Comprehensive Review Notes: Human Anatomy, Cell Biology, Histology, and the Integumentary System

Anatomy vs. Physiology

Anatomy is the study of body structures and their physical relationships, whereas Physiology is the study of how those structures function.

Principle of Complementarity

The physiological principle stating that function always reflects structure.

Levels of Biological Organization

Chemical level $\rightarrow$ Cellular level $\rightarrow$ Tissue level $\rightarrow$ Organ level $\rightarrow$ Organ system level $\rightarrow$ Organismal level.

Homeostasis

The active maintenance of stable internal physiological conditions around established set points.

Homeostatic Control Loop Components

Stimulus $\rightarrow$ Receptor/Sensor (detects change) $\rightarrow$ Afferent pathway $\rightarrow$ Control Center (integrates signal) $\rightarrow$ Efferent pathway $\rightarrow$ Effector (executes response).

Negative Feedback

A primary homeostatic mechanism that reverses or reduces the original stimulus to return a variable to its set point (e.g., thermoregulation, blood glucose control).

Positive Feedback

A mechanism that amplifies or accelerates the original stimulus, pushing the variable further from its initial state to manage infrequent events (e.g., oxytocin release during labor, platelet clotting).

Anatomical Position

Standard reference posture: standing upright, feet together, eyes facing forward, arms at sides, and palms facing forward.

Fluid Mosaic Model

Depicts the plasma membrane as a thin ($7\text{--}10\,\text{nm}$) phospholipid bilayer embedded with cholesterol ($\sim 20\%$), integral proteins, peripheral proteins, and carbohydrates.

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ ATPase)

A primary active transport carrier protein that pumps $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell per ATP hydrolysed.

Modes of Cell Signaling

Autocrine (acts on self), Paracrine (acts on nearby target cells), and Endocrine (hormones travel via bloodstream to distant target cells).

Cell Junction Types

Adherens junctions (cadherins + actin), Desmosomes (cadherins + intermediate filaments), Hemidesmosomes (integrins + ECM), Tight junctions (occludins seal intercellular space), and Gap junctions (connexons allow direct communication).

Exocrine Secretion Mechanisms

Merocrine (exocytosis; e.g., salivary glands), Apocrine (apical cytoplasm pinches off; e.g., mammary glands), and Holocrine (whole cell ruptures; e.g., sebaceous glands).

Epidermal Layers (Deep to Superficial)

Stratum basale, Stratum spinosum, Stratum granulosum, Stratum lucidum (thick skin only), and Stratum corneum.

Epidermal Cell Types

Keratinocytes (structural keratin), Melanocytes (melanin pigment synthesis), Dendritic/Langerhans cells (immune antigen presentation), and Tactile/Merkel cells (fine touch mechanoreceptors).

Layers of the Dermis

Papillary layer (loose connective tissue with dermal papillae) and Reticular layer (dense irregular connective tissue with cleavage lines).

Major Types of Skin Cancer

Basal cell carcinoma (stratum basale invasion, most common), Squamous cell carcinoma (keratinocytes of stratum spinosum), and Melanoma (melanocytes, highly metastatic, evaluated via ABCD rule).

Rule of Nines

A system evaluating burn severity by dividing the body into 11 regions accounting for $9\%$ each, plus the perineum at $$1\%

Anatomy vs. Physiology

Anatomy is the study of body structures and their physical relationships, whereas physiology is the study of how those structures function to perform life-sustaining processes.

Principle of Complementarity of Structure and Function

The physiological principle stating that function always reflects structure.

Levels of Biological Organization

Chemical level $\rightarrow$ Cellular level $\rightarrow$ Tissue level $\rightarrow$ Organ level $\rightarrow$ Organ system level $\rightarrow$ Organismal level.

Necessary Life Functions

Maintaining boundaries, movement, responsiveness, digestion, metabolism, excretion, reproduction, and growth.

Essential Survival Needs of the Human Body

Nutrients, oxygen, water, normal body temperature, and appropriate atmospheric pressure.

Homeostasis

The process of maintaining stable internal physiological conditions around established set points.

Components of a Homeostatic Control System

Stimulus $\rightarrow$ Receptor/Sensor $\rightarrow$ Afferent pathway $\rightarrow$ Control center $\rightarrow$ Efferent pathway $\rightarrow$ Effector $\rightarrow$ Response.

Negative Feedback Mechanism

A primary homeostatic mechanism where the response reduces or shuts off the original stimulus, moving the variable in the opposite direction of initial change.

Positive Feedback Mechanism

A mechanism where the response enhances or amplifies the original stimulus, moving the variable further in the same direction.

Standard Anatomical Position

Upright standing posture with feet together, eyes facing forward, arms at sides, and palms facing forward.

Directional Terms: Proximal vs. Distal

Proximal means closer to the origin of a body part or point of attachment; distal means farther from the origin or point of attachment.

Anatomical Planes of Section

Transverse (divides body into upper and lower parts), Frontal/Coronal (divides into anterior and posterior parts), and Sagittal/Midsagittal (divides into left and right parts).

Serous Membrane Layers

Parietal serosa (lines cavity walls) and Visceral serosa (covers organs within the cavity), separated by thin serous fluid.

Primary Biomolecules and Their Monomers

Nucleic acids (nucleotides), proteins (amino acids), lipids (phospholipids/fatty acids), and carbohydrates (monosaccharides).

Three Major Parts of a Human Cell

Plasma membrane (outer selective barrier), cytoplasm (intracellular fluid with organelles), and nucleus (cellular control center).

Fluid Mosaic Model

Depicts the plasma membrane as a thin ($7\text{--}10\,\text{nm}$) phospholipid bilayer embedded with cholesterol ($\sim 20\%$), integral proteins, peripheral proteins, and carbohydrates.

Factors Influencing Plasma Membrane Fluidity

Temperature (higher increases fluidity), fatty acid saturation (unsaturated fatty acids increase fluidity), and cholesterol content (modulates membrane stability).

Solute Permeability across the Plasma Membrane

Small nonpolar solutes (oxygen, carbon dioxide, steroids) are permeable; large polar solutes (carbohydrates, proteins) and charged ions are impermeable.

Simple Diffusion

Unassisted passive transport of small or lipid-soluble solutes directly across the phospholipid bilayer down a concentration gradient.

Osmosis

The passive diffusion of water across a selectively permeable membrane toward a region of higher solute concentration.

Tonicity Conditions

Isotonic (equal solute concentration, cell size unchanged), Hypertonic (higher external solute concentration, cell shrinks), and Hypotonic (lower external solute concentration, cell swells).

Facilitated Diffusion Types

Channel-mediated (movement through pore-forming transmembrane proteins) and carrier-mediated (movement via conformational changes of transport proteins).

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ ATPase)

A primary active transport protein that hydrolyzes ATP to move $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell.

Modes of Intercellular Signaling

Autocrine (acts on the secreting cell itself), Paracrine (acts on nearby target cells), and Endocrine (hormones travel via bloodstream to distant target cells).

Resting Membrane Potential

The voltage or electrical potential difference across the plasma membrane created by the separation of oppositely charged ions.

Anchoring Cell Junctions

Adherens junctions (cadherins + actin filaments), Desmosomes (cadherins + intermediate filaments), and Hemidesmosomes (integrins + extracellular matrix).

Communicating and Occluding Cell Junctions

Tight junctions (occludins seal intercellular spaces) and Gap junctions (connexons form direct channels allowing passage of small molecules).

Cellular Extensions Functions

Cilia (propel substances across the cell surface), Flagella (propel the entire cell, e.g., sperm), and Microvilli (increase surface area for absorption).

Phases of the Cell Cycle

Interphase ($\text{G}_1$, $\text{S}$ for DNA replication, $\text{G}_2$) and Mitotic Phase (Mitosis: prophase, metaphase, anaphase, telophase; Cytokinesis).

Four Primary Tissue Types

Epithelial, connective, muscle, and nervous tissue.

Key Characteristics of Epithelial Tissue

Tightly packed cells, apical/basolateral polarity, supported by underlying connective tissue, avascular but innervated, and highly regenerative.

Classification Criteria for Epithelium

Number of cell layers (simple, stratified, pseudostratified) and shape of surface cells (squamous, cuboidal, columnar).

Simple Squamous Epithelium

Single layer of flat disc-like cells; functions in filtration and diffusion (located in lung alveoli, kidney glomeruli, and blood vessel lumens).

Simple Cuboidal Epithelium

Single layer of cube-like cells with large central round nuclei; functions in secretion and absorption (located in kidney tubules and gland ducts).

Simple Columnar Epithelium

Single layer of tall rectangular cells often featuring microvilli or cilia; functions in absorption and mucus secretion (located in digestive and respiratory tracts).

Pseudostratified Columnar Epithelium

Single layer of cells of varying heights with nuclei at different levels; functions in secretion and propulsion (located in upper respiratory tract).

Stratified Squamous Epithelium

Multiple cell layers with flat apical surface cells; functions in protection against abrasion (located in skin, esophagus, and mouth).

Transitional Epithelium

Stratified epithelium with rounded surface cells that flatten when stretched; enables expansion and urine storage (located in ureters, bladder, and urethra).

Modes of Exocrine Secretion

Merocrine (exocytosis without loss of cytoplasm), Apocrine (apical cytoplasm pinches off), and Holocrine (entire cell ruptures).

Structural Components of Connective Tissue

Specialized cells, protein fibers (collagen, elastin, reticulin), and ground substance (which together form the extracellular matrix).

Primary Connective Tissue Cell Types

Fibroblasts (connective tissue proper), Chondrocytes (cartilage), Osteocytes (bone), and Adipocytes (fat tissue).

Fibers of Connective Tissue Matrix

Collagen fibers (resist pulling forces), Elastic fibers (provide stretch and recoil), and Reticular fibers (short thin fibers forming a supportive meshwork).

Types of Loose Connective Tissue

Areolar (cushions organs), Adipose (insulation and energy storage), and Reticular (supports immune cells in lymphoid organs).

Types of Dense Connective Tissue

Dense regular (parallel collagen; tendons/ligaments), Dense irregular (randomly arranged collagen; dermis/capsules), and Elastic (high elastin content; arterial walls).

Cartilage Tissue Types

Hyaline cartilage (flexible firm gel matrix; nose/trachea/ends of long bones), Elastic cartilage (rich in elastin; external ear/epiglottis), and Fibrocartilage (thick collagen fibers; intervertebral discs/pubic symphysis).

Three Types of Muscle Tissue

Skeletal (striated, multinucleated, voluntary), Cardiac (striated, branched, intercalated discs, involuntary), and Smooth (non-striated, spindle-shaped, involuntary).

Cells of Nervous Tissue

Neurons (excitable cells that generate and transmit electrical signals) and Glial cells (neuroglia that support, protect, and nourish neurons).

Three Steps of Tissue Repair

Inflammation (clot formation) $\rightarrow$ Organization (restoration of blood supply and temporary ECM formation) $\rightarrow$ Regeneration and Fibrosis (scab detachment and tissue restoration).

Regenerative Capacity Across Tissue Types

Extremely well (epithelia, bone, blood-forming tissue), Moderate (smooth muscle, dense regular connective tissue), Weak (skeletal muscle, cartilage), None (cardiac muscle, CNS nervous tissue).

Primary Embryonic Germ Layers

Ectoderm (epidermis and nervous system), Mesoderm (muscle, bone, connective tissues), and Endoderm (mucosal linings of digestive and respiratory tracts).

Major Functions of the Integumentary System

Protection (physical/chemical/biological barrier), thermoregulation, cutaneous sensation, vitamin D synthesis, excretion, and blood reservoir.

Cell Types of the Epidermis

Keratinocytes (structural keratin production), Melanocytes (melanin pigment synthesis), Dendritic/Langerhans cells (immune antigen presentation), and Tactile/Merkel cells (fine touch mechanoreceptors).

Epidermal Layers from Deep to Superficial

Stratum basale $\rightarrow$ Stratum spinosum $\rightarrow$ Stratum granulosum $\rightarrow$ Stratum lucidum (thick skin only) $\rightarrow$ Stratum corneum.

Layers of the Dermis

Papillary layer (superficial loose connective tissue with dermal papillae) and Reticular layer (deep dense irregular connective tissue with collagen bundles).

Primary Skin Pigments

Melanin (reddish-yellow to brownish-black pigment made by melanocytes), Carotene (yellow-orange plant pigment accumulating in stratum corneum/fat), and Hemoglobin (pinkish hue from oxygenated red blood cells).

Clinical Alterations in Skin Color

Cyanosis (blue/low oxygen), Erythema (redness/fever or inflammation), Pallor (paleness/anemia or stress), Jaundice (yellowing/liver dysfunction), and Ecchymosis (bruising/leaked blood).

Hair Follicle Growth Phases

Anagen phase (active hair growth phase), Catagen phase (end of active growth transition phase), and Telogen phase (follicle resting phase).

Major Types of Skin Cancer

Basal cell carcinoma (stratum basale invasion, most common/least malignant), Squamous cell carcinoma (keratinocytes of stratum spinosum), and Melanoma (melanocytes, highly metastatic).

ABCD Rule for Melanoma Detection

A = Asymmetry, B = Border irregularity, C = Color variation, D = Diameter larger than $6\,\text{mm}$.

Classification of Burn Depth

First-degree (epidermal damage only; redness/edema/pain), Second-degree (partial thickness: epidermis and upper dermis; blisters), and Third-degree (full thickness: destroys all layers and nerve endings).

Anatomy vs. Physiology

Anatomy is the study of body structures and their physical relationships, whereas physiology is the study of how those structures function to perform life-sustaining processes.

Principle of Complementarity of Structure and Function

The physiological principle stating that function always reflects structure.

Levels of Biological Organization

Chemical level $\rightarrow$ Cellular level $\rightarrow$ Tissue level $\rightarrow$ Organ level $\rightarrow$ Organ system level $\rightarrow$ Organismal level.

Necessary Life Functions

Maintaining boundaries, movement, responsiveness, digestion, metabolism, excretion, reproduction, and growth.

Essential Survival Needs of the Human Body

Nutrients, oxygen, water, normal body temperature, and appropriate atmospheric pressure.

Homeostasis

The process of maintaining stable internal physiological conditions around established set points.

Components of a Homeostatic Control System

Stimulus $\rightarrow$ Receptor/Sensor $\rightarrow$ Afferent pathway $\rightarrow$ Control center $\rightarrow$ Efferent pathway $\rightarrow$ Effector $\rightarrow$ Response.

Negative Feedback Mechanism

A primary homeostatic mechanism where the response reduces or shuts off the original stimulus, moving the variable in the opposite direction of initial change.

Positive Feedback Mechanism

A mechanism where the response enhances or amplifies the original stimulus, moving the variable further in the same direction.

Standard Anatomical Position

Upright standing posture with feet together, eyes facing forward, arms at sides, and palms facing forward.

Directional Terms: Proximal vs. Distal

Proximal means closer to the origin of a body part or point of attachment; distal means farther from the origin or point of attachment.

Anatomical Planes of Section

Transverse (divides body into upper and lower parts), Frontal/Coronal (divides into anterior and posterior parts), and Sagittal/Midsagittal (divides into left and right parts).

Serous Membrane Layers

Parietal serosa (lines cavity walls) and Visceral serosa (covers organs within the cavity), separated by thin serous fluid.

Primary Biomolecules and Their Monomers

Nucleic acids (nucleotides), proteins (amino acids), lipids (phospholipids/fatty acids), and carbohydrates (monosaccharides).

Three Major Parts of a Human Cell

Plasma membrane (outer selective barrier), cytoplasm (intracellular fluid with organelles), and nucleus (cellular control center).

Fluid Mosaic Model

Depicts the plasma membrane as a thin ($7\text{--}10\,\text{nm}$) phospholipid bilayer embedded with cholesterol ($\sim 20\%$), integral proteins, peripheral proteins, and carbohydrates.

Factors Influencing Plasma Membrane Fluidity

Temperature (higher increases fluidity), fatty acid saturation (unsaturated fatty acids increase fluidity), and cholesterol content (modulates membrane stability).

Solute Permeability across the Plasma Membrane

Small nonpolar solutes (oxygen, carbon dioxide, steroids) are permeable; large polar solutes (carbohydrates, proteins) and charged ions are impermeable.

Simple Diffusion

Unassisted passive transport of small or lipid-soluble solutes directly across the phospholipid bilayer down a concentration gradient.

Osmosis

The passive diffusion of water across a selectively permeable membrane toward a region of higher solute concentration.

Tonicity Conditions

Isotonic (equal solute concentration, cell size unchanged), Hypertonic (higher external solute concentration, cell shrinks), and Hypotonic (lower external solute concentration, cell swells).

Facilitated Diffusion Types

Channel-mediated (movement through pore-forming transmembrane proteins) and carrier-mediated (movement via conformational changes of transport proteins).