Renal Physiology Flashcards
1
Q
Functions of the kidneys
A
- Regulation of bld. ionic composition
- Regulation of bld. volume
- Regulation of bld. pH
- Regulation of bld. pressure
- Maintenance of bld. osmolarity
- Production of hormones (two)
- Excretion of wastes & foreign substances
2
Q
How does the kidneys regulate blood ionic composition?
A
Kidneys help regulate the blood levels of several ions:
- Na+
- K+
- Ca2+
- Cl-
- HPO4^2- (phosphate ions)
3
Q
How does the kidneys adjust blood vol.?
A
Conserve/Eliminate water in urine
- Inc. in bld vol. = inc. in bld pressure
4
Q
How does the kidneys regulate blood pH?
A
Kidneys excrete variable amt. of H+ into urine & conserve HCO3- (H+ buffer)
5
Q
How does the kidneys regulate bld. pressure?
A
Regulates bld pressure by secreting renin (enzyme) = activates RAAS pathway
- inc. renin = inc. bld. pressure
6
Q
How does the kidneys maintain bld. osmolarity?
A
Separately regulates loss of water & loss of solutes in urine
- maintain relatively constant bld. osmolarity close to 300 milliosmoles per litre (mOsm/liter)
7
Q
What are the hormones produced by the kidneys? does the kidneys
A
- Calcitriol: active form of vitamin D = helps regulate calcium homeostasis
- Erythropoietin = stimulates prod. of RBCs
8
Q
How does the kidneys excrete wastes & foreign substances?
A
Excrete wastes (formation of urine)
- wastes from metabolic rxns in body (ammonia & urea from deamination of a.a. / bilirubin from catabolism of hemoglobin)
- drugs & environmental toxins
9
Q
What happens in the renal corpuscle?
A
Production of filtrate
10
Q
What happens in the proximal convoluted tubule?
A
Reabsorption of water, ions, all organic nutrients
11
Q
What happens in the descending thin limb of the nephron loop?
A
Further reabsorption of water
12
Q
What happens in the thick ascending limb of the nephron loop?
A
Reabsorption of sodium & chloride ions
13
Q
What happens in the distal convoluted tubule?
A
Secretion (move from blood into tubular fluid –> become urine) of ions, acids, drugs, toxins
Variable reabsorption of water, Na+, Ca2+ (under hormonal control)
14
Q
What happens in the collecting duct?
A
Variable reabsorption of water & reabsorption/secretion of Na+, K+, H+, HCO3-
15
Q
What does the papillary duct do?
A
Delivers urine to minor calyx
16
Q
What are the 3 basic renal processes for formation of urine?
A
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
17
Q
What happens during glomerular filtration?
A
- Water & most solutes (except proteins) in bld. plasma move across the wall of glomerular capillaries
- Filtered & move into glomerular capsule & into renal tubule
(a.a. cannot pass through bc too big)
18
Q
What happens during tubular reabsorption?
A
- Filtered fluid flows through the renal tubules & collecting ducts
- Tubule cells reabsorb ~99% of the filtered water & many useful solutes
- Water & solutes return to the blood as it flows through the peritubular capillaries & vasa recta
19
Q
What happens during tubular secretion?
A
- Filtered fluid flows through renal tubules & collecting ducts
- Renal tubule & duct cells secrete other materials (metabolic wastes, drugs, excess ions) into the fluid
- Removes a substance from blood!
20
Q
How many % of plasma is filtered and excreted?
A
20% of plasma that passes through the glomerulus is filtered
<1% of filtered fluid is excreted
20
Q
What cells line the renal corpuscle?
A
Squamous cells
21
Q
What cells line the proximal convoluted tubule?
A
Cuboidal cells with abundant microvilli (got mitochondria)
22
Q
What cells line the descending thin limb of the Loop of Henle?
A
Squamous cells
23
Q
What cells line the thin ascending limb of the Loop of Henle?
A
Squamous cells (reabsorbs water)
24
What cells line the thick ascending limb of the Loop of Henle?
Low cuboidal cells
25
What cells line the distal convoluted tubule?
Cuboidal cells with few microvilli
26
What cells line the collecting duct?
- Principal cells (adjust electrolyte conc.)
- Intercalated cell (regulate pH balance)
27
What lines the papillary duct?
Columnar cells
28
How to find the amount of solute excreted?
Amount filtered - Amount reabsorbed + Amount secreted = Amount of solute excreted
29
% of each process
Plasma vol. entering afferent arteriole = 100%
- 20% of volume filtered
- 19% of fluid reabsorbed
- >99% of plasma entering kidney returns to systemic circulation
- <1% of vol. is excreted to external environment (fluctuates based on water consumption)
30
What is the outer wall of the glomerular (Bowman's) capsule lined with?
Capsular epithelium
- Continuous with visceral epithelium that covers glomerular capillaries
- Separated by capsular space
31
What does the visceral epithelium of the glomerular (Bowman's) capsule consist of?
Large cells (podocytes)
- complex processes/"feet" that wrap around specialized dense layer of glomerular capillaries
- Reinforces glomerular capsule bc. of bld. pressure is vv high
32
What are filtration slits?
Narrow gaps between adjacent pedicels (slender extensions of podocytes)
- Materials passing out of blood at glomerulus must be small enough to pass through the slits
33
What controls the filtration at the glomerulus?
1. Fenestration (pore) of glomerular endothelial cell --> prevent RBCs but allows all components of bld. plasma
2. Basal lamina of glomerulus --> prevent larger proteins
3. Slit membrane b/w pedicels --> prevent medium-sized proteins
34
What drives filtration across the walls of glomerular capillaries?
1. Glomerular blood hydrostatic pressure (55 mmHg)
2. Bowman's capsular hydrostatic pressure (15 mmHg)
3. Blood colloid osmotic pressure (30 mmHg)
35
What is the Bowman's capsular hydrostatic pressure?
15 mmHg
- Hydrostatic pressure exerted against filtration mbn by fluid already in the capsular space & renal tubule
- Opposes filtration & represents "back pressure"
Basically, liquid that is alr in the capsule itself --> opposing force = push against the filtration
36
What is blood colloid osmotic pressure due to?
30 mmHg
- Due to proteins in plasma but not in Bowman's capsule
- Pulls fluid back into the capillaries
(bc inside have protein, outside no protein = draw water back in)
37
What is the major force that induces glomerular filtration?
Glomerular blood hydrostatic pressure
55mmHg
38
What is the net filtration pressure (NFP)?
Glomerular Blood Hydrostatic Pressure - Capsular Hydrostatic Pressure - Blood Colloid Osmotic Pressure
= 55 - 15 - 30
= 10 mmHg (to drive continuous filtration
39
What is glomerular filtration rate (GFR) influenced by?
- Net filtration pressure
- Filtration coefficient
40
What is net filtration pressure?
Hydrostatic pressure - (colloid osmotic pressure + fluid pressure)
41
What is filtration coefficient?
- Surface area of glomerular capillaries available for filtration
- Permeability of interface b/w the capillary & Bowman's capsule
42
What controls the GFR?
1. Autoregulation --> local level
2. Autonomic regulation --> sympathetic division of ANS (inc. bld pressure = inc. GFR)
3. Hormonal regulation --> initiated by kidneys
43
How does arteriolar vasoconstriction affect GFR?
- Decreases GFR
Decreases blood flow into glomerulus = dec. glomerular capillary bld. pressure & dec net filtration pressure = dec. GFR
44
How does arteriolar vasodilation affect GFR?
- Increases GFR
Inc. bld. flow into glomerulus = inc. glomerular capillary bld. pressure = inc. net filtration pressure = inc. GFR
45
What are myogenic responses that maintains GFR (autoregulation of GFR)?
Changing diameters of:
- afferent arterioles
- efferent arterioles
- glomerular capillaries
46
What does a reduced blood flow/glomerular blood pressure trigger?
- Dilation of afferent arteriole
- Dilation of glomerular capillaries
- Constriction of efferent arterioles
47
What does a rise in renal bld. pressure cause?
- Stretches walls of afferent arterioles
- Causes smooth muscle cells to contract
- Constricts afferent arterioles
- Decreases glomerular bld. flow
48
Autoregulation maintains a nearly constant GFR when mean _________________ is b/w ______ and ______ mmHg.
Autoregulation maintains a nearly constant GFR when mean arterial blood pressure is b/w 80 and 180 mmHg.
49
What does the tubuloglomerular feedback mechanism involve?
Specialized combination of tubular & vascular cells of the juxtaglomerular apparatus (DCT)
50
What does the macula densa cells detect?
Changes in salt level of the fluid flowing past
51
What does increased salt in fluid cause the macula densa to do?
- Secrete ATP & adenosine
- Causes smooth muscles of adjacent afferent arterioles to constrict = reduce bld. flow into glomerulus & reducing GFR
Inc. salt means that flow rate along PCT & LOH is too high = too fast = cells X enough time to reabsorb the salt
52
What is renin secreted by granular cells involved in?
Involved in salt & water balance
- enzyme
53
What is the tubuloglomerular feedback mechanism in GFR autoregulation?
1. GFR inc.
2. Flow through tubule inc.
3. Flow past macula densa inc. + more salt
4. Paracrine (adenosine) from macula densa to afferent arteriole
5. Afferent arteriole constricts
6. Resistance in afferent arteriole inc.
7. Hydrostatic pressure in glomerulus dec.
8. GFR dec.
54
What is involved in hormonal regulation of the GFR?
- Renin-angiotensin- aldosterone system (RAAS)
- Atrial Natriuretic Peptide (ANP)
55
What are the stimuli that causes the juxtaglomerular complex (JGC) to release renin (3)?
1. Decline in bld. pressure at glomerulus --> due to dec. in bld. vol + fall in systemic pressures (e.g. haemorrhage)
2. Stimulation of juxtaglomerular cells by sympathetic innervation
3. Decline in osmotic conc. of tubular fluid at macula densa (low sodium)
56
What happens with angiotensin II activation?
- Constricts efferent arterioles of nephron --> elevates glomerular pressures & filtration rates
- Stimulates reabsorption of Na+ ions & water at PCT
- Stimulates secretion of aldosterone by adrenal cortex in DCT & collecting tubules --> inc. Na+, Cl-, water reabsorption, loss of K+
- Stimulates thirst
- Triggers release of antidiuretic hormone (ADH)/Vasopressin --> stim. reabsorption of water in DCT & collecting tubules
57
Does angiotensin II constrict efferent or afferent arterioles more?
Constricts glomerular arterioles but
- greater effect on efferent arterioles
58
How do kidneys continue to filter enough blood when there is a drop in bld. flow?
Angiotensin II constricts efferent arterioles more than afferent arterioles --> forces bld. to build up in the glomerulus --> inc. glomerular pressures --> maintain GFR
59
What happens when homeostasis is disturbed by dec. blood flow to kidneys?
slide 21 of renal physio
60
What is the dual control of aldosterone secretion?
Inc. plasma K+ secretion by principal tubular cells late in the nephron
- Stimulates aldosterone to inc. tubular K+ secretion = inc. urinary K+ excretion
Low Na+/ECF vol./arterial pressure = inc renin = inc angiotensin I = inc angiotensin II
- Stimulates aldosterone to inc. tubular Na+ reabsorption = dec. urinary Na+ excretion
61
What is K+ balance maintained by?
Excreting the amt. ingested (minus the amt lost in faeces & sweat)
62
What does hyperkalemia cause and how is it corrected?
(high plasma K+)
- cardiac arrhythmias & inc. excitability of neurons & skeletal muscles
Correction: inc. aldosterone release & secretion of K+
63
What does hypokalemia cause and how is it corrected?
(low plasma K+; result of kidney dz, diarrhoea, diuretics)
- muscle weakness & failure of resp muscles & heart
Correction: no secretion of K+ into collecting ducts
64
What does increased atrial stretch (caused by inc. BP --> Na+ retention/inc. vol./expansion of ECF vol.) cause the cardiac atria to secrete?
Hormonal atrial natriuetic peptide (ANP) and the cardiac ventricles secrete brain natriuretic peptide (BNP)
65
What does atrial natriuetic peptide (ANP) and brain natriuretic peptide (BNP) promote?
Promote natriuretic, diuretic, hypotensive effects to help correct original stimuli
66
What is the purpose of tubular reabsorption?
- All plasma constituents (except plasma proteins) indiscriminately filtered through glomerular capillaries
- Inc. wastes + desirable materials --> nutrients/electrolytes/etc
- Essential materials brought back into plasma by tubular reabsorption
67
What are the layers the reabsorbed substance must pass through?
1. Luminal/apical mbn of tubular cell
2. Cytosol of tubular cell
3. Basolateral mbn of tubular cell
4. (Diffuse through) Interstitial fluid
5. Capillary wall
- Can be passive diffusion or active (Na+K+ pump)
68
How is Na+ reabsorbed?
- Basolateral Na+-K+ pump actively tpt Na+ from tubular cell into the interstitial fluid
- Establishes a conc. gradient for passive movement of Na+ from lumen into tubular cell
