Connective Tissues - The Tissues of the Human Body PDF

Connective tissues - The tissues of the human body Lect 3 Describe the general features of connective tissue Describe some of the different types of connective tissue with reference to their location, structure and function The connective tissues is classified into two types embryonic and mature a)...

Connective tissues - The tissues of the human body Lect 3 Describe the general features of connective tissue Describe some of the different types of connective tissue with reference to their location, structure and function The connective tissues is classified into two types embryonic and mature a) Embryonic Connective Tissues Mesenchyme (embryonic) - - This embryonic connective tissue is important in the development phase of the cells, cells that can differentiate into other types of cells in the connective tissue, thus it gives rise to all other connective tissues. This mesenchyme consists of connective tissue cells (mesenchymal cells) in a semi-fluid ground substance containing reticular fibres. Mucous - Mucous CT has widely scattered fibroblasts embedded in helly-like ground substance. Supports the umbilical cord of the foetus, which protects the blood vessels that are going back and forth between the mom and foetus. b) Mature connective tissues A) Connective tissue proper - two types Loose CT and Dense CT 1. Loose connective tissue - loosely arranged between cells Type of loose connective tissues Location Structure Function Areolar connective tissue (many cells, fewer fibres) The most common type of connective tissue in the body. Widely distributed around almost every body structure. Like a “packing material”. Consists of fibres (collagen, elastic, reticular) arranged randomly and several kinds of cells (fibroblasts, macrophages, plasma cells, adipocytes, mast cells, and a few white blood cells) embedded in semi fluid ground substance (hyaluronic acid, chondroitin sulphate, dermatan sulphate, and keratan sulphate). Strength, elasticity, support. In the subcutaneous layer deep to skin; papillary (superficial) region of dermis of skin; lamina propria of mucous membranes; around blood vessels, nerves, and body organs. Adipose tissue Subcutaneous layer deep to skin, around heart and kidneys, yellow bone marrow, padding around joints and behind eyeball in eye socket. fibroblasts (called adipocytes) that are specialised for storage of triglycerides (fats) as a large, centrally located droplet. Cell fills up with a single, large triglyceride droplet, and cytoplasm and nucleus are pushed to the periphery of the cell. With weight gain, the amount of adipose tissue increases and new blood vessels form. Thus, an obese person has many more blood vessels than does a lean person, a situation that can cause high blood pressure, since the heart has to work harder. Most adipose tissue in adults is white adipose tissue (just described). Brown adipose tissue (BAT) is darker due to very rich blood supply and numerous pigmented mitochondria that participate in aerobic cellular respiration. BAT is widespread in the foetus and infant; adults have only small amounts Reduces heat loss through skin; serves as an energy reserve; supports and protects organs. In newborns, BAT generates heat to maintain proper body temperature. Adipose tissue is also an excellent source of stem cells, which are used in rejuvenation medicine to repair or replace damaged tissue. Reticular connective tissue Stroma (supporting framework) of liver, spleen, lymph nodes; red bone marrow; reticular lamina of basement membrane; around blood vessels and muscles. A fine interlacing network of reticular A fine interlacing fibres (thin form of collagen fibre) and network of reticular reticular cells fibres (thin form of collagen fibre) and reticular cells 2. Dense connective tissue - thicker and more densely packed, but have considerably fewer cells than loose connective tissue Type of Dense connective tissues Location Structure Function Dense regular connective tissue Forms tendons (attach muscle to bone), most ligaments (attach bone to bone), and aponeuroses (sheetlike tendons that attach muscle to muscle or muscle to bone). forms a shiny white extracellular matrix; mainly collagen fibres regularly arranged in bundles with fibroblasts in rows between them. Collagen fibres (protein structures secreted by fibroblasts) are not living, so damaged tendons and ligaments heal slowly. Provides strong attachment between various structures. Tissue structure withstands pulling (tension) along long axis of fibres. Dense irregular connective tissue fasciae (tissue beneath skin and around muscles and other organs), reticular (deeper) of collagen fibres; usually irregularly arranged with a few fibroblasts Provides tensile (pulling) strength in many directions region of dermis of skin, fibrous pericardium of heart, periosteum of bone, perichondrium of cartilage, joint capsules, membrane capsules around various organs (kidneys, liver, testes, lymph nodes); also in heart valves Elastic connective tissue Lung tissue, walls of elastic arteries, trachea, bronchial tubes, true vocal cords, suspensory ligaments of penis, some ligaments between vertebrae predominantly elastic fibres with fibroblasts between them; unstained tissue is yellowish. Allows stretching of various organs; is strong and can recoil to original shape after being stretched. Elasticity is important to normal functioning of lung tissue (recoils in exhaling) and elastic arteries (recoil between heartbeats to help maintain blood flow). B. Supporting connective tissue - two types cartilage and bone tissue 1. Cartilage Type of cartilage Location Structure Function Hyaline cartilage Most abundant cartilage in body; at ends of long bones, anterior ends of ribs, nose, parts of larynx, trachea, bronchi, bronchial tubes, embryonic and fetal skeleton. contains a resilient gel as ground substance and appears in the body as a bluish-white, shiny substance (can stain pink or purple when prepared for microscopic examination; fine collagen fibers are not visible with ordinary staining techniques); prominent chondrocytes are found in lacunae surrounded by perichondrium (exceptions: articular cartilage in joints and cartilage of epiphyseal plates, where bones lengthen during growth). Provides smooth surfaces for movement at joints, flexibility, and support; weakest type of cartilage and can be fractured Fibrocartilage Pubic symphysis (where hip bones join anteriorly), intervertebral discs, menisci (cartilage pads) of knee, portions Chondrocytes (cartilage is solely composed of cells) among clearly visible thick bundles of collagen fibers within extracellular matrix; Support and joining structures together. Strength and rigidity make it the strongest Elastic cartilage of tendons that insert into cartilage. lacks perichondrium type of cartilage. Lid on top of larynx (epiglottis), part of external ear (auricle), auditory (eustachian) tubes chondrocytes in threadlike network of elastic fibers within extracellular matrix; perichondrium (the CT that envelops cartilage where it is not at a joint) present Provides strength and elasticity; maintains shape of certain structures. 2. Bone tissue Type of bone tissues Spongy bone & Compact bone Location Both compact and spongy bone tissue make up the various parts of bones of the body Structure Compact bone tissue consists of osteons (haversian systems) that contain lamellae, lacunae, osteocytes, canaliculi, and central (haversian) canals Function Support, protection, storage; houses blood-forming tissue; serves as levers that act with muscle tissue to enable movement spongy bone tissue consists of thin columns called trabeculae; spaces between trabeculae are filled with red bone marrow. C. Liquid connective tissue Type of liquid connective tissue Location Structure Function Blood Within blood vessels (arteries, arterioles, capillaries, venules, veins), within chambers of heart. Blood consists of blood plasma and formed elements: red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes). Red blood cells: transport oxygen and some carbon dioxide; white blood cells: carry on phagocytosis and mediate allergic reactions and immune system responses; platelets: essential for blood clotting Lymph Lymphatic vessels carry lymph throughout the body. Lymph nodes are small masses of lymph tissue that filter out foreign materials (such as infectious microorganisms) from the lymph. Lymph nodes are found in various parts of the body, including the neck, armpits, groin, chest, and abdomen Lymph is a clear, yellowish fluid present in most tissues of the body. It is created as a result of the filtration of plasma. Similar to blood plasma, lymph mainly consists of water, along with other components such as proteins, lipids, glucose, ions, and cells The lymphatic system is a network of vessels and organs that regulates the amount of fluid in the human body. It also defends the body against infections. The lymphatic system complements the bloodstream functions by filtering pathogens from the blood and maintaining fluid balance. What are the components of the blood - fluid connective tissue? 1. Leukocytes (White Blood Cells): ○ Neutrophils and monocytes (macrophages) are phagocytic cells that engulf bacteria. ○ Basophils (mobile) and mast cells (immature, circulating; mature, fixed in tissues) release substances like histamine, which intensify the inflammatory reaction. ○ Eosinophils are effective against certain parasitic worms and play a role in acute allergic responses. ○ Lymphocytes are involved in the immune response. 2. Platelets: ○ Platelets are derived from megakaryocytes in red marrow. ○ Their primary function is clotting to prevent excessive bleeding. ○ They also secrete antibodies (Abs). 3. Erythrocytes (Red Blood Cells): ○ Erythrocytes transport oxygen (O₂) from the lungs to tissues and carry carbon dioxide (CO₂) back to the lungs for exhalation. Describe the general structure of compact bone Bone are composed of several CT types, including bone tissue (which is either compact or spongy) There are 4 types of of cells in bone tissues 1) Osteoprogenitor Cells: ○ Origin: Derived from mesenchyme stem cells, which forms most connective tissues. ○ Function: Unspecialized bone stem cells. ○ Cell Division: The only bone cells that undergo cell division. ○ Development: Resulting cells develop into osteoblasts. ○ Locations: Found along the inner portion of the periosteum, in the endosteum, and within bone canals containing blood vessels. 2. Osteoblasts: ○ Function: Bone-building cells. ○ Synthesis: They synthesize and secrete collagen fibers and other organic components needed for the extracellular matrix of bone tissue. ○ Initiation: Osteoblasts initiate calcification. ○ Maturation: As they surround themselves with extracellular matrix, they become trapped and transform into osteocytes. 3. Osteocytes: ○ Role: Mature bone cells. ○ Metabolism: Main cells in bone tissue, maintaining daily metabolism (nutrient exchange with blood). ○ Cell Division: Like osteoblasts, osteocytes do not undergo cell division. 4. Osteoclasts: ○ Origin: Derived from the fusion of up to 50 monocytes (a type of white blood cell). ○ Location: Concentrated in the endosteum. ○ Function: Responsible for bone resorption by releasing powerful lysosomal enzymes and acids that digest protein and mineral components of the extracellular bone matrix. Compact bone tissue is composed of repeating structural units called osteons, or haversian systems 1. Osteons (Haversian Systems): Structure: Repeating structural units in compact bone. Components: Each osteon consists of concentric lamellae arranged around an osteonic (haversian) canal. ○ Lamellae: Concentric lamellae resemble growth rings of a tree and are circular plates of mineralized extracellular matrix. ○ Central Canal: Contains blood vessels and nerves. 2. Lacunae and Canaliculi: ○ Lacunae: Small spaces between concentric lamellae that contain osteocytes (mature bone cells). ○ Canaliculi: Tiny canals radiating from lacunae, filled with extracellular fluid. ○ Osteocytes: Slender fingerlike processes of osteocytes extend into canaliculi, allowing communication between neighbouring osteocytes via gap junctions. 3. Nutrient Supply: ○ The interconnected system of canals (canaliculi and central canals) provides routes for nutrient exchange within the bone. ○ ○