Cell Physiology Cell - Basic Unit Of The Body - Maintains Homeostasis Homeostasis Structure Of The Cell

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Cell Physiology

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Cell - Basic unit of the body - Maintains Homeostasis

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If endocrine system fails, you are not capable of procreation Purely involuntary

Structure of the Cell

Homeostasis -

maintains the constancy of the extracellular components Maintains the normal values of all the substances in the extracellular

**Extracellular is the internal environment (Body Fluids, environment of the cell) Regulating systems 1. Nervous system Made up mostly of neurons Produce Nerve impulses – Action Potentials Rapid Onset Short Duration Localized – specific part or close to part of stimulation Muscles and Secretory Cells Voluntary (Skeletal Muscles) Involuntary (Smooth, Cardiac Cells, Secretory Cells) Mostly affects Mechanical or Secretory mechanism of the body

Golgi Apparatus – responsible for packaging of products of cellular activity Mitochondria – powerhouse PLASMA MEMBRANE Needed by Cell – inward Not Needed by the cell – outward -

composed of Lipids and Proteins

2. Endocrine system -

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Hormones Hormonal Control/ Humoral Slow/Delayed Onset Diffused – several parts of the body is affected Growth Hormone (slow) Long Duration Mostly affects all cells capable of metabolic activities Primary Role of Endocrine System = Regulate/ Control metabolic activities of the body/ Major regulating system responsible of cellular metabolism Reproduction = dependent mostly on the normal functioning of the Endocrine System

Polar Ends § Outer and inner surfaces of the cell membrane § Hydrophilic, Lipophobic

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Non Polar - Middle part of the cell membrane - Hydrophobic, Lipophilic Lipid Soluble Substances - can easily pass through the lipid bilayer - Can easily Penetrate Water Soluble Particles – Utilized membrane lined by proteins – Proteins can function as channels or barriers Lipids - Are amphipathic - Can combine with Water and Fats

2. Regulates cellular transport (Surface Antigens) – cell or non cell 3. Site of signal transduction – cell communication; presence of receptors 4. Acts as an anchor for structural proteins 5. Providing cellular stability 6. Anchors one cell to neighboring cells 7. Maintains Cell Shape Absorption – intake/ inwards Secretion – Releases needed substances Excretion – Releases not needed substances **Cell Membrane is not a solid membrane, it is a functioning membrane

Cholesterol - present in the inner bilayer Semi Permeable Membrane – Solvent Selectively Permeable – Solvent and a selection in the transport of solutes/ Human Cell Membrane

IONS

K+, Cl-

Tight Junctions = Zona Occludens Desmosomes = Zona Adherens § Mostly for Anchoring only

Aquaphorins – water channel/ water is easily transported **You can change the membrane permeability, for example, glucose, if needed by cell, you can change the permeability and allow the membrane to transport glucose – Insulin (Hormone) – Ligand Gating Mechanism Functions of the cell membrane: 1. Maintains the composition of ICF & ECF

 

Gap Junctions = Conexones § Anchoring § Can also serve as an area of communication/ transport of substances Basal Region -Has Hemidesmosomes which anchor cell to the basal region **If there are many tight junctions, it is hard to transport **There are many tight junctions in the cerebral capillaries Activities at the different parts of the cell:

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Apex – Release/Secretion of Agent/ Absorption Lateral – Cell Contact, - Cell Adhesion - Communication Base – Release if Absorbed substances - Generation of Ion Gradients (can eventually alter the electrical activity of the cells

- Source of enzymes - Skeletal framework - Stability

Composition of the cell membrane: 1. Lipids = 50-60% 2. Proteins = 40-50% 3. Carbohydrates - Minute amounts - Combined with a protein or a lipid (glycoprotein/glycolipid) - No pure Carbohydrate - It would be easier to recognize non cell antigen - Cell wall of the bacteria have pure carbohydrates Composition: A. LIPIDS (50-6O%) * Phospholipids = phosphatidylcholine, phosphatidylserine, phosphatidylethonolamine, phosphatidylinositol * Cholesterol = “moderator molecule” - provides mechanical stability as well as flexibility - makes the membrane less permeable to water - prevents lipid crystallization * Glycolipids B. B. PROTEINS (40-50%) 1. Integral Proteins/ Transmembrane Proteins § Amphipathic § Mostly utilized as channels, pores, or fenestrations 2. Peripheral Proteins § Present in the inner or outer surface § Do not traverse the membrane Functions of Peripheral Proteins: - Act as channels/carriers - Cell identity markers (antigens) - Receptors (hormones/NTA)

 

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C. CARBOHYDRATES - Never present on the inner surface - mostly incorporated with lipid or proteins - Glycolipid/ Glycoproteins – mostly present on the extracellular surface Functions: 1. Cell Identity Markers 2. Cell Communications 3. Acts as channels TRANSPORT ACTIVITIES Passive transport 1. Along a gradient - common gradients= pressure, concentration gradients - consider electrical charge of the substance and the charge of the area -Na+ going a (-) gradient = Passive 2. “Downhill” 3. No ATP consumption 4. Usually no “carrier” 5. Glycoprotein channels 6. No inhibition - almost always non specific 7. Equilibrium 8. Bidirectional transport 9. Hydrophilic CHON channels (gated/non-gated) 10. Living/Non-living cells 11. Water CHON carrier 12. “Carrier” facilitated diffusion - enhance the rate of passive transport

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- To produce a carrier protein, you need energy - Never seen in non living cells - Transport of Fructose 13. Lipophilic lipid bilayer 14. Specific/ non specific - based on the size or molecular weight Active Transport 1. Against a gradient - Na+ going to a + gradient = same charge repel (Active) 2. “Uphill” (pump) 3. ATP utilization (mitochondria) - dependent on the normal functioning mitochondria 4. Always involves “carrier” - it is the carrier that is directly utilizing energy 5. Glycoprotein channels 6. Undergoes inhibition 7. Saturation - number of carrier - activity of cell is continuous provided uou have a normal, functioning mitochondria/ continuous production of energy - if you utilized all the carriers, it will stop at maximum (still continuous) but there is no additional increase 8. Unidirectional 9. Hydrophilic CHON carriers (transporters) 10. Living cells 11. Always specific

 

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