🫁Honors Anatomy and Physiology Unit 17 – Homeostasis and Regulation

Key Concepts

• Homeostasis maintains stable internal conditions necessary for proper functioning of cells, tissues, and organs
• Involves monitoring internal environment and making adjustments to keep variables within normal range
• Utilizes negative feedback loops to counteract changes and restore balance
• Positive feedback loops amplify changes and push systems away from equilibrium
  • Less common than negative feedback in biological systems
  • Childbirth and blood clotting are examples of positive feedback
• Set points are optimal levels for variables (body temperature, blood glucose, etc.) that homeostatic mechanisms aim to maintain
• Sensors detect deviations from set points and send signals to control centers for corrective action
• Effectors carry out responses to bring variables back to set point

Homeostatic Systems

• Thermoregulation keeps body temperature within narrow range around 37°C (98.6°F)
  • Hypothalamus acts as thermostat, sensing changes and initiating appropriate responses
  • Effectors include sweat glands, blood vessels, and skeletal muscles
• Osmoregulation maintains proper water and electrolyte balance
  • Kidneys filter blood, reabsorb needed substances, and excrete excess water and solutes in urine
  • Antidiuretic hormone (ADH) and aldosterone regulate water and sodium reabsorption
• Blood glucose regulation keeps levels stable despite changes in food intake and energy expenditure
  • Pancreas secretes insulin to lower blood sugar and glucagon to raise it
• Acid-base homeostasis maintains blood pH around 7.4
  • Buffers, respiratory system, and kidneys work together to counteract pH changes
• Blood pressure regulation keeps systemic pressure within normal range
  • Baroreceptors detect changes and trigger adjustments in heart rate, contractility, and vascular tone

Feedback Mechanisms

• Negative feedback loops work to reduce deviations from set point and restore equilibrium
  • Consist of stimulus, sensor, control center, and effector components
  • Examples include thermoregulation, blood glucose regulation, and blood pressure control
• Positive feedback loops amplify changes and drive systems further from equilibrium
  • Less common in biological systems but play important roles in certain processes
  • Childbirth involves positive feedback between oxytocin release and uterine contractions
  • Blood clotting cascade is amplified by positive feedback to rapidly seal wounds
• Feedforward control anticipates disturbances and makes preemptive adjustments
  • Allows faster response than feedback control alone
  • Seen in regulation of blood glucose during exercise or after a meal

Endocrine System's Role

• Endocrine glands secrete hormones into bloodstream for transport to target cells
• Hormones act as chemical messengers, binding to receptors and triggering cellular responses
• Hypothalamus integrates nervous and endocrine systems, releasing releasing and inhibiting hormones to control pituitary gland
• Pituitary gland secretes tropic hormones that regulate other endocrine glands (thyroid, adrenals, gonads)
  • Anterior pituitary hormones include growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, and gonadotropins
  • Posterior pituitary stores and releases oxytocin and antidiuretic hormone made in hypothalamus
• Thyroid gland produces thyroxine (T4) and triiodothyronine (T3), which regulate metabolism, growth, and development
• Adrenal glands have two distinct regions with different functions
  • Adrenal cortex secretes mineralocorticoids, glucocorticoids, and androgens
  • Adrenal medulla releases catecholamines (epinephrine and norepinephrine) in response to stress

Nervous System's Role

• Nervous system provides rapid control and coordination of homeostatic responses
• Sensory receptors detect changes in internal and external environments and send signals to central nervous system (CNS)
• CNS integrates sensory input, compares to set points, and generates appropriate motor output
  • Hypothalamus plays key role in integrating homeostatic functions
  • Autonomic nervous system (ANS) controls involuntary functions like heart rate, digestion, and secretion
    • Sympathetic division of ANS mediates "fight or flight" response, increasing heart rate, blood pressure, and blood glucose
    • Parasympathetic division promotes "rest and digest" functions, conserving energy and resources
• Somatic nervous system controls voluntary movements and receives sensory input from skin, muscles, and joints
• Neurotransmitters and neuromodulators allow communication between neurons and effector cells
  • Acetylcholine, norepinephrine, serotonin, and dopamine are examples of neurotransmitters involved in homeostatic regulation

Common Disorders

• Diabetes mellitus results from insufficient insulin production (type 1) or insulin resistance (type 2), leading to high blood glucose
  • Complications include cardiovascular disease, kidney damage, and nerve damage
• Hypothyroidism occurs when thyroid gland produces too little thyroid hormone, causing fatigue, weight gain, and cold intolerance
• Hyperthyroidism involves excessive thyroid hormone production, leading to weight loss, rapid heartbeat, and heat intolerance
• Cushing's syndrome is caused by prolonged exposure to high levels of cortisol, resulting in weight gain, muscle weakness, and skin changes
• Addison's disease is characterized by insufficient production of adrenal hormones, leading to fatigue, weight loss, and low blood pressure
• Pheochromocytoma is a rare tumor of adrenal medulla that secretes excessive catecholamines, causing hypertension and palpitations
• Multiple endocrine neoplasia (MEN) syndromes are inherited disorders that cause tumors in multiple endocrine glands

Lab Work and Experiments

• Blood tests measure levels of hormones, electrolytes, and other substances involved in homeostatic regulation
  • Examples include thyroid function tests, glucose tolerance tests, and cortisol measurements
• Urinalysis assesses kidney function and provides information about water and electrolyte balance
• Imaging studies like ultrasound, CT, and MRI can visualize endocrine glands and detect tumors or abnormalities
• Animal models are used to study homeostatic mechanisms and test potential treatments for disorders
  • Knockout mice lacking specific genes help identify roles of hormones and receptors
  • Transgenic animals expressing human genes allow study of human diseases in vivo
• Cell culture experiments investigate cellular responses to hormones, neurotransmitters, and other signals
• Microarray and RNA sequencing technologies measure gene expression changes in response to homeostatic challenges

Real-World Applications

• Understanding homeostatic mechanisms informs treatment of diseases like diabetes, thyroid disorders, and adrenal insufficiency
  • Insulin therapy for diabetes mimics natural feedback regulation of blood glucose
  • Hormone replacement therapy corrects deficiencies in thyroid, adrenal, and sex hormones
• Knowledge of feedback loops guides design of drug dosing schedules to maintain stable levels and avoid adverse effects
• Biofeedback techniques allow individuals to consciously regulate physiological processes like heart rate and blood pressure
  • Used in stress management, pain control, and treatment of anxiety disorders
• Wearable technology and continuous glucose monitors provide real-time data for patients and healthcare providers to optimize management
• Environmental stressors like heat, cold, and high altitude challenge homeostatic systems and require adaptive responses
  • Athletes and military personnel train to improve performance under these conditions
• Chronobiology studies circadian rhythms and their impact on homeostatic functions, informing strategies for shift work and jet lag