Histology Lecture 4 - Connective Tissue Flashcards
What is mesentery?
A “sandwich” consisting of loose CT placed between two layers of simple squamous epithelium (mesothelium of peritoneum).
What are the two main components of the CT?
- Cellular components
2. ECM components
Name three examples of indigenous CT cells.
Mesenchymal cells, fibroblasts, adipocytes
Where do immigrant CT cells originate from?
From hematopoetic stem cells in bone marrow. They circulate in the blood and go into the CT to differentiate and perform their functions.
Name five examples of immigrant CT cells.
- Macrophages
- Lymphocytes
- Plasma cells
- Mast cells
- Polymorphonuclear leukocytes (eosinophils and neutrophils)
What are the two ECM components?
Fibrous and ground substance.
What makes up the fibrous component of the extracellular connective tissue?
Elastic fibers, collagen, reticular fibers (Type III collagen)
Where is dense regular connective tissue found?
Tendons, ligaments.
If tightly packed collagen arranged in a parallel fashion is seen, what type of connective tissue is this?
Dense regular CT
Densely packed collagen fibers that are not arranged in a parallel fashion are typical of what type of CT?
Dense irregular CT
What is the major cell type in dense CT?
Fibroblasts
What do fibroblasts synthesize?
Collagen, other ECM molecules like elastin, proteoglycans
Are fibroblasts immigrant or indigenous to the CT?
Indigenous
Where is Type III collagen found?
Reticular lamina/CT, blood vessels
Where is Type II collagen found?
Cartilage
Describe collagen structure.
Three alpha chains in a triple helix. Gly every three AAs allows for tight packing.
What is procollagen? How is mature collagen formed?
Procollagen is synthesized in fibroblast and secreted. It is then cleaved by peptidases and then assembles into fibrils, then cross-links with lysyl oxidase enzyme.
What disease results in the over-accumulation of collagen, leading to hardening and functional impairment of various organs like skin, GI tract, muscle?
Progressive Systemic Sclerosis.
What can result from vitamin C deficiency?
Scurvy - unable to hydroxylate proline and lysine.
What is the most common type of CT?
Loose CT
What does loose CT do? What is its composition?
Holds organs in place, attached epithelium to underlying tissues, surrounds blood vessels and nerves. Has a higher number of cells and ground substance, and lower abundance of fibers.
What do macrophages look like under LM?
They are seen as large, irregularly-shaped nuclei, and have cytoplasmic vacuoles (phagosomes) that contain phagocytized shit.
What do plasma cells do? Can they be found in CT?
They synthesize Igs, and can be found in loose CT
What do plasma cells like like under LM?
Plasma cells have nuclei with a “clock-face” appearance due to heterochromatin, and have a basophilic cytoplasm due to lots of RER for Ig synthesis.
How are Mast cells involved in anaphylaxis?
Their granules contain histamine and heparin (a vasodilator) which are both released when the cells bind an IgE (from a previous encounter with an antigen).
What stimulates polymorphonuclear leukocytes to enter the CT?
Chemotactic cytokines
What do polymorphonuclear leukocytes look like under LM?
They have bilobed/multilobed nuclei. Eosinic granules are bright red (eosinophilic), and neutrophils’ granules stain light pink.
What do Mast cells participate in?
Allergic reactions, and metachromasia occurs in these cells (there’s that one slide)
Where is elastic connective tissue found?
Blood vessels, skin, lungs
What are the two forms of elastic CT?
- Lamellar (found in large blood vessels predominantly as lamellae)
- Fibrillar (found in non-vascular tissues; it is distinguished from collagen by the presence of branching)
What is cutis laxa?
Caused by mutations in elastin gene. Characterized by loose, hanging, wrinkled skin.
What are the two types of Adipose tissue and what do they do?
White is for storage, brown is for heat production.
What do white adipose cells look like under LM?
They have a large non-staining fat storage vacuole, and squished nuclei, thin cytoplasm.
What do brown adipose cells look like under LM?
Polygonal cells with many lipid droplets inside.
Where is regular CT found and what is its function?
Forms a supportive, flexible network within and around organs and structures that must change size or volume (spleen, sinusoids, lymph nodes).
How is regular CT best visualized?
Its reticular fibers are seen well with silver stain
What synthesizes the reticular lamina?
Fibroblasts
What is ground substance?
The non-fibrillar material between cells. It is predominantly made of glycoproteins and proteoglycans. Made by fibroblasts.
What is ground substance made of and what does it do?
Made of proteoglycans and glycoproteins. It binds tissue components, mediates metabolic exchange, lubricates joints, provides reversible compressibility.
What type of CT lies beneath skin?
Dense irregular CT
What is lamina propria?
Loose CT
Collagen IV connects what to what?
Connects the basal lamina to the reticular lamina
What are reticular fibers made of? Are they branched.
Collagen III, yeah they’re branched.
