Lecture Notes Review: Understanding Energy, Cellular Junctions, Skin, and Skeletal System

Chapter 3 – Understanding Energy

Definition of Energy

• Energy is defined as the capacity to do work and is calculated as the product of force and distance.

• In the human body, energy drives every physiological process.

  • Examples include:

  • Muscle contraction

  • Nerve transmission

Forms of Energy

• Two main forms of energy exist:

  • Potential Energy:

  • This is stored energy, for example, the chemical bonds in molecules such as ATP (adenosine triphosphate).

  • Potential energy can be converted into kinetic energy during physiological processes.

  • Kinetic Energy:

  • This is energy in motion, exemplified by the movement of ions across a membrane or during muscle contractions.

• Conversion Example:

  • ATP hydrolysis releases potential energy to perform work, specifically powering muscle contractions.

ATP as an Immediate Energy Source

• ATP is characterized as the body’s immediate energy currency.

• The breakdown of ATP into ADP (adenosine diphosphate) and inorganic phosphate releases energy.

  • This released energy is utilized for several biological processes, including:

  • Active transport

  • Biosynthesis

  • Mechanical work

Forms of Energy in the Body

• Diverse forms include:

  • Chemical Energy: Stored in molecular bonds.

  • Electrical Energy: Involves the movement of charged particles.

  • Mechanical Energy: Related to the movement of structures.

  • Radiant Energy: Exemplified by light.

• Heat:

  • Notably, heat is considered the most abundant form of energy due to inefficiencies in energy transfer processes.

  • This phenomenon reflects the second law of thermodynamics.

Laws of Thermodynamics

1. First Law:

   • Energy cannot be created or destroyed; it only changes form.

   • In physiological contexts, chemical energy from food is transformed into kinetic and thermal energy.

2. Second Law:

   • Every energy transformation incurs a loss of usable energy as heat, resulting in an increase in entropy (disorder).

   • Example: The breakdown of ATP releases heat, contributing to the maintenance of body temperature.

Chemical Reactions and Metabolism

• Metabolism is defined as the sum of all chemical reactions occurring in the body.

  • Metabolism is divided into two categories:

  • Anabolism: Processes that build up molecules.

  • Catabolism: Processes that break down molecules.

• Chemical equations depict these reactions, highlighting reactants, products, and direction of change.

• Oxidation-Reduction (Redox) Reactions:

  • Crucial for metabolism:

  • Oxidation: Loss of electrons.

  • Reduction: Gain of electrons.

  • These reactions are fundamental to cellular respiration and ATP synthesis.

Chapter 5 – Cellular Junctions, Glands, and Membranes

Cellular Junctions

• Cellular junctions connect neighboring cells and maintain tissue integrity.

• Types of cellular junctions include:

  • Tight Junctions:

  • Seal neighboring cells together to prevent leakage.

  • Desmosomes:

  • Anchor cells to each other, enhancing resistance to mechanical stress.

  • Hemidesmosomes:

  • Anchor cells to the basement membrane.

  • Gap Junctions:

  • Facilitate communication between cells through ions and small molecules.

Glands

• A gland is defined as a cell or organ that secretes substances for further use in the body or for elimination.

• Exocrine Glands:

  • Possess ducts that carry secretions to a surface (e.g., sweat glands).

• Endocrine Glands:

  • Release hormones directly into the bloodstream (e.g., thyroid gland).

• Glands such as the pancreas perform both exocrine and endocrine functions.

• Exocrine Gland Classification:

  • Based on duct structure (simple or compound) and the arrangement of secretory cells (tubular, acinar, or tubuloacinar).

• Secretion Types:

  • Serous: Watery secretions.

  • Mucous: Viscous secretions.

  • Mixed Glands: Secrete both types.

• Modes of Secretion:

  • Merocrine: Involves exocytosis, e.g., sweat glands.

  • Apocrine: Secretion includes cellular fragments, e.g., mammary glands.

  • Holocrine: Involves cellular disintegration, e.g., sebaceous glands.

Membranes

• Body membranes encompass several types, including:

  • Mucous Membranes: Line cavities that open to the exterior.

  • Serous Membranes: Line closed cavities.

  • Cutaneous Membrane: Refers to the skin.

  • Synovial Membranes: Line joints.

• Specialized membranes include endothelium and mesothelium.

Tissue Growth and Repair

• Tissue growth occurs via:

  • Hyperplasia: Increase in the number of cells.

  • Hypertrophy: Increase in cell size.

  • Neoplasia: Abnormal growth of tissue.

• Differentiation: The specialization of cells.

• Metaplasia: Change from one mature tissue type to another.

• Stem Cells: Classified by their potential:

  • Totipotent: Can become any cell type.

  • Pluripotent: Can become many cell types.

  • Multipotent: Can become a few cell types.

  • Unipotent: Can become only one type of cell.

• Tissue repair methods:

  • Regeneration: Restoration of normal tissue function.

  • Fibrosis: Formation of scar tissue.

• Healing processes involve inflammation, formation of a clot, tissue regeneration, and remodeling.

• Atrophy: Refers to a reduction in tissue size due to disuse or aging.

• Necrosis: Pathological tissue death.

• Apoptosis: Programmed cell death, critical for normal development.

• Types of necrosis include:

  • Infarction: Resulting from loss of blood supply.

  • Gangrene: Related to decay due to infection.

Chapter 6 – The Skin and Subcutaneous Tissue Overview

Overview of the Integumentary System

• The integumentary system consists of the skin, hair, nails, and associated glands.

• Dermatology is the branch of medicine devoted to the study of this system.

Epidermis and Dermis

• The skin comprises two primary layers:

  • Epidermis:

  • Contains five layers in thick skin:

    • Stratum Basale

    • Stratum Spinosum

    • Stratum Granulosum

    • Stratum Lucidum

    • Stratum Corneum

  • Thin skin lacks the stratum lucidum.

  • Dermis:

  • Features two layers:

    • Papillary Layer (areolar tissue)

    • Reticular Layer (dense irregular tissue)

  • Dermal papillae contribute to fingerprints and enhance grip.

Cells of the Epidermis

• Types of epidermal cells:

  • Keratinocytes: Produce keratin.

  • Melanocytes: Synthesize melanin, contributing to pigmentation.

  • Tactile (Merkel) Cells: Detect touch sensations.

  • Dendritic Cells: Provide immune defense within the skin.

Skin Color and Surface Markings

• Skin color arises from:

  • Melanin

  • Hemoglobin

  • Carotene

• Abnormal skin coloration may indicate disease, examples include:

  • Cyanosis: Indicates low oxygen levels.

  • Erythema: Sign of increased blood flow.

  • Pallor: Reflects low blood flow.

  • Jaundice: Associated with the presence of bilirubin.

  • Albinism: Characterized by a lack of melanin.

Hair and Nails

• Types of hair:

  • Lanugo: Soft, fine hair in fetuses.

  • Vellus: Fine, short hair covering most of the body.

  • Terminal Hair: Coarse, thicker hair.

• Hair structure:

  • Comprised of three layers:

  • Medulla

  • Cortex

  • Cuticle

  • Hair growth occurs in cycles:

  • Anagen: Active growth phase.

  • Catagen: Regression phase.

  • Telogen: Resting phase.

• Hair shape and pigmentation determine its curliness and color.

• Nails consist of keratinized cells:

  • The growth zone is found at the nail matrix.

  • The visible part of the nail is called the nail plate, which covers the nail bed.

Cutaneous Glands

• Types of cutaneous glands:

  • Sweat Glands:

  • Include eccrine glands (function primarily in cooling).

  • Apocrine glands that produce scent.

  • Sebaceous Glands: Secrete sebum for lubrication.

  • Ceruminous Glands: Responsible for earwax production.

  • Mammary Glands: Secrete milk.

Skin Disorders

• Skin cancers include:

  • Basal Cell Carcinoma: Most common, originates in the basal layer.

  • Squamous Cell Carcinoma: Arises from squamous cells.

  • Malignant Melanoma: More severe form originating from melanocytes.

• Burns classification:

  • First-Degree Burns: Affect only the epidermis.

  • Second-Degree Burns: Involve both the epidermis and dermis.

  • Third-Degree Burns: Affect deeper tissues.

• Treatment strategies for burns involve fluid replacement and infection control.

Chapter 7 – Tissues and Organs of the Skeletal System Overview

Overview

• Osteology is the study of bones.

• The skeletal system comprises bones, cartilage, and ligaments.

• Main functions include:

  • Support: Structural framework for the body.

  • Protection: Safeguards vital organs.

  • Movement: Facilitates locomotion and posture.

  • Mineral Storage: Stores essential minerals.

  • Blood Cell Formation: Known as hematopoiesis, it occurs in the bone marrow.

Bone Structure

• Long Bone Structure:

  • Composed of:

  • Diaphysis: The shaft of the bone.

  • Epiphyses: The ends of the bone.

  • Epiphyseal Plate: The growth zone.

  • Articular Cartilage: Covers the surfaces at the joints.

  • Periosteum: A fibrous membrane covering the bone surface.

  • Endosteum: Lining the internal surfaces of the bone.

• Bone Types:

  • Compact Bone: Forms the outer shell of the bone.

  • Spongy Bone: Fills the ends and reduces bone weight.

  • Flat Bones: Structurally comprised of compact bone surrounding spongy bone.

Histology of Osseous Tissue

• Bone tissue includes several cell types:

  • Osteogenic Cells: Stem cells that can differentiate into other types of bone cells.

  • Osteoblasts: Responsible for bone formation (builders).

  • Osteocytes: Mature bone cells that maintain bone tissue.

  • Osteoclasts: Responsible for bone resorption (breakdown).

• Matrix composition:

  • Organic Components: Primarily collagen, which provides flexibility.

  • Inorganic Components: Minerals such as calcium phosphate, contributing to hardness.

• Osteons: These represent the structural units of compact bone, featuring central canals that house blood vessels.

• Spongy Bone: Lacks the organized structure of osteons and contains trabecular spaces filled with marrow.

• Bone marrow:

  • Red marrow (blood-forming) is predominant in children, while yellow marrow (fat-storing) is common in adults.

Bone Development and Growth

• Intramembranous Ossification:

  • Process through which flat bones (e.g., skull) develop.

• Endochondral Ossification:

  • Process where cartilage is replaced by bone in long bones.

• Growth occurs at the metaphysis through zones of proliferation (increase in cell number) and hypertrophy (increase in cell size), accounting for growth in height.

• Bone Remodeling:

  • Occurs throughout life in response to mechanical stress, maintaining structural integrity.

Physiology of Osseous Tissue

• Mineralization: The process of calcium deposition is performed by osteoblasts.

• Resorption: Breakdown of bone is executed by osteoclasts.

• Calcium Homeostasis:

  • Hormones involved include:

  • Calcitriol: Increases calcium levels.

  • Calcitonin: Decreases calcium levels.

  • Parathyroid Hormone: Increases calcium levels.

• Phosphate Regulation: Levels are similarly regulated through hormonal action.

• Vitamins and Hormones:

  • Key actors affecting bone metabolism and strength include vitamins A, C, D, and hormones such as estrogen, testosterone, growth hormone, and thyroid hormone.

Bone Disorders

• Fractures:

  • Types include:

  • Stress Fractures: Result from repetitive overuse.

  • Pathological Fractures: Occur due to underlying diseases.

• Healing Phases:

  • Healing process involves:

  • Hematoma formation

  • Development of a soft callus

  • Transition to a hard callus

  • Final remodeling of the bone structure.

• Osteoporosis:

  • Condition characterized by the loss of bone density, often due to imbalanced resorption and formation processes.

  • Particularly prevalent in postmenopausal women.

  • Treatment interventions include exercise, calcium supplementation, and vitamin D intake.