Important Diagrams Structural Organisation in Animals - Biology Class 11

Epithelial Tissue - Simple, Glandular

1. Types of Simple Epithelium

Definition: Epithelial tissue is a sheet of closely packed cells covering body surfaces and lining body cavities. Simple epithelium consists of a single layer of cells and is specialised for absorption, secretion and exchange of materials.

• Simple squamous epithelium - flattened, thin cells; suited for diffusion and filtration. Typical locations: alveoli of lungs, lining of blood vessels (endothelium), glomerular capsule.
• Simple cuboidal epithelium - cube-shaped cells with centrally placed nucleus; functions in secretion and absorption. Typical locations: kidney tubules, ducts of glands, thyroid follicles.
• Simple columnar epithelium - tall column-like cells; often have microvilli for absorption or goblet cells for secretion of mucus. Typical locations: lining of small intestine, stomach (non-ciliated columnar).
• Ciliated simple columnar epithelium - columnar cells bearing cilia; moves mucus and particles. Typical locations: bronchioles, uterine tubes.
• Pseudostratified ciliated columnar epithelium - appears stratified but all cells contact the basement membrane; often has goblet cells and cilia. Typical location: respiratory tract (trachea).

2. Types of Glandular Epithelium

Definition: Glandular epithelium is specialised to form glands that synthesise and secrete substances. Glands originate from epithelial cells and are classified by structure and mode of secretion.

• Unicellular glands - single secretory cells such as goblet cells that secrete mucus; found in intestinal and respiratory epithelium.
• Multicellular glands- many cells forming a secretory unit; classified as:
  • Exocrine glands - secrete onto epithelial surfaces through ducts (e.g., salivary glands, sweat glands, pancreas [exo portion]).
  • Endocrine glands - ductless; secrete hormones into blood (e.g., thyroid, adrenal).
• Modes of secretion in multicellular exocrine glands:
  • Merocrine (eccrine) - secretion by exocytosis without loss of cytoplasm (e.g., pancreatic acini, salivary glands).
  • Apocrine - apical portion of cell with secretory product is pinched off (e.g., mammary glands in some phases).
  • Holocrine - entire cell disintegrates to release secretion (e.g., sebaceous glands).

Connective Tissue - Areolar, Adipose, Dense, Special

1. Areolar Connective Tissue

Areolar tissue is a loose connective tissue with a matrix of collagen and elastic fibres and various cell types (fibroblasts, macrophages, mast cells). It binds tissues, holds interstitial fluid and provides defence against infection.

• Fibres: collagenous (strength), elastic (stretch), reticular (support).
• Cells: fibroblast (synthesise fibres), macrophages (phagocytosis), mast cells (histamine), adipocytes (scattered).
• Locations: beneath epithelium, around blood vessels and nerves, between organs.

2. Adipose Tissue

Adipose tissue is specialised for fat storage and cushioning. Cells (adipocytes) store triglycerides in a large central vacuole; nucleus is pushed to periphery.

• Functions: energy reserve, thermal insulation, mechanical cushioning, endocrine roles (leptin, adiponectin).
• Locations: subcutaneous layer, around organs (visceral fat), bone marrow cavity.

3. Dense Connective Tissue

Dense connective tissue is rich in collagen fibres and provides tensile strength.

• Dense regular connective tissue - parallel collagen fibres; resists unidirectional tension. Example: tendons and ligaments.
• Dense irregular connective tissue - collagen fibres arranged irregularly; resists tension from multiple directions. Example: dermis of skin.

4. Special Connective Tissues

These include tissues with specialised extracellular matrices and functions:

• Cartilage - chondrocytes in lacunae, matrix rich in chondroitin sulphate; types: hyaline, elastic, fibrocartilage; functions in support and cushioning (e.g., trachea, ear, intervertebral discs).
• Bone - osteocytes in lacunae, mineralised matrix (calcium phosphate); functions in support, protection, mineral storage; compact and spongy types.
• Blood - fluid connective tissue with plasma as matrix and formed elements (RBCs, WBCs, platelets); transports gases, nutrients and immune cells.
• Lymph - circulates immune cells; part of immune and fluid balance systems.

Types of Muscle Tissue

Muscle tissue is specialised for contraction. There are three types with distinct structure and control.

• Skeletal (striated) muscle - long cylindrical multinucleate fibres with obvious striations; under voluntary control; attached to bones for body movements.
• Smooth (non-striated) muscle - spindle-shaped cells with a single central nucleus and no visible striations; involuntary control; located in walls of hollow organs (intestine, blood vessels, urinary bladder).
• Cardiac muscle - branched striated fibres with one or two central nuclei; cells joined by intercalated discs that contain gap junctions for coordinated contraction; involuntary control; found in the heart.

Neuron

Definition: A neuron is a specialised nerve cell that conducts electrical impulses. It is the structural and functional unit of the nervous system.

• Cell body (soma) - contains nucleus and organelles; metabolic centre.
• Dendrites - short branched processes that receive signals and convey them to the cell body.
• Axon - long process that conducts impulses away from the cell body; may be myelinated to speed conduction.
• Myelin sheath - insulating layer formed by Schwann cells (PNS) or oligodendrocytes (CNS); nodes of Ranvier allow saltatory conduction.
• Synapse - junction between neurons where chemical neurotransmitters transmit the signal.

Morphology and Anatomy of the Cockroach

External morphology: The body of a cockroach is divided into three tagmata: head, thorax and abdomen. Key external features include compound eyes, long antennae, mouth parts (labrum, mandibles, maxillae, labium), three pairs of legs attached to the thorax, and typically two pairs of wings (tegmina and hind wings) in the thorax.

• Head: sensory and feeding structures (antennae, compound eyes, mouthparts).
• Thorax: three segments - prothorax, mesothorax, metathorax; each bears a pair of legs; meso- and metathorax bear wings.
• Abdomen: contains digestive, respiratory (tracheal system with spiracles), excretory (Malpighian tubules) and reproductive structures.

Morphology of the Cockroach

Internal systems (key points):

• Digestive system - foregut (pharynx, oesophagus, crop, proventriculus), midgut (stomach; site of digestion and absorption), hindgut (intestine, rectum).

Digestive System of cockroach

• Respiratory system - tracheal system; air enters through spiracles and distributes directly to tissues via tracheae and tracheoles.
• Circulatory system - open circulatory system with a dorsal heart and haemocoel where haemolymph bathes organs; limited role in oxygen transport.

Circulatory System of Cockroach

• Excretory system - Malpighian tubules that remove nitrogenous wastes and transport them to the gut for excretion.
• Nervous system - brain (supraoesophageal ganglion) and a ventral nerve cord with segmental ganglia.
• Reproductive system - sexually dimorphic; male and female reproductive organs located in the abdomen.

External morphology: Frogs are tailless amphibians with a short body, protruding eyes, webbed hind feet adapted for swimming and powerful hind limbs for leaping. Skin is moist and glandular and plays roles in respiration and osmoregulation.

Morphology of the Frog

Internal organisation - important organ systems:

• Digestive system - mouth → buccal cavity → pharynx → oesophagus → stomach → small intestine (duodenum, ileum) → large intestine → cloaca. Accessory organs: liver, pancreas.
• Respiratory system - lungs (simple sacs) and cutaneous respiration; buccal pumping helps ventilate lungs.
• Circulatory system - three-chambered heart (two atria, one ventricle) with partial separation of oxygenated and deoxygenated blood; systemic and pulmonary circuits.
• Excretory system - paired kidneys that produce urine which is stored in the urinary bladder before passing to the cloaca.
• Nervous and sensory systems - developed brain and cranial nerves; tympanum for hearing; eyes with nictitating membrane.
• Reproductive system - external fertilisation in most frogs; distinct male and female reproductive organs (testes, ovaries) with ducts opening into cloaca.

Digestive System of Frog

Male Reproductive System of Frog

Female Reproductive System of Frog