Question

using three examples from 2 body system explain the physiological concept of flow down gradients, e.g pressure gradients, electro-chemical gradients etc. can talk about airway resistance, blood vessel resistance in those gradient where ever it suits, example of system can be renal system talk about loop henle flow down gradient.. In your answer include the terms gradient and resistance. provide detailed answers in each example physiologically

Answer 1

1. Circulatory system :

Gradients:

Pressure gradient :

Liquids flow down their concentration gradients from areas of high pressure to areas of lower pressure. In practice, this means blood will flow from the arterial end of a vessel to the venous end.

This pressure gradient is primarily created by the pumping action of the heart. Relating to the above equation, the value for pressure is normally calculated as the mean difference between the start and the end of the vessel.

Resistance : depends on radius , viscosity, vessel length

Radius : As a vessel’s cross sectional area decreases, the average velocity of blood increases.

Therefore, we could consider that a capillary should have a high velocity because of its very small cross section. In fact, because capillary beds are connected in parallel, their collective cross section is vast. This gives capillaries a very slow flow overall.

Changing flow rate can also occur as a physiological response when a vessel’s smooth muscle relaxes or contracts to change the cross-sectional area. Thus altering the flow rate appropriately.

Viscosity: Blood viscosity is relatively consistent day-to-day, so this variable doesn’t massively impact our blood flow. However, in some conditions such as with chronic smokers or dehydration, blood composition can change and subsequently flow can change.

Vessel length : The longer a vessel is, the higher its resistance

Excretory system : electro chem gradient

Electrolytes help to regulate myocardial and neurological functions, fluid balance, oxygen delivery, acid–base balance, and much more.The most serious electrolyte disturbances involve abnormalities in the levels of sodium, potassium, and/or calcium.Kidneys work to keep the electrolyte concentrations in the blood constant despite changes in the body.

Na :  

The body has a potent sodium -retaining mechanism: the rennin– angiotensin system.In states of sodium depletion, aldosterone levels increase; in states of sodium excess, aldosterone levels decrease The major physiological controller of aldosterone secretion is the plasma angiotensin II level that increases aldosterone secretion

The body has potent sodium-retaining mechanisms and even if a person is on five mmol Na+/day they can maintain sodium balance. Extra sodium is lost from the body by reducing the activity of the renin –angiotensin system that leads to increased sodium loss from the body. Sodium is lost through the kidneys, sweat, and feces.

In states of sodium depletion, the aldosterone levels increase. In states of sodium excess, aldosterone levels decrease. The major physiological controller of aldosterone secretion is the plasma angiotensin II level that increases aldosterone secretion.

K+ :

Most of the total body potassium is inside the cells and the next largest proportion is in the bones.In an unprocessed diet, potassium is much more plentiful than sodium and it is present as an organic salt, while sodium is added as NaCl.

High potassium intake can potentially increase the extracellular K+ level two times before the kidney can excrete the extra potassium.A high plasma potassium increases aldosterone secretion and this increases the potassium loss from the body to restore balance.

Calcium :  

Calcium absorption is controlled by vitamin D, and calcium excretion is controlled by the parathyroid hormones.

There is a constant loss of calcium by the kidney even if there is none in the diet.Calcium in plasma exists in three forms: ionized, nonionized and protein bound.

Chlorine :  Chloride is the predominant extracellular anion and it is a major contributor to the osmotic pressure gradient between the intracellular fluid (ICF) and extracellular fluid (ECF). Chloride maintains proper hydration and functions to balance the cations in the ECF to keep the electrical neutrality of this fluid. The paths of secretion and reabsorption of chloride ions in the renal system follow the paths of sodium ions.