Overview
Organ systems do not work alone. Maintaining homeostasis requires multiple systems collaborating on each regulated variable.
Water balance
The cardiovascular, lymphatic, and urinary systems work together:
- The cardiovascular and lymphatic systems transport fluids and help sense solute and water levels and regulate pressure.
- The urinary system makes dilute urine when water is plentiful and concentrated urine when conserving water.
- The digestive system adjusts how much water it absorbs.
Temperature regulation
Several systems coordinate thermoregulation:
- When hot: skin blood vessels dilate, sweat evaporates to cool, and rapid breathing helps shed heat.
- When cold: blood vessels constrict, muscles contract and relax rapidly (shivering) to generate heat, and hair stands up to trap insulating air.
Blood glucose homeostasis
- Endocrine system: pancreas releases glucagon (low glucose) or insulin (high glucose).
- Digestive system/liver: performs glycogenolysis, glycogenesis, and gluconeogenesis.
- Nervous system: brain and digestive receptors trigger hunger to prompt eating.
- Circulatory system: transports glucose and hormones to cells.
Blood calcium levels
The parathyroid gland coordinates three effector systems through negative feedback:
- Skeletal system: osteoclasts resorb bone to release calcium.
- Urinary system: kidneys reabsorb calcium.
- Digestive system: the small intestine increases calcium absorption via active vitamin D.
Cell population balance
The endocrine and immune systems regulate cell populations — hormones affect cell survival and apoptosis, while immune cells identify and destroy aberrant cells.