Maintaining an Internal Balance Homeostasis Maintaining an Internal Balance

Homeostasis The property of a system, either open or closed, that regulates its internal environment so as to maintain a stable, constant condition. Multiple dynamic equilibrium adjustment and regulation mechanisms make homeostasis possible. Source: Wikipedia

Blood Glucose – An Example Glucose is the simple sugar known as “blood sugar” Glucose is required for brain function – the brain cannot use any other energy source A healthy body maintains a blood sugar level of between 80 mg/dL and 110 mg/dL (slightly higher right after meals)

The Role of Hormones When blood glucose levels are low, the hormone glucagon stimulates the conversion of glycogen in the liver to glucose Glucagon is a peptide hormone made of 29 amino acids. It is produced in the alpha cells of the (α-cells) of the islets of Langerhans, which are located in the pancreas.

The Role of Hormones When blood glucose levels are high, the hormone insulin stimulates the conversion of glucose to stored glycogen in the liver. Insulin is a peptide hormone made of 51 amino acids. It is produced in the beta cells of the (β-cells) of the islets of Langerhans, which are located in the pancreas.

Type I Diabetes Autoimmune disease destroys the beta cells of the pancreas Diabetic is dependent on exogenous insulin There is currently no cure, though there many approaches under research In North America, 5 – 10% of diabetics are Type I

Type II Diabetes A metabolic disorder due to insulin resistance (the cells are insensitive to the insulin that is present) Onset of disease can be postponed by proper nutrition and exercise 90 – 95% of North American diabetics are Type II. 20% of the population over age 60 are Type II

Blood Calcium: Example #2 Ca2+ ion is essential to organisms. It is functions include: A component of bone Neurotransmission and muscle contraction Fertilization As a cofactor in processes such as blood clotting

Calcium Homeostasis When blood calcium levels are low, the hormone parathyroid hormone, produced in the parathyroid glands, promotes absorption of calcium in the intestine conservation of calcium by the kidneys release of calcium from bone tissue

Calcium Homeostasis When blood calcium levels are high, the hormone calcitonin, produced in the thyroid gland, promotes elimination of calcium by the kidneys storage of calcium in bone tissue