TISSUES - Connective Tissue | Epithelial Tissue

Tissues

CHAPTER PREVIEW

An Introduction To Tissues

Epithelial Tissues and Glands 

• Definition of Epithelial Tissue

• Characteristics of Epithelial Tissue

• Classification / Types of Epithelial Tissue

• Simple Epithelium

• Stratified Epithelium 

• Glands (Glandular Epithelia) 

  * Exocrine Glands

  * Endocrine Glands

Connective Tissues

• Cartilage 

• Bone

• Joints

Muscular Tissue

• Definition 

• Classification

• Properties

• Functions

• Skeletal muscle

• Cardiac muscle

• Smooth muscle

Nervous Tissue

• Neuron

• Neuroglia / Glial cells

• Neurotransmitters

• Nerve fibres

• Receptors

• Reflexes

AN INTRODUCTION TO TISSUES

Learning Outcome

1. Define tissue

2. What is basic tissue 

3. What is tissue

4. Classify tissue with example

5. Classify tissue / Classify basic tissue

6. Mention the different types of tissue

7. Write short note on: Tissue 

8. What are the functions of tissue.

Questions

▸ Define tissue. / What is basic tissue? / What is tissue?

Definition of Tissue

Groups of specialized cells that are similar in structure and perform a common or related function are called tissues.

Questions

▸ Classify tissues. / Classify basic tissue.

Classification of Tissue

There are four basic types of tissue. They are:

• Epithelial tissue or epithelium

• Connective tissue 

• Muscular tissue, and

• Nervous tissue

Each tissue has subdivisions.

Question

▸ What are the functions of tissues?

Functions of tissues

1. Epithelial tissues have the following principal functions: 

• Absorption (e.g. the intestinal lining) 

• Secretion (e.g. parenchymal cells of glands)

2. Connective tissues have the following major functions: 

• Binding, support and protection of tissues/organs

• Transport 

• Insulation

• Storage of energy

3. Muscular tissues have the following main functions:

• Strong contraction 

• Body movements

4. Nervous tissue has the following main function: 

• Transmission of nerve impulses.

EPITHELIAL TISSUES AND GLANDS

Learning Outcome

1. Define and classify epithelial tissue with example 

2. Write down the classification of epithelial tissue

3. Classify epithelial tissue

4. Write down the characteristics of epithelial tissue

5. Give functions of epithelial tissue

6. Describe different types of epithelial tissue with diagram

7. What is gland

8. Classify glands with example 

9. What is ductless gland

10. Why some of the glands are called ductless glands

11. Name some ductless / endocrine glands 

12. Write down the difference between exocrine and endocrine glands

Question

▸ Define epithelial tissue.

Definition of Epithelial Tissue

Epithelial tissue is a tissue in which cells are arranged in continuous sheets, in either single or multiple layers, with little extracellular material between the cells. Epithelial tissues cover the body and lining cavities, hollow organs and tubes.

Characteristics of Epithelial Tissue

• Composed of aggregated polyhedral cells with very little extracellular matrix.

• The cells are either single or multiple layers which usually lie on a basement membrane.

• Avascular (absence of blood vessels).

Classification / Types of Epithelial Tissue

1. Covering (or lining)

2. Secretory (glandular)

• Covering or lining epithelial tissue may be:

(i) Simple (a single layer of cells) 

(ii) Pseudostratified, and

(iii) Stratified (two or more layers of cells)

Question

▸ Give functions of epithelial tissue.

Functions of Epithelial Tissue

1. Covering

2. Protection

3. Lubrication

4. Secretion

5. Absorption

6. Prevention of water loss

7. Distensibility

8. Facilitation of movement of the viscera

Question

▸ Describe various types of epithelial tissue with diagram.

Simple epithelium

• Simple epithelium consists of a single layer of identical cells resting on the basement

membrane.

• Where found: Simple epithelial tissues are characteristic of regions where secretion or absorption occurs, such as -

(i)  The lining of the digestive and urinary tracts 

(ii) The gas-exchange surfaces of the lungs.

Simple squamous epithelium

Structure: This is composed of a single. layer of flattened, tightly bound cells.

Distribution/Location

(i)   Lining of heart (endocardium) 

(ii)  Endothelial lining of blood and lymph vessels 

(iii) Mesothelium of the pleural and peritoneal cavities

(iv)  Lining of lung alveoli

(v)   Lining of some parts of renal tubules - loop of Henle

(vi)  Parietal layer of Bowman's capsule 

(vii) Lining of inner and middle ear.

Function:

(i)   Protection 

(ii)  Facilitates the movement of the viscera

(iii) Active transport by pinocytosis

(iv)  Gaseous exchange

(v)   Lubrication

Simple cuboidal epithelium

Distribution/Location:

(i)  Covering surface of ovaries (called 'germinal epithelium') 

(ii) Lining of kidney tubules 

(iii)  Lining of ducts of salivary glands and pancreas

Function:

(1) Protection

(ii) Secretion

(ii) Absorption

Simple columnar epithelium

Structure: This is formed by a single layer of cells, rectangular in shape, that often show cilia or microvilli and goblet cells.

Types:

(i)   Ciliated columnar epithelium, (in which cilia project from the apical surface of the columnar cells into the lumen).

(ii)  Non-ciliated (simple) columnar epithelium. (in which cell surface has no cilia). 

(iii) Simple columnar epithelium with micro-villi, projecting from the apical surface of the cells.

Distribution / Location:

(i)  Non-ciliated (simple) columnar epithelium Lining of digestive tract, gallbladder, and large ducts of some glands.

(ii) Ciliated columnar epithelium - Lining of uterine (fallopian) tubes, small bronchi of lungs.

Function:

(i)   Protection

(ii)  Secretion

(iii) Absorption 

(iv)  Lubrication

Pseudostratified columnar epithelium

Structure: This is composed of a single layer of ciliated, irregularly shaped cells that appears stratified. All of the cells connect the basement membrane.

Distribution / Location:

(i)  Lining of most of the nasal cavity, the trachea and bronchi. 

(ii) Lining of portions of the male reproductive tract.

Function :

(i)   Protection

(ii)  Secretion 

(iii) Transportation

Stratified epithelium

• Stratified epithelia consist of several layers of cells of various shapes.

• 4 types of stratified epithelial are - Stratified squamous, stratified cuboidal, stratified columnar, and transitional.

Stratified squamous epithelium

Structure: This is composed of a number of cells of different shapes; cells at the free edge are squamous.

Types:

(i) Non-keratinized stratified sqamous epithelium. This lacks keratin, cells of the outer layers are moistened.

Distribution / Location:

• Lining of the mouth, pharynx, oesophagus, vagina, and anal canal. 

• Conjunctiva of the eyes.

Functions:

• Protection 

• Secretion

(ii) Keratinized stratified squamous epithelium. The superficial cells are flattened (squamous), dead, loss nuclei, and filled with keratin.

Distribution / Location: Epidermis of the skin.

Function: Protection.

Stratified cuboidal epithelium 

Structure: This contains only two layers of cuboidal cells.

Distribution: Lining of the ducts of sweat glands.

Function: Absorption, secretion. 

Stratified columnar epithelium

Structure: Superficial cells are columnar, while the cells of the deeper layer are

polyhedral to cuboidal.

Distribution: Penile part of male urethra 

Function: Protection, secretion, absorption

Transitional epithelium

Structure: The superficial cells are rounded or dome-shaped. 

Distribution: Lining of the ureters and urinary bladder.

Function:

• Allows free distension and contraction. 

• Protection (by preventing reabsorption).

GLANDULAR EPITHELIUM (GLANDS)

Question

▸ What is gland? Classify glands with example / Define gland?

Definition of Gland

Classification of Glands

• According to how glands secrete their products: 

(i)   Exocrine glands-such as salivary glands.

(ii)  Endocrine glands, such as - thyroid gland.

(iii) Mixed (exocrine and endocrine) glands, such as- pancreas. 

• Structural classification of exocrine glands

(i) Merocrine.

Example -salivary glands, pancreas. 

(ii) Apocrine.

Example-mammary glands. 

(iii) Holocrine.

Example-sebaceous glands. 

• Classification of exocrine glands according to types of secretion:

(i)   Serous glands 

(ii)  Mucus glands

(iii) Mixed  (seromucus) glands

Exocrine Glands

Definition: Glands that discharge their secretion into the epithelial surface of the hollow organs through a duct, or tube, are called exocrine glands.

Question

▸ What is ductless gland? Why some of glands are named so.

Endocrine Glands /  Ductless Glands

Definition of Ductless Gland

• An endocrine gland is ductless gland. Endocrine glands lack ducts and release their secretions directly into the blood or lymph.

Question

▸ List the names of ductless glands.

Ductless glands include:

• Pituitary gland

• Thyroid gland 

• Parathyroid glands

• Adrenal (or suprarenal) glands 

• Pancreas (islets of Langerhans)

• Thymus

• Pineal gland

• Gonads (Ovaries and testes)

CONNECTIVE TISSUES

Learning Outcome

1. What is connective tissue? 

2. Give the classification and functions of connective tissue with example.

3. Write the functions of connective tissue.

Cartilage

1. Define cartilage.

2. Classify cartilage with their functions.

Bone

1. Define bone. 

2. Define and classify bone.

3. Mention the classification of bone

4. List the functions of bones / Write the functions of bone 

5. Write down the composition of bone.

6. Write the classification of bones morphologically 

7. What are the characteristics of long bone

8. Write short note on: Bone 

9. Write the difference between bone and cartilage

10. Define bone marrow

Joints

1. Define joint / What is joint

2. Define and classify joints / Classify joints with examples

3. Classify synovial joints with example

4. Write the functions of joint. 

5. What are the characteristics of a synovial joint

6. Write 5 important characteristics of synovial joint 

7. Draw and label synovial joint with its characters

8. Write short note on: Synovial joint 

9. Describe the movement of joint

Question

▸ What is connective tissue?

Definition of connective tissue

Connective tissue is one of the most abundant and widely distributed type of tissue in the body that binds together, supports, protects, insulates, separates, or transports different types of tissues and organs of the body.

Question

▸ Write the functions of connective tissue.

Functions of Connective Tissue

1. Supports and connects other tissues and cells together in organs

2. Protects organs 

3. Resists tearing

4. Stores energy reserves and acts as insulation

5. Transports materials within the body 

6. Provides defense to the body

Structural elements or components of connective tissues 

The major component of connective tissue is the extracellular matrix (ECM), consisting

protein fibres and ground substance 

There are also some specialized cells within the connective tissue.

Structural elements or components of connective tissues

1. Fibres of connective tissue:

• Collagen

• Reticular 

• Elastic

2. Cells of connective tissue: 

• Fibroblasts

• Adipocytes or fat cells

• Macrophages

• Mast cells 

• Plasma cells

• Leukocytes or white blood cells

Cells of Connective Tissue

LOOSE (AREOLAR) CONNECTIVE TISSUE

General organization:

It contains semisolid matrix with loosely organized cells and collagen and elastic fibres. The cells include - many fibrobalsts and some fat cells, mast cells and macrophages.

Distribution

• under the skin 

• between muscles

• surrounding blood vessels and nerves 

• in the alimentary canal (lamina propria)

• in glands supporting secretory cells.

DENSE CONNECTIVE TISSUE

It consists mostly of fibres and fewer cells than loose connective tissue.

Types:

1. Dense fibrous connective tissue (irregular and regular)

2. Elastic tissue

Dense (fibrous) irregular connective tissue

General organization :

Little ground substance; few cells (mostly fibroblasts); and randomly arranged much

collagen fibres.

Distribution:

• Dermis of skin

• Organ capsules

• Submucosa layer of digestive tract 

Function: Protects and supports organs; resists tearing.

Dense (fibrous) regular connective tissue

General organization:

Distribution:

• Ligaments

• Tendons

• Corneal stroma

• Aponeuroses

Function: Provides strong connections within musculoskeletal system; strong resistance to force

ELASTIC TISSUE

General organization:

The matrix consists mainly of masses of elastic fibres and few cells.

Distribution:

• Large blood vessel walls

• Trachea

• Bronchi

• Lungs

Function: Elastic tissue is capable of considerable extension and recoil, so it allows stretching or alteration of shape of some organs in the body

RETICULAR CONNECTIVE TISSUE (LYMPHOID TISSUE)

General organization:

Distribution:

• Bone marrow

• Liver

• Pancreas

• Adrenal glands 

• All lymphoid organs except the thymus

Function: Supports blood forming cells, many secretory cells, and lymphocytes in most lymphoid organs.

ADIPOSE TISSUE

Adipocytes are very large cells specialized for energy storage in lipid droplet(s) with triglycerides

Types: White and brown.

White Adipose Tissue

General structure:

White adipose tissue contains large adipocytes, ranging in diameter from 50 to 150 um. Each of these cells contain.

Distribution:

White adipose tissue is found in many organs throughout the body, such as kidneys, eyes, between muscles, under the skin and breasts.

Function: Fatty acids are released from white adipocytes when nutrients are needed.

Brown Adipose Tissue

General structure:

Contains adipocytes which are smaller than those of white fat. They contain primarily many small lipid droplets (multilocular) in cytoplasm with central nucleus 

Distribution: Newborn body.

Function: Maintains body temperature by producing heat on metabolism.

CARTILAGE

Question

▸ Define cartilage

Definition of cartilage

Cartilage is a tough, flexible form of connective tissue characterized by an extracellular matrix containing collagen and elastic fibres, and cells called chondrocytes.

Question

▸ Classify cartilage with examples.

Classification of cartilage 

1. Hyaline cartilage (Example: Articular cartilage)

2. Fibrous cartilage (Example: Intervertebral disc) 

3. Elastic cartilage (Example: Pinna of external ear)

Characteristic features of cartilage

• It is tough but flexible, provides a resilient rigidity to the structures it supports. 

• Cartilage always lacks blood vessels, lymphatics, and nerves.

Distribution and functions of cartilage

• Cartilage is found in areas that require support and movement, such as in skeleton and joints.

• Cartilage supports and shapes various structures, such as the auditory canal and intervertebral discs.

HYALINE CARTILAGE

• Hyaline cartilage is homogenous and glassy, smooth bluish-white tissue.

• It contains large numbers of collagen fibres, chondrocytes are in small groups within cell nests, and the matrix is solid and smooth.

• Perichondrium is usually present.

• Distributions:

(i)   Articular cartilage, (on the articular surfaces of long bones that form joints) 

(ii)  Costal cartilage (which attaches the rib to sternum) 

(iii) Part of the larynx, trachea and bronchi (i.e., respiratory tract) 

(iv)  Most of the embryonic skeleton is formed of hyaline cartilage before bone is formed

(v)   Epiphyseal plates (actively growing region near the end of long bones that provide for continued growth in length).

• Functions:

(i)  Provides smooth, low friction surfaces in joints 

(ii) Provides structural support for respiratory tract

ELASTIC CARTILAGE

• Elastic cartilage consists of numerous elastic fibres that make it extremely resilient and flexible. 

• The chondrocytes lie between the fibres.

• Cartilage is surrounded by perichondrium.

• Distribution

(i) External ear (pinna)

(ii) External acoustic meatus

(iii) Auditory tube 

(iv) Epiglottis and certain other laryngeal cartilage

• Functions:

(i) Provides flexible shape, and 

(ii) Supports soft tissues.

FIBROCARTILAGE

• It consists of type II collagen and large areas of dense connective tissue with type I collagen. 

• It also contains small chondrocytes in a hyaline matrix

• There is no perichondrium.

• Distributions

(i)   Intervertebral discs (pads between the bodies of the vertebrae of the spinal column)

(ii)  Semilunar cartilages (in knee joint) 

(iii) Symphysis pubis

(iv)  On the rim of the bony sockets of the hip and shoulder joints 

(v)   As ligaments joining bones

• Functions:

(i)  Provides cushioning, tensile strength. 

(ii) Provides resistance to tearing and compression.

BONE

Question

▸ Define and classify bone with examples.

Definition of bone

Bone is a specialized connective tissue composed of calcified extracellular matrix with three bone cells: osteoblasts, osteocytes, and osteoclasts; specialized to support the body and protect many internal organs.

Classification of bones

Bones can be classified in different ways as follows:

1. Histologically-

• Woven bone.    Examples => Developing and growing bones.

• Lamellar bone. Examples=> Adult bones of all normal region. 

2. By texures (macroscopically) -

• Compact bone.           Example=> Thick outer region (beneath the periosteum) of bones. 

• Cancellous/spongy bone. Example => Inner region of bones, adjacent to marrow cavities.

3. Morphologically (on the basis of shape and size) - 

(i) Long bones - These are considerably longer than they are wide. Examples => femur, tibia, fibula.

(ii) Short bones.  Examples => Carpal and tarsal bones.

(iii) Flat bones.  Examples => Sternum, ribs, scapula, parietal and frontal bones.

(iv) Irregular bones. Examples => Vertebrae, hip bone, and bones in the base of the skull.

(v) Pneumatic bones. Examples=> Maxilla, sphenoid, ethmoid.

(vi) Sesamoid bones. Example => Patella.

Question 

▸ Write down the composition of bone.

Composition of bone 

They contribute less than 2% of bone mass.

Two thirds of matrix is a mixture of calcium salts, mainly calcium phosphate. This inorganic matrix gives bone great hardness. The remaining third of matrix, called osteoid, is composed mainly of collagen fibres.

Bone cells

1 Osteoblasts: These are the bone-forming cells that secrete collagen and other constituents of bone tissue.

2. Osteocytes: These are the mature bone cells that monitor and maintain bone tissue. 

3. Osteoclasts: These cells are engaged in resorption of bone to maintain the optimum shape. This takes place at bone surfaces.

Microscopic Structure of Bone

Compact bone:

• It is made up of a large number of tube-shaped units called osteons (Haversian systems)

• Each osteon is made up of a central canal oriented parallel to the long axis of the bone. The central canal contains small blood vessels, lymphatics and nerves.

Perforating canals make links between neighbouring central canals.

Spongy bone:

• Microscopically the spongy bone is a framework formed from trabeculae.

• The trabeculae consist of a few lamellace and osteocytes interconnected by canaliculi 

Periosteum

Definition:

External surface of the bone is covered by a tissue layer, called periosteum. 

Periosteum is absent on articular surface of a bone. It is also absent from sesamoid bones (eg, patella).

Structure:

Periosteum is composed of two layers- 

• Outer fibrous layer. It is composed of collagen fibres and fibroblasts. 

• Inner cellular layer.

Functions of Periosteum: 

1. It gives attachment of muscle tendons and ligaments. 

2. It is concerned for blood supply of bone. 

3. It imparts shape to the bone and also protects the bone. 

4. It helps in subperiosteal bone growth and repair.

5. In injury, the cellular laye helps in union of fracture by osteoblasts.

Long bones

Question

▸ What are the characteristics of long bone

Characteristics (Parts) of long bones

• Long bones are longer then they are wide.

• Parts of a long bone: diaphysis, epiphyses, and metaphysis.

Epiphysis: This part is at the extreme ends of the bone where joints are formed.

Metaphysis: Part of the bone between the diaphysis and epiphysis - in a growing bone. 

• The diaphysis and epiphyses are separated by epiphyseal cartilage, which ossify when growth is completed.

• The diaphysis is composed of a tube of compact bone with a central medullary canal which is filled with yellow bone marrow.

• The epiphysis consists of an outer covering of compact bone with spongy (cancellous) bone inside 

• A long bone is almost completely covered by a double layered vascular membrane, called periosteum.

• One or more nutrient arteries supply blood to the shaft of the long bone. 

• The shaft is usually narrowest at the middle, and gradually expands at each end.

Question

► Enumerate the function of bone 

Write short note on: Function of bone

Functions of bones

• Provide shape and support: Bones provide a framework that supports the body and gives shape. For example, the rib cage supports the thoracic wall and gives body shape.

• Provide protection: Bones provide mechanical protection to vital organs.

• Provide sites for attachment of the muscles, tendons and ligaments.

• Movement. Bones allow movement of the body and its parts by forming joints that are moved by muscles. 

• Mineral storage. Bone is a reservoir for minerals, the most important of which are calcium phosphate. This is essential for maintenance of blood calcium levels.

• Blood cell formation (haemopoiesis). This occurs in red bone marrow present in the marrow cavities of certain bones.

OSTEOGENESIS / OSSIFICATION

Definition:

The process of bone formation is called ossification or osteogenesis.

Types of ossification: 

There are two processes of bone formation-

1. Intramembranous ossification, in which ossification takes place from membrane model of embryonic mesenchymal tissue.

2. Endochondral ossification, in which bones develop from a hyaline cartilage model. Example: long bones.

Question

► How long bones grow in length and width?

Growth of long bones 

Long bones are formed by endochondral ossification.

Ossification begins from the primary centres of ossification in the cartilage model. This accompanied by development of a bone collar at about 8 weeks of gestation. 

Later, the blood supply develops and bone tissue replaces cartilage as osteoblasts secrete bone matrix in the shaft.

After birth, long bones increase in length by interstitial growth of the epiphyseal plate (cartilage) and its replacement by bone. 

Appositional growth increases bone diameter / thickness.

BONE MARROW

Question

► Define bone marrow.

Definition

The medullary cavity of long bones and the spaces in the spongy bone contain the soft, gelatinous, highly vascular and cellular tissue known as bone marrow.

Types: Two-

• Red bone marrow

• Yellow bone marrow.

Functions of Bone Marrow 

1. Production and release of blood cells

2. Erythroclasia or destruction of R.B.C 

3. Store iron in the form of ferritin and hemosiderin

4. Play role in the inactivation of toxins or other toxic substances of the body

5. Perform immunological functions 

6. Bone forming cells are also formed in bone marrow

7. Perform several functions associated with connective tissue

JOINTS

Questions

► Define joint. / What is join? / Write the functions of joint.

Definition of joint

A joint is the site where two or more bones articulate or come together. 

Functions of joints

• Connect bones together.

• Allow the skeleton to move.

• Bear weight

Questions

► Classify joints with examples. 

► Classify synovial joints with examples of each.

Classification of joints

The two general types of joints are:

1. Synovial joints

2. Solid joints (fibrous and cartilaginous joints)

FIBROUS JOINTS

• Bones are united by fibrous tissue

• No joint cavity present

• Often permit no movement

• Three types:

(i)   Sutures (between bones of the skull)

(ii)  Gomphoses (between teeth and mandibular sockets)

(iii) Syndesmoses (middle radioulnar joint, inferior tibiofibular joint)

CARTILAGINOUS JOINTS

• Articulating bones are united by cartilage. 

• Lack of joint cavity.

• Two types:

(i) Synchondroses (Primary cartilaginous joints) 

Example - epiphyseal plates of long bones, joint between 1st rib and manubrium. 

(ii) Symphyses (Secondary cartilaginous joints)

Limited movement is allowed

Example - Intervertebral disc, pubic symphysis.

Question

► Write short note on: Synovial joint.

SYNOVIAL JOINTS

Definition:

Functionally they are known as diarthroses.

Question

► Draw and label synovial joint with its characteristics. 

► What are the characteristics of synovial joint. / Write 5 important characteristics of synovial joint

Characteristics of Synovial joint.

1. A layer of articular cartilage, usually hyaline cartilage, covers the articular surfaces of the opposing bone ends. 

2. Presence of a joint capsule consisting of an inner synovial membrane and an outer fibrous membrane.

3. The capsule encloses the joint cavity, which is a narrow cavity around the bone ends This is also called articular cavity). 

4. The joint cavity contains synovial fluid, secreted by synovial membranes. 

5. Presence of additional structures within the joint cavity, such as articular discs, fat pads, and miniscus.

6. Reinforcing ligaments: A number of bandlike ligaments that blend with the capsule provide additional stability at most synovial joints.

7. Varying degrees of movements are allowed at synovial joints.

                                                   [Ref.-Grays Anatomy for Students)

Question

► Describe the movement of joint

Movements of Synovial joints

Various type of movements take place at joints. The type of movement that occurs is determined by the type of joint and the associated muscles.

 Movements al synovial joints

MOVEMENT - DESCRIPTION

Flexion - Decrease in the angle of bones forming joint

Extension - Increase in the angle of bones forming joint

Dorsiflexion - Flexion of the foot at the ankle

Planter flexion - Extension of the foot at the ankle

Circumduction - Movement of the distal end of a bone in a circle while the proximal end forms the pivot joint

Pronation - Rotation of the forearm when the palm turned downward or posteriorly

Supination - Rotation of the forearm when the palm is turned upwards or anteriorly

Protraction - Movement of the mandible anteriorly

Retraction - Movement of the mandible posteriorly

MUSCLE TISSUE

Learning Outcome

1. Define muscle / What is muscle

2. Classify muscular tissue. Write down the differences among them

3. Classify muscle tissue 

4. Give the example of smooth muscle

5. Give the general properties of muscles

6. Mention the function of muscles

7. Give differences between skeletal, cardiac and smooth muscles

Questions

➤ Define muscle. / What is muscle?

Definition of muscle

Muscle is highly cellular, well vascularized tissue that is able to contract and relax, providing movement within the body and of the body itself.

Question

➤ Classify muscle tissue

Classification / Types of muscle tissue

• On the basis of morphologic and functional characteristics, muscle tissue can be classified into following three types:

1. Skeletal muscle (Striated muscle) 

2. Cardine muscle

3. Smooth muscle (Non-striated muscle)

• On the basis of control, muscles are classified into two types: 

1. Voluntary muscle, eg, skeletal muscle 

2. Involuntary muscle, eg, cardiac and smooth muscles.

Questions

➤ Give the general properties of muscles. / Mention the function of muscles.

Properties of muscles

1. Excitability is the ability of the muscle fibre to receive and respond to a stimulus. 

2. Conductivity is the ability of the muscle fibre to propagate a limited stimulus.

3. Contractility is the ability of the muscle fibre to shorten and thicken. 

4. Extensibility is the ability to be stretched or extended.

5. Elasticity is the ability of a muscle fibre to return to its resting length after contraction. 

6. Muscle tone is the continuous and partial contraction of the muscles with certain degree of tension

7. Rhythmicity is the ability to produce its own impulses regularly. Cardiac muscle has this propeny

Functions of muscles

• Producing movement. All movements of the body and its parts are a result of muscle contraction

• Maintaining posture. Skeletal muscles maintain posture. 

• Stabilizing joints. Muscles stabilize and strengthen the joints of the skeleton

• Generating heat. Muscles generate heat as they contract.

Question

➤ Shortly describe different types of muscle with example.

SKELETAL MUSCLE

• Skeletal muscle is composed of bundles of very long, cylindrical, multinucleated cells, termed muscle fibres, which show cross striations.

Organization skeletal muscle:

• Connective tissue sheaths -

o Epimysium is a dense connective tissue sheath that surrounds the entire muscle. 

o Endomysium - is a very thin, delicate layer of reticular fibres that surrounds the individual muscle fibre with the fascicle.

Structure of skeletal muscle fibres: 

• The cytoplasm of muscle cells, called sarcoplasm is packed with thread-like filaments. These are the contractile filaments (myofibrils). Each myofibril contains thick filaments (myosin) and thin filaments (actin).

• Each sarcomere is bounded at each end by a dense stripe called the 'Z' -line or 'Z' disk.

Question

➤ Describe cardiac muscle with diagram.

CARDIAC MUSCLE

This type of muscle tissue is found only in the wall of the heart.

Microscopic structure: 

• Cross striations are found in the cardiac muscle cells (fibres).

• This has significance in relation to the way the heart contracts.

Contraction is involuntary, vigorous, and rhythmic.

Question

➤ What are the properties of cardiac muscle? Describe any two of them.

Properties of cardiac muscle:

• Automaticity

• Conductivity

• Contractility

• Rhythmicity

• Excitability

Autorhythmicity:

It refers to the property of cardiac muscle which enables the heart to initiate its own impulse at constant rhythmical intervals. Because of this property the heart continues to beat.

Excitability:

It is the property by which the cardiac muscle responds to stimuli by producing an action potential.

SMOOTH MUSCLE

Microscopic structure:

• Fibres of smooth muscle are elongated, tapering, and non-striated cells

• Bundles of fibres form sheets of muscle. In most cases, two sheets of smooth muscle are present: longitudinal and circular layers of muscle fibres.

Distribution / Location:

• The blood vessels (arteries and veins)

• Parts of the respiratory tract, (from trachea to the alveolar ducts)

• Parts of urinary tract (ureters, urinary bladder)

• Digestive tract

• Ducts of glands

• Part of genital tract (uterus) 

• Larger lymphatic trunks

Functions of smooth muscle:

(1) Regulates the diameter of blood vessels (thereby regulating blood flow); and parts of the respiratory tract (thereby regulating inflow and outflow of air). 

(2) Propels contents of the alimentary tract, absorbs digested materials and eliminates unwanted substances.

(3) Regulates glomerular filtration, propels urine in the ureter

(4) Expels urine from the urinary bladder. 

(5) Expels content of uterus.

NERVE TISSUE

Learning Outcome

1. Define neuron / What is neuron

2. Draw and label neuron. Write down the functions of neuron 

3. What is the functional unit of nervous system? Draw and label the functional unit of nervous system

4. Describe a neuron with diagram 

5. What are the parts of neuron

6. List / Give the differences between axon and dendrite 

7. Define and classify neuron. / Classify neuron with diagram

8. Write short note on: Neuron

9. Write down the function of neuron

10. What is synapse? / Define synapse

Questions

➤ We short note on: Neuron

➤ What is neuron? / What are the parts of neuron?

➤ Define neuron. Draw and label a neuron / Define neuron with diagram

➤ Describe a neuron with diagram

➤ What is functional unit of nervous system? Draw and label the functional unit of nervous system.

Definition of neuron

Parts of Neuron

Most neurons consist of three main parts 

(1) Cell body, or perikaryon

(2) Dendrites 

(3) Axon

Dendrites and axon form the processes of neuron.

Cell Body (Perikaryon)

• The cell body is the part of neuron that contains the nucleus and surrounding cytoplasm. The nucleus is large and spherical, euchromatic (pale-staining) with a prominent nucleolus. The nucleus is surrounded by Nissl substance or Nissl bodies and neurofibrils.

• In the central nervous system (CNS), most neuronal perikarya occur in the gray matter, with axons concentrated in the white matter.

Dendrites

• The dendrites are usually short and branched processes of neuron, extending from the perikaryon. Dendrite divides like tree branches.

• They are specialized to receive stimuli from other neurons at unique site called synapses.

• They transmit impulses towards the perikaryon.

Axon

• The axon is a single long process of neuron.

• The cytoplasm of an axon, called axoplasm, is surrounded by a plasma membrane known as axolemma

• Axons end at synapses specialized to generate and conduct nerve impulses to other cells (nerve, muscle and gland cells).

Question

➤ Write down the function of neuron.

Functions of Neuron

1. Conduction of nerve impulse - Neurons communicate "messages of stimulation" in the form of nerve impulse (action potential)

2. Collection and integration of nerve impulse from various sources.

3. Transmission of propagated nerve impulses. 

4. Motor neurons are able to stimulate muscle cell throughout the body, including the cardiac muscle, diaphragm, intestines, urinary bladder and glands.

Questions

➤ Classify neuron. / Classify neuron with diagram.

Classification of Neuron

1. According to the number of processes extending from the cell body: 

• Bipolar neurons, with one dendrite and one axon.

2. According to function: 

• Sensory or afferent neurons, which receive stimuli from periphery to central nervous system. 

• Motor or efferent neurons, which send impulses to effector organs such as muscle

fibres and glands. 

3. According to the length of axon:

NEUROGLIA / GLIAL CELLS

Types of neuroglia

There are six types of neuroglia - four in the central nervous system (CNS) and two in th peripheral nervous system (PNS).

Neuroglia in the CNS:

Neuroglia in the PNS:

The two types of PNS neuroglia are - satellite cells and Schwann cells.

SYNAPSE

Questions

➤ What is synapse?/ Define synapse. / Write short note on: synapse.

➤ Define, draw and label a synapse

Definition:

Synapse is the junction between two neurons where one neuron ends and other neuron begins. It is the functional continuity between two neurons.

Structure:

Each synapse has three major components:

1. Presynaptic knob of the presynaptic neuron. The knob contains synaptic vesicles that are filled with neurotransmitters. 

2. Synaptic cleft, a narrow space between pre and postsynaptic membrane.

3. Postsynaptic membrane of the postsynaptic neuron or target cell. It contains highly selective receptors for neurotransmitters.

Classification of synapse 

1. Anatomical classification: axosomatic, axodendritic, axoaxonic. 

2. Functional classification: Electrical, and chemical.

Question

➤ Give the functions of synapse.

Functions of synapse

The main function of the synapse is to transmit the nerve impulses, i.e., action potential from one neuron to another. However, some of the synapses (called excitatory synapses) excite the transmission; on the other hand, some (called inhibitory synapses) inhibit the transmission of impulses.

Properties of synapse

• Synaptic response 

• Synaptic delay

• Inhibition

• Synaptic block

• Occlusion

• One way conduction

• Fatigue

• Convergence and divergence of nerve impulse

• Summation

NEUROTRANSMITTERS

Definition:

Important neurotransmitters:

• Acetylcholine 

• Histamine

• Noradrenaline

• Gamma-aminobutyric acid (GABA)

• Dopamine 

• Substance P

• Serotonin

• Nitric oxide

NERVE FIBRES

Definition:

Axons enclosed within sheaths of glial cells are called nerve fibres.

Classification of Nerve Fibres: 

1. Structurally-

(i)  Myelinated nerve fibres

(ii) Non-myelinated nerve fibres

2. On the basis of distribution - 

(i)  Somatic nerve fibres, which supply the skeletal muscles of the body. 

(ii) Visceral or autonomic nerve fibres, which supply the various internal organs of the body

3. On the basis of origin - 

(i)  Cranial nerve fibres

(ii) Spinal nerve fibres

4. Functionally-

(i)  Sensory nerve fibres (afferent nerve fibres) 

(ii) Motor nerve fibres (efferent nerve fibres)

Properties of Nerve Fibres

(i)   Excitability

(ii)  Conductivity

(iii) Refractory period

(iv)  Summation

(v)   Adaptation

(vi)  Infatigability

(vii) All-or-none law

RECEPTORS

Question

➤ We short note on: receptors

Definition: Receptors are the specialized tissues which can be stimulated by any change in external or internal environment.

Classification of receptors: Generally, the receptors are classified into two types-

1. Exteroceptors - which give response to external stimuli like touch, pain, temperature and pressure.

2. Interoceptors - which give response to stimuli arising from within the body. 

Example: baroreceptors of carotid and aortic bodies.

Types of sensory receptors

There are five basic types of sensory receptors -

1. Mechanoreceptors (or cutaneous receptors), e.g., free nerve endings, musele spindle, Golgi tendon receptors, baroreceptors of carotid sinuses and aorta etc. 

2. Thermoreceptors, e.g., cold receptor, warm receptor.

3. Chemoreceptors, e.g., free nerve endings.

4. Electromagnetic receptors, e.g., rods and cones.

5. Chemoreceptors, e.g., receptors of taste buds, olfactory epithelium etc.

Properties of receptors

• Excitability

• Adaptation

• Specificity

• Intensity discrimination

• Doctrine of specific nerve energies

• Projection.

REFLEXES

Question

➤ Describe a reflex. Draw and label a reflex arc.

Definition: Involuntary motor response due to any sensory stimulus is called reflex. 

Examples - Knee jerk, ankle jerk, stretch reflex etc.

Classification of Reflex:

1. Unconditioned (in born) reflexes -

• Superficial reflexes: e.g., planter abdominal, corneal etc. 

• Deep reflexes: e.g., knee jerk, ankle jerk etc.

• Visceral reflexes: e.g., papillary reflex, micturition reflex etc.

2. Conditioned (acquired) reflexes-e.g., writing reflex.

Reflex arc

The complete pathway of a reflex action is called reflex arc. It consists of the following parts: 

1. Afferent limb - consists of (i) receptor, and (ii) afferent nerve.

2. Centre

3. Efferent limb-consists of (i) efferent nerve, and (ii) an effector organ, e.g. muscle.

4. Synapse

CHAPTER SUMMARY

TISSUE AND ITS TYPES

• Histology is the study of tissues.

EPITHELIAL TUSSUE

• A basement membrane attaches epithelia to underlying connective tissue. 

• An epithelium consists mostly of cells with little extracellular material between the cells. It is avascular, but has nerve supply.

• The basement membrane of all epithelia is a thin extracellular layer of specialized proteins, which attaches epithelia to underlying connective tissues.

The basement membrane has two part: a basal lamina and a reticular lamina.

Morphological types of epithelia:

• An epithelium in which the basement membrane has one cell layer is simple; the cells of different simple epithelia range widely in height, from very thin or squamous, to roughly cuboidal, to very tall or columnar

• Simple squamous epithelium is found in parts of the body where filtration or diffusion occur.

• Simple cuboidal epithelium is involved in secretion and absorption.

• Specialized cells containing microvilli perform absorption. 

• Ciliated simple columnar epithelium is found in a few portions of the upper respiratory tract, where it moves foreign particles trapped in mucus out of the respiratory tract.

• Pseudostratified epithelia are thick and appear to have several cell layers; all cells attach to the basement membrane but not all extend to the free epithelial surface. 

Pseudostratified ciliated columnar epithelium is found in most of the upper respiratory tract. Nonciliated pseudostratified columnar epithelium lines the ducts of many glands, the epididymis, and part of the male urethra.

• Transitional epithelium, found only in the lining of the urinary system, is stratified, with large rounded surface cells protective against urine.

Glands / Glandular epithelium:

• A gland is a single or a group of epithelial cells that produce specialized secretions. 

• Exocrine glands have epithelial ducts carrying secretions to specific sites. The ducts of simple glands are unbranched and those of compound glands are branched. 

CONNECTIVE TISSUE

• Connective tissue is specialized to physically support and connect other tissues and maintain the water required for metabolic diffusion to and from cells.

• All connective tissues consist primarily of extracellular material rather than cells. 

• The extracellular matrix (ECM) of connective tissue proper usually consists of both large protein fibres and nonfibrous ground substance.

• Cells of connective tissue proper include fibroblasts, fibrocytes, macrophages, adipocytes, mast cells, plasma cells, lymphocytes and mesenchymal cells.

• The three types of fibres in connective tissue are collagen fibres, reticular fibres, and elastic fibres. 

• Types of connective tissue: Connective tissue proper is classified as loose or dense according to the amount of collagen and ground substance present.

• Loose connective tissue (or areolar tissue) has relatively more ground substance than collagen. 

• Dense irregular connective tissue is filled primarily with bundles of type I collagen fibres and some elastic fibres. It is found in the fascia, the dermis of skin, and membrane capsules around organs.

• Reticular tissue or lymphoid tissue consists of delicate network of type III collagen (reticulin). It is abundant in certain lymphoid organs.

• Mucoid tissue is an embryonic form of gel-like connective tissue with few cells, resembling mesenchyme. It is best seen around blood vessels in the umbilical cord. 

ADIPOSE TISSUE

• The defining cells of adipose tissue are adipocytes or fat cells. They are very large cells specialized for energy storage in lipid droplet(s) with triglycerides.

• White adipose tissue is found in many organs throughout the body. They typically form about 20% of the body weight in adults. Each adipocytes of white fat contain primarily one large lipid droplet (they are unilocular).

• Brown adipose tissue comprises up to 5% of the newborn body weight but smaller amounts in adults. Adipocytes of brown fat are typically smaller than those of white fat and contain primarily many small lipid droplets (they are multilocular)

CARTILAGE

• Cartilage is a tough, resilient type of connective tissue that structurally supports certain soft tissues, e.g., the respiratory tract, joints etc.

• Cartilage consists of cells (chondrocytes) and mainly of a flexible mass of extracellular matrix (ECM) 

• Hyaline cartilage is found at the ends of bones, in the nose, and in the respiratory structures.

BONE

Definition:

• Bone is a type of connective tissue with a calcified extracellular matrix (ECM), specialized to suppon the body, protect many internal organs and act as the body's Ca++ reservoir.

Histology:

• Bone tissue consists of cells surrounded by large amounts of extracellular matrix.

• Major cells in bone tissue are: osteoblasts, osteocytes, and osteoclasts.

• Within each osteon osteocytic lacunae, with canaliculi radiating through the lamellae, which allow all cells to communicate with the central canal.

• Spongy bone tissue does not contain osteons. It consists of trabeculae surrounding many red bore marrow-filled spaces. 

• External surface of bone is covered by a dense connective tissue layer called periosteum.

Types of Bone:

• Macroscopically-Compact bone, and cancellous (or spongy) bone. 

• Histologically-Lamellar bone, and woven bone (immature bone).

• Developmentally-Membranous, and cartilaginous.

• Morphologically-Long bones, short bones, flat bones, irregular bones, pneumatic bones, sesamoid bones.

Parts of long bone:

• A long bone has a diaphysis or shaft and two epiphyses or ends.

• In between the diaphysis and epiphyses there are epiphyseal plates.

Ossification (Osteogenesis):

• Bone forms by a process called ossification (osteogenesis). The two types of ossification are Intramembranous and endochondral ossification.

JOINTS

Classification of joints

• The two general types of joints are:

1. Synovial joints (diarthroses)

2. Synarthroses (Solid joints): Fibrous and cartilaginous joints.

• Freely mobile joints are called synovial joints or diarthroses. The joint cavity is enclosed within a tough, fibrous articular capsule.

• Major subtypes of synarthroses are: Synostoses (e.g., sutures), syndesmoses (e.g., inferior tibiofibular joint), symphyses (e.g., pubic symphyses).

• Movements at synovial joints: Flexion-extension, lateral flexion, hyperextension, abduction- adduction, circumduction, elevation-depression, protraction-retraction, inversion-eversion, dorsiflexion-plantar flexion, supination-pronation, and opposition. 

• Each intervertebral disc consists mainly of a thick outer layer of fibrocartilage forming annulus fibrosis, and an inner gel-like core, the nucleus pulposus.

MUSCLE TISSUE

• Muscular tissue consists of fibres that are specialized for contraction. 

• There are three major types of muscle: (1) skeletal or striated muscle, (ii) cardiac muscle, and (iii) smooth or visceral muscle.

• Skeletal muscle: Skeletal muscle cells or fibres are very long, multinucleated fibres, cylindrically shaped and with diameters up to 100 m. This muscle is striated and voluntary

• Smooth muscle: Smooth muscle fibres are individual small, fusiform (tapering) cells. This muscle is non-striated and involuntary; found in the walls of hollow internal structures (blood vessels and viscera)

NERVOUS TISSUE

• The nervous system consists of nerve cells (neurons) and supporting cells called glial cells (neuroglia). 

• Glial cells: they support neurons in many ways, consists of six major types-oligodendrocytes, astrocytes, ependymal cells, microglia, Schwann cells (neurolemmocytes), and satellite cells. 

• Synapse is the junction between two neurons where one neuron ends and other neuron begins. It is the functional continuity between two neurons. 

• Examples: acetylcholine, dopamine, noradrenaline etc.

• Nerve fibres: Axons enclosed within sheaths of glial cells are called nerve fibres. 

• Receptors are the specialized tissues which can be stimulated by any change in external or internal environment.

• Reflex: Involuntary motor response due to any sensory stimulus is called reflex. 

Examples-Knee jerk, ankle jerk, stretch reflex etc.

• Reflex arc: The complete pathway of a reflex action is called reflex arc.