Module 17: Fluid, Electrolyte, and Acid-Base Balance

Lesson 1: Body Fluids and Fluid Compartments

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Dưới đây là danh sách những thuật ngữ Y khoa của module Fluid, Electrolyte, and Acid-Base Balance.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: Fluid, Electrolyte, and Acid-Base Balance

antidiuretic hormone (ADH)
also known as vasopressin, a hormone that increases the volume of water reabsorbed from the collecting tubules of the kidney
dehydration
state of containing insufficient water in blood and other tissues
dihydroxyvitamin D
active form of vitamin D required by the intestinal epithelial cells for the absorption of calcium
diuresis
excess production of urine
extracellular fluid (ECF)
fluid exterior to cells; includes the interstitial fluid, blood plasma, and fluids found in other reservoirs in the body
fluid compartment
fluid inside all cells of the body constitutes a compartment system that is largely segregated from other systems
hydrostatic pressure
pressure exerted by a fluid against a wall, caused by its own weight or pumping force
hypercalcemia
abnormally increased blood levels of calcium
hypercapnia
abnormally elevated blood levels of CO2
hyperchloremia
higher-than-normal blood chloride levels
hyperkalemia
higher-than-normal blood potassium levels
hypernatremia
abnormal increase in blood sodium levels
hyperphosphatemia
abnormally increased blood phosphate levels
hypocalcemia
abnormally low blood levels of calcium
hypocapnia
abnormally low blood levels of CO2
hypochloremia
lower-than-normal blood chloride levels
hypokalemia
abnormally decreased blood levels of potassium
hyponatremia
lower-than-normal levels of sodium in the blood
hypophosphatemia
abnormally low blood phosphate levels
interstitial fluid (IF)
fluid in the small spaces between cells not contained within blood vessels
intracellular fluid (ICF)
fluid in the cytosol of cells
metabolic acidosis
condition wherein a deficiency of bicarbonate causes the blood to be overly acidic
metabolic alkalosis
condition wherein an excess of bicarbonate causes the blood to be overly alkaline
plasma osmolality
ratio of solutes to a volume of solvent in the plasma; plasma osmolality reflects a person’s state of hydration
respiratory acidosis
condition wherein an excess of carbonic acid or CO2 causes the blood to be overly acidic
respiratory alkalosis
condition wherein a deficiency of carbonic acid/CO2 levels causes the blood to be overly alkaline
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Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
The chemical reactions of life take place in aqueous solutions. The dissolved substances in a solution are called solutes. In the human body, solutes vary in different parts of the body, but may include proteins—including those that transport lipids, carbohydrates, and, very importantly, electrolytes. Often in medicine, a mineral dissociated from a salt that carries an electrical charge (an ion) is called an electrolyte. For instance, 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 basically the diffusion of water from regions of higher concentration of water to regions of lower concentration of water, along an osmotic gradient across a semi-permeable membrane. As a result, water will move into and out of cells and tissues, depending on the relative concentrations of the water and solutes found there. An appropriate balance of solutes inside and outside of cells must be maintained to ensure normal function.
Human beings are mostly water, ranging from about 75 percent of body mass in infants to about 50–60 percent in adults, 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 (Figure 1). Your brain and kidneys have the highest proportions of water, which composes 80–85 percent of their masses. In contrast, teeth have the lowest proportion of water, at 8–10 percent.
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 (Figure 2).

A. Intracellular Fluid

The ICF lies within cells and is the principal component of the cytosol/cytoplasm. The ICF makes up about 60 percent of the total water in the human body, and in an average-size adult male, the ICF accounts for about 25 liters (seven gallons) of fluid (Figure 3). This fluid volume tends to be very stable, because the amount of water in living cells is closely regulated. If the amount of water inside a cell falls to a value that is too low, the cytosol becomes too concentrated with solutes to carry on normal cellular activities; if too much water enters a cell, the cell may burst and be destroyed.

B. Extracellular Fluid

The ECF accounts for the other one-third of the body’s water content. Approximately 20 percent of the ECF is found in plasma. Plasma travels through the body in blood vessels and transports a range of materials, including blood cells, proteins (including clotting factors and antibodies), electrolytes, nutrients, gases, and wastes. Gases, nutrients, and waste materials travel between capillaries and cells through the IF. Cells are separated from the IF by a selectively permeable cell membrane that helps regulate the passage of materials between the IF and the interior of the cell.

The body has other water-based ECF. These include the cerebrospinal fluid that bathes the brain and spinal cord, 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.
The compositions of the two components of the ECF—plasma and IF—are more similar to each other than either is to the ICF (Figure 4). Blood plasma has high concentrations of sodium, chloride, bicarbonate, and protein. The IF has high concentrations of sodium, chloride, and bicarbonate, but a relatively lower concentration of protein. In contrast, the ICF has elevated amounts of potassium, phosphate, magnesium, and protein. Overall, the ICF contains high concentrations of potassium and phosphate (HPO4)2-, whereas both plasma and the ECF contain high concentrations of sodium and chloride.

Most body fluids are neutral in charge. Thus, cations, or positively charged ions, and anions, or negatively charged ions, are balanced in fluids. As seen in the previous graph, sodium (Na+) ions and chloride (Cl-) ions are concentrated in the ECF of the body, whereas potassium (K+) ions are concentrated inside cells. Although sodium and potassium can “leak” through “pores” into and out of cells, respectively, the high levels of potassium and low levels of sodium in the ICF are maintained by sodium-potassium pumps in the cell membranes. These pumps use the energy supplied by ATP to pump sodium out of the cell and potassium into the cell (Figure 5).
Hydrostatic pressure, the force exerted by a fluid against a wall, causes movement of fluid between compartments. The hydrostatic pressure of blood is the pressure exerted by blood against the walls of the blood vessels by the pumping action of the heart. In capillaries, hydrostatic pressure (also known as capillary blood pressure) is higher than the opposing “colloid osmotic pressure” in blood—a “constant” pressure primarily produced by circulating albumin—at the arteriolar end of the capillary (Figure 6). This pressure forces plasma and nutrients out of the capillaries and into surrounding tissues. Fluid and the cellular wastes in the tissues enter the capillaries at the venule end, where the hydrostatic pressure is less than the osmotic pressure in the vessel. Filtration pressure squeezes fluid from the plasma in the blood to the IF surrounding the tissue cells. The surplus fluid in the interstitial space that is not returned directly back to the capillaries is drained from tissues by the lymphatic system, and then re-enters the vascular system at the subclavian veins.

Hydrostatic pressure is especially important in governing the movement of water in the nephrons of the kidneys to ensure proper filtering of the blood to form urine. As hydrostatic pressure in the kidneys increases, the amount of water leaving the capillaries also increases, and more urine filtrate is formed. If hydrostatic pressure in the kidneys drops too low, as can happen in dehydration, the functions of the kidneys will be impaired, and less nitrogenous wastes will be removed from the bloodstream. Extreme dehydration can result in kidney failure.

Fluid also moves between compartments along an osmotic gradient. Recall that an osmotic gradient is produced by the difference in concentration of all solutes on either side of a semi-permeable membrane. The magnitude of the osmotic gradient is proportional to the difference in the concentration of solutes on one side of the cell membrane to that on the other side. Water will move by osmosis from the side where its concentration is high (and the concentration of solute is low) to the side of the membrane where its concentration is low (and the concentration of solute is high). In the body, water moves by osmosis from plasma to the IF (and the reverse) and from the IF to the ICF (and the reverse). In the body, water moves constantly into and out of fluid compartments as conditions change in different parts of the body.

For example, if you are sweating, you will lose water through your skin. Sweating depletes your tissues of water and increases the solute concentration in those tissues. As this happens, water diffuses from your blood into sweat glands and surrounding skin tissues that have become dehydrated because of the osmotic gradient. Additionally, as water leaves the blood, it is replaced by the water in other tissues throughout your body that are not dehydrated. If this continues, dehydration spreads throughout the body. When a dehydrated person drinks water and rehydrates, the water is redistributed by the same gradient, but in the opposite direction, replenishing water in all of the tissues.
The movement of some solutes between compartments is active, which consumes energy and is an active transport process, whereas the movement of other solutes is passive, which does not require energy. Active transport allows cells to move a specific substance against its concentration gradient through a membrane protein, requiring energy in the form of ATP. For example, the sodium-potassium pump employs active transport to pump sodium out of cells and potassium into cells, with both substances moving against their concentration gradients.

Passive transport of a molecule or ion depends on its ability to pass through the membrane, as well as the existence of a concentration gradient that allows the molecules to diffuse from an area of higher concentration to an area of lower concentration. Some molecules, like gases, lipids, and water itself (which also utilizes water channels in the membrane called aquaporins), slip fairly easily through the cell membrane; others, including polar molecules like glucose, amino acids, and ions do not. Some of these molecules enter and leave cells using facilitated transport, whereby the molecules move down a concentration gradient through specific protein channels in the membrane. This process does not require energy. For example, glucose is transferred into cells by glucose transporters that use facilitated transport (Figure 7).
Intravenous Fluid Therapy: When isotonic fluid, such as NaCl, is infused, there is an addition of fluid to the extracellular fluid (ECF) compartment. This is known as isosmotic volume expansion. The ECF volume increases, but there is no change in the osmolarity of ECF or intracellular fluid (ICF). As a result, water does not shift between the compartments, but plasma protein concentration and hematocrit decrease. Arterial blood pressure increases due to the expansion of ECF volume.

Increased Salt Intake: When there is an excessive intake of NaCl, resulting in hyperosmotic volume expansion, the osmolarity of ECF increases. Water shifts from ICF to ECF, causing ECF volume to increase and ICF volume to decrease. Plasma protein concentration and hematocrit decrease due to the increase in ECF volume.

Diarrhea: In cases of diarrhea, there is a loss of isotonic fluid, resulting in isosmotic volume contraction. The ECF volume decreases, but the osmolarity of ECF and ICF remains unchanged. Water does not shift between the compartments, but plasma protein concentration and hematocrit increase. Arterial blood pressure decreases due to the decrease in ECF volume.

Sweating in a Desert: Sweating in a desert leads to the loss of water, causing hyperosmotic volume contraction. The osmolarity of ECF increases as sweat is hyposmotic. ECF volume decreases due to the loss of volume in sweat. Water shifts out of ICF, resulting in an increase in ICF osmolarity and a decrease in ICF volume. Plasma protein concentration increases, but hematocrit remains unchanged due to water shifting out of red blood cells.

Syndrome of inappropriate antidiuretic hormone (SIADH): In SIADH, there is a gain of water, leading to hyposmotic volume expansion. The osmolarity of ECF decreases as excess water is retained. ECF volume increases, and water shifts into the cells, causing an increase in ICF volume. Plasma protein concentration decreases due to the increase in ECF volume, while hematocrit remains unchanged.

Adrenocortical Insufficiency: In adrenocortical insufficiency, there is a loss of NaCl, resulting in hyposmotic volume contraction. The osmolarity of ECF decreases, and ECF volume decreases due to decreased NaCl reabsorption. Water shifts into the cells, leading to an increase in ICF volume. Plasma protein concentration increases, and hematocrit increases as water enters red blood cells.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

Water content varies in different body organs and tissues, from as little as 8 percent in the teeth to as much as 85 percent in the brain.

The intracellular fluid (ICF) is the fluid within cells. The interstitial fluid (IF) is part of the extracellular fluid (ECF) between the cells. Blood plasma is the second part of the ECF. Materials travel between cells and the plasma in capillaries through the IF.

Most of the water in the body is intracellular fluid. The second largest volume is the interstitial fluid, which surrounds cells that are not blood cells.

The graph shows the composition of the ICF, IF, and plasma. The compositions of plasma and IF are similar to one another but are quite different from the composition of the ICF.

The sodium-potassium pump is powered by ATP to transfer sodium out of the cytoplasm and into the ECF. The pump also transfers potassium out of the ECF and into the cytoplasm. (credit: modification of work by Mariana Ruiz Villarreal)

Net filtration occurs near the arterial end of the capillary since capillary hydrostatic pressure (CHP) is greater than blood colloidal osmotic pressure (BCOP). There is no net movement of fluid near the midpoint of the capillary since CHP = BCOP. Net reabsorption occurs near the venous end of the capillary since BCOP is greater than CHP.

Glucose molecules use facilitated diffusion to move down a concentration gradient through the carrier protein channels in the membrane. (credit: modification of work by Mariana Ruiz Villarreal)

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Dưới đây là video và các luyện tập (practice) của bài này. Nghe là một kĩ năng khó, đặc biệt là khi chúng ta chưa quen nội dung và chưa có nhạy cảm ngôn ngữ. Nhưng cứ đi thật chậm và đừng bỏ cuộc.
Xem video và cảm nhận nội dung bài. Bạn có thể thả trôi, cảm nhận dòng chảy ngôn ngữ và không nhất thiết phải hiểu toàn bộ bài. Bên dưới là script để bạn khái quát nội dụng và tra từ mới.
Script:
  1. Your body is mostly water.
  2. Body fluids are aqueous solutions with differing concentrations of materials, called solutes.
  3. An appropriate balance of water and solute concentrations must be maintained to ensure cellular functions.
  4. If the cytosol becomes too concentrated due to water loss, cell functions deteriorate.
  5. If the cytosol becomes too dilute due to water intake by cells, cell membranes can be damaged, and the cell can burst.
  6. The human body’s fluids are compartmentalized into intracellular fluid within cells and extracellular fluid surrounding cells.
  7. Intracellular fluid, comprising 60% of total body water, maintains cellular stability.
  8. On the other hand, extracellular fluid, including plasma and interstitial fluid, facilitates transport of substances between cells and blood vessels.
  9. Additionally, various other fluids outside cells, like cerebrospinal fluid and synovial fluid, are also considered part of the extracellular fluid compartment.
  10. Hydrostatic pressure is the force exerted by a fluid against a wall and causes movement of fluid between compartments.
  11. Fluid can also move between compartments along an osmotic gradient.
  12. Active transport processes require ATP to move some solutes against their concentration gradients between compartments.
  13. Passive transport of a molecule or ion depends on its ability to pass easily through the membrane, as well as the existence of a high to low concentration gradient.
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