Muscle Types and Renal Function

Red Muscle Fibers
- Smaller size compared to white muscle fibers.
- Contain many mitochondria, blood vessels, and lipids.
- Classified as slow-twitch fibers; capable of sustained activities for prolonged periods.
- Rely heavily on aerobic respiration (uses oxygen).
- Examples include the breast muscles of ducks and geese, which require endurance for migratory flights.
White Muscle Fibers
- Larger size than red fibers and contain abundant glycogen.
- Classified as fast-twitch fibers; adapted for quick, short bursts of activity.
- More efficient in anaerobic respiration, allowing them to function with less oxygen.
- Associated with rapid, brief movements, such as those of a chicken.

Calcium's Role: Essential for muscle contraction and the release of acetylcholine at the neuromuscular junction.
Milk Fever in Cows:
- Occurs when calcium levels in the blood drop, leading to muscle weakness and paralysis.
- Symptoms include an S-shaped neck, inability to stand, and potential coma.
- Treatment includes administering calcium via mouth or direct injection.

Kidneys:
- Latin origin renal, meaning 'kidney'.
- Maintain osmolarity (~300 milliosmolar) for acid-base balance and waste elimination.
- Regulate water retention, especially in terrestrial birds and mammals.
Endocrine Functions:
- Produce erythropoietin, stimulating red blood cell production in the bone marrow.
- Regulate antidiuretic hormone (ADH), which decreases urine output and promotes water reabsorption.

Erythropoietin:
- Promotes the production of red blood cells, crucial for oxygen transport.
- Acknowledged for misuse in sports as a performance enhancer by increasing red blood cell count.
- Excessive erythropoietin can lead to complications, such as blood clotting and risk of death.
ADH and Aldosterone:
- ADH: Released from the posterior pituitary, increases water reabsorption in kidneys.
- Aldosterone: Retains sodium and regulates potassium levels, essential for muscle function.

Kidneys are located retroperitoneally, outside the peritoneal cavity, and are responsible for filtering blood.
They receive 20-25% of the cardiac output and consume a significant amount of oxygen (77-20% of total bodily oxygen).
Blood Flow Dynamics:
- The renal cortex receives around 80% of arterial blood, while 15% supplies the medullary region.

Kidneys play a vital role in maintaining homeostasis by regulating blood pressure, red blood cell production, and waste removal.
Kidney transplantation is feasible due to the organ's functionality, wherein one healthy kidney can suffice for survival, emphasizing their efficiency and importance in the body.