BIOL122 water and homeostasis II

What two structures make up the renal corpuscle?

The Glomerulus and Bowman’s Capsule.

What is the structural difference between the afferent and efferent arterioles, and what is its purpose?

The afferent arteriole has a larger diameter than the efferent arteriole. This difference creates high pressure within the glomerulus to drive the filtration of blood.

What substances are filtered into Bowman's capsule, and what is excluded?

Filtered: Water and small-to-medium solutes (e.g., glucose, amino acids, ions, waste products).

Excluded: Large plasma proteins (typically larger than 65 KD) and blood cells.

What are the three layers of the filtration membrane in the renal corpuscle?

1. Glomerular endothelial cells (Pores/Fenestrations): Allows all plasma components to pass but blocks blood cells.

2. Basal lamina of the glomerulus: Holds back large proteins.

3. Slit membrane between pedicels (podocytes): Holds back medium-sized proteins.

Why does the Proximal Convoluted Tubule (PCT) require a high number of mitochondria and microvilli?

Mitochondria: Provide the massive amount of ATP/energy needed for active transport processes.

Microvilli: Form a brush border that creates a large surface area maximized for reabsorption

What approximate percentages of water, sodium ($Na^+$), and glucose are reabsorbed in the PCT?

Water: ~65% (via osmosis).

Na+ ions: ~65% (via symporters and other mechanisms).

Glucose: 100% (via symporters).

How do the descending and ascending limbs of the Loop of Henle (LoH) differ in permeability?

Descending limb: Highly permeable to water (water moves out via osmosis into the highly concentrated medulla).

Ascending limb: Impermeable to water; actively and passively moves NaCl out into the medulla to maintain the salt concentration gradient.

What hormone acts on the Distal Convoluted Tubule (DCT) to increase sodium reabsorption?

Aldosterone. By enhancing $Na^+$ reabsorption, it inherently enables more water to be reabsorbed back into the blood via osmosis

Where is Antidiuretic Hormone (ADH / Vasopressin) synthesized and released?

It is made in the hypothalamus and released into the bloodstream from the posterior pituitary gland

What is the cellular mechanism of ADH in the collecting duct?

ADH stimulates the insertion of aquaporin 2 water channels into the principal cells of the collecting duct, drastically increasing its permeability to water.

What type of urine is produced in the complete absence of ADH?

Dilute urine. Without ADH, the collecting duct remains impermeable to water, preventing it from being reabsorbed.

What triggers the granular cells of the Juxtaglomerular Apparatus (JGA) to secrete Renin?

Dehydration, which results in a decrease in blood pressure or volume (detected as low BP in the distal tubule).

What hormone is released in response to overhydration, and what is its source?

Atrial Natriuretic Peptide (ANP) , which is released when the increased blood volume stretches the atria of the heart.

What is "natriuresis" and how does it help correct overhydration?

Natriuresis is the elevated excretion of sodium (Na+) and chloride (Cl-) in the urine. Water osmotically follows these electrolytes, resulting in the excretion of large amounts of dilute urine to lower blood volume.