Ch2 Connective Tissue

Connective Tissue Germ Layer

Mesoderm

Histology

The study of tissues and their relationships within organs

Four Principal Tissue Types

Epithelial tissue, Connective tissue, Muscle tissue, and Nervous tissue

Three Basic CT Components

Cells, protein fibers, and ground substance (Protein fibers + Ground substance = Extracellular Matrix)

Extracellular Matrix (ECM) Composition

Varying amounts of water, protein fibers, and dissolved molecules (e.g., glucose, oxygen)

Three Main CT Categories

1. Connective Tissue Proper (Loose & Dense), 2. Fluid Connective Tissue (Blood & Lymph), 3. Supporting Connective Tissue (Cartilage & Bone)

Cell Spacing in CT vs Epithelium

CT cells are scattered throughout the ECM and not in direct contact; epithelial cells are closely crowded together with minimal matrix

Primary Functions of CT

Physical protection, support & structural framework, binding of structures, storage, transport, and immune protection

Resident Cells vs Wandering Cells

Resident cells are stationary cells that maintain/repair ECM (e.g., fibroblasts, adipocytes); Wandering cells are mobile immune cells (leukocytes) that move through tissue for defense

Main Resident Cells in CT Proper

Fibroblasts (secrete fibers/ground substance), Adipocytes (store triglycerides), Mesenchymal stem cells (provide additional cell types)

Primary Wandering Cells in CT Proper

Mast cells (secrete heparin & histamine), Plasma cells (produce antibodies), Free macrophages (phagocytize bacteria/debris), Neutrophils/Lymphocytes (fight infection)

Three Types of Protein Fibers

1. Collagen fibers (strong, cable-like, pink in H&E), 2. Elastic fibers (flexible, recoil, black in Verhoff stain), 3. Reticular fibers (thin, branching meshwork forming stroma)

Three Types of Loose Connective Tissue

Areolar connective tissue, Adipose connective tissue, and Reticular connective tissue

Areolar Connective Tissue

Unspecialized "packing material" with loose fibers and viscous ground substance; surrounds nerves, blood vessels, and forms subcutaneous layer

Adipose Connective Tissue

Composed of adipocytes filled with a lipid droplet pushing the nucleus aside; functions in cushioning, insulation, and energy storage

Lipogenesis vs Lipolysis

Lipogenesis is the synthesis and storage of fat in adipocytes; Lipolysis is the breakdown and release of stored fat

Reticular Connective Tissue

Meshwork of reticular fibers, fibroblasts, and leukocytes; forms the supportive stroma of lymphatic organs (spleen, thymus, lymph nodes, bone marrow)

Three Types of Dense Connective Tissue

Dense regular connective tissue, Dense irregular connective tissue, and Elastic connective tissue

Dense Regular Connective Tissue

Tightly packed parallel collagen fibers aligned to withstand stress in one direction; low vascularity leads to slow healing (found in tendons & ligaments)

Dense Irregular Connective Tissue

Bundles of collagen fibers extending in all directions to withstand stress in multiple directions (found in deep dermis, periosteum, perichondrium, and organ capsules)

Elastic Connective Tissue

Branching elastic fibers providing resilience and recoil (found in vocal cords, suspensory ligament of penis, and walls of large/medium arteries)

Chondrocytes & Lacunae

Mature cartilage cells (chondrocytes) residing in small spaces called lacunae within a gel-like matrix

Cartilage Avascularity

Chondrocytes produce anti-angiogenic chemicals preventing blood vessel formation; nutrients/wastes exchange via diffusion through matrix

Perichondrium Layers

Outer fibrous layer (provides structural protection/support) and Inner cellular layer (contains chondroblasts for growth/maintenance)

Hyaline Cartilage

Glassy matrix; most common and weakest cartilage type; perichondrium present (found in articular ends of bones, fetal skeleton, costal cartilage, nose, trachea, larynx)

Fibrocartilage

Parallel coarse collagen fibers; resists compression and acts as a shock absorber; no perichondrium (found in intervertebral discs, pubic symphysis, and knee menisci)

Elastic Cartilage

Weblike mesh of dense elastic fibers around lacunae; highly flexible and resilient; perichondrium present (found in external ear and epiglottis)

Chemical Composition of Bone ECM

1/3 Organic components (collagen fibers providing flexibility/tensile strength) and 2/3 Inorganic components (calcium salts/phosphate providing compressional strength)

Compact Bone vs Spongy Bone

Compact bone forms a solid outer shell made of osteons; Spongy bone forms an internal latticework housing hematopoietic cells for blood cell production (hematopoiesis)

Osteon (Haversian System) Components

Central canal (houses blood vessels/nerves), Concentric lamellae (rings of hard matrix), Osteocytes in lacunae, Canaliculi (tiny channels connecting lacunae to central canal)

Blood Components

Formed elements (Erythrocytes/RBCs, Leukocytes/WBCs, Platelets) and Plasma (watery ground substance + dissolved protein fibers)

Two Fluid Connective Tissues

Blood (located in cardiovascular system) and Lymph (located in lymphatic system)

Three Layers of Fascia

1. Superficial Fascia (hypodermis; areolar & adipose tissue), 2. Deep Fascia (dense irregular CT), 3. Subserous Fascia (areolar tissue between deep fascia and serous membranes)

Myofascia & Myofascial Pain Syndrome

____ is a deep fascia covering muscles; ____ ___ ____ is a chronic pain disorder where trigger points cause referred pain in unrelated body parts

Four Body Membranes

Mucous membrane (lines open passageways), Serous membrane (lines sealed cavities), Cutaneous membrane (skin), Synovial membrane (lines joint cavities)

Metaplasia

Transformation of one mature epithelium into another form (e.g., ciliated columnar to stratified squamous in smokers' tracheas)

Hypertrophy vs Hyperplasia

Hypertrophy is an increase in tissue size due to increased cell size; Hyperplasia is an increase in tissue size due to increased cell number via mitosis

Neoplasia

Out-of-control cell growth forming an abnormal tissue mass (tumor)

Atrophy

tissue shrinkage

Tissue Changes with Aging

With increasing age, tissue repair and maintenance become less efficient, and cell and extracellular matrix replacement slows down significantly

Connective Tissue Fragility in Aging

As a person ages, connective tissues gradually lose elasticity and resiliency, becoming increasingly fragile and prone to damage

Age-Related Bone Loss (Osteopenia)

natural decrease in bone mineral density and bone strength that typically occurs with aging as bone resorption begins to exceed bone deposition

Osteoporosis

A more severe, progressive bone disease associated with aging where bone matrix density drops significantly, making bones brittle, weak, and susceptible to fractures

DEXA Scan (Dual-Energy X-Ray Absorptiometry)

A non-invasive diagnostic imaging scan used to measure bone mineral density, assess bone strength, and diagnose conditions like osteopenia and osteoporosis

Metaplasia and Aging/Environmental Stress

the adaptation of a mature tissue changing into another mature tissue type in response to chronic environmental stress or aging (e.g., respiratory epithelium in smokers)

Necrosis

irreversible tissue death accompanied by inflammation

Gangrene

a severe form of tissue necrosis