Human Anatomy and Physiology
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AConrad_Module8-Dehydration_0525211.pptxDehydration
Causes, Dangers, and Treatment
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Body Fluids
Chemical reactions happen in aqueous solutions
Solutes: Dissolved substances in a solution
Vary throughout the body
Proteins that transport
Lipids
Carbohydrates
Electrolytes
The chemical reactions in our bodies happen in aqueous solutions. The dissolved substances in a solution are called solutes. Solutes vary in different parts of the body but may include proteins. Including those that transport lipids, carbohydrates, and, very importantly, electrolytes (Betts et al., 2017).
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Electrolytes
A mineral separated from a salt that carries an ion.
Sodium ions (Na+)
Chloride ions (Cl-)
Osmosis is diffusion of water from higher concentration to lower concentration
Often in medicine, a mineral dissociated from a salt that carries an electrical charge (an ion) is called and electrolyte. For example, sodium ions (Na+) and chloride ions (Cl-) are often referred to as electrolytes. In the body, water moves through semi-permeable membranes of cells and from one compartment of the body to another by a process called osmosis. Osmosis is the diffusion of water from regions of higher concentration to those of lower concentration, along an osmotic gradient across a semi-permeable membrane. Resulting in water moving into and out of cells and tissues, depending on the concentrations of the water and solutes. A balance of solutes inside and outside of cells must be maintained to ensure normal function (Betts et al., 2017).
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Body Water Content
Infants – 75% of body mass
Adults – 50-60% of body mass
Elderly – as low as 45%
Brain and Kidneys – Highest proportion 80-85%
Teeth – Lowest proportion 8-10%
Human beings are mostly water, ranging from about 75 percent of body mass in infants to about 50–60 percent in adult men and women, to as low as 45 percent in old age. The percent of body water changes with development, because the proportions of the body given over to each organ and to muscles, fat, bone, and other tissues change from infancy to adulthood. The brain and kidneys have the highest proportions of water, which composes 80–85 percent of their masses. Teeth have the lowest proportion of water, at 8–10 percent (Betts et al., 2017).
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Fluid Compartments
Intracellular fluid (ICF) compartment is the system that includes all fluid enclosed in cells by their plasma membranes.
Extracellular fluid (ECF) surrounds all cells in the body.
plasma
Interstitial fluid (IF) that surrounds all cells not in the blood
Body fluids can be discussed in terms of their specific fluid compartment, a location that is largely separate from another compartment by some form of a physical barrier. The intracellular fluid (ICF) compartment is the system that includes all fluid enclosed in cells by their plasma membranes. Extracellular fluid (ECF) surrounds all cells in the body. Extracellular fluid has two primary constituents: the fluid component of the blood (called plasma) and the interstitial fluid (IF) that surrounds all cells not in the blood (Betts et al., 2017).
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Plasma osmolality
Osmolality is the ratio of solutes in a solution to a volume of solvent in a solution. Plasma osmolality is thus the ratio of solutes to water in blood plasma. Plasma osmolality value indicates the levels of hydration. A healthy body will keep plasma osmolality within a small range by using several things that regulate both water intake and output. Drinking water is voluntary. If someone is dehydrated, there is a net loss of water that results in insufficient water in the blood and other tissue. The water that leaves the body, as exhaled air, sweat, or urine, is eventually removed from blood plasma. As the blood becomes more concentrated, a sequence of physiological methods is triggered (Betts et al., 2017).
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Osmolality is the ratio of solutes in a solution to a volume of solvent in a solution.
Plasma osmolality is thus the ratio of solutes to water in blood plasma.
Dehydration is the net loss of water that results in insufficient water in blood and other tissues.
The water that leaves the body, as exhaled air, sweat, or urine, is ultimately extracted from blood plasma.
Thirst Response
Osmoreceptors are sensory receptors in the thirst center in the hypothalamus that monitor the concentration of solutes, known as osmolality, of the blood. If blood osmolality increases above its ideal amount, the hypothalamus sends signals that cause a conscious recognition of thirst. A person normally responds by drinking water. The hypothalamus of a dehydrated person also releases antidiuretic hormone through the posterior pituitary gland. ADH alerts the kidneys to regain water from urine and dilutes the blood plasma. The hypothalamus also sends signals by way of the sympathetic nervous system to the salivary glands in the mouth. Resulting in a decrease in watery, serous output and an increase in stickier, thicker mucus output. These variations in secretions result in a “dry mouth” and the feeling of thirst.
Decreased blood volume results in 2 more ways. First, baroreceptors, blood-pressure receptors in the arch of the aorta and the carotid arteries in the neck, detect a decrease in blood pressure.
The heart is alerted to increase its rate and/or strength of contractions to offset the lowered blood pressure. Second, the kidneys have a renin-angiotensin hormonal system that increases the production of the active form of the hormone angiotensin II, which helps stimulate thirst, but also stimulates the release of the hormone aldosterone from the adrenal glands. Aldosterone increases the reabsorption of sodium in the distal tubules of the nephrons in the kidneys, and water follows this reabsorbed sodium back into the blood (Betts et al., 2017).
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Not drinking enough water
Diarrhea
Vomiting
Sweating too much
Urinating too much
Fever
What causes dehydration?
The simplest cause of dehydration is a lack if drinking water. However, other causes may be diarrhea, vomiting, sweating, urinating, or fever. Some of which can be related to specific medications a person is taking.
Diabetes, ADH hyposecretion and overuse of diuretics are additional causes of dehydration (NIH, 2020).
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What is dehydration?
Dehydration is condition caused by the loss of too much fluid from the body.
More water than sodium
Causes extracellular fluid (ECF) osmolarity to rise
ECF is approximately 1/3 of the body’s water content
20% in plasma
CSF
Lymph
Synovial fluid
Pleural
Pericardial
Peritoneal
Aqueous humor
Dehydration is also known as a negative water balance. It occurs when the body eliminates significantly more water than sodium which increases ECF osmolarity.
The ECF accounts for the other one-third of the body’s water content. About 20% of the ECF is found in plasma.
Other water-based ECF include the CSF, lymph, the synovial fluid in joints, the pleural fluid in the pleural cavities, the pericardial fluid in the cardiac sac, the peritoneal fluid in the peritoneal cavity, and the aqueous humor of the eye. Because these fluids are outside of cells, these fluids are also considered components of the ECF compartment (Betts et al., 2017).
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Effects of profuse sweating on fluid compartments
Dehydration affects all fluid compartments. If a person loses a liter of sweat, most of it filters out of the bloodstream through the capillaries of the sweat glands. A liter of sweat would amount to approximately 1/3 of the blood plasma. However, as blood loses water, its osmolarity rises and the water from the tissue fluid enters the bloodstream to balance the loss. This raises the osmolarity of the tissue fluid, so water moves out of the cells to balance that. This ultimately causes the ICF, blood and tissue fluid to lose water. To excrete 1 liter of sweat, about 300 ml of water would come from the tissue fluid and 700 ml from the ICF. Sweating without fluid replacement can lead to losses greater than 1 L per hour (Betts et al., 2017).
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Potential complications of untreated dehydration
Heat exhaustion
Heat cramps
Seizures due to electrolyte loss
Hyponatremia
Hypernatremia
Hypocalcemia
Hypercalcemia
Hypomagnesemia
Low blood volume
Kidney failure
Coma
Heatstroke
Muscle cramps
Weariness
Headache
Dizziness
Feeling faint
Nausea
Pale, red, or dry skin
Confusion
Trouble walking
Dilated pupils
Vomiting
Inappropriate or uncharacteristic behavior
Rapid or racing heart rate
Rapid breathing
Seizures
Unconsciousness
Heat exhaustion occurs when your body overheats in response to external factors, like high temperature. Heat exhaustion can happen to anyone. It’s common in athletes, particularly those who exercise outdoors during extreme summer weather. It can also occur if you’re in a hot car or other indoor area that isn’t air-conditioned. Babies, small children, and older adults are more susceptible.
Heat cramps are the first stage of heat emergency. They usually happen when you’ve been physically active in the heat, but they can also occur if you haven’t been active.
Heat cramps are especially likely in the elderly or small children, overweight people, and people who have been drinking alcohol. Muscle pain and tightness are symptoms of heat cramps.
Heatstroke develops when the body is unable to effectively sweat to cool itself down. As core temperatures rapidly elevate, the skin becomes dry, and your heart rate begins to elevate (Taylor-Chavoustie, 2019).
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Strategies to treat dehydration
Rehydration
IV
Drink water
Electrolyte containing drink
Pedialyte
Things to avoid
Soda
Alcohol
Sweet drinks
Caffeine
Treatments for dehydration include rehydrating methods, electrolyte replacement, and treating diarrhea or vomiting, if needed.
Rehydration by drinking may not be possible for all people, like those who have severe diarrhea or vomiting. In this case, fluids can be given by IV which provides a solution that’s often a mix of water and electrolytes.
For those able to drink, drinking water along with an electrolyte-containing rehydration drink, such as a low-sugar sports or electrolyte drink, may be recommended. Children with dehydration are often directed to drink Pedialyte.
Avoid soda, alcohol , overly sweet drinks, or caffeine. These drinks can worsen dehydration (Taylor-Chavoustie, 2019).
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References
Betts, J. G., Desaix, P., Johnson, E., Johnson, J. E., Korol, O., Kruse, D., Poe, B., Wise, J., Womble, M. D., & Young, K. A. (2017). 26 FLUID, ELECTROLYTE, AND ACID-BASE BALANCE. In Anatomy & physiology (pp. 1174–1197). essay, OpenStax College, Rice University.
Nardone, R., Brigo, F., & Trinka, E. (2016, January). Acute Symptomatic Seizures Caused by Electrolyte Disturbances. Journal of clinical neurology (Seoul, Korea). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4712283
NIH. (2020, October 1). Dehydration. MedlinePlus. https://medlineplus.gov/dehydration.html.
Taylor-Chavoustie, C. (2019, September 19). What to Know About Dehydration. Healthline.com. https://www.healthline.com/health/dehydration.
