Structural Organisation in Animals

Animal Tissues

• Unicellular vs. Multicellular
  • Unicellular organisms: Single cell performs all functions like digestion, respiration, and reproduction.
  • Multicellular animals: Different groups of cells perform specific functions in an organized manner.
• Example: Hydra
  • Composed of different types of cells.
  • Each cell type can number in thousands.
• Human Body
  • Composed of billions of cells.
  • Cells work together in groups called tissues.
• Tissue
  • A group of similar cells performing a specific function.
  • Complex animals have four basic types of tissues.
• Formation of Organs and Systems
  • Tissues are organized to form organs (e.g., stomach, lungs, heart, kidneys).
  • Organs work together to form organ systems (e.g., digestive system, respiratory system).
  • Division of labour among cells, tissues, organs, and systems ensures the body’s survival.

Animal Tissues

• Types of Animal Tissues
  1. Epithelial Tissue
  2. Connective Tissue
  3. Muscular Tissue
  4. Neural Tissue
• Cell Structure and Function
  • The structure of cells varies according to their function, resulting in different types of tissues.

1. Epithelial Tissue

Definition and General Features:

• Epithelial tissue, or epithelium, has a free surface facing body fluids or the outside environment.
• It provides a covering or lining for body parts.
• Cells are compactly packed with little intercellular matrix.

Types of Epithelial Tissues:

1. Simple Epithelium
   • Single layer of cells.
   • Functions as a lining for body cavities, ducts, and tubes.
   • Types of Simple Epithelium:
     • Squamous Epithelium:
       • Single thin layer of flattened cells with irregular boundaries.
       • Found in blood vessel walls and air sacs of lungs.
       • Functions in diffusion.
     • Cuboidal Epithelium:
       • Single layer of cube-like cells.
       • Found in ducts of glands and parts of kidney nephrons.
       • Functions in secretion and absorption.
       • May have microvilli (e.g., proximal convoluted tubule of nephron).
     • Columnar Epithelium:
       • Single layer of tall and slender cells with nuclei at the base.
       • Found in the lining of stomach and intestine.
       • Functions in secretion and absorption.
       • May have microvilli.
     • Ciliated Epithelium:
       • Columnar or cuboidal cells with cilia on the free surface.
       • Moves particles or mucus in a specific direction.
       • Found in bronchioles and fallopian tubes.
2. Glandular Epithelium:
   • Specialized for secretion.
   • Types:
     • Unicellular: Isolated glandular cells (e.g., goblet cells of alimentary canal).
     • Multicellular: Cluster of cells (e.g., salivary gland).
   • Glands:
     • Exocrine Glands: Secrete substances like mucus, saliva, and digestive enzymes through ducts.
     • Endocrine Glands: Secrete hormones directly into the fluid bathing the gland (no ducts).
3. Compound Epithelium:
   • Multiple layers of cells.
   • Limited role in secretion and absorption.
   • Provides protection against chemical and mechanical stresses.
   • Covers the skin surface, buccal cavity, pharynx, and ducts of salivary glands and pancreatic ducts.

Cell Junctions in Epithelial Tissues:

• Tight Junctions: Prevent substances from leaking across tissues.
• Adhering Junctions: Cement neighboring cells together.
• Gap Junctions: Facilitate communication between cells by connecting their cytoplasm for rapid transfer of ions and molecules.

This structured organization allows epithelial tissues to perform diverse and essential functions in the body, from protection to secretion and absorption.

2. Connective Tissue

Definition and General Features:

• Connective tissues link and support other tissues and organs.
• They range from soft to specialized types like cartilage, bone, adipose, and blood.
• Most connective tissues, except blood, have cells that secrete collagen or elastin fibers, providing strength and flexibility.
• They also secrete modified polysaccharides that act as a matrix (ground substance).

Types of Connective Tissue:

1. Loose Connective Tissue:
   • Cells and fibers loosely arranged in a semi-fluid ground substance.
   • Examples:
     • Areolar Tissue: Found beneath the skin; supports epithelium.
     • Adipose Tissue: Stores fats; located mainly beneath the skin.
2. Dense Connective Tissue:
   • Fibers and fibroblasts are compactly packed.
   • Types:
     • Dense Regular Connective Tissue:
       • Collagen fibers arranged in parallel bundles.
       • Examples: Tendons (attach muscles to bones), ligaments (attach bones to bones).
     • Dense Irregular Connective Tissue:
       • Fibroblasts and collagen fibers oriented differently.
       • Example: Found in the skin.
3. Specialized Connective Tissue:
   • Includes cartilage, bones, and blood.
   • Cartilage:
     • Solid, pliable matrix; resists compression.
     • Example: Found in the tip of the nose, outer ear, joints, vertebral column.
   • Bones:
     • Hard, non-pliable ground substance rich in calcium salts and collagen fibers.
     • Provides structural support and protection for softer tissues and organs.
     • Example: Limb bones (weight-bearing functions), bone marrow (produces blood cells).
   • Blood:
     • Fluid connective tissue containing plasma, RBCs, WBCs, and platelets.
     • Main circulating fluid that transports various substances.

Key Components:

• Fibroblasts: Cells that produce and secrete fibers.
• Chondrocytes: Cells in cartilage.
• Osteocytes: Cells in bones.
• Plasma, RBCs, WBCs, Platelets: Components of blood.

Connective tissues play a crucial role in supporting and linking other tissues, providing structure, storing fats, and facilitating transport of substances in the body.

3. Muscle Tissue

General Features:

• Muscles are made of long, cylindrical fibers arranged in parallel arrays.
• These fibers contain fine fibrils called myofibrils.
• Muscle fibers contract (shorten) and relax (lengthen) in response to stimulation.
• Muscles move the body and maintain positions of body parts.
• There are three types of muscle tissue: skeletal, smooth, and cardiac.

Types of Muscle Tissue:

1. Skeletal Muscle:
   • Attached to bones.
   • Composed of striated (striped) fibers bundled together.
   • Enclosed in a sheath of tough connective tissue.
   • Example: Biceps.
2. Smooth Muscle:
   • Fibers taper at both ends (fusiform) and lack striations.
   • Held together by cell junctions and bundled in a connective tissue sheath.
   • Found in walls of internal organs like blood vessels, stomach, and intestines.
   • Involuntary muscles, not controlled by conscious thought.
3. Cardiac Muscle:
   • Found only in the heart.
   • Contractile tissue with fused plasma membranes (cell junctions).
   • Intercalated discs allow cells to contract as a unit.
   • When one cell contracts, neighboring cells also contract.

Key Points:

• Skeletal muscles are voluntary and can be controlled by thinking.
• Smooth muscles are involuntary and function automatically.
• Cardiac muscles work together to pump the heart efficiently.

Muscle tissue plays a crucial role in all body movements, maintaining posture, and ensuring the proper function of internal organs.

4. Neural Tissue

General Features:

• Neural tissue controls the body’s responses to changing conditions.
• It is composed of neurons and neuroglial cells.

Neurons:

• Neurons are the excitable cells of the neural system.
• They generate electrical disturbances when stimulated.
• These electrical signals travel swiftly along the neuron’s plasma membrane.
• When the signal reaches the neuron’s endings, it can stimulate or inhibit adjacent neurons and other cells.

Neuroglial Cells:

• Neuroglial cells protect and support neurons.
• They make up more than half the volume of neural tissue in the body.

Neural tissue is crucial for communication within the body, enabling it to respond to various stimuli and maintain overall function and coordination.

Organ and Organ System

Organ and Organ System

• Formation: Tissues form organs, which then form organ systems.
• Purpose: Organ systems coordinate activities of millions of cells.
• Example: The heart has epithelial, connective, muscular, and neural tissues.
• Trend: Complexity in organs and systems shows an evolutionary trend.
• Study: We study the morphology (external features) and anatomy (internal structure) of organisms.

Earthworm

• Habitat: Earthworms live in moist soil and burrows.
• Common Species: Pheretima and Lumbricus.

Morphology

• Body: Long and cylindrical, divided into 100-120 segments.
• Dorsal Surface: Marked by a dark median mid-dorsal line.
• Ventral Surface: Has genital openings.
• Anterior End: Contains the mouth and prostomium (a sensory lobe).
• First Segment: Called peristomium, contains the mouth.
• Clitellum: A dark band on segments 14-16 in mature worms.
• Body Regions: Preclitellar, clitellar, and postclitellar.
• Openings: Spermathecal apertures (segments 5-9), female genital pore (14th segment), male genital pores (18th segment).
• Setae: S-shaped structures in most segments aiding in locomotion.

Anatomy of Earthworm

Body Structure

• Body Wall: Covered by a thin cuticle, followed by the epidermis, two muscle layers (circular and longitudinal), and the coelomic epithelium.
• Epidermis: Single layer of columnar epithelial cells with secretory gland cells.

Digestive System

• Alimentary Canal: Straight tube from first to last segment.
  • Mouth: Opens into the buccal cavity (segments 1-3).
  • Pharynx: Muscular part.
  • Oesophagus: Narrow tube (segments 5-7).
  • Gizzard: Muscular, grinds soil and leaves (segments 8-9).
  • Stomach: Segments 9-14.
  • Intestine: Starts from 15th segment, ends at anus.
  • Typhlosole: Increases absorption area in the intestine (after segment 26).

Blood Vascular System

• Closed System: Blood is confined to heart and blood vessels.
  • Blood Vessels and Capillaries: Supply blood to gut, nerve cord, and body wall.
  • Blood Glands: Located in segments 4, 5, and 6; produce blood cells and hemoglobin.

Respiratory System

• No Specialized Organs: Respiration through moist body surface.

Excretory System

• Nephridia: Coiled tubules for excretion.
  • Septal Nephridia: Segments 15 to last.
  • Integumentary Nephridia: Segments 3 to last.
  • Pharyngeal Nephridia: Segments 4-6.
  • Function: Regulate body fluids, expel waste.

Nervous System

• Ganglia: Arranged segmentwise on ventral nerve cord.
  • Nerve Ring: Around pharynx, integrates sensory input and commands muscles.
  • Sensory Organs: Light and touch sensitive cells, chemoreceptors for taste.

Reproductive System

• Hermaphrodite: Both testes and ovaries in one individual.
  • Testes: Two pairs in segments 10 and 11.
  • Ovaries: One pair in segments 12 and 13.
  • Spermathecae: Store sperm during copulation (segments 6-9).
  • Mating: Mutual exchange of sperm, fertilization occurs in cocoons.

Importance to Farmers

• Soil Fertility: Make soil porous for plant roots.
• Vermicomposting: Increase soil fertility.
• Fishing Bait: Used in game fishing.

Cockroach

General Information

• Appearance: Brown or black, sometimes yellow, red, or green in tropical regions.
• Size: Ranges from 0.6 cm to 7.6 cm.
• Features: Long antennae, legs, and a flat upper body wall.
• Habitat: Nocturnal, live in damp places worldwide, common in human homes.
• Diet: Omnivores.
• Significance: Pests and disease vectors.

Morphology

Body Structure

• Common Species: Periplaneta americana.
• Size: 34-53 mm long.
• Body Segments: Divided into head, thorax, and abdomen.
• Exoskeleton: Hard, chitinous, and brown. Segments have hardened plates (sclerites).

Head

• Shape: Triangular.
• Mobility: Very mobile due to flexible neck.
• Eyes: Compound eyes.
• Antennae: Long and thread-like with sensory receptors.
• Mouthparts:
  • Labrum: Upper lip.
  • Mandibles: Biting and chewing.
  • Maxillae: Pair.
  • Labium: Lower lip.
  • Hypopharynx: Acts like a tongue.

Thorax

• Parts: Prothorax, mesothorax, and metathorax.
• Neck: Short extension of prothorax.
• Legs: Each thoracic segment has a pair of walking legs.
• Wings:
  • Forewings (Tegmina): Arise from mesothorax, dark and leathery.
  • Hind Wings: Arise from metathorax, transparent, used for flight.

Abdomen

• Segments: 10 in both males and females.
• Females:
  • 7th Sternum: Boat-shaped.
  • Brood/Genital Pouch: Contains female gonopore, spermathecal pores, and collateral glands.
• Males:
  • Genital Pouch: Contains anus, male genital pore, and gonapophysis.
  • Anal Styles: Present, thread-like.
• Anal Cerci: Jointed filamentous structures on the 10th segment in both sexes.

Anatomy of Cockroach

Digestive System

• Alimentary Canal: Divided into three regions – foregut, midgut, and hindgut.
  • Foregut:
    • Mouth opens into the pharynx.
    • Oesophagus leads to the crop (stores food).
    • Gizzard follows the crop, with muscles and chitinous teeth for grinding food.
  • Midgut:
    • Connected to foregut by hepatic/gastric caeca (6-8 tubules that secrete digestive juice).
  • Hindgut:
    • Starts at Malpighian tubules (100-150 tubules for excretion).
    • Ileum, colon, and rectum, ending at the anus.

Circulatory System

• Open System: Blood (haemolymph) bathes organs directly.
• Heart: Elongated tube with chambers, pumps blood to sinuses.

Respiratory System

• Tracheal System: Network of tubes.
  • Spiracles: 10 pairs of openings on body sides.
  • Tracheoles: Branching tubes for gas exchange.

Excretory System

• Malpighian Tubules: Remove waste from blood, convert it to uric acid.
• Other Organs: Fat body, nephrocytes, and urecose glands also help in excretion.

Nervous System

• Ganglia: Series of connected ganglia along the body.
  • Thorax: 3 ganglia.
  • Abdomen: 6 ganglia.
• Supra-oesophageal Ganglion: Brain controls antennae and eyes.
• Sense Organs: Antennae, compound eyes, maxillary and labial palps, anal cerci.
  • Compound Eyes: 2000 ommatidia for mosaic vision.

Reproductive System

• Dioecious: Separate male and female cockroaches.
  • Male:
    • Testes: In 4th-6th abdominal segments.
    • Vas deferens: Leads to ejaculatory duct.
    • Mushroom-shaped Gland: Accessory gland in 6th-7th segments.
    • Spermatophores: Bundles of sperms.
  • Female:
    • Ovaries: In 2nd-6th abdominal segments.
    • Ovarioles: Tubules containing ova.
    • Spermatheca: Stores sperm.

Reproduction and Development

• Ootheca: Capsule containing 14-16 eggs, produced by females.
• Paurometabolous Development: Through nymph stages, resembling adults.
  • Nymphs moult about 13 times to become adults.

Importance/Role

• Pests: Spoil food, spread diseases.
• Wild Species: Many have no economic importance.

Frogs

General Information

• Habitat: Live on land and in freshwater.
• Class: Amphibia, Phylum Chordata.
• Common Species in India: Rana tigrina.
• Body Temperature: Cold-blooded (poikilotherms), varies with the environment.
• Camouflage: Change color to blend in with surroundings (mimicry).
• Aestivation and Hibernation: Hide in burrows during extreme heat (summer sleep) and cold (winter sleep).

Morphology

• Skin:
  • Smooth and slippery due to mucus.
  • Always moist.
  • Dorsal Side: Olive green with dark spots.
  • Ventral Side: Pale yellow.
  • Absorbs water through the skin, doesn’t drink it.
• Body Parts:
  • Divided into head and trunk.
  • Neck and Tail: Absent.
  • Nostrils: Present above the mouth.
  • Eyes: Bulged, with a nictitating membrane for protection in water.
  • Tympanum (Ear): Membranous, receives sound signals.
• Limbs:
  • Forelimbs: End in four digits, smaller.
  • Hind Limbs: End in five digits, larger and muscular, with webbed feet for swimming.
• Sexual Dimorphism:
  • Males: Have vocal sacs (sound producing) and a copulatory pad on the first digit of forelimbs.
  • Females: Lack these features.

Anatomy

Organ Systems

• Body Cavity: Contains various organ systems like digestive, circulatory, respiratory, nervous, excretory, and reproductive systems.

Digestive System

• Parts: Alimentary canal and digestive glands.
• Alimentary Canal: Short due to carnivorous diet.
  • Pathway: Mouth → Buccal cavity → Pharynx → Oesophagus → Stomach → Intestine → Rectum → Cloaca.
• Digestive Glands:
  • Liver: Secretes bile, stored in the gall bladder.
  • Pancreas: Produces digestive enzymes.
• Digestion Process:
  • Food captured by bilobed tongue.
  • Stomach secretes HCl and gastric juices for digestion.
  • Bile and pancreatic juices digest fats, carbohydrates, and proteins.
  • Final digestion and absorption in the intestine.

Respiratory System

• On Land: Uses buccal cavity, skin, and lungs.
• In Water: Uses skin (cutaneous respiration).
• Lungs: Pink, sac-like structures in the thorax.
• Aestivation and Hibernation: Respiration through skin.

Circulatory System

• Type: Well-developed, closed.
• Heart: Three chambers (two atria and one ventricle) covered by pericardium.
• Blood: Plasma and cells (RBCs, WBCs, platelets). RBCs contain haemoglobin.
• Lymphatic System: Lymph, lymph channels, and lymph nodes.
• Special Systems:
  • Hepatic Portal System: Between liver and intestine.
  • Renal Portal System: Between kidney and lower body parts.

Excretory System

• Components: Kidneys, ureters, cloaca, and urinary bladder.
• Kidneys: Bean-like, located near the vertebral column.
• Ureters: In males, act as urinogenital ducts; in females, open separately into the cloaca.
• Bladder: Thin-walled, ventral to the rectum.
• Excretion: Urea, making frogs ureotelic.

Nervous System

• Types: Neural system and endocrine glands.
• Neural System:
  • Central: Brain and spinal cord.
  • Peripheral: Cranial and spinal nerves.
  • Autonomic: Sympathetic and parasympathetic.
• Brain: Divided into forebrain, midbrain, and hindbrain.
• Sense Organs: Touch (sensory papillae), taste (taste buds), smell (nasal epithelium), vision (eyes), and hearing (tympanum with internal ears).

Reproductive System

• Male:
  • Testes: Yellowish, near kidneys.
  • Vasa Efferentia: 10-12, connecting to kidneys.
  • Urinogenital Duct: Opens into the cloaca.
• Female:
  • Ovaries: Near kidneys, no functional connection.
  • Oviducts: Open into the cloaca.
  • Eggs: Lays 2500-3000 ova at a time.
• Fertilization: External, in water.
• Development: Involves a tadpole stage undergoing metamorphosis to become an adult.

Importance/Role

• Ecological Role: Eat insects, protect crops, and maintain ecological balance.
• Food: In some countries, frog legs are used as food.

Chapter Summary:

Cells, Tissues, Organs, and Organ Systems

• Cells, tissues, organs, and organ systems work together for survival.
• Tissue: Group of cells performing one or more functions.
• Epithelia: Sheet-like tissues lining body surfaces and cavities.
• Connective tissues: Bind, support, strengthen, protect, and insulate.
  • Soft connective tissues: Protein fibers and cells in a ground substance.
  • Specialized connective tissues: Cartilage, bone, blood, and adipose tissue.
• Muscle tissue: Helps in movement.
  • Skeletal muscle: Attached to bones.
  • Smooth muscle: In internal organs.
  • Cardiac muscle: In heart walls.
• Nervous tissue: Controls body responses.
  • Neurons: Basic units of nervous tissue.

Earthworm (Pheretima posthuma)

• Body covered by cuticle.
• Segments: Similar except for 14th, 15th, and 16th (clitellum).
• Setae: S-shaped bristles for movement.
• Spermathecal openings: Between segments 5-9.
• Genital pores: Female on 14th segment, male on 18th segment.
• Alimentary canal: Mouth, buccal cavity, pharynx, gizzard, stomach, intestine, anus.
• Closed blood vascular system: Heart and valves.
• Nervous system: Ventral nerve cord.
• Hermaphrodite: Both male and female reproductive organs.
• Fertilization and development: In cocoon.

Cockroach (Periplaneta americana)

• Body covered by chitinous exoskeleton.
• Divided into head, thorax, and abdomen.
• Thorax: Three segments, each with a pair of legs.
• Wings: Two pairs on 2nd and 3rd thoracic segments.
• Abdomen: Ten segments.
• Alimentary canal: Mouth, pharynx, oesophagus, crop, gizzard, midgut, hindgut, anus.
• Hepatic caecae: At junction of foregut and midgut.
• Malpighian tubules: At junction of midgut and hindgut, help in excretion.
• Salivary glands: Near crop.
• Open blood vascular system.
• Respiration: Through tracheae and spiracles.
• Nervous system: Ganglia and ventral nerve cord.
• Reproduction:
  • Male: Testes in 4th-6th segments.
  • Female: Ovaries in 2nd-6th segments.
  • Internal fertilization.
  • Female produces 9-10 ootheca.

Frog (Rana tigrina)

• Common frog in India.
• Body covered by skin with mucous glands.
• Respiration: Through skin in water, lungs on land.
• Body divided into head and trunk.
• Muscular tongue: Bilobed, used to capture prey.
• Alimentary canal: Oesophagus, stomach, intestine, rectum, cloaca.
• Digestive glands: Liver and pancreas.
• Closed circulatory system: Single circulation, nucleated RBCs.
• Nervous system: Central, peripheral, and autonomic.
• Urinogenital system:
  • Male: Pair of testes.
  • Female: Pair of ovaries, lays 2500-3000 ova.
  • External fertilization and development.
  • Eggs hatch into tadpoles, metamorphose into frogs.