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Saturday, February 18, 2012

Exploration of Structure and Functions of the Animal Tissues

I said I'll talk about Animal tissues in my previous post. As I said then here's the Animal tissue post with much details.

Introduction

The cells of muticellular animals are organized as tissues. Blood is a liquid tissue. 40% of the weight of an animal is muscle tissue. It is composed of specialized cells having the ability of contraction. The covering layer of all the external and internal surface of an organism is called the epithelial tissue. These are arranged in single or mutilayered sheets. Single layered tissues are called simple epithelium and the multilayered tissues are called compound epithelium. The nerve tissues are made by nerve cells or nerves. These cells are specially adapted to carry the nervous impulses.

Blood Tissues

The blood tissues consist of a few types of cells and it is in a packing tissue called plasma. The cells in the blood are red and white cells. Plasma is a pale straw-colored liquid. It consist of 90% of water and 10% of the various substances as suspension. The water is important in the plasma to translocate the substances all over the body. These substances are globulin, prothombin, fibrinogen, plasma protein and mineral salts. Prothombin is an important material in blood clotting.

The red cells give red color to blood. There are 5million - 5,000,000 red cells in 1mm3.One drop of blood has a volume of 50mm3.Having such a big amount shows the value of red cells. Obtaining oxygen from the lungs and carrying them to the tissues is done by the red blood cells. A red color pigment called haemoglobin is dissolved in the plasma and it gives red color. The lack of nucleus makes more room for haemoglobin in these cells. Red blood cells are originated from bone marrow and destroyed in the spleen. There are five types if white blood cells in structure and function. But the main two types are granulocytes and agranulocytes.

Platelets are the third constituent of blood which covered by membranes. They are fragments of cells and lack of nuclei. They help in the process of blood clotting. There are about 250,000 of platelets in 1mm3 of human blood. It is originated in the bone marrowand destroyed in the spleen as red blood cells.

Blood Constituent Function
1.)Granulocytes
  1. Nutrophils
  2. Eosinophils
  3. Basophils
Engulf germs and bacteria. Allergic responses.
  1. Produce heparine(Anti-Clotting protein)
  2. Produce hisstamine(Chemical stimulates the repair of damaged tissues)
2.)Agranulocytes
  1. Monocytes
  2. Lymphocytes
Engulf bacteria production of antibodies.

Muscle Tissue

Three distinct types of muscles can be identified. Muscle tissues have the ability of contraction. The movements of one part of the body could be done relatively to the other parts with the muscles.

Striated Muscles

These muscles are identified as voluntary muscles or skeletal muscles. The dark miofibril bands and light miofibril bands are seen with the naked eye in the cell plasma. The muscles attached to the skeleton are therefore called skeletal muscles. The movements of these muscles can be done voluntarily. They are called voluntary muscles. The muscle made up of muscle fibers. The bundles of muscle fibers are connected by perimysium fibers and surrounded by epimysium connective tissues. Once the stimulus understood the contraction occurs rapidly and fatigue quickly.

Unstriated Muscles

These muscles are identified as smooth muscles or unvoluntary muscles. It is introduced as unstriated as there is no strips. The muscles have elongated cells and a nucleus. Nucleus is surrounded by a small sarcoplasm. The rest of the cell is made up of flexible fibers. The fibers run along the cells and connect lightly. The wall of the organs like intestine and bladder are made up of unstriated muscles. These muscles help to pass the material through the systems. it is slowly contracted and slowly fatigued. It shows longitudinal contraction.

Cardiac Muscles

The heart is composed of cardiac muscles. The muscles have important properties as the other two types of muscles. They are not separated as uninucleus cells. Around the fibers there is a sarcolemma and cross striations. The fibers are not long as the skeletal muscles but the strips can be seen. The dark bands known as intercalated discs are situated individually. Cardiac muscles can contract and even be removed from the body and do not fatigue easily.

Epithelial Tissues

Simple Epithelium Tissues of Animals
Simple Epithelium Tissues of Animals
Epithelial tissues cover the internal and external surfaces of the body of an organism. The bottom layer of cells rest on a basement membrane composed of a collagen fiber network. The basement membrane is thin and soft. Epithelial cells are not supplied with blood. There are five types of epithelial tissues.

Simple Epithelium

Squamous Epithelium

Squamous epithelium occurs in areas such as renal capsules of the kidney, the alveoli of lungs and the blood capillary walls. The thickness of the tissue permits the diffusion of materials through it.

Cuboidal Epithelium

It forms a lining of many ducts such as salivary, thyroid, sweat and urinary collecting ducts of the kidney. The spherical nucleus is in the center of the cell. It performs the functions of secretory  glands.

Columnar Epithelium

These cells are tall and quite narrow. Each cell possesses a nucleus situated in various places. These cells are lined from the stomach to rectum. It performs the absorptive and secretory functions.

Ciliated Epithelium

Cells of these tissues bear numerous cilia at their free surfaces and always cilia show a movement. Ciliated epithelium lies inside the respiratory passages like nostrils, trachea and tracheoles. Cilia can trap the particles while passing through it.

Pseudostratified Epithelium

This layer of cells is attached to the basement membrane. But not all the cells reach the free surface. This epithelium is found lining in urinary track, trachea and trachedes.

Compound Epithelium

Stratified Epithelium

This tissue is made up of a number of cell layers and it is thick, rough and can resist the friction. The innermost cell layer is identified as germinal layer. The outer layer is transformed into a dead layer and flakes away. These cell layers are found in external skin surfaces, esophagus and buccal cavity.

Transitional Epithelium

All cells in this epithelium are able to modify their shape as they can be stretched and elongated. It consists of 3-4 of males and the urinary bladder
Summary

  • A tissue can be defined as a group of cells specialized for a particular function or functions.
  • There is a number of different types of tissues according to the structure and function in plant and animal bodies.
  • The tissues do an innumerable service in labor division in the muticellular organisms. 
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