Overview
This lecture covers the main concepts of excretion in humans, focusing on the organs involved, the structure and function of the kidney, and the processes that remove waste products from the body.
Excretion and Excretory Organs
- Excretion is the removal of toxic waste products of metabolism from the body.
- The main excretory organs in humans are:
- Lungs: remove carbon dioxide.
- Kidneys: filter blood to remove urea, excess water, and other waste.
- Liver: processes toxins and produces urea.
The Lungs and Excretion
- The lungs excrete carbon dioxide, which is a waste product of respiration.
- Carbon dioxide is transported from the body’s cells to the lungs via the bloodstream and is expelled during exhalation.
The Kidneys
- Kidneys filter the blood to remove excess water, urea, and other waste products.
- They help regulate the body’s water and salt balance, maintaining homeostasis.
- Waste products filtered by the kidneys are excreted as urine.
Structure of the Kidney
- Each kidney contains a large number of nephrons, which are the functional units responsible for filtration.
- The main parts of a kidney include:
- Cortex: outer region containing most of the nephrons.
- Medulla: inner region with structures involved in urine collection.
- Pelvis: central space where urine collects before moving to the ureter.
The Nephron
- Nephrons filter blood, remove waste, and produce urine.
- Each nephron consists of:
- Renal corpuscle: made up of the Bowman's capsule and the glomerulus, where filtration begins.
- Renal tubule: where selective reabsorption and further processing of filtrate occur.
Ultrafiltration
- Ultrafiltration takes place in the glomerulus, where high blood pressure forces water, ions, and small molecules into the Bowman's capsule.
- Large molecules, such as proteins and blood cells, remain in the bloodstream and do not pass into the filtrate.
Selective Reabsorption
- Useful substances like glucose, some salts, and water are reabsorbed from the renal tubule back into the blood.
- This process ensures that essential substances are not lost from the body.
- The remaining waste, including urea and excess water, forms urine, which is eventually excreted.
The Liver and Excretion
- The liver breaks down excess amino acids, producing urea as a waste product.
- Urea is transported in the blood to the kidneys for excretion.
- The liver also processes toxins and drugs, making them easier for the body to eliminate.
Key Terms & Definitions
- Excretion: removal of metabolic waste products from the body.
- Urea: a waste product formed in the liver from the breakdown of amino acids.
- Ultrafiltration: the process by which small molecules are filtered out of the blood in the glomerulus.
- Selective Reabsorption: the process where useful substances are reabsorbed from the renal tubule into the blood.
- Nephron: the functional unit of the kidney responsible for filtering blood and forming urine.
Action Items / Next Steps
- Review the structure and function of the nephron, including the renal corpuscle and renal tubule.
- Practice labeling diagrams of the kidney and nephron to reinforce understanding.
- Prepare examples of excretory products from each organ (lungs, kidneys, liver) for study and revision.
- Ensure understanding of the processes of ultrafiltration and selective reabsorption and their roles in excretion.