Comprehensive Study Notes for Human Physiology 261 Midterm

Introduction to Physiology

Physiology and Homeostasis

Physiology is the study of the normal functioning of a living organism and its component parts, including all its chemical and physical processes. Homeostasis refers to the maintenance of a relatively stable internal environment despite external changes.

• Homeostasis: The process by which organisms maintain a stable internal environment. Key variables include temperature, pH, and ion concentrations.

• Teleological vs. Mechanistic Approach: Teleological explanations focus on the purpose of a process ("why"), while mechanistic explanations focus on the process itself ("how").

• Placebo: An inactive substance or treatment used as a control in experiments.

• Hypothesis: A testable statement or prediction about the relationship between variables.

Molecular Interactions

Atoms, Ions, and Molecules

Understanding the basic building blocks of matter is essential for physiology.

• Cation: A positively charged ion (e.g., Na+, K+).

• Electrons: Negatively charged subatomic particles involved in chemical bonding and reactions.

• Essential vs. Nonessential Amino Acids: Essential amino acids cannot be synthesized by the body and must be obtained from the diet; nonessential amino acids can be synthesized by the body.

• pH Scale: Measures the concentration of hydrogen ions in a solution. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic.

Compartmentation: Cells and Tissues

Body Compartments and Cellular Structure

The body is organized into compartments separated by membranes, allowing for specialized functions.

• Body Compartments: Include intracellular (inside cells), intercellular (between cells), and extracellular (outside cells) spaces.

• Intracellular and Extracellular Ions: Intracellular fluid is high in K+ and proteins; extracellular fluid is high in Na+ and Cl-.

• Rules of Diffusion: Molecules move from areas of high concentration to low concentration; rate depends on temperature, size, and membrane permeability.

Cellular Organelles and Functions

• Rough Endoplasmic Reticulum (Rough ER): Synthesizes proteins for secretion or membrane insertion.

• Golgi Body/Apparatus: Modifies, sorts, and packages proteins and lipids for delivery.

• Tay-Sachs Disease: Affects lysosomes, leading to accumulation of undigested lipids in neurons.

Cell Membrane and Proteins

• Cell Membrane Function: Acts as a barrier, controls entry/exit of substances, and facilitates communication.

• Cell Membrane Proteins: Include channels, carriers, receptors, and enzymes.

• Cholesterol: Stabilizes membrane fluidity and structure.

Energy and Cellular Metabolism

Energy Concepts

• Energy: The capacity to do work; in cells, energy is stored in chemical bonds.

• Activation Energy: The minimum energy required to start a chemical reaction.

• Exergonic Reactions: Release energy (e.g., cellular respiration).

Enzymes and Protein Synthesis

• Enzymes: Biological catalysts that speed up reactions by lowering activation energy.

• Enzyme Specificity: Each enzyme acts on a specific substrate.

• Steps of Protein Synthesis: Transcription (DNA to mRNA) and translation (mRNA to protein).

Membrane Dynamics

Transport Mechanisms

• Exocytosis: Process by which cells expel materials in vesicles.

Communication, Integration, and Homeostasis

Levels of Organization

• Levels: Molecule → Cell → Tissue → Organ → Organ System → Organism.

Neurons: Cellular and Network Properties

Resting Membrane Potential and Neuron Anatomy

• Resting Membrane Potential: The electrical charge difference across the cell membrane at rest, typically -70 mV.

• Neuron Anatomy: Includes dendrites, cell body (soma), axon, and axon terminals.

CNS vs. PNS; Ganglia vs. Nuclei

• CNS (Central Nervous System): Brain and spinal cord.

• PNS (Peripheral Nervous System): All neural tissue outside the CNS.

• Ganglia: Clusters of neuron cell bodies in the PNS.

• Nuclei: Clusters of neuron cell bodies in the CNS.

Sensory/Afferent vs. Motor/Efferent Neurons

• Sensory (Afferent) Neurons: Carry information to the CNS.

• Motor (Efferent) Neurons: Carry commands from the CNS to effectors (muscles/glands).

Action Potentials

• Phases: Depolarization, repolarization, hyperpolarization.

• Overshoot Point: When membrane potential becomes positive during action potential.

• All-or-None Principle: Action potentials occur fully or not at all.

• Refractory Period: Time during which a neuron cannot fire another action potential.

• Absolute vs. Relative Refractory Period: Absolute: no action potential possible; Relative: possible with stronger stimulus.

• Excitatory Postsynaptic Potential (EPSP): Graded depolarization that brings the membrane potential closer to threshold.

• Na+/K+ Pump: Maintains resting membrane potential by pumping 3 Na+ out and 2 K+ in per ATP hydrolyzed.

The Central Nervous System

Metabolic Needs and Cerebrospinal Fluid

• Metabolic Needs: The brain requires a constant supply of oxygen and glucose.

• Cerebrospinal Fluid (CSF): Cushions the brain and removes waste.

Learning and Sensory Pathways

• Associative Learning: Linking two stimuli or events together.

• Nonassociative Learning: Change in response to a single stimulus.

• Sensory Pathways: Most sensory information travels to the thalamus before reaching the cortex; olfactory pathways are an exception.

Sensory Physiology

Special Senses

• Middle Ear Structures: Include ossicles (malleus, incus, stapes) that transmit sound vibrations.

• Taste: Five basic sensations: sweet, sour, salty, bitter, umami. Each is triggered by specific chemicals.

• Nociceptors: Sensory receptors for pain.

• Eye Anatomy: Includes cornea, lens, retina, optic nerve.

• Pathway of Light: Cornea → Aqueous humor → Lens → Vitreous humor → Retina.

• Pathway of Vision: Retina → Optic nerve → Thalamus → Visual cortex.

Metabolism and Energy Balance

Carbohydrate Metabolism

• Glycogen: Storage form of glucose in liver and muscle.

• Fasted vs. Fed State: Fed state promotes storage (insulin); fasted state promotes mobilization (glucagon).

• Gluconeogenesis: Formation of glucose from non-carbohydrate sources.

• Glycogenolysis: Breakdown of glycogen to glucose.

• Cells of the Pancreas: Alpha cells (glucagon), beta cells (insulin), delta cells (somatostatin).

• Ketone Bodies: Produced from fatty acids during prolonged fasting.

Endocrine System

Glands and Hormones

• Thyroid Gland: Produces thyroid hormones (T3, T4) regulating metabolism.

• Hypothalamus: Controls pituitary gland; links nervous and endocrine systems.

• Posterior Pituitary: Releases oxytocin and vasopressin (ADH).

• Anterior Pituitary: Releases ACTH, TSH, GH, LH, FSH, prolactin.

• Parathyroid Gland: Regulates calcium levels via parathyroid hormone (PTH).

• Adrenal Gland: Cortex produces corticosteroids; medulla produces catecholamines (epinephrine, norepinephrine).

• Hormonal Classifications: Peptide, steroid, and amine hormones.

• Hyperthyroidism vs. Hypothyroidism: Excess vs. deficient thyroid hormone production.

Cardiovascular and Respiratory Physiology

Perfusion and Ventilation

• Perfusion: Blood flow through tissues.

• Ventilation: Movement of air into and out of the lungs.

• Alveoli: Tiny air sacs for gas exchange.

• Surfactant: Reduces surface tension in alveoli, preventing collapse.

• Functions of Respiratory System: Gas exchange, pH regulation, protection, vocalization.

• Types of Alveolar Cells: Type I (gas exchange), Type II (produce surfactant).

• Pulmonary Ventilation: Total movement of air in and out of lungs per minute.

• Inspiration vs. Expiration: Inspiration is active (diaphragm contracts); expiration is usually passive (diaphragm relaxes).

• Respiratory Volumes and Capacities: Measured by spirometry (e.g., tidal volume, vital capacity).

Blood and Hematology

Blood Components and Functions

• Erythropoietin: Hormone stimulating red blood cell production.

• Thrombopoietin: Hormone stimulating platelet production.

• Hematocrit: Percentage of blood volume occupied by red blood cells.

• Plasma: Liquid component of blood, contains water, proteins, nutrients, hormones.

• Hemolysis: Destruction of red blood cells.

• Fibrinolysis: Breakdown of blood clots.

• Function of Red Blood Cells: Transport oxygen and carbon dioxide.

• RBC Lifespan and Destruction: RBCs live ~120 days; destroyed in spleen and liver, components recycled.

• Functions of Platelets: Blood clotting (hemostasis).

Table: Comparison of Intracellular and Extracellular Fluid Composition

Component	Intracellular Fluid	Extracellular Fluid
Major Cation	K+	Na+
Major Anion	Phosphate, proteins	Cl-, HCO3-
Protein Concentration	High	Low

Key Equations

• Nernst Equation (for equilibrium potential):

$E = \frac{RT}{zF} \ln \left( \frac{[\text{ion}]_{\text{outside}}}{[\text{ion}]_{\text{inside}}} \right)$

• Ohm's Law (for membrane potential):

$I = \frac{V}{R}$

• Fick's Law of Diffusion:

$\text{Rate of diffusion} = \frac{(\text{surface area}) \times (\text{concentration gradient}) \times (\text{membrane permeability})}{\text{membrane thickness}}$

Additional info: Some explanations and table entries were expanded for clarity and completeness based on standard physiology textbooks.