Question

1. which solute(s) (salts, glucose, or urea) change in the blood from inside and outside of the kidney when the water intake changes? why do you think this is the case?

Explanation:

1. Solute Analysis:

• Salts (e.g., Na⁺, Cl⁻): The kidneys regulate salt concentration via mechanisms like the renin - angiotensin - aldosterone system (RAAS) and antidiuretic hormone (ADH) - related pathways. When water intake decreases, blood volume drops, and the kidneys reabsorb more salt (and water) to maintain blood pressure and osmolarity. When water intake increases, the kidneys excrete more salt to prevent fluid overload and keep osmolarity stable.
• Urea: Urea is a waste product, but its concentration in the blood is also affected by water balance. When water intake is low, the kidneys reabsorb more water, which can lead to a relatively higher concentration of urea in the blood (as less water is excreted to dilute it). When water intake is high, more water is excreted, and urea concentration may decrease as it is more diluted or excreted along with the excess water.
• Glucose: In a healthy individual, glucose is reabsorbed completely in the kidneys (unless blood glucose levels are extremely high, like in diabetes). So, changes in water intake do not typically cause significant changes in blood glucose levels related to kidney function (the main regulation of blood glucose is via insulin and glucagon from the pancreas).

1. Reasoning for Salt and Urea:

• The kidneys' main functions include osmoregulation (maintaining water - salt balance) and excretion of waste. Salts are crucial for maintaining blood osmolarity and blood pressure. Urea, although a waste, is also involved in the osmotic gradient in the kidneys (especially in the medulla for water reabsorption). So, when water intake changes, the kidneys adjust the reabsorption and excretion of salts and urea to maintain homeostasis. Glucose, as mentioned, is not regulated by the kidneys in terms of its blood concentration in response to water intake (in normal physiology).

Answer:

The solutes that change in the blood (from inside and outside the kidney) when water intake changes are salts (e.g., sodium, chloride) and urea. Glucose does not typically change in response to water intake (in healthy individuals) because the kidneys reabsorb glucose completely (unless blood glucose is pathologically high). Salts change because the kidneys regulate salt - water balance to maintain blood pressure and osmolarity. Urea changes as its concentration is affected by the amount of water reabsorbed or excreted (since urea is excreted with water, changes in water intake alter its blood concentration).