urinary 2

Question 1

The glomerular filtration rate (GFR) is the volume of filtrate formed by both kidneys per minute.

Answer 1

The heart pumps about 5 L of blood per minute at rest.

About 20% (~1 L/min) of that blood enters the kidneys to be filtered.

Average filtrate production (GFR):

Men: ~125 mL/min (range 90–140 mL/min)

Women: ~105 mL/min (range 80–125 mL/min)

Question 2

The glomerular filtration rate (GFR) is the volume of filtrate formed by both kidneys per minute.

Answer 2

The heart pumps about 5 L of blood/min at rest.

About 20% (~1 L/min) enters the kidneys to be filtered.

Average filtrate production (GFR):

Men: ~125 mL/min (range 90–140 mL/min)

Women: ~105 mL/min (range 80–125 mL/min)

This equals ~180 L/day in men and ~150 L/day in women.

> 95% of this filtrate is reabsorbed back into the blood.

Only about 1–2 L of urine is produced each day.

Question 3

What affects glomerular filtration rate (GFR) and how does filtration occur?

Answer 3

Influenced by:

Hydrostatic pressure

Colloid osmotic pressure

Occurs as:

Pressure forces fluid and solutes through a semipermeable membrane

Solute movement is limited by particle size

Question 4

What is hydrostatic pressure and how does it affect fluid movement?

Answer 4

Hydrostatic pressure = pressure a fluid exerts against a surface

When fluid is on both sides of a barrier:

Each fluid exerts pressure in opposite directions

Net fluid movement occurs toward the area of lower pressure

Question 5

What is osmosis and how does osmotic pressure work?

Answer 5

Osmosis = movement of water (solvent) across a membrane impermeable to solute

Creates osmotic pressure until solute concentrations equalize on both sides

Water moves toward the higher solute concentration as long as a difference exists

Question 6

What happens during osmosis?

Answer 6

Movement of water (solvent) across a membrane impermeable to solute

Creates osmotic pressure until solute concentrations are equal

Water moves toward the higher solute concentration

Question 7

What are the glomerular capillaries and Bowman’s capsule in the kidney?

Answer 7

Glomerular capillaries:

Tiny blood vessels inside the glomerulus.

Site where blood is filtered.

High hydrostatic pressure forces water and small solutes out of blood.

Bowman’s capsule:

Cup-shaped structure surrounding the glomerulus.

Collects the filtrate (water, ions, small molecules) from glomerular capillaries.

Proteins and blood cells cannot pass, so filtrate is mostly protein-free.

Question 8

Why does water move from the glomerular capillaries into Bowman’s capsule during filtration? How does osmotic pressure affect this process?

Answer 8

Filtration membrane fenestrations limit the size of particles that can cross into Bowman’s capsule.

Glomerular capillary osmotic pressure: ~30 mmHg (due to plasma proteins).

Bowman’s capsule osmotic pressure: ~0 mmHg (almost no proteins present).

Consequence: There is no osmotic gradient pulling water back into the capsule.

Net effect: Water is primarily pushed out of capillaries by hydrostatic pressure, not pulled by osmotic pressure.

Question 9

What forces determine fluid movement across the glomerular capillaries into Bowman’s capsule, and how is net filtration pressure (NFP) calculated?

Answer 9

NFP

Fluid movement: Water and small solutes are pushed from glomerular capillaries into Bowman’s capsule.

Driving force: Hydrostatic pressure in glomerular capillaries (GBHP) pushes fluid out.

Opposing forces:

Capsular hydrostatic pressure (CHP) — fluid already in Bowman’s capsule resists further movement.

Blood colloid osmotic pressure (BCOP) — plasma proteins in blood pull water back into capillaries.

Net Filtration Pressure (NFP) formula:

GBHP
−
CHP
−
BCOP
NFP=GBHP−CHP−BCOP

Typical value: ~10 mmHg, enough to drive filtration despite opposing pressures.

Key point: Filtration is mainly driven by hydrostatic pressure, while osmotic and capsular pressures oppose it.

Question 10

Why is glomerular filtration sensitive to small changes in blood pressure or osmolarity, and how does the kidney respond?

Answer 10

Back (Answer):

Low net filtration pressure (NFP) (~10 mmHg) means:

Small changes in blood pressure or blood osmolarity can greatly affect filtrate volume.

Kidney response:

Uses autoregulation to maintain relatively constant glomerular filtration rate (GFR).

Mechanisms adjust afferent arteriole diameter and other factors to stabilize filtration.

Question 11

Front (Question):
How does the kidney use autoregulation to maintain stable glomerular filtration rate (GFR) when blood pressure changes?

Answer 11

ack (Answer):

Autoregulatory principle: Smooth muscle in arterioles responds to stretch — Bayliss Effect: stretched muscle contracts to resist changes.

If blood pressure rises:

Afferent arterioles contract (reduce blood flow into glomerulus)

Efferent arterioles slightly dilate
→ Limits increase in GFR

If blood pressure drops:

Afferent arterioles dilate (increase blood flow)

Efferent arterioles slightly constrict
→ Helps maintain GFR

Question 12

What is the effect of renal autoregulation on glomerular filtration, and what happens when blood pressure drops too low?

Answer 12

Autoregulation outcome:

Maintains relatively steady blood flow into glomerulus

Maintains stable glomerular filtration rate (GFR) over a wide range of systemic blood pressures

Effective range: Mean arterial pressure (MAP) > 60 mmHg

Below 60 mmHg:

Autoregulation fails

Renal function is impaired

Can lead to systemic disorders and threaten survival

Question 13

How does sympathetic nervous system activity affect kidney blood flow and glomerular filtration?

Answer 13

Kidney innervation: Sympathetic neurons via celiac plexus and splanchnic nerves.

Low sympathetic activity (resting):

Arterioles vasodilate

Increased blood flow through kidneys

Higher glomerular filtration rate (GFR)

High sympathetic activity (stress, exercise, shock):

Arterioles vasoconstrict

Reduced blood flow through glomerulus

Lower GFR, less filtrate produced

Question 14

If blood pressure falls too much,
the sympathetic nerves will also
stimulate the release of …….
* Additional …… increases
production of the powerful
vasoconstrictor …………

• ………………….. will also
  stimulate ………….
  production to augment
  blood volume through
  retention of more….and
  …

Answer 14

If blood pressure falls too much,
the sympathetic nerves will also
stimulate the release of renin
* Additional renin increases
production of the powerful
vasoconstrictor angiotensin
II
* Angiotensin II will also
stimulate aldosterone
production to augment
blood volume through
retention of more Na+ and
water

Question 15

how many liteirs of filtrate per day

how much urine

Answer 15

180

2 litters

Question 16

The main structures responsible for
recovery of urine are

Answer 16

• Proximal convoluted tubule
• Loop of Henle
• Distal convoluted tubule
• Collecting ducts

Question 17

What happens to the filtrate from the glomerular corpuscle to the ureters?

Answer 17

The glomerular corpuscle produces a filtrate free of cells and large proteins. As it moves from the PCT to the ureters, it is modified by reabsorption and secretion until it becomes true urine.

Question 18

: How do different parts of the nephron handle water and solutes?

Answer 18

A: Each nephron segment varies in reabsorption:

PCT: recovers most Na⁺, K⁺, glucose, amino acids, vitamins, and a large portion of water.

Loop of Henle & DCT: recover additional water (~90% total).

Collecting ducts: only ~10% of water (~18 L) reaches here

Question 19

Q: How is water reabsorption in the nephron regulated?

Answer 19

A: Water reabsorption is tightly controlled:

Directly: by ADH (controls water) and aldosterone (controls sodium).

Indirectly: by renin.

Collecting ducts: respond to hydration:

High plasma osmolarity → more water reabsorbed, urine volume ↓ (dehydrated)

Low plasma osmolarity → less water reabsorbed, urine volume ↑ (well-hydrated)

Question 20

How does aldosterone regulate sodium, water, and blood pressure?

Answer 20

Secreted by: adrenal cortex in response to angiotensin II.

Action: stimulates principal cells to produce Na⁺/K⁺ channels and Na⁺/K⁺ ATPase pumps.

Effect: ↑ Na⁺ reabsorption → ↑ water reabsorption → ↑ blood volume → ↑ blood pressure.

Question 21

Q: What hormone opposes aldosterone and how?

Answer 21

: Atrial natriuretic peptide (ANP) antagonizes aldosterone by promoting salt and water excretion. It is released when atrial pressure is high.

Question 22

Q: How is water reabsorbed in the nephron?

Answer 22

Obligatory water reabsorption: In the PCT, Na⁺ is actively pumped into interstitial space and diffuses into peritubular capillaries; water follows passively to maintain isotonicity.

Facultative water reabsorption: In the collecting ducts, water reabsorption is regulated by aquaporins (activated/inactivated by ADH).

Question 23

what are the two surfaces

Answer 23

Apical surface: This is the side of the cell that faces the inside of a tube, cavity, or organ—basically the “open space” where substances enter or exit. For example, in the kidney tubule, it faces the filtrate. Think of it as the “inside-facing” side.

Basal surface: This is the side of the cell that faces the underlying tissue or basement membrane. It’s where the cell attaches and often where substances exit to get into the blood or connective tissue. Think of it as the “outside-facing” side.

✅ Key idea: Apical = towar

Question 24

Q: How do nephron cell surfaces move substances?

Answer 24

Apical surface (facing lumen): Na⁺ brings in Cl⁻, Ca²⁺, glucose, amino acids, PO₄³⁻ (symport) or exchanges for H⁺ (antiport).

Basal surface (facing blood): moves substances out toward the blood

Question 25

How is bicarbonate (HCO₃⁻) reabsorbed in the nephron?

Answer 25

In the PCT lumen, HCO₃⁻ combines with H⁺ → H₂CO₃. Carbonic anhydrase converts H₂CO₃ → CO₂ + H₂O, which diffuse across the apical membrane into the cell. This process is essential for acid–base balance.

Question 26

How is bicarbonate (HCO₃⁻) reabsorbed in the PCT?

Answer 26

Inside the cell, CO₂ + H₂O → HCO₃⁻. HCO₃⁻ is co-transported with Na⁺ across the basal membrane into the interstitial space. Na⁺/H⁺ antiporter moves H⁺ back into the lumen, continuing the cycle.

Question 27

Q: What are the sections of the Loop of Henle and how do cortical vs juxtamedullary loops differ?

Answer 27

Sections: Descending: thin & thick Ascending: thin & thick Cortical nephrons: loops short, stay mostly in cortex/outer medulla Juxtamedullary nephrons: loops long, extend deep into medulla

Question 28

Q: How does the Loop of Henle recover Na⁺ and water, and how does filtrate osmolarity change?

Answer 28

Descending loop: water exits via osmosis through permanent aquaporins → filtrate becomes hypertonic (~1200 mOsm/kg at the bottom). Ascending loop: Na⁺ and other ions actively transported out, water cannot follow → filtrate becomes hypotonic as it rises. Overall: Loop creates a concentration gradient to recover water and salts efficiently.

Question 29

Q: What happens in the thick ascending limb of the Loop of Henle?

Answer 29

Made of simple cuboidal cells and completely impermeable to water (no aquaporins). Na⁺ is actively pumped out of the filtrate. Because ions leave but water can’t, the filtrate becomes hypotonic. The pumped-out Na⁺ helps create the hyperosmotic medulla.

Question 30

Q: Why does blood flow slowly through the vasa recta?

Answer 30

To preserve the countercurrent multiplier system. Slow flow lets blood cells lose and regain water safely (no shrinking or bursting). Prevents the washout of Na⁺ and urea, keeping the medullary osmotic gradient intact for water and solute reabsorption.

Question 31

How is urine transported from the kidney to the bladder?

Answer 31

Urine drains from nephrons → calyces → renal pelvis in the hilum. The renal pelvis narrows into the ~30 cm ureter. Urine is moved not by gravity, but by peristaltic waves in the ureter. A one-way physiological sphincter at the bladder entrance prevents urine from flowing backward into the ureter.

Question 32

Q: What are the key structural features of the urinary bladder?

Answer 32

Collects urine from both ureters. Has detrusor muscle (crisscrossing smooth muscle) that makes it highly stretchable. Lined with transitional epithelium, which can expand and contract with volume changes. Adult bladder volume ranges from near zero to ~500–600 mL.

Question 33

Q: How is urination (micturition) controlled, and when does the urge become strong?

Answer 33

At ~150 mL, you feel the urge to pee, but you can easily hold it. Voluntary control depends on keeping the external urethral sphincter contracted. As the bladder fills to ~300–400 mL, voluntary control eventually fails → incontinence.

Question 34

How does normal micturition (urination) occur?

Answer 34

Stretch receptors in the bladder wall send signals to the sacral spinal cord when the bladder fills. This triggers a parasympathetic reflex → detrusor muscle contracts and the internal urethral sphincter relaxes. Actual voiding is controlled voluntarily by the external urethral sphincter (skeletal muscle).

Question 35

Bladder Position: Female vs Male

Answer 35

Females The bladder sits in front of the uterus, behind the pubic bone, and in front of the rectum. During late pregnancy, the growing uterus squishes the bladder, so there's less room → more frequent peeing. Males Similar basic position (behind the pubic bone, in front of the rectum). No uterus, obviously. Prostate sits just under the bladder, and the urethra is longer