The Kidney is Crucial In Osmoregulation and Excretion
- The kidney filters out about 20% of water and solutes from blood plasma before selectively absorbing substances the body requires.
- This makes it an organ crucial in both osmoregulation and excretion for the body to maintain homeostasis.
Osmoregulation prevents osmotic imbalances, while excretion eliminates harmful substances.
Osmoregulation Is How The Kidney Maintains Balance
Osmoregulation
Osmoregulation is the process of maintaining the balance of water and solutes in the body.
- Osmoregulation ensures the osmotic concentration of blood remains stable, around 300 milliosmoles per litre (mOsm/L).
- The kidney achieves this by adjusting urine concentration.
How does the structure of the nephron reflect evolutionary adaptations in desert animals?
Excretion Removes Metabolic Waste
Excretion
Excretion is the removal of metabolic waste products.
Urea and Other Waste Products
- Urea is a nitrogenous waste product formed from the breakdown of amino acids in the liver.
- Urea, along with excess ions, drugs, and pigments, is filtered out in the glomerulus and excreted in urine.
Urochrome, a pigment from hemoglobin breakdown, gives urine its yellow color.
The Kidney Filters Blood and Maintains Homeostasis
- The kidney filters blood, reabsorbs essential substances, and removes waste.
- Its functional unit is the nephron, which consists of several specialized parts:
The Nephron Is the Kidney’s Functional Unit
1. Glomerulus and Bowman's Capsule
- Ultrafiltration occurs here.
- High pressure forces water, ions, glucose, and urea out of the blood into the Bowman's capsule.
- Large molecules like proteins remain in the blood.
The glomerulus acts like a sieve, allowing small molecules to pass while retaining larger ones.
2. Proximal Convoluted Tubule (PCT)
- Selective reabsorption happens here.
- Essential substances like glucose, amino acids, and most water are reabsorbed into the blood.
Microvilli in the PCT increase surface area for reabsorption, making the process highly efficient.
3. Loop of Henle
- This structure creates a concentration gradient in the kidney medulla.
- Descending limb: Permeable to water, which is reabsorbed into the medulla.
- Ascending limb: Impermeable to water, actively transports sodium ions into the medulla, increasing its osmotic concentration.
Think of the Loop of Henle as a two-way street: water exits on the way down, and salts are pumped out on the way up.
4. Distal Convoluted Tubule (DCT) and Collecting Duct
- Fine-tuning of water and ion reabsorption occurs here, regulated by hormones like aldosterone and antidiuretic hormone (ADH).
- The collecting duct adjusts urine concentration based on the body's hydration status.
- Don't confuse the roles of the descending and ascending limbs of the Loop of Henle.
- Only the descending limb is permeable to water.
The kidney also excretes excess ions, drugs, and pigments absorbed from food.
Self reviewWhat is the primary nitrogenous waste product excreted by the kidneys?
