TISSUES

Tissue- is a group of similar cells specialized

for the performance of a common function.

- The study of tissues is called Histology

- the cells in multicellular animal maybe divided into 2. Somatic cells or body

cells and Germ cells, having to do only with reproduction and continuance of species.

There are 4 major groups of somatic tissues, and these are:

1. Epithelial Tissues

2. Connective Tissues

3. Muscular Tissues

4. Nervous Tissues

Epithelial Tissues- form the covering or lining of all free body surfaces, both external and internal.

- consists of renewable sheets of cells

- supported by basement membrane which separates epithelial tissues from underlying, adjacent tissues.

Functions of Epithelial Tissue:

1. Absorb (the lining of the small intestine)

2. Transport ( kidney tubules)

3. Excrete ( sweat glands)

4. Protect ( skin )

5. Contain nerve cells for sensory reception (taste buds in the tongue)

Structures of Epithelial Tissues:

Layers:

1. Simple – consisting of only one layer of cells.

2. Stratified – consisting multiple slacked layers

3. Pseudostratified ciliated columnar epithilium

- possess cilia and appears layered but not.

- appears layered because of their nuclei are at two or more levels within the cell of the tissue.

Shapes:

1. Squamous Epithelium or flat

2. Cuboidal Epithelium or cube shaped

3. Columnar Epithelium or column like

Squamous Epithelium

Simple Cuboidal Epithelium Lining

Columnar Epithelium Cells

Connective Tissue- binds together and supports other

structures

- divided throughout an extracellular matrix

- derived from the Mesenchyme, a generalized embryonic tissue that can differentiate also into vascular and smooth muscle. (also considered the most primitive connective tissue)

Two General Types of Connecticve Tissues

1. Loose Connective Tissue

- strong, flexible fibers of protein collagen are interwoven with fine elastic, and reticular fibers giving it its elastic consistency and making it an exellent binding tissue.

2. Fibrous Connective Tissue

- the collagen fibers are densly packed and may lie parallel to one another, creating very strong cords, such as tendons and ligaments.

Kinds of Connective Tissues

1. Adipose Tissue

- is a type of loose connective that consists of large cells that store lipids.

- consists scattered, rounded or branched in form, with intercellular spaces occupied by delicate fibers.

- also known as fat tissues

- cells accumulate in large numbers to form what is commonly known as fat.

- Two minor cell types are present; fibroblasts, which produce fibers, and macrophages, which are phagocytes.

Adipose Tissue

2. Cartilage

-is a firm yet elastic matrix (chondrin) secreted by small groups of rounded cartilage cells or Chondrocytes

embedded within it and covered by a thin, fibrous Perichondrium.

- Is a hard yet flexible tissue that supports such structures as the outer ear and forms the entire skeleton of such animals as sharks and rays.

- Cells called Chondrocytes lie within spaces called Lacunae that are sorrounded by a rubbery matrix that chomdroblasts secrete.

- the matrix gives the cartilage its strength and elasticity.

Cartilage

3. Bone or Osseous Tissue

- Like other connective tissues, bone consists of cells, fibers and ground substance but differs because the extracellular matrix is calcified.

- the rigid extracellular matrix has several functions

* Provides an internal support for the body and attachment for muscles and tendons.

* Protects vital organs of the cranial and thoracic cavity, and encloses the blood forming elements of the bone marrow.

* Provides a reservvoir of ionic calcium essential for many cellular processes of the body.

Macroscopic Structure of the Bone

A. Diaphysis: shaft of the bone

B. Epiphysis: end of a long bone

C. Metaphysis: area between the diaphysis and the epiphysis

D. Epiphyseal plate (growth plate)

E. Medullary Cavity: central cavity of bone occupied by bone marrow

F. Trabeculae: irregular lattice of thin columns of bone sorrounded by bone marrow

G. Articular Cartilage: Hyaline cartilage covering joint surfaces

H. Periosteum: external covering of bone

I. Endosteum: internal covering of bone

Bone Cells

A. Osteoprogenitor Cell

1. A mesenchymeal sterm cell that can undergo mitotic division and differentiate into an osteoblast.

2. Osteoprogenitor calls are located on the immer cellular layer of the periosteum, the endosteum and lining osteonic canals.

3. These calls are most active during bone growth, but large numbers are reactivated in adult life in repair of fractures.

4. They also differentiate into osteoblasts during the continous process of bone remodeling

B. Osteoblasts

1. Cells that are derived from osteoprogenitor cella\s and are responsible for the synthesis of the organic components of bonw matrix, which is called osteoid.

2. They are located on the surface of bone tissue and resemble epithelium. When the cells are active they have a cuboidal appearance; and when their activity declines, they flatten

3. They have the structure expected of cells that are actively engaged on protein synthesis, such as extensive rough ER, well developed Golgi complex and numerous secretory vesicles.

4. The cells have cytoplasmic processes that bring them in contact with neighboring cells.

D. Osteocytes

1. When osteoblast has completely sorrounded itself and its cytoplasmic processes with matrix, the cell is now termed an osteocyte.

2. The space on which the cell resides os termed lacuna. The thin cylindrical spaces that house cytoplasmic processes are called canaliculi. Canaliculi also contain extracellular fluid carrying nutrients to nourish osteocytes.

3. Processes of adjacent cells make contact via gap junctions, which allow ions and small molecules to travel from cell to cell.

D. Osteoclasts

1. Large, motile, multinucleated, bone-resorbing cells derived from blood monocytes that occupy depressions in the bone matrix undergoing active resorption.

2. Adhere tightly to established bone matrix and acidify the surface by the use of a proton pump that actively transports H ionsonto the surface of the bone. Lysosomal enzymes are released by exocytosis and degrade the organic components of bone.

3. The degraded minerals on organic components are endocytosed by the osteoclast and delivered to nearby capillaries to enter the circulation.

Bone Coverings

A. Periosteum:

1. The external covering of bone, except in areas where tendons and ligaments insert into bone and on the surfaces covered by articular cartilage.

2. Consists of 2 layers

a. Outer fibrous layer – collagenous connective tissue that contains many blood vessels.

b. Inner Cellular Layer – layer that contains osteoprogenitor cells that have osteogenic potential

3. Sharpey’s Fibers: Bundles of periostal collgen fibers that penetrate the bone matrix and strongly adheres the periosteum to bone.

B. Endosteum

-Thin layer of osteoprogenitor cells, osteoblasts and a small amount of connective tissue that lines all internal surfaces of cavities within bone including the osteonic canals and marrow spaces.

One or Osseous Tissue (Haversian Canal)

4. Blood

- is a connectie tissue in which a fluid called plasma suspends specialized re and white blood cells plus platelets.

- a viscous fluid pumped all throughout the body

- mesoderm in origin

- transports various substances throughout the bodies of animals.

- Erythrocytes (Red Blood Cells)

- composed of cells, fibers and amorphous ground substance.

Functions:

1. Carry oxygen and nutrients to the cell and carry waste materials – CO2 away from the cells to kidneys and lungs.

2. Immune System

3. Homeostasis in the body.

Ground Substance/Matrix:

- fluid and protein in the plasma

Albumin = are to maintain the osmotic pressure of the blood.

Cells:

1. Erythrocytes (RBC)

2. Leukocytes (WBC)

3. Thrombocytes/ blood platelets

Fibers:

- these are the potential fibers of fibrinogen which are converted to fibrils fiber during blood clotting.

- Clotted solid. Which rapidly stops blood flow from the wound.

Note - blood clots occur when platelets interact with and respond to collagen fibers that they encounter when they leave the circulaing system in response to a wound.

Human Red Blood Cells Platelets and T-lymphocyte (Erythocytes = red; platelets = yellow; T-lymphocyte = light green)

Red Blood Cells

Muscle Tissue- is the driving force, the power behind movement in most vertebrates and invertebrates.

- specialized for contractility

- most common tissue in the body of most animals.

- made of elongated cells made for contraction.

- allows movement.

3 Important Properties of Muscle Tissue

1. Excitability (or irritability)- the capacity to receive and respond stimulus.

2. Extensibility –the ability to be stretched

3. Elasticity –the ability to return to its original shape after being stretche or contracted.

3 kinds of muscle Tissue

1. Smooth Muscle (or unstriated involuntary)

2. Skeletal Muscle (or striated voluntary)

3. Cardiac Muscle (or striated involuntary)

Smooth Muscle

- is formed of spindle –shaped cells, each containing a single nucleus

- cells are arranged closely to form sheets

- not striated

- mostly found in the walls of hollow organs

- are organized into sheets of muscle circling the wall of the alimentary canal, blood vessels, respiratiry passages, and urinary and genital ducts.

- moves substances or objects( foodstuffs, urine, baby) along internal passageways

- also called involuntary muscle because higher brain centers do not control its contractions.

Smooth Muscle Tissue

Skeletal Muscle

-is composed of striated muscle fibers (cells) containing many peripheral nuclei.

- are those attached to the skeleton and are typically organized into sturdy, compact bundles or bands.

- extremely long, cylindrical, multinucleate cells that may reach from one end of the muscle to the other.

- the characteristic light and dark bands(striations) represents the fine structure of the myofibrils that make up the fibers.

- a.k.a. voluntary muscle because nercous system consciously controls its contractions.

- for voluntary movement or locomotion

Skeletal Muscle

Cardiac Muscle

- is the muscle of the vertebrate heart

- consists of closely opposed, but separate, uninucleate cell fibers that appear branching and interconnected.

- contains specialized cell junctions called Interlaced Disks that allow ions to (action potential) to move quikly from cell to cell.

- can be found in the walls of the heart

- as the walls of the heart contract, cardiac muscle tissue propels blood onto the circulation; involuntary control.

Striated Muscle Fibers

Heart Muscle Cell (nucleus, mitochondria, actin-myosin)

Heart Muscle Tissue

Nervous Tissue- is composed of several different types of cells:

- is highly specialized for the property of irritability and conductivity.

- can be found in the brain, spinal cord, and nerves.

- transmits electrical signals from sensory receptors to the spinal cord or brain, and from the spinal cord or brain to effectors(muscles and glands)

Nerve – group of fibers or process bound together by a connective tissue.

Neurons

- Impulse conducting cells

- Structural and functional unit of the nervous system.

- arranged in chains

Synapse – point of contact between neurons

Dendrite – the process that transmits stimuli to the cell body

Axon – carries impulses away from the cell body

Bipolar cells – one dendrite and one axon

Multipolar Cells – multiple dendrites and single axon

Ganglion – a group of nerve cell bodies, with their conspicuous nuclei when outside the central nervous system.

Neuroglia

- cells involved with protection and, support, and nourishment

- serve as delicate packing to hold neurons apart and may also aid in nutrition of neurons.

*Nerve fibers are sheathed by special cells called Schwann Cells.

*Nodes of Ranvier- marks the end of the Schwann call and the beginning of another.

Peripheral Glial Cells

- cells that form sheaths and help protect, nourish, and maintain the peripheral nervous system.

Organization of a Neuron

Large Multi-polar Neuron

Pyramidal Neurons