Homeostasis & Negative Feedback – Lecture Review

25 question-and-answer flashcards covering key definitions, ranges, mechanisms, and examples of homeostasis and negative feedback from the lecture.

What is the definition of homeostasis in human physiology?

The process that maintains critical body variables within an acceptable range, creating a dynamic equilibrium.

Which word parts form “homeostasis” and what do they mean?

Homeo = similar; stasis = state, indicating a ‘similar’ rather than ‘exactly the same’ state.

Give the normal body-fluid pH range that homeostasis tries to maintain.

Approximately 7.38 – 7.42 (often rounded to 7.4).

What is the typical acceptable resting heart-rate range for most adults?

Roughly 60–80 beats per minute (some clinicians extend to 60–100 bpm).

State the commonly cited ‘normal’ systemic blood-pressure value and what each number represents.

120/80 mm Hg; 120 mm Hg is systolic (ventricular contraction) and 80 mm Hg is diastolic (ventricular relaxation).

List the acceptable fasting blood-glucose range in mg/dL.

About 75–95 mg dL⁻¹.

What core body-temperature value is often quoted as ‘normal,’ and its Celsius equivalent?

98.6 °F, which equals 37 °C.

Describe a ‘dynamic equilibrium.’

A balanced state that fluctuates up and down within limits rather than remaining absolutely constant.

What general outcome occurs when the body drifts outside of homeostatic ranges?

Illness or, in extreme cases, death.

Which regulatory process—negative or positive feedback—maintains homeostasis?

Negative feedback.

Why is negative feedback called “negative”?

Because the body’s response moves the variable in the opposite direction of the original deviation, reversing the change.

Using blood glucose as an example, explain negative feedback when glucose falls to 60 mg/dL.

Low glucose is sensed; the body responds (e.g., via glucagon release) to raise glucose back into the 75–95 mg/dL range.

Using blood glucose as an example, explain negative feedback when glucose rises to 135 mg/dL.

High glucose triggers insulin release, promoting glucose uptake into cells, lowering blood glucose back to the acceptable range.

Which hormone is chiefly responsible for lowering elevated blood-glucose levels?

Insulin.

What two body responses exemplify negative feedback control of core temperature?

Sweating to cool an elevated temperature and shivering to warm a lowered temperature.

Name the three common components found in every negative-feedback loop.

Input signal, integrating (control) center, and output signal.

Differentiate systemic (long-distance) versus local negative-feedback control.

Systemic uses the nervous/endocrine systems to act body-wide; local acts at the site of disturbance without central involvement.

Identify the typical integrating centers for systemic negative feedback.

The nervous system (e.g., brain, hypothalamus) or endocrine glands (e.g., pituitary, pancreas).

List the six expanded elements of a systemic negative-feedback loop.

Stimulus → Sensor → Input signal → Integrating center → Output signal → Target organ → Response.

Define hypoxia.

A lower-than-acceptable oxygen concentration at body tissues.

In local hypoxia of the big toe, which gas is released by endothelial cells to cause vasodilation?

Nitric oxide (NO).

How does vasodilation increase oxygen delivery during local hypoxia?

It enlarges the vessel’s lumen, increasing blood flow and thus oxygen supply to the affected tissue.

Where in the brain is the primary ‘thermostat’ that integrates body-temperature signals?

The hypothalamus.

What effect does shivering have on body temperature, and why is this negative feedback?

Shivering produces heat, raising low body temperature back to the acceptable range; the response opposes the initial drop.

Why does the lecturer emphasize the term is not “homoasis”?

Because ‘homo’ (same) would imply an unchanging state, whereas homeo-stasis means maintaining a similar but variable range.