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Body Fluid Compartmentalization
|Fluid||Volume test||Percentage of fluid from total body water/%||Volume of fluid/L|
|Intracellular||Antipyrin – D2O||40||28|
|Extracellular||Plasma||Evans blue – 131J||5||3.5|
|Interstitial fluid||Inulin – Manitol – Saccharose||15||10.5|
- Distribution volume of an administered substance (VD)/its plasma concentration: Amount of the given compound – amount of the excreted compound.
- Circulation-involved organs: GIT, skin, liver, and kidney.
Percentage of Body Fluids/%
Are of two types, Passive and Regulated.
Factor it Depends on
|Diffusion||Solubility of the substance in water/ in lipids.|
|Osmosis||The number of dissolved particles.|
|Filtration: The movement of a substance due to osmotic and hydrostatic pressure – controlling interstitial fluid’s resorption and production.||Whether oncotic pressure difference exceeds the hydrostatic pressure difference (no filtration) or vice versa (ultrafiltration; water moving out of the capillary).|
|Facilitated diffusion||A generally selective carrier with limited specificity is required; leading to a limited capacity.||Amino acids Phosphate|
|Cotransport:||Symport||Both substances move in the same direction||Na+ and Glucose; with glucose using Na+’s concentration gradient as a driving force into the cell.|
|Antiport||The substance move in opposite directions||Ca2+ and H+|
Active: ATP is uncleaved > Closed channel. Phosphorylation (following splitting of ATP) > Open channel.
Mediators: Na/K – Ca/H – K/H – & Na/H ATPase.
- They contain filter selectivity filters inside aqueous pores.
- Transport capacity: 6×104 particles per event.
|Extracellular-ligand-gated||ACh nicotinic receptor|
|Mechanically gated||Oxytocin receptor|
Characterized by an extremely rapid movement between states of: Active (open) > depolarized membrane – Deactivated (closed) > depolarized membrane – Elicitable (closed) > polarized membrane.
|Mechanical||Adhering incl. desmosomes/occluding junctions||For the mechanical stability of and adhesion between cells.|
|Electrical||Gap junctions||Through connexons.
In e.g. intercalated discs of the myocardium.
|Humoral Regulation||Signaling modes: autocrine – paracrine – juxtacrine – endocrine – neurocrine||Through a receptor, a ligand, possibly a second messenger.|
|Nervous Regulation||Inducing responses in excitable cells||Overlaps with humoral regulation.|
Meeting point of humoral and nervous regulation:
- The adrenal medulla.
- The hypothalamal-hypophysial axis.
Features of Homeostasis
The maintenance of constant conditions within an internal environment. Said internal environment may be e.g. the total body fluid, or that in specific compartments e.g blood or organelles.
Blood pressure – muscle tension level.
Parameters which can be regulated:
- osmotic pressure
- body fluids’ volume
- ion concentration
Levels of Regulation
|Local/ Metabolic||Chemicals: pO2, pCO2, pH.
Local hormones: Prostaglandins.
|Autoregulation||In muscles: Myogenic; as the blood flow in them is maintained at a near-constant level despite changes in perfusion pressure.
In the heart:
|Systemic||Humoral regulation. Nervous regulation.|
Regulatory Time Definition
The time between the start of a regulatory event and the return of the target-parameter to its original/resting value.
- Direct and indirect negative feedback
- Positive feedback
- Feedback in series and in parallel (in the same-direction process or on an event of another process).
Example of its detrimental effect when non-physiological: Hemorrhage > decrease in the amount of blood returning to the heart > decrease in contractility and cardiac output > decrease in blood pressure > decrease in coronary flow >: Death results in the case that no negative feedback mechanisms take over.
Notes by: Lina El Rifaie