Ch 19 LO: Renal physiology

19.1.1 What are the 6 functions of the kidney?

1. Regulation of MAP and blood volume

• Work with CVS to maintain ECF volume

2. Regulation of osmolarity

• Tied to behavioral drives, including thirst

3. Ion balance

• Balance dietary intake with urinary loss (Na+, K+ and Ca2+)

4. pH homeostasis

• Excretes H+ or HCO3- to maintain stable plasma pH

5. Excretion of wastes

• Excrete metabolic wastes, or foreign substances (xenobiotics) Creatine, urea, uric acid

6. Production of hormones

• Synthesizes erythropoietin (RBC production), renin (RAAS system), and vitamin D conversion

19.2.1 What is the anatomical path of a drop of water from Bowman’s capsule to urine leaving the body?

Bowman’s capsule →
Proximal tubule →
Loop of Henle (descending → ascending) →
Distal tubule →
Collecting duct →
Renal pelvis →
Ureter →
Bladder →
Urethra → Outside body

19.2.2 how do you trace a drop of blood from the renal artery to the renal vein?

Renal artery →
Segmental arteries →
Interlobar arteries →
Arcuate arteries →
Cortical radiate arteries →
Afferent arteriole →
Glomerulus →
Efferent arteriole →
Peritubular capillaries / vasa recta →
Venules →
Renal vein

19.2.3 what is the anatomical relationship between the vascular and tubular elements of a nephron? (diagram)

Blood vessels wrap around tubules → allows exchange (reabsorption & secretion)

19.3.1 What are the three processes of the nephron.

1. Filtration
   Blood → tubule (Bowman’s capsule)

2. Reabsorption
   Tubule → blood (keeps useful stuff)

3. Secretion
   Blood → tubule (adds wastes)

19.3.2 What is the volume and osmolarity changes of filtrate as it passes through each section of the nephron?

• Bowman’s capsule:
  ~180 L/day, ~300 mOsm (isosmotic)

• Proximal tubule:
  Volume ↓, still ~300 mOsm

• Loop of Henle:

  • Descending: water leaves → osmolarity ↑

  • Ascending: salt leaves → osmolarity ↓ (~100 mOsm)

• Distal tubule & collecting duct:
  Hormone-controlled → final urine (~1.5 L/day)

19.4.1 Describe the filtration barriers between the blood and the lumen of the nephron and explain how they can be modified to

control filtration

Three barriers to filtration:

Glomerular capillary endothelium

• Fenestrated capillaries

• Blood cells are not filtered

• Negatively charged surface repels most proteins

Basal lamina

• Extracellular matrix fibers act as a course sieve

(net)

• Blocks proteins

Podocytes

• Octopus-shaped cells wrap around glomerular

capillaries

19.4.2 Describe the pressures that promote and oppose glomerular filtration.

Promote filtration:

• Glomerular hydrostatic pressure (~55 mmHg)

  • fluid pushing on the walls, primary force that pushes blood to filtrate (sets up filtrate).

Oppose filtration:

• Osmotic pressure (~30 mmHg)

  • proteins in plasma promote reabsorption

• Colloid capsule pressure (~15 mmHg)

  • bowman’s capsule hydrostatic pressure

👉 Net filtration ≈ 10 mmHg outward

19.4.3 Define glomerular filtration rate and give average values for GFR.

Glomerular Filtration Rate (GFR)

• Volume of fluid that filters into the

• GF pressure = hydrostatic pressure - colloid osmotic - capsule pressure

Bowman's capsule per unit of time

• Average GFR is 125 mL/min (180 L/day)

• indicator of kidney function

19.4.4 Explain how GFR can be influenced by local and reflex control mechanisms.

Local (autoregulation):

• Myogenic autoregulation (afferent arteriole constriction in response to high MAP, strech)

• Tubuloglomerular feedback (macula densa detects changes in filtration rate)

External:

• Sympathetic nervous system (decreased GFR)

• Hormones

  • angiotensin II - vasoconstrictor, especially of efferent arteriole

  • prostaglandins - vasodilator

19.5.1 – Distinguish between transcellular transport and paracellular pathways.

• Transcellular: through cells (membranes)

• Paracellular: between cells (tight junctions)

19.5.2 Describe and give examples of active and passive reabsorption in the proximal tubule.

Active:

• Na⁺ (primary driver via Na⁺/K⁺ pump)

  • active because there is high Na+ on both sides

• Glucose (SGLT transporters)

Passive:

• anions (-) that move following the electrical gradient of sodium

• Water (osmosis)

  • follows solute reabsorption to keep equilibrium

• urea - passive diffusion, paracellular.

19.5.2.5 Sodium linked reabsorption in proximal tubule

LO 19.5.3 – Using glucose, create graphs to show filtration, transport maximum, and renal threshold of a substance reabsorbed by protein-mediated transport.

Type-1 diabetes and glucose transport illustrate reabsorption and saturation

• 100% glucose is filtered at glomerulus

• Normally, 100% glucose is reabsorbed in prox. tubule

Lack of insulin → high [glucose] in blood → high

[glucose] in filtrate

• Glucose transporters get saturated with glucose

• Glucose is excreted in urine instead

LO 19.6.1 – Explain and give examples of the importance of tubular secretion in renal function.

Purpose:

• eliminate drugs/toxins

• regulate K⁺ and H⁺

Examples:

Enhances excretion of a given substance like:

• Xenobiotics

• K+ and H+

• Metabolites

• Organic anions

Diagram an example of tertiary active transport

Secretion of organic anions through OAT

• sodium gradient moves along with dicarboxylates, creating dicarboxylate gradient in cell

• OAT concentrates organic anions in the cell using energy from dicarboxylate gradient moving out.

LO 19.7.1 – Explain in words the relationship between the excretion of a solute and its renal clearance.

Relationship:
Excretion = Filtration − Reabsorption + Secretion

Clearance = how fast substance is removed from plasma

LO 19.7.2 – Explain how clearance can be used as an indirect indicator of renal handling of a solute.

• Clearance = GFR → no reabsorption/secretion

• Clearance < GFR → reabsorption

• Clearance > GFR → secretion

Examples:

• Inulin → GFR marker

• Glucose → reabsorbed

• Penicillin → secreted

what is the renal clearance formula?

Formula and variables:

C = (Ux x V)/Px

• C = renal clearance (mL/min)

• Ux = urine concentration of substance (mg/mL)

• V = volume of urine produced per minute (mL/min)

• Px = plasma concentration of substance (mg/mL)

what are important substance values for clearance?

creatinine & inulin - 100 % cleared bc freely filtered n none reabsorbed or secreted

glucose - 0% cleared because all gets reabsorbed to plasma

penicillin - 150% bc freely filtered AND half is secreted to urine as well