2.3 Homeostasis and Physiological Regulation

Homeostasis keeps our bodies in balance, like a thermostat for our insides. It maintains key variables like temperature and blood sugar within safe ranges, allowing us to adapt to changes and stay healthy.

Feedback loops are the body's way of self-regulating. Negative feedback counteracts changes, while positive feedback amplifies them. These systems work together to keep us functioning optimally in various conditions.

Homeostasis and Physiological Regulation

Homeostasis and internal stability

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  Spotlight on Homeostasis – MHCC Biology 112: Biology for Health Professions View original

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• Homeostasis maintains a stable internal environment despite external changes (temperature, pH, glucose)
• Ensures optimal functioning of cells, tissues, and organs by keeping variables within narrow ranges
• Allows the body to adapt to changing conditions (exercise) and stressors (injury, illness)
• Prevents damage to biological systems caused by excessive fluctuations (hyperthermia, hypoglycemia)

Feedback loops in physiology

• Negative feedback loops maintain stability by counteracting changes in a controlled variable
  • Components include receptors (thermoreceptors), control centers (hypothalamus), and effectors (sweat glands)
  • Thermoregulation maintains body temperature around 37℃
  • Blood glucose regulation keeps levels between 70-110 mg/dL
  • Baroreceptor reflex adjusts heart rate and blood vessel diameter to control blood pressure
• Positive feedback loops amplify changes in a controlled variable leading to a rapid response
  • Blood clotting cascade amplifies initial clotting factors to form a stable clot
  • Uterine contractions during childbirth become stronger and more frequent until delivery
  • Action potential generation in neurons involves rapid depolarization and repolarization

Control mechanisms for key variables

• Body temperature regulation
  • Hypothalamus serves as the control center integrating signals from thermoreceptors
  • Effectors include sweat glands (cooling), blood vessels (vasodilation/vasoconstriction), and skeletal muscles (shivering)
• Blood glucose regulation
  • Pancreas secretes insulin (lowers glucose) and glucagon (raises glucose) in response to blood sugar levels
  • Effectors include liver (glycogenolysis, gluconeogenesis), skeletal muscles (glucose uptake), and adipose tissue (lipolysis)
• pH regulation
  1. Respiratory system alters ventilation rate to adjust blood CO2 levels (↑CO2 = ↓pH, ↓CO2 = ↑pH)
  2. Renal system adjusts $HCO_3^-$ reabsorption and $H^+$ excretion to maintain pH
  3. Buffer systems (bicarbonate, phosphate, proteins) minimize pH changes by accepting or donating $H^+$

Nervous and endocrine system cooperation

• Nervous system provides rapid response to stimuli through electrical impulses
  • Autonomic nervous system (sympathetic and parasympathetic) regulates heart rate, blood pressure, digestion, and respiration
• Endocrine system offers slower, longer-lasting response through hormones secreted into the bloodstream
  • Hormones (insulin, cortisol, thyroid hormones) bind to receptors on target cells to elicit a response
• Hypothalamus links the two systems by controlling the pituitary gland which regulates various endocrine glands
• Feedback loops involve both systems to maintain homeostasis (cortisol release during stress, thyroid hormone regulation of metabolism)