Topic 3 - Homeostasis

What is homeostasis?

The maintenance of stable and constant conditions in the body’s internal environment (interne omgewing) around a set point.

Why do cells matter in homeostasis?

You are made of cells

What is the internal environment?

The fluid surrounding cells — includes interstitial fluid + blood plasma.

What percentage of the body is water?

60% of the body is fluid.

How is extracellular fluid divided?

1/3 of total body water is extracellular fluid

What is interstitial fluid?

The fluid directly surrounding cells within tissues and organs.

What is blood plasma?

The fluid portion of blood — the “interstitial fluid” of bloodstream cells.

How do interstitial fluid and plasma exchange substances?

Through capillaries

Why is the internal environment called a buffer zone?

It protects cells from fluctuations in the external environment (temperature

What variables must be regulated for homeostasis?

Temperature

What is a set point?

The normal target value a variable is maintained around (e.g.

Why is homeostasis dynamic?

Because the external environment is constantly changing and the body must constantly adjust to maintain stability.

What two processes are required to maintain homeostasis?

Communication and regulation (control mechanisms).

What is biological communication?

Chemical signals

What is regulation or control in homeostasis?

Feedback mechanisms to keep variables near their setpoint.

What is local communication?

Cells communicate with nearby cells using autocrine and paracrine signaling.

What is autocrine signaling?

A cell releases a chemical messenger that acts on itself.

What is paracrine signaling?

A cell releases a chemical messenger that acts on neighboring cells in the same tissue.

What is local control?

A change in a tissue is sensed by nearby cells which respond locally to correct it.

Example of local chemical messengers?

Eicosanoids such as prostaglandins and thromboxanes that mediate inflammation.

What is long-distance communication?

Coordination between organs across the body using nervous

What is a reflex control pathway?

A long-distance loop including a sensor

What is a sensor in a reflex pathway?

A structure that detects changes in a regulated variable (e.g.

What is the integration center?

The part of the body (often brain or endocrine gland) that receives input and decides on a response.

What is an effector?

A cell

What is negative feedback?

A response that reverses or opposes the initial stimulus to return the variable to its set point.

Example of negative feedback?

Temperature regulation (cooling when too warm

What is positive feedback?

A response that reinforces the initial stimulus

Examples of positive feedback?

Blood clotting and childbirth (parturition).

Why is positive feedback rare?

Because it destabilizes the system and moves it away from homeostasis.

What is the nervous system's role in long-distance control?

Neurons release neurotransmitters to act on nearby cells (rapid and specific).

What is the endocrine system's role in long-distance control?

Endocrine glands release hormones into the blood to act on distant target organs (slow and widespread).

What is the neuroendocrine system?

A neuron releases a chemical messenger into the blood instead of onto another cell

Why does the body use two long-distance systems?

Because the nervous system is fast and specific

What are cytokines?

Small peptides that can act as autocrine

Why is homeostasis essential?

Because cells require stable conditions to survive—disruption leads to dysfunction or death.

What happens when homeostasis fails?

Illness