4.3: Connective Tissues: Supports and Protects

Characteristics of Connective Tissues

1) All types of connective tissue originate from mesenchyme 2) Connective tissues vary widely in appearance and function but all forms share three basic components. 3) Many types of connective tissue are highly vascular and contain sensory receptors that detect pain, pressure, temperature, and other stimuli

Diversity of Connective Tissues

1) Connnective Tissue proper: includes connective tissues with many types of cells and extracellular fibers in a gel-like ground substance a) Loose Connective Tissues (areolar tissue, adipose tissue, reticular tissue) b) Dense connective tissues (Dense regular, dense irregular, elastic) ------------------------- 2) Fluid Connective Tissues a) Blood b) Lymph -------------------- 3) Supporting connective tissues a) Cartialge b) bone

Functions of Connective Tissues

1) Establish a structural framework for the body 2) Transport fluids and dissolved materials 3) Protect delicate rogans 4) Support, surround, and interconnect other types of tissue 5) Store energy reserves, especially in the form of triglycerides 6) Defend the body from invading microorganisms.

Location of Connective Tissue

1) Most abundant tissue in the body 2) Never exposed to the outside environment

Supporting Connective Tissues

Differ from connective tissue proper in have a less diverse cell population and a matrix containing much more densely packed fibers. Supporting connective tissues protect soft tissues and support the weight of part or all the body. a) Cartilage: solid, rubbery matrix containing chondrocytes. All cartilage is surrounded by a membrane of connective tissue called the perichondrium. i) Hyaline cartilage: Found connecting the ribs to the sternum, covering the articular surfaces of long bones, supporting the respiratory passageways such as the trachea, and forming the tip of the nose and part of the nasal septum. Has an amorphous matrix with few visible fibers. It provides stiff but somewhat flexible support and reduces friction between bony surfaces. ii) Elastic cartilage: found in the ear and epiglottis. Has many more elastic fibers within the matrix and is therefore more flexible. iii) Fibrous cartilage: Found within the intervertebral discs, the meniscus of the knee, and pubic symphysis. Has many more collage fibers within its matrix and is therefore very strong. b)Bone: solid, crystalline matrix containing osteocytes. All bone is surrounded by a membrane of connective tissues called the periosteum. i) A typical long bone is hollow, and its walls contain two different types of bone. The weight bearing outer layer consists of well-organized compact bones, whereas a finer network of spongy bone lines the internal cavity. ii) Compact bone is composed of numerous functional units called osteons. iii) Each osteon possesses a hollow central canal through which blood vessels and nerves pass through the bone. iv) The central canal is surrounded by several concentric rings of rigid matrix called lamellae. v) Along each lamella are small open spaces in which the osteocytes reside. These open spaces are called lacunae. vi) The lacunae are attached to each other and to the central canal by fine passageways that form a branching network for the exchange of materials between the blood vessels and osteocytes. These passageways are called canaliculi.

Dense Connective Tissues

Fibers are densely packed together a) Dense regular: all collagen fibers are oriented parallel to each other providing strength along the axis of the collagen fibers. Found in cords (such as tendons) or sheets (ligaments). Tendons connect muscle to bone. Ligaments connect bones to bones. b) Dense irregular: Collagen fibers are non-parallel forming an interwoven network. These tissues provide strength in many directions such as the dermis of the skin c) Elastic: when elastic fibers outnumber collagen fibers, the tissue has a springy, resilient nature that allows it to tolerate cycles of extension and recoil. This elastic tissue is bound between the vertebrae of the spinal column and the erectile tissues of the penis. Do not need to know this for lab.

Loose connective tissues

Fibers created a loose, open framework a) Areolar tissue: most common form of connective tissue proper in adults. It is the general packing material in the body. Attaches skin to underlying body parts and is sometimes called the superficial fascia. All of the cell types found in other forms of connective tissue proper can be found in areolar. b) Adipose tissue: Found deep to the skin, especially at the flanks, buttocks, and breasts. It also forms a layer that provides padding within the orbit of the eyes, in the abdominopelvic cavity, and around the kidneys. The distinction between areolar tissue and adipose is the larger number or adipocytes (fat cells) c) Reticular Tissue: found in the liver, kidney, spleen, lymph nodes, and bone marrow where it forms a tough, flexible network that provides support and resists distortion. In reticular tissue, reticular fibers create a complex supporting network known as a stroma. Fixed macrophages and fibroblasts are present but these cells are seldom visible. Don not need to know for the lab practical

Connective tissues vary widely in appearance and function but all forms share three basic components

a) Specialized cells: the cells present in each type of connective tissue helps to distinguish the various types from one another. A few of the cells are listed here: i) Fibroblast cells: produce connective tissue ii) Chondrocytes: produce cartilage iii) Osteocytes: produce bone iv) Hemocytoblast: Produce blood b) Extracellular protein fibers: three primary fibers are produced in connective tissues i) Elastic fibers: slender, straight, and very stretchy. They recoil to their original length after stretching or distortion. ii) Collagen fibers: thick, straight or wavy, and often forms bundles. They are very strong and resist stretching. iii) Reticular fibers: strong fibers that form a branching network of scaffolding. c) Ground substance: material that fills the space between the cells and surrounds the extracellular fibers. In some connective tissues the ground substance is gel-like while in others it is liquid based and in others it is rigid or calcified. Ground substance and extracellular fibers make up the matrix of connective tissues.

Fluid Connective Tissues

have distinctive populations of cells suspended in a watery matrix that contains dissolved proteins. a) Blood: flows within the cardiovascular system i) Possesses a water matrix called plasma ii) Hemocytoblasts give rise to three formed elements suspended in the plasma: red blood cells, white blood cells, and platelets iii) Red blood cells. aka erythrocytes: transport oxygen and, to a lesser degree, carbon dioxide iv) White blood cells aka leukocytes; help defend the body from infection and disease v) Platelets aka thrombocytes; cell fragments that are involved in the clotting response that seals broken blood vessels. b) Lymph- flows within the lymphatic system i)Forms an interstitial fluid enters a lymphatic vessel ii) Lymph passes through lymph nodes where it is cleaned and filtered.