1. The maintenance of normal volume and composition of extracellular and intracellular fluids is vital to life. List and briefly describe the kinds of homeostasis involved. In males and females, intracellular fluid has a greater proportion of total body water than does extracellular fluid. Give-and-take between the ICF and the ECF happens across plasma membranes by osmosis, diffusion, and carrier-mediated transport. The kinds of homeostasis involved are fluid Balance, electrolyte Balance, and Acid–Base Balance. Fluid balance is when the quantity of water we gain each day is equivalent to the amount we lose to the environment.
The upkeep of normal fluid balance includes regulating the content and sharing of body water in the ECF and the ICF. The digestive system is the main source of water gains; a small amount of extra water is generated by metabolic activity. With electrolyte balance, it involves balancing the amounts of absorption across the digestive tract with amounts of loss at the kidneys. Everyday our body fluids gain electrolytes from drinks or foods we take in, and in turn, loose them through urinating, sweating and defecating. “If the gains and losses for every electrolyte are in balance, you are said to be in electrolyte balance.” We are in acid–base balance when the making of hydrogen ions in our body is exactly offset by their loss. When acid–base balance occurs, the pH of body fluids stays within normal limits. Stopping a reduction in pH is the main problem, because our body produces a variety of acids during normal metabolic tasks.
2. Why does maintaining fluid balance in older people require a higher water intake than in a normal, healthy adult under age 40? Water encompasses 55% in elderly people and is vital for cellular homeostasis and life. With respect to heat stress, water lost through perspiring decreases water content of plasma, and the elderly are less capable to compensate for amplified blood viscosity. Not only do they require a physiological hypodipsia, but this can be exaggerated by central nervous system disease and by dementia. Together with less fluid intake, with advancing age there is a decrease in total body water. The elderly have impaired renal fluid conservation mechanisms and have impaired responses to heat and cold stress. All of these factors add to an increased risk of hypohydration and dehydration in the elderly.
3. Why does potassium concentration rise in patients with acidosis? What is this called? What effects does it have? Sweat is a hypotonic solution that has Na+ in lower concentration than the ECF. As a consequence, a person who is sweating copiously loses more water than salt, and this loss leads to a increase in the Na+ concentration of the ECF. The water content of the ECF declines as the water loss happens, so blood volume falls. Clinically, this condition is often called volume depletion. Because volume depletion happens simultaneously that blood is being shunted away from the kidneys, kidney function is damaged and waste products collect in the blood.
4. Saline solution is used to reverse hypotonic hydration. Are body cell membranes permeable to saline? Explain your response. Body cell membranes are permeable to saline. The permeability of membranes is controlled by the mass of the “pores” or “holes”. The size of the pores can be altered in reaction to pressure and hormones. Some membranes selectively permit channel of certain ions or molecules and dismiss all others.
5. Explain the renin-angiotensin mechanism. Constant abnormalities in the Na+ concentration in the ECF happen only when there are severe complications with fluid balance, such as dehydration or overhydration. When the body’s water content increases enough to lessen the Na+ concentration of the ECF below 136 mEq/L, a state of hyponatremia (natrium, sodium) occurs. When body water content drops, the Na+ concentration increases; when that concentration surpasses 145 mEq/L, hypernatremia exists.
Renin is an enzyme secreted into the blood from specified cells that surround the arterioles at the entry to the glomeruli of the kidneys (the renal capillary networks that are the filtration units of the kidney). The renin-secreting cells, which comprise the juxtaglomerular apparatus, are delicate to changes in blood flow and blood pressure. The main stimulus for increased renin secretion is diminished blood flow to the kidneys, which may be triggered by loss of sodium and water (as a result of diarrhea, persistent vomiting, or extreme perspiration) or by thinning of a renal artery.
6. Explain how ADH compensates for blood that contains too many solutes. Osmoreceptors in the hypothalamus respond to alterations in blood composition, such as less water and too many solutes. The posterior pituitary is notified to release antidiuretic hormone (ADH) which journeys through the blood to its target organ, the kidney. In the kidney, the collecting ducts answer back to ADH by reabsorbing more water. When this happens, more water comes back to the blood, while lesser amounts of concentrated urine are made. ADH is released and additional water is reabsorbed from the filtrate until blood solute concentration comes back to normal.