Connective tissues. Dr. Hersh Abdul Ham-Karim BVM&S, PG Dip, MSc and PhD

Transcription

1 Connective tissues Dr. Hersh Abdul Ham-Karim BVM&S, PG Dip, MSc and PhD

2 Connective tissue (CT) Connective tissue is a term applied to a basic type of tissue of mesodermal origin, which is sparsely populated by cells and contains an extensive extracellular matrix consisting of protein fibers, glycoproteins, and proteoglycans. CT provides structural and mechanical support for other tissues, and to mediate the exchange of nutrients and waste between the circulation and other tissues. All connective tissues are composed of: 1. Cells 2. Extracellular matrix (ECM) a. Fibers b. Ground substance

3 Functions of CT Support: Structural support is the major function of connective tissue, which forms the framework upon which all other body tissues are assembled. Defense physical: The viscosity of the extracellular matrix, slows the progress of many bacteria and foreign particles. Defense immunologic: Foreign bodies that successfully penetrate epithelia are intercepted by immuno-responsive cells that inhabit the underlying connective tissue. Repair: Rapidly closing any breaches in the body's protective barriers. Storage: Reserves of water, electrolytes, and reserve energy in the form of lipids are stored in adipocytes. Transport: CT is thus a crossroads for transporting substances to and from other tissues.

4 Cells of CT There are two major groups of cell in connective tissue: 1. Fixed cells (resident cells): Are derived from mesenchyme and are continuously present in the tissue (e.g., fibroblasts, adipocytes, mast cell, etc). 2. Free cells (visitant cells): Enter and leave the blood stream to migrate through and function in connective tissues (e.g., neutrophils, eosinophil, basophil, monocyte, lymphocytes, and plasma cells)

5 1. Fibroblasts: Fibroblasts are spindle-shaped flat cells with minute processes spreading out of the cell body. The cells have flattened nucleus containing 1-2 nucleoli. When fibroblasts are active, cellular organelles like Golgi apparatus and rough endoplasmic reticulum become more prominent. Secrete both fibers and ground substance of the matrix

6 2. Mast cells. Mediate immediate hypersensitivity reaction by releasing immune modulators (Histamine) from cytoplasmic granules, in response to antigen binding with cell surface antibodies. Structure: Round to oval-shaped cells. Round, usually centrally located nucleus. Well-defined cytoplasm filled with secretory granules containing immunemodulatory compounds (e.g., histamine).

7 3. Macrophages. Derived from blood monocytes; monocytes enter connective tissue from the bloodstream and rapidly transform into macrophages that function in phagocytosis, antigen processing, and cytokine secretion. Comprise the mononuclear phagocyte system of the body; include Kupffer cells in the liver, alveolar macrophages in the lung, microglia the central nervous system, Langerhan s cells in the skin, and osteoclasts in bone marrow.

8 Extracellular matrix 1. Fiber Collagen Fibers: Large fibers made of the protein collagen and are typically the most abundant fibers. Promote tissue flexibility. Elastic Fibers: Intermediate fibers made of the protein elastin. Branching fibers that allow for stretch and recoil. Reticular Fibers: Small delicate, branched fibers that have same chemical composition of collagen. Forms structural framework for organs such as spleen and lymph nodes.

9 2. Ground substance It is an amorphous gelatinous material. It is transparent, colourless, and fills the spaces between fibres and cells Functions: Forms a gel-like matrix (cells and fibers are embedded). Provides a medium for passage of molecules and cells migrating through the tissue.

10 Types of CT The main criteria for classification are the amount and type of ECM, arrangement and kinds of fibers, and abundance cell types; Connective tissue Embryonic Adult Mesenchyme Mucous Proper supportive specialized Loose Dense Bone Cartilage Adipose Reticular Elastic Blood Regular Irregular

11 Embryonic CT Mesenchyme: Unspecialized CT of early week of embryonic life, which further differentiates into all CT. Mucous: Embryonic connective tissue with abundant ground substance and delicate collagen fibers; present in the umbilical cord.

12 Adult CT 1. True (proper) CT a. Loose (areolar) CT b. Dense CT Highly cellular, numerous cell types present. Fewer and smaller caliber collagen fibers compared with dense. Fewer cells, mostly fibroblasts. Highly fibrous with larger caliber collagen fibers. Abundant ground substance. Minimal ground substance. Highly vascularized. Poorly vascularized. diffusion of nutrients, wastes and provides padding between and around organs and tissues. provides strength.

13 b. Dense connective tissue Dense regular CT The parallel arrangement of bundles of collagen fibers. Forms tendons, ligaments Provide strong attachment between various structures Dense irregular CT Randomly-arranged collagen fibers and a few fibroblasts Forms the capsule of organs and the dermis of the skin. Provide strength fibroblasts collagen

14 2. Supportive connective tissue a. Cartilage It is a type of connective tissue which is tough, and flexible. Like other connective tissues, it consists of cells and ECM. Unlike other CT, does not contain vessels and nerves. The strength of cartilage is due to collagen fibers and the resilience is due to the presence of chondroitin. Most cartilage is surrounded by the perichondrium. Fibrocartilage is the exception.

15 Components of Cartilage Perichondrium: Capsule-like sheath of dense connective tissue that surrounds cartilage. Harbors the vascular supply for avascular cartilage. Connects cartilage with the surrounding tissues. a) Fibrous layer; Outer portion, composed of dense connective tissue, serves as a source of reserve cells for the chondrogenic layer. b) Chondrogenic layer; Inner more cellular portion contains chondroblasts which create the major component, the extracellular matrix, of the cartilage.

16 Cells: Chondroblasts Lie on the surface of cartilage in the chondrogenic layer of perichondrium. Secrete extracellular matrix around them, thus becoming. Chondrocytes Are chondroblasts that have surrounded themselves with matrix. Lie within cartilage in potential spaces called lacunae. Secrete and maintain extracellular matrix. Are frequently located in isogenous groups, a cluster of chondrocytes, resulting from the proliferation of a single chondrocyte. Extra cellular matrix: Fiber & ground substance

17 Types of Cartilage 1. Hyaline Cartilage: Composition : Presence of isogenous group. Ground substance appears homogenous & takes blue stain. Collagen fibers in ground substance have same refractive index as that of ground substance. Perichondrium is present in all except in articular cartilage. Incidence: articular surfaces, wall of large respiratory passages larynx, trachea, bronchi, epiphyseal plate, ventral ends of ribs, embryonic temporary skeleton Functions: Reduces friction at joints, movement and support

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20 2. Elastic Cartilage: Composition Chondrocytes similar to hyaline cartilage, housed in lacuna singly or in pairs. Extracellular matrix fibrils of collagen II and network of fine elastic fibers, less amount of ground amorphous substance On the surface - perichondrium is identifiable. Itprovides both strength and elasticity to certain parts of the body. Incidence: epiglottis, auricle of the ear,eustachian tube, cuneiform and corniculate cartilages in larynx

21 auricle Eustachian tube

22 3. Fibrocartilage Composition Chondrocytes small, spindle-shaped, similar to fibroblasts arranged singly or in long rows Extracellular matrix great number of collagen I fibers acidophilic, amorphous matrix less abundant Perichondrium is not identifiable. Incidence: Intervertebral disc, articular disc, pubic symphysis, labrum of ball and socket joint. Functions: Shock absorbers, Provides sturdiness without impeding movement

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24 b. Bone Bone is a hard and rigid tissue, consists of living cells with large amounts of matrix. Functions of bone: Mechanical structures for movement and protection of vesira Home for hematopoietic tissue Storage for elements and minerals homeostatic regulation of blood calcium level Storage of adipose tissue: yellow marrow

25 Cells: 1. Osteo-progenitor cells: Flattened, elongated ovoid nuclei, derived from mesenchymal cells, located in periosteum, endosteum and stromal component of BM. 2. Osteoblasts: They are cuboidal to columnar cells have the epitheloid appearance with intensely basophilic cytoplasm. The bone-forming cells derived from osteo-progenitor cells, which produce and secrete matrix proteins and transport mineral into the matrix.

26 3. Osteocytes: Osteocytes are spider-shaped cells. Transport materials between blood and bone and to maintain surrounding matrix; they do not divide or secrete matrix. 4. Osteoclasts: Osteoclasts are large, multinucleated cells, have small projections (microvilli) that is the cell s active region. They function in bone resorption by removing local mineralized matrix.

27 Surface coverings of bone 1. Periosteum: The outer surface of the bone and consists of two layers. 1. Fibrous layer: consists mainly of the dense irregular connective tissue, contains arteries, veins, lymphatic vessels and sensory nerves. 2. Osteogenic layer: An inner (cambium) layer of loose, richly vascularized CT contains progenitor cells that develop to osteoblasts. Function: Attachment Sites for the Muscle Tendons and Ligaments Nourishment of the Bones and Muscles Bone Growth and Repair

28 Endosteum: It is a thin layer of connective tissue that lines the inner surfaces of all bones (the cavities within the bone). Also contains both osteoblasts, osteoclasts, and/or osteo-progenitor cells that line all interior surfaces of bone except for lacunae and canaliculi. Serves as a means of bone growth and/or resorption.

29 Microscopic Appearance of Bone: The orientation of collagen fibers in the bony matrix determines whether a bone is either primary (woven) or mature (lamellar) bone. 1. Lamellar or mature bone or secondary. Composed of cylindrical units called osteon. Osteon consist of concentric lamellae of bone matrix surrounding a central canal called Haversian canal, which contain the vascular and nerve supply of osteon. Within the bone matrix are spaces called Lacunae, each containing osteocyte. The osteocyte extends numerous processes into a small tunnels called canaliculi. Canaliculi serves for the passage of substances between the osteocytes and blood vessels.

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31 Mature spongy bone is structurally similar to mature compact bone except that the tissue is arranged as trabeculae. The matrix of bone is lamellated. Osteocytes get nutrients directly from circulating blood.

32 2. Woven or immature bone or primary bone Possibly will be either spongy or compact. Woven bone is found on the growing ends of an immature skeleton or, in adults, at the site of a healing fracture. Characterized by random deposition of fine collagen and increased cellularity contains osteocytes that are more numerous and spherical than those of lamellar bone. Relatively low mineral contents. Seen in embryonic development, fracture, and repair.

33 2. Specialized CT: A. Blood It is a biological red liquid circulating in the arteries and veins under the impulse of the heart. Functions of blood Transports gases, nutrients, waste, cells and hormones throughout the body. Regulates temperature and water content of cells. Protects against blood loss through clotting. Protects against disease through phagocytic white blood cells and antibodies.

34 The main components of blood include is made up of plasma which is a highly viscous liquid and 3 different types of blood cells that are floating around in it.

35 1. Plasma: A typical sample of plasma is composed of 90% water, 8% protein, 1% inorganic salts, 0.5% lipids and 0.1% sugar, the rest being made of lesser components. The three main groups of proteins in plasma are the blood coagulation (fibrinogen) proteins, albumin, and the globulins. The globulins can be divided into; alpha globulins (proteases, anti-proteases and transport proteins). beta globulins (transferrin, other transport proteins) gamma globulins (mainly immunoglobulins). The plasma proteins are nearly all derived from synthesis in the liver, with the exception of the immunoglobulins which are synthesised by plasma cells.

36 2. Cellular component a. Erythrocyte (RBC) RBCs constitute the largest number of cells in the blood about 5.2 million mm3 (man), 4-5 million (woman) biconcave disc shape no nucleus contain hemoglobin Life span in blood 120 days main function is gases transport

37 b. Platelets (thrombocytes) Small, biconvex disks. Non-nucleated cell formed in the bone marrow from the cytoplasm of cells called megakaryocytes. Platelets have a life span of about 10 days. Their numbers in circulating blood range from to /mL. Function: initiate blood clots

38 c. Leucocyte WBC mm3 (healthy adult) act mainly outside blood vessels in the tissues main function is defence. classification of leukocytes classification system is based on appearance of the granule o Granulocytes Neutrophil, Basophile and Eosinophil o Agranulocytes Lymphocytes and Monocytes

39 1. Granulocyte Neutrophil the most common type of leucocyte in blood Compose 60-70% of the leukocytes Life Span: < 1 week About 9-12 µm in diameter (thus larger than RBC). Nucleus is polymorphonuclear - has 3-5 lobes linked together by fine threads of chromatin Cytoplasm contains granules, which are lysosomes that contain enzymes for digestion of phagocytosed particles, e.g. bacteria.

40 Eosinophil Compose 1-6% of the leukocytes Nucleus is bilobed Life span < 2 weeks Cytoplasm contains ovoid, acidophilic granules (bright pink), which are larger than those of neutrophils Granules are lysosomes that contain enzymes that can degrade phagocytosed particles. Important in allergic reactions, parasitic infections, and phagocytosis of Ab-Ag complexes.

41 Basophil constitute less than 1% of leucocytes. Lobulated nucleus often obscured by granules Life Span: 1-2 years basophilic cytoplasmic granules (dark blue), containing heparin (anti-coagulant) and, histamine (vasodilator). Function in allergic reactions and inflammatory response.

42 2. Agranulocyte a. Lymphocytes are the smallest cells in the white cell series, being only slightly larger than erythrocytes. constitute 20-30% of leucocytes. Life Span: variable (few days to several years) Round dense nucleus. Small lymphocytes (inactivate) have very little cytoplasm. Two populations, one that can become T- lymphocytes and the other B- lymphocytes. When activated by encounter with foreign antigen presented by a macrophage - become large lymphocytes that are capable of mitosis. Round nucleus Ovoid nucleus Small lymphocytes Large lymphocytes

43 * Plasma cells. Secrete antibodies to provide humeral immunity. Derived from B-lymphocytes. Structure: Oval-shaped cells. Round, eccentrically located nucleus. Basophilic cytoplasm due to large amounts of rough endoplasmic reticulum. Well-developed Golgi complex appears as a distinct, unstained region in the cytoplasm near the nucleus and, for that reason, is often referred to as a negative Golgi.

44 b. Monocytes They are the largest cells in the white cell series, comprise 3-10 per cent of the leukocytes Large, eccentric nucleus either oval, kidneyshaped or horseshoe-shaped with delicate chromatin that is less dense than that of lymphocytes. Life Span: few days in blood, several months in connective tissue Migrate through blood to the tissues; once in tissues they differentiate into phagocytes (macrophages) Macrophages, by releasing cytokines after activation, coordinate inflammatory and defensive reactions. The vacuoles contain chemicals that digest the foreign particles chromatin nucleus

45 B. Adipose cells (adipocytes, fat cells) Their functions are to Store lipids inside the body. Types: a. Yellow fat (unilocular). Each cell contains a single droplet of neutral fat (triglycerides) for energy storage and insulation. Minimal cytoplasm, present as a rim around the lipid droplet. Flattened, crescent-shaped nucleus that conforms to the contour of the lipid droplet. b. Brown fat (multilocular). Cells contain numerous, small lipid droplets. Large numbers of mitochondria. Present mostly during early postnatal life in humans, abundant in hibernating animals for heat production.