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phty251 > epithelial/renal > Flashcards

epithelial/renal Flashcards

1
Q

5 functions of epithelia cells

A

protection, absorption, secretion, sensation, filtration

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2
Q

“definition” of epithelia

A
  • cells are connected barrier/compartment
  • cells have a polarity
  • different protein expression
  • diff. epithelia = diff. behaviour = diff. regulation
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3
Q

describe tight junctions

A

connects 2 adjacent plasma membranes of 2 cells, separates apical from basolateral membrane side

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4
Q

what junction defines the properties of the paracellular pathway and how?

A

tight junctions control the properties of paracellular pathways by enabling polarity, thus constrains diffusion of solutes and fluids

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5
Q

describe gap junctions

A

gap junctions connect cytoplasm of cells via connexins, allows exchange of small molecules ( but not large proteins)

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6
Q

describe desmosomes

A

desmosomes connext cells tightly via cadherin whihc are connected to intermediate filaments for stabilisation. strengthens epithelial cell layer against physical forces such as shear stress.

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7
Q

explain the differences between the basolateral and apical membrane of epithelial cells

A 
apical membrane (AKA mucosal)
- faces lumen of organ
- contains microvilli
- variable water permeability 
basolateral membrane (AKA serosal)
- faces ISF
- high water and K+ permeability 
- expresses Na+/K+ ATPase
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8
Q

explain the difference between absorptive and secretory epithelia

A

absorptive epithelia
- transport from mucosal to serosal solution (eg: kidney, intestine)
- absorption driven by Na+ transport
secretory epithelia
- transport from serosal to mucosal solution (eg: salivary glands)
- secretion driven by Cl- transport

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9
Q

explain mechanism of simple diffusion

A

ions and molecules can move through a membrane if it is permeable, down conc. gradient

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10
Q

explain mechanism for facilitated diffusion, with example

A

requires a specific membrane protein, donw conc. gradient. eg: AQPs GLUT (basolateral side)

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11
Q

explain mechanism for active transport, give an example of primary active transport and secondary active transport

A

requires a specific membrane protein and energy, against conc gradient

  • primary active = Na+/K+ ATPase
  • secondary active = Na+ such as SGLT1 and SGLT2
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12
Q

explain how glucose can enter and exit an epithelial cell

- draw it out if have time ?

A
  • glucose enters the epithelial cell on the apicla side via Na+ dependant glucose transporters (SGLTs)
  • glucose can enter the cell on the apical side due to its sodium gradient, thus sodium provides the driving force to transport glucose against its gradient
  • glucose leaves the cell on the basolateral side via glucose transporters (GLUTs)/facilitated diffusion
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13
Q

what is the consequence of sodium absorption in leaky epithelium

A

in leaky epithelium, the consequence of sodium absorption is that the lumen becomes negative;y changed and the interstitium becomes positively charged. as a result, this drives paracellular absorption of chloride, thus drives both paracellular and transcellular reabsorption of H20.

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14
Q

what are the driving forces for water secretion?

A

Cl- and Na+ secretion

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15
Q

what drives sodium secretion in secretory epithelium?

A

Cl- absorption

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16
Q

name 5 functions of kidney

A
  • water homeostasis
  • salt/ion homeostasis
  • drug excretion
  • pH regulation
  • nutrient reabsorption
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17
Q

5 compounds found in normal urine

A
  • water
  • creatine
  • urea
  • H+
  • Nh3
  • Na+
  • k+
  • drugs
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18
Q

5 compounds found in pathologic urine

A
  • glucose
  • blood
  • haemoglobin
  • protein
  • bacteria
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19
Q

explain the mechanism of water secretion in leaky secretory epithelia

A
  • Na+/K+ ATPase generates the electrochemical gradient using ATP as primary active transporter
  • NKCC1 on basolateral side uses electrochemical gradient to build up Cl- conc. inside the cell
  • the apical Cl- channal (CFTR) facilitates Cl- secretion to the luminal side
  • the Cl- secretion makes the luminal side more -ve, facilitating Na+ secretion via the paracellular pw
  • the Cl- and Na+ secretion generates an osmotic gradient from ISF (low) to lumen (high)
  • the osmotic gradient facilitates water secretion via the trans and paracellular pw
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20
Q

explain the mechanism of chloride secretion in secretory epithelia

A
  • Na+/K+ ATPase generates a low Na+ conc. inside the cell that can be used by transporters or channels on both sides of the membrane
  • Na+ gradient is then used by NKCC1 on the basolaterla side to facilitate secretion of Na+, K+, 2Cl-, and chloride is secreted apically via CFTR
  • Na+ and K + are absorbed on the basolateral side
  • apical Cl- secretion results in a -vely charged lumen and a +vely charged interstitium driving paracellular sodium secretion
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21
Q

proceeses of kidney,name a substance for each:

  • needs to partly reabsorbed
  • needs to be fully reabsorbed
  • needs to be entirely secreted
A
  • Na+/K+ needs to partly reabsorbed
  • glucose needs to be entirely reabsorbed
  • drugs such as PAH need to be entirely secreted
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22
Q

what does the filtration barrier in the glomerulus look like?

A
  • fenestrated capillary endothelium
  • basement membrane (3 layers)
  • epithelial podocyte w foot processes and filtration slits
23
Q

what are the criteria for exclusion of a molecule at the filtration barrier? give an example for what is and what inst excluded

A

exclusion at filtration barrier depends on size and charge of molecules

  • glucose and Na+ are filtered
  • albumin not filtered
24
Q

what is the main driving force for filtration?

A

blood pressure; pressure at the glomerular capillary

25
Q

what are the forces opposing filtration?

A

pressure of fluid in bowman space

osmotic pressure of glomerular capillaries

26
Q

explain the osmotic driving force for filtration?

A

osmotic P of the glomerular capillaries is represented by albumin in the blood that does not contribute to the total osmotic value of blood. due to the fact that albumin is not filtered, it creates an osmotic force in the glomerular capillaries

27
Q

what are 4 properties if a substance that can be used to determine filtration rate and give an example

A 
freely filtered
not re-absorbed
not secreted
not toxic
- eg: inulin (exogenous sugar)
28
Q

define renal clearance

A

clearance = the plasma volume thats cleared from a substance per time.

29
Q

what are the clearance values for glucose, PAH, and creatine?

A

C(glucose) = 0 mL/min
C(PAH) = 600 mL/min
C(creatinine) =mL/min

30
Q

define GFR

A

glomerualr filtration rate is the filtered plasma volume per time in all glomeruli in the kidneys.

31
Q

how can you estimate the value for GFR?

A

estimate GFR by measuring creatinine in the blood and urine, and the urine volume per time. then you need to calculate the clearance for creatinine because creatinine is ONLY filtered

32
Q

what does the clearance of creatinine represent?

A

clearance of creatinine is a measure for GFR. it is independent of the conc. of creatinine in the blood and independent of reabsorption and secretion processes in the kidney

33
Q

explain the term filtered load and explain why it stays linear with increasing plasma glucose concentration

A

filtered load = the amount of substance saturated per time. filtration cannot be saturated, therefore a increasing concentration of glucose in the plasma will result an increase in the filtered load.

34
Q

how do you calculate the filtered load?

A

filtered load = (plasma conc. of substance) x GFR

GFR = 125mL/min

35
Q

draw out and explain how glucose is reabsorbed in the early proximal tubule in the kidney

A

diagram should include;

  • SGLT2 on apical surface
  • GLUT2 and Na+/K+ ATPase on basolateral side
  • 90% of glucose reabsorption occurs here
36
Q

what are the key differences between SGLT2 and SGLT1?

A
  • SGLT1 is present in kidney and intestine
  • SGLT2 is unique to kidney and responsible for 90% of glucose reabsorption
  • both are secondary active transporters
  • ratio for SGLT2 is 1 : 1
  • SGLT2 has low affinity but high capacity for glucose
  • ratio for SGLT1 is 2 Na+ : 1 glucose
  • SGLT1 has high affinity but low capacity fo glucose.
37
Q

which two organs control BP and how do they do this?

A

heaert controls BP through SV

kidneys control BP through sodium and water homeostasis therefore blood volume

38
Q

what percentage of sodium is reabsorbed in different part of the nephron

A
  • 66% Na+ reabsorbed in PCT
  • 25% reabsorbed in TAL
  • 5% in DCT
  • 3 % IN CCT
39
Q

name 3 diuretics and their target channel/transporter and area of the nephron

A

loop diuretis (furesomide) - NKCC2 in TAL
thiazides - NCC in DCT
amiloride - ENaC in CCT

40
Q

in what part of the nephron is Na+ reabsorbed both para and transcellularly? how is it absorbed in other parts of the nephron?

A
  • in PCT and TAL = para and transcellular Na+ reabsorption

- DCTand CCT = transcellular reabsorption only

41
Q

which hormone controls sodium reabsorption and which part of the nephron is controlled by this hormone?

A

aldosterone controls sodium reabsorption in the DCT and acts by inserting more ENaC transporters on apical side of epithelium

42
Q

how is the secretion of aldosterone regulated?

A

regulated via the renin-angiotensin system in response to low plasma volume to increase water retention

43
Q

explain the counter current multiplier system, what transporter it involves, and the effect on sodium reabsorption

A
  • countercurrent multiplier system helps keep the interstitium hypertonic
  • NKCC2 when inhibited by loop diuretic/furesomide in TAL controls water reabsorption
  • the counter current multiplier system is responsible for 25% of sodium reabsorption.
44
Q

explain how osmolarity of urine develops in the nephron starting from the PCT and ending with the CCT

A

primary urine coming from PCT is isotonic - becomes hypertonic at the tDLH due to water reabsorption - turns into hypotonic due to Na+ reabsorption in TAL - then becomes hypotonic (dehydration, anti-diuresis, high water retention) or hypertonic (hydration, duiresis, low water reabsorption) in CCT

45
Q

what hormone controls water reabsorption in the collecting duct?

A

Anti-diuretic hormone/ vasopressin

46
Q

what are the inductors for the release of ADH

A
  • low bloood pressure

- high blood osmolarity

47
Q

wherre about in body do we sense changes in BP or blood osmolarity?

A

baroreceptors in the aorta and carotid sinus project to the medulla oblongata and then to periventricular neurons in the brain, where they are coordinated with inputs from osmoreceptors to facilitate vasopressin release from pituitary gland

48
Q

explain how vasopressin can change water permeablity and therefore water re-absorption in the kidney

A

ADH binds to the V2 receptor at the basolateral membrane of the CCT. this via adenylate cyclase and PKA increases the insertion of AQP2 into the apical membrane and increases water permeability

49
Q

define acidosis and alkalosis

A 
acidosis= increase in arterial H+ conc. (pH less than 7.4) 
alkalosis = decrease in arterial H+ conc. (pH more than 7.4)
50
Q

name the 4 different acid-base disturbances?

A
  • respiratory alkalosis
  • respiratory acidosis
  • metbaolic alkalosis
  • metabolic acidosis
51
Q

give an example for a cause and condition of respiratory acidosis, and how it can be compensated

A

respiratory acidosis can be caused by hypoventilation eg: asthma, compensation = increase in reabsorption of bicarbonate in kidney

52
Q

explain the regulation of low plasma volume response by kidney

A
  • low plasma volume = arterial BP goes down, GFR goes down
  • sympathetic nerve activity goes up
  • low NaCl conc. at macula densa cells and high sympathetic nerve activity triggers release of renin from junxtaglomerular cells
  • renin helps produce angiotensin ll from liver
  • angiotensin ll (vasoconstrictor) facilitates synthesis of aldosterone
  • aldosterone increases Na+ and water reabsorption in collecting duct
53
Q

explain the regulation of high plasma volume response by kidney

A
  • high plasma volume triggers receptors via distension in heart
  • this distension leads to a release of ANP (atrio-natiuretic peptide/factor)
  • high plasma ANP levels reduce plasma aldosterone
    high plasma ANP levels dilate afferent and constrict efferent arterioles, increasing GFR
  • high plasma ANP levels reduce Na+ reabsorption and increase Na+ excretion
54
Q

what are the three important places in the nephron where water is reabsorbed and approx. %?

A

PCT - 66%
tDLH - 25%
CCT - 2-8%

phty251 (6 decks)

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