Study Notes on Structural Organization of Animals

Study Notes on Structural Organization of Animals

ANIMAL TISSUES

The structure of the cells vary according to their function. Therefore, the tissues are different and are broadly classified into four types: (i) Epithelial, 2) Connective, (iii) Muscular and (iv) Neural.
Epithelial Tissue We commonly refer to an epithelial tissue as epithelium- This tissue has a free surface.
These faces either a body fluid or the outside environment and thus provides a covering or a lining for some part of the body.
The cells are compactly packed with little intercellular matrix.
There are two types of epithelial tissues namely simple epithelium and compound epithelium.
Simple epithelium is composed of a single layer of cells and functions as a lining for body cavities, ducts, and tubes.
The compound epithelium consists of two or more cell layers and has protective function as it does in our skin.
The squamous epithelium is made of a single thin layer of flattened irregular boundaries. They are found in the walls of blood vessels Boundary.

The cuboidal epithelium is composed of a single layer of a)squamous b) Cuboidal (c) Concave-like cells.
This is commonly found in ducts of glands and tubular parts of nephrons in kidneys and its main functions are secretion and absorption.
The epithelium of proximal convoluted tubule (PCT) of nephron in the kidney has microvilli. The columnar epithelium is composed of a single layer of tall and slender cells.
Their nuclei are located at the base. Free surface may have microvilli.
They are found in the lining stomach and intestine and help in secretion and absorption.
If the columnar or cuboidal cells bear cilia on their free surface they are called Ciliated epithelium.
Their function is to move particles or mucus in a specific direction over the epithelium.
They are mainly present in the inner surface of hollow organs like bronchioles and fallopian tubes.
Some of the columnar or cuboidal cells get specialised for secretion and are called glandular epithelium.
They are mainly of two types: unicellular, consisting of isolated glandular cells. And multicellular, consisting of cluster of cells (salivary gland).
On the basis of the mode of pouring of their secretions, glands are divided into two categories namely exocrine and endocrine glands.
Exocrine glands secrete mucus, saliva, earwax, oil, milk, digestive enzymes and other cell products.
These products are released through ducts or tubes. In contrast, endocrine glands do not have ducts.
Their products called hormones are secreted directly into the fluid bathing the gland.
Compound epithelium is made of more than one layer (multi-layered) of cells and thus it has a limited role in secretion and absorption.
Their main function is to provide protection against chemical and mechanical stresses.
They cover the dry surface of the skin, the moist surface of buccal cavity, pharynx, inner lining of ducts of salivary glands and of pancreatic ducts.
Three types of cell Junction are found in the epithelium and other issues. These are called as it adhering and gap Junctions.
Tight Junctions help to stop substances from leaking across a tissue.
Adhering Junctions perform cementing to keep neighbouring cells together.
Gap junctions facilitate the cells to communicate with each other by connecting the cytoplasm of adjoining cells, for rapid transfer of ions, small molecules and sometimes big molecules.

CONNECTIVE TISSUE

Connective tissues are most abundant and widely distributed in the body of complex animals.
They are named connective tissues because of their special function of linking and supporting other tissues/organs of the body.
The range from soft connective tissue to specialised types which include cartilage bone adipose and blood.

LOOSE CONNECTIVE TISSUE.

These are cells and fibers loosely arranged in a semi fluid ground substance
Adipose tissue is one of example of loose connective tissues located mainly beneath the skin.
Areolar tissue is another example of these tissues.

DENSE CONNECTIVE TISSUE.

These are fibres and fibroblasts are compactly packed in the dense connective tissue.
In the dense regular and dense irregular, connective tissue the collagen fibers are present in rows between many parallel boundaries.

BONES.

Bones have a hard and non- pliable ground substance rich in calcium salt collagen fibers.
These provide strength and frame work to the body.

BLOOD.

Blood is a fluid connective tissue containing plasma, red blood cells, white blood cell, and platelets.
The main circulating fluid that helps in the transportation of various substance.

MUSCLE TISSUE.

The muscle is made of many long cylindrical fibres arranged in parallel arrays.
These fibres are composed of numerous fine fibrils, called myofibrils.
Muscle fibres contract (shorten) in response to stimulation, then relax (lengthen) and return to their uncontracted state in a coordinated fashion.
Their action moves the body to adjust to the changes in the environment and to maintain the positions of the various parts of the body.
In general, muscles play an active role in all the movements of the body.
Muscles are of three types, skeletal, smooth, and cardiac.
Skeletal muscle tissue is closely attached to skeletal bones.
In a typical muscle such as the biceps, striated (striped) skeletal muscle fibres are bundled together in a parallel fashion.
A sheath of tough connective tissue encloses several bundles of muscle fibres also stimulated to contract.
The smooth muscle fibres taper at both ends (fusiform) and do not show strations Cell functions hold them together and they are bundled together in a connective tissue sheath.
The wall of internal organs such as the blood vessels, stomach and Intestine contains this type of muscle tissue Smooth muscles are involuntary as their functioning cannot be directly controlled.
Cardiac muscle tissue is a contractile tissue present only in the heart.

Cell functions fuse the plasma membranes of cardiac muscle cells and make them stick together Communication junctions (Intercalated discs) at some fusion points allow the cells to contract as a unit.
when one cell receives a signal to contract, its neighbours are also stimulated to contract.

NEURAL TISSUE

Neural tissue exerts the greatest control over the body’s responsiveness to changing conditions.
The neuroglia cell which constitute the rest of the neural system protect and support
neurons Neurogtia make up more than one half the volume of neural tissue in our body.
When a neuron is suitably stimulated. an electrical disturbance is generated which swiftly travels along its plasma.

ORGAN AND ORGAN SYSTEM

The basic tissues mentioned above organise to form organs which in tum associate to form organ systems in the multicellular organisms.
Such an organisation is essential for more efficient and better coordinated activities of millions of cells constituting an organism.
Each organ in our body is made of one or more type of tissues.
Heart consists of all the four types of tissues, i.e., epithelial, connective, muscular and neural.

EARTHWORM

Earthworm is a reddish brown terrestrial invertebrate that inhabits the upper layer of the moist soil.
During day time, they live in burrows made by boring and swallowing the soil.
In the gardens, they can be traced by their faecal deposits known as worm castings.
The common Indian earthworms are Pheretima and Lumbricus.

MORPHOLOGY

Earthworms have long cylindrical body. The body is divided into more than hundred short segments which are similar (metameres about100-120 in number).
The dorsal surface of the body is marked by a dark median mid dorsal line (dorsal blood vessel) along the longitudinal axis of the body.
The ventral surface is distinguished by the presence of genital openings (pores). Anterior end consists of the mouth and the prostomium.
A lobe which serves as a covering for the mouth and as a wedge to force open cracks in the soil into which the earthworm may crawl.
The prostomium is sensory in function. The first body segment is called the peristomium (buccal segment) which contains the mouth. In a mature worm.
The segments 14-16 are covered by a prominent dark band of glandular tissue called clitellum.
the body is divisible into three prominent regions – preclitellar, Clitellar and postelltellar segments.
The Four pairs of spermathecal apertures are situated on the ventro-lateral sides of the intersegmental grooves, i.e., 5h-gth segments.
A single female genital pore is present in the mid-ventral line of 14th segment.
A pair of male genital pores are present on the ventro-lateral sides of the 18^th
Numerous minute pores called nephridiopores open on the surface of the body.
In each body segment, except the first, last and Clitellum, there are rows of S-shaped setae, embedded in the epidermal pits in the middle of each segment.
The Setae can be extended or retracted, Their principal role is in locomotion.

COCKROACH

Cockroaches are brown or black bodied animals that are included in class Insecta of Phylum Arthropoda, Bright yellow, red and green coloured cockroaches have also been reported in tropical regions.
Their size ranges from 4 inches to 3 inches (0.6-7.6 cm) and have long antenna, legs and flat extension of the upper body wall that conceals head.
They are nocturnal omnivores that live in damp places throughout the world.
They have become residents of human homes and thus are serious pests and vectors of several diseases.

MORPHOLOGY

The adults of the common species of cockroach, Periplaneta americana.
These are about 34-53 mm long with wings that extend beyond the tip of the abdomen in males.
The body of the cockroach is segmented and divisible into three distinct regions – head, thorax and abdomen The entire body is covered by a hard chitinous exoskeleton (brown in colour).
In each segment, exoskeleton has hardened plates called sclerites (tergites dorsally and sternites ventrally) that are joined to each other by a thin and flexible articular membrane (arthrodial membrane)