Biology on Osmosis and Homeostasis

Water movement in cells occurs via osmosis, balancing concentration inside and outside the cell.
Imbalanced water concentration can lead to cell swelling and bursting or shrinking and loss of function.

Osmoregulation maintains osmotic potential by controlling water and salt concentrations within narrow limits.
Land-dwelling animals must conserve water and consume water directly.
Tissue fluid surrounding mammalian cells originates from blood capillaries.

Kidneys are the primary organs for homeostatic control of water balance in mammals.
The liver also contributes to homeostasis, including the breakdown of excess amino acids and removal of toxins.

The liver performs around 500 functions, crucial for homeostasis.
Deamination occurs in the liver where excess amino acids are processed by hepatocytes.
The amino group from amino acids is converted into ammonia, then urea, less toxic for kidney excretion.
The ornithine cycle facilitates the conversion of ammonia into urea.

Mammalian osmoregulation is primarily conducted by the kidneys, producing hypertonic urine to conserve water.
Kidneys are dark reddish-brown organs located in the abdominal cavity, protected by fat.

Control water potential of blood plasma.
Remove urea and substances affecting water balance.
Blood plasma passing through kidneys is filtered, creating urine stored in the bladder.

Kidneys serve both excretion (urea removal) and osmoregulation functions.
Approximately 120 cm³ of blood passes through kidneys per minute; all blood is filtered roughly every hour.
Daily filtration is about 180 dm³.

Kidneys consist of nephrons, microscopic tubules measuring 2-4 cm long, with around 1.5 million nephrons per kidney.
Main nephron functions include:
- Ultrafiltration
- Selective reabsorption
- Tubular secretion
Two main types of nephrons:
- Cortical Nephrons: Predominantly in the renal cortex with short loops of Henle; about 85% of human nephrons.
- Juxtamedullary Nephrons: Have long loops of Henle penetrating the medulla; efficient in producing concentrated urine.