Physiology Flashcards
1
Q
What is osmolarity
A
Concentration of osmotically active particles present in a solution
2
Q
How do you calculate osmolarity
A
Molar concentration of the solution x number of osmotically active particles
E.g. 150mM NaCl
150 x 2 = 300 mosmol/l
3
Q
What is tonicity
A
Effect a solution has on cell volume
4
Q
3 types of tonicity
A
Isotonic
Hypotonic
Hypertonic
5
Q
Hypotonic solution effect on cell
A
Water moves into cell
6
Q
Hypertonic solution effect on cell
A
Water moves out of cell
7
Q
Isotonic solution effect on cell
A
No change in cell volume
8
Q
Tonicity is dependent on
A
Osmolarity
Ability of solutions to cross the cell membrane
9
Q
Total body water is made of what compartments
A
Intracellular fluid + Extracellular fluid
10
Q
Extracellular fluid includes
A
Mostly interstitial fluid
plasma
Lymph
Transcellular fluid
11
Q
How do you measure the body fluid compartments
A
Use tracers
For TBW = 3H20
For ECF = Inulin
For plasma = labelled albumin
12
Q
Water loss occurs at
A
Skin
Lungs
Sweat
Faeces
Urine
13
Q
Hot weather causes increase / decrease in water loss from lungs
A
Decrease
14
Q
Hot weather causes increase / decrease in water loss from urine
A
Decrease (since more is lost in sweat; decreased excretion of urine is a compensatory mechanism)
15
Q
How is water balance achieved when there is extra water loss due to exercise / hot weather / cold weather
A
Increased water ingestion
Decreased excretion of water by kidneys to a certain extent, not sufficient alone
16
Q
Describe the characteristics of ionic composition of ICF and ECF
A
There is always more Na+, Cl-, HCO3- in ECF than ICF
There is always more K+ in ICF than ECF
17
Q
Why is regulation of ECF volume essential
A
Because it contain plasma so regulation of ECF is required for regulation of blood pressure
18
Q
Gain in NaCl in ECF causes
A
Osmolarity of ECF to increase
Causes fluid to move from ICF into ECF
ICF decreases
= fluid homeostasis
19
Q
Na+ is mainly present in which body fluid compartment
What does this imply for the compartment
A
ECF
So it is a major determinant of ECF volume
20
Q
K+ plays a key role in
A
Establishing membrane potential
21
Q
K+ is mainly in which body fluid compartment
A
ICF
22
Q
Functions of the kidney
A
Regulate volume, osmolarity, composition of body fluids
Excretion of waste produces and exogenous foreign compounds (drugs / additives)
Secretion of renin
Secretion of erythropoietin
Conversion of vitamin D into active form
23
Q
Functional unit of kidneys
A
Nephron
24
Q
General function of nephron
A
Filter out tubular fluid
Reabsorb substances from the fluid or secrete substances into the tubular fluid
25
Vessels in nephron
Afferent arteriole -> Glomerulus -> efferent arteriole -> peritubular capillaries -> venule -> vein
26
What is Glomerulus
Cluster of blood vessels located in bowman's capsule where filtering of the blood occurs
27
What is the bowman's capsule
where waste in blood is filtered out of glomerular capillaries and enters the lumen of bowman's capsule which then enter the Proximal tubule
28
Bowman's capsule is made of what cells
Podocytes
29
Which are the 3 filtration barriers
Capillary endothelium
Basal lamina
Podocytes
30
Why can't proteins enter the glomerular filtrate
Net negative charge of basal lamina repel the proteins
Too big to go through the pores of endothelium
31
Except from capillary endothelial cells, the glomerulus also contains
Mesangial cells
32
Function of mesangial cells
control glomerular filtration
provide structural support
33
How do mesangial cells control glomerular filtration
Mesangial cells can contract which narrows the capillary lumen hence less flow of blood = less filtration
34
Location of mesangial cells
intercapillary space
Between the afferent and efferent arterioles
35
2 types of nephron
Juxtamedullary
Cortical
36
Which type of nephron is predominant in humans
Cortical nephron (80%)
37
Differences between juxtamedullary and cortical nephron
Juxtamedullary nephron has longer loop of Henle
Juxtamedullary nephron does not have peritubular capillaries, it has 1 capillary called vasa recta
38
Route of vasa recta
Follows the loop of Henle
39
The diameter of afferent arteriole is larger / smaller than efferent arteriole
Larger
40
Renin is secreted by
Granular cells
41
4 parts of the nephron
Renal corpuscle
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
42
Renal corpuscle consists of
Glomerulus and Bowman's capsule
43
Function of Renal corpuscle
Production and collection of glomerular filtrate
44
Function of proximal convoluted tubule
Reabsorption of water, amino acids, glucose
45
Function of loop of Henle
Creation of hyper osmotic environment in medulla
46
Function of distal convoluted tubule
Absorption of water, Na+, bicarbonate, K+ and H+
for acid-base and water balance
47
What proportion of sodium is reabsorbed in proximal tubule and through which mechanism
70% by active transport
48
What proportion of glucose and amino acids is reabsorbed in proximal tubule and through which mechanism
All glucose and amino acids; by co-transport
49
What feature do the lining of proximal convoluted tubule have to increase reabsorption
Microvilli
50
Histological differences between proximal and distal convoluted tubules
PCT larger
PCT less well defined lumen margin due to microvilli
51
How does the thickness of loop of henle vary
Descending limb - first thick then thin limbs
Ascending limb - thick limb
52
Type of epithelial cell that lines the loop of Henley
thick limbs (ascending and descending limbs) - simple cuboidal
thin limbs (descending limb) - simple squamous
53
Is there microvilli in distal convoluted tubule
No, very sparse apical microvilli
54
Reabsorption of Na+ hence water in DCT is controlled by which hormone
Aldosterone
55
Reabsorption of water in collecting duct is controlled by which hormone
ADH
56
How does ADH increase water reabsorption in collecting duct
Increase aquaporin channels
57
The epithelium of minor, major calyxes, ureter, bladder and urethra
Urothelium
58
Urothelium type of epithelium
transitional epithelium
59
What is transitional epithelium
= properties lie between stratified squamous and simple non-stratified
60
What are the cells of urothelium that is facing the lumen called
Umbrella cells
61
Special properties of umbrella cells and why
thickened and inflexible membrane, to provide a highly impermeable barrier
62
Layers below the urothelium (from inner to outer)
Connective tissue
Smooth muscle
Adventitia
Serosa
63
The smooth muscle in urinary bladder is called
Detrusor muscle
64
Function of detrusor muscle
Contract to
- push urine out of bladder
- prevent back flow of semen during ejaculation
- prevent back flow of urine into ureter
65
Pressures that are included in the net filtration pressure for glomerular filtration
Bowman's capsule fluid pressure
Glomerular capillary blood pressure
Capillary oncotic pressure
Bowman's capsule oncotic pressure
66
Which pressure is the key driver of glomerular filtration
Glomerular capillary blood pressure
67
Pressures that pushes plasma through the filtration barriers
Glomerular capillary blood pressure
Bowman's capsule oncotic pressure ( but 0 mmHg)
68
Pressures that draws fluid away from bowman's capsule
Bowman's capsule hydrostatic pressure
Capillary oncotic pressure
69
What is capillary oncotic pressure
Due to presence of plasma proteins = higher osmolarity than filtration fluid hence wants to draw fluid back into vessel
70
Why is bowman's capsule oncotic pressure 0 mmHg
because there is no plasma proteins in filtration fluid hence no oncotic pressure that will try to draw water in
71
Normal net filtration pressure
10 mmHg
72
GFR =
filtration coefficient x net filtration pressure
73
Filtration coefficient can change depending on
how permeable the glomerular membrane is
74
Why is glomerular capillary blood pressure constant throughout
Because the afferent arteriole has a wider diameter than efferent arteriole
75
What happens to GFR when there is an increase in arterial BP
Increase in arteriole BP -> increase in BP in afferent arteriole -> increase in Glomerular capillary BP -> increase in net filtration pressure -> increase in GFR
76
What happens to urine volume when there is an increase in GFR
Increases
77
Changes in systemic arterial BP does not necessarily result in changes in GFR. Why is that
Due to auto regulation, compensatory mechanisms ; but only to a certain extent
78
what are the 2 mechanisms of auto regulation to prevent changes in GFR
Myogenic
Tubuloglomerular feedback
79
What is the myogenic auto regulation of GFR
Increase in BP causes vascular smooth muscle to stretch -> causes constricting of arteriole -> less blood flowing through to glomerulus
80
What is the tubuloglomerular autoregulation of GFR
1. Rise in GFR
2. more NaCl flow through the tubule
3. constriction of afferent arterioles
81
Tubuloglomerular auto regulation involves which type of nephron
Juxtaglomerular
82
Effect of kidney stones in GFR
Stone blocking fluid causing fluid to accumulate -> Increases bowman's capsule fluid pressure -> lower net filtration pressure -> GFR decrease
83
Effect of diarrhoea in GFR
diarrhoea causes dehydration causing higher osmolarity in blood
so increase in capillary oncotic pressure
hence draws more fluid out
reduces net filtration pressure
= decrease in GFR
84
What is plasma clearance
measures how effectively kidneys can clean the blood of a substance
each substance will have their own specific plasma clearance
85
What is plasma clearance
measures how effectively kidneys can clean the blood of a substance
each substance will have their own specific plasma clearance
86
Plasma clearance =
rate of excretion of X / plasma concentration of X
87
Rate of excretion of X =
[X in urine] x Urine production rate
88
What is used to measure the GFR
Inulin clearance = GFR
89
Why is inulin used to measure GFR
Because it is freely filtered at glomerulus but it is not absorbed / metabolised hence can be measured in urine
90
If clearance < GFR
Substance is reabsorbed into the tubule
91
If clearance = GFR
Neither reabsorbed nor secreted
92
If clearance > GFR
Substance is secreted into tubule
93
If clearance > GFR
Substance is secreted into tubule
94
What is reabsorption
water and solutes within the tubule are transported into the bloodstream
95
Around how much plasma entering the glomerulus is being filtered
20%; 80% of the plasma is not filtered and leaves via efferent arteriole
96
Kidneys reabsorb what % of fluid and salt
99%
97
Kidneys reabsorb what % of glucose and amino acids
100%
98
Kidneys reabsorb what % of creatinine
0%
99
What is reabsorbed in the proximal tubule
67% of all salt and water
100% of glucose and amino acids
Phosphate
Sulphate
Lactate
100
What is secreted in the proximal tubule
H+
Neurotransmitters
Bile pigements
Uric acid
Drugs
Toxins
101
2 routes reabsorption takes place
transcellular ( through cells)
paracellular ( between cells)
102
How does transcellular reabsorption occur
Primary active transport
Secondary active transport
Facilitated diffusion
103
How is Na+ reabsorbed back into capillary
1. Basolateral sodium potassium ATPase transports K+ into the tubular cell in exchange for sodium out of the cell = reabsorbed
2. This creates a concentration gradient for Na+ between the filtrate and tubular cell
3. So sodium in the filtrate enters the tubular cell via facilitated diffusion (and this sodium will later be transported out via sodium potassium ATPase)
4. Reabsorption of Na+ sets up an electrochemical gradient that drives the passive movement of Cl- via the paracellular route
104
Describe the paracellular route of Cl-
1. Cl- moves passively into the interstitial fluid (between tubular cell and capillary) via paracellular route due to electrochemical gradient set up by Na+
2. forms NaCl
3. NaCl reabsorbed
4. Sets up a osmotic gradient that drives passive movement of water via the paracellular route
5. Because the water movement is dependent on NaCl, their reabsorption are equal
6. so no change in osmolarity in filtrate fluid
105
Why is the filtrate in proximal tubule isosmotic
Because the reabsorption of NaCl and water is equal
106
Na+ is reabsorbed everywhere in the nephron except
descending limb of loop of henle
107
What is transport maximum
maximum rate at which we can reabsorb a particular substance
108
What determines the limit for transport maximum
saturation of the specific transport systems of substance = i.e. if more substances come in, they cannot be reabsorbed
109
Why is transport maximum important in relation with glucose
Glucose transport maximum is 375mg/min; exceeding this = glucose in urine
110
What is renal threshold
the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine. - this can be reabsorbed depending on the transport maximum
111
Renal threshold and transport maximum varies between substances. Why is it beneficial for renal threshold to be lower than transport maximum for certain substances - glucose / amino acids
This means that some glucose/ amino acids will be in the urine but because transport maximum is higher, all of those substances can be reabsorbed up to a certain extent
112
Function of loop of Henle
Generates a cortico-medullary solute concentration gradient
in order to form hypertonic urine
113
Describe the flow of fluid in loop of Henle
Countercurrent flow - the flow of fluid in both limbs are opposing each other
114
Why is there an osmotic gradient in the medulla
Due to difference in permeability of water and salt for descending and ascending limbs
115
Describe the permeability to water and NaCl for descending and ascending loops of henle
Descending - permeable to water, not to NaCl
Ascending - impermeable to water, NaCl can be reabsorbed
116
Mechanism of sodium reabsorption in ascending loop of Henle
via Na K Cl transporter (triple transporter)
117
The reabsorption of water in descending limb of loop of Henle uses
Countercurrent flow mechanism
118
Describe the countercurrent flow mechanism
1. Na+ and Cl− are actively pumped out of the filtrate in ascending limb
2. Water does not follow because it is impermeable to water
3. This causes the osmolarity of the interstitial fluid to be raised
4. Water moves out of the descending limb by osmosis
5. But Solute cannot enter the descending limb
6. Because water is moving out of DL, osmolarity of fluid in DL is raised while the interstitial fluid is lowered
7. concentrated fluid in DL then moves into AL, process begins again
119
What drugs blocks the triple transporter in ascending limb and why
Loop diuretics
So less Na+ reabsorbed = increased excretion of water (less water reabsorbed from descending loop) = decreased blood pressure
120
Osmolarity of fluid leaving the ascending loop of Henle
Hypotonic (low osmolarity)
121
What structure is involved in countercurrent exchange
Vasa recta
122
Describe the countercurrent exchange mechanism
As the concentrated fluid flows next to the vasa recta, the electrolytes and water that have been reabsorbed from the filtrate diffuse out of the fluid and into the blood vessels
123
What property of vasa recta allows countercurrent exchange mechanism to work
It is freely permeable to water and NaCl
Blood flow to vasa recta is slow
124
Describe the change in blood osmolarity in vasa recta
Rises as it goes down into the medulla - because solute is reabsorbed from the concentrated interstitial fluid
Decreases as it rises back up into the cortex - because water in interstitial fluid is reabsorbed
125
Slow blood flow in vasa recta allows
maintains the solute concentration gradient in the medulla
because solute that is reabsorbed into blood can go back out into the interstitial fluid
126
Effect of low ADH
1. collecting ducts in the kidney remain relatively impermeable to water
2. This means that water cannot be effectively reabsorbed
3. Since the urine is not concentrated in the collecting ducts, there is no significant driving force to draw water out of the descending limb
4. = weak concentration gradient in medulla
5. = large amount of diluted urine
