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Cells and homeostasis summary
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Summary of 2 pages for the course Anatomy at BCU (The physiology)
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Cells and homeostasis summaryPhysiology studies the function of different types of cells that form tissue, various tissues form
organs, which form organ systems that together make an organism. The 11 different organ systems
are: Integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic,
respiratory, digestive, renal/urinary and reproductive system. The different systems overlap and
interact. Each organ system needs to function effectively for the body to function to full capacity.
Cells are made up of organelles, which are structures in the cell that are specialised for a certain task
in the cell and like the organs that make a body function, organelles make a cell do its job.
Organelles are enclosed by a similar membrane as the cell membrane that delineates the cell. All
membranes of the cell are made of fatty phospho-lipids that separates watery environments into
different compartments (e.g. separating cytoplasm from outside world), because water-soluble
molecules can only go where they are allowed by specialised proteins that stretch across the
membrane.
Proteins are large molecules, like little machines that can do a specific job in the cell or even in the
organelle. E.g. enzymes that break a molecule in two, transporter proteins that drag a water-
soluble molecule through the fatty membrane. Proteins consist of a chain of many different amino
acids, which is produced by ribosomes that can be found free in the cytoplasm (producing protein
in the cytoplasm) or on endoplasmic reticulum (filling the endoplasmic reticulum with protein).
The sequence of amino acids (type of protein) is determined by the gene for that protein, a part of the
DNA that contains the instruction code that can be copied to identical messenger RNA, in a process
called transcription (letter by letter). The process of making an amino acid chain (protein) following
the mRNA copy of the instructions, is called translation. The DNA is kept safe in the nucleus.
Proteins move from endoplasmic reticulum to the Golgi apparatus, which functions as a ‘sorting
office and distribution centre’ from where they are transported to various parts of the cell according
to needs or released by fusion of the vesicle membrane with the cell membrane.
Mitochondria form the power plants of the cell, where fuel (glucose or fatty acids) is burned with
oxygen to form water and carbon dioxide. The energy released in this process of aerobic cellular
respiration, is captured in ATP molecules that act as small rechargeable batteries, used to power all
cellular processes that need energy.
Homeostasis refers to mechanisms that ensure a stable internal environment, despite a changing
external environment. Organisms have homeostatic control over vital physiological factors using
negative feedback systems; when the actual value of a factor (sensed by receptors/sensors)
deviates from its set norm, the controller will be notified by the sensor and activate effector organs
to adjust that factor in a direction opposite (hence ‘negative’) to the deviation, until it reaches the set
norm again.
Like room temperature can be controlled bi-directionally by central heating and an air conditioner,
homeostatic control systems can activate effectors that drive the physiological factor back to its set
norm in both directions. For example body thermo-regulation uses different effector organs to
oppose temperatures higher than the set norm of 37 (e.g. sweating, skin vasodilation) or oppose
lowering of the temperature (e.g. skin vasoconstriction, goose bumps, shivering).
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