Connective tissues are tissues that support and connect other tissues in the body. There are several types of connective tissues including areolar, adipose, fibrous, elastic, blood, bone, and cartilage. Each connective tissue contains a unique matrix or intercellular material. Areolar tissue contains collagen and elastin fibers to connect tissues. Adipose tissue contains adipocytes that store fat. Fibrous tissue contains parallel collagen fibers that provide strength. Bone tissue contains calcium salts and collagen to form a hard matrix. Cartilage tissue contains proteins and carbohydrates to form a flexible but firm matrix.

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Connective Tissue
 Connective tissues are the group of cells which supports & connects other tissue and parts of
body.
 Connective tissue has few cells. They consist of intercellular substances or matrix.
 There are several kinds of connective tissue, some of which may at first seem more different
than alike.
 The types of connective tissue include areolar, adipose, fibrous, and elastic tissue as well
as blood, bone, and cartilage.
 The matrix is a structural network or solution of nonliving intercellular material.
 Each connective tissue has its own specific kind of matrix.
 The matrix of blood, for example, is blood plasma, which is mostly water.
 The matrix of bone is made primarily of calcium salts, which are hard and strong.
Types of connective tissue
Fig: Summary of Connective Tissue
BLOOD
 Blood consists of cells and plasma; cells are the living portion.

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 The matrix of blood is plasma, which is about 52% to 62% of the total blood volume in the
body.
 The water of plasma contains dissolved salts, nutrients, gases, and waste products.
 Blood cells are produced from stem cells in the red bone marrow, the body’s primary
hemopoietic tissue (blood-forming tissue), which is found in flat and irregular bones such as
the hip bone and vertebrae.
 The blood cells are red blood cells, platelets, and the five kinds of white blood cells:
neutrophils, eosinophils, basophils, monocytes, and lymphocytes.
Fig: Connective tissues. (A) Blood. (B) Areolar. (C) Adipose.
AREOLAR CONNECTIVE TISSUE
 The cells of areolar (or loose) connective tissue are called fibroblasts.
 A blast cell is a “producing” cell, and fibroblasts produce protein fibers.
 Collagen fibers are very strong; elastin fibers are elastic, that is, able to return to their
original length, or recoil, after being stretched.
 These protein fibers and tissue fluid make up the matrix, or non-living portion, of areolar
connective tissue.
 Also within the matrix are mast cells that release inflammatory chemicals when tissue is
damaged, and many white blood cells, which are capable of self-locomotion.
 Areolar tissue is found beneath the dermis of the skin and beneath the epithelial tissue of all
the body systems that have openings to the environment.
 Areolar connective tissue with its mast cells and many white blood cells is advantageously
located to seize pathogens before they get to the blood and circulate throughout the body.

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Fig: Adipose tissue (human, from a lymph node specimen).
*Adipocytes (A) are distended polygonal cells filled with lipid, which has been extracted by the
tissue processing. This leaves only the plasma membranes with scant cytoplasm and nuclei
(arrows),occasionally visible compressedagainst the cell periphery. Small blood vessels (BV)
penetrate the adipose tissue; larger vessels are seen on the right. (Courtesy of Mr Peter
Helliwelland the late Dr Joseph Mathew, Department of Histopathology, Royal Cornwall
Hospitals Trust, UK.)
ADIPOSE TISSUE
 The cells of adipose tissue are called adipocytes and are specialized to store fat in
microscopic droplets.
 The amount of matrix in adipose tissue is small and consists of tissue fluid and a few collagen
fibers.
 Most fat is stored subcutaneously in the areolar connective tissue between the dermis and the
muscles. .
 Adipose tissue is now considered an endocrine tissue, because it produces at least one
hormone.
 For example, Leptin is an appetite-suppressing hormone secreted by adipocytes to signal
the hypothalamus in the brain that fat storage is sufficient.
 Adipocytes secrete at least two chemicals that help regulate the use of insulin in glucose and
fat metabolism.
 Adipose tissue is also involved in inflammation, the body’s first response to injury, in that it
produces cytokines, chemicals that activate white blood cells.

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FIBROUS CONNECTIVE TISSUE
 Fibrous connective tissue consists mainly of parallel (regular) collagen fibers with a few
fibroblasts scattered among them.
 This parallel arrangement of collagen provides great strength, yet is flexible. The locations of
this tissue are related to the need for flexible strength.
Fig: Elastic fibers, seen as fine, dark, relativelystraight fibers in a whole-mount preparation of
mesentery, stained for elastin. The wavy pink bands are collagen bundles and oval grey nuclei
are mainly of fibroblasts.
 The outer walls of arteries are reinforced with fibrous connective tissue, because the blood in
these vessels is under high pressure.
 Tendons and ligaments are made of fibrous connective tissue. Tendons connect muscle to
bone; ligaments connect bone to bone. During movement, it affords the mechanical strength.
 Fibrous connective tissue has a relatively poor blood supply, which makes repair a slow
process.
 Elastic connective tissue is also found surrounding the alveoli of the lungs. The elastic fibers
are stretched during inhalation, and then recoil during exhalation to squeeze air out of the
lungs.
BONE
 The prefix that designates bone is “osteo,” so bone cells are called osteocytes. The matrix of
bone is made of calcium salts and collagen and is strong, hard, and not flexible.
 In the shafts of long bones such as the femur, the osteocytes, matrix, and blood vessels are
in very precise arrangements called Haversian systems or osteons.

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 Bone has a good blood supply, which enables it to serve as a storage site for calcium and to
repair itself relatively rapidly after a simple fracture.
 Some bones, such as the sternum (breastbone) and pelvic bone, contain red bone marrow,
the primary hemopoietic tissue that produces blood cells.
 Other functions of bone tissueare related to the strength of bone matrix. The skeleton supports
the body, and some bones protect internal organs from mechanical injury.
Fig: Connective tissues. (A) Fibrous. (B) Cartilage. (C) Bone.
CARTILAGE
 The protein–carbohydrate matrix of cartilage does not contain calcium salts, and also differs
from that of bone in that it contains more water, which makes it resilient.
 It is firm, yet smooth and flexible.
 Cartilage is found on the joint surfaces of bones, where its smooth surface helps prevent
friction.
 The tip of the nose and external ear are supported by flexible cartilage.
 The wall of the trachea, the airway to the lungs, contains firm rings of cartilage to maintain an
open air passageway.
 Discs of cartilage are found between the vertebrae of the spine. Here the cartilage is a firm
cushion; it absorbs shock and permits movement.
 Within the cartilage matrix are the chondrocytes, or cartilage cells. There are no capillaries
within the cartilage matrix, so these cells are nourished by diffusion through the matrix, a slow
process.

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 This becomes clinically important when cartilage is damaged, for repair will take place very
slowly or not at all.
Fig: Dense regular connective tissue in a tendon. Thick parallel bundles of type I collagen
(here stained pink) give tendon its white colour in life. The elongated nuclei of inactive
fibroblasts (tendon cells) are visible between collagen bundles.
Fig: A generalized mucosa and supporting tissues

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Mast cells
 Mast cells are important defensive cells. They occur particularly in loose connective tissues
and in the fibrous capsules of certain organs such as the liver, and are numerous around
blood vessels.
Mucoid tissue
 Mucoid tissue is found chiefly as a stage in the development of connective tissue from
mesenchyme.
 It exists in Wharton’s jelly, which forms the bulk of the umbilical cord, and consists
substantially of extracellular matrix, largely made up of hydrated mucoid material and a fine
meshwork of collagen fibers, in which nucleated, fibroblast-like cells with branching
processes are found.
MUSCULAR TISSUE
 Muscle tissue is specialized for contraction.
 When muscle cells contract, they shorten and bring about some type of movement. There
are three types of muscle tissue: skeletal, smooth, and cardiac. The movements each can
produce have very different purpose.
Fig: Muscular tissues. (A) Skeletal. (B) Smooth. (C) Cardiac.

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Types of Muscular Tissue
SKELETAL MUSCLE
 Skeletal muscle may also be called striated muscle or voluntary muscle.
 The skeletal muscle cells are cylindrical, have several nuclei each, and appear striated, or
striped.
 The striations are the result of the precise arrangement of the contracting proteins within the
cells. Skeletal muscle tissue makes up the muscles that are attached to bones.
 These muscles are supplied with motor nerves, and thus move the skeleton.
 They also produce a significant amount of heat, which is important to help maintain the body’s
constant temperature.
 Each muscle cell has its own motor nerve ending.
 The nerve impulses that can then travel to the muscles are essential to cause contraction.
SMOOTH MUSCLE
 Smooth muscle may also be called involuntary muscle or visceral muscle.
 The cells of smooth muscle have tapered ends, a single nucleus, and no striations.
 The term visceral refers to internal organs, many of which contain smooth muscle.
 The functions of smooth muscle are actually functions of the organs in which the muscle is
found.
 In the stomach and intestines, smooth muscle contracts in waves called peristalsis to propel
food through the digestive tract. In the walls of arteries and veins, smooth muscle constricts
or dilates the vessels to maintain normal blood pressure.
 The iris of the eye has two sets of smooth muscle fibers to constrict or dilate the pupil, which
regulates the amount of light that strikes the retina.

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CARDIAC MUSCLE
 They are branched, have one nucleus each, and have faint striations.
 The cell membranes at the ends of these cells are somewhatfolded and fit into matching folds
of the membranes of the next cells. (Interlock the fingers of both hands to get an idea of what
these adjacent membranes look like.)
 These interlocking folds are called intercalated discs, and permit the electrical impulses of
muscle contraction to pass swiftly from cell to cell.
 This enables the heart to beat in a very precise wave of contraction from the upper chambers
to the lower chambers.
 Cardiac muscleas a whole is called the myocardium,and forms the walls of the four chambers
of the heart. Its function, therefore, is the function of the heart, to pump blood.
 The contractions of the myocardium create blood pressure and keep blood circulating
throughout the body, so that the blood can carry out its many functions.
 Cardiac muscle cells have the ability to contract by themselves.
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Reference
1. Essentials of Human Anatomy & Physiology 5th
Ed by Valerie C. Scanlon & Tina
Sanders
2. Gray’s Anatomy, The Anatomical Basis of Clinical Practice 41st
Ed by Elsevier