Cellular phsyiology

Physiology is the study of the mechanical, physical, and biochemical functions of living organisms.

The Fundamentals

Solutions: a homogenous mixture of solute within solvent (e.g. salt in water, oxygen in water)

Colloids: s a substance with components of one a homogeneous mixture (a solution) and a heterogeneous mixture with properties also intermediate between the two. Typical membranes restrict the passage of dispersed colloidial particles more than they restrict the passage of dissolved ions or molecules; i.e. ions or molecules may diffuse through a membrane through which dispersed colloidal particles will not. The dispersed phase particles are largely affected by the surface chemistry existent in the colloid. Examples: butter, milk, cream, asphalt, ink, glues, etc.

Molarity: Molarity (M) denotes the number of moles of a given substance per litre of solution.

Electrolytes: An electrolyte is a substance containing free ions which behaves as an electrically conductive medium.

Osmosis: is the net movement of water through a selective permeable membrane from a region of low solute potential to a region of high solute potential (or equivalently, from a region of high solvent potential to a region of low solvent potential). The partially permeable membrane must be permeable to the solvent, but not to the solute, resulting in a pressure gradient across the membrane.

Osmolarity: osmoles/litre

Osmolality: osmoles/kilogram

Tonicity: is the ability of a solution to cause water movement. It is in reference to hypertonic, hypotonic and isotonic cellular states.

The Medical Physiology: water balance, electrolyte balance

Clinical Insights: dehydration, diarrhoea, oedema

Appropriate regulation of membrane water, eg permeability and body solutes, is a fundamental requirement of all living organisms. The distribition of fluids and their electrolyes, proteins and macromolecules is normally controlled by a wide range of mechanisms. These occur at the cellular level to maintain a physiological balance of fluids content between the cells themselves, adn the extracellular environment. Broadly, the latter includes the extra- or intercellular spaces (sometimes called the interstitial space), blood plasma, lymphatic fluid, lung airspace, the luminal contents of the guy and numerous other 'extra-tissue' compartments in organs. Control of fluid distribution, its hydrostatic pressure and hte process of solute transport is a major function of the vascular sstem and the kidneys. These in turn maintain the correct fluid compositions of organs as diverse as the brain (cerebrospinal fluid), cartilage (fluid-rich matrix), cornea and the lens of the eye (cellular coverings of these tissues).

Body fluid composition is a vital component of the maintenance of internal stability. This is not constant but changes within a controlled physiological range that contributes to homeostasis.

Important Lecture Content:

- Total Body Water (TBW) is approximately 60% of body mass
- Extracellular Fluid (ECF) is approximately 20% of body mass
- ECF is composed of plasma water contained in the blood vessels, intersitial fluid in the extracellular matrix, water in lymph vessels and transcellular water in spaces such as the joints, cerebrospinal fluid and eye chambers
- Intracellular Fluid (ICF) is approximately 40% of body mass
- The capillary membrane barrier is highly permeable to water and electrolytes
- The cell membrane is highly permeable to water, not electrolytes

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