Homeostasis Flashcards

Homeostasis

  • The body's internal environment remains relatively constant within physiological limits.

  • Proper functioning of body cells depends on this equilibrium (internal balance).

  • Each body system contributes to the maintenance of homeostasis in some way.

Objectives

  • Outline the concept of homeostasis and state the role of negative feedback.

  • Outline the maintenance of homeostasis for selected factors in the body.

Maintenance of Homeostasis

  • Homeostatic mechanisms are controlled by the nervous system and the endocrine system.

  • The nervous system detects imbalances and sends messages in the form of nerve impulses to organs that can correct the imbalance (e.g., increase sweating to reduce body temperature).

  • The endocrine system corrects imbalances by secreting molecules, called hormones, into the bloodstream (e.g., insulin is secreted to reduce glucose levels in the blood).

Feedback Mechanisms

  • Cycle of events involves controlled conditions in the body being monitored and re-monitored.

  • Each monitored variable is termed a controlled condition.

  • Three basic components:

    • Receptor

    • Control center

    • Effector

Components of a Feedback Mechanism

1. Receptors

  • Detect changes in a controlled condition.

  • Send information to the control center.

  • Examples of controlled conditions that can fluctuate: pH, temperature, water levels, calcium, nutrient levels, oxygen and carbon dioxide levels, etc.

2. Control Center

  • Brain or specific organs.

  • Sets the range for a particular 'controlled condition'.

  • Evaluates input received from receptors and generates output commands (to correct the imbalance).

  • Output commands sent to target tissues (effectors) via nerve impulses or hormones.

3. Effectors

  • Receive output from the Control Center.

  • Produce a response that changes the controlled condition (corrects the imbalance).

  • Are either muscles (that contract) or glands (that produce a secretion).

Negative Feedback

  • Negative feedback occurs when a response to a stimulus reverses or eliminates the change in a controlled condition.

  • Many controlled conditions are regulated using negative feedback to maintain homeostasis.

  • Without the maintenance of homeostasis, the body cells and systems do not function properly, and disorders arise, for example:

    • hypertension (high blood pressure)

    • hyperglycaemia (high blood glucose levels)

    • acidosis/alkalosis (low or high blood pH levels)

Regulation of Blood Pressure

  • External or internal stimuli increase BP, and baroreceptors (pressure-sensitive receptors) detect higher BP.

  • Nerve impulses are sent to the brain for interpretation (control center).

  • Responses are sent via nerve impulse to the heart and blood vessels (effectors), which decrease heart rate and vasodilate the blood vessels.

  • BP drops, and homeostasis is restored.

  • The decrease in BP reverses and eliminates the original stimulus (hence negative feedback).

    • Body’s responses to a decrease in blood pressure below the normal range are to increase heart rate and constrict blood vessels.

Regulation of Blood Glucose

  • Fluctuations occur constantly throughout the body.

  • Rising blood glucose level stimulates insulin secretion by the pancreas.

  • Insulin stimulates glucose uptake by cells and glycogen formation in the liver.

  • Blood glucose falls to the normal range (about 90 mg/100 ml90 \text{ mg/100 ml}

  • Declining blood glucose level stimulates glucagon secretion by the pancreas.

  • Glucagon stimulates glycogen breakdown in the liver.

  • Blood glucose rises to the normal range.

Positive Feedback Mechanisms

  • A few hormonal regulatory systems work via positive feedback.

  • Positive feedback occurs when the response to a change in a controlled condition strengthens or enhances the change.

  • Example: During childbirth, the hormone oxytocin stimulates contractions of the uterus, and uterine contractions, in turn, stimulate more oxytocin release, a positive feedback effect.

Health Professionals and Homeostasis

  • Almost all controlled conditions in the human body are kept within a healthy range by negative feedback systems.

  • Therefore, the focus is on understanding negative feedback.

  • When someone becomes unwell, at least one of their negative feedback control systems won't be functioning normally.

  • The role of a health professional is to intervene in order to help return a patient's 'controlled conditions' to normal.

  • Examples: Nurses, doctors, and other allied health professionals.