Histology - Connective Tissue

Why do collagen fiber bundles stain acidophilic?

Collagan fibers (proteins) are positively charged which means they bind to eosin to make collagen fibers acidophilic.

What cells produce collagen type-I? How does it appear and what does it bind to?

Collagen is the most abundant protein in the animal. Collagen in CT is produced by fibroblasts (more actively) and fibrocytes (less actively). unstained fresh collagen fibers appear white when present in great numbers (tendons and ligaments) collagen binds eosin dye (pink to red)

Which cells produce extra cellular matrix? What are the main components of ECM?

Extracellular matrix (ECM) is produced by fibroblasts/fibrocytes and then extruded from the cell. Two main components of ECM: 1) protein fibers and 2) proteoglycans

Function of adipose cells? Location of nucleus?

Store fat accumulate lipid to such an extent that the nucleus is displaced to one side cells appear large and empty because lipid is dissolved during tissue preparation fat cells are more often found in groups

describe identfiying features of a plasma cell. Why do you find plasma cells in the lamina propia (loose connective tissue) underlying the epithelium of jejunum?

1) Basophilic cytoplasm 2) Eccentrically located nucleus 3) Pale staining Golgi apparatus (right outside nucleus) Plasma cells release antibodies and jejunum in stomnach which is nasty so they fihgt it off.

Function of connective tissue?

1) connects and holds other tissues 2) provides support for other tissues 3) important in defense mechanisms

Why does the ECM of connective tissue stain basophilic?

Because of proteoglycans which are negatively charged and bind to hematoxylin to make it basophilic.

General function of brown adipose tissue?

Brown fat is prominent in newborn animals. In the newborn, thermogenesis by brown-fat mitochondria is vital to survival, as is in hibernating animals. In human infants, it comprises up to 5% of body weight but diminishes with age.

Function of fibroblast? Nucleus facts?

Fibroblasts: actively synthesize and secrete proteins/other substances that are found in the extracellular, fibrous matrix of connective tissue. Nucleus is ovoid and lightly basophilic (euchromatic) because chromatin is more exposed or less condensed in this active cell. Only nucleus is visible

Function of fibrocytes? Nucleus facts?

Fibrocyte is a less active version of fibroblast. Nucleus is narrower, elongated, and dark basophilic (heterochromatic) because chromatin is more condensed in this less active cell. In a fully mature CT, you will find more fibrocytes. Although fibrocytes are less active, they are important for maintaining the connective tissue matrix.

Examples and composition and reticular connective tissue? Physiological significance of reticular fibers in lymph node?

Found in blood-forming organs (hematopoietic organs; spleen, lymph nodes), liver, endocrine glands, smooth muscle, and nerve fibers. Reticular CT contains a complex network of reticular cells and reticular fibers (collagen type-III). Reticular fibers are made by reticular cells. The physiological function of reticular fibers in the lymph node: Reticular fibers form a meshwork (reticulin) in lymphatic tissues. This meshwork creates a sponge-like structure that filters the fluid picked up by vessels that lead to it.

Multiocular or brown adipose tissue (brown fat): Nucleus location? Size compared to white adipocytes? Location of it? Vascularization? Color due to what?

It is called multilocular adipose tissue because of multiple, small lipid droplets in cells. Brown adipocytes are smaller than white adipocytes. Nucleus is centrally located (compare this with unilocular adipose tissue). Brown fat cells contain many mitochondria. Tan to reddish-brown tissue color is due to: 1. abundant mitochondria-->mitochondriacontaincytochromes.Cytrochromescontainthehemegroupwhichhsdslightredcolor 2. rich vascular supply Brown adipose tissue is abundant in rodents and hibernating animals, located primarily in the axillary and neck regions. In domestic animals, brown adipose tissue is less abundant.

Function of macrophages? Shapoe of macrophage and shape/location of nucleus?

Major functions of macrophage are: A) to phagocytize foreign and dead cells B) to secrete substances that participate in defense and repair mechanisms Active macrophages are large, ovoid, or spherical cells with foamy cytoplasm and an oval or kidney-shaped nucleus located eccentrically.

Function of plasma cells? Shape of plasma cells? Shape/location of nucleus? Cytoplasm stain and what else about an organelle?

Plasma cells produce antibodies. Plasma cells are ovoid in shape. Nucleus: i) round or oval and ii) eccentrically located (pushed to one side). Cytoplasm is basophilic (due to abundant RER), with a pale staining area (negative Golgi image) adjacent to the nucleus

What are proteoglycans composed of? Function of one of the components in proteoglycans? Charge? What do they do?

They contain a protein core + GAGs (polysaccharide chains called glycosaminoglycans). Proteoglycans resemble a brush, with the central metal core representing the protein core and many fine bristles representing GAGs. Functions of GAG in proteoglycans: Due to the abundance of hydroxyl, carboxyl, and sulfate groups, GAGs are highly negatively charged. These negative charges attract and bind large number of water molecules. Therefore, proteoglycans form hydrated gels that permit rapid diffusion of nutrients and metabolites through the tissue matrix (space between cells).

Where are mast cells located? Shape of mast cells? Function of mast cells (2 things)?

They occur in varying numbers in loose connective tissue, especially along small blood vessels. They are generally ovoid cells: -cytoplasm contains coarse basophilic granules -nucleus is often obscured by many cytoplasmic granules. The function of mast cells is to synthesize chemical mediators of the inflammatory response. The most prominent of these chemical mediators are: A) histamine causes vasodilation, which increases the permeability of blood capillaries and venules B) heparin is an anticoagulant whose role in connective tissue is not clear

Uniocular or white adipose tissue (white fat): Nucleus location? Why is it called yellow tissue/fat? Location of it? Vascularization?

Unilocular is the more abundant of the two types. It is called unilocular because of a large, single lipid droplet in the mature white fat cell. Nucleus is pushed to one side of the cell.This tissue is sometimes called yellow adipose tissue or yellow fat because dietary carotenoid pigments accumulate in lipid droplets. White adipose tissue is well vascularized, but not as richly as brown adipose tissue. Location: subcutaneous tissue, omentum, mesentery, etc

What are the two types of adipose tissue?

Uniocular and multiocular

General functions of white adipose tissue?

a.Energy store/Fat Metabolism b. Thermal Insulation c. Cushion - shock absorption

Dense irregular CT: Predominant cells? Examples? How is it formed?

collagen type-I are irregularly organized. Predominant cell types are fibroblasts and fibrocytes. Examples: skin dermis, capsule of organs Fibroblasts become aligned in an irregular manner. Therefore, collagen type-I are organized in an irregular manner. Irregular organization of collagen fibers lead to a 3-dimensional network that provides resistance to stress from all directions (skin).

Dense regular CT: Predominant cells? Examples? How is it formed?

collagen type-I are regularly organized. Predominant cell types are fibroblasts and fibrocytes. Examples: tendons and ligaments. Fibroblasts become aligned in a regular (linear/parallel) manner. Therefore, collagen type-I fibers are organized in a regular manner. Due to the linear/parallel organization of tough collagen type-I, tendons can transmit great amount of forces developed in the muscle to the bone in a linear manner.

What are the three types of protein fibers?

collagen, reticular fibers, elastic fibers

Composition of loose connective tissue? Examples of where it is found? Cells involved in it? Types of fibers involved?

most abundant form of connective tissue high ratio of cells: collagen type-I. delicate consistency and less resistant to stress examples: under epithelial tissue; surrounds lymphatics, and blood vessels Most common cell types are fibroblasts (few fibrocytes), but other cells are present in varying numbers depending on the location and physiological state of the tissue. Types of Fibers: Collagen type-I, elastic fibers, and reticular fibers (collagen type-III).

Composition of dense connective tissue? Examples of where it is found? Cells involved in it? Types of fibers involved in dense irregular CT and dense regular CT?

not as abundant as loose connective tissue high ratio of collagen type-I: cells tough consistency and more resistant to stress Cells: Most common cell types are fibroblasts. In mature tissues, fibrocytes may predominate. Types of Fibers --> Mostly collagen type-I in dense irregular and dense regular CT.

Review last slide with mixed or seromucous glands because there is an exam question on it.

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What are elastic fibers/where are they? How do they stain?

present in organs whose functions require elasticity in addition to tensile strength In H&E sections, elastic fibers appear as light pink strands when present in large quantities

What type of cell synthesizes collagen type-III fibrils in the lymph node?

reticular cell

What are reticular cells? Composition of function?

reticular cells synthesize reticular fibers (fine strands of type-III collagen) do not confuse reticular cells with reticulocytes (immature erythrocytes)

What does reticular fibers do? Composed of what and stain like what?

reticular fibers (collagen type- III) form delicate, flexible network in blood-forming organs such as: capilarries, muscle fibers, nerves not visible in H&E preparations but can be demonstrated by silver stain (stains black).

Why does the lymph node require collagen type-III, but not collagen type-I?

reticular fibers are made of collagen type-III which are fine strands and form meshwork in lymphatic tissue. Collagen type I is used in connective tissue.