Connective Tissue/Blood Flashcards
Connective Tissue Functions
- Provides the structural integrity of tissues and organs – (provides the “glue” for stability)
- Provides mechanical properties – offering both tensile and compressive properties as needed
- Provides environment for differentiation and residence for immune cells (e.g. plasma cells, macrophages)
- Facilitates exchange of metabolites, electrolytes and water
- Energy storage - i.e., white adipose tissue
- Heat production – i.e. brown adipose tissue
- Repair and restoration of tissue architecture following damage (e.g. nerve regeneration)
Connective Tissue Components
Cells (indigenous and immigrant)
Extracellular matrix (fibers and ground substance)
Indigenous Cells
Arise within the CT:
- mesenchymal cells (embryonic)
- fibroblasts
- adipocytes
- osteogenic cells and their derivatives (specialized CT)
- chondrogenic cells and their derivatives (specialized CT)
Mesenchymal Cells
multipotent stem cells that can differentiate into:
- myocytes (muscle cells)
- adipocytes (fat cells)
- chondrocytes (cartilage cells)
- osteoblasts (bone forming cells)
- neurons
Mesenchyme
Mesenchyme cells embedded in hydrated extracellular matrix (ECM)
Fibroblasts
- most common cell in most CTs
- synthesize most ECM components
- cytoplasm and ECM stain similarly – thus usually just see nuclei
- have capacity to differentiate into myofibroblasts (both in normal and wound-healing conditions)
Adipocytes
Lipid filled cells, white and brown
White Adipocytes
Unilocular
Brown Adipocytes
Multilocular
Immigrant Cells
Originate from hematopoietic stem cells in bone marrow:
- macrophages (derived from monocytes)
- mast cells
- lymphocytes
- plasma cells (derived from B-lymphocytes)
Macrophages
- derived from blood monocytes that have migrated into connective tissues
- these cells have many roles in addition to scavenging debris, including important
functions in both the innate and adaptive immune systems and in inflammation
Mast Cells
- derived from bone marrow precursors
- central nucleus with cytoplasm packed with granules
- granules exhibit metachromasia
- granules contain heparin (anticoagulant) & histamine (vasodilator)
In severe allergic reactions, body-wide degranulation can lead to anaphylaxis (BP drops, bronchial constriction, rash)
Lymphocytes
Subset of B and T cells
Recirculate (blood -> tissue -> blood)
Small, dark nuclei and little cytoplasm
Often found wandering into epithelia
Plasma cell
- differentiated B-lymphocytes
- synthesize antibody, of same specificity as parent B-cell
- found in loose CTs
- “clock-face” heterochromatin pattern
- eccentric nucleus
- prominent, perinuclear golgi apparatus
- abundant RER
Extracellular Matrix (ECM) - Fibers
Fibrillar & non-fibrillar collagen
Elastic
Fibrillar collagens
Makes up extracellular matrix
I – nearly everywhere
II – cartilage mostly
III – many organs
V, XI, XXIV and XXVII - restricted locations
Type I Collagen
- the most abundant protein in body (90%)
- nearly ubiquitous (a notable exception is hyaline cartilage)
Defects:
Ehlers Danlos syndrome
Scar tissue is largely comprised of type I collagen; keloids can result from localized collagen accumulation
Type II Collagen
- abundant in hyaline cartilage
- found in many organs during development; in adult in eye and ear
Type III Collagen
Reticular fibers
- highly branched
- visualization requires special stains (e.g. silver)
Locations:
- many lymphoid organs
- liver
- reticular dermis (skin)
Non-fibrillar Collagens
- Represent most known collagens (28 and counting…..)
- Basement membrane (type IV)
- Fibril-associated
- Most require special techniques to localize (e.g. immunohistochemistry)
Crosslinking of hydroxylysine & hydroxyproline in collagen fibrils catalyzed by
lysyl- and prolyl-hydroxylase
Crosslinking of elastin fibrils catalyzed by
lysyl oxidase
Elastic Fibers
One of fibers that makes up extracellular matrix
Synthesis:
- deposition of fibrillin scaffold
- addition of elastin
- crosslinking is achieved with lysyl oxidase
Diseases:
Marfan Syndrome: Fibrillin-1 is mutated in Marfan syndrome (leading to aneurisms, scoliosis, hyperextensible joints). Fibrillin sequesters TGF-β and regulates its bioavailability. Excess TGF-β in Marfans may predispose to many of the phenotypes.
Cutis Laxa: mutations in elastin lead to skin that is loose, wrinkled an lacking elasticity. In severe cases, internal organs may be affected.
Ground substance is made up of
proteoglycans
glycosaminoglycans
glycoproteins
Has hydrated shell around glycosaminoglycans (GAGs)
Characteristics of ground substance
1) Highly charged – thus hygroscopic (hydrated)
2) Charge confers compressive resistance (e.g. articular cartilage)
3) Limited protein components (poor staining qualities)
4) Permits nutrient/gas exchange (especially in avascular tissues)
“Empty space” is
Ground substance (proteoglycans, glycosaminoglycans & glycoproteins)
Types of Connective Tissue
- Dense regular
- Dense irregular
- Loose (areolar)
- Elastic
- Adipose
- Reticular
- Blood
- Cartilage (covered separately)
- Bone (covered separately)
Dense regular CT
- collagenous tissues with densely packed fibers arranged in parallel
- provide tensile strength to:
- tendons (connecting muscle to bone)
- ligaments (connecting bone to bone)
Dense irregular CT
varied collagen fiber & fibroblast nuclei orientations
Loose connective tissue
Elastic Connective Tissue - Describe
Elastic CTs per se are CTs that contain more elastic components that collagenous components
Reticular Tissue
Branched type III collagen
- supports channels in liver, lymph nodes and spleen
- present in other organs for support (e.g. dermis)
- usually require special stains to visualize
Identify the cells
- Neutrophil
- Platelet
- Eosinophil
- Lymphocyte
- Neutrophil
- Basophil
- Monocyte
- RBCs
Erythrocytes
most common formed elements in the blood and are specialized for transport of oxygen and carbon dioxide
- anuclear biconcave discs, approximately 7.5 μM in diameter; this shape significantly increases surface area as compared to a sphere
- their predecessors are immature cells known as reticulocytes (R) that display some cytoplasmic basophilia due to the still-present ribosomes; reticulocyte numbers provide a good measure of erythropoietic activity
- rbcs live approximately 4 months and are usually cleared by the spleen
White Blood Cells
Granulocytes
- neutrophils (60-70%)-polymorphonuclear leukocytes
- barely-visible granules in cytoplasm; 3 to 5 lobed nucleus
- eosinophils (2-4%)
- large eosinophilic granules; bilobed nucleus
- basophils (<1%)
- large, abundant, basophilic (and metachromatic) granules; usually bilobed nucleus (often obscured by granules)
Agranulocytes (aka mononuclear leukocytes)
- lymphocytes (25-33%)
- variable amounts of cytoplasm (generally very little); round, uniform dark-stained nucleus
- monocytes (3-8%)
- largest WBC; ovoid, kidney-, or horseshoe- shaped nucleus; pale cytoplasm
Neutrophils
60-70%
represent one of the three types of granulocytes (they contain specific cytoplasmic granules) and also possess multilobed nuclei. Neutrophils are the most numerous of the white blood cells. About half of these cells are in the blood and the other half in the tissues. (Following inflammation, the pool of dead neutrophils/products = pus)
- short lifespan (2-6 days)
- nucleus with 3-5 lobes
- Barr body (inactivated X chromosome) usually visible (see arrow in panel b, left)
- main function in defense is phagocytosis
- also function to trap pathogens by exocytosing enzymes as well as their DNA to form sticky “traps
Eosinophils
2-4%
less common than neutrophils but like them, are found in both blood and tissues
- lifespan of days to weeks in tissues
- bilobed nucleus (usually)
- prominent eosinophilic granules
- oval granules are distinctive with a rod-shaped core often visible (TEM required)
- function in phagocytosis and release of granules that contain enzymes and proteins that are toxic to many pathogens
Basophils
least common of the leukocytes (<1%). These may also be seen in blood and tissues (during inflammation)
- bilobed nucleus (usually)
- prominent basophilic granules usually obscure the nucleus
- can be distinguished from mast cells by the following criteria:
a) bilobed nucleus (mast is single)
b) usually observed in blood (mast cells only seen in CTs) - like mast cells, they have IgE receptors
- function in allergic and parasitic reactions, releasing histamine and cytokines
Lymphocyte
25-33%
second most common leukocyes in blood. Two types usually visible in smears: small and large. Lymphocytes are abundant in tissues and lymphoid organs
Small lymphocyte characteristics:
- high nuclear/cytoplasmic ratio (very little cytoplasm visible)
- consist of T-cells and B-cells and their subsets:
- B-cells are essential for humoral immunity through their role in antibody production (plasma cells are the effector cells that produce the antibodies and represent terminally differentiated B cells)
- T-cells are essential for cell-mediated immunity
Monocyte
3-8%
largest and usually the third most abundant type of leukocyte
- large indented (or U-shaped) nucleus
- pale stained cytoplasm containing fine granules (lysosomes)
- is the precursor cell for macrophages, osteoclasts and dendritic cells, all of which differentiate following extravasation into the tissues
Platelets
“Thrombocyte” - blood clot cell
- formed in the bone marrow as fragments from megakaryocytes (<1000 generated per cell)
- rbc:platelet ≈ 10:1 to 20:1
- contain a central granulomere (G) and peripheral hyalomere (H)
- exist in resting (R) and activated (A) forms
Functions:
1) aggregation to seal vessel damage
2) facilitate clot formation (conversion of soluble fibrinogen to the fibers in a clot (fibrin)
ID Tissue
Loose (areolar) CT (lamina propria). Loose bundles of collagen fibers, various cells and a significant amount of ground substance.
ID Tissue
Dense irregular CT (skin). Compact bundles of collagen fibers, unorganized, running in various directions. Fibroblasts scattered throughout.
ID Tissue
Dense regular CT (tendon). Highly organized collagen fibers running in the same direction, nuclei of fibroblast all lined-up, little ground substance between bundles of collagen.
ID
Type I Collagen H&E (arrows are fibroblast nuclei)
ID and describe
Highly organized lamellae of corneal collagen (mostly type I), each fibril having a small, uniform diameter; this configuration is necessary for transparency
ID Type and location
Reticular fibers in the liver
Using silver stain
- Made up mainly of type III collagen.
- Form extensive network of heavily glycosylated thin fibers.
- Not visible in H&E sections.
- Stains black with silver stains, magenta with PAS.
- Present in reticular lamina of basal membrane, surround adipocytes, smooth muscle and nerve fibers.
- Form supportive stroma for many organs (e.g. liver, lymphoid tissues, etc.)
ID Type and location
Elastic lamellae in the wall of the aorta
ID Type
1. Brown adipocyte has many small lipid droplets in the cytoplasm
2. White adipocytes contains a large, single lipid droplet in the cytoplasm.
ID Type
Macrophages
These cells have phagocytic properties and are derived from monocytes in blood
The cytoplasm is usually pale and eosinophilic
There are abundant lysosomes in the cytoplasm
There also may be phagocytic vacuoles containing ingested materials
Functions include defense (ingestion of bacteria, immune system etc.), turnover of CT components
ID Type
Mast Cells
Derived from progenitor cells in the bone marrow
Central, round nucleus, surrounded by granules
Exhibit metachromasia (the granules in the cells stain a deep purplish-red in a slide stained with toluidine blue dye)
Source of vasoactive mediators (histamine, heparin, chemotactic factors etc.) in cytoplasmic granules
Possess IgE receptors and serve important roles allergic hypersensitivity reactions and can lead to anaphylactic shock when body-wide degranulation occurs
ID Type
Plasma cell
Plasma cells derive from B lymphocytes in the CT
Excentric nucleus with distinctive peripheral ‘cartwheel’ or ‘clockface’ arrangement of heterochromatin, along with a central nucleolus
Cytoplasm basophilic due to extremely well-organized rough ER
Active cells have large, pale, perinuclear Golgi apparatus
These cells secrete immunoglobulins
A tissue sample analyzed for composition shows mainly ground substance rich in hyaluronic acid, with elastic and collagen fibers. The sample most likely came from which type of connective tissue?
Loose
ID Type
Comparison of both loose and dense irregular CT; also note adipose CT
ID Types
ID Type
Mast Cell
- derived from bone marrow precursors
- central nucleus with cytoplasm packed with granules
- granules exhibit metachromasia
- granules contain heparin (anticoagulant) & histamine (vasodilator)
- IgE receptors
ID Type
Eosinophils (2-4%)
- lifespan of days to weeks in tissues
- bilobed nucleus (usually)
- prominent eosinophilic granules
- oval granules are distinctive with a rod-shaped core often visible (TEM required)
- function in phagocytosis and release of granules that contain enzymes and proteins that are toxic to many pathogens
ID Type
Neutrophils (60-70%)
These represent one of the three types of granulocytes (they contain specific cytoplasmic granules) and also possess multilobed nuclei. Neutrophils are the most numerous of the white blood cells. About half of these cells are in the blood and the other half in the tissues. (Following inflammation, the pool of dead neutrophils/products = pus)
- short lifespan (2-6 days)
- nucleus with 3-5 lobes
- Barr body (inactivated X chromosome) usually visible (see arrow in panel b, left)
- main function in defense is phagocytosis
- also function to trap pathogens by exocytosing enzymes as well as their DNA to form sticky “traps”
ID Type
Basophils (<1%)
Basophils are the least common of the leukocytes in blood (<1%). These may also be seen in tissues (during inflammation).
Characteristics:
- bilobed nucleus (usually)
- prominent basophilic granules usually obscure the nucleus
- can be distinguished from mast cells by the following criteria:
a) bilobed nucleus (mast is single)
b) usually observed in blood (mast cells only seen in CTs) - like mast cells, they have IgE receptors
- function in allergic and parasitic reactions, releasing histamine and cytokines
Review
