Getting and Using Nutrients Feedback Mechanisms A cycle of events in which information from one step controls or affects a previous step. Homeostasis-the maintenance of a stable internal environment in the body Getting and Using Nutrients Glucose is the primary food source

Getting and Using Nutrients Glucose is the primary food source Blood-glucose feedback mechanism Glucose molecules cannot enter most cells by osmosis Transport proteins-help move glucose molecules through the cell membrane See Figure 2 on Page 541

Maintaining Homeostasis Nervous System-senses internal and external environments Uses electrical impulses and chemical messengers to respond to senses Nervous System Feedback Nerves carry responses to environmental conditions Carried by electrical impulses and neurotransmitters

Endocrine System Endocrine System-collection of glands and groups of cells that produce chemical messengers called hormones Regulate many of the body’s important functions The body’s water level