Chapter 4 Histology

Connective Tissues

Connective tissues

connect all the other tissues in the body to one another

Connective tissues

The ECM is a prominent feature for most connective tissue types with cells scattered throughout

Connective tissues function

• Connecting and binding

• Support

• Protection

• Transport

Connective tissues function: Connecting and binding

Connective tissues anchor tissue layers in organs and link organs

together.

Connective tissues function: Support

Bone and cartilage support the weight of the body

Connective tissues function: Protection

Bone tissue protects certain internal organs and cartilage and fat provides shock absorption. Components of the immune system are found throughout different connective tissues.

Connective tissues function: Transport

Blood is a fluid connective tissue that is the main transport medium in the body

Connective tissues are divided into two basic groups that differ in their cell-types and ECM

components:

• connective tissue proper

• specialized connective tissue

Connective tissue proper

also known as general connective tissue, widely distributed in the

body. These tissues connect tissues and organs to one another and are components of the internal architecture of some organs

Cells of connective tissue proper:

• Resident cells

• Migrant cells

Resident cells

permanently inhabit the tissue in which they are found

Migrant cells

migrate into different areas of the body depending on the situation

Fibroblasts

the most common resident cell

Fibroblasts

make protein fibers, ground substance, components of the ECM, and continually

produce collagen proteins

Adipocytes

fat cells, are found in many different connective tissues

Adipocytes

filled with a single large lipid inclusion (fat droplets)

Mast cells

immune system cells that release substance (such as histamine), causing

inflammation; a protective response that activates the immune system

Phagocytes

immune system cells, can ingest foreign substances, microorganisms, and dead

or damaged cells by phagocytosis

Four basic types of connective tissue proper

• – Loose connective tissue

• – Dense connective tissue

• – Reticular tissue

• – Adipose tissue

Areolar connective tissue

loose connective tissue, is mostly ground substance, with all three

types of protein fibers, fibroblasts, and occasionally adipocytes, all suspended in ground

substance.

Areolar connective tissue

found beneath the epithelium of the skin, in the membranes lining body

cavities, and within the walls of hollow organ

Areolar connective tissue

contains and supports blood vessels vital to avascular epithelial tissues and houses

immune cells that protect the body from microorganisms.

Dense connective tissue

known as fibrous connective tissue, is mostly protein fibers,

grouped into the following three classes

• Dense irregular connective tissue

• Dense regular connective tissue

• Dense regular elastic connective tissue

Dense irregular connective tissue

predominantly disorganized collagen fiber bundles

Dense irregular connective tissue

strong, resists tension in all three planes of movement, and is found in high

tension areas like the dermis deep to the skin and surrounding organs and joints

Dense regular connective tissue

found in tendons and ligament that are subject to tension in one plane of

movemen

Dense regular elastic connective tissue

known as elastic tissue, is mostly parallel-oriented

elastic fibers with randomly oriented collagen fibers

Dense regular elastic connective tissue

found in the walls of organs that must stretch to perform their function, such as

large blood vessels (ex: aorta) and certain ligaments

Reticular tissue

composed mostly of reticular fibers produced by reticular cells, that form fine

networks that can support small structures like blood and lymphatic vessels

Reticular tissue

Forms weblike nets to trap old and foreign cells in lymph nodes and spleen, forms part of the basement membrane

Adipose tissue

nown as fat tissue, consists of fat-storing adipocytes and surrounding

fibroblasts and ECM

Adipose tissue

The fat droplets (vacuoles containing lipid inclusions) can increase the adipocyte size to the

point where surrounding fibroblasts and ECM are scarcely visible

Adipose tissue

Besides fat storage, this tissue also provides insulation, warmth, shock absorption, and

protection. This tissue is the major energy reserve in the body

White adipose tissue

predominant fat tissue; appears white; adipocytes with one large lipid

inclusion in cytosol; deep to skin as subcutaneous fat, and in abdomen, breasts, hips, buttocks, and thighs; visceral fat surrounds heart and abdominal organs

Brown adipose tissue

less common; has brown appearance due to numerous mitochondria in

cytoplasm and vast blood supply; contains multiple lipid inclusions; more readily converted to energy to produce heat in cold temperature

Specialized connective three types of tissue:

cartilage, osseous tissue, and blood

Cartilage

found in the joints between bones, in the ear, nose, and segments of the

respiratory tract

Cartilage

tough, flexible tissue that absorbs shock and resists tension, compression, and

shearing forces.

Cartilage is populated with two cell types

• Chondroblasts

• Chondrocytes

Chondroblast

immature cells that divide by mitosis and make most of the ECM.

Chondrocyte

cells eventually surround themselves in small cavities or lacunae in the

ECM to become mature and largely inactive

Avascular Cartilage

blood supply is limited

• Oxygen and nutrients must diffuse from the blood vessels to to supply the chondroblasts and chondrocytes

Perichondrium

the outer sheath of dense irregular collagenous connective tissue

Hyaline cartilage

the most abundant cartilage in the body

Hyaline cartilage ECM

mostly ground substance made of small bundles of a fine collagen type that give the tissue a glossy bluish-gray appearance.

Hyaline cartilage location

found in articular cartilage on the ends of bones at joints, linking the sternum to the ribs, framing sections of the respiratory tract, and in the nose

Articular

relating to joints

Fibrocartilage

filled with bundles of collagen fibers with little room for ground substance in the ECM.

Fibroblasts

reside in the tissue in addition to chondroblasts and chondrocytes and fill the ECM with collagen and some elastic fibers

Fibroblast

The tissue has great tensile strength with some degree of elasticity

Fibroblasts Location

Found in between the bones of fibrous joints and forms articular discs that improve the fit of bones in joints

Elastic cartilage

mostly elastic fibers in its ECM allowing this tissue to vibrate

Elastic cartilage location

Found in a limited number of structures such as the external ear where it assists with detection of sound in the air and the larynx where it assists with the production of sound

Osseous tissue

supports the body, protects our vital organs, provides attachments for the muscles that allow for movement, stores calcium, and houses bone marrow, which produces blood cells and stores fat

Osteoid

composed of about 35% organic components consisting of collagen fibers and ground substance

• emaining 65% of ECM is inorganic calcium phosphate crystals making bone one of the hardest substances in the body

Osteoblasts

“bone-builders”

Osteoblasts Location

found on periosteum-the outer surface of bones closely associated with a dense irregular collagenous connective tissue covering called the where they carry out the process of bone deposition

Osteoblasts

synthesize and secrete the organic ECM and chemicals involved in trapping calcium in the ECM

Osteocytes

osteoblasts that have surrounded themselves in lacunae in the ECM

• maintain mineral concentrations of the matrix

Osteoclasts

large, multinucleated bone destroyers that carry out the process of bone resorption

• Allows for calcium reabsorption into the blood

Blood

unique connective tissue with a liquid ECM called plasma

• Plasma proteins provide a variety of functions including transport and blood clotting

Erythrocytes

bind to and transport oxygen through the body

Leukocytes

function in immunity

Platelets

fragments that have a major role in blood clotting

Muscle tissues

specialized for contraction

Myocyte

main component of muscle tissue

• Muscle cells have the ability to respond to electrical or chemical stimulation.

Striated muscle cells

have myofilaments that are arranged in alternating light and dark regions that appear striped

Smooth muscle cells (non striated)

have myofilaments but they are arranged in irregular bundles instead of repeating light and dark regions

Tree types of muscle tissue

• Skeletal muscle tissue

• Cardiac muscle tissue

• Smooth muscle tissue

Skeletal muscle tissue

found attached to the skeleton where contraction produces body movement

multinucleate

multiple nuclei in a single cell

Skeletal muscle

must be stimulated by the nervous system to contract: under voluntary control.

Components of skeletal muscle issue

• Endomysium

• Perimysium

Muscle fibers

Most skeletal muscle cells are long, nearly the length of the muscle:

Endomysium

small amounts of ECM that surrounds muscle tissue; helps hold

muscle fibers together in tissue

Perimysium

connective tissue that surrounds bundles of fibers (fascicles)

Cardiac muscle tissue location

found only in the heart, is composed of cardiac muscle cells

Cardiac muscle tissue description

• involuntary

• short, branched and usually have only one nucleus

Cardiac muscle tissue description

has dark line separating individual cardiac muscle cells, not seen in skeletal muscle, called intercalated discs that contain gap junctions and tight junctions

• contract as a unit.

Smooth muscle tissue

consists of smooth muscle cells whose contractions are involuntary

Smooth muscle tissue location

found in the walls of nearly every hollow organ, blood vessels, the eyes, the skin and the ducts of certain glands

Smooth muscle cells

flattened cells with one centrally located nucleus

Nervous tissues

of cells capable of generating, sending, and receiving messages that makes up most of the brain, spinal cord, and nerves.

Nervous tissue components

Neurons and Neuroglial

Neurons

sending and receiving messages. They are excitable cells. Once mature, neurons no longer divide by mitosis.

Cell body (soma)

the center of the neuron where the nucleus and most organelles are found

Axon

extends from the soma, moves an action potential (AP) from the soma to a target cell (neuron, muscle cell, or gland).

Dendrites

extensions protruding from the soma, are short with multiple branches. Receive messages from the axons of neighboring neurons and deliver the impulses to the soma

Neuroglial cells

various functions that support neuron activities

• Neuroglia anchor neurons and blood vessels in place, monitor extracellular fluid, speed

  up the rate of AP, and circulate fluid surrounding the brain and spinal cord.

• Neuroglial cells are able to divide by mitosis.

Membranes

thin sheets of one or more tissues, that line body surface or cavity

Membranes consist

superficial epithelial layer and a connective tissue layer that sometimes contains smooth muscle

True membranes

include serous and synovial membranes

• True membranes do not open to the outside

  of the body

Membrane-like structures

include mucous and cutaneous membranes;

• they don’t fit the above structural and functional definitions but perform many of the same functions

Serous membranes or serosae

line the pericardial, peritoneal, and pleural body

Serous membranes consist

(a thin layer of simple

squamous epithelium), a basement membrane, and a layer of connective tissue.

Mesothelial cells produce

serous fluid to reduce friction created by organs moving within their respective membranes.

Serous membranes fold over

giving the appearance of two layers

outer parietal layer

in contact

with the body wall