Introduction to Physiology & The Cell: Structure and Function

Chapter 1: Introduction to Physiology

Overview of Physiology

Physiology is the study of the functions of living organisms and their parts. It explores how the body’s structures work together to maintain life and health.

• Physiology: Focuses on body functions, integrating principles from biochemistry, engineering, and physics.

• Anatomy: The study of body structures—what the body is made of and how to identify its parts.

• Applied Physiology: Examines how structure and function are integrally related.

Hierarchy of Structural Organization

The human body is organized into a hierarchy of increasing complexity:

• Chemical Level: Atoms combine to form molecules (e.g., H2O, CO2, O2, lipids, glucose, proteins).

• Cellular Level: Cells are the basic units of life.

• Tissue Level: Groups of similar cells perform common functions.

• Organ Level: Different tissues combine to form organs with specific functions.

• Organ System Level: Organs work together to accomplish a common goal.

• Organism Level: All organ systems function together to sustain life.

Cells & Tissues – A Refresher

• Cells: Smallest living units; over 200 types in the human body. "Form follows function."

• Tissues: Groups of cells working together for a common function.

• Four Major Tissue Types:

  • Nervous: Specialized for communication via electrical signals.

  • Muscle: Specialized for contraction and movement.

  • Epithelial: Forms barriers, covers/lines surfaces, and forms glands.

  • Connective: Provides support, anchors, and links body parts.

Nervous Tissue

• Neurons: Transmit information via electrical signals; responsible for communication, control, sensory input, integration, and motor output.

• Neuroglia (Glial Cells): Support and protect neurons.

Muscle Tissue

• Function: Movement, thermoregulation, extensibility, elasticity, contractility, and excitability.

• Types:

  • Skeletal Muscle: Voluntary movement, striated.

  • Smooth Muscle: Involuntary, found in organs.

  • Cardiac Muscle: Involuntary, found in the heart, electrically excitable.

Epithelial Tissue

• Sheet-like arrangement of cells with an underlying basement membrane.

• Forms barriers, covers or lines hollow spaces (e.g., cavities, vessels).

• Can be simple (one layer) or stratified (multiple layers); shapes include squamous, columnar, and cuboidal.

Epithelium Forms Glands

• Exocrine Glands: Secrete products into ducts leading to external environments (e.g., sweat, salivary glands).

• Endocrine Glands: Secrete hormones into the bloodstream for distant effects (e.g., adrenal, thyroid, pituitary glands).

Connective Tissue

• Most abundant and diverse tissue type; provides support, anchors, and links body parts.

• Less cellular, more extracellular matrix (fibers, ground substance).

• Includes blood cells, lymph, bone cells, fibroblasts, and adipocytes (fat cells).

Organs and Organ Systems

• Organs: Formed from multiple tissues working together.

• Organ Systems: Groups of organs working together for a common function.

• Organ systems may overlap due to shared organs (e.g., male urinary and reproductive systems share the urethra).

Body Fluid Compartments & Semipermeable Membranes

Body fluids are separated by semipermeable membranes, maintaining distinct compartments:

• Total Body Water (TBW): All water contained in the body.

• Intracellular Fluid (ICF): Fluid within cells.

• Extracellular Fluid (ECF): Fluid outside cells, including plasma (in blood) and interstitial fluid (between cells).

Compartment	Volume (L)
TBW	42
ICF	28
ECF	14
Plasma	3
Interstitial Fluid	11

Additional info: These values are for a reference 70-kg adult and may vary with body size and composition.

Homeostasis

Homeostasis is the maintenance of stable internal conditions (especially in the ECF) despite external changes.

• Regulated variables include composition, temperature, and volume of ECF.

• All organ systems (except reproductive) contribute to homeostasis.

• The body regulates ECF rather than ICF for more systemic effects.

Negative Feedback

Negative feedback is the primary mechanism for maintaining homeostasis.

• A change in a regulated variable triggers a response that opposes the initial change.

• Components: sensor (detects change), integration center (processes information), effector (produces response).

• Example: Blood glucose regulation—insulin lowers blood glucose when it rises above normal.

Positive Feedback

Positive feedback amplifies the initial stimulus; less common in homeostasis.

• Example: LH secretion from the pituitary stimulates estrogen secretion from the ovaries, which further stimulates LH secretion.

Practice Applying Knowledge

• Hemorrhage: Loss of whole blood (55-60% plasma). Without new fluids, plasma volume can be restored by shifting interstitial fluid into the bloodstream.

• Exercise: Challenges variables such as temperature, pH, and oxygen levels, requiring homeostatic regulation.

Chapter 2: The Cell – Structure & Function

Biomolecules

Biomolecules are organic molecules essential for life, built primarily from carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.

• Carbon: Forms the backbone of biomolecules due to its four valence electrons, allowing complex structures.

Types of Biomolecules

• Carbohydrates: Polar, hydrophilic molecules; main energy source; monomers are monosaccharides (e.g., glucose).

• Lipids: Non-polar, hydrophobic molecules; include triglycerides, phospholipids, steroids; important for energy storage and membrane structure.

• Proteins: Polymers of amino acids; functions depend on R-group; structural, enzymatic, and regulatory roles.

• Nucleic Acids: DNA and RNA; store and transmit genetic information.

Functional Groups in Biomolecules

Functional Group	Chemical Formula	Structure	Chemical Property
Hydroxyl	-OH	—O—H	Polar
Sulfhydryl	-SH	—S—H	Polar
Phosphate	-HPO4	—O—P=O (2 O-)	Polar
Carbonyl	-COOH	—C=O—OH	Acid
Amino	-NH2	—N—H2	Base

Carbohydrates

• Composed of carbon, hydrogen, and oxygen in ring-like structures.

• Polar and water-soluble (hydrophilic).

• Examples: Glucose (blood sugar), glycogen (storage form in animals).

Lipids

• Non-polar, hydrophobic molecules (do not dissolve in water).

• Types include triglycerides (fats), phospholipids, steroids, and eicosanoids.

• Triglycerides: Three fatty acids bound to a glycerol backbone.

• Phospholipids: Amphipathic molecules with a polar head and non-polar tails; form cell membranes.

• Steroids: Four carbon ring structure; includes cholesterol and hormones like testosterone.

Proteins

• Polymers of amino acids; function depends on the sequence and conformation (shape).

• Levels of structure: primary (sequence), secondary (alpha-helix, beta-sheet), tertiary (3D folding), quaternary (multiple polypeptides).

• Types: fibrous (structural), globular (functional), mixed.

Nucleotides and Nucleic Acids

• Nucleotides: Monomers with roles in energy transfer (ATP, ADP), intracellular signaling (cAMP), and genetic material (DNA, RNA).

• Nucleic Acids: DNA (double-stranded, nucleus), RNA (single-stranded, nucleus and cytoplasm).

• Types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), transfer RNA (tRNA).

Basic Cell Structure

• Plasma Membrane: Phospholipid bilayer with embedded proteins; acts as a barrier and regulates transport.

• Nucleus: Control center containing genetic material.

• Cytoplasm: Fluid (cytosol) and organelles inside the cell.

The Plasma Membrane: Fluid Mosaic Model

• Composed of a phospholipid bilayer with proteins, cholesterol, and carbohydrates.

• Proteins serve as channels, receptors, and support structures.

• Carbohydrates are involved in cell recognition and signaling.