Connective Tissue and Immune Cells Overview

Study Notes

Significance of stem cell origin of CT cells: Connective tissues originate from the mesoderm layer of the embryonic tissue, containing mesenchymal stem cells.
Correlation of cell structure to function: Fibroblasts, the most common CT cells, synthesize and secrete extracellular components like fibers and ground substance. Inactive fibroblasts (fibrocytes) are smaller and more ovoid with less organelles. Myofibroblasts are transitional forms that aid in wound healing.
CT cell response to conditions: CT cells respond to physiological (normal) and pathological (disease) conditions, including immune responses, hypersensitivity reactions, tissue repair, and inflammation.
Types of white blood cells: White blood cells are categorized by their origin and histological features.
Lymphocyte maturation & receptor expression: Lymphocyte maturation and the expression of receptors are important for immune function in different medical conditions.
Types of Connective Tissue: Connective tissue forms a continuum with other tissue types such as epithelial, muscle, and nervous tissue to create a functionally integrated body.
CT Origin and Components: Connective tissue is comprised of cells and extracellular matrix (ground substance and fibers).

Fibroblasts: The most abundant cell type in CT; responsible for synthesizing and secreting extracellular components like fibers and ground substance. Active fibroblasts have active protein synthesis machines, particularly in wound healing. Inactive fibrocytes are smaller and more ovoid, with fewer organelles. Myofibroblasts, a transitional form, resemble smooth muscle cells, with actin and myosin filaments, and contribute to wound healing.
Adipose Cells: Fully differentiated; do not divide; synthesize and store triglycerides. Two types: unilocular (single large lipid droplet) and multilocular (smaller lipid droplets). Unilocular adipose cells are characterized by a signet ring profile due to the large lipid droplet.

Characteristics: Ovoid shape with a centrally located, spherical nucleus, containing granules with various chemical mediators (e.g., heparin, histamine, leukotrienes, interleukins, TNF-α).
Function: Play a crucial role in the immune system by initiating inflammatory responses, particularly immediate hypersensitivity reactions (e.g., allergic reactions).

Characteristics: Large cells with irregular surfaces and surface projections (filopodia); abundant lysosomes indicating active phagocytosis. Derived from monocytes.
Function: Phagocytose unwanted material (cellular debris, bacteria, foreign particles); present epitopes to T lymphocytes to elicit an immune response; involved in immune responses.

Characteristics: Cytoplasm intensely basophilic except for the prenuclear area displaying a pale appearance(negative Golgi image) which is typically a characteristic of plasma cells. Derived from B lymphocytes.
Function: Secrete antibodies.

Origin: All leukocytes originate in the bone marrow.
Classification: Categories include granulocytes (neutrophils, eosinophils, basophils) and non-granulocytes (lymphocytes, monocytes).

Characteristics: Abundant, multilobed nucleus; pale cytoplasm; often the first responders to infections.
Function: Phagocytose bacteria; a line of defense.

Characteristics: S-shaped nucleus; abundant basophilic granules.
Function: Release granules containing histamine and heparin; important in allergic reactions.

Characteristics: Largest white blood cells in a blood smear; kidney-shaped or oval nucleus; abundant lysosomes.
Function: Phagocytize debris and pathogens, play a crucial role in the inflammatory response.
Macrophages: Mature form in connective tissue, perform phagocytosis, initiate immune responses, present antigens to T cells.

Characteristics: Rounded cells that have a slightly indented, round nucleus that occupies most of the cell.
Types: Divided into B cells, T cells, and null cells.
Function: Essential for adaptive immunity; B cells produce antibodies; T cells directly attack infected cells; null cells mediate nonspecific immune responses.