ANIMAL TISSUE

 

ANIMAL TISSUE

PREPARED BY MR. ABHIJIT DAS 

INTRODUCTION

Tissue consists of group of similar cells along with their intercellular matrix performing a specific function.

These tissues are organized in specific proportion and pattern to form an organ like stomach, lung, kidney, heart etc.

When two or more organs perform a common function by their physical and chemical interaction, they together form organ system such as digestive system, respiratory system, cardiovascular system etc.

Cells, tissues, organs and organ systems split up the work (division of labour) and contribute to the survival of the body as a whole.

Tissues are broadly classified into four types:

·        Epithelial tissue

·        Connective tissue

·        Muscular tissue

·        Neural tissue

EPITHELIAL TISSUE

Ø This tissue has a free surface which faces either a body fluid or air thus provides a covering or a lining for some part of the body.

Ø The cells are tightly packed with little intercellular matrix.

Ø There are two types of epithelial tissues; simple epithelium and compound epithelium (or stratified epithelium).

Ø Simple epithelium is composed of a single layer of cells.

Ø Stratified epithelium consists of two or more layers and has protective function as it does in our skin.

Figure Credit: Jayashree Baidya

On the basis of structural modification of cells, simple epithelium is further divided into 3 types.

·        Squamous epithelium

·        Cuboidal epithelium

·        Columnar epithelium

SQUAMOUS EPITHELIUM

Figure Credit: Jayashree Baidya

The squamous epithelium is made of a single layer of flattened cells.

They are involved in functions like forming a diffusion boundary and filtration boundary.

They are found in the walls of blood vessels and alveoli of lungs.

Figure Credit: Jayashree Baidya

CUBOIDAL EPITHELIUM

Figure Credit: Jayashree Baidya

It is composed of a single layer of cube like cells.

Its main functions are secretion and absorption.

Location: Ducts of glands and tubular parts of nephrons (DCT) in kidneys.

The epithelium of proximal convoluted tubule (PCT) of nephron in the kidney has microvilli. That’s why the tissue present at PCT is known as BRUSH BORDER CUBOIDAL EPITHELIUM.

Figure Credit: Jayashree Baidya

COLUMNAR EPITHELIUM

Figure Credit: Jayashree Baidya

It is composed of a single layer of tall and slender (thin) cells.

Free surface may have microvilli (BRUSH BORDER COLUMNAR EPITHELIUM).

They help in secretion and absorption.

Location: stomach(columnar epithelium) and small intestine(brush border columnar epithelium).

Figure Credit: Jayashree Baidya

CILIATED EPITHELIUM

CILIA: hair like structure (not a part of cytoplasm)

If the columnar and cuboidal cells bear cilia on their free surface they are called ciliated epithelium.

Their function is to move particles or mucus in a specific direction over the epithelium.

Location of ciliated cuboidal epithelium: lower respiratory tract.

Location of ciliated columnar epithelium: upper respiratory tract, ovary (fallopian tube).

Figure Credit: Jayashree Baidya

CONNECTIVE TISSUE

They are named connective tissues because of their special function of linking and supporting other tissues/organs of the body.

They are most abundant and widely distributed throughout the body.

In all connective tissues except blood, the fibroblast cells secret fibres which are structural proteins (collagen/elastin).

The fibres provide strength, elasticity and flexibility to the tissue.

The matrix of connective tissues are made up of proteins and carbohydrates.

Connective tissues are classified into three types:

·        Loose connective tissue

·        Dense connective tissue

·        Specialised connective tissue

LOOSE CONNECTIVE TISSUE

In this tissue cells and fibres are loosely arranged.

It is further divided into two categories:

·        Areolar tissue

·        Adipose tissue

AREOLAR TISSUE

Areolar tissue present beneath the skin.

It provides support to epithelium.

It is the weekest and most abundant.

ADIPOSE TISSUE

Adipose tissue stores fat.

It is also known as fat tissue or fatty tissue that is mainly composed of fat cells called adipocytes.

Adipocyte contains large globules of fat known as lipid droplets.

Adipocytes are predominantly found around the organs in the abdominal cavity.

Adipose tissues are also located beneath the skin.

The excess of nutrients which are not used immediately are converted into fats and are stored in this tissue.

DENSE CONNECTIVE TISSUE

In this tissue cells and fibres are compactly or densely arranged.

It is further divided into two categories:

·        Dense regular tissues

·        Dense irregular tissues

Tendons and ligaments are examples of dense regular tissues. Tendons attach skeletal muscles to bones and ligaments attach one bone to another bone.

Dense irregular connective tissues provide covering to other structures such as pericardium (covering of heart), periosteum (covering of bone), and perichondrium (covering of cartilage).

SPECIALISED CONNECTIVE TISSUE

Skeletal connective tissues and fluid connective tissues come under specialised connective tissue.

Bone and cartilage are two types of skeletal connective tissue.

Blood and lymph are two types of fluid connective tissue.

BONE

Bones are hard and non-pliable.

Bones are rich in calcium salts and collagen fibres which give bone its strength.

Bone is the main tissue that provides structural frame to the body.

Bones support and protect other tissues and organs.

The bone cells (osteocytes) are present in the spaces called lacunae.

Red bone marrow is the site of production of blood cells.

CARTILAGE

Cartilage tissues are solid and pliable.

They are mainly of three types:

·        Hyaline cartilage

·        White fibrous cartilage

·        Elastic cartilage

HYALINE CARTILAGE

They are apparently fibreless.

They are weakest and most abundant.

Location: C shaped rings of trachea, end of long bones, larynx etc.

WHITE FIBROUS CARTILAGE

They contain collagen fibres. That’s why they are the strongest.

Location: vertebral column.

ELASTIC CARTILAGE

They contain yellow elastic fibres.

They are elastic in nature.

Examples of elastic cartilage: pinna of ear, tip of nose, epiglottis, Eustachian tube etc.

BLOOD

Blood is a fluid connective tissue containing blood cells (RBC, WBC, platelets) and plasma.

It is the main circulating fluid that helps in the transport of various substances.

MUSCLE TISSUE

Muscle cells are known as myofibres or muscle fibres.

Myofibres can contract and relax providing movement within the body (movement) and of the body (locomotion).

Muscle tissues are of three types:

·        Skeletal muscle tissue

·        Smooth muscle tissue

·        Cardiac muscle tissue

SKELETAL MUSCLE TISSUE

Skeletal muscle tissue is described as skeletal because it is closely attached to the skeletal bone.

They are also known as voluntary muscles (because you can move them whenever you want).

They are otherwise known as striated muscles because striations (stripes) can be seen under microscopic observation.

Skeletal muscle cells are cylindrical shaped and multinucleated (they have more than one nucleus).

They are found in muscles of limbs, eyelids, tongue, abdominal wall etc.

Skeletal muscle contraction is stimulated by motor nerve impulses.

SMOOTH MUSCLE

Smooth muscles are found in internal organs (visceral organs e.g. lungs, liver, pancreas, intestine etc.)

They are spindle shaped and uninucleated.

They are also known as involuntary muscle (you cannot move at will)

They are non-striated, as they do not have any striation.

CARDIAC MUSCLE

This muscle is found in the wall of heart.

They are branched and slightly striated.

They are also uninucleated.

NERVOUS TISSUE/NEURAL TISSUE

Two types of cells are found in nervous tissue:

·        Neurons (excitable cells)

·        Glial cells (non-excitable cells)

Neurons transmit signals/information.

Glial cells support the neurons.

Figure Credit: Yostnarani Sethy