Homeostasis

What is homeostasis?

The maintenance of a relatively stable internal environment despite changes inside or outside the body.

Why is homeostasis important?

Cells and enzymes function best within suitable conditions, so maintaining stable internal conditions allows the body to function properly.

What is a stimulus?

A change in the internal or external environment that can be detected by the body.

What is a receptor?

A specialised cell or structure that detects a stimulus.

What is a coordinator/control centre?

A part of the body that processes information and coordinates a response, such as the brain or an endocrine gland.

What is an effector?

A muscle or gland that carries out a response to a stimulus.

What is a response?

The action produced by an effector in reaction to a stimulus.

What is the basic homeostatic pathway?

Stimulus → receptor → coordinator/control centre → effector → response.

What is negative feedback?

A feedback mechanism where the response reverses or reduces the original change, bringing a condition back toward its normal range.

Give an example of negative feedback.

Sweating when body temperature becomes too high.

What is positive feedback?

A feedback mechanism where the response amplifies or increases the original change.

Give an example of positive feedback.

Childbirth contractions becoming stronger until the baby is born.

Negative vs positive feedback

Negative feedback reduces the original change; positive feedback increases or amplifies the original change.

What is thermoregulation?

The maintenance of a relatively stable body temperature.

What happens when the body gets too hot?

Sweating increases and blood vessels near the skin dilate, increasing heat loss.

What is sweating?

The production of sweat by sweat glands. Evaporation of sweat removes thermal energy and cools the body.

What is vasodilation?

The widening of blood vessels near the skin, increasing blood flow to the surface and increasing heat loss.

What happens when the body gets too cold?

Shivering increases and blood vessels near the skin constrict, reducing heat loss.

What is vasoconstriction?

The narrowing of blood vessels near the skin, reducing blood flow to the surface and conserving heat.

How does shivering warm the body?

Rapid involuntary muscle contractions generate heat.

What is blood glucose homeostasis?

The regulation of blood glucose concentration within an appropriate range.

Which organ produces insulin and glucagon?

The pancreas.

What is insulin?

A hormone released when blood glucose is high that helps lower blood glucose by promoting glucose uptake and storage.

What happens when blood glucose is too high?

The pancreas releases insulin, causing cells to take up glucose and promoting storage of glucose, which lowers blood glucose.

What is glucagon?

A hormone released when blood glucose is low that helps increase blood glucose.

What happens when blood glucose is too low?

The pancreas releases glucagon, which promotes the breakdown of stored glycogen into glucose, increasing blood glucose.

Insulin vs glucagon

Insulin lowers blood glucose; glucagon raises blood glucose.

What is glycogen?

A storage form of glucose, mainly stored in the liver and muscles.

What is osmoregulation?

The regulation of water and dissolved substances in the body.

What organs are especially important for water balance?

The kidneys.

What do the kidneys do?

They filter blood and regulate water, salts and waste products, producing urine.

What is ADH?

Antidiuretic hormone, which increases water reabsorption by the kidneys when the body needs to conserve water.

What happens when the body is dehydrated?

More ADH is released, causing the kidneys to reabsorb more water and produce a smaller volume of concentrated urine.

What happens when the body has excess water?

Less ADH is released, so less water is reabsorbed and a larger volume of dilute urine is produced.

What is the nervous system?

A communication system that uses electrical signals and neurotransmitters to produce rapid responses.

What is the endocrine system?

A communication system that uses hormones carried through the blood.

Nervous vs endocrine system

The nervous system usually produces faster, shorter-lasting responses; the endocrine system usually produces slower, longer-lasting responses.

What are hormones?

Chemical messengers released by glands and transported through the blood.

What are the three main parts of a homeostatic control system?

Receptor, control centre/coordinator and effector.

Why is negative feedback important in homeostasis?

It prevents conditions from changing too far from their normal range.