Homeostasis Flashcards

Homeostasis

Homeostasis maintains steady states within a living organism. Cannon introduced the concept in 1920. It involves maintaining internal conditions within narrow limits through regulatory mechanisms.

Significance of Homeostasis

A stable internal environment is essential for optimal cell function. Homeostasis is crucial because internal and external changes can affect MRSGREN. Unsuitable conditions like altered pH or temperatures can be detrimental.

Mechanisms of Homeostatic Control

The body monitors changes via the nervous (rapid, neurotransmitters) and endocrine (slower, hormones) systems. These systems correct abnormalities through negative and positive feedback.

Hormones vs. Nerves

Feature	Nerves	Hormones
Message Type	Electrical impulses (neurotransmitters at synapses)	Chemical
Transport	Neurones	Blood
Speed	Fast	Slow
Response Duration	Short	Long
Target Specificity	Specific areas	General

Components of a Feedback System

Receptors: Detect changes (e.g., Merkel's disk, Pacinian corpuscle).
Afferent Nerves: Transmit sensory information.
Monitor (Control Center): Processes information (e.g., brain).
Efferent Nerves: Relay signals to target organs.
Target Organs (Effectors): Restore homeostasis.

Common Receptors and Their Stimuli

Receptor	Stimulus
Ampullae of Lorenzini	Electric fields, salinity, temperature
Baroreceptors	Pressure in blood vessels
Chemoreceptors	Chemical stimuli
Electromagnetic radiation receptors	Electromagnetic radiation
Electroreceptors	Electric fields
Hydroreceptors	Humidity
Infrared receptors	Infrared radiation
Magnetoreceptors	Magnetic fields
Mechanoreceptors	Mechanical stress or strain
Nociceptors	Damage or threat of damage to body tissues (leads to pain perception)
Osmoreceptors	Osmolarity of fluids
Photoreceptors	Visible light
Proprioceptors	Sense of position
Thermoreceptors	Temperature
Ultraviolet receptors	Ultraviolet radiation

Sensory Nerve Pathway to Brain

Stimulus: Energy enters the eye.
Reception: Receptors detect light.
Transduction: Light converts to action potentials.
Transmission: Signals sent to the brain via the optic nerve.
Interpretation: Occurs in the primary visual cortex.

Monitor Sends Message to Target Organs

The primary motor cortex initiates motor tracts to the spinal cord, affecting skeletal muscle.

Feedback Mechanisms

Positive Feedback

Positive feedback amplifies changes.

Example: Childbirth
1. Baby's head pushes against the cervix.
2. Nerve impulses transmit to the brain.
3. The brain releases oxytocin.
4. Oxytocin stimulates uterine contractions.
Example: Milk Let-Down
- Enhances the original stimulus.

Negative Feedback

Negative feedback opposes changes, maintaining stability.

Example: Temperature Control
- Increased Body Temperature:
  - Stimulus: Temperature exceeds $37°C$ .
  - Sensors: Nerve cells.
  - Control: Brain.
  - Effector: Sweat glands.
  - Response: Sweating, vasodilation.
- Decreased Body Temperature:
  - Stimulus: Decreased temperature.
  - Sensors: Nerve cells.
  - Control: Hypothalamus.
  - Effector: Muscles, blood vessels.
  - Response: Shivering, vasoconstriction.
Example: Blood Glucose Regulation
- Insulin released when glucose is high; release stops when glucose drops.

Neural Response

The nervous system controls heart rate.

Accelerator Nerve: Increases heart rate.
Vagus Nerve: Decreases heart rate.

Hormonal Response

Comparison of Nervous and Endocrine Systems

Feature	Nervous System	Endocrine System
Type of message	Electrical	Chemical
Carried by	Neurones	Blood
Speed of transmission	Fast	Slow

Positive Feedback Loops in Detail

Homeostatic circuits use negative feedback to maintain a set point. Positive feedback loops amplify the starting signal, typically in processes needing completion:

Baby's head presses on the cervix.
Neurons send signals to the brain.
The brain releases oxytocin.
Oxytocin increases uterine contractions.
More oxytocin is released until the baby is born.