Renal system Flashcards
1
Q
Major functions of the urinary system
A
- filter blood to remove toxins, metabolic wastes + excess ions from circulation
- produce urine
- returned filtered nutrients + important ions back to blood
2
Q
list 2 basic renal funcrions
A
- water and ion balance
- regulation of BP (through Na balance + renin-angiotensin system)
3
Q
describe the blood flow through the kidney
A
renal artery
afferent arterioles
nephrons via glomerulus
(renal corpuscle
peritubular capillaries)
4
Q
where are the two types of nephrons found
A
cortex = cortical nephron
medulla = juxtamedullary nephron
5
Q
describe the flow of filtrate through the nephron
A
- glomerulus
- proximal convoluted tubule
- nephron loop
- distal convoluted tubule
- collecting duct (becomes urine)
6
Q
nephron basic structure + function
A
- filters blood plasma to form urine
- renal corpuscle + renal tubule
7
Q
how is filtrate produced from the blood at the renal corpuscle
A
- blood enters through afferent arteriole
- moves through glomerular capillary at the glomerulus
-> portions that are too large to be filtered exit through the efferent arteriole
->the rest becomes the glomerular filtrate - glomerular filtrate moves into the PCT
8
Q
what is the glomerulus
A
a knot of capillaries
9
Q
what is the glomerular capsule
A
forms outer wall of renal corpuscles + encapsulates glomerular capillaries
-> connected to initial segment of renal tubule
10
Q
describe how filtration occurs + what is filtered at the renal corpuscle
A
- passive process (via BP)
-> forces water + small solutes across the membrane into capsular space - solutes filtered = metabolic wastes + excess ions, glucose, free fatty acids, AAs + vitamins
11
Q
what solutes are excluded from filtration by the glomerulus
A
larger solutes:
plasma
proteins
blood cells
12
Q
function of PCT
A
tubular reabsorption
- reabsorption of water, ions + organic nutrients
13
Q
function of thick descending limb of nephron loop
A
pumps Na+ + Cl- ions out of tubular fluid
14
Q
function of thick ascending limb
A
create high solute concentrations in peritubular fluid
15
Q
function of thin descending limb
A
freely permeable to water but X solutes -> water movement helps concentrate tubular fluid
16
Q
DCT function
A
- active secretion of ions, acids, drugs + toxins
- selective reabsorption of Na+ + Ca2+ from tubular fluid
- selective reabsorption of water to concentrate tubular fluid
17
Q
structure + function of juxtaglomerular complex
A
- formed by macula densa (specialised DCT cells) + juxtaglomerular cells
- senses changes in filtrate conc. + flow rate in DCT
- secretes renin + EPO
18
Q
function of collecting ducts
A
- variable reabsorption of water (conc. tubular fluid)
- variable reabsorption + secretion of Na+, K+, H+ + bicarbonate ions
- delivery of urine
19
Q
3 basic steps to process of urine formation
A
- filtration @ glomerulus
2 + 3. absorption + secretion @ various points along the nephron
20
Q
3 functions of renal tubule
A
- reabsorb all useful nutrients entering filtrate
- reabsorb more than 90% of water
- secrete waste products eg. unwanted ions
21
Q
how does the tubular fluid eventually become urine
A
due to valuable substances eg. glucose being reabsorbed into peritubular capillaries + waste substances eg. excess H+ being secreted out of peritubular capillaries
22
Q
how are drugs filtered by the kidneys
A
- X filtered at glomerulus (except small drugs)
- enter efferent arteriole
- peritubular capillaries pass drugs back into the nephron
- drugs excreted in urine
23
Q
what structures does filtrate have to pass to get from the glomerular capillary to the bowman’s capsule of the renal corpuscle
A
- capillary endothelial pores
- dense layer (basal lamina)
- filtration slits
24
Q
function of foot process of podocyte (on glomerular capillary)
A
increase SA
25
what is the value of filtration pressure in the renal corpuscle
10mmHg
26
what 3 pressures make up filtration pressure
1. Glomerular hydrostatic pressure (GHP) = pressure fluid in plasma exerts (+55)
2. Capsular hydrostatic pressure (CsHP) = pressure of filtrate arriving in capsule + exerting pressure on capillary wall (-15)
3. Blood-colloid osmotic pressure (BCOP) = pressure generated by left behind proteins drawing H2O back (-30)
27
what 2 things is net filtration pressure governed by
hydrostatic pressure (fluid pressure)
colloid osmotic pressure (of materials in solution) on either side of capillary walls
28
what is glomerular filtration rate + what does it depend on
- amount of filtrate the kidneys produce each minute = average 125L/min
- depends on filtration pressure
29
how is GFR controlled (3 things)
- autoregulation of GFR (intrinsic - at kidneys)
- autonomic regulation (extrinsic - by Sym. NS)
- hormonal regulation (extrinsic - intitiated by kidneys though)
30
how does autoregulation maintain GFR and what is this in spite of
- by changing diameters of afferent arterioles, efferent arterioles + glomerular capillaries
-> through myogenic mechanisms + tubuloglomerular feedback
- despite changes in local BP + blood flow
31
what is the myogenic mechanism of GFR control + how does this occur if increase in renal blood flow or BP (eg. running)
- stretches walls of eff. arterioles
- causes smooth muscle cells to contract
- constricts aff. arterioles
= decreases glomerular blood flow therefore decrease glomerular cap. BP + net filtration pressure
32
what is the myogenic mechanism of GFR control + how does this occur if decrease in renal blood flow decreases glomerular pressure eg. lying down
- dilation of afferent arteriole
- dilation of glomerular capillaries
- constriction of eff. arterioles to increase glomerular blood flow
= increased glom. cap. BP + net filtration pressure
33
process of tubuloglomerular feedback
1. GFR increases
2. flow through tubule increases
3. flow past macula densa increases
4. paracrine signal from macula densa to afferent arteriole
5. afferent arteriole constricts
6. resistance in afferent arteriole increases
7. hydrostatic pressure in glomerulus decreases
8. GFR decreases = homeostasis
34
outside what BP range are extrinsic mechanisms for regulation of GFR activated
80-160mmHg
35
effects of increased symp. NS activityin terms of the renal system
vasoconstriction of efferent arterioles
-> decreases blood flow to glomerulus + decreases GFR)
= results in more time to reabsorb H2O + slows loss of filtrate
36
what 3 stimuli cause the release of renin in the renin-angiotensin system
- decrease blood volume + decline in aff. arteriole BP
- stimulation of granular cells by renal sympathetic nerves
- decreased osmotic conc. of tubular fluid (detected by macular densa)
37
what is the action of renin the renin angiotensin pathway
- renin converts angiotensinogen to angiotensin 1
- angiotensin converting enzyme (ACE) converts angiotensin 1 into angiotensin 2
- angiotensin 2 increases BP
38
6 major functions of angiotensin 2 to stimulate GFR
1. increase symp. motor tone by constricting venous reservoirs, increasing Q + stimulating peripheral vasoconstriction
2. constricting eff. arts. of nephron to increase glomerular pressures + filtration rate
3. stimulates reabs. of Na+ + H2O at PCT
4. stimulates secretion of aldosterone from adrenal cortex to increase Na+ reabs.
5. stimulates thirst
6. triggers ADH -> stimulate h2O reabs. in distal DCT + collecting system
39
what are natriuretic peptides + where are they released
- released by heart in response to very large increase in blood volume or pressure
- ANP released by atria
- BNP (brain NP) released by ventricles
40
function of natriuretic peptides
trigger dilation of aff. arts + constriction of eff. arts.
- elevates glomerular pressures to increase GFR
- increase urine production to get rid of excess fluid
41
what is the osmolarity of the ECF
300 mosm/L
42
what ions do the majority of ECF conc. + volume regulation
Na+ + Cl-
43
what is the main site of Na+ + H2O reabs. and what percentages are reabsorbed
PCT
65% of each reabs.
-> pass into interstitial fluid + peritubular capillaries -> back to bloodstream
44
how is Na+ reabsorbed from the PCT into interstitial fluid by active transport
- Na+ high in tubule lumen
- Na+ enters cell through various membrane proteins via epithelial Na channel (EnaC) - moves down electrochem gradient
- Na pumped out of cell via ATP pump (in exchage for sodium)
45
how is Na+ reabsorbed from the PCT to the interstitial fluid by secondary active transport
- Na+ moves down its electrochem gradient using the SGLT protein to pull glucose into the cell against its conc. gradient
- glucose diffuses out of the basolateral side of the cell using the GLUT protein
- Na+ is pumped out by the ATP pump
46
what is renal threshold
the conc. of a substance dissolved in the blood above which the kidneys begin to excrete it into the urine
47
what is the renal threshold for the PCT in regards to glucose
180 mg/dL
-> exceeded commonly in type 1 diabetics
48
what is the clinical issue of having high blood glucose in terms of the glomerulus
- interferes w/ function of glomerulus -> X process proteins properly = proteinuria
- also cause scarring of glomerulus (glomerulosclerosis) = kidneys X filter waste products from blood
-> kidney failure of CKD
49
what percentages of Na+ + H2o does the nephron loop reabsorb
25% Na+
15% H2O
50
describe the process of sodium reabsorption in the thick ascending limb
- 1200 mOsm enter ascending loop of Henle
- salts reabsorbed (Na+ K+ + Cl-)
- H2O X follow solute b/c limb impermeable to water
- 100 mOsm leaving loop (v. diluted)
51
how is water reabsorbed in the nephron loop + where does this occur
via osmosis in the thin descending limb only
52
what occurs in the thin descending limb
- osmosis moves water into peritubular fluid, leaving solutes behind
- osmotic conc. of tubular fluid increases (b/c decreased H2O -> 1200 mOsm)
53
describe countercurrent multiplication
countercurrent = exchange of tubular fluids occurs in opp. directions
-> fluid in descending limb moves towards renal pelvis
-> fluid in ascending limb moves towards cortex
multiplication = effect of exchange -> ascending limb solute effects descending limb water exchange
-> positive feedback loop
54
benefits of countercurrent multiplication
- effectively reabsorbs solutes + water before tubular fluid reaches DCT
- establishes conc. gradient
-> permits passive reabsorption of water from tubular fluid in collecting system (regulated by circulating ADH)
55
what percentages of Na+ + H2o are reabsorbed by the DCT + collecting ducts
9% na+
19% H2O
56
what is the process of reabsorption + secretion at the DCT
1. aldosterone from the capillaries combines w/ a cytoplasmic receptor
2. hormone-receptor complex initiates proptein production pathway in P cell of nephron
3. new protein channels + pumps made
4. result in increased Na+ reabsorption + K+ secretion
57
summarise the DCT + collecting ducts water + Na+ reabs.
sodium reabs. by:
- na channel
- na+-K+ exchange pump
water reabs. by:
- aquaporins stimulated by ADH
collecting ducts:
- water reabsorbed in medulla region in same mechanism
58
why is ECF volume + concentration important
b/c conc. of solutes determines body functions
59
function of ADH
water reabs. -> controls fluid conc.
- prevents changes in cell volume
- increase in plasma osmolarity triggers ADH release (decrease conc.)
60
function of aldosterone
sodium reabs. -> controls fluid volume
- regulates BP
- decrease in plasma volume triggers aldosterone release
61
mechanism of ADH
- stimulates incorporation of water channels (aquaporins) in DCT + mainly collecting ducts
- allows for h2o to be reabs. along collecting ducts conc. gradient
- fastest way to restore balance to ECF conc./osmolarity
62
where does ADH come from
hypothalamus -> stored in posterior pituitary
63
what triggers the release of ADH
increased ECF concentration triggers osmo-receptors
64
process of ADH causing insertion of aquaporins into the apical membrane
1. ADH binds to membrane receptor of b.L side
2. receptor activates cAMP second messenger system
3. cell inserts AQP2 water pores into apical membrane
4. water is absorbed by osmosis into the blood
65
aldosterone mechanism process
1. aldosterone combines w/ a cytoplasmic receptor
2. hormone-receptor complex initiates PPP -> makes new protein channels + pumps
-> causes increased na+ reabs. + K+ secretion
66
what is the third mechanism of ECF volume + conc. control
natriuretic peptide release
67
how do diuretics work
slow renal absorption of water + cause diuresis
-> common treatment for high BP + heart failure
- caffeine inhibits Na+ reabs.
- alcohol inhibits ADH secretion
68
what pH is defined as acidosis
<7.35
69
what pH is defined as alkalosis
>7.45
70
list the 5 chemical buffer systems + their overall function
- protein
- carbonic acid - bicarbonate
- haemoglobin
- phosphate
- ammonia
-> act quickly to buffer pH changes (short term)
71
how does the carbonic acid-bicarbonate system increase pH
- sodium bicarbonate dissociates to form HCO3-
- bicarbonate ion gains H+ to form H2CO3
- carbonic acid immediately dissociates to H2O + CO2 which are exhaled
72
describe the steps to respiratory compensation for acidosis
1. chemical buffering - H+ has increased
2. CO2 decreases to from H2CO3 -> H+ and HCO3- decrease
3. decreased CO2 stimulates ventilation
4. HCO3- levels drop even more (not good) but H+ closer to normal
-> HCO3- must be replaced by kidneys
73
how is HCO3- replaced in respiratory compensation for an acidosis
- reabsorb all remaining in kidneys
- generate new HCO3- in kidneys
-> when urinating excess H+, HCO3- it was combined with is replaced
74
how does renal compensation for an alkalosis occur
- kidneys secrete less H+
- some filtered HCO3- is not reabsorbed
- plasma HCO3- is reduced, causing the reaction to move and generate more H+
75
what are 2 examples of respiratory acid-base disorders
- resp acidosis = emphysema
- resp alkalosis = sustained hyperventilation
76
what are 2 examples of metabolic acid-base disorders
- metabolic acidosis = ketoacidosis from uncontrolled diabetes
- metabolic alkalosis = from vomiting
