Overview
This lecture introduces the kidneys, covering their structure, main functions, and their critical role in filtering blood and maintaining homeostasis.
Kidney Anatomy & Blood Flow
- Each kidney can hold about 22% of the body's blood at any time.
- About 1.1 liters of blood flow through the kidneys per minute, circulating all blood every 5 minutes.
- Blood enters the kidney via the renal artery and exits through the renal vein.
- Urine exits the kidney through the ureter.
Main Kidney Functions
- The kidneys regulate blood pH, osmolality (solute concentration), and waste removal.
- Two main functions: filtration (removing waste and some useful molecules from blood) and collection (retaining important substances, excreting waste).
- The smallest functional unit of the kidney is the nephron, which performs both filtration and collection.
Kidney Microanatomy
- The renal cortex is the outer shell of the kidney, where part of the nephron is located.
- The renal medulla is the inner region, also containing nephron segments.
- The nephron transitions between cortex and medulla, influencing what gets reabsorbed or excreted.
- The renal calyx (plural: calyces) is the first point where urine collects.
- Multiple calyces drain into the renal pelvis, the central collecting region.
- Urine flows from the renal pelvis into the ureter, which leads to the bladder.
Kidney Hilum
- The renal hilum is the area where the renal artery, vein, and ureter exit the kidney.
Purpose: Homeostasis
- Kidneys maintain homeostasis (stable internal environment) in the body.
- They regulate blood pH by controlling hydrogen ions.
- Kidneys regulate blood pressure by adjusting salt (sodium and chloride) excretion.
- They maintain proper osmolality and remove waste products, mainly urea.
Key Terms & Definitions
- Renal artery — Blood vessel that brings blood to the kidney.
- Renal vein — Vessel carrying filtered blood away from the kidney.
- Ureter — Tube carrying urine from the kidney to the bladder.
- Nephron — Smallest functional unit of the kidney, responsible for filtration and collection.
- Renal cortex — Outer layer of the kidney.
- Renal medulla — Inner region of the kidney.
- Renal calyx (calyces) — First area where urine collects in the kidney.
- Renal pelvis — Central collecting area for urine in the kidney.
- Renal hilum — Region where vessels and ureter exit the kidney.
- Homeostasis — Maintenance of a stable internal environment.
Action Items / Next Steps
- Review detailed nephron structure and function in the next lecture.