Body Systems and Homeostasis October 27th, 2008

Levels of Organization The body has different levels of organization, from simple (1) to more complex (4). 1 2 3 4 Cells Tissue Organ Organ System

Homeostasis The organ systems must maintain homeostasis. Homeostasis is when organisms keep the environment inside their body stable, despite changes in the external environment. Homeostasis in the body is maintained by feedback loops.

A Nonliving Example The thermostat in your house (negative feedback loop) Temperature set to 75o Thermostat senses temperature change and switches on heating system Room temperature decreases Room temperature increases Thermostat senses temperature change and switches off heating system

Feedback Loops Negative Feedback Loop – reverse direction of change back to set point. Sweating when hot Shivering when cold Positive Feedback Loop – change continues away from set point. Fever

Positive Feedback or Negative Feedback

Body Systems There are 11 distinct organ systems in your body (see pages 892 & 893 in your text).

Cardiovascular System Structures include: Nose Trachea Lungs Heart Blood vessels Blood Function: Provides oxygen needed for cellular respiration and removes excess carbon dioxide from the body. Brings oxygen, nutrients, and hormones to cells; fights infection; removes cell waste; helps to regulate body temperature.

Nervous System Structures include: Brain Spinal cord Peripheral nerves Function: Recognizes and coordinates the body’s response to changes in its internal and external environment.

Endocrine System Structures include: Hypothalamus Pituitary Thyroid Parathyroid Adrenals Pancreas Ovaries (in females) Testes (in males) Function: Controls growth, development, and metabolism, and maintains homeostasis.