Animal Tissue | General Awareness for SSC CGL PDF Download

In multicellular organisms, a group of similar cells and intercellular substances that perform a specific function is called a tissue.

Epithelial Tissue

This tissue provides covering or lining for parts of the body, with cells that are tightly packed without intercellular spaces.

• Simple Epithelium: Composed of a single layer of cells, it lines body cavities, ducts, and tubes.
• Compound Epithelium: Consisting of two or more layers of cells, it serves a protective function.
• Squamous Epithelium: Made up of a single layer of flattened cells with irregular boundaries, found lining blood vessels and air sacs of the lungs.
• Cuboidal Epithelium: Composed of a single layer of cube-like cells, found in the ducts of glands and the tubular part of the kidney nephron, facilitating absorption and secretion.
• Columnar Epithelium: Made up of tall, slender cells with nuclei located at the base. The free surface may have microvilli, and it is found lining the stomach and intestines. The ciliated type is known as ciliated epithelium.
  
• Glandular Epithelium: Specialized columnar and cuboidal epithelium for secretion, which can be unicellular (e.g., goblet cells in the alimentary canal) or multicellular (e.g., salivary glands).
  

The primary function of compound epithelium tissue is to protect against chemical and mechanical stress, covering dry surfaces like the skin and moist surfaces like the buccal cavity. Epithelial cells are joined by intercellular material to form specialized junctions.

Connective Tissues

These are the most abundant and widely distributed tissues, linking and supporting other tissues. Except for blood cells, all connective tissues secrete fibers of structural proteins like collagen or elastin, providing elasticity and flexibility.

• Loose Connective Tissue: Contains cells and fibers loosely arranged in a semi-fluid ground substance, including areolar and adipose tissues.
  
• Dense Connective Tissue: Contains fibers and fibroblasts tightly packed in either regular or irregular patterns. In dense regular connective tissues, collagen fibers are arranged in rows between parallel bundles, as seen in tendons and ligaments.
  

Specialized Connective Tissues: Includes cartilage, bones, and blood. Blood is a fluid connective tissue consisting of plasma, red blood cells, white blood cells, and platelets, facilitating the transport of various substances between organs.

Muscle Tissue

Each muscle consists of long cylindrical fibers arranged parallel to one another. These fibers are made up of fine fibrils called myofibrils. Muscle fibers contract and relax in response to stimulation.

Neural Tissue

The fundamental unit of the neural system is the neuron, with neuroglial cells providing protection and support to the neuron. When a neuron is stimulated, electrical impulses are generated and travel along the plasma membrane (axon). Tissues organize to form organs, which then associate to form organ systems in multicellular organisms.

Earthworm

• The earthworm is a reddish-brown terrestrial invertebrate that lives in the upper layer of moist soil.
• Common Indian earthworms include Pheretima and Lumbricus.
• Earthworms have a long cylindrical body divided into segments called metameres.
• The ventral surface contains the genital pore, and the dorsal surface has a mid-dorsal line.
• The first body segment is called the peristomium and contains the mouth.
  
• Segments 14-16 are covered by a dark band called the clitellum.
• A single genital pore is located on the mid-ventral line of the 14th segment, and a pair of male genital pores is present on the 18th segment on the ventro-lateral side.
• All segments except the 1st, last, and clitellum contain S-shaped setae for locomotion.
• The alimentary canal is a straight tube running from the first to the last segment, consisting of a buccal cavity, muscular pharynx, esophagus, gizzard (which grinds soil particles and decaying leaves), stomach, and small intestine leading to the anus.
• Between segments 26-35, the intestine has an internal median fold called the typhlosole, which increases the effective area of absorption.
• The closed vascular system includes the heart, blood vessels, and capillaries, with blood glands located in the 4th, 5th, and 6th segments producing blood cells and hemoglobin, which is dissolved in blood plasma.
• Earthworms lack respiratory organs and respire through their moist skin.
• Excretory organs are coiled segmental tubules called nephridia, of which there are three types: septal nephridia, integumentary nephridia, and pharyngeal nephridia.
• The nervous system is represented by ganglia arranged segment-wise on the ventral paired nerve cord.
• In the anterior region (3rd and 4th segments), the nerve cord bifurcates and joins the cerebral ganglia dorsally to form a nerve ring.
• Earthworms are hermaphrodites, with two pairs of testes located in the 10th and 11th segments.
• The prostate and spermatic ducts open to the surface as male genital pores on the 18th segment.
• A pair of ovaries is attached to the intersegmental septum of the 12th and 13th segments, with female genital pores opening on the ventral side of the 14th segment.
  
• During mating, mutual exchange of sperms occurs.
• Mature sperms and egg cells, along with nutritive materials, are deposited in a cocoon in the soil where fertilization takes place.
• Earthworms are known as "friends of the farmer" because they make burrows in the soil, making it porous for respiration and root penetration.
• They are also used for vermicomposting and as bait in game fishing.

Cockroach (Periplaneta americana)

• Cockroaches are nocturnal, omnivorous organisms that inhabit damp places worldwide. Their bodies are segmented and can be divided into the head, thorax, and abdomen, all covered by a hard chitinous exoskeleton.
  
• The triangular head is formed by the fusion of six segments, providing flexibility. It bears compound eyes and antennae that help monitor the environment. The thorax consists of three parts: the prothorax, mesothorax, and metathorax, to which the forewings and hindwings are attached. The abdomen comprises 10 segments.
  

Digestive System of Cockroach

•  The alimentary canal is divided into the foregut, midgut, and hindgut. 
•  Food is stored in the crop, and the gizzard grinds the food particles. 
•  At the junction of the midgut and hindgut, yellow-colored filamentous Malpighian tubules are present, aiding in excretion. 
•  The blood vascular system is of the open type with poorly developed blood vessels. 
•  The haemolymph consists of colorless plasma and haemocytes. 
•  The respiratory system includes a network of tracheae that open through 10 pairs of spiracles on the lateral sides. 
•  The nervous system consists of a series of fused, segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side. 
•  The cockroach's nervous system is distributed throughout its body. 
•  Each compound eye contains about 2000 hexagonal ommatidia, allowing the cockroach to receive multiple images of an object, a type of vision known as mosaic vision, which has higher sensitivity but lower resolution. 
•  Cockroaches are dioecious.
  
•  The male reproductive system includes a pair of testes, one on each lateral side in the 4th-6th abdominal segments. 
•  The female reproductive system consists of two large ovaries situated in the 2nd-6th abdominal segments. 
•  Fertilized eggs are encased in capsules called oothecae, with each female producing 9 to 10 oothecae. 
•  Cockroaches are pests that destroy food and contaminate it with smelly excreta. 

Frog (Rana tigrina)

• Frogs are cold-blooded organisms capable of changing colors to camouflage from predators. Their bodies are divided into a head and trunk, with bulged eyes covered by a nictitating membrane.
• Male frogs differ from females by having vocal sacs and a copulatory pad on the first digit of the forelimb.
  
• The digestive system includes the alimentary canal and digestive glands. Digestion starts in the stomach, and final digestion occurs in the small intestine, where digested food is absorbed by villi and microvilli on the inner wall.
• Frogs use their skin as an aquatic respiratory organ (cutaneous respiration). On land, they respire through their skin, buccal cavity, and lungs.
• The vascular system is well-developed and closed, with a three-chambered heart and blood consisting of plasma, RBCs, WBCs, and platelets.
• Frogs also have a lymphatic system comprising lymph, lymph channels, and lymph nodes.
• The excretory system, which includes a pair of kidneys, ureters, cloaca, and urinary bladder, eliminates nitrogenous wastes.
• Frogs excrete urea, making them ureotelic animals.
• The system of control and coordination is highly evolved, involving both neural systems and endocrine glands.
• Frogs have well-organized male and female reproductive systems.
• The male reproductive organs consist of a pair of yellowish ovoid testes, attached to the upper part of the kidneys by the mesorchium.
• The female reproductive organs include a pair of ovaries situated near the kidneys.
• Fertilization is external and occurs in water, with development involving a larval stage called the tadpole, which undergoes metamorphosis to become an adult.

Reproductive systems of frog

Male / Female