PHYSIO 3200 Exam 4

What hormones do kidneys produce?

EPO, renin, active vitamin D

What are the two main parts of the nephron?

Renal corpuscle (filter) and tubule (modify)

What is ultrafiltrate?

Plasma without proteins and cells

What cannot be filtered?

Red blood cells and most proteins

What are the 3 layers of the filtration barrier?

Endothelium, basement membrane, podocytes

Direction of reabsorption?

Tubule → blood (capillaries)

Direction of filtration?

Blood (capillaries) → tubule

Direction of secretion?

Blood (capillaries) → tubule

Equation for excretion?

Filtered + Secreted − Reabsorbed

What are the two pathways for reabsorption from lumen to interstitial fluid?

• Between cells (paracellular)

• Through cells (transcellular)

How do substances move from interstitial fluid to blood?

Bulk flow into peritubular capillaries

What are the two types of mediated transport?

Primary active and secondary active transport

Example of primary active transport in kidney?

Na⁺/K⁺-ATPase

What does Na⁺/K⁺-ATPase do?

Pumps Na⁺ out of cell (into blood) using ATP

Example of secondary active transport?

Glucose + Na⁺ cotransport

How does glucose reabsorption work?

Glucose moves uphill using Na⁺ moving downhill

How does glucose leave the cell?

Facilitated diffusion

What happens when Tmax is exceeded?

Substance appears in urine

Why does glucose appear in urine in diabetes?

Filtered load exceeds Tmax → not all reabsorbed

What happens in the proximal tubule?

Majority of reabsorption

What is the role of the loop of Henle?

Creates medullary osmotic gradient

What happens in distal tubule + collecting duct?

Fine-tuning of reabsorption

What controls distal tubule function?

Hormones

What is GFR?

Volume of fluid filtered per unit time

What must be true for a substance to measure GFR?

• Freely filtered

• Not reabsorbed

• Not secreted

Which segment is hormonally regulated?

Distal tubule / collecting duct

If a substance is reabsorbed, what happens to excretion?

Decreases

What is filtered load?

Amount of a substance filtered into the tubule per unit time

Equation for filtered load?

GFR × Pₛ

If plasma concentration increases, what happens to filtered load?

Increases

What is clearance?

Volume of plasma cleared of a substance per unit time

Equation for clearance?

(V × Uₛ) / Pₛ

What does clearance measure?

Overall kidney handling of a substance

What does it mean if clearance = GFR?

No reabsorption or secretion

What does it mean if clearance < GFR?

Net reabsorption

What does it mean if clearance > GFR?

Net secretion

Substance used to measure GFR?

Inulin

Clinical estimate of GFR?

Creatinine

Substance used to measure renal plasma flow?

PAH

What is renal plasma flow?

Volume of plasma entering kidneys per unit time

When does clearance = RPF?

When substance is filtered and completely secreted

Normal RPF value?

~625 mL/min

What drives Na⁺ reabsorption?

Na⁺/K⁺-ATPase

Where does Na⁺ reabsorption occur?

All segments except descending loop

Why is Na⁺ important?

Drives reabsorption of other substances

What determines water reabsorption?

Osmosis

Key phrase for water movement?

Water follows Na⁺

Direction of water movement?

Hypoosmotic → hyperosmotic

What are aquaporins?

Water channels

Where is water permeability always high?

Proximal tubule

What hormone regulates water permeability?

ADH (vasopressin)

What does ADH do?

Increases water reabsorption → concentrated urine

What is osmolarity?

Total solute concentration

Range of urine osmolarity?

50–1400 mOsm

Where is renin released from?

Juxtaglomerular cells of afferent arteriole

What triggers renin release?

Low BP, low Na⁺, sympathetic activation

What is the function of RAS?

Increase BP

When is ANP released?

High blood volume

What does ANP do?

Decreases Na⁺ reabsorption

Where is ADH produced?

Hypothalamus

What does ADH do?

Increases water reabsorption

Which pathway responds to severe BP changes?

Baroreceptor pathway

Which pathway regulates ADH minute-to-minute without changing Na⁺ excretion?

Osmoreceptor pathway

H₂O is regulated by what hormone?

Vasopressin

Where does H₂O regulation occur?

Collecting Duct

What is diuresis?

Increased urine output

What is water diuresis?

↓ water reabsorption → hypoosmotic urine

What controls K⁺ excretion?

Secretion

Where is K⁺ secreted?

Cortical collecting duct

What is the most abundant intracellular ion?

K⁺

How does high K⁺ indirectly increase excretion?

Stimulates aldosterone release

How does high K⁺ directly increase excretion?

Stimulates Na⁺/K⁺ pump in tubule cells

What is the PRIMARY factor controlling K⁺ excretion?

Plasma K⁺ concentration

What stimulates aldosterone release?

• Angiotensin II

• High plasma K⁺

What inhibits aldosterone?

ANP

What does aldosterone do to Na⁺?

Increases Na⁺ reabsorption

What does aldosterone do to K⁺?

Increases K⁺ secretion

Relationship between Na⁺ and K⁺ in this system?

Na⁺ reabsorption → K⁺ secretion

Where is most Ca²⁺ stored in the body?

Bone (~99%)

Where is Ca²⁺ regulation controlled?

Distal convoluted tubule

Where is most Ca²⁺ reabsorbed?

Proximal tubule (not regulated)

What stimulates PTH release?

Low plasma Ca²⁺

What does PTH do in bone?

Increases Ca²⁺ release

What does PTH do in kidney?

ncreases Ca²⁺ reabsorption

What does PTH do in GI tract?

Increases Ca²⁺ absorption (via vitamin D)

Net effect of PTH?

Increases plasma Ca²⁺

What determines pH?

Free H⁺ concentration

What are nonvolatile acids?

Produce H⁺ from fixed acids from metabolism (e.g., sulfuric, phosphoric)

How are nonvolatile acids removed?

Kidneys

What are volatile acids?

Produces H⁺ from CO₂-derived acids

How are volatile acids removed?

Lungs