Epithelial And Connective Tissues Question And Answers

Epithelial tissue

The epithelial tissue includes epithelium and glands.

Epithelium

Question 1. Define epithelium and list its characteristic features.
Answer.

The epithelium is a sheet of cells, adhered on its basal surface to the basement membrane. It is made up of single or more layers of cells. It lines the body surface, body cavities and interior of tubular organs. It also forms both exocrine and endocrine glands.

Epithelium Characteristic features

• Basal surface of epithelium rests on a basement membrane called basal lamina.
• There is minimal amount of intercellular substance.
• It is avascular and nourished by diffusion from underlying connective tissue capillaries.
• It is derived from all the three germ layers, e.g. epithelium of skin from ectoderm, epithelium of urinary tract from mesoderm and epithelium of GIT from endoderm.
• It has a high regeneration capacity.
• Its cells are held together by tight cell junctions.

Question 2. Classify various types of Epithelium.
Answer.

The epithelium is classified into three types:

Simple epithelium: It is made up of single layer of cells.

Pseudostratified epithelium: It is made up of single layer of cells of varying heights. The nuclei of cells lie at various levels giving a false appearance of many layers of cells, hence the name pseudostratified.

Compound/stratified epithelium: It is made up of multiple layers of cells.

Question 3. Classify simple Epithelium.
Answer.

Depending on the shape of the cells forming the epithelium, it is classified into three types:

Simple squamous epithelium: It is made up of flattened cells that are bound together in a mosaic-like pattern.

Simple cuboidal epithelium: It is made up of cube-like cells.

Simple columnar epithelium: It is made up of tall columnar cells.

Question 4. Briefly describe Simple Squamous Epithelium.
Answer.

It is formed by a single layer of flat cells. They have length and breadth, but hardly any thickness.

Simple Squamous Epithelium Characteristic features

• Cells are flat and arranged in single layer.
• On the surface view, the cells look polygonal and are arranged in a mosaic-like pattern.

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• Nucleus is flat, centrally located and shows bulging in profile view.
• Cells are bound to each other by tight junctions.
• It forms thin smooth membrane.

Simple Squamous Epithelium Functions

• Helps in active transport of nutrients and rapid diffusion of gases and water.
• Acts as a selective barrier.
• Facilitates movements of viscera in various serous cavities.

Simple Squamous Epithelium Sites

• Alveoli of lungs
• Serous membranes
• Parietal layer of Bowman’s capsule
• Endothelium of blood and lymph vessels
• Loop of Henle

Question 5. Write a short note on Simple Cuboidal Epithelium.
Answer.

It is formed by a single layer of cuboidal cells.

Simple Cuboidal Epithelium Characteristic features

• Cells are shaped like cubes
• Nucleus is round and centrally placed

Simple Cuboidal Epithelium Function

Mainly responsible for secretion

Simple Cuboidal Epithelium Sites

• Thyroid follicles
• Proximal convoluted tubule (PCT) of kidney
• Germinal epithelium of ovary

Question 6. Write a short note on simple columnar epithelium.
Answer.

It is formed by a single layer of columnar cells.

Simple Columnar Epithelium Characteristic features

• Cells are elongated and have more length than width. The length of cells is almost three times more than the width.
• Nucleus is elongated/oval and located near the base.

Simple Columnar Epithelium Functions

• Secretion
• Absorption
• Transport

Simple Columnar Epithelium Sites

• Stomach
• Large intestine
• Cervical canal of uterus

Question 7. Enumerate the various subtypes of the columnar epithelium.
Answer.

Depending on surface specializations (e.g. presence of microvilli and cilia), the subtypes of columnar epithelium are as follows:

• Columnar epithelium with brush border
• Columnar epithelium with striated border
• Columnar epithelium with ciliated border

The details are given in Table.

Types, Functions and Sites of Columnar Epithelium

Question 8. Write a short note on the Pseudostratified Epithelium.
Answer.

The pseudostratified epithelium is a simple columnar epithelium giving the false appearance of stratified epithelium.

Pseudostratified Epithelium Characteristic features

• Cells of variable height are arranged in single layer.
• Long cells reach the surface of lumen.
• Short cells do not reach the surface of lumen.
• Nuclei are basal.
• Nuclei of short and tall cells lie at dif erent levels giving a false appearance of many layers of cells.

Subtypes of pseudostratified epithelium

Pseudostratified, nonciliated columnar epithelium: The luminal surface of cells does not possess cilia, e.g. male urethra and ductus deferens.

Pseudostratified, ciliated columnar epithelium (respiratory epithelium): The luminal surface of cells possesses cilia, e.g. larynx (except vocal cords), trachea, bronchi, nasal cavity (except olfactory region) and paranasal air sinuses.

Question 9. Write a short note on the stratified squamous nonkeratinized epithelium.
Answer.

Stratified Squamous Nonkeratinized Epithelium Characteristic features

• Cells are arranged in many layers (i.e. multilayered epithelium).
• Deeper cells are columnar.
• Middle cells are cuboidal/polyhedral.
• Superficial cells are flat/squamous and do not show keratinization.

Stratified Squamous Nonkeratinized Epithelium Function

Protection (i.e. prevents wear and tear)

Stratified Squamous Nonkeratinized Epithelium Sites

• Oral cavity
• Tongue
• Oesophagus
• Vagina
• Anal canal
• Cornea

Question 10. Write a short note on the stratified squamous keratinized epithelium.
Answer.

Stratified Squamous Keratinized Epithelium Characteristic features

They are same as that of stratified squamous nonkeratinized epithelium except that the surface cells undergo keratinization (i.e. cells become dead, lose their nucleus and get filled with keratin).

Stratified Squamous Keratinized Epithelium Function

Protection (i.e. prevents wear and tear)

Stratified Squamous Keratinized Epithelium  Sites

• Skin
• Vestibule of nose
• External auditory meatus
• Lower part of anal canal

Question 11. Write a short note on the Transitional Epithelium.
Answer.

The transitional epithelium (urothelium) is special variety of stratified epithelium.

Transitional Epithelium Characteristic features

• Cells are arranged in five to six layers.
• Deeper cells are columnar.
• Middle cells are polygonal/pear shaped.
• Superficial cells are umbrella shaped and may show two nuclei.

Transitional Epithelium Special features

• The appearance of epithelium varies during relaxed and stretched states of the hollow organs and tubes which it lines.
• It undergoes two types of transitions.
  • Transition in the surface of cells. When the organ or tube is relaxed, they are umbrella shaped; but when the organ or the tube is distended, they become flattened.
  • Transition in the number of layers of cells. When the organ or the tube is relaxed, it is made up of five to six layers of cells; but when distended or stretched, it is made up of only two or three layers.

Transitional Epithelium Function

The surface membrane of superficial cells is thick and called cuticle. It forms effective urine–blood barrier (i.e. it prevents the absorption of toxic substances of urine into the blood).

Note: The luminal surface of transitional epithelium is covered by a layer of thick eosinophilic lamella of glycoprotein called cuticle which may account for its impermeability to urine into blood.

Transitional Epithelium Sites

Epithelial lining of urinary tract, e.g.:

• Major and minor calyces
• Renal pelvis
• Ureter
• Urinary bladder
• Proximal part of urethra

Question 12. Enumerate the various specializations of the free surface (apical surface) of the epithelial cells. List their characteristic features.
Answer.

The epithelial cells present three types of surface specializations on their free surface:

• Microvilli
• Stereocilia
• Cilia

The characteristic features of three types of surface specializations are given in Table.

Characteristic Features of Surface Specialization

Glands

Question 1. Define Gland.
Answer.

A gland is an organ that consists of specialized epithelial cells and produce secretions. The material secreted by gland is usually in liquid form such as enzyme, hormone, mucus and fat.

Classify glands according to the mode of their secretion.

According to the mode of secretion, the glands are classified into three types – merocrine, apocrine and holocrine. The details are as follows:

Merocrine: The secretion is released by exocytosis of the cell membrane in the form of secretory granules, e.g. most glands of the body such as salivary glands and pancreas.

Apocrine: The secretion first accumulates in the apical portion of the cell. Then the apical portion of the cell along with the secretion is pinched off and discharged. The pinched-off portion of the cell becomes a part of secretion, e.g. mammary glands.

Holocrine: In this type, the entire secretory cell along with the secretory product is shed. In this way, the entire cell becomes a part of the secretion, e.g. sebaceous glands.

Connective Tissue

Question 1. What is connective tissue? Enumerate its three essential components.
Answer.

The connective tissue as its name indicates binds or supports the other tissues of the body. It is found throughout the body. It consists of cells that are separated from each other by abundant extracellular matrix, which is secreted by the cells themselves. The matrix itself is made up of two components: (a) fibres and (b) ground substance.

Thus, the three essential components of connective tissue are as follows:

• Ground substance
• Fibres
• Cells

Question 2. Write a short note on the Loose Connective Tissue.
Answer.

Loose Connective Tissue Features

• It is most widely distributed connective tissue in the body.
• It consists of loosely woven network of all the three types of fibres (e.g. collagen, elastic and reticular).
• It contains almost all kinds of connective tissue cells (e.g. fat cells, fibroblasts, macrophages, plasma cells and mast cells).
• Its fibres and cells are embedded in semifluid ground substance.

Loose Connective Tissue Functions

• Provides support to epithelium.
• Acts as a packing material to keep various structures of the body in place.

Loose Connective Tissue Sites

• Underneath the epithelium
• In the superficial fascia
• Around muscles, blood vessels, nerves and viscera

Question 3. Enumerate the cells Present in the Connective Tissue.
Answer.

The cells present in the connective tissue are of two types: fixed and free cells. The fixed cells are long-lived cells and always remain in the connective tissue, while the free cells are short-lived wandering cells that are continuously replaced by the cells of the blood. The cells of connective tissue are given in the Table.

Types of Connective Tissue Cells

Question 4. Write a short note on lymphocytes.
Answer.

• The lymphocytes are type of white blood cells (WBCs) which circulate in the blood and present in large numbers in the lymphatic tissue, such as lymph nodes and spleen.
• Each lymphocyte possesses a large, spherical, dark-staining nucleus, which occupies most of the cell and is surrounded only by a thin rim of cytoplasm.

Types of lymphocytes

The lymphocytes develop from pluripotent stem cells in red bone marrow and then travel through blood into lymphoid tissue where they are activated and become immunocompetent, i.e. they respond to antigens.

Although lymphocytes originate from one source but functionally they are differentiated into two main types – B lymphocytes and T lymphocytes.

B lymphocytes: They are short lived. They are activated by an antigen. When activated by an antigen, they undergo active division and differentiate to form plasma cells. The plasma cells synthesize antibodies against antigen to destroy them. They are short lived and responsible for antibody-mediated (humoral) immunity.

T lymphocytes: They are activated in the thymus and become immunocompetent. They are long lived and are responsible for cell-mediated immunity.