Describe how feedback mechanisms maintain homeostasis in the human body, using examples such as the regulation of body temperature and blood glucose, and identify factors that disrupt homeostasis (TEKS Biology, Reporting Category 4; stability and change; cause and effect).

What this topic is asking

The Biology TEKS ask you to describe how feedback mechanisms maintain homeostasis in the human body, with examples such as body temperature and blood glucose, and to identify what disrupts homeostasis. For STAAR Reporting Category 4 you need to explain the detect, respond, restore loop of negative feedback and apply it to a scenario. This is a stability and change and cause-and-effect topic that extends cellular homeostasis to the whole organism.

Homeostasis at the body level

This is the whole-organism version of the cellular homeostasis covered in homeostasis and cellular regulation. At the body level, organ systems (especially the nervous and endocrine systems) coordinate the responses.

Negative feedback: detect, respond, restore

This detect-respond-restore loop is the single most useful idea for this topic. Almost any homeostasis question can be answered by identifying the change, the response that opposes it, and the return to normal.

Two key examples

Body temperature. Normal human body temperature is about 37 degrees Celsius.

• If the body gets too hot, it sweats (evaporation cools the skin) and blood vessels near the skin widen to lose heat, bringing the temperature down.
• If the body gets too cold, it shivers (muscle activity generates heat) and skin blood vessels narrow to conserve heat, bringing the temperature up.

Blood glucose. The body keeps blood glucose within a narrow range.

• After a meal, blood glucose rises; the body releases insulin, which makes cells take up glucose and the liver store it, lowering glucose back toward normal.
• Between meals, blood glucose falls; the body releases glucagon, which makes the liver release stored glucose, raising glucose back toward normal.

Both examples are negative feedback: the response always opposes the change.

When homeostasis is disrupted

Homeostasis can be disrupted by factors such as disease or infection (for example, a pathogen or a condition like diabetes, where blood glucose regulation fails), injury, genetic disorders, and extreme environmental conditions (very high or low temperature). When a feedback mechanism cannot keep a condition in range, the body's cells and enzymes are affected, which can cause illness. STAAR often frames disruption questions around a condition (such as diabetes) or an extreme situation and asks what happens or how the body tries to respond.

Try this

Q1. Describe the three steps of a negative feedback loop. [2]

• Cue. A change is detected; the body responds in a way that opposes the change; the condition is restored toward its set point.

Q2. Explain how the body responds when it gets too hot. [2]

• Cue. It sweats (evaporation cools the skin) and widens skin blood vessels to lose heat, lowering the temperature back toward normal.