerations
The nephron's system is complex and includes additional regulatory hormones like angiotensin and aldosterone. This lecture provides a foundational understanding.