adaptations.pdf

Cellular adaptaion  control of cell growth Review of the cell cycle Cellular adaptaion Increased workload = Adaptation Stress = reversible injury Increased stress = Irreversible injury  Control of cell growth Cells in a multicellular organism communicate through...

Cellular adaptaion  control of cell growth Review of the cell cycle Cellular adaptaion Increased workload = Adaptation Stress = reversible injury Increased stress = Irreversible injury  Control of cell growth Cells in a multicellular organism communicate through chemical signals Hormones act over a long range Local mediators are secreted into the local environment Some cells communicate through direct cell-cell contact  Control of cell growth Cells are stimulated when extra cellular signalling molecules bind to a receptor Each receptor recognises a specific protein (ligand) Receptors act as transducers that convert the signal from one physical form to another.  Signalling molecules Most signalling molecules cannot pass through the cell membrane – Their receptors are in the cell membrane Small hydrophobic signal molecules can diffuse directly into the cell cytoplasm – Their receptors are cytoplasmic or nuclear  Signalling molecules Hormones – Insulin, – Cortisol – etc Local mediators – Epidermal Growth Factor (EGF), – Platelet Derived Growth Factor (PDGF) – Fibroblast Growth Factor (FGF) – TGFβ – Cytokines, e.g. Interferons, Tumour necrosis factor (TNF)  Receptors There are three main classes of receptors…. Ion-channel-linked receptors G-protein-linked receptors Enzyme-linked receptors  Receptors Ion channel-linked receptors are important in neural signalling G-protein and enzyme linked receptors respond by activating cascades of intracellular signals These signals alter the behaviour of the cell  Cell signalling and proliferation cells proliferate when stimulated by growth factors These bind mainly to receptor tyrosine kinases These signalling pathways override the normal brakes on proliferation These brakes are part of the cell cycle control system This ensures that cells divide only under appropriate circumstances  Phases of the cell cycle S phase – DNA replicates M phase – nucleus divides (mitosis) and cytoplasm divides (cytokinesis) G1 phase – gap between M and S phase G2 phase – between S and M phase  According to the cell cycle the cell of the body divided in to 1 2 3 And this affect the adaptive response Labile cells Skin, mucous membrane Stable cells Liver Pancreas Kindey Permanenet cells Neurons, Cardiac and skeletal muscles. Adaptations in Nature Cellular adpatations Cellular Adaptation – Hypertrophy – Hyperplasia – Atrophy – Metaplasia Hypertrophy An increase in cell size, and resultant increase in organ size Increase in cell size Causes of Hypertrophy Physiological Need of the body Pathological Hypertrophy Left Ventricular Hypertrophy … due to Hypertension Hypertrophy of smooth muscles Pyloric stenosis , Compensatory hypertrophy Kidney Gross changes : Enlarged & Heavy organ, Ultra structural level Increased DNA & RNA , protein, cell organelles synthesis  Hyperplasia Hyperplasia Hyperplasia Hyperplasia Hyperplasia Hyperplasia is … Increased Number of cells  Physiological hyperplasia Hormonal induced : Breast during lactation, Uterus in pregnancy, Prostate in old men Compensatory hyperplasia Liver cells, Skin  Pathological Endometrial hyperplasia Skin warts Wound healing (excessive) Atrophy Reduced number & size of cells.  Atrophy: causes Reduced workload Loss of innervation Reduced blood supply Inadequate nutrition Loss of endocrine stimulation Ageing Physiological Lymphoid tissue , Thymus Breast - after menopause 80 yrs old 30 yrs old Pathological Atrophy Starvation Ischemic Disuse Neuropathic – Polio Endocrine Pressure Gross : Small , Shrunken organ Metaplasia Metaplasia  Metaplasia One mature adult tissue is replaced by another. Ex: Smoking: Replacement of pseudo‑stratified columnar epithelium of the lungs by stratified squamous epithelium. Metaplasia may also be seen within mesenchymal tissue. Soft tissues that undergo trauma may be replaced by mature bone.  Hypoplasia Incomplete development of an organ with reduced cell numbers  Increased workload = Adaptation Hypertrophy Metaplasia Hyperplasia Hyperplasia Atrophy Hyperplasia Cell Types  Summary Cells communicate through signalling pathways Signalling pathways influence the cell cycle control system This determines a cells ability to divide A cells replicative capacity influences its adaptive responses to changes in the tissue environment  Th ank yuoooooo