Responses of Cells to Environmental Influences By Kari Edge

Objective Explain how blood glucose levels remain balanced with environmental influences.

Responses of Cells to Environmental Influences Mature cells in all tissues are constantly changing in response to metabolic or behavioral demands as well as to injury or infection from environmental influences. Two examples of environmental inputs that cells respond to are glucose and oxygen.

Blood Glucose Levels Insulin is produced by the beta cells in the islets of Langerhans and it reduces the level of blood glucose. Glucagon is produced by the alpha cells in the islets and it increases the blood glucose level. -Blood glucose levels are controlled by insulin and glucagon

Blood Glucose Level con’t. The availability of glucose for cellular metabolism is done by the adjustment of insulin and glucagon concentration in the blood. These are more or less triggered by eating and not eating. Eating causes blood glucose levels to rise above normal, therefore stimulating the pancreatic B-cells to respond by releasing insulin into the blood.

Blood Glucose Level con’t. Insulin then circulates in the blood and binds to insulin receptors on muscle cells and adipocytes. The insulin receptors [receptor tyrosine kinase(RTK)] send signals through a pathway that leads to the activation of protein kinase B. The protein kinase B triggers the fusion of vesicles containing GLUT4 glucose transporters to the plasma membrane.

Blood Glucose Level con’t The increased number of GLUT4 on the cell surface increases glucose influx, thus lowering blood glucose levels. If blood glucose level falls below 5mM, pancreatic alpha cells start secreting glucagon. Then the glucagon receptors, usually in liver cells is coupled to the Gs proteins.

Blood Glucose Level con’t. This activates adenylyl cyclase, leading to the cAMP-mediated cascade that inhibits glycogen synthesis and promotes glycogenolysis. Liver cells can then convert the glucose 1-phosphate which is produced in glycogenolysis, therefore raising the blood glucose level back to normal.

Blood Glucose Level Diagram ).

Diabetes mellitus Results from a deficiency in the amount of insulin released from the pancreas. Type I diabetes is caused by an autoimmune process that destroys the insulin producing B-cells in the pancreas. Type II diabetes is the most common, however it’s cause is still not well understood.

Summary When you eat food, insulin is the natural hormone made in the pancreas that helps the sugar enter your cells, where it is used for energy. When someone's body does not produce enough insulin or use the insulin properly they have diabetes. %20Type1_Diabetes_animated/type1%20diabetes_animated/anatomy.h tml