Lesson 4: Connective Tissue Flashcards
What are the main components of connective tissue?
Cells, fibers, and extracellular matrix (ECM).
composed by different cell types but all deriving from mesenchyme cells of mesoderm origin
What are the primary functions of connective tissue?
Support, protection, transport, insulation, and storage of energy.
The composition of the ECM determines the charachteristics and function of each connective tissue
How is connective tissue classified?
Into connective tissue proper (non-specialized),
supportive connective tissue, and fluid connective tissue (specialized).
What is the embryonic origin of connective tissue?
Mesoderm.
What are the two types of embryonic connective tissue?
Mesenchyme and mucous connective tissue.
What is mesenchyme composed of?
Star-shaped mesenchymal cells, ground substance, and reticular fibers.
Where is mucous connective tissue found?
In the umbilical cord as Wharton’s jelly.
What are the two subtypes of connective tissue proper?
Loose connective tissue and dense connective tissue.
Where is loose connective tissue commonly found?
Beneath epithelia and around blood vessels and nerves.
What are the two types of dense connective tissue?
Dense regular and dense irregular connective tissue.
What is the primary function of dense regular connective tissue?
To provide tensile strength in one direction (e.g., tendons, ligaments).
How does dense irregular connective tissue function?
Provides strength in multiple directions (e.g., dermis of the skin).
What are the resident cells of connective tissue?
Fibroblasts, macrophages, mast cells, and adipocytes.
What are the transient cells in connective tissue?
White blood cells (lymphocytes, neutrophils, eosinophils, and monocytes), plasma cells, macrophages.
What is the primary role of fibroblasts?
To synthesize collagen, elastic and reticular fibers, and ECM carbohydrates.
How do macrophages contribute to immunity?
They phagocytose pathogens and present antigens to lymphocytes.
What do mast cells release during inflammation?
Histamine, heparin, and cytokines.
What is the function of adipocytes in connective tissue?
Energy storage, insulation, and cushioning.
What are the main components of ECM?
Protein fibers (collagen, elastic, reticular) and ground substance.
What is the role of ground substance?
To provide a medium for diffusion and resist compression.
Made of : water, electrolytes, Specialized molecules: glycoproteins, glycosaminoglycans, proteoglycans, enzymes
What are glycosaminoglycans (GAGs)?
Long unbranched polysaccharides that attract water and resist compression.
What is the function of proteoglycans in ECM?
To provide structural support and facilitate cell signaling.
Connection, anchoring and support of the body and its organs
Transport of metabolites between capillaries and tissues
Repair of injury (via cell proliferation and fibers formation)
Cell differentiation, activation, localization
Name examples of adhesive glycoproteins in ECM.
Fibronectin and laminin.
What is the most abundant protein in the human body?
Collagen.
What are the main types of collagen and their locations?
Type I (skin, tendons, bone, cornea)-most common type, Type II (cartilage), Type III (reticular fibers, loose c.t., blood vessel walls, dermis), Type IV (basal lamina of epithelium and kidney glomeruli).
What is the role of collagen fibers?
To provide tensile strength and structural integrity and resist mechanical stress.
What is the function of elastic fibers?
To allow tissues to stretch and recoil.
Where are elastic fibers commonly found?
Skin, large arteries, and elastic cartilage.
What are reticular fibers made of?
Type III collagen.
What is the role of reticular fibers?
To form supportive frameworks for organs such as lymph nodes and bone marrow.
What are the two types of adipose tissue?
White adipose tissue and brown adipose tissue.
What is the primary function of white adipose tissue?
Energy storage and cushioning.
What is the function of brown adipose tissue?
Heat production through thermogenesis.
Where is brown adipose tissue predominantly found?
In newborns and around the neck and thorax in adults.
What are examples of specialized connective tissue?
Cartilage, bone, blood, and lymph.
What is unique about cartilage ECM?
It contains chondroitin sulfate and aggrecan for resilience.
What are the three types of cartilage?
Hyaline cartilage, elastic cartilage, and fibrocartilage.
What distinguishes fibrocartilage from other types?
It has abundant collagen fibers for tensile strength and lacks a perichondrium.
Where is elastic cartilage found?
In the external ear, epiglottis, and Eustachian tube.
What are the two types of bone tissue?
Compact bone and spongy bone.
What cells are involved in bone resorption?
Osteoclasts.
What cells maintain bone matrix?
Osteocytes.
What is the basic structural unit of compact bone?
The osteon or Haversian system.
What are the phases of wound healing?
Inflammatory phase, proliferative phase, and remodeling phase.
What is the role of fibroblasts during wound healing?
To produce new collagen and ECM components.
What type of collagen predominates in scar tissue?
Type I collagen.
What are the cellular components of blood?
Red blood cells, white blood cells, and platelets.
What is the primary role of plasma?
Transport nutrients, hormones, and waste products.
What protein is most abundant in plasma?
Albumin.
What is the function of lymphatic connective tissue?
Immune defense and transport of interstitial fluid back to the bloodstream.
Where are lymphoid nodules found?
In lymph nodes, tonsils, and Peyer’s patches.
What is Marfan Syndrome?
A disorder caused by mutations in fibrillin-1, affecting elastic fibers.
What is osteogenesis imperfecta?
A condition caused by defective collagen synthesis, leading to brittle bones.
What causes Ehlers-Danlos Syndrome?
Mutations affecting collagen synthesis, leading to hyperelastic skin and joints.
How does scurvy affect connective tissue?
Vitamin C deficiency leads to defective collagen synthesis, causing bleeding gums and poor wound healing.
What happens in rheumatoid arthritis?
Inflammation damages synovial connective tissue, causing joint pain and deformity.
What are myofibroblasts?
Cells closely related to fibroblasts, but characterized by the presence of actin filaments of a-smooth muscle actin (a-SMA).
Present in damaged tissues, important during wound healing and in pathological conditions (fibrosis, tumors).
What are macrophages?
Phagocytic cells that derive from bone marrow progenitors during Embryogenesis or circulating monocytes
Macrophages differentiate once in the tissues
10-30µmdiameter
spindle or stellate shape, kidney-
shaped nucleus
abundant lysosomes
present in connective tissue, but greatly increased during inflammation
when in a resting state, macrophages are associated with collagen fibers by adhesion
life span: 2-3 months. Have a low rate of proliferation to renew the population
What are the defense functions of macrophages?
Phagocytosis of microbes, damaged cells, debris, antigen presentation, and secretion of cytokines and enzymes.
How do macrophages contribute to homeostasis?
Through trophic functions, such as tissue repair after damage.
What happens when macrophages are activated?
They detach from collagen fibers, migrate by ameboid movement, and increase phagocytosis activity.
What structural changes occur in activated macrophages?
Increased rough endoplasmic reticulum (RER), Golgi apparatus, cytoskeleton, and lysosomes.
What roles do activated macrophages play in tissue maintenance?
They clean dead cells, cell debris, aged erythrocytes, and foreign particles like bacteria and cancer cells.
Why are macrophages referred to as “plastic cells”?
They adapt to environmental signals and perform various roles depending on tissue needs.
How do macrophages interact with tumors?
They play dual roles, either promoting or inhibiting tumor growth based on signals from the tumor microenvironment.
What is the unique structural feature of adipocytes?
The nucleus and thin cytoplasm are displaced peripherally due to continuous fat accumulation.
Do adipocytes divide?
No, their total number is determined during early life and remains constant in adulthood
What additional functions do adipocytes perform besides lipid storage?
They release cytokines and hormones and can support cancer growth in certain environments.
What is the origin of mast cells?
They arise from bone marrow precursor stem cells, circulate in the blood, and differentiate in connective tissue.
What is the role of granules in mast cells?
The granules contain inflammatory mediators like histamine, heparin, and leukotrienes.
How do mast cells mediate allergic reactions?
By releasing granule contents in response to allergens binding to IgE receptors on their surface.
What are the main types of leukocytes found in connective tissue?
Neutrophils, lymphocytes, monocytes, eosinophils, and basophils
How do leukocytes migrate into connective tissue?
By crossing small veins and capillaries via diapedesis (a finger-like protrusion or a pseudopodium penetrates between two endothelial cells).
What triggers leukocyte recruitment to tissue?
Pro-inflammatory mediators, cytokines, and chemokines at sites of inflammation.
What are the key steps in leukocyte extravasation?
Rolling, activation, arrest, diapedesis, and migration.
What are collagen fibers composed of?
Long, flexible, non-branched fibers made of collagen.
Where are collagen fibers commonly found?
In tendons, bone, cartilage, and skin.
What are the key intracellular stages of collagen synthesis?
Synthesis in the rer, triple helix assembly in the rough ER, modification in the Golgi apparatus, fibrils assembly (extracellular), covalent cross-linking (extracellular), and secretion as procollagen.
What is the role of vitamin C in collagen synthesis?
It is essential for hydroxylation of proline and lysine residues, stabilizing the triple helix structure.
How is procollagen converted to collagen extracellularly?
Procollagen is cleaved by peptidases and assembled into fibrils and fibers.
What is the repeating structural feature of collagen fibrils?
A sequence of closely spaced transverse bands repeating every 68 nm.
What amino acids are abundant in collagen fibers?
Glycine, proline, and lysine.
What is the diameter range of collagen fibrils?
0.2–0.5 μm.
What processes are involved in collagen turnover?
Synthesis by fibroblasts and degradation by matrix metalloproteinases (MMPs) and phagocytes.
What are the roles of MMPs in collagen turnover?
Degrading ECM components during tissue remodeling, wound healing, and pathological conditions (inflammation, atherosclerosis, tumor invasion and fibrogenesis).
What regulates MMP activity?
TIMPs (tissue inhibitors of metalloproteinases).
Where are reticular fibers commonly found?
In the liver, spleen, lymph nodes, and bone marrow.
What are reticular fibers?
Small, branched fibers filling spaces and providing thin stroma of organs.
What is the primary function of reticular fibers?
To form a supportive stroma in organs and assist in the basement membrane structure.
Keep organ cells together
What are elastic fibers?
Intermediate fibers made of elastin. Branching fibers that allow tissues to respond to stretch and distension
Produced by FIBROBLASTS and VASCULAR SMOOTH MUSCLE CELLS
What are the two main components of elastic fibers?
Elastin (amorphous core) and fibrillin (microfibrils).
What is the primary function of elastic fibers?
To allow tissues to stretch and return to their original shape.
may be stretched to 150% of their resting length without breaking
Where are elastic fibers predominantly located?
In the skin, large blood vessels, lungs, and elastic cartilage.
What are the phases of elastogenesis?
Intracellular production of fibrillin and tropoelastin, with extracellular assembly into elastic fibers.
What condition results from mutations in the Fibrillin-1 gene?
Marfan Syndrome, characterized by defects in elastic fibers and connective tissue.
What are the clinical features of Marfan Syndrome?
Skeletal, ocular, and cardiovascular abnormalities.
What are proteoglycans composed of?
A core protein covalently linked to glycosaminoglycan (GAG) chains.
What are glycosaminoglycans (GAGs)?
GAGs are long, unbranched polysaccharides composed of repeating disaccharide units.
What is unique about the disaccharide units in GAGs?
They contain one modified sugar (either N-acetylgalactosamine or N-acetylglucosamine) and a uronic acid (such as glucuronate or iduronate).
Why are GAGs highly negatively charged?
Due to sulfate and carboxyl groups on the sugar residues.
What are the physical properties of GAGs?
They are highly hydrated, viscous, and have low compressibility, making them effective as lubricants and shock absorbers.
What is the role of GAGs in connective tissue?
They provide mechanical support, mediate hydration, and serve as lubricants.
Name some physiologically significant GAGs.
Hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparin, heparan sulfate, and keratan sulfate.
How is hyaluronic acid different from other GAGs?
It does not contain sulfate and is not covalently attached to proteins as a proteoglycan.
Where are proteoglycans found?
In the extracellular matrix and on cell surfaces.
What are proteoglycan aggregates, and what is their function?
Aggregates are proteoglycans linked to hyaluronic acid, functioning as shock absorbers.
Give an example of a proteoglycan aggregate.
Aggrecan, found in cartilage.
What is mucopolysaccharidosis?
A group of lysosomal storage diseases caused by defects in enzymes that degrade GAGs and proteoglycans.
What are the clinical consequences of mucopolysaccharidosis?
Accumulation of undegraded molecules, leading to tissue and organ dysfunction.
What is fibronectin’s role in the extracellular matrix (ECM)?
It links cells to ECM components and mediates cell adhesion and migration.
How does fibronectin contribute to cellular processes?
By binding integrins and reorganizing actin microfilaments.
What is laminin?
A glycoprotein that binds ECM components and cell surface receptors, aiding in adhesion.
Where is laminin found?
In the basement membrane, interacting primarily with integrins.
What is osteopontin, and where is it found?
A glycoprotein found in bone that facilitates osteoclast attachment and calcium sequestration.
What role does osteopontin play in bone remodeling?
It mediates osteoclast activity on bone surfaces.
