🐅Animal Physiology Unit 13 – Physiological Systems: Regulation & Adaptation

Key Concepts and Definitions

• Physiology studies the functions and mechanisms of living organisms and their parts
• Homeostasis maintains a stable internal environment despite external changes through regulation of variables (temperature, pH, glucose levels)
• Negative feedback loops counteract changes in a regulated variable to return it to a set point
  • Consists of a receptor, control center, and effector
  • Examples include thermoregulation and blood glucose control
• Positive feedback loops amplify changes in a regulated variable, moving it away from the set point (blood clotting, childbirth)
• Endocrine system secretes hormones that act as chemical messengers to regulate physiological processes
• Nervous system uses electrical and chemical signals to transmit information and coordinate body functions
  • Includes the central nervous system (brain and spinal cord) and peripheral nervous system (sensory and motor neurons)
• Adaptation refers to physiological adjustments that enhance an organism's survival and reproduction in a specific environment

Physiological Systems Overview

• Cardiovascular system transports oxygen, nutrients, hormones, and waste products throughout the body
  • Includes the heart, blood vessels, and blood
  • Regulated by neural and hormonal mechanisms to maintain blood pressure and flow
• Respiratory system facilitates gas exchange between the environment and the body
  • Consists of the lungs, airways, and respiratory muscles
  • Controlled by the brainstem to adjust breathing rate and depth based on oxygen demand and carbon dioxide levels
• Digestive system breaks down food, absorbs nutrients, and eliminates waste
  • Includes the gastrointestinal tract, liver, pancreas, and gallbladder
  • Regulated by hormones (insulin, glucagon) and neural signals to control digestion and nutrient absorption
• Urinary system filters blood, maintains fluid and electrolyte balance, and removes metabolic waste
  • Consists of the kidneys, ureters, bladder, and urethra
  • Regulates blood volume, pH, and osmolarity through hormones (antidiuretic hormone, aldosterone) and neural control
• Immune system defends the body against pathogens and foreign substances
  • Includes white blood cells, lymphoid organs (spleen, thymus), and antibodies
  • Coordinated by cytokines and other signaling molecules to mount specific immune responses
• Musculoskeletal system provides support, protection, and movement
  • Consists of bones, joints, skeletal muscles, tendons, and ligaments
  • Regulated by hormones (growth hormone, thyroid hormone) and neural signals to control growth, repair, and muscle contraction

Homeostasis and Feedback Mechanisms

• Homeostasis is the maintenance of a stable internal environment despite changes in the external environment
• Set point is the optimal level or range for a physiological variable (body temperature, blood glucose)
• Negative feedback loops restore deviations from the set point
  • Thermoregulation example: If body temperature rises, receptors detect the change, the hypothalamus (control center) signals effectors (sweat glands, blood vessels) to cool the body until temperature returns to the set point
  • Blood glucose regulation example: If blood sugar increases, the pancreas releases insulin to stimulate glucose uptake by cells and lower blood glucose to the set point
• Positive feedback loops amplify changes in a regulated variable, moving it away from the set point
  • Blood clotting example: Injured blood vessels release clotting factors that activate more clotting factors, rapidly forming a clot to stop bleeding
  • Childbirth example: Stretching of the cervix during labor stimulates the release of oxytocin, which causes stronger uterine contractions, further stretching the cervix and releasing more oxytocin until the baby is delivered
• Feedforward mechanisms anticipate disturbances and make preemptive adjustments to maintain homeostasis
  • Anticipatory thermogenesis example: Before eating, the body increases heat production to counteract the expected drop in temperature from food intake
• Acclimatization is the physiological adjustment to environmental changes over a short time (days to weeks)
  • High-altitude acclimatization example: Increased red blood cell production and breathing rate to compensate for lower oxygen levels

Endocrine System and Hormonal Regulation

• Endocrine glands secrete hormones directly into the bloodstream to regulate target cells and organs
• Hormones are chemical messengers that bind to specific receptors on target cells to initiate physiological responses
  • Steroid hormones (cortisol, estrogen) are lipid-soluble and can cross cell membranes to bind to intracellular receptors and alter gene expression
  • Peptide hormones (insulin, growth hormone) are water-soluble and bind to cell surface receptors to activate signaling cascades
• Hypothalamus is the main link between the nervous and endocrine systems, producing releasing and inhibiting hormones that control the pituitary gland
• Pituitary gland is the "master gland" that secretes hormones regulating growth, metabolism, reproduction, and stress responses
  • Anterior pituitary example: Releases growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, and gonadotropins
  • Posterior pituitary example: Releases antidiuretic hormone and oxytocin
• Thyroid gland produces thyroid hormones (T3 and T4) that regulate metabolism, growth, and development
• Adrenal glands consist of the cortex and medulla
  • Adrenal cortex secretes glucocorticoids (cortisol), mineralocorticoids (aldosterone), and androgens
  • Adrenal medulla releases catecholamines (epinephrine and norepinephrine) in response to stress
• Pancreas contains endocrine cells (islets of Langerhans) that secrete insulin and glucagon to regulate blood glucose levels
• Negative feedback loops control hormone secretion to maintain homeostasis
  • Hypothalamic-pituitary-thyroid axis example: Thyroid hormone levels regulate the release of thyroid-stimulating hormone from the pituitary and thyrotropin-releasing hormone from the hypothalamus

Nervous System Control

• Nervous system uses electrical and chemical signals to transmit information and coordinate body functions
• Neurons are the basic functional units of the nervous system
  • Consist of a cell body, dendrites (receive signals), and an axon (transmits signals)
  • Communicate through electrical synapses (gap junctions) and chemical synapses (neurotransmitters)
• Action potentials are the electrical signals that propagate along the axon
  • Generated by changes in membrane potential due to the flow of ions (sodium, potassium) through voltage-gated channels
  • All-or-none response: If the threshold is reached, an action potential is triggered and propagates without diminishing
• Neurotransmitters are chemical messengers released from the presynaptic neuron that bind to receptors on the postsynaptic cell
  • Excitatory neurotransmitters (glutamate) increase the likelihood of an action potential in the postsynaptic neuron
  • Inhibitory neurotransmitters (GABA) decrease the likelihood of an action potential in the postsynaptic neuron
• Central nervous system (CNS) consists of the brain and spinal cord
  • Brain regions include the cerebral cortex (higher cognitive functions), cerebellum (motor coordination), and brainstem (vital functions)
  • Spinal cord transmits signals between the brain and the body and controls reflexes
• Peripheral nervous system (PNS) includes sensory and motor neurons that connect the CNS to the rest of the body
  • Sensory (afferent) neurons convey information from sensory receptors to the CNS
  • Motor (efferent) neurons transmit signals from the CNS to effectors (muscles, glands)
    • Somatic nervous system controls voluntary movements through skeletal muscles
    • Autonomic nervous system regulates involuntary functions (heart rate, digestion, secretion)
      • Sympathetic division prepares the body for "fight or flight" responses
      • Parasympathetic division promotes "rest and digest" activities
• Reflexes are rapid, involuntary responses to specific stimuli that involve a sensory neuron, interneuron, and motor neuron
  • Knee-jerk reflex example: Tapping the patellar tendon stretches the quadriceps muscle, activating sensory neurons that synapse with motor neurons in the spinal cord, causing the quadriceps to contract and the leg to extend

Adaptation to Environmental Challenges

• Organisms adapt to environmental challenges through physiological, behavioral, and evolutionary mechanisms
• Thermoregulation is the maintenance of a stable body temperature
  • Endotherms (mammals, birds) generate heat internally and maintain a constant body temperature through insulation, vasodilation/vasoconstriction, and sweating/panting
  • Ectotherms (reptiles, amphibians) rely on external heat sources and regulate body temperature through behavior (basking, seeking shade)
• Osmoregulation is the control of water and solute balance
  • Freshwater fish maintain a higher solute concentration than their environment, constantly taking in water and excreting dilute urine
  • Marine fish maintain a lower solute concentration than seawater, losing water and actively excreting salt through gills and kidneys
  • Terrestrial animals conserve water through concentrated urine, dry feces, and respiratory countercurrent exchange
• Oxygen availability varies with altitude, water depth, and environmental conditions
  • High-altitude adaptation example: Tibetans have higher oxygen saturation, more efficient oxygen utilization, and lower hemoglobin levels compared to lowlanders
  • Diving mammal adaptation example: Seals and whales have increased oxygen storage in blood and muscles, reduced heart rate, and peripheral vasoconstriction during dives
• Circadian rhythms are endogenous 24-hour cycles that regulate physiological processes and behavior
  • Synchronized by external cues (light-dark cycle) and controlled by the suprachiasmatic nucleus in the hypothalamus
  • Jet lag example: Rapid travel across time zones disrupts the alignment between the internal circadian clock and the external light-dark cycle, leading to sleep disturbances and other symptoms
• Hibernation is a seasonal adaptation that allows animals to conserve energy during periods of low food availability and harsh environmental conditions
  • Characterized by reduced metabolic rate, lower body temperature, and slower heart and breathing rates
  • Example: Ground squirrels hibernate for several months, relying on stored fat reserves and periodic arousals to maintain body functions

Case Studies and Real-World Applications

• Diabetes mellitus is a metabolic disorder characterized by high blood glucose levels due to insufficient insulin production (type 1) or insulin resistance (type 2)
  • Physiological consequences include polyuria, polydipsia, weight loss, and long-term complications (neuropathy, retinopathy, cardiovascular disease)
  • Treatment involves insulin replacement, dietary management, and medication to improve insulin sensitivity
• Stress response is a physiological reaction to physical, mental, or emotional challenges
  • Hypothalamic-pituitary-adrenal axis activation leads to cortisol release, increasing blood glucose, heart rate, and blood pressure
  • Chronic stress example: Prolonged exposure to stressors can lead to impaired immune function, digestive problems, and mental health disorders
• Altitude sickness occurs when individuals ascend to high altitudes too quickly, leading to hypoxia (low oxygen levels)
  • Symptoms include headache, nausea, fatigue, and shortness of breath
  • Prevention involves gradual ascent, proper acclimatization, and maintaining hydration
• Circadian rhythm disorders result from misalignment between the internal body clock and the external environment
  • Shift work disorder example: Night shift workers often experience sleep disturbances, fatigue, and digestive issues due to disrupted circadian rhythms
  • Treatment involves maintaining a consistent sleep schedule, light therapy, and melatonin supplementation
• Performance-enhancing drugs are substances used to improve athletic or cognitive performance
  • Anabolic steroids example: Synthetic derivatives of testosterone that promote muscle growth and strength but can cause liver damage, cardiovascular problems, and hormonal imbalances
  • Stimulants example: Drugs like amphetamines and methylphenidate that increase alertness and reduce fatigue but can lead to addiction, anxiety, and cardiovascular stress
• Jetlag is a temporary circadian rhythm disorder that occurs after rapid travel across multiple time zones
  • Symptoms include daytime fatigue, nighttime insomnia, digestive disturbances, and mood changes
  • Management strategies involve adjusting to the new time zone by exposing oneself to sunlight, maintaining a regular sleep schedule, and using melatonin to shift the circadian rhythm

Review Questions and Practice Problems

1. Describe the components of a negative feedback loop and provide an example of how it maintains homeostasis.
2. Compare and contrast the roles of the sympathetic and parasympathetic divisions of the autonomic nervous system.
3. Explain how hormones regulate physiological processes and give an example of a negative feedback loop involving hormones.
4. What is the difference between endotherms and ectotherms in terms of thermoregulation?
5. How do marine and freshwater fish maintain osmotic balance in their respective environments?
6. Describe the role of the hypothalamus in linking the nervous and endocrine systems.
7. What are the main differences between steroid and peptide hormones in terms of their structure and mechanism of action?
8. Explain the process of an action potential and its role in neural communication.
9. How do organisms adapt to high-altitude environments, and what are some examples of high-altitude adaptations?
10. Describe the physiological consequences of chronic stress and how it affects various body systems.
11. A patient exhibits symptoms of polyuria, polydipsia, and unexplained weight loss. What metabolic disorder might they have, and how is it characterized?
12. Explain the concept of circadian rhythms and how disruptions can lead to jet lag and shift work disorder.
13. How does the body respond to an acute stressor, and what physiological systems are involved in the stress response?
14. What are performance-enhancing drugs, and what are some examples of their effects on the body?
15. An individual travels from New York to London, crossing five time zones. What symptoms might they experience due to jet lag, and how can they manage these symptoms?