Lecture 7 - Connective Tissue PDF

Lecture 7 Connective tissue Presented by : Histology department LOs: 1- List the components of connective tissue. 2- Describe the structure and correlated functions of different connective tissue fibers. 3- List types of connective tissue cells. 4- Describe the structure of connective tissue...

Lecture 7 Connective tissue Presented by : Histology department LOs: 1- List the components of connective tissue. 2- Describe the structure and correlated functions of different connective tissue fibers. 3- List types of connective tissue cells. 4- Describe the structure of connective tissue cells with correlation to its function. 5- Define different types of connective tissue proper. 6.Identify types of specialized connective tissue.  Connective tissue is the most Nice to know abundant tissue and is present everywhere in the body. It is found in skin, membranes,muscles, bones, nerves, and all internal organs. Connective tissue has various forms: a) It exists as delicate webs that hold internal organs together. b) It also exists as strong cords, rigid bones. c) it can also form a fluid: blood Types of connective tissue: 1. Connective tissue proper. 2. Cartilage 3. Bone 4. Blood Nice to know  Supports organs and cells. Medium for exchange of nutrients and wastes between the blood and cells. Protects against microorganisms. Repairs damaged tissues. Stores fat (adipose ct).  General characters of the connective tissue: It consists of cells(few) widely separated by: fibers and intercellular substance ↑↑. It is penetrated by blood vessels, lymphatics and nerves. It is mesodermal in origin. The components of connective tissue are: 1. Cells. 2. Fibers. 3. Intercellular substance ( extracellular matrix- ground substance) 6  long, slender protein that is secreted from a cell called: fibroblasts. There are three main types of fibers: 1.Collagen fibers: are tough and provide tensile strength. It form bundles (e.g. tendon) 2.Elastic fibers: allow for stretch & recoil Y (blood vessels). 3.Reticular fibers: make networks (in cellular organs). Collagen and reticular fibers are both formed by proteins of the collagen family. Elastic fibers are formed of the protein elastin. Nice to know  Collagen is the most abundant protein in the human body. There are at least 28 different types of collagen (named type I, II, III, IV, …….). The most common collagen types in connective tissue proper are types I and III collagen. Type –I accounts for 90% of collagen in human body. By EM: Fibers have axial periodicity (striations). Nice to know  Collagen fibers are thick, strong, unbranched fibrous protein. Collagen fibers have great tensile strength, which gives strength to the tissues. Site: tendons, bone, cartilage, skin (dermis), etc. Nice to know Nice to know  Types of collagen According to the amino acids sequence, there are many types of collagen fibers, more than 20 types. Type Type I Tendons, ligaments, bones, dermis of the skin, dentin of teeth. Type II Cartilage matrix Type III Reticular fibers (present in network that supports the parenchymal organs e.g. spleen) Type IV The basement membranes. Basal lamina 10  Types of collagen According to the amino acids sequence, there are many types of collagen fibers, may reach to 20 types. type site Type I Tendons, ligaments, bones, dermis of the skin, dentin of teeth. Type II Cartilage matrix Type III Reticular fibers (present in network that supports the parenchymal organs e.g. spleen, liver)  clinical disorders arising from errors in collagen synthesis (Ehler Danlos S.) Ehlers–Danlos syndrome (structural weakness in connective tissue). Symptoms: Hyper-extensible skin. Hyper extendible joints recurrent joint dislocation. Nice to know  A clinical disorders arising from genetic errors in collagen synthesis, Collagen fibers are present in bone matrix , so there is bone impairment. symptoms: repeated bone fractures, and bone deformities. Nice to know Nice to know  Disorders of collagen formation Scurvy & keloid Keloid Nice to know Reduced collagen formation Nice to know due to vitamin C deficiency Local swelling caused by -Bleeding gums abnormal large amounts -Poor wound healing of collagen that forms in -Loose teeth scars of the skin - Poor bone development 12  They are extremely thin, branching and anastomosing fibers forming network (reticulum). It composed of type III collagen; they have higher carbohydrate content than other collagen fibers. They also show transverse striations (periodicity). Because of their high carbohydrate content, they stain by PAS and silver salts. Sites: Type-III collagen fibers hold the cells of some organ like: liver , spleen. Nice to know  Elastic fibers are thin coiled branching fibers. These fibers may be stretched up to 150% of their resting length, they recoil after removal of stretch. No Transverse striations. Each fiber is composed of a core of elastin protein surrounded by a sheath of fibrillin microfibrils. Main sites : the stroma of the lungs, the wall of large blood vessels (arteries). Fibrillin Elastin microfibrils Elastin occurs as fenestrated sheets called elastic lamellae. Nice to know  Nice to know In this syndrome there are 2 defects: A defect in collagen fibers synthesis. decreased fibrillin (which is a scaffold for elastic fiber formation). Because the walls of large arteries are rich in elastic fibers and also collagen fibers support their wall, and because the blood pressure is high in the aorta, patients with this disease often have aortic swellings called aneurysms, which if ruptured leads to sudden death. Other organs are also affected.  It is highly hydrated, transparent and viscous (jelly like) that fills the space between cells & fibers. So it acts as lubricant and a barrier to the penetration of invaders. It is a mixture of: Nice to know 1.Glycosaminoglycans (GAGs): (linear polysaccharide) as: hyalurinic acid. 2.Proteoglycans (protein + GAGs ↑) 3. Adhesive glycoproteins (protein ↑ + GAGs) as: (fibronectin, integrin &laminin)  Fixed cells Transient cells Have little movement Migrated to tissue from Permanent residents in ct. the blood in response to stimuli 1.Fibroblasts 1. Macrophages 2.Pericytes 2.Plasma cells 3.Mast cells 3.Leucocytes 4.Adipocytes 21  Fixed cells: originate locally and remain in the connective tissue. It includes: Fibroblasts, pericytes, adipose cells, mast cells, and fixed macrophages. Nice to know Transient cells: originate elsewhere and remain temporarily in connective tissue. It includes: certain macrophages, plasma cells, Leukocytes (different WBCs).  Active fibroblasts are spindle shaped (fusiform) and contain well-developed rough endoplasmic reticulum (RER) and many Golgi complexes (characters of protein secreting cells). Synthetically active, they produce collagen, elastic fibers and most of the ground substance (components of the ECM). They have a great role in wound healing & formation of SCAR. Nice to know  The healing of surgical incisions and other Nice to know wounds depends on activity and growth of fibroblasts. In some rapidly closing wounds, a cell called the myofibroblast appear. Myofibroblasts are like fibroblasts but contain increased amounts of actin and myosin so they can contract. Their contraction decreases the size of the wound and accelerate repair a process called wound contraction. Nice to know  Origin: embryonic mesenchymal stem cells and may retain a pluripotential role. Sites: along capillaries. They contain actin, myosin, So they assist to modify blood flow through capillaries. During blood vessel formation and repair: pericytes Nice to know proliferate and differentiate to form smooth muscles, fibroblasts and endothelial cells in new vessels.  Nice to know Origin: arise from blood stem cells in bone marrow. They have similar characteristics as basophils. By LM: central spherical nucleus; coarse, deeply stained metachromatic granules. By TEM: Their surfaces are folded, have a well- developed Golgi complex, scant RER, and many dense secretory granules. x secretory granules contain histamine and heparin. Mast cells provide immediate histamine release responses triggered by antigens.  -Synthesis, storage and secretion of active substances that lead to the manifestations & symptoms of inflammation and allergic reactions: -Heparin: anticoagulant. -Histamine : increases vascular permeability, vasodiltation , smooth muscle contraction of bronchi. -Eosinophil and neutrophil chemotactic factors: attract leukocytes. -Prostaglandins: increase bronchial smooth muscles contraction and mucus secretion.  Allergic rhinitis Allergic Rhinitis: Histamine is released from mast cells in the nasal mucosa Increased vascular permeability Swelling of mucosa feeling stuffed up Itchy nose, runny nose. Treatment: is with antihistamines (diphenhydramine) Or Nasal mast cell stabilizers, (like cromolyn) , may decrease the release of histamine, & other mediators 20 Origin: mesenchymal stem cells. Adipogenesis occurs prenatally & postnatally in early neonatal life & decrease thereafter. Adipocytes do not normally undergo cell division because they are fully differentiated cells. We have 2 types of fat cells (adipocytes): a. Unilocular (white) adipose cells b. Multilocular (brown) adipose cells: Nice to know Types of fat cells: a. Unilocular (white) adipose cells L/M: (H&E) Large oval cells contain a single large fat droplet that squeezes the cytoplasm & nucleus. The nucleus is eccentric (peripheral) & flat (compressed). The cytoplasm is a thin rim around the large single fat droplet, pushing the cytoplasm and nucleus against the cell membrane. By H&E fat appears as empty spaces because it dissolves during preparation. By Special stains it stained: - orange with Sudan III.  Unilocular adipocytes by EM: fat appears large rounded & moderately electron dense. These cells have receptors for insulin, growth hormone, norepinephrine & glucocorticoids to control the uptake and release of free fatty acids and triglycerides. Function: 1. Synthesis and storage of fat. 2. Heat insulation. 3. Supporting and shock absorbing function e.g. fat around the kidney. Nice to know Types of fat cells: b. Multilocular (brown) adipose cells: They are smaller than unilocular adipose cells. The fat is stored as many small fat droplets. The nucleus is spherical & centrally located. They have a lot of mitochondria. There are many blood vessels around them. Sites: In new born, From 2-5% of body weight (back, neck and shoulders). In adults few and scattered (around kidney , adrenal glands, aorta and mediastinum). Function: Heat production and warming the blood (thermogenesis). Nice to know  Origin: in the bone marrow as monocytes. They have phagocytic ability. They specialize in removal of dead cells & tissue debris. So they are abundant at sites of inflammation.  Active macrophages have: pseudopodia, an eccentric kidney-shaped nucleus, phagocytic vacuoles, lysosomes, and residual bodies. Macrophages are present in the connective tissue of most organs and have different names in various regions of the body, ex. 1) Kupffer cells in the liver. 2) Dust cells in the lungs 3) Osteoclasts in bone 4) Langerhans cells in skin 5) Microglia in the central nervous system.  Function of macrophage: 1. They specialize in removal of dead cells & tissue debris. 2.They are antigen presenting cells, break the antigen into epitopes, and place the epitopes on their cell surface to present it to immuno-competent T helper cells. 3.In some diseases macrophages may increase in size and fuse to form multinuclear giant cells 4.They play an important role in early stage of repair after tissue damage. Origin: arise from activated B lymphocytes. Function: responsible for humoral immunity ( antibody producing cells). These ovoid cells contain an eccentric nucleus possessing clumps of heterochromatin, which appear to be arranged in a Cart wheel appearance/ clock face. Their cytoplasm is deeply basophilic because of an abundance of RER. A prominent area adjacent to the nucleus appears pale and contains the Golgi complex (negative Golgi image). (ccc of protein secreting cells)  Granulocytes Origin: from blood stem cells (in bone marrow). are white blood cells that leave the bloodstream and enter the loose connective tissue, where they perform their specific functions during inflammation. Neutrophils phagocytose, kill, and digest bacteria. When they die in the battle they form Pus. Eosinophils : damage the parasites & increase in allergy. Basophils: similar to mast cells. Nice to know  The variety of connective tissue types in the body is due to differences in: 1. Composition of ground substance. 2.Type arrangement & amount of cells and fibers. 1.Embryonic connective tissue: a. Mucoid connective tissue(gelatinous). 2. Connective tissue proper:- a. loose connective tissue proper. b. Dense collagenous (regular or irregular) connective tissue proper. 3. Specialized connective tissue:- a. Adipose connective tissue b. Reticular connective tissue c. Elastic connective tissue. Nice to know 1. Mucous (mucoid) tissue (Wharton jelly): main constituent of the umbilical cord. It consists of: jelly-like matrix + some collagen fibers. Large stellate fibroblasts.  Mucoid connective tissue Cells: Fibroblasts. Fibers: Few fibers Ground matrix. Jelly-like “mucous” (abundant) Place: umbilical cord 1) Loose connective tissue (areolar tissue) possesses: 1. All types of fibers, (fibers are fewer than dense connective tissue). 2. All types of cells (cells are more than dense connective tissue). 3. Abundant matrix (soft sticky gel). a. This tissue is well vascularized, flexible& not very resistant to stress. b. It is more abundant than dense connective tissue and It is the connective tissue that fills in the spaces just deep to the skin. It makes up the fascia of the body, which is the fibrous material that helps bind the skin, muscles, bones, and other organs of the body together. Nice to know  Nice to know 2) Dense (collagenous) connective tissue contains: 1. More fibers (collagen fibers) 2. Fewer cells (fibroblasts) than loose connective tissue. It is classified into two types:- a. Dense, irregular collagenous connective tissue (most common): which contains dense collagen fiber bundles that have no definite orientation. Site: the dermis of skin and capsules of organs. b. Dense, regular collagenous connective tissue, which Nice to know contains dense collagen fiber bundles arranged in a parallel fashion and fibroblasts are present in-between fibers. site: in tendons and ligaments.  Adipose connective tissue is the primary site for storage of energy (in the form of triglycerides). There are 2 types of adipose tissue:- 1.White adipose tissue: is composed of unilocular adipose cells & present in: Subcutaneous tissue all over the body. It acts as an insulator and as a body cushion (shock absorber). It functions also as Endocrine organ? It is the only source of hormone leptin Leptin helps regulate the appetite (Controls how hungry or full we feel) 2. Brown adipose tissue is composed of multilocular adipose cells, which contain many large mitochondria. (1) This tissue is capable of generating heat. (2) This tissue is found in infant (reduced in adults). Thermogenin, a trans-membrane protein in mitochondria in brown fat, is responsible for heat production, without forming ATP This is important in human babies, who cannot shiver to generate heat.  Elastic connective tissue is composed of: 1. branching elastic fibers. 2. Some fibroblasts filling the interstitial spaces. It is present in the lungs, elastic cartilage, and elastic ligaments and in large (conducting) blood vessels (Aorta). it forms sheets / lamellae. Nice to know  OBESITY: body mass index is greater than 30 kg/m2. May lead to metabolic syndrome (Insulin resistance, type II diabetes mellitus, fatty liver disease, and cardiovascular disease). It is either: hypertrophic obesity: increase in adipose cell size (adult onset), hypercellular obesity increase in the number of adipose cells that begins in childhood and is usually lifelong).  Reticular connective tissue consists mostly of a network of branched reticular fibers (type III collagen) taained by silver or PAS. It forms the stroma of lymphatic organs (spleen, lymph node,….), bone marrow, and endocrine glands.  Textbooks guide The human body in health and disease: 77-79. USMLE step 1 lecture notes 2006-2007 BRS: cell biology & Histology: 90-102 47