Tissue : Group of cells having similar structure and function is called tissue. In general tissue forming cells have common origin.
General Features of Tissues
In a tissue cells remain together by a non-living intercellular substance.
1. Intercellular substance is jelly-like.
2. The tensile strength of tissues is due to collagen fibers.
3. A substance found in space is called tissue fluid.
4. Each tissue has networks of nerves, blood capillaries and lymphatics.
5. A continuous exchange of blood plasma and tissue fluid between blood capillaries and cells of the tissue takes place.
6. Change gives cellular respiration and exchange of metabolites between these two.
Historical backgournd : Herophilus is called the father of anatomy. The word “tissue” was coined by Bichat.
In 17th century Marcello Malpighii founded microscopic anatony. In 19th century the name histology was coined.
“Nomina Histologica” published by International Anatomical Nomenclature Committee (IANC) contains rules for the nomenclature of histological studies.
Types of Tissue
In a triploblastic animal tissues develop from ectoderm, mesoderm and endoderm. Tissues are of four types—
1. Epithelial, 2. Connective, 3. Muscular, 4. Nervous.
Epithelial Tissue The term Epithelial tissue was coined by Dutch anatomist Ruysch. Epithelium tissue is formed of one or more layers of cells upon all external and internal exposed surfaces of the body and organs characterstics—
1. In this tissue cells are placed very close to each other.
2. These tissues have very small intercellular space.
3. Basement membrane is composed of glycoprotien and reticular fibres.
4 . Cells may bear microvilli or flagella etc.
5. Cells are connected by different connections.
Functions of Epithelia
1. It protects from dehydration, infection, mechanical and chemical injuries.
2. In intestine, kidney etc it acts as absorptive surface.
3. It acts as selective barrier across surface.
4. It provides conduction of mucus and other fluids.
5. It is exclusively receptive.
6. It brings in regeneration.
Classification : These tissues are classified into two types—
1. Simple epithelium and
2. Compound epithelium
1. Simple epithelium :
1. Squamous epithelium
2. Cuboidal epithelium
3. Columnar epithelium
4. Ciliated epithelium
5. Glandular epithelium
6. Sensory epithelium
7. Germinal epithelium
2. Pseudostratified epithelium.
3. Stratified epithelium :
1. Stratified squamous epithelium
2. Stratified cuboidal epithelium
3. Stratified columnar epithelium
4. Transitional epithelium
Simple epithelium
1. Simple squamous epithelium :
1. This is plate or scale like.
2. Cells of this tissue are flattened and fitted together by means of junctions.
3. This is also known as pavement epithelium.
4. Nucleus is oval shaped spherical in the centre of cell.
2. Simple cuboidal epithelium :
1. It is found in sweat glands, uriniferous tubules, cliliary body, choroid of eye and thin bronchioles.
2. Germinal epithelium is also cuboidal.
3. Cuboidal epithelium acts as secretive, absorptive and excretionary.
3. Simple columnar epithelium :
1. Its cells are tall and prismatic.
2. Nucleus is elongated and placed basally.
3. Its cells secrete mucus and have a very short life span of 2 to 3 days.
4. Ciliated epithelium :
1. This tissue has cuboidal or columnar cells.
2. Their free ends bear cilia.
3. Incessant movement is shown by Cilia.
4. It occurs in retina and neck of uriniferous tubules.
5. Glandular epithelium :
1. It has columnar.
2. They form most important components of glands.
6. Sensory epithelium :
1. It has columnar cells.
2. Outer ends of the cells bear neurosensory hairs and inner ends are attached with the nerve fibres.
3. The cell are usually found single or in groups or interested between epithelial cells.
4. It is found in retina, tongue, internal ear, ampullae and lining of buccal cavity etc.
7. Germinal epithelium :
1. It has cuboidal cells.
2. They have immense power of division.
Pseudostratified epithelium
1. It has ciliated or columnar cells.
2. It is single layered but all cells are not of same size.
3. It is found in lining of olfactory chamber and lining of trachea.
Stratified epithelium
1. Stratified squamous epithelium :
1. It is the main protective epithelium of the body.
2. Mainly it is two layered to multilayered.
3. Cells of different layers are not similar.
4. Two types of stratified squamous epithelia are commonly found.
(a) Non-keratinized :
(i) Cells do not loose nucleus. Keratin is at most absent.
(ii) It is found in cornea, lining of buccal cavity, vagina etc.
(b) Keratinized :
(i) Cells loose nucleus and keratin is found in the cells.
(ii) Its keratinized layer is water proof.
2. Stratified cuboidal epithelium
1. It has cuboidal cells.
2. It is found in conjectiva, linings of the ducts of sweat glands, some part of anal canal etc.
3. Stratified columnar epithelium :
1. It has columnar cells.
2. It is found in lining of the ducts of sweat sebaceous glands and mammary glands.
3. It is mainly found in embryo.
4. Transitional epithelium :
1. It has flattened, non-keratinized, plastic cells.
2. The cells are in the form of large cuboial plates.
3. Cells exist in 2 to 6 layers.
4. The main feature of epithelium “the basement membrane” is absent.
5. It is found in urinary system.
Glandular Tissue
Glands are generally unicellular or multicellular. All glands are formed by the folding of epithelia. Cells of the glands are cuboidal and carry out secretory functions. Classification of glands based on branching of ducts :
1. Simple glands and
2. Compound glands.
Classification based on shape of secretory unit.
1. Tubular glands.
2. Acinus glands.
3. Aleveolar glands.
4. Tubulo-Alveolar glands.
Classification based on secretion and function.
Holocrine glands, 2. Apocrine glands, 3. Merocrine glands.
2. Connective Tissue
About one third of body mass is made up of connective tissues. Connective tissues are responsible for binding together various tissues to the organ to support different parts of the body. Connective tissue has both the cellular and extracellular components.
Hertwig in 1883 was the first to coin the word, ‘Mesenchyma’ for the mesoderm bulk between ectoderm and endoderm.
About 30% of the body weight is constituted by connective tissue.
These tissues have both the cellular and extracellular components. The cellular part plays a role of active defence while extracellular part provides support and protection against mechanical stress and strain.
Characteristics : Intracellular matrix which is—
1. Composed of hyaluronic acid is a gel like ground substance.
2. Between the molecules of hyaluronic acid tissue fluid remains traped.
3. Different cells are loosely scattered in the matrix.
4. Fibres and matrix are secreted by the cells.
5. Mesoderm is mainly responsible for the development of connective tissue.
Classification : There are following three categories of connective tissue.
(a) Connective tissue proper:
(i) It is widely distributed simplest tissue.
(ii) It makes eyelids, penis scrotum, support of glands, nerves, vessels etc.
(iii) It consist of extracellular matrix and cells.
(iv) Ground substance is non-fibrous.
(v) Fibres are of three types namely white collagen fibres, yellow elastic fibres and reticular fibres.
(vi) Cells of the connective tissue are fibroblasts, microphages, plasma cells, flat cells and pigment cells.
Important connective tissues are—
(A) Skeletal Tissue : It is the hard internal frame work of body. It gives support to various organs and body. It is called endoskeleton. It has two types of tissues—one is cartilage and other is bone.
(i) Cartilage : Cartilage is a connective tissue. It is composed of cells and fibres. It is more elastic than bone. Cartilage are of four types.
(a) Fibro-cartilage : It is white, tough, strong and resilient.
(b) Elastic cartilage : Composed of yellow elastic fibers.
(c) Hyaline Cartilage : It is bluish and transparent. It gets calcify after 40 years of age.
(d) Calcified Cartilage : These are calcified and with time loose elasticity.
(ii) Bone : It is a mineralized connective tissue. Its tissue part is 30% and mineral part is 70%.
Bones are of many types—
(a) Long bones, (b) short bones,
(c) flat bones, (d) irregular bones,
(e) pneumatic bones, (f) sesamold bones, (g) supernumerary bones.
According to development bones are classfied as:
(a) Membrane bones, (b) cartilaginous bones, (c) membrano-cartilaginas bones.
(B) Liquid Connective Tissue : These are circulating tissues and are responsible for the transport of various metabolites.
Features : Plasma is their common matrix.
Corpusles are their various types of cells.
Plasma is without fibres.
They are of three types—Blood, lymph and C.S.F.
Blood
1. It is in the form of fluid.
2. It forms 9% of body mass.
3. Its osmetic pressure is 7.6 atmosphere.
4. It has 55% plasma by volume.
5. Blood is composed of plasma & corpuscles.
6. It contains 14-16 gm/100 ml as Haemoglobin.
Lymph
Lymph is almost like blood but without RBC. It has more W B.C.
(i) Blood and lymph together transport nutrients.
(ii) Transport waste materials.
(iii) Transport hormones.
(iv) Transport gases like O2, CO2 etc.
(v) Blood maintains body temperature.
(vi) It prevents haemorrhage due to its clotting properties.
Cerebrospinal Fluid (C.S.F.)
It is formed by choroid plexus and secreted into the Ventricles of brain. It is about 5 ml. in a newly born child and about 125 ml. in an adult.
Main function of C.S.F. is to provide a protective jacket around brain and spinal cord. It also does nutritional and excretory function.
MUSCULAR TISSUE
Muscular tissues are contractile tissues which are responsible for the movements in the body. These tissues constitute about 50% mass of the body. They are composed of muscle fibres.
Muscules are of three types :
1. Skeletal muscle 2. Smooth muscle 3. Cardiac muscle
1. Skeletal Muscle : This muscle is also called as stripped, somatic or voluntary muscle Its main characterstics are—
(i) These muscles are found attached to skeleton.
(ii) They have voluntary control.
(iii) Their response to stimuli is quick.
(iv) They are controlled by cerebral cortex.
(v) These muscles help the body to adjust with environment.
(vi) Muscle fibres are multi-nucleated cylindrical cells.
(vii) These muscles are made up of myofilaments.
(viii) Myofilaments are made up of actin, myosin and tropomyosin.
(ix) Each muscle is made up bundles of muscles fibrus.
(x) The entire muscle have an outer sheath of connective tissue.
(xi) It joins with bone by tendon muscle fibres are
(i) Red fibres and (ii) White fibres
Muscle tissue has two parts
(i) Fleshy part and (ii) Fibrous part
NERVOUS TISSUE
Nervous tissue make about 2.4% of the body weight. Nervous tissue has about 50% lipid and 40% proteins.
1. Nervous tissue is made up of two types of cells namely,
2. Neurons or excitable cells
Neurological cells or non excitable cells. Neurons are of following types,
(a) Unipolar (b) Pseudounipolar
(c) Non-polar (d) Bipolar (e) multipolar
Neuron : It arises from a single embryonic cell. They are of the following types :
1. According to number of process. (a) Unipolar, (b) Pseudounipolar,
(c) Nonpolar, (d) Bipolar, (e) Multipolar.
2. According to length of axon :
(a) Golgi type I, (b) Golgi type II.
3. According to function : (a) Sensory, (b) Motor, (c) Adjustor neuron.
Impulse Transmission : The impulses are transmitted by electrochemical process. The speed of impulses is about 15 m/sec. Impulse conduction depends upon.
1. Permeabillity of axon membrane.
2. Osmotic equilibrium between axoplasm and E.C.F.
3. Electrical equivalance between axoplasm and E.C.F.
Some important terms—
1. Fracture : bone break.
2. Paralysis : loss of motor power.
3. Muscular Spasm : caused by muscle pull.
4. Disused atrophy : non-use of the muscle causes muscle to become weak. It is known disused atrophy.
5. Hypertroply : Over use of muscle.
6. Wasting : Size reduction of muscle.
7. Muscle Fatigue : Muscle inability to contract. It is due to accumulation of lactic acid.
8. Anaemia : Loss of R.B.C.
9. Twitch : Sudden contraction of a muscle.
10. Muscle tone : Partial contraction of muscle.
