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What is the definition of physiology, and how do function ('why') and process ('how') differ in shivering?

Physiology is the study of the normal functions of living organisms and their parts. Function ("why") asks what a process accomplishes, such as shivering generating heat to maintain body temperature. Process ("how") explains the mechanism, such as cold triggering motor pathways that cause rapid, involuntary muscle contractions.

What are the hierarchical structural levels of organization in living organisms?

Molecules → Cells → Tissues → Organs → Organ Systems → Organisms. The cell is the smallest structural and functional unit of life.

What are the seven core unifying themes of human physiology?

1. Homeostasis 2. Biological energy use 3. Structure-function relationships 4. Molecular interactions 5. Compartmentation 6. Mechanical properties of cells, tissues, and organs 7. Communication.

What are the definitions and properties of covalent, ionic, and hydrogen bonds?

Covalent bonds share electrons and are the strongest. Ionic bonds form from electrostatic attraction between oppositely charged ions after electron transfer. Hydrogen bonds are weak attractions between hydrogen and electronegative atoms such as oxygen or nitrogen.

How are a mole and molarity defined and measured in biological systems?

A mole is 6.02 × 10²³ particles of a substance. Molarity is the concentration of solute measured in moles per liter of solution (mol/L or M).

What is the physical and physiological difference between a ligand and a receptor?

A ligand is a molecule that binds specifically to a receptor. A receptor is a target protein with a binding site that recognizes the ligand and initiates a cellular response.

What are the seven major categories of soluble proteins that dissolve in body fluids?

1. Enzymes 2. Membrane transporters 3. Signal molecules 4. Receptors 5. Binding proteins 6. Regulatory proteins 7. Immunoglobulins.

What is the difference between receptor specificity and protein isoforms?

Receptor specificity is the ability of a protein to selectively bind a particular ligand or related group of ligands. Isoforms are similar proteins with slightly different amino acid sequences that perform the same general function but may have different affinities or regulation.

How are proteins activated by cofactors and proteolytic cleavage?

Cofactor activation occurs when an inorganic ion or organic coenzyme binds to a protein and activates it. Proteolytic activation occurs when an inactive precursor protein is cleaved into its active form.

What is the difference between up-regulation and down-regulation of membrane receptors?

Up-regulation increases the number of active receptors when ligand levels are chronically low. Down-regulation decreases active receptors when ligand levels are chronically high.

What is protein saturation and how does it relate to the Transport Maximum (Tm)?

Saturation occurs when all binding sites on enzymes, carrier proteins, or receptors are occupied. Once saturated, increasing ligand concentration cannot increase the reaction or transport rate. This maximum is called the Transport Maximum (Tm) for transport.

How do temperature, pH, and protein concentration physically affect protein activity?

Temperature and pH can change a protein's 3D shape and cause denaturation, disrupting its binding site. Protein concentration determines the total number of available binding sites and therefore the cell's capacity to bind ligands.

What is the role of regulatory feedback loops, and how do negative and positive feedback differ?

Feedback loops regulate physiological variables. Negative feedback counteracts the initial stimulus and returns a variable toward its set point. Positive feedback reinforces the stimulus and pushes the variable farther from its set point until an outside factor stops the loop.

What are the physiological roles of major animal cell organelles, and which is abundant in skeletal muscle?

Mitochondria produce ATP and are abundant in skeletal muscle. Ribosomes make proteins. Smooth ER makes lipids and stores calcium. Rough ER processes proteins. Golgi modifies, sorts, and packages proteins. Peroxisomes neutralize toxic substances. Lysosomes digest debris and worn-out organelles.

What are the structural characteristics, unique features, and locations of epithelial tissue?

Epithelial tissue has little extracellular matrix, is avascular, and consists of tightly connected sheets of cells. It may have microvilli for absorption or cilia for moving material. It covers body surfaces, lines organs and tubes, and forms glands.

What are the structural characteristics, matrix types, and functions of connective tissue?

Connective tissue has abundant extracellular matrix that may be liquid, gelatinous, or calcified. It supports, protects, and connects organs and bones. Cartilage is unique because it is avascular.

What are the unique characteristics and three types of muscle tissue?

Muscle tissue is excitable and specialized for generating force and movement. The three types are skeletal muscle (voluntary), cardiac muscle (involuntary), and smooth muscle (involuntary).

What are the structural characteristics and primary locations of nerve tissue?

Nerve tissue contains neurons with branched processes and is specialized for rapid electrical and chemical communication. It is concentrated in the CNS and extends throughout the body.

What are the three biological types of physiological work, and how do they differ?

Chemical work makes or breaks chemical bonds. Transport work moves substances across membranes. Mechanical work produces physical movement such as muscle contraction or cilia movement.

How is energy defined in physiological terms?

Energy is the physical capacity to perform chemical, transport, or mechanical work.

What is the difference between catabolic and anabolic chemical reactions in metabolism?

Catabolism breaks down larger molecules into smaller molecules and releases energy. Anabolism uses energy to build larger molecules from smaller molecules.

What are the five primary regulatory control loops that cells use to manage metabolic pathways?

1. Control enzyme concentrations 2. Use allosteric and covalent modulators 3. Use different enzymes for reversible reactions 4. Compartmentalize enzymes 5. Maintain an optimal ATP-to-ADP ratio.

What are the differences between allosteric and covalent modulators of enzymes?

Allosteric modulators bind reversibly to a regulatory site and change enzyme shape. Covalent modulators form or break chemical bonds with the enzyme, such as phosphorylation.

What are the three general steps of cellular respiration, and where does each occur?

1. Glycolysis occurs in the cytoplasm and produces pyruvate, ATP, and NADH. 2. The citric acid cycle occurs in the mitochondrial matrix and produces NADH, FADH₂, CO₂, and ATP. 3. The electron transport chain and oxidative phosphorylation occur across the inner mitochondrial membrane and produce most cellular ATP.

What are the specific metabolic needs and constraints of the brain and spinal cord?

The CNS has very high metabolic demands and relies mainly on glucose and aerobic ATP production. It cannot store much glucose or perform anaerobic respiration effectively, making it highly vulnerable to low oxygen or low blood glucose.

What is the key difference between passive and active transport across cell membranes?

Passive transport moves substances down their concentration gradient and does not require ATP. Active transport moves substances against their gradient and requires energy.

What is the difference between simple diffusion and facilitated diffusion across membranes?

Simple diffusion moves small, nonpolar, lipid-soluble molecules directly through the lipid bilayer. Facilitated diffusion moves polar, charged, or hydrophilic molecules down their gradient through membrane proteins.

What are the seven core physical properties that govern the process of diffusion?

1. Passive process 2. Moves from high to low concentration 3. Continues until dynamic equilibrium 4. Fast over short distances and slow over long distances 5. Increases with temperature 6. Decreases with larger molecular size 7. Can occur in an open system or across a partition.

What is Fick's Law of Diffusion, and how does each variable affect the rate of diffusion?

Rate of diffusion = (Surface Area × Concentration Gradient × Membrane Permeability) ÷ Membrane Thickness. Increasing surface area, concentration gradient, or permeability increases diffusion. Increasing membrane thickness decreases diffusion.

According to Fick's Law, what three factors determine membrane permeability to a molecule?

1. Lipid solubility 2. Molecular size 3. Lipid composition of the membrane.

In a membrane crossing race between CO₂, glucose, Cl⁻, and a fatty acid, what is the order from fastest to slowest?

CO₂ → Fatty Acid → Glucose → Cl⁻.

What are the three structural classes of membrane proteins, and how are they integrated into the bilayer?

1. Integral proteins span the lipid bilayer. 2. Lipid-anchored proteins are covalently attached to membrane lipids. 3. Peripheral proteins are loosely attached to integral proteins or phospholipid heads.

What are the four functional classes of membrane proteins, and what physiological roles do they play?

1. Structural proteins connect membranes to the cytoskeleton or form junctions. 2. Membrane enzymes catalyze reactions. 3. Receptors bind signals. 4. Transporters move substances across membranes.

What is the difference between channel proteins and carrier proteins in membrane transport?

Channel proteins form continuous water-filled pores for rapid movement of ions and water. Carrier proteins bind specific substances and change shape to move them across the membrane.

What triggers chemically, voltage, and mechanically gated channels between open and closed states?

Chemically gated channels respond to ligand binding. Voltage-gated channels respond to changes in membrane potential. Mechanically gated channels respond to physical forces such as stretch, vibration, or pressure.

How are carrier proteins classified based on transport direction?

Uniport moves one type of substance. Symport moves two or more substances in the same direction. Antiport moves substances in opposite directions.

What is the difference between primary and secondary active transport in energy source and gradient creation?

Primary active transport directly uses ATP to move substances against their gradient. Secondary active transport uses energy stored in an electrochemical gradient created by primary active transport.

What are the three defining properties shared by carrier proteins and enzymes?

1. Specificity 2. Competition 3. Saturation.

What are the differences between phagocytosis, endocytosis, and exocytosis?

Phagocytosis engulfs large particles such as bacteria and debris. Endocytosis brings fluid or solutes into the cell by membrane infolding. Exocytosis releases substances when vesicles fuse with the cell membrane.

What is the difference between hydrostatic pressure (HP) and osmotic pressure (OP) in fluid movement?

Hydrostatic pressure pushes fluid out of a blood vessel. Osmotic pressure created by non-penetrating solutes such as plasma proteins pulls water into the vessel.

What is the difference between electrical signals and chemical signals in cell-to-cell communication?

Electrical signals are changes in membrane potential caused by ion movement. Chemical signals are molecules released into the extracellular fluid that communicate with other cells.

What is the difference between gap junctions and contact-dependent signals in local cell communication?

Gap junctions directly connect the cytoplasm of adjacent cells and allow chemical and electrical signals to pass. Contact-dependent signaling requires direct interaction between surface molecules on neighboring cells.

What is the difference between autocrine and paracrine chemical signaling?

Autocrine signals act on the same cell that released them. Paracrine signals diffuse through interstitial fluid and act on nearby cells.

What are the differences between endocrine hormones, neurotransmitters, and neurohormones?

Endocrine hormones enter the blood and travel to distant target cells. Neurotransmitters cross a small synaptic gap to act on nearby target cells. Neurohormones are released by neurons into the blood to act on distant targets.

Where are receptor proteins located based on whether their ligands are lipophilic or lipophobic?

Lipophilic ligands can cross the lipid bilayer and bind intracellular receptors in the cytosol or nucleus. Lipophobic ligands generally bind receptors on the cell membrane.

What are the four major categories of membrane receptors?

1. Receptor-channel 2. Receptor-enzyme 3. G protein-coupled receptor (GPCR) 4. Integrin receptor.

What is the molecular mechanism of the Tyrosine Kinase receptor-enzyme signaling pathway?

1. A signal molecule binds the receptor. 2. Tyrosine kinase becomes activated. 3. The kinase transfers phosphate from ATP to target proteins. 4. Phosphorylation produces the cellular response.

What are the step-by-step events of the GPCR Adenylyl Cyclase-cAMP second-messenger cascade?

1. Signal binds GPCR. 2. GPCR activates a G protein. 3. G protein activates adenylyl cyclase. 4. Adenylyl cyclase converts ATP to cAMP. 5. cAMP activates protein kinase A (PKA). 6. PKA phosphorylates target proteins and triggers a cellular response.

What is the difference between a receptor agonist and a receptor antagonist?

An agonist binds to a receptor and activates it, mimicking the normal ligand. An antagonist binds to a receptor and blocks activation.

How do different receptor isoforms determine the response of blood vessels to epinephrine?

Epinephrine causes vasoconstriction through alpha receptors on intestinal blood vessels but causes vasodilation through beta-2 receptors on skeletal muscle blood vessels.

What is antagonistic control in control systems, and how does it regulate heart rate?

Antagonistic control uses opposing inputs to regulate a target and maintain homeostasis. Sympathetic activity increases heart rate, while parasympathetic activity decreases heart rate.

What is the difference between central and peripheral sensory receptors?

Central receptors are located in or near the brain. Peripheral receptors are located outside the brain and include chemoreceptors, osmoreceptors, thermoreceptors, baroreceptors, proprioceptors, and mechanoreceptors.

What are the structural pathways of simple endocrine, simple neural, and complex neuroendocrine reflex control loops?

Simple endocrine: Stimulus → endocrine sensor/integrating center → hormone → effector → response. Simple neural: Stimulus → receptor → afferent neuron → CNS → efferent neuron → effector → response. Complex neuroendocrine: Stimulus → receptor → afferent neuron → CNS → efferent neuron/neurohormone → endocrine center → hormone → effector → response.

What is the difference between molarity and osmolarity, and how does solute dissociation affect them?

Molarity is moles of solute per liter. Osmolarity is total osmotically active particles per liter. Dissociation increases the number of particles and therefore increases osmolarity.

What are the key differences between osmolarity and tonicity?

Osmolarity measures the total concentration of solute particles immediately after a solution is introduced. Tonicity describes the solution's effect on cell volume after water movement and depends on non-penetrating solutes.

What is the difference between penetrating and non-penetrating solutes?

Penetrating solutes can cross the membrane, such as urea. Non-penetrating solutes cannot freely cross the membrane, such as Na⁺.

What is the ECF osmolarity, tonicity, and cell volume change when drinking massive amounts of plain water?

ECF becomes hypo-osmolar and hypotonic. Water moves into cells, causing them to swell and potentially lyse.

What is the ECF osmolarity, tonicity, and cell volume change during an IV infusion of a 300 mOsm urea solution?

ECF is initially iso-osmolar but the solution is hypotonic because urea penetrates cells. Water moves into cells, causing them to swell.

What is the ECF osmolarity, tonicity, and cell volume change when eating a highly nutrient-rich, heavy meal?

ECF becomes hyper-osmolar but hypotonic because nutrients enter cells. Water moves into cells, causing them to swell.

What is the ECF osmolarity, tonicity, and cell volume change during an IV infusion of 300 mOsm NaCl?

ECF is iso-osmolar and isotonic. There is no net water movement, so cell volume does not change.

What is the ECF osmolarity, tonicity, and cell volume change during an IV infusion of 300 mOsm glucose and 300 mOsm salt?

ECF becomes hyper-osmolar but isotonic. Glucose enters and is metabolized while non-penetrating NaCl remains outside, resulting in no net water movement and no change in cell volume.

What is the ECF osmolarity, tonicity, and cell volume change when eating a highly salty meal with no fluids?

ECF becomes hyper-osmolar and hypertonic. Water leaves cells, causing them to shrink.

What are the differences between osmotic, chemical, and electrical equilibrium states in cells?

Osmotic equilibrium means water concentration is equal on both sides. Chemical equilibrium means each solute is equally distributed. Electrical equilibrium means net positive and negative charges are balanced.

How can a cell achieve electrical equilibrium without achieving chemical equilibrium?

Electrical equilibrium can occur when positive and negative charges are balanced even though different ion species are distributed unequally.

Why is perfect chemical or electrical equilibrium sometimes impossible for a cell to achieve?

Non-permeable substances and indivisible particles can prevent perfectly equal distributions.

What is the difference between neurons and neuroglia?

Neurons are excitable cells that generate and carry electrical and chemical signals. Neuroglia are supporting cells that protect, nourish, insulate, and maintain the environment around neurons.

What is the primary role of autonomic ganglia?

Autonomic ganglia are relay stations where preganglionic autonomic neurons synapse with postganglionic neurons to coordinate involuntary visceral functions.

How is the resting membrane potential (RMP) established and maintained by K⁺ leak and the Na⁺/K⁺ pump?

The RMP is about -70 mV. K⁺ leak channels allow K⁺ to leave the cell, leaving negative proteins inside. The Na⁺/K⁺ ATPase maintains gradients by pumping 3 Na⁺ out and 2 K⁺ in using ATP.

What rapid ion flux occurs upon cellular activation to depolarize the membrane potential?

Na⁺ permeability rapidly increases, allowing Na⁺ to enter the cell and depolarize the membrane.

What is the exact role of voltage-gated Ca²⁺ channels in synaptic transmission?

An action potential opens voltage-gated Ca²⁺ channels in the axon terminal. Ca²⁺ enters the terminal and triggers synaptic vesicles to fuse with the membrane and release neurotransmitters.

What are the four methods used to clean up the synaptic cleft and end target cell activation?

1. Diffusion away from the cleft 2. Uptake by neuroglia 3. Reuptake by the presynaptic neuron 4. Enzymatic degradation.

What are the four primary characteristics of graded potentials?

1. Vary in magnitude 2. Are decremental 3. Have no absolute refractory period 4. Can summate.

What are the four primary characteristics of action potentials?

1. All-or-none 2. Non-decremental 3. Have absolute and relative refractory periods 4. Originate at the axon hillock/trigger zone when threshold is reached.

What is the all-or-none principle in action potential generation?

Once threshold is reached, an action potential has the same magnitude and duration regardless of stimulus strength. A stronger stimulus increases action potential frequency rather than size.

What is the difference between absolute and relative refractory periods?

During the absolute refractory period, no stimulus can trigger another action potential because Na⁺ channels are open or inactivated. During the relative refractory period, a stronger-than-normal stimulus can trigger another action potential.

Why can't an action potential reverse direction and move back toward the cell body?

The membrane behind the action potential is in its refractory period, so its Na⁺ channels cannot immediately reopen. This prevents backward propagation.

What three main factors affect the conduction velocity of an action potential?

1. Axon diameter: larger axons conduct faster. 2. Temperature: higher temperatures increase conduction speed. 3. Myelination: increases conduction through saltatory conduction.

What is hyperkalemia, and how does it cause hyperexcitability in neurons?

Hyperkalemia is high extracellular K⁺. It reduces the K⁺ concentration gradient, causing less K⁺ to leave the cell and making the resting membrane potential more positive and closer to threshold.

What is the difference between an EPSP and an IPSP?

An EPSP is a graded depolarization that moves the membrane closer to threshold. An IPSP is a graded hyperpolarization that moves the membrane farther from threshold.

What happens when EPSP A (+10 mV), IPSP B (-6 mV), and EPSP C (+6 mV) reach the axon hillock at the same time?

The net change is +10 mV. Because this is below the +15 mV threshold, no action potential occurs.

What happens when EPSP C (+6 mV) and EPSP A (+10 mV) reach the axon hillock at the same time?

The net change is +16 mV. Because this exceeds the +15 mV threshold, an action potential occurs.

What happens when EPSP A (+10 mV) fires alone, and how can it reach threshold?

A alone produces +10 mV, which is below the +15 mV threshold. Repeated rapid stimulation can produce temporal summation and reach threshold.

What is the precise step-by-step sequence of events during an action potential?

1. Graded depolarization reaches threshold. 2. Na⁺ activation gates open. 3. Na⁺ enters and rapidly depolarizes the membrane. 4. Na⁺ channels inactivate near the peak. 5. K⁺ channels open and K⁺ exits, causing repolarization. 6. K⁺ channels close slowly, causing hyperpolarization. 7. Na⁺ channels reset and the resting membrane potential is restored.

What is the sequence of the five divisions of the brain from lowest to highest in information processing?

Medulla Oblongata → Pons → Hypothalamus → Cerebellum → Cerebrum.

Where are the three vital centers of the Central Nervous System located?

The three vital centers are located in the medulla oblongata.

Which areas of the brain regulate ventilation, and what does damage to them cause?

The pons and medulla oblongata regulate ventilation. Damage to these areas can cause loss of ventilation regulation.

What region of the brain is the primary relay center for almost all sensory information?

The thalamus is the primary relay and processing center for almost all sensory information before it reaches the cerebral cortex, except olfaction.

Why does a stroke-induced tissue infarct in the thalamus cause widespread numbness and tingling?

The thalamus relays most sensory information to the cerebral cortex, so damage can disrupt sensory signal transmission.

What are the primary cognitive functions associated with the cerebral cortex?

Memory formation, prediction, language, complex thought, and analysis.

What central homeostatic role does the hypothalamus perform?

The hypothalamus regulates homeostasis of autonomic and endocrine functions, including water balance, osmolarity, and body temperature.

What region of the brain is responsible for processing emotion, memory, and learning?

The limbic system.

What tissues are under the involuntary control of the Autonomic Nervous System (ANS)?

Cardiac muscle, smooth muscle, and glands.

What receptor subtypes are found between pre- and post-ganglionic neurons and at target effectors in the parasympathetic division?

Nicotinic receptors are used between pre- and post-ganglionic neurons. Muscarinic receptors are used at target effector tissues.

What neurotransmitters are utilized by the sympathetic division?

Acetylcholine (ACh) is used at sympathetic ganglia. Norepinephrine (NE) is commonly used at sympathetic effector synapses.

What class of receptors consists of alpha and beta subtypes, and where are they located?

Adrenergic receptors have alpha and beta subtypes and are found at target effectors of the sympathetic division.

What physiological processes would be selectively impaired by a functional disorder in the sympathetic division?

Fight-or-flight responses and physical excitement would be impaired. Parasympathetic functions such as digestion, urination, defecation, and salivation would still be promoted.

What branch of the efferent nervous system typically exhibits antagonistic control over target tissue output?

The autonomic division.

What brain structure is compromised if a patient shows a marked decrease in cerebrospinal fluid (CSF) production?

The choroid plexus, which produces cerebrospinal fluid.

Which glial cell class is dysfunctional if a drug administered for the kidneys starts crossing into and affecting the brain?

Astrocytes, because they help form and maintain the blood-brain barrier.

What physiological activities are regulated by the enteric division of the nervous system?

Local visceral activities and reflexes within the digestive system.