Unit 4 Flashcards
Study
What are the consequences of a typical North American diet high in NaCl on body osmolarity without water intake?
Consuming 9g NaCl per day without additional water leads to an increase in [Na+] in the extracellular fluid (ECF), resulting in hyperosmolarity and potential cell shrinkage. If the kidneys are not clearing any salt, 1.1 L extra water per day is needed to maintain normal [Na+] in ECF.
How does the body respond to increased salt ingestion?
Ingested NaCl without change in volume leads to increased osmolarity, causing vasopressin secretion, thirst, increased water intake, increased renal water reabsorption, increased ECF volume, and increased blood pressure. Cardiovascular reflexes then lower blood pressure, and the kidneys excrete salt and water to normalize osmolarity and blood pressure.
Describe the reabsorption and secretion process in the nephron.
The nephron filters 180 L/day with 100% volume at Bowman’s capsule. Proximal tubule reabsorbs ~70% fluid and solute. Loop of Henle receives 30% volume, with the ascending loop being hypo-osmotic relative to plasma. Distal tubule and collecting duct fine-tune water/salt balance under endocrine control.
What happens to cell volume when high NaCl intake is not offset by water?
Cells shrink due to hyperosmolarity of the extracellular fluid.
Explain how the body’s osmoregulation mechanisms respond to high NaCl intake without an increase in volume.
Upon high NaCl intake, osmoregulation begins with the secretion of vasopressin and the sensation of thirst, leading to increased water intake and retention. This results in an increase in extracellular fluid volume, which elevates blood pressure. Cardiovascular reflexes and kidney excretion then act to reduce blood pressure and return osmolarity to normal.
How much fluid is reabsorbed in the proximal tubule of the nephron?
Approximately 70% of the fluid is reabsorbed in the proximal tubule.
What role does the loop of Henle play in urine concentration?
The loop of Henle establishes a concentration gradient that allows for the regulation of urine concentration and volume.
What stimulates aldosterone secretion and what are the implications of this secretion on ion balance and blood pressure?
Aldosterone secretion is stimulated by increased plasma [K+] and decreased blood pressure. It activates the renin-angiotensin-aldosterone system (RAAS) to increase Na+ reabsorption and K+ secretion, which in turn helps to increase blood volume and pressure.
What cellular mechanisms does aldosterone activate in the adrenal cortex?
Aldosterone acts on intracellular receptors to induce gene expression for new pumps and channels, particularly increasing the number of epithelial sodium channels (ENaC) and Na+/K+ ATPase pumps.
What are the specific roles of aldosterone at the apical and basolateral membranes of principal cells?
At the apical membrane, aldosterone increases Na+ import and K+ export, while at the basolateral membrane, it enhances the activity of Na+/K+ ATPase pumps.
Explain the dual impact of aldosterone on sodium and potassium homeostasis.
Aldosterone facilitates sodium reabsorption and potassium secretion in the distal nephron, aiding in fluid balance and preventing hyperkalemia.
How do the actions of aldosterone contribute to blood pressure regulation?
By increasing Na+ reabsorption, aldosterone contributes to water retention, which increases extracellular fluid volume and blood pressure.
What physiological conditions prompt the adrenal cortex to release aldosterone?
The adrenal cortex releases aldosterone in response to high plasma potassium levels or low blood pressure, as part of the body’s effort to maintain electrolyte balance and blood pressure.
What is the result of aldosterone-induced Na+ reabsorption in the distal nephron?
Enhanced Na+ reabsorption in the distal nephron leads to an increase in blood volume and pressure, as water passively follows the reabsorbed sodium.
Describe the process of aldosterone-mediated gene expression and its outcome in the distal nephron.
Aldosterone stimulates gene expression for sodium channels and pumps in the distal nephron, resulting in increased sodium reabsorption and potassium secretion.
What percentage of body potassium is found in the extracellular fluid (ECF)?
Only a small proportion (2%) of the body’s potassium is in the ECF, with the majority inside cells.
Why is it important to maintain ECF potassium concentrations within a narrow range?
ECF potassium concentrations are crucial in determining the resting membrane potential and excitability of excitable cells.
What are the effects of hyperkalemia on cellular function?
Hyperkalemia reduces the concentration gradient across the cell membrane, causing cells to be depolarized, which can lead to cardiac arrhythmias.
What is the role of the renin-angiotensin system (RAS)?
The RAS regulates blood pressure and fluid balance, where renin converts angiotensinogen to angiotensin I, which is then converted to angiotensin II by ACE, leading to aldosterone release.
What is the function of granular cells in the juxtaglomerular apparatus?
Granular cells secrete the enzyme renin, which is involved in salt and water balance regulation.
What condition can result from hypokalemia, and how does it affect cell function?
Hypokalemia can cause cells to become hyperpolarized, leading to muscle weakness.
Explain the pathophysiology of how hyperkalemia and hypokalemia can affect cardiac and muscle cell function.
Hyperkalemia causes cells to depolarize prematurely, increasing the risk of arrhythmias, while hypokalemia leads to hyperpolarization, which decreases excitability and can result in muscle weakness.
Describe the regulatory mechanisms that the juxtaglomerular apparatus uses to control renal blood flow and filtration rate.
The juxtaglomerular apparatus regulates GFR by using the macula densa cells to detect changes in sodium chloride concentration, signaling granular cells to release renin, and altering arteriole resistance to adjust renal blood flow.
What are the components of the juxtaglomerular apparatus and their functions?
The juxtaglomerular apparatus includes the macula densa, which senses sodium chloride levels in the distal tubule, and the granular cells (JG cells), which secrete renin in response to low blood pressure.