Introduction To Histology
Question 1. What is histology?
Answer.
Histology is the study of the various tissues of the body at the microscopic level. Histology provides the structural and functional correlation of an organ or tissue – an important prerequisite to studying abnormal tissue (i.e. pathology).
Question 2. Define the terms histology and tissue.
Answer.
The term histology is derived from the Greek words ‘histos’ = tissue and ‘logos’ = a branch of study. The term tissue is derived from the French word ‘tissue’ = weave. The name was so given because when a section of tissue is seen under a microscope, it appears as if its various components are woven with each other.
Question 3. Enumerate the four basic types of tissues in the body and give their main functions.
Answer.
The four basic types of tissues in the body and their functions are given in Table.
Types and Functions of Basic Tissues
Question 4. Define a cell and describe its structure in brief.
Answer.
The cell is a basic structural unit of the living tissue.
Cell Structure Each cell consists of a cell membrane enclosing the cytoplasm with a nucleus within it.
Thus, three structural components of a cell are:
- Cell membrane/plasma membrane
- Cytoplasm
- Nucleus
The cell membrane (also called plasma membrane) forms the boundary of a cell and acts as a barrier between the cytoplasm and the external environment.
The cytoplasm is a fluid material that surrounds the nucleus and is itself surrounded by a cell membrane.
It consists of a cytoplasmic matrix with organelles and inclusions suspended in it. The various metabolic activities of the cell take place in the cytoplasm.
The nucleus is a membrane-bound structure, usually present in the centre of the cell. It contains various genes that control the development, structure and various activities of the cell.
The nuclei consist of a nuclear envelope, nuclear matrix, chromatin material and nucleolus.
Question 5. Enumerate the important organelles present in the cytoplasm.
Answer.
Organelles are components of a cell which have a specific function, essential for the survival and propagation of the cell. These are as follows:
- Mitochondria
- Ribosomes
- Golgi apparatus
- Endoplasmic reticulum
- Lysosomes
- Centrioles
- Microfilaments and microtubules
Question 6. Write a short note on mitochondria.
Answer.
- The mitochondria are sausage-shaped double membrane-bound cell organelles present in the cell cytoplasm.
- They are called powerhouses of the cell because they generate energy in the form of adenosine triphosphate (ATP).
- Each mitochondrion is made up of two parallel membranes, which are structurally similar to the plasma membrane.
Read And Learn More: Selective Anatomy Notes And Question And Answers
- The outer membrane is continuous.
- The inner membrane is arranged in a series of folds called cristae.
- The inner membrane encloses the mitochondrial matrix, which contains mitochondrial DNA.
Significance
- The metabolites of cells are utilized by the mitochondria and form high energy substance – the ATP. The ATP is then utilized for the activity of the cell.
- The number of mitochondria is very high in metabolically active cells, i.e. liver cells/hepatocytes contain about 2500 mitochondria per cell; in sperm, the mitochondria are clustered around its middle piece; and in ciliated cells, the mitochondria are located in the apical portion of the cell just below the cilia.
Question 7. Write a short note on the endoplasmic reticulum.
Answer.
The endoplasmic reticulum is a network of a series of flattened interconnecting membranous tubules and sacs.
It is of two types – smooth and rough.
- Smooth endoplasmic reticulum (SER) is devoid of ribosomal granules. It synthesizes lipids, glycogen and steroid hormones and is associated with the detoxification of drugs.
- The rough endoplasmic reticulum (RER) is studded with ribosomes. The ribosomes are the sites of synthesis of new proteins, e.g. the enzymes and hormones in the cell, that are exported from the parent cell to be used by other cells of the body.
Question 8. Write a short note on the Golgi apparatus/Golgi complex.
Answer.
The Golgi complex is a cytoplasmic organelle that is composed of stacks of closely packed flattened and curved membranous sacs. It is usually located in the juxtanuclear region. The Golgi complex has a convex and a concave surface.
- The first one faces towards the rough endoplasmic reticulum (RER) and nucleus, while the latter faces towards the cell membrane. The convex surface is called the forming face (cis-face) and the concave surface is called the maturing face (trans face).
- The Golgi apparatus is the site of processing and packaging of proteins synthesized by RER. The proteins move from RER to the Golgi apparatus, where they are first processed and then packaged into small, membrane-bound vesicles called secretory granules. These vesicles are stored, and when needed, move to the plasma membrane through which proteins are exported.
Functions of Golgi complex
- Processing and packaging of proteins
- Modification of proteins to form glycoproteins and lipoproteins
- Production of lysosomes with RER
- Involvement in membrane synthesis
Question 9. What are ribosomes? Give their functions.
Answer.
- The ribosomes are small granules made up of ribonucleic acid and ribosomal proteins.
- They are produced in the nucleolus and then migrate into the cytoplasm.
- They are attached in groups on the surface of the endoplasmic reticulum making it rough – the rough endoplasmic reticulum.
- They are also scattered singly (free ribosomes) or in groups in cytoplasm (polyribosomes).
Function Synthesis of new protein
Question 10. What is a centrosome?
Answer.
- The centrosome is a small, specialized spherical area of cytoplasm near the nucleus.
- It consists of two components: pericentriolar area and centrioles. The pericentriolar area is made up of a network of protein fibres.
- The centrioles are two rod-shaped hollow structures located in the centre of the pericentriolar area. The long axis of one centriole is at right angle to the other.
- Each centriole is a hollow cylindrical structure with its wall being made up of three groups of three microtubules (triplets) arranged in a circular fashion.
Functions
- The pericentriolar area forms the mitotic spindle during cell division.
- Centrioles take part in the formation of cilia and flagella.
Question 11. Enumerate the various cytoplasmic cell inclusions.
Answer.
The cytoplasmic inclusions are nonliving and nonfunctional entities of cell cytoplasm. They do not take part in the cell metabolism.
Various types of cytoplasmic inclusions:
- Glycogen
- Lipid
- Pigments
- Secretory granules
Question 12. Describe the cell cycle in brief.
Answer.
The cell cycle is defined as a period of time taken by a cell to divide into two daughter cells. In most of the adult somatic cells, the cell cycle takes 20–24 hours. It is divided into four phases of different durations.
The four phases of the cell cycle occur in sequence as G1→S→G2→M.
- G1 phase (12 hours): It is the crucial period of the cell cycle during which the cell determines to undergo cell division. It is the period of synthesis of various metabolites required for cell division.
- S phase (6 hours): It is the period of DNA synthesis. It is also called the synthetic phase.
- G2 phase (4 hours): It is the period during which the fidelity of DNA replication is checked, and errors, if any, are corrected.
- M phase (2 hours): It is the period during which the cell actually divides.
Question 13. Write a short note on mitosis.
Answer.
The mitosis is the most common type of cell division and occurs in almost all somatic cells. It results in two genetically identical cells.
Mitosis Features
- In this type of cell division, the diploid parent cell gives rise to two identical diploid daughter cells. The daughter cells also receive an equal amount of cytoplasm.
- In this type of cell division, DNA replication occurs prior to cell division, thus doubling the amount of DNA (46, 4N) and yielding double-stranded chromosomes.
- During mitosis, 23 pairs of chromosomes replicate. The two identical sets of chromosomes move to the opposite poles of the parent cell, which then divides into two daughter cells. Each daughter cell receives a set of 23 pairs of chromosomes (diploid number), i.e. 46, 2N.
Question 14. What are the various stages of mitotic cell division?
Answer.
Various stages of mitotic cell division:
- Prophase
- Metaphase
- Anaphase
- Telophase
The events occurring during these phases of mitotic division are given in Table.
Events Occurring During Mitotic Cell Division
Question 15. Describe the meiosis in brief without giving its stages.
Answer.
The meiosis is a special type of cell division that occurs only in germ cells. By meiotic division, the diploid germ cell gives rise to four haploid gametes. Meiosis involves two successive cell divisions: meiosis 1 and meiosis 2.
Prior to meiosis, the DNA (2N) replicates to form double the amount of DNA (4N), but the chromosome number remains diploid (2N).
Meiosis 1: During meiosis I, the DNA is reduced to a diploid (2N) amount but chromosome number is halved to haploid value (1N).
- Meiosis 1 is reductional division and heterotypical.
- Meiosis 2 During meiosis 2, the amount of DNA is reduced to haploid but the chromosome number remains haploid.
Meiosis 2: Meiosis 2 is similar to mitosis and homotypical. This means that when the ovum is fertilized with spermatozoon, the resultant zygote has 46 chromosomes called a diploid number. Thus, the child has some characteristics inherited from the mother and some from the father.
Question 16. Enumerate the differences between mitosis and meiosis.
Answer.
The differences between mitosis and meiosis are given in Table.
Differences Between Mitosis and Meiosis
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