Human Physiology 261: Comprehensive Midterm Study Guide

Physiology Fundamentals

Definition and Scope of Physiology

Physiology is the study of the functions and mechanisms occurring in living organisms. It explains how cells, tissues, and organs work together to sustain life.

• Teleological Approach: Explains physiological processes by their purpose ("why").

• Mechanistic Approach: Explains processes by their underlying mechanisms ("how").

• Placebo: An inert substance used in experiments to test the effect of treatments.

• Hypothesis: A testable statement predicting the outcome of an experiment.

Homeostasis

Concept and Importance

Homeostasis refers to the maintenance of a stable internal environment despite external changes. It is essential for normal physiological function.

• Examples: Regulation of body temperature, blood glucose, and pH.

• Mechanisms: Negative feedback loops are common, where a change triggers a response that counteracts the initial change.

Molecular Interactions

Cations, Electrons, and Amino Acids

Molecules interact through chemical bonds and electrical charges.

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

• Electrons: Negatively charged particles involved in chemical bonding.

• Essential Amino Acids: Cannot be synthesized by the body; must be obtained from diet.

• Nonessential Amino Acids: Can be synthesized by the body.

pH Scale

The pH scale measures hydrogen ion concentration, indicating acidity or alkalinity.

• Formula: $\text{pH} = -\log_{10}[\text{H}^+]$

• Range: 0 (acidic) to 14 (basic); 7 is neutral.

Compartmentation: Cells and Tissues

Body Compartments

The body is divided into compartments separated by membranes.

• Intracellular: Inside cells.

• Intercellular: Between cells.

• Extracellular: Outside cells; includes plasma and interstitial fluid.

Intracellular and Extracellular Ions

• Intracellular: High K+, low Na+, high protein concentration.

• Extracellular: High Na+, low K+, lower protein concentration.

Rules of Diffusion

• Movement from high to low concentration.

• Rate depends on temperature, concentration gradient, and membrane permeability.

Cellular Organelles and Functions

Key Organelles

• Rough Endoplasmic Reticulum (ER): Protein synthesis.

• Golgi Apparatus: Modifies, sorts, and packages proteins.

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

Cell Membrane

• Function: Regulates entry and exit of substances.

• Proteins: Channels, carriers, receptors, enzymes.

• Cholesterol: Maintains membrane fluidity.

Protein Synthesis Steps

1. Transcription (DNA to mRNA)

2. Translation (mRNA to protein)

3. Post-translational modification (Golgi apparatus)

Exocrine Glands

• Secrete substances via ducts (e.g., sweat, salivary glands).

Levels of Organization

• Cell → Tissue → Organ → Organ System → Organism

Energy and Cellular Metabolism

Energy Concepts

• Activation Energy: Minimum energy required for a reaction.

• Exergonic Reactions: Release energy.

Enzymes

• Biological catalysts; speed up reactions.

• Specificity: Each enzyme acts on a specific substrate.

Membrane Dynamics

Exocytosis

• Process by which cells expel materials via vesicles.

Neurons: Cellular and Network Properties

Resting Membrane Potential

• Difference in charge across the cell membrane at rest.

• Typical value: -70 mV

• Formula: $\text{RMP} = \frac{RT}{F} \ln \left( \frac{[\text{K}^+]_{\text{out}}}{[\text{K}^+]_{\text{in}}} \right)$ (Nernst equation for K+)

CNS vs. PNS

• CNS: Brain and spinal cord.

• PNS: Peripheral nerves.

Ganglia vs. Nuclei

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

• Nuclei: Clusters in the CNS.

Sensory/Afferent vs. Motor/Efferent Neurons

• Sensory/Afferent: Carry information to CNS.

• Motor/Efferent: Carry commands from CNS to effectors.

Neuron Anatomy

• Dendrites: Receive signals.

• Axon: Transmits signals.

• Cell body: Contains nucleus.

Phases of Neuronal Action Potential

1. Resting state

2. Depolarization

3. Overshoot

4. Repolarization

5. Hyperpolarization

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

• Refractory Period: Time when neuron cannot fire another action potential.

• Absolute: No action potential possible.

• Relative: Action potential possible with stronger stimulus.

Excitatory Postsynaptic Potential (EPSP)

• Depolarizes postsynaptic membrane, increasing likelihood of action potential.

Na+/K+ Pump Function

• Maintains ion gradients by pumping 3 Na+ out and 2 K+ in.

• Formula: $\text{ATP} + 3\text{Na}^+_{\text{in}} + 2\text{K}^+_{\text{out}} \rightarrow 3\text{Na}^+_{\text{out}} + 2\text{K}^+_{\text{in}} + \text{ADP} + \text{P}_i$

The Central Nervous System

Metabolic Needs of the Brain

• High demand for oxygen and glucose.

Cerebrospinal Fluid (CSF)

• Protects and nourishes the brain.

Learning Types

• Associative: Linking two stimuli.

• Nonassociative: Change in response to a single stimulus.

Sensory Physiology

Sensory Pathways

• Most travel to the thalamus; exception: olfactory pathway goes directly to cortex.

Middle Ear Structures and Functions

• Tympanic membrane: Vibrates in response to sound.

• Ossicles: Transmit vibrations to inner ear.

Taste Sensations

• Five types: sweet, sour, salty, bitter, umami.

• Each triggered by specific chemicals (e.g., sweet by sugars).

Nociceptors

• Detect pain stimuli.

Anatomy of the Eye

• Pathway of Light: Cornea → Pupil → Lens → Retina.

• Pathway of Vision: Retina → Optic nerve → Brain.

Metabolism and Energy Balance

Glycogen

• Storage form of glucose in liver and muscle.

Fasted vs. Fed State Metabolism

• Fasted: Glucagon increases, promoting gluconeogenesis and glycogenolysis.

• Fed: Insulin increases, promoting glucose uptake and storage.

Gluconeogenesis

• Formation of glucose from non-carbohydrate sources.

Glycogenolysis

• Breakdown of glycogen to glucose.

Pancreatic Cells and Functions

Cell Type	Function
Alpha	Secrete glucagon
Beta	Secrete insulin
Delta	Secrete somatostatin

Ketone Bodies

• Produced during prolonged fasting; alternative energy source.

Endocrine System

Endocrine Glands and Hormones

Gland	Hormones
Thyroid	Thyroxine (T4), Triiodothyronine (T3)
Hypothalamus	Releasing/inhibiting hormones
Posterior Pituitary	ADH, Oxytocin
Anterior Pituitary	GH, ACTH, TSH, LH, FSH, Prolactin
Parathyroid	Parathyroid hormone (PTH)
Adrenal Cortex	Cortisol, Aldosterone
Adrenal Medulla	Epinephrine, Norepinephrine

Hormonal Classifications

• Peptide: Made of amino acids (e.g., insulin).

• Steroid: Derived from cholesterol (e.g., cortisol).

• Amino acid-derived: (e.g., epinephrine).

Thyroid Disorders

• Hyperthyroidism: Excess thyroid hormone; increased metabolism.

• Hypothyroidism: Deficient thyroid hormone; decreased metabolism.

Cardiovascular and Respiratory Physiology

Perfusion

• Delivery of blood to tissues.

Ventilation

• Movement of air in and out of lungs.

Alveoli and Surfactant

• Alveoli: Site of gas exchange.

• Type I cells: Gas exchange.

• Type II cells: Produce surfactant.

• Surfactant: Reduces surface tension, prevents alveolar collapse.

Pulmonary Ventilation

• Inspiration: Air enters lungs.

• Expiration: Air exits lungs.

Respiratory Volumes and Capacities

• Tidal Volume (TV): Air moved per breath.

• Vital Capacity (VC): Maximum air exhaled after maximum inhalation.

• Residual Volume (RV): Air remaining after exhalation.

Blood Physiology

Key Blood Components

• Erythropoietin: Stimulates RBC production.

• Thrombopoietin: Stimulates platelet production.

• Hematocrit: Percentage of RBCs in blood.

• Plasma: Liquid component of blood.

Hemolysis and Fibrinolysis

• Hemolysis: Destruction of RBCs.

• Fibrinolysis: Breakdown of blood clots.

Red Blood Cells (RBCs)

• Function: Transport oxygen and carbon dioxide.

• Lifespan: ~120 days.

• Destruction/Recycling: Occurs in spleen and liver; iron recycled.

Platelets

• Essential for blood clotting.

Additional info: Some explanations and examples were expanded for clarity and completeness.