Animal Tissue Types: Epithelial Tissue

Structural Organisation in Animals

• The topic will cover Animal Tissue, Organ and Organ systems, and Structural Organisation in Some Animals.

Tissue

• Tissue refers to a group of similar cells specialised for performing a common function.
• The term "Tissue" was first used by Bichat.
• Histology Definition: The study of tissue.
• Mayer coined the term 'Histology' in 1819.
• Marcello Malpighi is known as the founder of Histology.

Animal Tissue Types:

• Epithelial tissue
• Connective tissue
• Muscular tissue
• Nerve tissue

Epithelial Tissue

• Origin: Ectodermal
• Function:
  • Covers outer surfaces of body organs.
  • Lines cavities of hollow organs.
• Cell Arrangement: Cells are compactly arranged and held together by intercellular junctional complexes with the lower most layer resting on a basement membrane.
• Epithelial Tissue Types: Covering and Glandular epithelia categorized based on function.

Covering Epithelia

• Location: Nearest to the environment
• Functions:
  • Protection
  • Respiration
  • Secretion
  • Assimilation
  • Elimination of waste products

Types of Covering Epithelium

• Can be simple or unilaminar (single layered), stratified or compound or multilaminar (multilayered) and specialised epithelium, based on the number and arrangement of cell layers along with the shape of the cells.

Simple Epithelium:

• Squamous:
  • Location- Cavity of major organs (heart, air sacs of lungs)
  • Function- Absorption, exchange of material, filtration.
• Cuboidal:
  • Location- Tubules and ducts of glands, surface of ovary.
  • Function- Absorption and secretion.
• Columnar:
  • Location- Gastrointestinal tract.
  • Function- Secretion of materials from special goblet cells and absorption.
• Ciliated:
  • Location- Respiratory tract, Fallopian tube
  • Function- Movement of mucus, urine, egg, etc.
• Pseudo-stratified:
  • Location- Salivary glands, male urethra, trachea
  • Function- Protection and movement of secretion from glands.

Stratified Epithelium:

• Squamous:
  • Location- Epidermis of skin and hair, oral cavity, tongue
  • Function- Protection against abrasion.
• Columnar:
  • Location- Epiglottis, mammary gland ducts, parts of urethra.
  • Function- Protection and secretion.
• Cuboidal:
  • Location- Sweat glands, female urethra, anal canal
  • Helps mechanical and chemical stress.

Specialised Epithelium:

• Transitional:
  • Location- Wall of urinary bladder
  • Function- Allows expansion, capability to modify shape.
• Neurosensory:
  • Location- Lining of retina, tongue, ear
  • Function- Main receivers of stimuli.
• Pigmented:
  • Location- Basal layer of retina and posterior part of iris
  • Function- Provide the eye its colour.

Glandular Epithelia

• Function of Glandular Epithelia: Specialized for secretion of hormones, sweat, mucus, enzymes, and other products.
• Types Based on Cell Number:
  • Unicellular (e.g., goblet cells of alimentary canal)
  • Multicellular (e.g., salivary gland)
• Types are based on the mode of pouring of their secretions. The glands may be exocrine or endocrine.
  • Exocrine- Secretion releases through ducts or tubes.
  • Endocrine- Hormones secreted directly into blood.

Exocrine Glands Classified

• Mucus Glands:
  • Location: Goblet cell of intestine
  • Function: Secretion of mucus.
• Serous Glands
  • Location: Sweat glands
  • Function: Secretion of clear watery fluid or sweat.
• Mixed Glands
  • Location: Gastric glands and pancreatic glands
  • Function: Secretion of gastric and pancreatic juices.
• Types of Excretory Units:
  • Simple: Secretory units all of the same type.
  • Compound: More than one type of secretory units.

Types Based on Secretory Nature:

• Holocrine:
  • Location: Sebaceous glands
  • Function: Complete secretory unit disintegration.
• Merocrine:
  • Location: Sweat, Salivary and Intestinal glands.
  • Function: Secretion by diffusion.
• Apocrine:
  • Location: Mammary glands
  • Function: Secretion accumulates in the apical part, then is released.
• Simple and compound glands can be further classified into tubular (tube-like secretory unit), acinous (rounded) and alveolar (flask-shaped).

Cell Junctions

• Definition: Structures that provide structural and functional links between the adjacent epithelial cells.
• Types of Cell Junctions:
  • Tight junctions (zonula occludens)
    • Function- Checks the flow of materials.
    • Example- Brain.
  • Gap junctions
    • Function- Facilitate communication between cells by connecting cytoplasm; allows rapid transfer of ions, small molecules and sometimes big molecules.
  • Adhering junctions
    • Function- Perform cementing function to keep neighbouring cells together.

Connective Tissues

• Abundance: These are the most abundant and widely distributed tissue in the body.
• Origin: Mesodermal
• Functions:
  • Bind tissues of an organ
  • Support parts of the body
  • Packaging around organs.
• Hertwig (1883) coined "mesenchyma" for mesodermal tissue between ectoderm and endoderm. Composition: Cellular and extracellular components

Connective Tissue Types:

• Connective Tissue Proper
• Supportive Connective Tissue
• Vascular Connective Tissue

Connective Tissue Proper

• Matrix: Viscous, gel-like matrix of proteoglycans.
• Types of Loose Connective Tissue:
  • Areolar Tissue
    • Location: Beneath epithelia of hollow visceral organs, skin, and blood vessels.
    • Cell Type:
      • Fibroblasts- synthesise collagen and elastin
      • Macrophage- large irregular amoeboid
      • Plasma Cells- synthesise antibodies
      • Mast Cells- containing basophilic granules of heparin (anticoagulant), serotonin (vasoconstrictor) and histamine (vasodilator).
  • Adipose Tissue
    • Location:Beneath skin, heart, blood vessels, kidney, and bone.
    • Function: Stores fats and reduces heat loss.
    • Types:
      • White/yellow tissue (single layered fat droplet)
      • Brown Tissue tissue (multiple small fat droplets)
• Dense Connective Tissue
  • Matrix: Compact bundles of collagen fibers
  • Types:
    • Dense Regular
      • Fibres present in rows between many parallel bundles of fibres
      • White fibrous (e.g., tendon connects muscle and bone) and yellow elastic (e.g., ligament connecting bone and bone)
    • Dense Irregular
      • Fibroblasts with many fibres oriented differently (e.g., in skin).

Supportive Connective Tissue

• Types: Cartilage and bone.
  • Cartilage:
    • Solid, semi-rigid matrix.
    • Composed of chondrin (protein) secreted by chondrocytes.
    • Contains collagen fibres.
• Three types of cartilage as following
  • Hyaline:
    • Locations: Larynx, nasal septum, tracheal rings, costal cartilage, ends of bones.
  • Fibrous:
    • Location: Connected bones like pubis symphysis in pelvis and form intervertebral discs
  • Elastic:
    • Provides strength and maintains shape
    • Locations- Ear pinna, tip of the nose, epiglottis, Eustachian tube, larynx.
  • Bone
    • Solid, rigid.
    • Parts: periosteum, matrix, endosteum, bone marrow.
  • Periosteum
    • Outer dense white fibrous sheath of bone.
  • Matrix
    • Form of layers, the lamellae- namely Haversian, concentric, interstitial which are heavily deposited with apatite salts of Ca and phosphorus.
  • Lacunae:
    • False irregular spaces.
    • Contain osteocytes (metabolically inactive cells).
  • Endosteum
    • Lined the medullary/marrow cavity
    • Osteoblasts- Bone forming cells that secrete ossein protein in the matrix.
  • Bone Marrow
    • Soft fatty tissue.
    • Types:
      • Red bone marrow (active tissue)
        • Occurs in spongy parts of bone, red in color because presence of RBCs
      • Yellow bone marrow (passive tissue)
        • Occurs in shafts of bone, yellow color because presence of adipocytes

Vascular Connective Tissue

• Called fluid connective tissue, circulates through the cardiovascular system.
  • Blood
    • Composed of Plasma (55%) and blood cells (45%).
• Plasma
  • Contents: Water (90-92%), inorganic salts (Na, Cl, K, Mg, etc.), plasma proteins (albumin, globulin, fibrinogen and prothrombin), nutrient and organic waste material, regulatory substances (hormones and enzymes) and gases (O2, CO2 and N2).
• Blood Cells
  • Erythrocytes (Red Blood Cells/RBCs)
    • Circular, biconcave, non-nucleated, with haemoglobin respiratory pigment.
    • Erythropoiesis: Formation of erythrocytes
    • Occurs in the red bone marrow of adults and in liver and spleen of foetus
    • Rouleaux formation- Adherence of RBCs together
    • Spleen, bone marrow and liver are sites for RBC destruction
    • Graveyard of RBCs: The spleen.
    • RBC counted using haemocytometer.
    • RBCs lifespan is 120 days
    • Rabbit lifespan of RBCs is 80 days
    • Frog lifespan of RBCs is 100 days
  • Leucocytes (White Blood Cells/WBCs)
    • Largest blood cells, circular or irregularly shaped with nucleus.
    • Life Span 3-4 Days
    • Nucleus Shape Grouping: Nuclear shape and cytoplasmic granules divides leucocytes into two main groups.
• Granulocytes (Granular with lobed nucleus) - Neutrophils- Highly lobulated nucleus (2-7 lobes) - Contain hydrolyzing enzymes that kill microbes by phagocytosis and stimulate interferons production, antiviral substances. - Eosinophils- Large size and bilobed nucleus - Phagocytose antigen-antibody complexes and increase on allergic conditions like asthma and hay fever. - Basophils Small in size, between neutrophils and eosinophils - Located in 2-3 lobes of nucleus and release heparin (anticoagulant) and histamine.
• Agranulocytes (Agranular with non-lobed nucleus) - Monocytes- Large corpuscles with eccentrically placed kidney-shaped nuclei - Active phagocytes transformed into macrophages - Lymphocytes- Smallest leucocytes with large, round dense nuclei - Non-motile, non-phagocytic and are named by origin - T-lymphocytes- Formed in thymus - B-lymphocytes- Formed in bone marrow and are involved with immunity and antibody production.
  • Blood platelets (Thrombocytes)
    • Round or oval, biconvex discs, formed by fragmentation of megakaryocytes.
    • Thrombopoiesis Formation of platelets takes place in bone marrow.
    • Platelets lifespan is about one week.
    • Platelets contain substances that promote blood clotting, like thromboplastin
  • Lymph
    • Colourless, connective tissue made of plasma and WBCs mostly lymphocytes.
    • Lacks RBCs, platelets and blood proteins.
    • Carries materials from tissues to blood stream and direction
    • Lacteals- Lymph capillaries in the intestinal villi, associated with the absorption of digested food.

Muscular Tissue

• Origin: Mesodermal except iris and ciliary body of eyes which are ectodermal in origin.
• Study of muscles: Called Myology.
• Contribute most to weight of body (about 40%-50%).
• Muscle cells are always elongated, slender and spindle-shaped fibre like cells. The cells are of three types, i.e. striated, non-striated and cardiac muscles

Differences Between Striated, Smooth (non-striated) and Cardiac Muscles

Striated muscle

• Location- Limbs, tongue, pharynx, beginning of oesophagus
• Size and shape Long, cylindrical with blunt ends
• Nucleus- Multinucleate, peripheral
• Myofibrils- The presence of dark bands, the light reflects highly vascular properties
• Mitochondria and glycogen granules- Numerous
• Innversion- From CNS
• Branching- Unbranched
• Mode of contraction- Contract rapidly for short period, get fatigued very soon

Smooth muscle

• Location- In the wall of all visceral organs
• Size and shape- Short and spindle-shaped with flat ends
• Nucleus- Uninucleate, nucleus central
• Myofibrils- Lack bands
• Mitochondria and glycogen granules- Less vascular
• Innversion- From ANS
• Branching- Unbranched.
• Mode of contraction- Contract slowly for long period as do not get fatigued

Cardiac muscle

• Location- Myocardium of heart
• Size and shape- Short, cylindrical with pointed ends
• Nucleus- Uninucleate, nucleus central
• Myofibrils- Bands present
• Mitochondria and glycogen granules- Highly vascular
• Innversion- Both CNS and ANS
• Branching- Branched
• Mode of contraction- Contract rapidly, rhythmically and never gets fatigued.

Nervous Tissue

• Specialised tissues with no intercellular spaces, and the function is receiving stimuli/conducting impulses to control body functions.
• They have no power to divide, form the nervous system.
• Composed of ependymal cells, neurons and the neurosecretory & neuroglial cells.
  • Neuroglial cells
    • Astrocytes or macroglia
      • Supporing cells with repair function.
    • Oligodendrocytes
      • Maintain myelin sheath.
    • Microglia
      • Specialised macrophages and scavenger for nervous system -Structure of neuron consists of dendrites, cyton or cell body, nucleus, axon, synaptic buttons, Nissl's granules, neurilemma and nodes of Ranvier

Organ and Organ System

• Tissues organise to form organs, essential for more coordinated activities of cells.
• The Major Vertebrate Organ Systems includes:
  • Integumentary, Digestive, Respiratory, Circulatory, Urinary, Skeletal, Muscular, Nervous, Endocrine, Reproductive, and Immune systems.
  • Each system has components and functions.
  • Components and functions:
    • Integumentary system
      • Components- Skin, hair, nails and sweat glands
      • Function- Covers the body and protects it
    • Digestive system
      • Components- Mouth, oesophagus, stomach, intestine, liver and pancreas
      • Function- Digests and absorbs soluble nutrients from ingested food
    • Respiratory system
      • Components- Lungs, trachea and other air passage ways.
      • Function- Exchanges of gases (mainly O2 and CO2)
    • Circulatory system
      • Components- Heat, blood vessels, blood, lymph and lymph nodes.
      • Function- Transports materials throughout the body and connects various organ systems
    • Urinary system
      • Components- Kidney, bladder and associated ducts.
      • Function- Removes nitrogenous metabolic wastes from the blood stream
    • Skeletal system
      • Components- Bones, cartilage and ligaments.
      • Function- Protects the body and provides support for locomotion and movement.
    • Muscular system
      • Components- Skeletal muscle, cradiac muscle and smooth muscle
      • Function- Produces body movement and heat
    • Nervous system
      • Components- Nerves, sense organs, brain and spinal cord
      • Function- Receives stimuli, integrates information and directs the body.
    • Endocrine system
      • Components- Pituitary, adrenal, thyroid and other ductless glands.
      • Function- Coordinates and integrates body activities
    • Reproductive system
      • Components- Testes, ovaries and associated reproductive structures..
      • Function- Carries out reproduction.
    • Immune system
      • Components- Lymphocytes, macrophages and antibodies.
      • Function- Removes foreign bodies from the bloodstream.

Structural Organisation in Some Animals

• Cockroach
  • Brown-coloured, nocturnal and omnivorous insects.
  • Live in warm, damp places with plenty of food

Morphology of Cockroach

• Body regions are the Head, thorax and abdomen.
• Sclerites: hardened plates on each segment.
• Arthrodial Membrane- join sclerites on each segment.
• Mouth parts: labrum, a pair of mandibles, a pair of maxillae and a labrium.
• A pair of walking legs- In each thoracic segment.
• Opaque dark forewings, called tegmina- Cover hindwings.
• The hindwings: Used in flight.
• Abdomen in Both Sexes consists of 10 segments
• The 7th segment together with the 8th and 9th sterna forms brood or genital pouch, whose anterior part:
  • Female Gonopore
  • Spermathecal Pores
  • Collateral Glands
• Genital pouch: Lies at the hind end of abdomen.
• Bound Dorsally: 9th and 10th terga-Bound Ventrally: with the 9th sternum.
• Male cockroach, contains a pair of the thread-like anal styles.
• Filamentous Structures called anal cerci from the 10th segment

Anatomy of Cockroach

• Digestive System

  Divisible into foregut, midgut and hindgut

  • Pharynx followed by oesophagus, and opens into a sac-like crop used to store food
  • Hepatic/Gastric present at the junctions.

• Circulatory System

  Open type with blood in open spaces. Flows through the haemocoel.

  • Consists of elongated muscular tube, which lying along
  • The Dorsal Line of Thorax: Heart.
  • Blood from these sinuses Enter in Hearts through ostia and blood is pumped anteriorly to sinuses again.

• Respiratory System

  • Network of trachea opens through spiracles on sides.
  • Opening of spiracles regulated by sphincters.

• Excretory System

  • Excretory system is composed of Malpighian tubules, fat body, nephrocytes and uricose glands which help in excretion. 100-150 yellow coloured thin filamentous tubules
  • Nervous System consists of segmentally arranged joined by paired longitudinal connective tissue
  • Sensory Organs are composed of Antennae and Sensory receptors
  • Compound eyes: Hexagonal ommatidia.

• Reproductive system

  • Cockroaches as Diecious animals, they have the best developed of the reproductive organs.
  • The male have testes found in the abdominal segments
  • The female reproductive system are consisted large ovaries

Earthworm Morphology

• Cylindrical in shape, it is divided into similar segments or metameres
• Has first body segment called the peristomium containing the mouth within.
• 14-16 segments of the earthworm are covered in prominent dark band.
• Ventrolateral sides of the earthworm, have spermathecal which contains sperms.

Anatomy of Earthworm

• Straight alimentary canal, Calciferous glands, Neutralises the humoral acids.
• Circulatory system has No breathing devices.
• Nervous system consists of light and touch sensitive organs with chemo receptors.
• Earthworms uses direct reproduction and a sexual developoment.

Frogs

• Poikilotherms that have mimicry ability.
• Hibernation & aestivation, take shelter during peak seasons.

Frog Morphology

• Their Skin is very Smooth, they have a very unique body structure and they have sexual identification.

Anatomy:

• Digestive system: Short alimentary canal and digestive glands.
• Respiratory organ: Respiration through skin while on land.
• Vascular: Closed type
• Excretory: A pair of kidneys and ureters
• Control: Present endocrine gland.

Reproduction of Frogs

• Males have a pair of yellowish testes.
• Females have a pair of ovaries
• With external fertilization involves larva stage called tadpole, this is caused by thyroxine hormone of thyroid gland.

This lesson covers animal tissues, focusing on epithelial tissue. It discusses the origin, function, and arrangement of cells in epithelial tissues. The lesson further categorizes epithelial tissues based on their covering and glandular functions.