Biology Tissue Types

Animal Tissues

• In animals, a group of similar cells along with intercellular substances perform a specific function, which is called tissue.
• There are four basic types of tissues: Epithelial, Connective, Muscular, and Neural.

Epithelial Tissue

• Epithelial tissue is also known as epithelium (pl.: epithelia).
• It has a free surface, which faces either a body fluid or the outside environment.
• Cells are compactly packed with little intercellular matrix.
• There are two types of epithelial tissues: 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.
• Simple epithelium is further divided into three types based on structural modification of cells: Squamous, Cuboidal, and Columnar.

Glandular Epithelium

• Some columnar or cuboidal cells get specialized for secretion and are called glandular epithelium.
• There are two types of glandular epithelium: unicellular (isolated glandular cells) and multicellular (cluster of cells).
• Glands are divided into two categories: exocrine and endocrine glands.
• Exocrine glands secrete products like mucus, saliva, earwax, oil, milk, and digestive enzymes.
• Endocrine glands do not have ducts, and their products (hormones) are secreted directly into the fluid bathing the gland.

Connective Tissue

• Connective tissues are the 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.
• Connective tissues are classified into three types: Loose connective tissue, Dense connective tissue, and Specialised connective tissue.

Loose Connective Tissue

• Loose connective tissue has cells and fibers loosely arranged in a semi-fluid ground substance.
• Examples include areolar tissue present beneath the skin and adipose tissue, which is specialized for fat storage.

Dense Connective Tissue

• Dense connective tissue has fibers and fibroblasts compactly packed.
• There are two types of dense connective tissue: Dense regular and Dense irregular.
• Examples include tendons, ligaments, and the skin.

Specialised Connective Tissue

• Specialised connective tissues include cartilage, bone, and blood.
• Cartilage is a solid and pliable ground substance that resists compression.
• Bones are hard and non-pliable, rich in calcium salts and collagen fibers, providing structural frame to the body.
• Blood is a fluid connective tissue containing plasma, red blood cells, white blood cells, and platelets.

Muscle Tissue

• Muscle tissue is made up of many long, cylindrical fibers arranged in parallel arrays.
• There are three types of muscles: Skeletal, Smooth, and Cardiac.

Skeletal Muscle Tissue

• Skeletal muscle tissue is closely attached to skeletal bones.
• Muscle fibers are bundled together in a parallel fashion.
• Examples include the biceps.

Smooth Muscle Tissue

• Smooth muscle fibers are tapering at both ends and do not show striations.
• Cell junctions hold them together, and they are bundled together in a connective tissue sheath.
• Examples include the walls of internal organs such as blood vessels, stomach, and intestine.

Cardiac Muscle Tissue

• Cardiac muscle tissue is a contractile tissue present only in the heart.
• Cell junctions fuse the plasma membranes of cardiac muscle cells, making them stick together.

Neural Tissue

• Neural tissue exerts the greatest control over the body's responsiveness to changing conditions.
• Neurons are excitable cells, and neuroglial cells protect and support neurons.
• Neuroglia 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 membrane.

Organ and Organ System

• The basic tissues organize to form organs, which in turn associate to form organ systems in multicellular organisms.
• Each organ in our body is made up of one or more types of tissues.
• An example is the heart, which consists of all four types of tissues.
• The complexity in organ and organ systems displays an evolutionary trend.### Earthworms
• Earthworms are reddish-brown, terrestrial invertebrates that inhabit the upper layer of moist soil.
• They live in burrows during the day and come out at night to feed on decaying organic matter.
• They can be traced by their faecal deposits, known as worm castings.
• Common Indian earthworms are Pheretima and Lumbricus.

Morphology

• Earthworms have a long, cylindrical body divided into over 100 short segments.
• The dorsal surface has a dark median mid-dorsal line, while the ventral surface has genital openings.
• The anterior end has a mouth and a sensory prostomium, which serves as a wedge to open cracks in the soil.
• The body can be divided into three regions: preclitellar, clitellar, and postclitellar segments.
• Clitellar segments have a prominent dark band of glandular tissue.

Anatomy

• The body wall is covered by a thin, non-cellular cuticle, epidermis, two muscle layers, and an innermost coelomic epithelium.
• The alimentary canal is a straight tube running from the first to the last segment of the body.
• The digestive system includes a mouth, buccal cavity, pharynx, oesophagus, gizzard, stomach, and intestine.
• The excretory system consists of nephridia, which are segmentally arranged coiled tubules that regulate the volume and composition of body fluids.
• The nervous system is represented by ganglia arranged segment-wise on the ventral paired nerve cord.
• The sensory system includes light and touch-sensitive organs, as well as chemoreceptors.

Reproductive System

• Earthworms are hermaphrodites, with both testes and ovaries present in the same individual.
• Two pairs of testes are present in the 10th and 11th segments, and two pairs of ovaries are present in the 12th and 13th segments.
• Mutual exchange of sperm occurs between two worms during mating.

Importance of Earthworms

• Earthworms make soil porous, allowing for better respiration and penetration of developing plant roots.
• They are used as bait in game fishing.

Cockroaches

• Cockroaches are brown or black-bodied animals that belong to the class Insecta and phylum Arthropoda.
• They have a long antenna, legs, and a flat extension of the upper body wall that conceals the head.
• They are nocturnal omnivores that live in damp places and are serious pests and vectors of several diseases.

Morphology

• The body of the cockroach is segmented and divided into three distinct regions: head, thorax, and abdomen.
• The head is triangular in shape and lies anteriorly at right angles to the longitudinal body axis.
• The head bears a pair of compound eyes, antennae, and mouthparts.

Anatomy

• The alimentary canal is divided into three regions: foregut, midgut, and hindgut.
• The digestive system includes a mouth, pharynx, oesophagus, and salivary glands.
• The excretory system consists of malpighian tubules, which are present at the junction of the midgut and hindgut.### Alimentary Canal of Cockroach
• The crop, also known as a sac-like structure, is used for storing food.
• The crop is followed by the gizzard or proventriculus.
• The gizzard has an outer layer of thick circular muscles and a thick inner cuticle forming six highly chitinous plates called teeth.
• The gizzard helps to grind food particles.

Blood Vascular System of Cockroach

• The blood vascular system is an open type.
• Blood vessels are poorly developed and open into a space called the haemocoel.
• Visceral organs located in the haemocoel are bathed in blood (haemolymph).
• The haemolymph is composed of colourless plasma and haemocytes.

Heart of Cockroach

• The heart is an elongated muscular tube lying along the mid-dorsal line of the thorax and abdomen.
• The heart is differentiated into funnel-shaped chambers with ostia on either side.
• Blood from sinuses enters the heart through ostia and is pumped anteriorly to sinuses again.

Respiratory System of Cockroach

• The respiratory system consists of a network of trachea that open through 10 pairs of small holes called spiracles present on the lateral side of the body.
• Thin branching tubes (tracheal tubes subdivided into tracheoles) carry oxygen from the air to all parts of the body.
• Exchange of gases takes place at the tracheoles by diffusion.

Excretion in Cockroach

• Excretion is performed by Malpighian tubules.
• Each tubule is lined by glandular and ciliated cells.
• The tubules absorb nitrogenous waste products and convert them into uric acid, which is excreted out through the hindgut.

Nervous System of Cockroach

• The nervous system consists of a series of fused, segmentally arranged ganglia joined by paired longitudinal connectives on the ventral side.
• Three ganglia lie in the thorax, and six in the abdomen.
• The nervous system is spread throughout the body.

Reproductive System of Cockroach

• Cockroaches are dioecious, meaning they have separate sexes.
• The male reproductive system consists of a pair of testes, a pair of vasa deferentia, a pair of seminal vesicles, and a pair of ejaculatory ducts.
• The female reproductive system consists of two large ovaries, a pair of oviducts, and a pair of spermatheca.

Frogs

• Frogs are amphibians that belong to the class Amphibia and phylum Chordata.
• They are cold-blooded, meaning their body temperature varies with the temperature of the environment.
• Frogs have the ability to change colour to hide from their enemies (camouflage).

Morphology of Frogs

• The body of a frog is divisible into the head and trunk.
• A neck and tail are absent.
• The skin is smooth and slippery due to the presence of mucus.
• The colour of the dorsal side of the body is generally olive green with dark irregular spots.

Anatomy of Frogs

• The body cavity of frogs accommodates different organ systems, such as the digestive, circulatory, respiratory, nervous, excretory, and reproductive systems.
• The digestive system consists of the alimentary canal and digestive glands.
• The circulatory system is a well-developed closed type.
• The respiratory system involves cutaneous respiration in water and pulmonary respiration on land.
• The nervous system involves the brain, spinal cord, and peripheral nerves.
• The excretory system consists of a pair of kidneys, ureters, cloaca, and urinary bladder.