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Intermediate Human Physiology > Renal System > Flashcards

Renal System Flashcards

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1
Q

What are the components of the renal system?

A

Kidneys, Ureters, Bladder and Urethra

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2
Q

What is the peritoneum?

A

Double membrane coating of the abdominal organs

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3
Q

How are the kidneys retroperitoneal?

A

They are located behind the peritoneum in an adipose capsule

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4
Q

What percentage of cardiac output do the kidneys receive?

A

20-25%, around 1.25L/min

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5
Q

What happens to the blood that enters the glomerulus?

A

20% is filtered into the nephron, most is reabsorbed, and a small volume becomes urine

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6
Q

What are the 5 sections of the nephron?

A

Renal corpuscle containing Glomerulus + Bowman’s capsule
Proximal convoluted tubule (PCT)
Loop of Henle (thin descending limb, thick ascending limb)
Distal convoluted tubule (DCT)
Collecting duct (CD)

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7
Q

What are the 2 types of nephron?

A

Cortical (85%) - shoot loops surrounded by peritubular capillaries
Juxtamedullary (15%) - long loop surrounded by vasa recta into medullary pyramid, forms straight vessels

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8
Q

Which type of nephron is central to the formation of concentrated urine?

A

Juxtamedullary

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9
Q

What distinct epithelium characteristic does the PCT contain?

A

Epithelial cells have microvilli, mitochondria

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10
Q

What distinct epithelium characteristic does the CD have?

A

Consists of principal cells + intercalated cells

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11
Q

What are principal cells?

A

Binds to ADH (anti-diuretic hormone) and aldosterone.
Involved in reabsorption of H2O and Na+ from filtrate and secretion of K+

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12
Q

What are intercalated cells?

A

Reabsorb K+ and HCO3- and secrete H+

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13
Q

What is the role of the juxtaglomerular apparatus (JGA)?

A

Blood pressure regulation and Na+ balance

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14
Q

What are the 2 components of JGA?

A

Mascula densa - specialised epithelia cells at the start of the DCT that detect Na+ levels in tubular fluid

Juxtaglomerular granular cells - specialised smooth muscle cells of afferent arteriole that secrete renin in response to low NaCl

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15
Q

What are the primary functions of the renal system?

A

Excretion of waste
Osmoregulation
Regulation of blood pressure and volume
Acid-base balance
Endocrine production of hormones
Gluconeogenesis

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16
Q

What are the nitrogenous waste products and where did they come from?

A

Urea and NH3 from deamination of AAs
Creatinine from breakdown of creatine phosphate
Uric acid from breakdown of nucleic acids
Urobilin from breakdown of Hb
Steroid hormones from hepatic transformation like progesterone/testosterone

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17
Q

What are examples of excretion of exogenous molecules?

A

H2O soluble drugs - aminoglycoside antibiotics
Lipid soluble drugs following hepatic transformation into hydrophilic forms - propranolol
Other ingested products - pesticides, food additives

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18
Q

What are the main ions that kidneys regulate in plasma electolyte concentration?

A

Extracellular - Na+, Cl-
Intracellular - K-, HPO42-

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19
Q

What is osmoregulation?

A

Process by which kidneys maintain H2O and electrolyte balance
Maintains body fluid of 300mOsm/L despite variable intake

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20
Q

How is acid-base balance important?

A

For regulation of blood pH by variable excretion of H+ and conservation of HCO3-
This is the only means of elimination of sulphruric+phosphoric acid generated from protein catabolism

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21
Q

What is the function of the hormone erythropoietin?

A

Regulation of RBC production
Stimulates production of RBCs by bone marrow in response to hypoxia
Loss of this results in severe anaemia

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22
Q

What is the function of the hormone renin?

A

Released from juxtaglomerular cells of afferent arteriole
Involved in blood pressure regulation and Na reabsorption

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23
Q

What is the function of 1:25-dihydroxycholecalciferol (calcitriol)?

A

Active form of Vit D produced by hydroxylation of 25-hydroxycholecalciferol
Calcium deposition in bones, calcium+phosphate absorption from gut

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24
Q

What are the main components of urine?

A

H2O (96%)
Nitrogenous waste (2.5% mostly urea, creatinine, uric acid and NH3)
Electrolytes (1.5%)
Other trace substances/toxins

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25
What is the typical daily urine output?
Around 1.5L/day (can range from 500ml to 18L) Min. of 500ml to excrete all waste (50g)
26
What are the 3 processes of urine formation?
Filtration - at glomerulus Reabsorption - across nephron tubule into peritubular and vasa recta blood Secretion - out of peritubular blood and into nephron tubules for secretion
27
What is the equation for the rate of excretion of a substance?
Rate of glomerular filtration + secretion - reabsorption
28
What happens at the glomerular filtration?
Occurs at renal corpuscle via ultrafiltration Passive movement of plasma ultrafiltrate across glomerular capillary wall and into Bowman's capsular space Majority is reabsorbed to produce 1.5L urine
29
What are the 3 layers of filtration membrane?
Glomerulus capillary endothelium Glomerulus capillary basement membrane Bowmen's capsule podocyte epithelial cells
30
What is the glomerulus capillary endothelium?
Highly permeable endothelial cells fenestrated with pores - makes it more permeable than non-renal capillaries Is permeable to blood plasma solutes but not platelets/blood cells
31
What is the glomerular basement membrane?
Non-cellular extracellular matrix fused between endothelium and podocytes Has collagen fibres + negatively charged glycoproteins Permits filtration of H2O and small solutes Negative charge repels anionic plasma proteins - protein filtration limited
32
What are visceral podocyte epithelial cells?
Modified epithelia podocytes forming wall of Bowman's capsule Foot processes (pedicels) extend from each cell to wrap around capillaries Filtration slits are spaces between pedicels - each have thin membrane Slits act as size selective filters (6-7nm)
33
What factors affect filtration?
Size and charge Small, positively charges molecules filtered more easily (water, glucose, AAs) Filtration is negligible beyond molecular mass of 70kDa (blood cells, most proteins)
34
What is glomerular filtration rate (GFR)?
Amount of filtrate formed by kidneys/min Determined by net filtration pressure produced by apposing forces of hydrostatic pressure+colloid osmotic pressure Is 125mL/min or 180L/day
35
What happens in the process of reabsoption?
Occurs at PCT via transcellular and paracellular routes Active and passive processes driven by Na+ gradient set by Na+/K+-ATPase pump on basolateral membrane Ion transport drives H2O reabsorption by osmosis Facultative reabsorption occurs in remainder of tubule influenced by hormones
36
What products are reabsorbed and which are excreted in the urine?
Reabsorbed (mostly at PCT) - all glucose+AAs, most H2O+electrolytes (Na+, Cl-, K+, HCO3-), some urea Exreted - all creatinine, 50% urea, <1% H2O, electrolytes
37
What happens at secretion?
Active and passive transfer of substances from peritubular blood and tubular cells into glomerular filtrate K+, H+ (important in acid-base balance), urea, ammonium ions, some drugs (penicillin)
38
What is osmolarity?
Number of osmotically active particles in solution capable of promoting movement of H2O across a semi-permeable membrane by osmosis
39
What is the role of osmoreceptors?
Sense ECF osmolarity and signal kidney action
40
What is the role of anti-diuretic hormone (ADH)?
Primary effector hormone which regulates volume and osmolarity of urine through facultative reabsorption of H2O
41
What is osmotic pressure?
Pressure required to prevent H2O movement and restore equal volumes Proportional to solute conc. that can't cross membrane
42
What is the osmole?
Moles of solute contributing to osmotic pressure
43
What is osmolality?
Measures the conc. of osmotically active particles/Kg of solvent (Osm.Kg-1) Remains constant regardless of temp. and pressure
44
What is osmolarity?
Measures the conc. of osmotically active particles/L of solution (Osmol.L-1) Volume of solution varies as changes in solute added, temp. and pressure
45
What are the 3 states of osmotic balance in the ECF and how do they effect RBCs?
Isotonic - no change in RBC shape Hypotonic - lower solute conc., cell swelling Hypertonic - higher solute conc., cell shrinking
46
Where osmoreceptors found?
In anterior hypothalamus
47
How fast is the response to change in osmoreceptors?
Is very rapid (mins) and sensitive activated by +/-3mosmol kg-1
48
Where is ADH synthesised?
By neurosecretory cells in paraventricular nucleus of anterior hypothalamus for secretion by posterior pituitary gland
49
What does diuresis mean?
Low ADH - large volume of dilute (hypo-osmotic) urine secreted
50
What does high ADH mean?
A small volume of concentrated (hyper-osmotic) urine is produced
51
What is the condition where there is a lack of ADH?
Diabetes insipidus - causes excretion of high volumes of dilute urine
52
Describe the negative feedback loop for ADH
Dehydration increases plasma osmolality Hypothalamic osmoreceptors signal increased ADH release ADH increases kidney H2O reabsorption Hypothalamic lateral preoptic nucleus osmoreceptors activate thirst Leads to decrease in plasma osmolality
53
How does ADH affect kidneys?
ADH binds to V2 receptor on basolateral membrane of late DCT/CD principal cells Stimulates via cAMP second messenger transport of Aquaporin-2 forming channels in apical membrane Increases permeability of medulla CD to urea - increases interstitial osmolarity and H2O reabsorption
54
What is Na+ regulated by?
Action of aldosterone on principal cells of CD Stimulus is fall in circulating volume/blood pressure
55
What is renin?
Released by JGA in response to low blood volume and pressure
56
What do granular and macula densa cells do?
Granular - within afferent arterioles, release renin Macula densa - in distal tubule where it enters renal cortex passing through angle of afferent and efferent arterioles, chemoreceptors sense Na+
57
What regulates renin release?
Renal afferent arteriole baroreceptors Neural beta-adrenergic receptor mechanism DCT Macula densa (MD) cell mechanism
58
What is the role of afferent arteriole baroreceptors?
Sense decreased blood volume (pressure) Stimulate renin release by granular cells of JGA
59
What is the role of beta-adrenergic receptor mechanisms?
Detect decreased blood volume (pressure) located in aortic arch and carotid sinus Increased sympathetic innervation - stimulates renin by granular cells
60
What is the role of MD cell mechanisms?
Sense Na+ in distal tubule filtrate of nephron Decreased blood volume (pressure) reduces GFR - reduces NaCl delivery to distal tubule of nephron Stimulates MD cell release of prostoglandins (PGE2) - stimulate renin release by granular cells of JGA
61

Intermediate Human Physiology (7 decks)

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