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Physiology S2 > Physiology of the Renal System > Flashcards

Physiology of the Renal System Flashcards

1
Q

What are the main functions of the urinary system?

A
  • excretion
  • homeostasis
  • acid-base balance
  • secretion (renin, calcitrol, erytropoetin)
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2
Q

What does the urinary system secrete?

A
  • renin,
  • calcitrol,
  • erytropoetin
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3
Q

What products are excreted from the urinary system?

A
  • product of metabolism
  • water
  • hormones
  • vitamins
  • toxic substances
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4
Q

How do kidneys maintain homeostasis?

A
  • maintains blood volume
  • maintains the composition of body fluids
  • excretes waste products (urea, creatinine, uric acid, NH3) toxic to the organism
  • regulates the blood concentration of ions (Na+, K+, Cl-, Ca2+, sulphate, phosphate, bicarbonate)
  • regulates pH by secreting H+
  • regulates arterial blood pressure (maintaining osmolarity and water volume)
  • gluconeogenesis (produces glucose from substances other than carbohydrates)
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5
Q

State examples of waste products excreted by the urinary system.

A
  • urea,
  • creatinine,
  • uric acid,
  • ammonia,
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6
Q

What three important hormones does the kidney produce?

A
  • erythropoietin (EPO)
  • calcitriol
  • renin
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7
Q

What is the function of erythropoietin? Explain its release.

A

Stimulates the formation and maturation of erythrocytes.

lower red blood cell count –> lower O2 in blood –> kidney secretes EPO –> EPO travels into bone marrow & stimulates red blood cell rpoduction –> more erythrocytes & correct oxygen supply

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8
Q

What is the function of calcitriol? Explain its release.

A
  • role in the metabolism of vitamin D and calcium
  • stimulates osteoblasts to produce collagen
  • calcitriole = active form of vitamin D = vital importance in the regulation of calcium homeostasis
  • active vitamin D is needed to reabsorb Ca2+ in the small intestine
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9
Q

What is the function of renin? Explain its release.

A
  • releases prostaglandins
  • part of the RAAS (renin-angiotensin-aldosteron system)
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10
Q

Explain the renin-angiotensin-aldosteron system.

A

1) juxtaglomelural cells synthesise renin
2) renin is released into blood.
3) renin catalyses the enzymatic reaction changing angiotensin I to angiotensin II (+angiotensin converting enzyme ACE (lungs))
4) angiotensin II causes:
- vasoconstriction (kidney, skin, abdominal organs)
- stimulated the release of aldosterone (from the adrenal cortex into the blood)
5) aldosterone regulates electrolyte and water balance, by promoting the uptake of Na+, and the excretion of K+

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11
Q

What is the urinary system composed of?

A

1) 2 kindeys (produce urine)
2) urinary excretory pathways:
- ureter
- urinary bladder
- urethra

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12
Q

What is the location of the kidneys?

A
  • under the peritoneum of the upper abdominal wall,
  • one on each side of the spine
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13
Q

Where is urine formed? How is it excreted?

A

formed: kidneys
excreted: by the urinary tract

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14
Q

What does each nephron contain?

A

1) vascular component: capillary network (from which fluid is filtered)
- renal conruscle / malpighian corpuscle
- consists of: bowmans capsule and glomerulus (capillary tuft)
- function: plasma filtration + formation of primary urine

2) tubular component: long tubular processing
- function: reabsorption and secretion processing
- consists of: proximal tubule, loop of Henle, distal tubule, and collecting duct

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15
Q

What are the different types of nephrons?

A

1) CORTICAL NEPHRONS:
- glomerulus in cortex
- short loop of Henle (barely extend into the medulla)

2) MEDULLARY NEPHRONS:
- glomerulus in inner region of cortex (close to the medulla)
- long loops of Henle (passing deeply into the medulla)

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16
Q

What is the renal (malphigian) corpuscle?

A
  • the nephrons initial filtering component
  • Glomerulus- capillary tuft, recieving blood supply from the afferent arteriole and passes into the efferent arteriole
  • Bowman’s capsule- surrounds the glomerulus
  • composed of visceral (inner) and parietal (outer) layers
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16
Q

What happens with the glomelural fitrate?

A
  • drains into Bowman’s capsule –> proximal convoluted tubule
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17
Q

What is special about the endothelium?

A

It is fenestrated (has small pores which allow small molecules through)

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18
Q

What is special about the podocytes of the glomerulus?

A
  • have negative charge
  • podocytes and the basement membrane stops proteins from getting through into the tubular fluid
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19
Q

What is the function of the Macula densa in the glomerulus?

A

function as chemoreceptors

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20
Q

What type of nephrons do dogs and cats have?

A

only juxtamedullary nephrons

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21
Q

What is the first filtration part of the nephron?

A

renal (malphigian) corpuscle:
- glomerulus
- bowman’s capsule

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22
Q

What is the macula densa?

A

epithelial cells in contact with the arterial wall

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23
Q

What is the juxtaglomerular apparatus? What cells is it composed of? What is its function?

A

cells: granular cells (secrete renin)
function: - secrete renin
- regulate renal blood flow
- GFR
- indirectly modulates Na+ balance
- modulated blood pressure

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24
Q

What happens within the juztaglomerular apparatus when blood pressure is low?

A

blood pressure low
renin secreted
angiostensin II produced
increased reabsorption of Na and water
increased blood pressure

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25
Q

What are the three major renal exchange processes? Where do they occur?

A

glomerular filtration - renal capsule
reabsorption - renal tubules
secretion - renal tubules

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26
Q

Where does glomerular filtration occur? What does it produce?

A

location: renal corpuscle
forms: primary urine

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27
Q

Explain the direction of flow in reabsorption and secretion.

A

reabsorption: tubule to blood
secretion: blood to tubule

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28
Q

How large is the filtration surface within the glomerulus? How much solution is filtered in the glomerular apparatus? What happens to the rest of the solute which causes the smaller amount of urine?

A

filtration surface: 1.5 m^2
volume: 180-200L
- rest (97%) is reabsorbed –> only 1.5-2L of urine

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29
Q

What are the layers of the Glomerular filter?

A

1) the capillary endothelium
2) basal membrane
3) epithelium of the Bowman’s capsule (podocytes)

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30
Q

What are podocytes?

A

Special cells which have numerous pseudopodia (pedicels) that interdigitate to form filtration slits along the capillary wall.

31
Q

How large are the pores of the slit membrane (podocytes)?

A

20-30nm

32
Q

What is the surface of podocytes and slit membrane covered with? Why?

A

covered with glycocalyx:
- negative electrical charge:
- repells proteins (preventing their passage into the urine)

33
Q

What does the negative electrical charge of the podocyte surface cause?

A

repelling of proteins –> proteins do not pass into the urine

34
Q

What is the smallest plasma protein? What happens with it?

A
  • albumin
  • filtered through the glomerular filter
  • reabsorbed by endocytosis in the proximal tubules
35
Q

What does glomerular filtration depend on?

A
  • pressure gradient across the filtration slit (endothelium, basal membrane and podocytes)
  • blood circulation through the kidneys
  • permeability of the filtration barrier
  • filtration surface
36
Q

Explain the composition of the solution which passes through glomerular filtration.

A
  • similar to blood plasma
  • WITHOUT proteins!
37
Q

What are the different forces acting on glomerular filtration?

A

1) glomerular capillary hydrostatic pressure (blood hydrostatic pressure against the capillary wall)
2) glomerular osmotic pressure (presence of solutes (proteins) in blood)
3) bowman’s capsule hydrostatic pressure (pressure of filtrate against boeman’s capsule wall)
4) bowman’s capsule osmotic pressure (pressure of solutes in the filtrate)
5) net filtration rate (fluid moves from the glomerulus into the capsule)

38
Q

What is the net filtration rate?

A

The speed at which fluid moves from the glomerulus into the capsule.

39
Q

What is the glomerular filtration rate?

A

The volume of plasma filtered per unit of time from the glomerulus into the Bowman’s capsule.

horse: 380 mL/min
dog: 55 mL/min

directly proportional to body mass

40
Q

What is the filtration fraction?

A

glomerular filtration rate / renal plasma flow

41
Q

What is reabsorbed in the proximal convoluted tubule? How?

A
  • Glucose, amino-acids, sodium (pumped out of the tubules, by active transport (ATP needed))
  • Chloride (follows sodium (accumulation of positive charges draws chloride out))
  • Water (osmosis)
  • compounds present in high concentration in the filtrate but low in the blood can move through diffusion.
42
Q

Explain glucose reabsorption.

A
  • Transporter of glucose has a limited capacity to carry glucose back into the blood.
  • secondary active transport (glucose transports with Na+ as co-transport (ATP dependent Na-K pump)).
43
Q

What is glucosuria?

A

Glucose fails to be reabsorbed and remains in the urine.

44
Q

Explain the percentages of reabsorbed molecules in the proximal convoluted tubules. Is reabsorption regulated?

A
  • 70% Na+ & H2O
  • 100% amino acids & glucose
  • fraction of bicarbonates, potassium, phosphate and calcium
  • filtrate at the end should be iso-osmolar to the filtrate at the beginning
45
Q

What does the proximal convoluted tubule secrete? Why?

A

ammonia- act as a buffer for the secreted H+
creatine- assess kidney functioning

46
Q

How should the filtrate be at the end of the PCT in comparison to its beginning?

A

iso-osmolar

47
Q

Explain th eprocess of reabsorption in the loop of Henle.

A

descending loop:
- permeable to water
- no sodium pumps

ascending loop:
- permeable to Na+, Cl-and K+ (into interstitial fluid)
- impermeable to water
- many sodium pumps

48
Q

What does the loop of Henle form which is important for water reabsorption in the convoluted tubule?

A

osmotic gradient

49
Q

What does the ascending loop contribute to?

A

Making the urine less concentrated.

50
Q

What is urine at the final portion of the descending limb of the loop of Henle? hyper/iso/hypo - tonic

A

hypertonic

51
Q

What is urine at the final portion of the ascending limb of the loop of Henle? hyper/iso/hypo - tonic

A

hypotonic

52
Q

Explain the function of the loop of Henle. What depends on its length?

A
  • longer= more concentrated filtrate and medullary interstitial fluid
  • importance: collecting tubule runs through the hyperosmotic medulla –> reabsorbs more H2O
53
Q

Do desert animals have a longer or shorter loop of Henle? Why?

A
  • longer loop of Henle
  • reabsorb more H2O
  • more concentrated urine
54
Q

What is different about the distal convoluted tubule and collecting duct?

A
  • different tubular walls
  • tight junctions
  • membrane is impermeable to water
  • cell membrane has receptors (bind and respond to hormones (ADH and aldosterone))
55
Q

What does the binding of hormones cause? What hormes? Where are they present?

A

DCT and CT:
- hormones: ADH and aldosterone
- binding of hormones modifies membrane permeability to water and ions

56
Q

What happens when ADH (vasopresin) is low?

A
  • no binding to receptors
  • H2O is not reabsorbed back into the blood
  • H2O remains in the renal tubule
  • high urine volume
57
Q

What happens when an individual is dehydrated?

A

ADH is released by the post-pituitary gland:
- binds to receptors in the convoluted tubule
- channels open (aquaporins)
- H2O moves into the interstitial fluid and blood
- low urine volume
- water is retained in human

58
Q

Where are the neurosecretory neurons for ADH located? What do they monitor?

A
  • location: hypothalamus
  • monitor: blood osmotic pressure
59
Q

How do neurosecretory neurons for ADH control ADH secretion?

A

if blood osmotic pressure is high:
- increased ADH secretion and release
- increased water reabsorption
- dilution of blood
- lowered blood osmotic pressure
- decreased urine volume

if blood osmotic pressure is low:
- decreased ADH secretion and release
- decreased water reabsorption
- increased blood osmotic pressure
- increased urine volume

60
Q

What does hypernatremia cause?

A
  • water retention
  • high blood pressure
61
Q

What does hyponatremia cause?

A

hypotension

62
Q

What does blood pressure regulate?

A
  • sodium movement in the tubules
  • GFR (glomerular filtrate rate) (sensed by the macula densa of the JGA (juxtaglomerular apparatus)
63
Q

What happens if blood pressure is too low?

A

juxtaglomerular cells of the JGA secrete renin!!

64
Q

What happens when renin is secreted into the blood by juxtaglomerular cells?

A

renin transforms angiotensinogen into angiotensin I.
angiotensin I –(ACE)–> angiotensin II
angiotensin II causes the adrenal cortex to release aldosterone.

aldosterone promotes Na+ reabsorption

65
Q

What does aldosterone promote?

A

sodium reabsorption in the distal convoluted tubule and collecting duct.

66
Q

What hormone promotes sodium dumping by the distal convoluted tubule and collecting duct?

A

Atrial Natriuretic Peptide (ANP):
- vasodilator!!

67
Q

What does the urinary tract consist of?

A
  • 2 ureters
  • urinary bladder
  • urethra
68
Q

Is urine composition altered after it has exited the kidney?

A

No, the epithelial layer of the urinary tract is impermeable to water.

69
Q

What is the function of ureters?

A

Facilitate the passage or urine from the kidney to the bladder for storage.

70
Q

How are ureters innervated? What happens when these nerves are stimulated?

A
  • rich sympathetic and parasympatheric nerves
  • stimulation of sympathetic nerves: inhibition of contractions
  • stimulation of parasympathetic nerves: stimulation of contractions
71
Q

State the innervation of the urinary bladder.

A
  • autonomic innervation (sympathetic and parasympathetic)
  • somatic innervation
72
Q

What is a cystogram?

A

A graph relating intravesical pressure (bladder pressure) to volume.

73
Q

What does the filling of the bladder lead to?

A
  • increase in bladder volume
  • increase in cavity radius
  • increase in wall tension
  • NO change in pressure !
74
Q

What is micturation? What is it controlled by?

A
  • process of urine voiding from bladder
  • reflex process (opening of urethral smooth muscle)

controlled by:
- sacral parasympathetic nervous system
- bladder stretch receptors send impulses to the sacral spine
- impulses sent to brain cortex (notify need for urination)

75
Q

Explain the chemical composition of urine.

A
  • urea
  • creatine
  • uric acid
  • carbohydrates
  • enzymes
  • fatty acids
  • hormnes
  • sodium
  • potassium
  • chloride
  • magnesium
  • calcium
  • ammonia
  • water (95%)

Physiology S2 (17 decks)

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