IB Sports, exercise and health science Topic A.1.2.1 Mechanisms and Processes Maintaining Homeostasis Revision Notes (SL/HL) | RevisionDojo

Homeostasis: Maintaining Internal Balance

Definition

Homeostasis

Homeostasis is the maintenance of a stable internal environment within an organism, ensuring optimal conditions for cellular processes.

Homeostasis is the self-regulating process that maintains a stable internal environment for optimal body function, despite changes in external or internal conditions.
It ensures that physiological variables such as temperature, pH, heart rate, and blood pressure remain within narrow limits.

Key Characteristics of Homeostasis

Self-regulating: The body constantly monitors and adjusts conditions.
Dynamic equilibrium: Conditions fluctuate within a narrow range rather than being completely static.
Essential for survival: Disruptions in homeostasis can lead to disease or dysfunction.

Common Mistake

A common misconception is that homeostasis keeps the body completely unchanging. In reality, it involves constant small adjustments that maintain stability.

Feedback Mechanisms

Hormone secretion is typically regulated by feedback mechanisms, ensuring that hormone levels are kept within a certain range.

Negative Feedback

Definition

Negative feedback

Negative feedback is a homeostatic mechanism in which a change in a physiological condition triggers a response that counteracts the initial change, maintaining balance.

In negative feedback, the output of a process inhibits its own production, helping to maintain homeostasis.

How Negative Feedback Works

A stimulus causes a change in the internal environment.
Receptors detect the change and send signals to the control center (often the brain).
The control center processes the information and signals an effector to reverse the change.
The effector restores the condition to its normal state, stopping the response.

Definition

Effector

A specialized cell or structure that detects changes in the internal or external environment and sends signals to the control center.

Definition

Effector

A structure (e.g., muscle or gland) that responds to signals from the control center to restore homeostasis.

Homeostatic Process	Stimulus (Change)	Response (Negative Feedback)
Body Temperature Regulation	Increase in body temperature	Sweating and vasodilation (heat loss)
Blood Glucose Control	High blood glucose	Insulin release → Lowers glucose
Blood Pressure Regulation	High blood pressure	Heart rate decreases, blood vessels dilate
Oxygen Levels in Blood	Low oxygen levels	Increased breathing rate to absorb more oxygen

Example

When thyroid hormone (T3 and T4) levels in the blood are low, the hypothalamus releases TRH (thyrotropin-releasing hormone), which stimulates the pituitary gland to release TSH (thyroid-stimulating hormone).
This stimulates the thyroid gland to produce more thyroid hormones.
Once thyroid hormone levels are restored to normal, negative feedback inhibits the release of TRH and TSH.

Positive Feedback

Definition

Positive feedback

Positive feedback is a physiological mechanism in which a change in a condition leads to an amplified response, moving further away from homeostasis.

Positive feedback amplifies the output of a process, making it more pronounced.

Process	Stimulus (Change)	Response (Positive Feedback)
Childbirth (Labor Contractions)	Pressure on cervix	Oxytocin release → Stronger contractions
Blood Clotting	Vessel injury	Platelets release chemicals → More clotting
Lactation (Milk Ejection Reflex)	Baby suckles	Oxytocin release → More milk production

Example

Oxytocin and childbirth:

During labor, the stretching of the cervix stimulates the release of oxytocin from the pituitary gland.
Oxytocin causes uterine contractions, which push the baby toward the cervix, causing further stretching and even more oxytocin release.
This process continues until the baby is delivered.

Common Mistake

A common misconception is that all feedback is negative feedback.

Key distinction:

Negative feedback = Stabilizes the body (homeostasis).
Positive feedback = Intensifies a process (not homeostasis).

Blood pH Regulation

Normal arterial blood pH range: 7.35–7.45.
Below 7.35 = acidosis; above 7.45 = alkalosis. Both disrupt enzyme function and oxygen transport.
Blood pH is driven primarily by CO₂: ↑CO₂ → ↑H⁺ in blood → ↓pH.
Monitored by: respiratory centre in the medulla oblongata + chemoreceptors (carotid bodies, aortic bodies, medulla).
Mechanism: ↓pH → medulla ↑ ventilation rate and depth → more CO₂ exhaled → H⁺ falls → pH normalised (negative feedback).

Regulation of the Heart: Intrinsic and Extrinsic Control

The regulation of heart function depends on both intrinsic and extrinsic mechanisms, ensuring that oxygenated blood reaches tissues efficiently.

Intrinsic Regulation

Intrinsic regulation occurs within the heart itself without external influence.
The heart has its own built-in pacemaker system that generates electrical impulses.
The conduction system of the heart consists of specialized autorhythmic cells that generate and spread electrical impulses:

Nice try, unfortunately this paywall isn't as easy to bypass as you think. Want to help devleop the site? Join the team at https://revisiondojo.com/join-us. exercitation voluptate cillum ullamco excepteur sint officia do tempor Lorem irure minim Lorem elit id voluptate reprehenderit voluptate laboris in nostrud qui non Lorem nostrud laborum culpa sit occaecat reprehenderit

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.

Duis aute irure dolor in reprehenderit

Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit.

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

Unlock the rest of this chapter with a free account