Structural Organisation in Animals | Chapter 7 | NCERT | NEET

Structural Organisation in Animals

  • Cells: the fundamental structural and functional unit of all living organism is called Cell.
  • Tissue: A group of similar cells alongwith intercellular substances perform a specific function. Such an organisation is called Tissue.
  • Organs: Tissue are organised in specific pattern and proportion to form an Organs like stomach, lung, Heart, and Kidney.
  • Organ System: When two or more organs perform a similar function by their physical and chemical interaction, they together form Organ System, e.g., digestive system, respiratory system, etc.
  • Cells, Tissues, Organs, and Organ Systems splits up the work in a way that exhibits division of labour and contribute to the survival of the body as a whole. 

# On the basis of Structure and Function

Tissue Function
1. Epithelium tissue(Origin– Ecto, Meso, Endo)
  • Covering and lining.
2. Connective tissue(Origin– Mesoderm)
  • To connect structures.
  • Provides structural framework.
  • To transport substances.
3. Muscular tissue(Origin– Mesoderm with some Exception)
  • Helps in movements and locomotion.
4. Nervous tissue(Origin– Ectoderm)
  • To generate and conduct impulse.

1. Epithelium tissue

  • First to form during the embryonic period.
  • Power of Regeneration- High(maximum)
  • Epithelium tissue grew on connective tissue.
  • Epithelium surface either faces body fluid or the outer environment.
  • Blood vessels and lymph vessels don’t penetrate.
  • Epithelium tissue has negligible intercellular spaces.
  • Blood supply absent[Nutrition via diffusion(from connective tissue)]

Intercellular functions:


  • Finger-like projection of a cell which enters into the cytoplasm of another cell.
  • Formed in stretchable(transition) epithelium.


  • Are cementing structure formed between cells.
  • Provides mechanical support.
  • Present in stratified epithelium.
  • Known as Macula Adherens.

Tight junction-

  • Prevent leakage across the cells.

Gap junction-

  • Facilitates the communication across the cells through which ions, small molecules can pass.

Surface Modification of Plasma Membrane of Epithelium tissues


  • Minute Process
  • Non-motile
  • Non-contractile
  • Function: Increases surface area along with Absorption and secretion.
  • Examples: PCT of Nephron, Gall bladder, Wall of the intestine


  • Long cylindrical process
  • Motile
  • Contractile
  • Function: It propels the substances or Mucus unidirectionally
  • Examples: Fallopian tube, Trachea, Bronchioles, Ependymal epithelium


  • Conical structure
  • Non-motile
  • Non-contractile
  • Function: to increases surface area
  • Examples: Epididymis, Vas-deferens

# Simple Epithelium:

  • Made up of single layer of cells.
  • Forms lining of body cavities, ducts, and tubules.

1. Simple Squamous Epithelium-

  • Cells are flat, scale like with irregular boundaries.
  • Functions: filtration, diffusion


  1. Bowmann’s capsule(Podocytes),
  2. Alveoi of lungs(pneumocyte type-1),
  3. Blood vessels(Endothelium),
  4. lining of lymph vessels,
  5. loop of Henle,
  6. Mesothelium(lining of coelom),
  7. Inner lining of Heart(Endocardium),
  8. Outer membrane of intestine

2. Simple Cuboidal Epithelium-

  • Cube like cells
  • Function: Absorption, Secretion, and Excretion


  1. Vesicles of thyroid
  2. Acini of Pancreas
  3. Sweat glands
  4. Iris, Ciliary body, & Choroid
  5. Tubular part of Nephron
  6. Lining of ovaries and testes


I. Brush-bordered Simple Cuboidal Epithelium- 

Examples: PCT of Nephron

II. Ciliated Simple Cuboidal Epithelium-

Examples: Neck of Nephron, Collecting duct

3. Simple Columnar Epithelium-

  • Cells- pillar like[tall & Slender]
  • Nucleus is present at base
  • Function: Absorption, Secretion


  1. Liver
  2. Bile duct


I. Ciliated Simple Columnar Epithelium:

Examples: fallopian tube, Ependymal Epithelium

II. Stereociliated Simple Columnar Epithelium

Examples: Epididymis, Vas-deferens

III. Brush bordered Simple Columnar Epithelium

Examples: Gall bladder

IV. Glandular Simple Columnar Epithelium

Examples: Stomach, Large intestine, Uterus

V. Brush border glandular Simple Columnar Epithelium

Examples: Small intestine

4. Pseudostratified Epithelium-

  • Modification of Columnar Epithelium
  • Two types of cell- large cells, small cells
  • Nucleus present at different level but cells are present on single basement membrane.


  1. Respiratory epithelium of nasal chamber
  2. Trachea
  3. Bronchioles

# Compound Epithelium:

  • Multi-layered
  • Protects from chemical and mechanical stress

1. Transitional Epithelium(Stretchable)-

  • On stretching- Basement membrane- disappear
  • Interdigitations are present


  1. Renal Pelvis
  2. Ureter
  3. Urinary bladder
  4. Proximal part of Male Urethra

2. Stratified Squamous Epithelium-

  1. Keratinized stratified squamous epithelium
  2. Non-Keratinized stratified squamous epithelium
Keratinized stratified squamous epithelium Non-Keratinized stratified squamous epithelium

  • Epidermis of Skin
  • Hairs, nails
  • Horns, hooves

  • Buccal cavity & Oral cavity
  • Inner lining of lips, cheeks, hard palate
  • Pharynx, Oesophagus
  • Lining of vagina, anus
  • Cornea of eye

3. Stratified Cuboidal Epithelium-

  • Uppermost cells & innermost cells- Cube like


  1. Secretory duct of sweet gland,
  2. salivary gland,
  3. sebaceous gland,
  4. mammary gland,
  5. pancreas

4. Stratified Columnar Epithelium-

I. Ciliated epithelium

Examples: Larynx

II. Non-ciliated epithelium

Examples: Epiglottis


  • Cell or group of cells which produces chemical secretion is called Gland.
  • All the Gland are derived from Epithelium tissue(cuboidal & columnar cells)
  • All the glands are derived from 3 Germ layers: Ectoderm, Mesoderm, and Endoderm

# On the basis of Number of cells-

a) Unicellular:

  • Examples- Goblet cells, Paneth cells

b) Multicellular:

  • Examples- Except Goblet & Paneth cells

# On the basis of method of Secretion-

a) Exocrine:

  • Duct- present
  • Secretion- sweat, oil, tears, saliva, milk, earwax.etc.

b) Endocrine:

  • Duct- absent
  • Secretion- Hormones(they pour their secretion directly into fluid bathing the gland)

c) Heterocrine:

  • Both Exocrine & Endocrine part are present.
  • Examples- Pancreas, gonads

Connective tissue

  • Also called as Mesenchyme because it is derived from Mesoderm.
  • Most abundant tissue and widely distributed for linking & support.
  • Connective tissue Consist of Cells, Fibre, and Matrix.


1. Fibroblast cells:

  • Maximum in number
  • Largest size
  • Shape- irregular due to cytoplasmic process
  • Are Undifferentiate cells- change into Osteoblast and Chondroblast
  • Functions: Produces fibres and secrete Matrix(chief matrix producing cells).

2. Macrophages:

  • Also known as Histeocytes
  • Shaped- Amoeboid
  • Nucleus- Bean shape
  • Are agranular but due to Lysosome they appear Granules.
  • Functions: Phagocytosis, Scavenger cells(destroy damage or dead cells)

3. Mast cells:

  • Shape- amoeboid
  • Nucleus- S-shape
  • Secrete Matrix
  • Secretions: Histamine, Serotonin, Heparin

4. Lymphocytes:

  • Shape- amoeboid
  • Function: defense & production of Antibodies

5. Plasma cells:

  • Amoeboid shape
  • Clone of Lymphocytes
  • Nucleus- Centre, Chromatin arranged in spoke
  • Also known as “Cart Wheel Cells”
  • Function: formation of Antibody

6. Adipose cells:

  • Oval shape
  • Fat is deposited in form of fat Globule.


1. Collagen fibres:

  • White, Bright fibres
  • Collagen protein
  • Most abundant fibres
  • Shape- wavy
  • They are arranged in bundles
  • Tough fibres
  • On boiling convert into Gelatin

2. Elastic fibres:

  • Yellow fibres
  • Elastin protein
  • Shape- singly branched
  • Elastic in nature
  • Highly Resistant to chemicals

3. Reticulate fibres:

  • Reticulin protein
  • Also known as Arzyrophil fibres(because it can be stained by Ag-salt)
  • Highly branched
  • Delicate fibres
  • Present in Lymphoid organs.


  • Made up of Mucopolysaccharide(Hyaluronic acid)
  • Secreted by fibroblast cell & Mast Cell.


Connective tissue proper:

A. Loose Connective tissue-

1. Areolar connective tissue

  • Also known as Spongy connective tissue
  • Most abundant connective tissue
  • Cells & fibres are loosely arranged in ground substances.
  • Fibroblast, Macrophages, Mast cells are more in number.
  • Collagen fibre & Elastic fibres are present
  • Reticular fibres are absent.
  • Provides support framework for Epithelium.
  • Present beneath the skin
  • Examples- tela subcutanea(connect skin with muscle), Sub-mucosa of trachea, Bronchioles, Stomach, Oesophagus, Intestine

2. Adipose Connective tissue

  • Modification of Areolar connective tissue.
  • In Areolae- adipose cells are present

B. Dense Connective tissue-

  • Fibres and fibroblast are compactly packed.
  • Dense Regular- Cord
  • Dense irregular- sheath

On the basis of fibres, Dense connective tissue

White fibrous CT Yellow fibrous CT
Collagen/white fibres- More

Yellow fibres- Absent

Reticular fibres- Absent

Cord– Tendon(connect bone to muscle)

Sheath– Epimysium, Periosteum, Perichondrium, Pericardium, Dura matter, Renal capsule, Glisson Capsule, Cornea

Elastic fibre- More

Collagen fibre- Less

Reticular fibre- Absent

Cord– Ligament(connect Bone to Bone)

Sheath– walls of blood vessels & lymph vessels, true vocal cord, present in the skin.

C. Reticular fibrous Connective Tissue-

  • Known as Lymphoid tissue
  • Found in Lymphoid organs
  • Matrix- Lymph
  • Ex- Spleen, Payer’s patches, Endosteum(yellow bone marrow)

D. Mucoid Connective tissue-

  • Known as Embryonic tissue
  • Matrix- jelly like[wharton’s jelly]
  • Ex- Umbilical cord, vitreous humor(eye)

Specialised Connective tissue:

1. Skeletal Connective tissue-

a) Cartilage

  • The intercellular material of cartilage is solid and pliable and resists compression.
  • Cells of this tissue (chondrocytes) are enclosed in small cavities within the matrix secreted by them. 
  • Most of the cartilages in vertebrate embryos are replaced by bones in adults.
  • Cartilage is present in the tip of nose, outer ear joints, between adjacent bones of the vertebral column, limbs and hands in adults.

b) Bone

  • Bones have a hard and non-pliable ground substance rich in calcium salts and collagen fibres which give bone its strength.
  • It is the main tissue that provides structural frame to the body.
  • Hardest Bones support and protect softer tissues and organs.
  • . The bone cells (osteocytes) are present in the spaces called lacunae. 
  • Limb bones, such as the long bones of the legs, serve weight-bearing functions.
  • They also interact with skeletal muscles attached to them to bring about movements. 
  • The bone marrow in some bones is the site of production of blood cells.

2. Fluid Connective tissue- 

Blood is a fluid connective tissue containing Plasma, RBC, WBC and Platelets. It is the main circulating fluid that helps in the transport of various substances. you will learn more about blood in chapter 17(Breathing and Exchange of gases) & 18(Body fluids and circulating).

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