Type of Tissue

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Groups of similar cells combine to create tissues.

Four types of tissue:

1. Epithelial Tissue

Epithelial Tissue (covering)

- consist of a sheet of cells that cover the body surface, forms the skin

- lines body cavities

- Epithelium forms the boundaries between different environments

- nearly all substances received or given off by the body must pass through an epithelium

- forms glands, such as thyroid and adrenal

- has capacity to absorb, secrete, filter and protect

- the surface of most epithelial tissue is not in contact with other tissue but is exposed to the external or internal environment, this is called the apical surface

- the surface facing the inside of the body is called the basal surface

- a permeable, thin basement membrane attaches epithelial tissues to the underlying connective tissue

- epithelial tissues make up 3 types of membranes. A membrane is a thin, sheet-like layer of tissue that covers a cell, organ, or structure:

1 - Cutaneous membranes - covers the surface of the body exposed to the external environment, know as the skin

2 - Serous membranes - line body cavities not open to the external environment and cover many of the organs. Release a thin watery fluid that lubricate the organs and prevent friction

3 - Mucous membranes - found on the surface of tubes that open directly to the exterior, eg) lining the respiratory, digestive, urinary and reproductive tracts. The film of mucous coats and protects underlying cells.

2. Connective Tissue

Connective Tissue (support)

- most abundant tissue in the body

- specialised to support and hold together the body and it's parts, transport substances through the body and protect the body from foreign substances

- made of matrix, fibres and cells. The matrix of connective tissue is made up of 90% ground substance, the balance of the following fibres:

- Collagen fibres - tough and strong, minimal stretch. Occur in bundles. Called white fibres.

- Reticular fibres - delicate fibres found in networks that support small structures such as capillaries, nerve fibres and the basement membrane

- Elastic fibres - extensible and elastic. found in stretchy tissue. Made from a protein called elastin. Called yellow fibres.

Connective Tissue Cell types

Fibroblast - connective tissue

Chondroblast - cartilage

Osteoblast - bone

Hemocytoblast - blood

Changing proportions of collagen and elastic and reticular fibres make the tissue as a tough as tendons or as soft as the tissue that covers muscle. Calcium salts added make the tissue rigid, such as bone.

Connective tissue is thixotropic, solidify when cold or left undisturbed, become more fluid when warmed or stirred. If not stretched and warmed by muscular activity, connective tissue becomes stiff and less flexible.

Therapeutic massage stretches, strokes, and moves tissue and generate heat to make connective tissue more fluid, allowing greater mobility and encouraging blood flow.

Collagen fibres tend to bind together by hydrogen-bonding with disuse and chronic pressure. Inflammation is a factor in the bonding process called adhesions. Nerves and blood vessels get caught in the adhesions and range of motion is reduced or pain results.

The major connective tissue classes (in order from rigid to softest) are:

A. Bone

B. Cartilage

C. Dense fibrous

D. Loose fibrous

E. Blood

A. Bone

Four features that enable them to work together:

hard cells and rigid matrix

articulate with other bones

a connective tissue structure called periosteum covers every bone and provide vessels for nutrition, bone cells for growth, and attachments for ligaments and tendons

remodelling of the existing bone matrix is responsible for shaping bones

Bone Regeneration

Bones are a very dynamic and active tissue.

Renewal takes places at the cellular and tissue level

Every week we recycle 5-7% of our bone mass

Broken bones are first treated by reduction which brings bones end back into alignment, then the area is immobilised by cast to allow for healing. Healing time is 8 to 12 weeks but longer for weight bearing bones.

Four stages of healing:

Haematoma formation. Acute inflammation lasts for approx 4 days. Due to trauma to the bone, periostium and soft tissue around the break, blood gathers at the injury site to form a clot, known as a haematoma.

Cellular proliferation. The dead bone cells and damaged vessels elicit a typical inflammatory response.

Callus formation. The haematoma gradually forms a fibrous junction between the fractured ends, which becomes a fibrous callus, then cartilage, then bone.

Officication. The final stage of laying down bone tissue. The fracture is bridged and firmly united. Osteoclasts resorb excess callus.

Bone Remodelling

Remodelling occurs after resorbtion of the callus and laying down of trabecular bone along the line of stress. Complete remodelling can take years.

Abnormal bone growth and healing

Imbalances between bone formation and bone resoption underlie nearly every disease process that effects the skeleton. eg) Osteoperosis, Osteomalacia and Pagets disease.

Complications that can arise in bone fracture healing include:

Compartment syndrome - swelling after a fracture that puts pressure on the blood vessels to the point where not enough blood can get to the muscles around the fracture. Decreased blood supply can cause the muscle to die.

Neurovascular injury - in very severe fractures the arteries and nerves around the injury site can be damaged.

Infection - open fractures can become infected when the broken bones tear through the skin and are exposed to the air

Post-traumatic arthritis - fractures that extend into the joint, or bones that meet at an abnormal angle in the joint can cause premature arthritis.

Growth abnormalities - fracture in the growth plate of a child can cause many problems. Premature partial or complete closure of a growth plate means that one side of a bone or the whole bone stops growing before the other side, the bone grows at an abnormal angle.

Delayed union - a fracture that takes longer to heal than expected

Nonunion - a fracture that fails to heal in a reasonable amount of time

Malunion - a fracture that does not heal in a normal alignment

B. Cartilage

Less hard than bone but more flexible. Consists of 3 types:

Hyaline - most abundant cartilage and covers the ends of bone where they form joints

Elastic - white cartilage providing great movement due to elastin fibres, eg) supports the external ear

Fibrocartilage - a yellow cartilage which forms cushion-like discs between the vertebrae of the spine

C. Dense fibrous

Consists predominantly of collagen fibres creating a dense connective tissue. Forms rope-like structures such as: tendons and ligaments

D. Loose fibrous

Are softer and have more cells and fewer fibres than any other connective tissue, except blood. They consist of:

Areolar - most widely distributed connective tissue in the body. Found under the skin. Fascia is a connective tissue belonging to this group.

Adipose - actually fat. Adipose tissue forms the subcutaneous tissue beneath the skin where it insulates and protects the body.

Reticular - delicate network of interwoven reticular fibres associated with reticular cells. Forms an internal supporting framework that can support many free blood cells (mainly lymphocytes)

E. Blood

Blood or vascular tissue is a connective tissue because it has a matrix (plasma) and ground substance (blood cells).

3. Muscle Tissue

Responsible for movement and heat production in the body.

Three type of muscle tissue which differ in 1. structure of cells, 2. location in the body, 3. function, 4. means by which they are activated:

Skeletal muscle - lognest cell types consisting of striations. The only muscle type subject to conscious control. Can contract rapidly, excerting tremendous force.

Cardiac muscle - occurs only the heart. Also striated but not voluntary. Contraction is at a steady rate.

Smooth muscle - found in the walls of hollow visceral organs (other than the heart). No striations. No voluntary control. Contraction is slow.

Structural Organisation of Skeletal muscle

A muscle consists of hundreds to thousands of muscle cells plus the connective tissue wrappings, blood vessels and nerves.

A muscles is made up of a number of fascicles surrounded by epimysium. Each fascicle is is made up of muscle cells or fibres surrounded by perimysium. Each muscle fibre within the fascicle is surrounded by endomysium and contains myofibrils. Myofibrils are composed of myofilaments, the contractile elements of muscles. Myofibrils occupy most of the cell and are appear banded and aligned to adjacent myofilbrils composed of sarcomeres arranged end to end. Sarcomeres are the contractile unit within a segment of a myofibril and are made up of contractile proteins. Sarcomeres have a thin (actin) filament and a thick (myosin) filament.

The sliding of the contractile protein actin filaments past the tick myosin filaments is what produces muscle shortening or contraction.

Muscle Contraction - the sliding filament theory

Refers to the movement of the thin actin filaments sliding past the thick myosin filaments so that the actin and myosin fibres overlap only slightly.

When muscle fibres are activated by the nervous system, the cross bridges (myosin heads) attach to the active myosin binding sites on the actin thin filaments and the sliding begins. Each cross bridge attaches and detaches several times during contraction. Calcium levels and Neurotransmitters such as Acetylcholine (ACh) control the transmission of nerve impulses to the Sarcomere and the presence of Calcium ions allows the interaction of occur.

Motor Unit

Each muscle is served by at least one motor nerve which contains hundreds of motor neuron axons. As an axon enters a muscle it branches into a number of axonal terminals, each of which forms a neuromuscular junction with a single muscle fibre. The motor neuron and all the muscle fibres it supplies is called a motor unit. When a motor unit fires, all the muscle fibres it innervates respond by contracting.

Muscle Proprioceptors

Muscle spindles (stretch receptors) - primary propriocepters in the muscle that are sensitive to changes in muscle length.

Golgi tendon organ - proprioceptor in the tendon near the end of the muscle fibre is sensitive to changes in muscle tension.

Proprioceptors provide information about the movement and position of our body, head, arms and legs. Proprioceptors also trigger certain protective reflexes.

The stretch reflex - activated when the proprioceptors sense too much stretch or force on a muscle or tendon. The reflex causes the stretched muscle to contract, shorten and protect the muscle or tendon from injury.

A classic reflex arc - the patellar tendon reflex (knee jerk reflex)

A reflex arc is a neural pathway that controls an action reflex.

4. Nervous Tissue

Highly specialised tissue, it senses, transmits and interprets impulses. Makes up the nervous system consisting of the brain, spinal cord and nerves which regulate and control body function.

Composed of 2 major cell types:

Neurons - the cell itself that generates and conducts nerve impulses

Supporting cells - the non-conduction part that supports, insulates and protects the delicate neurons.