Covers homeostasis and how the body keeps its internal conditions stable, starting with the three components of a regulatory loop: receptor, control centre and effector, illustrated with blood glucose, temperature and blood pressure. It then contrasts open-loop and closed-loop systems, humoral and neural control, and negative and positive feedback, alongside anticipatory and feedforward regulation. The final section sets out intracellular, local and whole-body levels of regulation. The note includes five pictures and a comparison of feedback types.
Topic 1 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 2 sections, about 1,003 words (7 min of reading), with 15 flashcards.
In this note
Introduction
Levels of Physiological Regulation: From Cells to the Whole Body
Introduction
Homeostasis is the maintenance of the constancy (enduring and unchanging) of the internal organs and systems
What are the three mechanisms for Homeostasis regulations
Receptor: It acts as the sensory unit, detecting deviations from the set point (desired level) of a specific physiological variable like blood sugar, temperature, or pressure. Examples include temperature receptors in the skin or glucose-sensing cells in the pancreas.
Control Center: This is the decision-making unit, often the brain (for nervous system interactions) or other control centers like the hypothalamus. It receives information from the receptor, compares it to the set point, and determines the necessary corrective action.
Effector: These are the "actioners" of the system, carrying out the control center's instructions to influence the physiological variable. Examples include sweat glands for temperature regulation, muscles for blood vessel dilation, or hormone-secreting glands like the pancreas for blood sugar control.
Effector: Insulin promotes glucose uptake by cells, lowering blood sugar back to the set point.
Body Temperature Regulation:
Sensor: Skin thermoreceptors detect temperature changes.
Control Center: Hypothalamus activates sweating and vasodilation.
Effectors: Sweating releases heat, and vasodilation increases blood flow to the skin, lowering body temperature.
Blood Pressure Regulation:
Sensor: Baroreceptors in arteries detect pressure changes.
Control Center: Brain decreases heart rate and dilates blood vessels.
Effectors: Lower heart rate and wider blood vessels reduce pressure.
Types of Regulatory systems
Open-Loop Systems:
Definition : The Output in open-loop systems does not directly influence future actions. The system operates based on a predetermined program or fixed instructions, without feedback mechanisms to adjust based on results.
Digestive secretions: Salivary glands begin secreting saliva upon the sight or smell of food, anticipating digestive needs, but don't receive direct feedback about the actual amount of food consumed.
Closed-Loop Systems:
Definition: Closed-loop systems are characterized by feedback mechanisms. Sensors monitor the output of the system, and this information is fed back to the control center, which adjusts future actions based on the difference between the actual output and the desired outcome.
Examples
Blood pressure regulation: Baroreceptors in blood vessels detect pressure changes, sending signals to the brain. The brain then adjusts heart rate and blood vessel diameter to maintain optimal pressure, forming a negative feedback loop.
Humoral:
Slow & Steady: Uses hormones for widespread, long-lasting effects.
Examples: Blood sugar, temperature, reproduction.
Neural:
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