Overview
This lecture covers the process of urine formation in the kidneys, including filtration, reabsorption, secretion, and factors affecting urine concentration.
Urine Formation Processes
- Filtration occurs in the glomerulus, where water and small solutes move from blood to nephron.
- Reabsorption primarily happens in the proximal convoluted tubule, retrieving water, glucose, amino acids, and ions back into the blood.
- Secretion involves the active transport of substances from blood into the nephron, aiding in removal of excess ions and wastes.
- The loop of Henle establishes a concentration gradient, allowing for water reabsorption in the collecting duct.
- The distal convoluted tubule fine-tunes ion balance and pH of urine, influenced by hormones.
Regulation of Urine Concentration
- Antidiuretic hormone (ADH) increases water reabsorption in the collecting duct, reducing urine volume.
- Aldosterone promotes sodium reabsorption and potassium secretion in the distal tubule.
- Atrial natriuretic peptide (ANP) inhibits sodium reabsorption, increasing urine output.
Micturition (Urination)
- Micturition reflex involves stretch receptors in the bladder wall signaling the spinal cord.
- Parasympathetic stimulation causes bladder contraction and relaxation of the internal urethral sphincter.
- Conscious control allows voluntary relaxation of the external urethral sphincter.
Key Terms & Definitions
- Glomerulus — Capillary network in the nephron where filtration occurs.
- Proximal Convoluted Tubule (PCT) — Nephron segment responsible for reabsorbing most filtered substances.
- Loop of Henle — Nephron section that creates a medullary concentration gradient.
- Distal Convoluted Tubule (DCT) — Fine-tunes urine composition under hormonal control.
- Collecting Duct — Final site for water reabsorption and urine concentration.
- Antidiuretic Hormone (ADH) — Hormone that increases water reabsorption in the kidneys.
- Aldosterone — Hormone increasing sodium reabsorption in the distal nephron.
- Micturition — Process of expelling urine from the bladder.
Action Items / Next Steps
- Review the steps of urine formation and the impact of hormones.
- Study diagrams of nephron structure and urine flow.
- Complete assigned textbook readings on kidney function.