Lecture 22: Renal 5 — Regulation, Water & Salt Balance -

What are the kidneys' four major roles in blood composition?

Waste removal, water balance, electrolyte balance, and pH regulation.

What three factors affect blood composition?

Diet, cellular metabolism, and urine output.

Why must water intake and output be balanced?

To maintain blood volume and body-fluid concentration.

What is insensible water loss?

Water lost without noticing, such as through skin and breathing.

What is osmolality?

Number of dissolved particles per kilogram of water.

What happens to plasma osmolality after losing more water than salt?

It increases.

What happens to plasma osmolality after drinking excess water?

It decreases.

What hormone is also called antidiuretic hormone (ADH)?

Vasopressin.

Where is ADH produced?

In the hypothalamus.

Where is ADH released into the blood?

From the posterior pituitary.

What stimulates ADH release?

Increased plasma osmolality and significant decreases in blood volume or pressure.

What do hypothalamic osmoreceptors detect?

Changes in the concentration of body fluids.

Where does ADH act in the kidney?

Mainly the collecting ducts.

How does ADH change collecting-duct cells?

It promotes insertion of aquaporin water channels.

What are aquaporins?

Membrane channels that allow water to move through cells.

What happens to urine volume when ADH increases?

Urine volume decreases.

What happens to urine concentration when ADH increases?

Urine becomes more concentrated.

What happens when ADH is low?

Less water is reabsorbed and more dilute urine is produced.

What is the renin-angiotensin-aldosterone system (RAAS)?

A hormone pathway that helps restore low blood pressure and blood volume.

What triggers renin release?

Low renal perfusion pressure or signals of low tubular NaCl.

Which cells release renin?

Juxtaglomerular (granular) cells in the kidney.

What does renin do?

Converts angiotensinogen into angiotensin I.

Where is angiotensinogen made?

The liver.

What does ACE do?

Converts angiotensin I into angiotensin II.

What does angiotensin II do to blood vessels?

Causes vasoconstriction, raising blood pressure.

What hormone does angiotensin II stimulate?

Aldosterone.

Where is aldosterone secreted?

Adrenal cortex.

What does aldosterone do in the kidney?

Increases Na+ reabsorption and K+ secretion in distal nephron segments.

How does aldosterone indirectly help retain water?

Retained sodium promotes water retention when water can follow.

What is atrial natriuretic peptide (ANP)?

A hormone released by the heart when atria stretch from increased volume.

What triggers ANP release?

Increased atrial stretch due to high blood volume.

What does ANP promote in the kidneys?

More sodium and water excretion.

How does ANP affect blood volume?

It tends to lower blood volume.

How do ADH and aldosterone differ?

ADH directly increases water reabsorption; aldosterone increases sodium reabsorption.

How do RAAS and ANP differ?

RAAS generally conserves salt and water; ANP promotes their excretion.

What is diuresis?

Increased urine production.

What is natriuresis?

Increased sodium excretion in urine.

What does thirst help regulate?

Water intake to restore fluid balance.