renal 1-6 Flashcards
(114 cards)
1
Q
What are the eight basic functions of the renal system?
Hint - 1 metabolism, 1 count, 1 detoxify, 1 homeostasis, 3 regulation, 1 gluco-related
A
- remove waste products of metabolism
- RBC count
- detoxify free radicals + some drugs
- calcium homeostasis
- body fluid pH regulation
- fluid balance and BP regulation
- electrolyte regulation
- gluconeogenesis during starvation
2
Q
What are the six organs of the renal system?
Hint - 1K and 3Us
A
- kidneys (L+R)
- ureters (L+R)
- urinary bladder
- urethra
3
Q
What is the location of the kidneys?
Hint - faces the spine and poles LT 36
A
- between peritoneum + posterior abdominal wall → concave medial border faces vertebral column
- upper pole T12 and lower pole L3
- protected by R11-12 with R kidney lower than L (liver)
4
Q
What are the vital statistics of one kidney in terms of how heavy, long, wide and thick?
(Hint - comes up to around 150cm squared)
A
- 130-160g
- 10-12 cm long
- 5-7 cm wide
- 3 cm thick
(about the size of a bar of soap)
5
Q
What are the names of the deep, middle and superficial layers of the kidney and what are their structures and functions?
(Hint - RAR → deep and middle layer have very similar structure)
A
- renal capsule → smooth, trauma barrier made of dense, irregular CT to maintain kidney shape - continuous with outer ureter layer (deep)
- adipose capsule → fatty tissue, trauma barrier which maintains kidney position (middle)
- renal fascia → dense, irregular CT which anchors kidney to abdominal wall and structures (superficial)
6
Q
What is the renal cortex, renal medulla, renal parenchyma, renal sinus and renal lobe?
(HInt - parenchyma is basically the whole kidney, renal sinus is the leftovers the day after, renal lobe is that small Egyptian section)
A
- renal cortex: (= bark) → superficial layer, smooth and brownish
- renal medulla: (= inner portion) → deep, striated and reddish
- renal parenchyma: renal cortex + medulla
- renal sinus: remaining structures → fat, pelvis, calyces, blood vessels, nerves
- renal lobe: renal pyramid, overlying renal cortex area and ½ adjacent renal column
7
Q
How much blood supply do the kidneys obtain relative to their size?
A
low body mass but receive ¼ of CO via L+R renal arteries (from ABD aorta)
8
Q
What is the complex blood pathway through the kidneys?
HInt - rita skeeter is an ignorant, angry grasshopper endof - also segarc
A
renal artery → segmental arteries → interlobar arteries → arcuate arteries → interlobular arteries → afferent arterioles → glomerular capillaries → efferent arterioles
9
Q
What is the pathway of blood through the kidneys from an efferent arteriole (a type of portal vessel)?
(Hint - E-V-I/A)
A
efferent arteriole → vasa recta (medullary capillaries) → interlobular/arcuate veins
10
Q
What is a nephron?
A
- blind-ended tube which is the functional unit of kidney supplied by an afferent arteriole
- made of renal corpuscle (glomerulus + bowman’s capsule) and renal tubule
11
Q
What are the glomerulus, bowman’s capsule and podocytes?
Hint - bc → where filtrate gathers + continuous
A
- ball of capillaries inserted into Bowman’s capsule → initial site of urine production (supplied by AA + drained EA)
- site of blind-end of nephron which is capsular space where filtrate collects
- inner visceral layer which envelope glomerular capillaries
12
Q
What is a renal tubule composed of?
Hint - P + D, L, C
A
- PCT, distal tubule (2 tubular segments)
- Loop of Henle
- collecting duct
13
Q
What are the two types of nephrons and what are their relative proportions?
(Hint - CJ)
A
- cortical (85%) → glomeruli in outer 2/3 of cortex and short loops of Henle
- juxtamedullary (15%) → glomeruli in inner 1/3 of cortex and long loops of Henle
14
Q
What is the structure of the proximal tubule?
(Hint - two types of c epithelia, has beginning + end which start out dodgy and then straighten themselves out in the end)
A
- cuboidal/columnar epithelium
- early part (pars convolute) → convoluted
- late part (pars recta) → straight
15
Q
What is the loop of Henle?
Hint - very basic - the shape and the two types of limbs
A
U-shaped loop with descending and descending limbs
16
Q
What are the structures of the thin and thick segments of the loop of Henle?
(Hint - epithelia, which parts of limbs, metabolic activity and water permeability for thin)
A
- thin segments: simple squamous epithelium, lower part of descending limb + sometimes ascending, low metabolic activity and high water permeability
- thick segments: simple cuboidal epithelium, initial part of descending + ascending limb, metabolically active (mitochondria)
17
Q
What is the structure of the juxtaglomerular apparatus?
Hint - where does the LoH start + return, MD, j cells
A
- final part of ascending loop of Henle returns to afferent/efferent arterioles of same nephron
- macula densa (thick ascending limb columnar cells)
- juxtaglomerular cells (afferent arteriole SM cells)
18
Q
Which epithelium is found in the early and late parts of the distal convoluted tubule?
A
cuboidal
19
Q
Which two types of cells are found in the late part of the distal convoluted tubule and what do they regulate?
(Hint - π - acidity and urine hormones/enzymes - calate = anhydrase)
A
- principal cells (ADH + aldosterone receptors)
2. intercalated cells (carbonic anhydrase activity, pH)
20
Q
What is the structure of the collecting duct?
(Hint - cells like distal C tubules, receives fluid from, in internal region Bellisimo ducts which drain into a part of the internal kidneys)
A
- cells similar to late DCT
- receives fluid from 6 distal tubules
- in the medulla, pair up to form ducts of Bellini which drain into minor calyces
21
Q
What is nephroptosis?
Hint - ghost kidney from L3 to L5
A
when kidney descends more than 2 vertebral bodies (‘floating kidney’)
22
Q
What are peritubular capillaries and what are they called when they surround the PCT, DCT and loop of Henle?
(Hint - clue is in the name and used to suck things up and release them, name is the synonym for “straight arteries”)
A
- tiny blood vessels alongside nephrons → allow reabsorption + secretion
- ‘vasa recta’
23
Q
What is the lymphatic drainage of the kidneys?
(Hint - bloodstream fluid to cells by c. action, bathes tissues with new name IS, collects rubbish and drains into lymph vasculature)
A
- fluid from circulating blood leaks into body tissues by capillary action → carrying nutrients to cells
- fluid bathes tissues as interstitial fluid
- collects waste products, thendrainsaslymphinto lymphaticvessels + capillaries
24
Q
What is a UTI, where is it more common and why?
A
- infection that can affect bladder, kidneys and tubes connected to them
- more common in women as they have shorter urethra than men
- often caused by catheters becoming infected w/ bacteria etc…
25
Where do the three renal systems develop from and how are they deposited? See notes for diagram.
(Hint - in the middle layer, deposited around middle during gi system development between P + L meso)
- develop from intermediate mesoderm
| - deposited either side of midline during gastrulation → between paraxial + lateral plate mesoderm
26
Which three structures develop craniocaudally to form the renal system?
(Hint - pro-mes-met)
1. pronephros (cervical nephrotomes)
2. mesonephros
3. metanephros
27
Describe the formation of the pronephros (cervical nephrotomes) including time-scales.
(Hint - 5-7 neck segments of middle meso produces tomes/vesicles which then disappear)
- 5-7 paired cervical segments of intermediate mesoderm produce nephric vesicles
- nephric vesicles/nephrotomes (hollow epithelial balls which are vestigial remnants) are formed early week 4 and disappear by the end of it
28
How does the mesonephros form during week 4 and why do we end up with 30 pairs of mesonephric tubules in the end rather than 40? see notes for diagrams.
(Hint - TC region form msnprhic tubes either end, due to the dropping of tubules)
- in the thoracolumbar region during early week 4 mesonephric tubules form from mesonephric ridges either side of intermediate mesoderm
- 40 pairs of mesonephric tubules produced craniocaudally → 30 pairs in total due to cranial regression
29
How does the formation of the mesonephros occur during weeks 5-6?
(Hint - number of L. mesonephric tubules reduced again by falling process, then the ball of capillaries and its lid created from differentiation of the L. mesonephric tubules)
- massive cranial regression so 20 pairs of lumbar mesonephric tubules
- mesonephric tubules differentiate into abbreviated excretory units → bowman’s capsule and glomerulus (the renal corpsucle) from dorsal aorta
30
What is a MEU and what is it made up of?
mesonephric excretory unit → renal corpuscle + mesonephric tubule
31
Describe the formation of mesonephric (Wolffian) ducts during week 4.
(Hint - originate in T spinal region and grow c, longitudinal middle rods condense to tubules, diverge into L spinal region, fuse ventrally with cloac. and then cavitate to produce inner region)
- originate in thoracic region + grow caudally
- longitudinal intermediate mesoderm rods that condense dorsolaterally to mesonephric tubules
- diverge from intermediate mesoderm in lumbar region
- fuse with ventrolateral walls of cloaca (bladder) by day 26 → cavitate at distal end to produce lumen
32
State the roles of MEUs in the formation of the mesonephros during weeks 5-10.
(Hint - passage to the embryological bladder, urine-production then stopped at week 10, then how it remains after in males and females)
- lateral tips of MEUs fuse with mesonephric duct to allow their passage to the cloaca
- MEUs functional in week 6 and 10 → produce small amounts of urine and regress after week 10
- in males, mesonephric duct becomes part of the genital system (SEED) and in regress in females remnants may persist (i.e. epoophoron)
33
Describe the metanephros including time-scales.
(Hint - formed in S region, penetrate sacral middle derm encouraging joining of u-bud, u-tip called ampulla which causes aggregation and lobe formation and separation via sulcus, lots of even lobes formed by week 16 and then filled so smoother appearance)
- formed in sacral region by pair of ureteric buds from distal mesonephric duct (sprout end of week 4)
- penetrate sacral intermediate mesoderm region called metanephric blastema → encourages bifurcation of ureteric bud
- ureteric growing tip is called ampulla → cap-like aggregation near this structure causes lobe formation separated by sulcus
- 14-16 lobes formed by week 16 → sulci eventually filled so lobulated appearance obscured
34
What is reciprocal interaction?
(Hint - differentiation of U + CDs depending on meta-b → give rise to renal organs, differentiation of n depending on UBs)
- differentiation of ureters + collecting ducts dependent on metanephric blastema giving rise to kidneys
- differentiation of nephrons dependent on ureteric bud
35
When do the sulcus and the lobe of a kidney form?
- sulcus → at 6 weeks
| - lobes → at 16 weeks
36
Describe the formation of the nephrons and collecting system of the kidneys (see notes for help).
(Hint - week 6 caps around ampullae of CDs, CD distinct from nephron, DTs + CTs connect → functional MEUs in week 10)
- during week 6, metanephric tissue caps form around ampullae of bifurcating collecting ducts
- collecting duct embryologically distinct from the nephron
- distal tubules connect fully with collecting tubules in week 10 and become functional MEUs
37
What is the main function of fetal urine in embryological development?
to assist in production of amniotic fluid
38
When is normal ascent (rise) of the kidneys complete and what is the abnormal ascent of the kidneys?
- by week 9
| - transient inferior arteries fail to regress causing accessory renal arteries to form
39
State two kidney abnormalities due to the abnormal ascent of the kidneys.
- pelvic kidney
| - horseshoe kidney
40
How does the urinary tract develop as part of the renal system and how does this differ between males and females?
(Hint - c split by us to form pus and r, s + a → bladder, c → F urethra, m + p urethra → M urethra, distal PUS → vv (F) + PU (M))
(see notes for diagram)
• cloaca split by urorectal septum in weeks 4-6 to form primitive urogenital sinus (PUS) and rectum
- superior PUS + allantois → bladder
- constricted pelvic urethra → urethra (F)
- membranous and prostatic urethra → urethra (M)
• distal part of PUS (urogenital sinus) expands and becomes:
→ vaginal vestibule (F)
→ penile urethra (M)
41
How does the bladder develop as part of the renal system from week 6-12?
(Hint - week 6 root of m. duct turns inside out into b. wall, pushes origin of u. buds into it creating ureter holes, meso. duct pushed inferiorly to pelvic urethra, extros. wall of m. duct joined with b. wall → forming that SM part)
(see notes for diagram)
- week 6 → root of mesonephric duct exstrophies (turns inside out) into bladder wall
- pushes origin of ureteric buds into bladder wall, creating ureteric openings
- causes opening of mesonephric duct to be pushed inferiorly to level of pelvic urethra
- exstrophied wall of mesonephric duct incorporated into bladder wall, forming smooth trigone of bladder
- process complete by week 12
42
What are each of the following common renal developmental abnormalities:
a) unilateral/bilateral renal agenesis
b) multicystic dysplastic kidney
c) autosomal recessive polycystic kidney (Hint - PCOS)
d) branchiootorenal syndrome
e) duplication (bifid pelvis)
f) megaureter
g) ureteral-pelvic junction obstruction
h) calyceal cyst or diverticulum (Hint - to with just cysts)
i) calyectasis (Hint - to with fluid + cysts)
a) absence of one/two kidney(s)
b) a collection of large renal cysts
c) cysts causing kidney enlargement → may lead to pulmonary and renal complications
d) can result in malformation of kidneys (disruption of reciprocal induction of epithelial ureteric bud and mesenchymal metanephric blastema in developing embryonic kidney)
e) absence of ureter
f) abnormally-dilated ureter
g) part of kidney blocked so urine can’t move through
h) cystic activity within kidney/s
i) calyces of kidney dilated and swollen with excess fluid
43
How does body water (BW) compare in males and females?
- standard physiological male → has 10% more BW is water than the standard female
- higher adipose tissue content + lower BW in females (responsible for TBW variation too)
44
What is a compartment and why is this used?
- compartment: a small space or subdivision for storage (not always the same)
- “virtual” compartment = made up of multiple cells/compartments
- used for convenience to allow meaningful discussion
45
Describe the distribution of TBW in percentages.
| Hint - first at a cellular level with the more extra one having a pit of fluid
```
Body fluid (100%)
• extracellular fluid (35%)
- interstitial fluid (25%)
- plasma (8%)
- transcellular fluid (2%)
• intracellular fluid (65%)
```
46
Describe the features of the virtual intracellular fluid (ICF) compartment including its major ions.
(Hint - within cells and anions - KPO and P)
- contained by cell membranes
- K⁺ is major cation
- proteins and PO₄³⁻ are major anions
47
Describe the features of the virtual extracellular fluid (ECF) compartment including its major ions.
(Hint - non-intc, Na and HCOCL)
- non-intracellular compartment features:
- Na⁺ is major cation
- Cl- and HCO₃- major anions
48
Describe the ECF sub-compartment that is plasma fluid.
| Hint - plasma is usually found in blood vessels, lots of oil and egg, but mostly watery
- contained within vasculature
- lots of protein and lipid
- majority fluid
49
Describe the virtual ECF sub-compartment that is interstitial fluid (ISF).
(Hint - space it occupies and how it is separated from plasma, what it does to cells and what it is the link between and protein content, what happens to excess ISF via lymphatics)
- occupies interstitial space separated from plasma fluid by capillary endothelium
- bathes cells and is the link between ICF and blood plasma → low in protein
- excess drains into plasma compartment via lymphatic system
50
Describe the ECF sub-compartment that is transcellular fluid (TCF) and its functions
(Hint - all leftovers - functions are UCL GSC)
• everything else, separated from plasma by another epithelial layer → specialised functions include:
- urine
- CSF
- lymph
- GI tract contents + secretions
- synovial fluid
- compartments of eye + ear
51
How can we measure compartment volumes using dilution principles?
- use known quantity of dye (tracer) to target compartment
| - after equilibration, measure dye conc. and (formula) calculate compartment volume
52
How can we measure compartment volumes using colorimetry?
- make up number of dye (tracer) solutions of known concentration
- shine light through and measure intensity of penetration
- plot conc. against intensity to create a calibration curve (intensity x and concentration y) and use to find unknown volume
53
What is osmolality analogous to and what is meant by a dissociating/non-dissociating substance?
(Hint - the M system and literally means to what level the dissociation has occurred)
- analogous to moles (identical for non-dissociating substances)
- non-dissociating is when dissociation is not fully complete, so acc 1.9 mosmol/kg H₂O
- non-dissociating substance, i.e. glucose → 1 mmol/kg, H₂O glucose x 1 = 1 mosmol/kg H₂O
- dissociating substance i.e. NaCl → 1 mmol/kg H₂O, NaCl x 2 = 2 mosmol/kg H₂O
54
What is hydrostatic pressure?
pressure exerted by a fluid on walls of a compartment
55
What is osmotic pressure?
| Hint - pressure needed to move water in
pressure required to prevent net movement of water across semi-permeable membrane (equal value to hydrostatic but movement IN rather than OUT)
56
What is an isotonic solution?
| Hint - in relation to its effect on fluid volume
solution which does not cause changes in cell volume
57
What is an isosmotic solution?
| Hint - iso means the same as
solutions having the same osmolality
58
What is the relationship between an isotonic and isosmotic solution?
- isotonic solutions always isosmotic
| - isosmotic solutions not always isotonic
59
What will happen to RBCs suspended in isosmotic urea solution (compared to RBC ICF)?
(Hint - something still occurs)
will still haemolyse because urea readily diffuses and equilibrates across PM and cancels own osmotic pressure
60
What are effective osmoles? Give an example of this.
| Hint - cause movement through the referred membrane + exerting osm. pressure i.e. salt compared to ICF
- cause net water movement by being impermeant through reference membrane and exerting osmotic pressure
- e.g. extracellular Na⁺ compared with ICF, but not plasma compartment
61
What are ineffective osmoles? Give an example of this.
| Hint - move right across to cancel osmoles i.e. precursor of urine
- diffuse readily across membranes cancelling own osmotic pressure
- e.g. urea in previous example
62
# Define plasma protein oncotic pressure (π).
(Hint - OPP)
osmotic pressure exerted by plasma proteins
63
What are large impermeant anions important in?
| Hint - TFD
transcapillary fluid dynamics
64
What is the Gibbs-Donan effect?
| Hint - rule on d ions and non-d on side 1 to do with osmotic pressure
• a rule for how diffusible ions distribute
• non-diffusible protein anions on side 1
- if the total number of ions side 1 > side 2, then side 1 exerts a greater osmotic pressure
(see formula sheet for more info)
65
What is bulk flow?
| Hint - inactive solute movement in capillaries/veins/arteries + their membranes
passive solute movement → occurs in vessels and in a form of filtration across capillary membranes
66
What are Starling forces?
| Hint - forces which determine movement in/out of capillaries
- the forces that determine capillary filtration and reabsorption i.e. movement of water and solutes between plasma and ISF compartments
67
What proportion of movements are by by Starling forces?
90% movement by ordinary diffusion and 10% by Starling forces
68
In a model capillary, what is capillary hydrostatic pressure (P) dependent on?
(Hint - AEV)
- arterial BP
- extent of transmission i.e. arteriolar resistance
- venous pressure (resistance to flow)
69
In a model capillary, what value is plasma protein oncotic (colloid) pressure (π) and why is it usually constant?
(Hint - 5-side square)
- about 25 mmHg
| - as plasma proteins effectively are impermeable (makes them effective osmoles)
70
What is the Bowman’s capsule at the site of?
blind end of nephron
71
What does a glomerular filter produce and how is glomerular ultrafiltrate modified?
- an ultrafiltrate (molecular level filteration) of plasma
| - modified along renal tubule until urine formed in collecting ducts
72
What are the three layers of a glomerular filter?
1. capillary endothelium → fenestrated capillaries which block cells + platelets
2. basement membrane → main filtration barrier secreted by podocytes, negatively-charged and consists of collagen + glycoproteins
3. podocytes → phagocytic structures with pedicels + maintain BM as a supplementary filtration barrier (found at negatively-charged glycocalyx)
73
What is filtration and what is it used for?
- free filtration of anything below size of 7000 Da i.e. - glucose, AAs, salts, urea freely filtered
- negative charges prevent filtration of most proteins
74
State the four Starling forces and their values in ideal capillaries.
(Hint - P means hydrostatic pressure and π means oncotic pressure → bc, c, c, bc)
- Pbc = Bowman’s capsule hydrostatic pressure (10 mmHg)
- Pcap = capillary hydrostatic pressure (45 mmHg)
- πcap = capillary protein oncotic (colloid) pressure (25 mmHg)
- πbc = 0 mmHg (protein not normally filtered)
75
How does Pcap compare in a glomerular capillary bed and an ideal capillary and why?
- Pcap glomerular capillary bed > ideal capillary
| - higher BP in ideal capillary
76
What is GFR indirectly proportional to and how is this value quantified?
- GFR ∝ NFP
| - NFP = “forces favouring filtration – forces opposing filtration”
77
What is the filtration coefficient (Kf) and where is it used?
(Hint - function of GC + area for f → gives real measurements cap, bc, cap)
- function of glomerular capillary permeability and area for filtration
- used to give real GFR measurements:
GFR = Kf (Pcap - Pbc - πcap)
78
What are the normal GRF and Kf values?
| Hint - Kf = GFR/10
- normal GFR: 125 ml/min
| - normal Kf is 12.5 ml/min/mmHg
79
Name the five factors affecting GFR.
| Hint - all values oncotic, hydrostatic, bc, cap, and K
- Kf (filtration coefficient)
- capillary hydrostatic pressure
- capillary oncotic pressure
- bowman’s capsule hydrostatic pressure
- bowman’s capsule oncotic pressure
80
What BSA is GFR normalised to?
| Hint - 1. something 3 in m2
- 1.73m2 BSA when comparing GFRs from different individuals
| - approx 125 ml/min/1.73m2
81
How much of the total RBF is filtered and why?
| Hint - the rest is contained in the jails of the body
- only 0.6/1.1L of blood filterable (RPF - renal plasma flow)
- as the rest is in cells
82
If normal GFR is 125 ml/min what is the RPF percentage of this value in comparison?
approx 20% (80% unfiltered)
83
What happens to RBF and GFR when resistance in glomerular arterioles:
a) is controlled in arterioles
b) decrease in afferent arterioles
c) increase in afferent arterioles
d) decrease in efferent arterioles
e) increase in efferent arterioles
(Hint - in AA you need both values to change to reverse the effect but with EA the two values need to be affected differently)
a) RBF same, GFR same
b) RBF increases, GFR increases
c) RBF decreases, GFR decrease
d) RBF increases, GFR decreases
e) RBF decreases, GFR increases
84
What are RBF and GFR throughout normal BP range and which two mechanisms does the process of their autoregulation use?
(Hint - fine if BP is fine but generally self-regulated by kidneys via 2 mechanisms: m and t feedback)
- RBF and GFR constant throughout normal BP range
- thus, regulated by kidney itself (‘auto’)
- 2 mechanisms:
1. Myogenic feedback
2. Tubuloglomerular feedback
85
What is the juxtaglomerular apparatus?
| Hint - the u-shaped loop, DT close to rc, contact with AA + EA via this
- loop of Henle, distal tubule region passes close to renal corpuscle
- contact with afferent and efferent arterioles via juxtaglomerular apparatus
86
How does tubuloglomerular feedback regulate GFR when it increases above the threshold?
(Hint - NaCl and fluid flow in DT, MD and NO causing constriction of afferents, all the things which initially changed back to normal)
- high GFR = high NaCl and fluid flow in distal tubule
- sensed by macula densa (MD) which inhibits NO secretion → causes vasoconstriction of AA
- GFR, NaCl levels and fluid flow in distal tubule return to normal
87
Describe neural regulation of RBF and GFR.
| Hint - to do with nerves and denervation and how GFR is regulated via these two things
• rich sympathetic innervation to kidney (AA wall) but tonic activity low so denervation has little effect
• however, increased nerve activation (e.g. exercise) leads to:
- vasoconstriction of AA
- reduces RBF and GFR
• works in reverse too: low BP → AA dilates to increase RBF + GFR
• conservation/redirection mechanism where GFR can get as low as a few ml/min
(see diagram in notes for detail)
88
How may glomerular filtrate composition change with disease?
- kidney disease caused by elevated levels of blood glucose, the central feature of diabetes
- some people with glomerular disease (i.e. nephrotic syndrome) when kidneys lose lots of protein in urine causing extra fluids and salt in body
89
What are the active and passive transport mechanisms in relation to proximal tubule function and what are their functions?
- reabsorption → reabsorb useful substances from tubule lumen into blood
- filtration and secretion → secrete less useful substances from blood into tubule lumen
(NB: both processes aid homeostasis)
90
Where does most kidney reabsorption occur and what does it involve?
(Hint - PCT stealing back salt, dissolved things and water, how Na⁺ transporters are used (1) symp and (2) anti, where energy from primary)
- in PCT reclaiming useful filtered substances, H₂O and solutes
- involves Na⁺ transporters:
1. symporters → 2+ crossing membrane in same direction
2. antiporters; 2+ solutes crossing membrane in opposite direction
- energy for both is derived indirectly from ATP via primary active transport
91
What is the Transport maximum (Tm) and when may fluctuation of this value occur?
- the upper capacity limit (mg/min) of transporters
| - fluctuation can result from diseases i.e. diabetes → glucose in urine
92
What does solute reabsorption drive and how does this process differ in the proximal tubule and collecting duct?
(Hint - water, needed in one place and optional in the other)
- solute reabsorption drives H₂O reabsorption (via osmosis)
- proximal tubule: H₂O reabsorbed with solutes = obligatory (requiured)
- collecting duct: H₂O reabsorption needs-driven = facultative (sometimes)
93
Where does reabsorption occur to and from?
| Hint - L → p
lumen (of nephron) → peritubular capillary
94
What do Na⁺ transporters in the PCT achieve?
| Hint - almost full reabsorption
- near 100% reabsorption of organic solutes (i.e. glucose, AAs)
- 80-90% HCO₃-
- 65% H₂O, Na⁺, K⁺
- 50% Cl-
- variable Ca2⁺, Mg2⁺, PO₄³⁻
95
What is the Na-K Pump located and which molecules does it drive the secondary transport of?
(Hint - hagc)
```
• located basolaterally, uses ATP, keeps intracellular Na⁺ low
• drives secondary transport of:
- glucose
- amino acids
- HCO₃-
- Cl-
```
96
Describe the transport occurring in the two following diagrams using an ATP pump.
1.
- Na⁺ moves into PCT cell via facilitated diffusion (carrier protein)
- Na⁺-K⁺ pump then used to pump out Na⁺ for every K⁺ ion entering from basal lamina of peritubular capillary
2.
- Na⁺ and glucose both inside cell
- glucose and Na⁺ (ATP) symporter uses K⁺ to move glucose into cell all while pumping Na⁺ out of cell
- capillaries low in glucose so they absorb it
97
Describe sodium bicarbonate reabsorption using the two following diagrams.
- filtered NaHCO₃ enters lumen
- Na⁺-H⁺ and Na⁺-K⁺ ATP pumps drive HCO₃- (bicarbonate) ions into cells → these ions reabsorbed passively following Na⁺
- can recombine with H⁺ ions to increase pH and dissociate from it to decrease pH
- H⁺ + HCO₃⁻ → H₂CO₃ (carbonic acid)
- CA in brush border of PCT cells combines CO₂ + H₂O
- CO₂ reabsorbed across tubular cell
98
How does secretion in the glomerulus occur and why is PAH (para-aminohippuric acid) significant in this?
(Hint - substances small and leave, AT required for secretion, PAH is FF, tml, not retaken in, rbf marker)
• most secreted substances small and filtered
• active transport required for secretion
• para-aminohippuric acid:
- freely-filtered
- Tm limited secretion
- not reabsorbed
- indicator of RBF
99
What is inulin clearance and how would it be worked out for substance x?
- volume of plasma cleared of a substance in a given time
- clearance of x = (filtration of x + secretion of x) – reabsorption of x
(see sheet for official formula)
100
What is inulin and how does this make it useful to measure?
- freely-filtered polysaccharide which is not reabsorbed or secreted
- hence, inulin clearance, can be used to work out GFR (U inulin)
(see sheet for official formula)
101
Compare the creatinine clearance and inulin clearance methods of calculating GFR.
- inulin must be infused (not endogenous)
- creatinine endogenous, no infusion required
- but, small amount secreted so measured GFR is overestimated
- creatinine is by-product of muscle metabolism; GFR more accurate if subject at rest
102
What is renal paradox?
| Hint - the reason that we know loops of henle concentrate urine
- only mammals and birds can concentrate urine
- only they have loops of Henle
- therefore they are vital to concentrating ability
103
For which three reasons is fluid leaving the loop of Henle dilute compared to plasma?
(Hint - CCM, interactions between different loops, optional water handling in CDs due to ADH)
- counter-current multiplication used to generate medullary hypertonicity
- interaction between loops of Henle, distal tubules and collecting ducts
- facultative water handling in collecting ducts (ADH)
104
Why is a hypertonic medulla important?
needed to concentrate urine so without ADH water can’t move out of filtrate
105
How is urine generated?
- DL permeable and AL impermeable
- ability of TAL (thick ascending limb) to extrude Na⁺ to medullary interstitium
- basolateral Na-K ATPase
- transverse osmotic gradient (200mOsmol/kg H₂O) leading to large longitudinal one
106
How does the loop of Henle help to generate medullary hypertonicity?
- fluid entering = osmolality of 290 but increases near bottom of loop
- movement of Na/Cl out of fluid used to dilute/conc. it
- i.e. for every 2 K⁺, 3 Na⁺ sent out
107
What is a counter-current multiplication?
- an arrangement which multiplies the small transverse osmotic gradient between the AL and DL (200mOsmol/kg H₂O difference) into a larger longitudinal one
- i.e. counter-flow of tubular fluid due to hairpin bend in loop
- more conc. fluid to bottom and less conc. to the top
108
What is meant by facultative H₂O handling?
- handling according to need in DCT and collecting ducts
- collecting duct has two sections; cortical collecting duct (CCD) and medullary collecting duct (MCD)
- DCT, CCD and MCD impermeable to H₂O, urea and NaCl
- ADH increases H₂O permeability of segments by need
109
What effect does ADH have on the collecting duct?
- increased H₂O reabsorption in cortical CD (fluid osmolality: 90 → 290 mOsmol/kg/H₂O)
- remaining fluid enters medullary CD for further H₂O reabsorption
- too much reabsorption in medulla would negate medullary hypertonicity
- so most H₂O reabsorption occurs in cortical collecting duct
(see diagram for more detail)
110
Urea is freely filtered at glomerulus so how much is passively reabsorbed into the PCT?
(Hint - half)
50%
111
Urea concentration increases in DL and along loop due to passive diffusion from interstitium, why?
- distal tubule/cortical CD impermeable to urea and to H₂O (ADH)
- as H₂O leaves cortical CD, urea conc. rises
- ADH activates urea uniporter in medullary CD
- urea diffuses along gradient: medullary CD interstitium
- TAL/DL (along tubule) distal tubule/cortical CD
- cycle repeats
hence, interstitium has high urea concentration
112
What is 50% of medullary hypertonicity due to?
urea recycling
113
How do long and short nephrons compare and what are they all capable of?
- 15% nephrons juxtamedullary (long) and 85% cortical (short)
- all nephrons drain into collecting ducts which pass through medulla → all capable of concentrating urine
114
What are juxtamedullary nephrons specifically used for and in which species can are they found to compare?
- for urine concentrating by generating medullary hypertonicity
- i.e. camels vs humans
