The Cell in Health and Disease
Question 1. Write a note on growth factors and their receptors.
Answer:
Role of growth factors: It stimulates the activity of genes that are required for cell growth and cell division.
Important growth factors and their role in Cancers
1. Epidermal growth factor (EGF) and transforming growth factor (TGF)
- Two factors share a common receptor (EGFR)
- EGFR1 mutations are seen in cancers of the lung, head, neck, and breast, glioblastomas
- ERBB2 receptor (HER2 or HER2/neu) is overexpressed in breast cancer.
Read and Learn More Preparatory Manual of Pathology Question and Answers
2. Hepatocyte growth factor (HGF) or scatter factor (SF)
- c-MET—receptor for HGF is mutated in renal and thyroid papillary carcinoma.
3. Platelet-derived growth factor (PDGF)
- Exert their effects by binding to two cell surface receptors, PDGFR- α and PDGFR-β
- Stored in platelet granules
- Stimulates hepatic stellate cells in the liver induces fibrosis and stimulates wound contraction.
4. Vascular endothelial growth factor (VEGF)
Includes VEGA/VEGF, VEGF-B, VEGF-C, VEGGED, and PIG (placental growth factor)
Signal through three tyrosine kinase receptors: VEGFR-1, VEGFR-2, and VEGFR-3
- VEGFR-1 plays a role in inflammation
- VEGFR-2 has vasculogenic and angiogenic properties
- VEGFR-3 induces the production of lymphatic vessels (lymph angiogenesis).
5. Transforming growth factor β(TGF-β)
- It is a potent fibrogenic agent
- Enhances the production of collagen, fibronectin, and proteoglycans
- Inhibits collagen degradation by decreasing matrix proteases and increasing tissue inhibitors of metalloproteases (TIMPs), thus leading to the development of fibrosis
High TGF- expression is seen in hypertrophic scars, systemic sclerosis, and Marian syndrome.
Question 2. Write a short note on fibronectin.
Answer:
Adhesive glycoproteins and adhesion receptors
- Involved in cell-to-cell adhesion, and adherence of cells to the extracellular matrix (ECM).
- Includes fibronectin (the major component of the interstitial ECM), laminin (a major constituent of the basement membrane), and integrins (cell adhesion molecules).
Fibronectin
- Disulfide-linked heterodimer
- Synthesized by fibroblasts, monocytes, and endothelium
- Can bind to extracellular matrix components like collagen, fibrin, heparin, and proteoglycans
- Helps in the healing of wounds, which plays a role in ECM deposition, angiogenesis, and reepithelialization.
Question 3. Discuss stem cells in detail.
Answer:
Stem cells: These give rise to various differentiated tissues.
Two important properties of stem cells
- Self-renewal property: This permits the stem cells to maintain their numbers.
- Asymmetric division: One daughter cell population enters a differentiation pathway and gives rise to mature cells, while the other population remains undifferentiated.
Types
1. Embryonic stem cells:
- Present in the inner cell mass of a blastocyst
- Have limitless replicative potential and can give rise to any cell, hence are called totipotent
- Can give rise to specialized cells of all three germ cell layers.
2. Tissue stem cells (adult stem cells):
- Present in stem cell niches
- Can produce cells, that are normal constituents of parent tissue
- For example, hematopoietic stem cells, and mesenchymal stem cells.
Examples of stem cell niches
- In skin: Located in a bulge area of the hair follicle, in sebaceous glands, and in the lower layer of the epidermis.
- Small intestine: Located near the base of the crypt, above Paneth cells.
- Liver: Liver stem cells (oval cells) are located in the canals of Hering (structures that connect bile ductules to parenchymal hepatocytes).
- Cornea: Found at the limbus.
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