APHYS102 Ch. 26

One way the kidneys maintain HCO3- balance is by __________.

generating new HCO3- The most important renal mechanism for regulating acid-base balance of the blood involves controlling blood bicarbonate (HCO3-) levels. This is achieved by conserving or generating HCO3- and excreting HCO3-.

Antidiuretic hormone (ADH) acts on the __________ to __________ water excretion.

kidneys; decrease Antidiuretic hormone (ADH) acts on the kidneys to decrease water excretion. When ADH levels are high, most or all of the filtered water is reabsorbed and a small amount of concentrated urine is excreted. When ADH levels are low, less water is reabsorbed and dilute urine is excreted.

T/F: Parathyroid hormone (PTH) increases Ca2+ deposition in the bones.

False Parathyroid hormone (PTH) is released in response to low Ca2+ levels. PTH causes the release of Ca2+ from the bones, increases absorption of Ca2+ by the small intestine, and increases calcium reabsorption in the proximal convoluted tubule of the kidneys.

T/F: Most of the hydrogen ions in the body come from acidic substances in the foods we ingest.

False Small amounts of acids enter the body via ingested foods. However, most H+ ions originate as metabolic by-products or end products. For example, the breakdown of phosphorus-containing proteins, the anaerobic breakdown of glucose, fat metabolism, and the loading and transport of CO2 in the blood all serve as sources of hydrogen ions in the body.

T/F: The most abundant cation in extracellular fluid is potassium.

False The most abundant cation (or positively charged ion) in the extracellular fluid (ECF) is sodium (Na+). The most abundant anion (or negatively charged ion) in the ECF is chloride (Cl-). The most abundant cation in the intracellular fluid (ICF) is potassium (K+). The most abundant anion in the ICF is hydrogen phosphate (HPO4-).

T/F: Most fluid in the body is in the extracellular fluid (ECF) compartment.

False Water in the body occupies two main fluid compartments. Most fluid (about two-thirds) is in the intracellular fluid (ICF) compartment. ICF is fluid found inside of cells. The rest of our body water (about one-third) is in the extracellular fluid (ECF) compartment. The ECF consists of plasma and interstitial fluid (IF), the fluid in the spaces between tissue cells.

Most water is excreted via the __________.

Kidneys Water output occurs by several routes. Water that vaporizes out of the lungs in expired air or diffuses directly through the skin is called insensible water loss. Some water is also lost in perspiration and feces. The rest, about 60% of the total water output, is excreted by the kidneys in urine.

Which of the following is NOT an electrolyte?

glucose Electrolytes are inorganic substances that dissociate into ions in water. Examples of electrolytes include salts [for example, sodium chloride (NaCl) and magnesium chloride (MgCl2)] and ions [for example, potassium (K+)]. Nonelectrolytes have bonds (usually covalent bonds) that prevent them from dissociating in water. Most nonelectrolytes are organic molecules. For example, glucose, lipids, urea, creatinine, and cholesterol are nonelectrolytes.

Which of the following is associated with a swelling of cells?

hypotonic hydration Hypotonic hydration causes hyponatremia (low concentration of Na+ in the extracellular fluid), leading to cell swelling. Edema (tissue swelling) is an atypical accumulation of fluid in the interstitial space, leading to tissue (not cell) swelling. Edema can be caused by any event that increases fluid loss from the blood to the tissues, or that prevents effective return of fluid from the interstitial space to the bloodstream.

Which of the following would increase sodium excretion?

progesterone Reabsorption of sodium does not exhibit a transport maximum. In healthy individuals, nearly all sodium in the renal filtrate is reabsorbed in the proximal convoluted tubules of the kidneys. Atrial natriuretic peptide (ANP) and progesterone increase Na+ excretion. Progesterone appears to decrease NaCl reabsorption by blocking the effect aldosterone has on the renal tubules. Aldosterone is the key regulator of sodium reabsorption in the kidney. It encourages Na+ reabsorption. Estrogens, like aldosterone, encourage Na+ reabsorption. Glucocorticoids enhance tubular reabsorption of sodium.

Someone who is suffocating would develop __________.

respiratory acidosis The most common cause of acid-base imbalance is respiratory acidosis, a result of elevated blood levels of CO2 due to shallow breathing, suffocation, or lung diseases that impede O2 and CO2 exchange.

Hyperventilation can lead to __________.

respiratory alkalosis Decreased CO2 levels will increase blood pH. If one hyperventilates, the levels of CO2 drop to below normal levels and can cause respiratory alkalosis. Increased CO2 will lower blood pH. In response to high CO2 levels, the rate of and depth of breathing will increase in an effort to vent off excess CO2. If one is unable to breathe, CO2 levels increase, leading to respiratory acidosis.

The most important factor that influences K+ secretion is __________.

the concentration of K+ in the ECF The single most important factor that influences K+ secretion is the concentration of K+ in the ECF.

Which of the following has the LEAST influence over the pH of blood plasma?

the phosphate buffer system The bicarbonate buffer system is the primary buffer system for the ECF. Because the phosphate buffer system is present in low concentrations in the ECF (approximately one-sixth that of the bicarbonate buffer system), it is relatively unimportant for buffering blood plasma. However, it is a very effective buffer in urine and in ICF, where phosphate concentrations are usually higher.

Which of the following puts infants at increased risk for dehydration?

their inefficient kidneys At birth, the kidneys are inefficient; these infant kidneys do not concentrate urine or conserve water efficiently, putting infants at risk for dehydration. Vomiting, diarrhea, and a high rate of insensible water loss also increase the risk for dehydration.