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Mammalian physiology > Urinary system - Lectures 19-20 > Flashcards

Urinary system - Lectures 19-20 Flashcards

1
Q

What are the 6 functions of kidneys?

A
  1. regulation of extracellular fluid volume and blood pressure
  2. regulation of osmolarity
  3. maintenance of ion balance (Na+/K+ important for membrane potential)
  4. homeostatic regulation of pH
  5. excretion of wastes (urea)
  6. production of hormones (erythropoeitin, renin, activation of vit D)
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2
Q

do we need both kidneys?

A

nope! they act as functional reserve = we don’t need both

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3
Q
  • what is the functional unit of a kidney?
  • how many renal pyramids do we have?
  • how many nephrons? what % is cortical nephrons? vs juxtamedullary nephrons?
  • _______ artery –> _______ artery –> ______ arterioles –> __________ –> ______ vein –> _________ vein
A
  • nephrons!
  • 6 to 8
  • 1-1.3 million: 80-85% cortical vs 15-20% juxtamedullary
  • renal artery –> arcuate artery –> afferent arterioles –> glomerulus –> arcuate vein –> renal vein
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4
Q

each nephron has _______ element and ________ element
- explain pathway of each

A

VASCULAR ELEMENT:
- afferent arteriole –> glomerulus/capillaries –> efferent arteriole –> peritubular capillaries (rolled around tubules ish) OR vasa recta (along the loop of Henle) –> veinules –> veins
TUBULAR ELEMENT:
- bowman’s capsule (contains glomerulus) –> proximal tubule (very close to bowman’s capsule) –> descending limp of loop of Henle (shorter thick section than ascending) –> ascending limp (longer thick section) –> distal tubule –> collecting duct –> bladder

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5
Q

where is the main exchange happening in the vascular elements of the kidney?

A

at peritubular capillaries!
- vs glomerulus = more area of filtration!

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6
Q

ascending part of loop of Henle goes between what and what? –> what is that region called?
- what specific cells does it contain? function?

A

afferent and efferent arterioles –> juxtaglomerular apparatus
- macula densa –> can detec how much sodium in filtrate –> based on that, produces paracrine factors (ATP, adenosine) that affect neighbouring cells to contract = reduce flow of afferent and efferent arterioles
*also granular cells that produce rennin hormone –> promotes angiotensin pathway to decrease blood pressure

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7
Q

explain how kidney filters, reabsorb and secrete
FILTRATION:
- fluid from ______ into _______
- occurs where?
- filtered ______ is called ______?
REABSORPTION
- materials from _______ are passed back into _______
- occurs where?
SECRETION
- material from ______ into ________
- occurs where?

A

FILTRATION:
- fluid from blood into lumen of nephron
- occurs at renal corpuscule
- filtered plasma is called filtrate –> excreted unless reabsorbed
REABSORPTION:
- filtrate back to blood
- peritubular capillaries
SECRETION:
- blood to lumen of tubule
- peritubular capillaries

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8
Q

nephron modifies _____ ______ and _________
1. filtrate is almost identical to ________ at the renal corpuscule –> how many L per day, whats the osmolarity?
2. about ____% filtrate is reabsorbed by ________ tubules –> how many liters remain? osmolarity?
3. filtrate in loop of Henle: more/less solute is reabsorbed than water –> how many L remain, osmolarity?
4. distal tubule and collecting duct: some ________ and ________ –> how many L remain, osomolarity?

A

fluid volume and osmolarity
1. plasma
- 180L/day, 300 mOsm
2. 70% –> by proximal tubules
- 54L/day remains, 300 mOsm
3. more solute reabsorbed than water, water becomes diluted
- 18L/day remains, 100 mOsm
4. reabsorption and secretion
- 1.5L/day remains, 100-1200 mOsm depending on hydration state

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9
Q

place the 4 following words: excreted, reabsorbed, secreted, filtered:
amount ______ = amount _______ - amount _________ + amount ________

A

excreted = filtered - reabsorbed + secreted

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10
Q

which 2 are 100% filtered into the filtrate and get all reabsorbed in the blood after?

A

glucose and amino acids

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11
Q

why so much absorption in proximal tubules? (2)

A
  1. cells only have 1 layer of epithelial cells –> have microvilli to increase surface area
  2. lots of ATP pumps on epithelial cells for active transport
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12
Q

processing/functions of:
1. renal corpuscule (glomerulus + bowman’s capsule) (1)
2. proximal tubule (2)
3. loop of henle (2)
4. distal nephron (distal tubule + collecting duct) (1)

A
  1. RENAL CORPUSCULE
    - filtration of mostly protein-free plasma from capillaries into capsule
  2. PROXIMAL TUBULE
    - isoosmotic reabsorption of organic nutrients, ions and water
    - secretion of metabolites and xenobiotic molecules like penicillin
  3. LOOP OF HENLE
    - reabsorption of ions in excess of water to create dilute fluid in lument
    - countercurrent arrangements contributes to concentrated interstitial fluid in the renal medulla
  4. DISTAL NEPHRON
    - regulated reabsorption of ions and water for salt and water balance and pH homeostasis
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13
Q

filtration occurs in the renal corpuscule: blood has to pass through
1. _______ –> (2)
2. _______ ___________
3. ________ of ________ ________ (2)

A
  1. GLOMERULAR CAPILLARY ENDOTHELIUM
    - fenestrated capillaries (lots of holes)
    - Glycocalyx (gel like glycoprotein/glycolipid) –> carries negative charge (plasma proteins also have negative charges so can’t pass through)
  2. BASEMENT MEMBRANE
  3. EPITHELIUM OF BOWMAN’S CAPSULE
    - podocytes (projections that link with each other –> space between the projections = filtration slits)
    - mesangial cells (smooth muscles cells that can contract)
    *mostly glomerular capillary endothelium, basement membrane and podocytes create a 3-layer filtration barrier
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14
Q
  • how many percent of plasma that passes through glomerulus is filtered?
  • how many percent is reabsorbed
  • how many percent is excreted to external environment?
A

100% plasma volume entering afferent arteriole
- 80% continues to efferent arteriole, 20% filters through and becomes filtrate
- >19% reabsorbed in peritubular capillaries
- <1% of volume is excreted to external environment (>99% of plasma entering kidney returns to systemic circulation)

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15
Q

what can pass through glomerular capillary? (4)
- what can’t pass through? (3)

A
  • h2o, aa, glucose, ions can passe through
  • proteins (bc too negative and too big), RBC, WBC
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16
Q

what are the 3 pressures that influence glomerular filtration?
- favors or opposes filtration?

A
  1. CAPILLARY BLOOD PRESSURE (PH)
    - hydrostatic pressure (around 55 mmHg) (still pretty high because directly coming from aorta) –> favors filtration
  2. CAPILALRY COLLOID OSMOTIC PRESSURE (pi)
    - due to proteins in plasma! –> around 30 mm Hg
    - opposes filtration (pulls fluid back to plasma)
  3. CAPSULE FLUID PRESSURE (Pfluid)
    - hydrostatic pressure inside Bowman’s capsule (around 15 mmHg)
    - opposes filtration
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17
Q

Net pressure = ____ - _____ - ______ = _____ mm Hg into/out of Bowman’s capsule
- filtration or absorption?

A

PH - pi - Pfluid = 10 mm Hg INTO Bowman’s capsule
- filtration!

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18
Q

what is the glomerular filtration rate (GFR)?
- influenced by (2)
- controlled primarily by regulating what?

A

volume of fluid filtered per unit time
- influenced by
1) net filtration pressure (renal blood flow and blood pressure)
2) filtration coefficient (surface areas of glomerular capillaries available for filtration + permeability of filtration slits)
- controlled primarily by regulating blood flow through renal arterioles

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19
Q

decrease or increase GFR
1. increase resistance in AFFERENT arteriole
2. increase resistance in EFFERENT arteriole
3. decrease resistance in AFFERENT arteriole
4. decrease resistance in EFFERENT arteriole

A
  1. decreased GFR bc less blood gets to glomerulus (less renal blood flow and less capillary blood pressure)
  2. increased GFR bc less blood can flow into efferent (decreases renal blood flow but increases PH in glomerulus)
  3. increased GFR bc more blood gets to glomerulus
  4. decreased GFR bc blood rapidly flow away
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20
Q

is GFR relatively constant?
- if so, how?

A

yes! it says constant because it has autoregulation that maintains a nearly constant GFR when mean arterial blood pressure is between 80 and 180 mm Hg

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21
Q

GFR is subject to autoregulation via 2 pathways + what can also influence?

A
  1. MYOGENIC RESPONSE
    - intrinsic ability of vascular smooth muscle to respond to pressure changes (ie stimulus causes af/efferent tubules to expand –> reflex response ish to contract and decrease diameter) (mesangial cells)
    - similar to autoregulation in other systemic arterioles
  2. TUBULOGLOMERULAR FEEDBACK
    - paracrine crontrol
    - juxtaglomerular apparatus: macula densa cells detect NaCl in filtrate (if lots of NaCl, release ATP-adenosine for contraction) + granular cells secrete enzyme renin
    * HORMONES AND AUTONOMIC NEURONS can also influence GFR
    - by changing resistance in arterioles (SNS can activate b1 receptor and induce contraction)
    - by altering filtration coefficient
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22
Q

8 steps of negative tubuloglomerular feedback loop of of the juxtaglomerular apparatus
- starts with increase in GFR

A
  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 (mesangial cells contract)
  6. resistance in afferent arteriole increases (= less blood comes in)
  7. hydrostatic pressure in glomerulus decreases
  8. GFR decreases
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23
Q

what type of cells produce rennin hormone?
- does rennin increase or decrease blood pressure? how?

THIS WAS END OF LECTURE 19. MORE ON THIS IN LECTURE 20

A
  • granular cells near juxtaglomerular apparatus
  • rennin increases blood pressure
    1. when [Na+] decreases–> rennin is produced
    2. rennin cuts angiotensinogen (protein produced by liver) into angiotensin I
    3. angiotensin I (not functional) is converted to angiotensin II by angiotensin converting enzyme (ACE)
    4.1 angiotensin will increase aldosterone release from adrenal gland cortex –> aldosterone will increase water absorption
    4.2 angiotensin II is a powerful vasoconstrictor
    5. blood pressure increases
24
Q
  • reabsorption may be _____ or ______
  • 2 pathways for reabsorption
  • which pathway is used the most?
A
  • active (need ATP) or passive (uses concentration gradient or osmotic gradient)
    1. TRANSEPITHELIAL TRANSPORT (TRANSCELLULAR TRANSPORT)
  • substances cross apical and basolateral membranes of the tubule epithelial cells
  • apical side –> basal side –> interstitial fluid –> peritubular capillaries)
    2. PARACELLULAR PATHWAY:
  • substances pass through the cell-cell junction between 2 adjacent cells
  • transcellular transport is used the most!
25
Q

what re 3 different ways to transport Na+?

A
  1. leaking channels: leak into cell is [] gradient
  2. cotransport –> symporter or antiporter (ie Na+/glucose or Na+/aa or Na+/H+ or Na+/K+/Cl-/Cl- channel
  3. Na+ K+ ATPase pump
26
Q

do amino acids and glucose pass through the glomerulus to becomes the filtrate?

A

yes they do cause they are smaller molecules! but almost 100% get reabsorbed in the proximal tubule to return to bloodstream/get to the peritubular capillaries

27
Q

how is glucose reabsorbed from tubule lumen to intestitial fluid?

A
  1. Na+ moving down chemical gradient uses the SGLT protein to pull glucose into cell against its concentration gradient (symporter)
  2. glucose enters proximal tubule cell + diffuses out of the basolateral side of cell using GLUT protein (going down [ ] gradient)
  3. Na+ is pumped out of proximal tubule cell into interstitial fluid by Na+K+ ATPase to reestablish [ ] gradient
28
Q

does the reabsorption of glucose into blood active or passive reabsorption?

A

active because need ATPase to reestablish Na+ gradient!

29
Q
  • what is the renal threshold?
  • renal transport can reach _______
    –> what does it mean?
  • what is the Transport maximum (Tm)
A
  • plasma concentration at which a substance first appear in urine –> ie glucosuria/glycosuria = glucose in urine
  • saturation! maximum rate of transport that occurs when all carriers are occupied by/saturated with substrate
  • Tm = transport rate at saturation
30
Q
  1. what is the hydrostatic pressure in afferent arteriole vs efferent arteriole vs peritubular capillaries
  2. what is the osmotic pressure?
  3. what is the net driving pressure at glomerulus vs in peritubular capillaries? –> promotes filtration or reabsorption?
A
  • Afferent: around 55 mm Hg (high bc coming from aorta)
  • efferent: around 35 mm Hg (lower bc lost liquid in glomerulus)
  • peritubular capillaries: around 10 mm Hg
    2. 30 mm Hg everywhere
    3. - glomerulus: 55 pushing out of capillaries - 30 (pi) pushing in - 15 fluid pressure –> 10 mm Hg pushing out = filtration!
  • peritubular capillaries: 10 pushing out - 30 pushing in - 20 fluid presure pushing in = -40 mm Hg –> favors reabsorption into blood!
31
Q
  • what is secretion?
  • secretion allows important homeostatic regulation of 2 ions
  • increasing secretions will increase/decrease nephron excretion
  • 2 important transporters?
A
  • active movement of molecules from extracellular fluid into nephron lumen
  • K+ and H+
  • increase secretion = increase excretion! (bc you secrete into the tubules)
    1. organic anion transporter family (OAT) –> substrates compete to bind to OATs due to their broad specificity
    2. Na+-dicarboxylate cotransporter (NaDC)
32
Q

2 reasons for secretion

A
  1. if molecules were too big to get filtrated at glomerulus
  2. if you want to get rid of even more of the molecule –> excrete it out through urine
33
Q

explain transport/secretion of an organic anion from interstitial fluid to tubule lumen. 4 steps

A
  1. direct active tranport: Na+ K+ ATPase keeps intracellular [Na+] low (K+ into proximal tubule cell, Na+ out into interstitial fluid)
  2. secondary indirect active transport: Na+-dicarboxylate cotransporter (NaDC) concentrates a dicarboxylate inside the cell using energy stored in the [Na+] gradient (Na+ AND a-KG- come into cell from basolateral membrane)
  3. tertiary indirect active transport: basolateral organic anion transporters (OAT1-3) concentrate organic anions (OA-) inside the cell using energy stored in the dicarboxylate gradient (a-KG- goes out, OA- comes into cell)
  4. OA- enter lumen in exchange for dicarboxylate (DC- enters cell from apical side + OA- exits cell from apical side)
34
Q

are there organic anion transporters? or cation transporters? or both?

A

both!

35
Q

what is reabsorbed vs secreted in
1. PROXIMAL TUBULE
2. ASCENDING LIMB
3. DISTAL DUBULE
4. COLLECTING DUCT

A
  1. PROXIMAL TUBULE
    R: Na+ (67%), Cl-, K+, Ca2+, glucose (100%), urea
    S: PAH! (para-aminohippurate)
  2. ASCENDING LIMB
    R: Na+ (25%), Cl-, K+, Ca2+
    S: Urea
  3. DISTAL TUBULE
    R: Na+ (around 8%), Cl-, Ca2+
    S: NOTHING
  4. COLLECTING DUCT
    R: Na+, Cl-, urea
    K+ –> net reabsorption or secretion depending on intake

*dont need to worry about urea

36
Q

what percent is excreted/what is the net renal handling?
- Na+
- Cl-
- K+
- Ca2+
- Glucose
- Urea
- PAH (para-aminohippurate)

A
  • Na+: around 1%
  • Cl-: around 1%
  • K+: variable!
    low intake: 2% excreted
    normal intake: 10-20% excreted
    high K+ intake: net secretion up to 150% of filtered load
  • Ca2+: around 1%
  • Glucose: 0%
  • Urea: 30-50% excreted
  • PAH: 500% excreted!
37
Q

do beavers or kangarous have longer loop of Henles?

A

kangarou = longer loop of henle
- range from 100 to 5000 mOsm –> can create a big osmotic gradient bc not a lot of access to water: pee is gonna be very concentrated
VS beavers: juxtamedullar nephrons will be much shorter
- max osmolarity = 500 mOsm

38
Q

what is the osmolarity of urine? what does is represent?
- what ion contributes the most to blood’s osmolarity?

A
  • represents how much water is excreted into urine
  • low osmolarity = high water
  • high osmolarity = low water, high solute
  • around 300 mOsm for human urine but can vary a lot! from 100 to 1200 mOsm
  • Na+ contributes to around 50% of osmolarity in blood
39
Q

what are the 3 wastes we need to get rid of via urine?

A
  1. creatinine (from creatine phosphate) –> [creatinine] in urine can estimate your body muscle mass
  2. urea from protein metabolism (ammonia from aa)
  3. uric acid
40
Q

_______ _________ _________ allows urine to be concentrated
- depends on what?

A

medullary interstitial osmolarity
- depends on cortical nephron (80-85%) and juxtamedullary nephron (15-20% –> affects osmotic gradient)

41
Q
  1. fluid in descending loop of Henle gains/loses water by osmosis to medulla
  2. cells in thick/thin portion of ascending limb of loop are permeable/impermeable to water and actively transport ____ out of lumen into medulla
  3. fluid leaving loop of Henle is more/less diluted than fluid entering (what osmolarity?)
  4. distal nephron: permeability to _____ is under control of _______ –> filtrate will become more/less concentrated
  5. collecting duct: can secrete/reabsorb additional solute –> filtrate can become even more dilte/concentrated
A
  1. loses water (aquaporines!)
  2. thick –> impermeable to water (no aquaporines) –> actively transport Na+ out of lumen
  3. fluid leaving is more dilute (100 mOsm) than fluid entering (300 mOsm)
  4. to water is under control of hormones –> if aquaporines are there, filtrate becomes more concentrated bc water is reabsorbed
  5. reabsorb additional solute, making filtrate more dilute
42
Q

SCHÉMA:
1. ______osmotic fluid (osmolarity?) leaving the proximal tubule becomes progressively more/less concentrated in the descending limb bc of what?
2. osmolarity at the bottom of loop of Henle?
3. __________ of solute in the thick ascending limb creates _____osmotic fluid (osmolarity?)
4. osmolarity at the top of loop of Henle before entering Distal tubule?
5. permeability of water and solutes in distal tubule and collecting duct is regulated by ________
6. final urine osmolarity depends on reabsorption in what?

A
  1. isoosmotic fluid (300 mOsm) –> more concentrated bc water is reabsorbed
  2. 1200 mOsm
  3. removal/reabsorption of solute creates hypoosmotic fluid (osmolarity decreases from 1200 to 100)
  4. 100 mOsm
  5. hormones
  6. in collecting duct
43
Q
  • what is the osmolarity in the renal cortex? same all the way through?
  • vs renal medulla?
A
  • CORTEX: 300 mOsm all the way through. isosmotic to plasma
  • MEDULLA: 300 mOsm close to cortex and becomes progressively more concentrated: 600 –> 900 –> 1200 mOsm
44
Q

which hormone makes the collecting duct epithelium permeable to water?
- where is it produced and when?
- what is its other name?
- what are its 2 functions?

A

vasopressin!
- produced in hypothalamus when [Na+] is low and BP is low
- anti-diuretic hormone (ADH)
1. add aquaporines/water channels to collecting tubules –> so that water can be reabsorbed into vasa recta capillaries which increases blood volume and increase BP
2. contract blood vessels at body extremities (ie hands) which decreases circulation to peripheral to keep more blood for core functions

45
Q

what is the effect of increasing vasopressin on urine concentration? vs no vasopressin?

A
  • with vasopressin, urine is more concentrated (1200 mOsm) bc more water gets reabsorbed in vasa recta capillaries
  • without vasopressin, water stays in collecting duct and urine is dilute (100 mOsm)
46
Q

what are the 4 steps that make vasopressin add water pores to apical membrane?

A
  1. vasopressin (from blood) binds to membrane receptor on basolateral membrane of collecting duct cell
  2. receptor activates cAMP second messenger system
  3. cAMP tells cell to insert AQP2 water pores (vesicle that merges with plasma membrane) on apical membrane of collecting duct cell
  4. water is absorbed by osmosis into collecting duct cell and then into blood
47
Q

what 2 things make up the renal countercurrent multiplier? what do they remove/secrete?

A
  1. loop of Henle: transfers solutes by active transport (ascending limb) into medulla) = filtrate becomes hyposomotic vs extracellular fluid/medulla osmolarity increases (from 100 to 1200 mOsm)
  2. vasa recta: removes water!
48
Q

what happens if vasa recta and loop of Henle both flow in the same direction?

A
  • both will leave at 100 mOsm instead of filtrate leaving at 100 mOsm and blood leaving at 300 mOsm
49
Q
  • which salts are reabsorbed in the ascending loop of Henle?
  • how are they reabsorbed?
A
  • Na+, K+, Cl-
  • through the Na+ K+ Cl- Cl- cotransport NKCC channel (all 3 solutes enter apical membrane of cells of ascending loop)
  • then Na+ passes basolateral membrane into interstitial fluid via Na+ K+ ATPase
  • K+ and Cl- go out of cell into interstitial fluid via channels
50
Q

which hormone controls sodium balance?
- where is it produced?
- what stimulates its secretion?
- what does it do?
- what are its target cells? what do they do? (2)

A

ALDOSTERONE! (steroid hormone)
- adrenal cortex
- low blood pressure + high extracellular [K+]
- increases reabsorption of Na+ and secretion of K+ in the distal tubules and collecting ducts
- target cells = P cells (principal cells) in distal tubule
1. increased opening time of epithelial Na+ channel (ENaC) and renal outer membrane K+ channels (ROMK)
2. increased activity of Na+-K+ ATPase

51
Q

5 steps of how aldosterone acts on principal cells

A
  1. aldosterone (blood) enters P cell of distal nephron and combines with cytoplasmic receptor
  2. hormone-receptor complex initiates transcription in nucleus (bc aldosterone is a steroid hormone)
  3. translation and protein synthesis makes new protein channels and pumps
  4. aldosterone-induced proteins modulate existing channels and pumps
  5. result is increased Na+ reabsorption and K+ secretion
52
Q

Renin-Angiotensin System (RAS)
- when is it activated?
- what is secreted by what? –> what does that enzyme do? (2 conversions ish)
- what are the 3 stimuli to this pathway?

A
  • when blood pressure decreases
  • juxtaglomerular cells secrete renin
    1. renin converts angiotensinogen to angiotensin 1
    2. angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II
    3 STIMULI:
    1. granular cells are sensitive to blood pressure
    2. sympathetic stimulation from cardiovascular center
    3. paracrine feedback from macula densa cells
53
Q

what are the effects of angiotensin II? (6)
- main goal?

A
  1. stimulates adrenal cortex to produce aldosterone
  2. increases vasopressin secretion
  3. stimulates thirst
  4. potent vasoconstrictors (one of the most potent)
  5. activation of ANG II receptors in cardiovascular contorl center increases sympathetic output to heart and blood vessels
  6. increases proximal tubule Na+ reabsorption (via Na+ H+ exchanger)
    MAIN GOAL = increase blood pressure!
54
Q

what type of peptides promote Na+ and water excretion? (opposite to ADH and vasopressin) (2)
- what is natriuresis?

A

NATRIURETIC PEPTIDES:
1. atrial natriuretic peptide (ANP or atriopeptin) –> produced in atrial myocardial cells –> promote Na+ excretion
2. brain natriuretic peptide (BNP) –> produced in ventricular myocardial cells and certain brain neurons
- natriuresis = urinary Na+ loss

55
Q

how to natriuretic peptides promote water excretion? by decreasing _______ ________ –> 3 ways

A

decreasing blood volume!
1. dilates afferent arterioles, increasing GFR
2. decreases Na+ reabsorption in collecting ducts
3. suppress RAS

Mammalian physiology (13 decks)

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