Connective Tissues

Connective Tissues

Connective tissues are one of the primary tissue types.

Overview

  • Connective tissues bind structures, provide support and protection, serve as frameworks, fill spaces, store fat, produce blood cells, protect against infections, and help repair tissue damage.

  • Connective tissue cells are farther apart than epithelial cells and have abundant extracellular matrix (ECM) between them.

  • The ECM in connective tissues determines tissue density.

Components of Connective Tissue

  • Cells

  • Fibers (collagen, elastic, reticular)

  • Extracellular ground matrix

  • Ground substance

Connective Tissue Cells

  • Categorized into fixed and wandering cells.

  • Fixed cells: reside in the specific connective tissue type for an extended period.

    • Examples: fibroblasts and mast cells.

  • Wandering cells: move through and appear in tissues temporarily, usually in response to an injury or infection.

    • Examples: macrophages & lymphocytes.

  • Fibroblasts

    • Most common type of fixed cell in connective tissues.

    • Produce fibers into the extracellular matrix of connective tissues.

  • Macrophages

    • Specialized to carry on phagocytosis.

    • Clear foreign particles from tissues, providing an important defense against infection.

  • Mast cells

    • Large and widely distributed in connective tissues.

    • Usually near blood vessels.

    • Release heparin, a compound that prevents blood clotting.

    • Also release histamine.

Role of Mast cells, phagocytes and pathogens

  • Harmful things enter the body that causes Injury and Inflammation.

  • Inflammation: Includes pain, warmth, swelling and redness.

Connective Tissue Fibers

  • Collagen fibers

    • Thick threads of the protein collagen, the major structural protein of the body.

    • Have great tensile strength.

    • Important components of body parts that hold structures together, such as ligaments and tendons.

    • Much of the human body consists of the protein collagen.

    • Found in bone and cartilage, skin, ligaments, tendons, and the dentin of teeth.

    • Collagen is in the eyes, blood vessel linings, and basement membranes.

    • Defects in collagen cause a variety of medical problems because of its abundance and wide distribution in the body.

  • Marfan syndrome

    • One of the protein fibers in the connective tissue is defective, leading to weaker connective tissue.

    • People with Marfan syndrome tend to grow taller, have longer arms, legs, fingers, flat feet, and have lax joints.

    • As people with Marfan syndrome get older the weaker connective tissue can cause medical problems. These medical problems mainly affect the heart, aorta, lungs, joints and eyes.

  • Elastic fibers

    • Composed of a spring-like protein called elastin.

    • Weaker than collagen fibers, but they are easily stretched and will resume their original lengths and shapes when the force acting upon them is removed.

    • Abundant in body parts normally subjected to stretching such as the lungs.

  • Reticular fibers

    • Highly branched and form delicate supporting networks in a variety of tissues, including those of the spleen.

Classification of Connective Tissue

  • Connective tissue proper

    • Loose connective tissue (fewer fibers, more ground substance)

      • Areolar

      • Adipose

      • Reticular

    • Dense connective tissue (more fibers, less ground substance)

      • Regular

      • Irregular

      • Elastic

  • Supporting connective tissue

    • Cartilage (semisolid matrix)

      • Hyaline

      • Fibrocartilage

      • Elastic

    • Bone (solid matrix)

      • Compact

      • Spongy

  • Fluid connective tissue

    • Blood

Loose Connective Tissue

  • Areolar Connective Tissue

    • Forms delicate, thin membranes throughout the body.

    • The cells of this tissue, mainly fibroblasts, separated by a gel-like ground substance that contains collagen and elastic fibers

    • Found in the subcutaneous layer beneath the skin.

    • Found around blood vessels, nerves, and body organs.

  • Adipose tissue

    • Develops when certain cells (adipocytes) store fat in droplets in their cytoplasm.

    • Lies:

      • beneath the skin

      • in spaces between muscles

      • around the kidneys

      • behind the eyeballs

      • on the surface of the heart

  • Reticular Connective Tissue

    • Composed of thin, reticular fibers in a three- dimensional network.

    • Helps provide the framework of certain internal organs, such as the liver and spleen.

Dense Connective Tissue

  • Dense Regular Connective Tissue

    • Consists of many closely packed, thick, collagen fibers and a few cells, mostly fibroblasts. Collagen is very strong, enabling the tissue to withstand pulling forces.

  • Dense Irregular Connective Tissue

    • Fibers of dense irregular connective tissue are thicker, interwoven, and more randomly distributed.

    • The irregularly placed fibers allow the tissue to sustain tension exerted from many different directions.

    • Dense irregular connective tissue is in the dermis, which is the deep skin layer.

  • Elastic Connective Tissue

    • Mainly consists of elastic fibers.

    • Found in the layers within the walls of certain hollow internal organs:

      • the larger arteries

      • some portions of the heart

      • the lung and airways

Liquid Connective Tissue: Blood

  • Plasma (55%)

    • Medium for transporting materials in the blood.

    • Water

    • Proteins

      • Albumins 60%

      • Globulins 36%

      • Fibrinogen 4%

    • Other solutes

      • Regulatory substances

      • Waste products

  • Formed elements (45%)

    • Red blood cells

      • Transport oxygen.

    • White blood cells

      • Defend the body against disease.

    • Platelets

      • Cell fragments essential to blood clotting.

  • Blood Composition (by weight)

    • Plasma: 92%

    • Formed Elements: 8%

  • Normal Ranges

    • Platelets: 150,000−400,000150,000 - 400,000

    • White Blood Cells: 7,000−10,0007,000 - 10,000

    • Red Blood Cells: 4-6 million

Types and Function of Blood Cells

  • Red Blood Cells (RBCs)

    • Each red blood cell contains hemoglobin molecules.

    • Circulate for about 120 days.

  • White Blood Cells (Leukocytes)

    • Granular

      • Neutrophil (60-70%)

        • Phagocytosis.

      • Eosinophil (2-4%)

        • Effective against parasitic worms.

      • Basophil (0.5-1%)

        • Involved in inflammation and allergic reactions.

    • Agranular

      • Lymphocytes (20-25%)

        • B cells: destroy bacteria and inactivate toxins.

        • T cells: attack viruses, fungi, transplanted cells, cancer cells, and some bacteria; responsible for rejection of transplanted organs.

        • Natural killer (NK) cells: attack a wide variety of infectious microbes and tumor cells.

      • Monocyte (3-8%)

        • Phagocytosis.

  • Platelets

    • Small blood cells consisting of some cytoplasm surrounded by a plasma membrane.

    • Produced in the bone marrow from megakaryocytes.

    • Play a vital role in blood loss by the formation of platelet plugs, which seal the holes in the blood vessels and release chemicals that aid blood clotting.

Red Blood Cell Death and Recycling

  1. Red blood cell death and phagocytosis

  2. Globin broken down into amino acids

  3. Amino acids reused for protein synthesis

  4. Heme

  5. Fe3+Fe^{3+} released

  6. Fe3+Fe^{3+} binds to Transferrin

  7. Fe3+Fe^{3+} stored as Ferritin

  8. Erythropoiesis in red bone marrow

  9. Bilirubin

  10. Biliverdin

  11. Vitamin B12B_{12}

  12. Urobilinogen

  13. Urobilin in urine

  14. Stercobilin in faeces

  • Process occurs in macrophage in spleen, liver, or red bone marrow

Neutrophils and Macrophages

  • Active in phagocytosis.

  • Among WBCs, neutrophils respond most quickly to tissue destruction by bacteria.

  • Neutrophils produce:

    • enzyme lysozyme which destroys certain bacteria

    • defensins, proteins that destroys against bacteria.

Basophils

  • Mimic mast cells in their function.

  • At sites of inflammation, they leave capillaries, enter tissues, and release granules that contain heparin, histamine, and serotonin.

  • These substances intensify the inflammatory reaction and are involved in hypersensitivity (allergic) reactions.

Basophils (blood) and Mast cells (tissue)

  • Do NOT Attack other cells

  • Create an environment that is conducive to defense by releasing chemicals

    • Histamine:

      • Promotes vasodilation and increased vascular permeability

    • Heparin: Anti-coagulant

    • Prostaglandins: Vasodilation, Pain, and Fever

    • Pyrogen: any substance that elicits fever

    • Chemotactic factors: chemicals that attract other immune cells

Lymphocytes

  • Most lymphocytes continually move among lymphoid tissues, lymph, and blood, spending only a few hours at a time in blood.

  • Three main types of lymphocytes are B cells, T cells, and natural killer (NK) cells.

Lymph

  • Interstitial fluid moves into the lymphatic capillaries to become lymph.

Lymphatic System Flow

  1. Systemic Capillaries

  2. Interstitial fluid moves into the Lymphatic capillaries

  3. Lymph Node

  4. Lymphatic Vessels

  5. Pulmonary Capillaries

Major Lymphatic Vessels

  • Jugular trunk

  • Right lymphatic duct

  • Right brachiocephalic vein

  • Internal jugular vein

  • Thoracic duct

  • Subclavian trunk

  • Bronchomediastinal

  • Intercostal trunk

  • Intestinal trunk

  • Lumbar trunk

  • Lymphatic vessels

Supporting Connective Tissue

  • Cartilage

  • Bone

Cartilage

  • Provides support, frameworks, and attachments.

  • Protects underlying tissues; and forms structural models for many developing bones.

  • Cartilage extracellular matrix is abundant and is largely composed of either collagen or elastic fibers embedded in a gel-like ground substance.

  • Hyaline Cartilage

    • The most common type, has very fine collagen fibers in its extracellular matrix

    • It is found on the ends of bones in many joints, in the soft part of the nose, and in the supporting rings of the respiratory passages.

    • Parts of an embryo’s skeleton begin as hyaline cartilage “models” that bone gradually replaces.

  • Elastic cartilage

    • This is more flexible than hyaline cartilage because its extracellular matrix has a dense network of elastic fibers. It provides the framework for the external ears and parts of the larynx.

  • Fibrocartilage

    • Very tough tissue

    • Has many collagen fibers.

    • It is a shock absorber

    • It forms pads (intervertebral discs) between the individual bones of the spinal column.

    • It also cushions bones in the knees and in the pelvic girdle

Bone (Osseous Tissue)

  • Spongy Bone

    • Found on epiphysis

    • Small needle-like pieces of bone

    • Many open spaces

  • Compact Bone

    • Dense and smooth

  • Chemical Composition

    • Organic

      • Cells

      • Ground Substance

        • Proteoglycans & glycoproteins

      • Collagen Fibers

    • Inorganic

      • Ca-Phosphate = hydroxyapatites = 65%

  • Bone Matrix

    • The collagen and mineral components are responsible for the major functional characteristics of bone.

    • Without mineral: Flexibility

    • Without collagen: Fragile

  • Bone Cells

    • Osteocyte (maintains bone tissue)

    • Osteoblast (forms bone matrix)

    • Osteogenic cell (stem cell)

    • Osteoclast (resorbs bone)

  • Functions of Bone

    • Support - surrounding tissue

    • Protect - vital organs and other tissues

    • Movement - attachment for muscles

    • Mineral homeostasis - mineral balance for the body

    • Blood cell formation - hematopoiesis

    • Storage - mineral salts

  • Bone Disorders

    • Osteoporosis

      • Reduced mass makes bones weak

    • Rickets/Osteomalacia

Muscular Tissue

  • Muscle tissue is one of the four primary tissue types of the body consisting of cells that have the special ability to shorten or contract in order to produce movement of the body parts.

  • It is categorized into three distinct types: skeletal, cardiac, and smooth.

Organization of Skeletal Muscle

  • Muscle

  • Fascicles

    • Organized bundle of muscle fibers.

  • Muscle Fiber

    • Single muscle cell

  • Myofibrils

    • Collection of myofilaments

  • Myofilaments

    • Actin filament

    • Myosin filament

Functions of Skeletal Muscles

  • Produce skeletal movement

  • Maintain posture and body position

  • Support soft tissues

  • Guard entrances and exits

  • Maintain body temperature

  • Store nutrient reserves

Cardiac Muscle

  • Myocardium

Smooth Muscle

  • Found in the walls of hollow organs throughout the body.

  • Smooth muscle contractions are involuntary movements (not consciously controlled).

  • The arrangement of cells within smooth muscle tissue allows for contraction and relaxation with great elasticity.

  • The smooth muscle in the walls of organs like the urinary bladder and the uterus allow those organs to expand and relax as needed.

  • The smooth muscle of the alimentary canal (the digestive tract) facilitates the peristaltic waves that move swallowed food and nutrients.

  • In the eye smooth muscle changes the shape of the lens to bring objects into focus.

  • Artery walls include smooth muscle that relaxes and contracts to move blood through the body.

Nervous Tissue

Sensory and Motor Neurons

  • Sensory neurons: Towards brain

  • Motor neurons: Away from brain

Neuron

  • Functional unit of nervous system

  • Consists of:

    • Cell body

    • Processes

      • Terminal

      • Synapses

      • Nucleus

      • Perikaryon

      • Axon hillock

      • Dendrite

      • Axon