Renal Function

Question 1

kidney:
- shape
- size
- weight
- regions

Answer 1

Bean shaped organ
11cm long, 5cm wide, 3cm thick
Weight: 130g
2 regions
- Cortex (outer)
- Medulla (inner)

*main job is to filter blood, remove waste, and keep water, electrolytes, and pH balanced.

Question 2

functional unit of kidney

Answer 2

Nephrons
- each kidney has 1–1.5 million nephrons

Question 3

what are the 2 types of nephron

Answer 3

Cortical nephrons (85%)
– handle most waste removal
– reabsorption of nutrients.

Juxtamedullary nephrons
– help concentrate urine by controlling water balance

Question 4

what are the main processes of kidney

Answer 4

1. Renal blood flow
   – blood enters kidney through renal artery.
2. Glomerular filtration
   – blood is filtered at the glomerulus, producing filtrate.
3. Tubular reabsorption
   – useful substances (water, glucose, electrolytes) are taken back into blood.
4. Tubular secretion
   – extra waste, acids, or ions are added to urine.

Question 5

how much renal blood flows through the kidneys per minute and the renal plasma blood flow

Answer 5

Renal blood flow ≈ 1200 mL/min
Renal plasma flow ≈ 600–700 mL/min

Question 6

briefly explain the renal blood flow pathway

Answer 6

Renal artery – brings blood into kidney.

Afferent arteriole – carries blood into the glomerulus.

Glomerulus – capillary network where filtration happens.

Efferent arteriole – carries blood away (smaller than afferent → creates higher pressure for filtration).

Peritubular capillaries – surround proximal & distal tubules → reabsorb nutrients and adjust
urine.

Vasa recta – (around juxtamedullary nephrons) →
exchange of water and salts → maintain medulla’s osmotic gradient (important for urine concentration)
[go back to circulation]

Renal vein – returns filtered blood back to circulation.

*smaller efferent arteriole creates high pressure in the glomerulus, pushing plasma out to form filtrate.

Question 7

briefly explain the Urinary Filtrate Flow (Pathway of Urine)

Answer 7

1. Bowman’s capsule – collects filtrate.
2. Proximal Convoluted Tubule (PCT) – reabsorbs most water, glucose, electrolytes.
3. Descending Loop of Henle (LOH) – reabsorbs water.
4. Ascending LOH – reabsorbs salts (Na+, Cl−), impermeable to water.
5. Distal Convoluted Tubule (DCT) – fine-tuning; hormones act here (Aldosterone, PTH).
6. Collecting duct – final concentration of urine (ADH effect).
7. Renal calyces → Ureter → Bladder → Urethra – urine storage and excretion.

*Plasma = liquid part of blood; it’s what gets filtered in the kidney.

Question 8

where does filtration of plasma occur?

Answer 8

glomerulus

Question 9

what structure creates high glomerular pressure for filtration?

Answer 9

the smaller efferent arteriole

Question 10

A coil of ~8 capillary lobes located inside Bowman’s capsule.

Answer 10

glomerulus
- filter blood plasma into Bowman’s capsule

Question 11

3 main factors affecting glomerular filtration

Answer 11

cellular structure
glomerular pressure
filtration barrier integrity

Question 12

what are the 3 layers of the glomerular filtration barrier

Answer 12

1. fenestrated capillary endothelium
   - it has pores that increase permeability = allow water and small solutes through but not blood cell
   - CAPILLARY PERMEABILITY
2. basement membrane
   - act as a size and charge filter
   - block large proteins

[When the glomerular basement membrane (GBM) is damaged, proteins (like albumin) that are normally too big or repelled to pass through can now leak into the urine (proteinuria)]

3. visceral epithelium
   - has podcytes
   - repels -ve charge molecules

Question 13

Specialized cells of Bowman’s capsule with foot-like processes that form slit pores for filtration.

Answer 13

podocytes

Question 14

A property of the filtration barrier that repels negatively charged proteins (e.g., albumin), preventing them from being filtered.

Answer 14

shield of negativity

Question 15

Why is glomerular pressure important?

Answer 15

helps push plasma and solutes out of the capillaries into Bowman’s capsule

Question 16

glomerular filtration is affected by

Answer 16

1. Glomerular structure (barrier layers)
   [If these layers are healthy → only water and small solutes pass
   If damaged (like in kidney disease) → proteins or even blood cells can leak into urine]
2. Pressures (hydrostatic & oncotic)
   [Hydrostatic pressure (from blood flow) pushes fluid out into Bowman’s capsule
   Oncotic pressure (from plasma proteins) pulls water back into blood
   Capsule pressure resists fluid entry
   The balance of these decides how much filtrate is made (Net Filtration Pressure)]
3. RAAS system (renin–angiotensin–aldosterone feedback)
   [adjusts blood flow and pressure]

Question 17

why is the glomerular pressure matters?

Answer 17

afferent arteriole (incoming) is wider than the efferent arteriole (outgoing)
= creates hydrostatic pressure inside the glomerulus.

that pressure pushes plasma fluid through the filtration barrier into Bowman’s capsule.

opposing forced that resist filtration:
1. Fluid pressure in Bowman’s capsule – pushes back against incoming filtrate.
2. Oncotic pressure – the “pull” of plasma proteins in the blood that hold water back.

Net Filtration Pressure = hydrostatic pressure – (Bowman’s capsule pressure + oncotic pressure)

Question 18

what are the opposing forces (that resist filtration):

Answer 18

1. Fluid pressure in Bowman’s capsule
   – pushes back against incoming filtrate.
2. Oncotic pressure
   – the “pull” of plasma proteins in the blood that hold water back.

Net Filtration Pressure = hydrostatic pressure – (Bowman’s capsule pressure + oncotic pressure)

Question 19

Which arteriole is smaller: afferent or efferent?

Answer 19

Efferent arteriole (this creates high glomerular pressure).

Question 20

What structure helps autoregulate glomerular filtration rate (GFR)?

Answer 20

Juxtaglomerular apparatus (JGA)
- adjusts the blood vessel size to keep filtration steady even if systemic blood pressure changes

Question 21

if blood pressure drops and rises, what will happen to the afferent and efferent arterioles

Answer 21

If BP drops:
Afferent arteriole dilates (opens wider).
Efferent arteriole constricts (narrows).

= maintains glomerular pressure to keep filtration going.

If BP rises:
Afferent arteriole constricts.
This protects the glomerulus from too much pressure and damage.

Question 22

this responds to charge in BP and plasma sodium content

Answer 22

Renin–Angiotensin–Aldosterone System (RAAS)
- monitored by juxtaglomerular apparatus

[if blood pressure or sodium drops, the juxtaglomerular apparatus (JGA) detects it = then it will raise BP and vol.]

[JGA = juxtaglomerular cells (afferent arteriole) + macula densa (DCT)]

Question 23

juxtaglomerular cells (afferent arteriole) + macula densa (DCT)

Answer 23

juxtaglomerular apparatus (JGA)

Question 24

steps in Renin–Angiotensin–Aldosterone System (RAAS)

Answer 24

1. JGA releases renin.
2. Renin converts angiotensinogen → angiotensin I.
3. In the lungs, ACE converts angiotensin I → angiotensin II (active).
4. Angiotensin II actions:
   - Dilates afferent & constricts efferent arterioles → keeps glomerular pressure steady.
   - Increases Na⁺ & water reabsorption in proximal tubule.
   - Stimulates aldosterone (adrenal cortex) → keeps more Na⁺ & water.
   - Stimulates ADH (hypothalamus) → keeps more water.

Question 25

what is the negative feedback of the RAAS

Answer 25

When BP and sodium normalize, renin secretion stops

Question 26

what happens if blood pressure is too low

Answer 26

- Kidneys need enough blood pressure to push plasma through the glomerulus (for filtration). - If blood pressure is too low, filtration slows down or even stops → waste isn’t removed properly. 1. Glomerular filtration rate (GFR) drops → less filtrate is made. 2. Reabsorption and secretion are hampered because less fluid reaches the nephron. 3. Body risks waste buildup + less water/electrolyte balance. RAAS helps: The Juxtaglomerular Apparatus (JGA) senses ↓ BP or ↓ sodium It releases renin, starting the RAAS cascade. RAAS raises BP by: - Constrict BV (angiotensin II) - Keeping more Na⁺ and water (aldosterone + ADH) - Adjusting arteriole size (afferent dilates, efferent constricts) → restores glomerular pressure

Question 27

when the glomerulus filters plasma, how much filtrate is being produced

Answer 27

~120 mL of fltrate per minute. [iIf the body lost all of that, we’d quickly lose essential water, glucose, amino acids, and salts. to prevent this, the nephron reabsorbs useful substances back into the bloodstream through tubular reabsorption.]

Question 28

what are the 2 mechanism of reabsorption

Answer 28

1. Active transport (needs energy + carrier proteins) - Glucose, amino acids, salts → PCT. - Sodium → PCT & DCT. - Chloride → ascending Loop of Henle. 2. Passive transport (no energy, moves with gradient) - Water → PCT, descending Loop of Henle, collecting duct (not ascending loop). - Urea → PCT & ascending Loop of Henle

Question 29

summary table of tubular reabsorption

Answer 29

transes

Question 30

this the movement of substances from blood → filtrate

Answer 30

tubular secretion [blood (peritubular capillaries) → into the filtrate (tubular fluid) helps the body get rid of wastes and maintain balance of hydrogen, potassium, drugs, toxins, etc]

Question 31

How is secretion different from reabsorption?

Answer 31

reabsorption returns substances to blood secretion removes substances from blood into filtrate

Question 32

functions of tubular secretion

Answer 32

1. Remove waste products not filtered by the glomerulus. - Example: Many drugs and toxins are bound to plasma proteins → too big to filter. - In the proximal tubule, they detach from proteins → secreted into urine. 2. Maintain acid–base balance (pH 7.4). - Blood buffers acids by secreting H⁺ ions into filtrate. - Conserves bicarbonate (HCO₃⁻), the main blood buffer.

Question 33

briefly explain acid-base mechanism

Answer 33

1. H⁺ + Bicarbonate Recycling (PCT) - H⁺ secreted into filtrate binds with filtered HCO₃⁻. - Prevents HCO₃⁻ loss → returns it to blood. - Reabsorbs almost 100% of filtered bicarbonate. 2. H⁺ + Phosphate (Distal Nephron) - H⁺ combines with phosphate (PO₄³⁻) → excreted as acid phosphate. 3. H⁺ + Ammonia (NH₃) (PCT & Collecting Duct) - Tubules produce NH₃ from glutamine breakdown. - NH₃ + H⁺ → NH₄⁺ (ammonium). - NH₄⁺ is excreted in urine.

Question 34

which parts of the nephron handle H⁺ excretion with ammonia?

Answer 34

Proximal tubule and collecting duct

Question 35

What is the overall role of phosphate and ammonium in urine?

Answer 35

They act as buffers, removing H⁺ to maintain blood pH. H⁺ combines with phosphate → excreted as acid phosphate in urine Tubules make NH₃ → binds H⁺ → forms NH₄⁺ → excreted in urine

Question 36

purpose of the glomerular filtration test

Answer 36

they test the filtering ability of the glomeruli (GFR – glomerular filtration rate).

Question 37

formula to find creatinine clearance

Answer 37

C = UV / P [ ● C = clearance (mL/min) = GFR ● U = urine creatinine concentration (mg/dL) ● V = urine volume per minute (mL/min) ● P = plasma creatinine concentration (mg/dL)]

Question 37

what formula is used to find glomerular filtration rate, GFR)

Answer 37

Cockcroft-Gault Formula - held adjust drug dose in patients w impaired kidney function formula sa transes (Subtract age from 140 → older age → lower kidney function. Multiply by body weight in kg → bigger body → higher creatinine production. Divide by (72 × serum creatinine) → higher creatinine → lower kidney function. Multiply by 0.85 for females → adjust for sex differences.)