Physiology: Buffers and Hormones Quiz

Chapter 26: Fluid, Electrolyte, and Acid-Base Balance

• This chapter covers fluid, electrolyte, and acid-base balance in the human body.
• Understanding these processes is crucial for correctly interpreting patient test results in a healthcare setting.
• A video, "Why This Matters (Career Connection)," is available online.
• Body fluids consist of water and solutes distributed in three main compartments.
• Total body water percentage varies based on age, body mass, and relative fat content; infants have higher percentages.

26.1 Body Fluids Consist of Water and Solutes in Three Main Compartments

• Total body water amount in adults averages 40 Liters.
• The two major fluid compartments are intracellular fluid (ICF) and extracellular fluid (ECF).
• ICF makes up approximately two-thirds of total body fluid (25L).
• ECF makes up approximately one-third of total body fluid (15L).
• Plasma (3L) and interstitial fluid (12L) are two major compartments within ECF.
• Other compartments like lymph, cerebrospinal fluid (CSF), and various secretions are part of the ECF.

Body Water Content

• Total body water varies based on age and body mass (and body fat).
• Infants have 73% or more body water, while old age individuals have about 45%.
• Adult males generally have 60% body water (due to more muscle mass). Muscle tissue contains about 75% water
• Fat tissue has less than 20% water (lower than other tissues).
• Adult females usually have 50% body water due to generally higher fat content.

Composition of Body Fluids

• Water is the universal solvent.
• Dissolved solutes include electrolytes and nonelectrolytes.
• Electrolytes dissociate into ions, carrying electrical charges, and increasing osmotic power.
• Non-electrolytes do not dissociate into ions (e.g., glucose). Electrolyte concentrations are expressed in milliequivalents per liter.
• Atomic weight and ion charge influence equivalent concentrations.
• ECF and ICF have different electrolyte compositions (e.g., Na+ vs K+).
• Blood plasma, interstitial fluid, and intracellular fluid have varying electrolyte concentrations, shown in a figure.

Fluid Movement Among Compartments

• Continuous exchange and mixing of fluids between compartments occur.
• Water moves freely between compartments down osmotic gradients.
• Solute differences between compartments drive water movement (which doesn't last for very long).
• Fluid leaks from arteriolar ends of capillaries, most of which are reabsorbed at venule ends; lymphatics collect excess fluid.
• Exchanges between interstitial fluid (IF) and intracellular fluid (ICF) occur across plasma membranes.
• Movement of water between compartments is primarily osmotic, with ion movement being selective across cell membranes.

Exchange of Gases, Nutrients, Water, and Wastes Between the Three Compartments of the Body

• The figure shows exchange between the three fluid compartments in the body, including plasma, interstitial fluid, and intracellular fluid.
• Different types of substances move in different directions.

Fluid Intake and Output Regulation

• Water intake must match output (~2500 mL/day).
• 90% or more of water intake comes from ingested foods and drinks.
• Metabolic water (from metabolism) contributes to daytime water needs.
• Insensible water loss is from skin and airways.
• Sensible loss occurs from urine, sweat, and feces.
• Osmolality is regulated around 280-300 mOsm.
• Rising osmolality stimulates thirst and ADH release.
• Decreasing osmolality inhibits thirst and ADH.
• A figure describes major sources of water intake and output per day.

Regulation of Water Intake

• The hypothalamic thirst center controls the thirst mechanism.
• Osmoreceptors in the hypothalamus respond to a 1-2% rise in plasma osmolality, triggering thirst.
• A decrease in blood volume or pressure also stimulates thirst.
• Angiotensin II or baroreceptors contribute to thirst signals.
• Relief of dry mouth, stomach and intestinal osmoreceptors, and stretch receptors provide feedback to inhibit thirst.

Regulation of Water Output & Influence of ADH

• Obligatory water losses such as insensible loss and urine (500 ml/day minimum) must be compensated for with intake.
• Fluid intake, diet, and variable amounts of sweat (significantly in heat) and feces (with significant diarrhea) influence urine volume and concentration.
• Kidneys start eliminating excess water 30 minutes after ingestion, peaking in about an hour.
• ADH release takes time to inhibit.
• ADH influences water reabsorption in collecting ducts, with ADH release leading to concentrated urine.
• Blood volume loss and blood pressure can trigger ADH release.
• Several factors (like severe dehydration, traumatic burns, severe blood loss) stimulate ADH release.

Disorders of Water Balance

• Dehydration (ECF fluid loss) arises due to factors like significant blood loss, severe burns, prolonged vomiting or diarrhea, or excessive sweating. Symptoms include thirst, dry mouth and skin, and decreased urine output (oliguria). Potentially dangerous impacts include weight loss, mental confusion, and even hypovolemic shock.
• Hypotonic hydration (excessive water ingestion): ECF osmolality decreases, causing net osmosis of water into tissue cells leading to cell swelling. Symptoms include severe disturbances, nausea, vomiting, muscular cramping, and cerebral edema, potentially leading to death. Can be treated with hypertonic saline.
• Edema (accumulation of interstitial fluid): Tissue swells, not cells (no change in ICF). Increased interstitial fluid volume may result from decreased lymphatic drainage. This may affect the normal diffusion of nutrients and oxygen from blood to tissues. Symptoms related to any underlying medical conditions that may cause edema are possible.

Regulation of Electrolytes: Sodium, Potassium, Calcium, and Phosphate

• Electrolyte balance relates to salt balance, encompassing acids, bases, and some proteins.
• Electrolytes control fluid movements and supply minerals for excitability, secretion, and cell membrane permeability.
• These substances include sodium (Na+), potassium (K+), calcium (Ca2+), and phosphate (HPO42–).
• Electrolytes are taken in via ingestion, and lost through perspiration, feces, urine, and vomiting.
• Imbalances in these substances can have significant consequences.

Regulation of Potassium Balance

• Potassium is the most abundant intracellular cation, essential for excitatory cell (like neurons and muscles) function.
• ICF-ECF K+ concentrations directly affect resting membrane potential, causing depolarization or hyperpolarization.
• Imbalances, like increased or decreased ECF K+, can impair electrical function.

Regulation of Calcium and Phosphate Balance

• 99% of calcium is stored in bones as calcium phosphate salts.
• ECF calcium levels are regulated by parathyroid hormone (PTH) and other hormones.
• • PTH enhances bone resorption (release of calcium), promotes calcium reabsorption by kidneys, and stimulates vitamin D activation to increase calcium absorption from the intestines.
• Vitamin D (calcitriol) plays a role in maintaining calcium balance.
• Imbalances in calcium levels have various consequences (e.g., neurological issues or heart problems).

Regulation of Anions

• Chloride (Cl-) is the major anion accompanying sodium in ECF.
• Cl- helps maintain ECF osmolality.
• During acidosis, Cl- reabsorption may lessen to compensate.
• Most other anions have transport maxima and any excess is excreted.

Chemical Buffers and Respiratory Regulation

• Chemical buffers, the immediate defense against pH changes.
• Respiratory systems eliminate CO2 (decreasing carbonic acid); this is a faster process.
• Renal systems eliminate metabolic acids (a slower process to restore balance).
• The kidneys also maintain the alkaline reserve.

Clinical-Homeostatic Imbalances

• Severe electrolyte deficiencies may lead to salt cravings (e.g., Addison Disease).
• Pica (abnormal cravings) occurs due to deficiencies in some essential minerals.
• A variety of imbalances (e.g., acidosis or alkalosis) can have significant and dangerous health consequences.

Influence of Atrial Natriuretic Peptide (ANP)

• ANP is involved with regulating blood pressure and volume.
• ANP inhibits ADH, renin, and aldosterone production, thus promoting vasodilation via decreasing production of angiotensin II to decrease blood volume and pressure.

Test your knowledge on the role of buffer systems and hormones in the body with this quiz. It covers topics such as the phosphate buffer system, protein buffering, and the effects of aldosterone. Get ready to explore essential physiological concepts related to fluid balance and hormone regulation.