Renal - Intro to Renal Physiology Flashcards
1
Q
Define
Internal Sea
A
Salty ECF
2
Q
How is the internal sea of land vertebrates maintained?
A
By controlling the quanity of H2O and Plasma Constituents
3
Q
Kidney Function
When there is a surplus of H2O or ions in ECF kidneys…
A
Kidneys eliminate in urine
4
Q
Kidney Function
When there is a deficit of H2O or ions in ECF kidneys…
A
Kidneys limit losses until more is ingested
H2O or ions are stored/held onto until more is ingested (not in urine)
5
Q
What are the main functions of the kidney?
A
Eliminate waste/toxins (endogenous and exogenous)
Regulation of Water and Electrolyte Balances
Regulation of Erthrocyte Production
Regulation of 1,25-Dihydroxyvitamin D3 (calcitriol) production
Regulation of Acid-Base Balance
A WET BED
Acid-base balance, Water removal, Erthropoiesis, Toxin removal, Blood pressure control, Electrolyte balance, Vitamin D activation
6
Q
Kidney Function
Electrolyte balance
What does it control and why?
A
Control of ECF osmolarity essential for maintenance of cell volume
Control of ECF volume key to long-term regulation of BP
7
Q
Kidney Function
Erthropoiesis
A
Kindey secretes erythropoietin which stimulates the production of RBCs in bone marrow
Not enough erythropoietin can cause anemia
8
Q
Kidney Function
Vitamin D activation
A
Increasing VD in intestines, increases reabsorption of plasma calcium and PO4^3-
1,25-Dihydroxyvitamin D3 (calcitriol)
Calcitrol is the final product of VD -> when not enough calcium is obtained from bones
9
Q
Kidney Function
Acid-Base Balance
A
Kidney has a pivotal role: distribuances can be completely corrected thru changes in H+ secretion and HCO3- reabsorption and production
10
Q
Pathway
Urine
A
- Kidneys form urine
- Ureters carry urine to bladder
- bladder stores urine
- urine is preiodically emptied through urethra
11
Q
Define
Nephron
A
Functional unit of kidney
2 components: vascular/tubular
1.2 million nephrons/kidney
12
Q
Renal Blood Supply
Renal blood flow is _ by humoral factors
A
autoregulated
13
Q
Pathway
Renal Blood Supply
How does blood flow through the renal system?
A
- Afferent Arterioles
- Glomerular Capillaries (Glomerulus)
- Efferent Arterioles
- Peritublar Capillaries
- Vase recta (sometimes)
- renal vein
14
Q
Renal Blood Supply
Afferent Arterioles
What do they do/where do they go?
A
Brings blood to the glomerular capillaries
1/kidney
Blood “Arrives”
Major area of blood flow control
15
Q
Renal Blood Supply
Glomerulus
What are they? What do they do?
Glomerular Capillaries
A
Small tuft of capillaries sandwhiched between two arterioles
Filters blood from Afferent Arterioles and drains remaining to Efferent Arterioles
16
Q
Renal Blood Supply
Efferent Arertioles
What do they do/where do they go?
A
Drains blood from the glomerular capillaries
blood not filtered by glomerulus “exits” to peritubular capillaries
17
Q
Renal Blood Supply
Peritubular Capillaries
What are they/where do they go?
A
A second bed of capillaries that lie after the efferent arterioles and surround the cortical regions of the nephron
Returns blood from the efferent arterioles to the renal vein
18
Q
Renal Blood Supply
Vasa Recta
What do they do/where do they go?
A
Specialized capillaries that dip into the renal medulla and surround the loop of Henle
The help maintain the concentration gradient and return fluid to renal vein
Continuation of the Efferent Arteriole in the medulla
Not every peritubular capillary leads to a vasa recta
19
Q
General Overview
Vascular Component of Nephron
A
Afferent Arteriole
Glomerulus
Efferent Arteriole
Peritubular Capillaries
20
Q
General Overview
Tubular Component of Nephron
A
Bowman’s Capsule
Proximal Tubule
Loop of Henle
Distal tubule
Collecting duct
21
Q
General Overview
Combined Vascular/Tubular component of Nephron
A
Juxtaglomerular Apparatus
22
Q
General Overview of Nephron Functions
Afferent Arteriole
Generally Define Function
A
Carries blood to the glomerulus
23
Q
General Overview of Nephron Function
Glomerulus
Generally Define Function
A
A tuft of capillaries that filters a protein-free plasma into the tubular component
24
Q
General Overview of Nephron Function
Efferent Arteriole
Generally Define Function
A
Carries blood from the glomerulus
25
# General Overview of Nephron Function
Peritubular Capillaries
| Generally Define Function
Supply the renal tissue
Involved in exchanges with the fluid in the tubular lumen
26
# General Overview of Nephron Function
Juxtaglomerular Apparatus
| Generally Define Function/Structure
Produces substances involved in the control of kidney function
Fluid proceeds to distal tubule
Specialized combo of tubular and vascular cells
| Important in regulating blood pressue and GFR
27
# General Overview of Nephron Function
Bowman's Capsule
| Generally Define Function
Collects the glomerular filtrate
Double walled cup like invagination
## Footnote
Increases surface area for diffusion
28
# General Overview of Nephron Function
Proximal Tubule
| Generally Define Function
uncontrolled reabsorption and secretion of selected substances occur here
Major site of reabsorption
## Footnote
Close to glomerulus
29
# General Overview of Nephron Function
Loop of Henle
| Generally Define Function
Establishes an osmotic gradient in the renal medulla that is important in the kidney's ability to produce urine of varying concentration
## Footnote
Has an ascending and descending limb
30
# General Overview of Nephron Function
Distal Tubule
| Generally Define Function
Variable, controlled reabsorption of Na+ and H2O and secretion of K+ and H+ occur here
31
# General Overview of Nephron Function
Collecting Duct
| Generally Define Function
Variable controlled reabsorption of Na+ and H2O and secretion K+and H+ occur here
Fluid leaving the collecting duct is urine which enters the renal pelvis
## Footnote
Urine leaves for excretion
32
What are the two types of nephrons?
Cortical Nephrons
Juxtamedullary Nephrons
33
How are coritcal and juxtamedullary nephrons distinguished?
By their location and length of their structures
34
# Define
Cortical Nephrons
| Location, Structure, Function
Located mostly in cortex; extend just into outer medulla
Short loop of Henle
Surrounded by peritubular capillaries (continuation of EA, in the cortex)
Reabsorption and Secretion
35
# Define
Juxtamedullary Nephrons
| Location, Structure, Function
Extend deep into medulla
Long loop of Henle
Efferent arterioles form peritubular caps and vasa recta (continuation of EA, in the medulla)
Reabsorption, Secretion, Concentrate/dilute urine
36
Both types of nephrons are involved in...
| Functions
Secretion and Reabsorption
37
Only the juxtamedullary nephron involves...
| Functions
Concentration and dilution of urine
38
3 processes involved in urine formation
Glomerular Filtration
Tubular Reabsorption
Tubular Secretion
39
# Define
Glomerular Filtration
| What is it? Where does it go?
Pressure (primarily BP) leads to a seperation thru a semipermeable membrane
Found in Glomerulus -> fluid that is filtered into bowman's capsule
Doesn't contain cells or protein
| "Pushing a portion of plasma onto a conveyor belt" (indiscriminate)
## Footnote
Cells and protein move through glomerulus to bowman's capsule
Passive
40
# Define
Tubular Reabsorption
| What is it? Where does it go?
Fluid filtered into bowman's capsule/Tubular Lumen is reabsorped into peritubular capillary
Selective
Moves substances back into blood flow
Unwanted substances remain in urine (Filtrate)
41
# Define
Tubular Secretion
| What is it? Where does it go?
Selectively adding substances from blood to filtrate
Mechanism for more rapidly eliminating selective substances
Peritubular Capillaries to Tubular Lumen
| 2nd chance for body to get rid of in urine
42
# Ways substances can be filtered or rebasorbed
The substance is freely filtered and not reabsorped
| What happens to the substance?
## Footnote
Substance ends up in urine
Filtration only
| EX: Inulin
43
# Ways substances are filtered and reabsorbed
The substance is freely filtered and partly reabsorbed
| What happens to the substance?
Filtration, partial reabsorption
| EX: Na+, K+, H2O
44
# Ways substances are filtered and reabsorped
The substance is freely filtered and entirely reabsorbed
| Substances you don't want to lose
Filtration, Complete Reabsorption
| EX: Glucose and Amino Acids
45
# Ways substanes can be filtered and reabsorped
The substance is freely filtered and entirely secreted
| Rarest; None returns to blood
Filtration, Secretion
| Ex: Para-aminohippurate, PAH
46
# Glomerular Filtration Barrier
3 layers of the Glomerular Filtration Barrier
Glomerular Capillary Wall (Endothelium)
Basement Mebrane
Inner Layer of Bowman's Capsule (Epithelium)
47
# Glomerular FIltration Barrier
Glomerular Capillary Wall
| Structure, Function
Perforated by many Ig pores
100x more permeable than caps elsewhere in the body
endothelium has "-" charge
48
# Glomerular FIltration Barrier
What is the purpose of the negative charge on the Glomerular Capillary Wall and Basement Membrane?
Helps prevent negatively charged substances from getting through into the filtrate
| Like proteins
49
# Glomerular FIltration Barrier
Basement Membrane
| Structure
Acellular gelatinous layer
composed of collagen and glycoproteins
| Negatively Charged
50
# Glomerular Filtration Barrier
Inner Layer of Bowman's Capsule
| Function/Structure
Filtration slits between the podocyte processes that encircle the capillaries
| Filtration slit diaphragm is composed of podocyn
51
# Glomerular FIltration Barrier
What is freely filtered through the Glomerular FIltration Barrier?
Water
Electrolytes
Molecules - MW less than 5,200
| Small ions and molecules
52
# Glomerular FIltration Barrier
What is variably filtered through the Glomerular FIltration Barrier?
Molecules, including up to MW of ~68,000 - 69,000 depending on: Size, Shape, Charge
| Long cylindrical filters better than spherical
Mid sized molecules
53
# Glomerular FIltration Barrier
What is not filtered through the Glomerular FIltration Barrier?
Larger Proteins
54
# Golmerular Filtration
What forces are involved in (drive) filtration across the glomerulus?
Starling Forces
Major force is Glomerular Capillary Hydrostatic Blood Pressure
| Drives filtrate into Bowman's Capsule
55
# Golmerular Filtration
What does Glomerular Capillary BP (Pg) depend on?
Arterial pressure
Afferent arteriole resistance
Efferent arteriole resistance
56
# Golmerular Filtration
Why do the afferent and efferent arteriole have a large effect on Glomerular Capillaries?
| Why do the GC have a larger pressue than the the peritubular capillaries
Glomerular capillaries are located between the AA and EA, which results in them having a much higher pressure than the peritubular capillaries
57
# Golmerular Filtration
Why is a high glomerular pressure necessary?
To drive glomerular filtration
58
# Golmerular Filtration
Why is it necessary for peritubular capillaries to have a lower pressure?
To permit reabsorption of fluid from the renal interstitium
59
# Golmerular Filtration
Plasma-Colloid Pressure
| Define
Unequal distribution of plasma proteins across the glomerular membrane not in bowman's capsule
| Water returns to the glomerulus
60
# Golmerular Filtration
What type of pressure is exerted by fluid in Bowman's Capsule?
| Define
Fluid in BC exerts a hydrostatic pressure
61
# Golmerular Filtration
What is the filtration force in Golmerular Filtration?
Golmerular Capillary Blood Pressure
62
# Golmerular Filtration
What are the opposing filtration forces in Golmerular Filtration?
Plasma-Colloid Osmotic Pressure + Bowman's Capsule Hydrostatic Pressure
63
# Golmerular Filtration
A postive net filtration favors....
Filtration
64
# Golmerular Filtration
A negative net filtration favors...
Reabsorption
65
# Golmerular Filtration
What is the difference between net filtration along the glomerular capillaries vs. most capillaries in the body?
There is net filtration along the entire length of the glomerular capillaries
## Footnote
The opposing forces are still increasing but always less than Pgc
Oncotic pressure continues increasing along the capillary due to remaining proteins as everything else filters out
66
What effect do changes in resistance of AA or EA have on blood flow? Why?
The have the same effect because they are in series
67
# Effect of changes in resistance on Renal Blood Flow (RBF) and GFR
At baseline, when resistance is the same in AA and EA...
| In general, what happens to pressure
Pressure in GC = 60
AA and EA resistance = 1
Pressure in Peritubular Capillary = 20
68
# Effect of changes in resistance on Renal Blood Flow (RBF) and GFR
When the AA is constricted and the EA is not, what happens to GFR and RBF?
GFR and RBF both decrease
Pressure in GC = 40
AA resistance = 1.5
EA resistance = 1
Pressure in Peritubular Capillary = 13
69
# Effect of changes in resistance on Renal Blood Flow (RBF) and GFR
When the EA is constricted and the AA is not, what happens to GFR and RBF?
GFR increases and RBF decreases
Pressure in GC = 70
AA resistance = 1
EA resistance = 1.5
Pressure in Peritubular Capillary = 10
70
# Effect of changes in resistance on Renal Blood Flow (RBF) and GFR
When the AA is dilated and the EA is not, what happens to GFR and RBF?
GFR and RBF both increase
Pressure in GC = 70
AA resistance = 0.5
EA resistance = 1
Pressure in Peritubular Capillary = 30
71
# Effect of changes in resistance on Renal Blood Flow (RBF) and GFR
When the EA is dilated and the AA is not, what happens to GFR and RBF?
GFR decreases and RBF increases
Pressure in GC = 50
AA resistance = 1
EA resistance = 0.5
Pressure in Peritubular Capillary = 30
72
# Effect of changes in resistance on Renal Blood Flow (RBF) and GFR
Hydrostatic pressure in the glomerulus is controlled by....
Relative tone of afferent and efferent arterioles
73
# Define
Glomerular Filtration Rate (GFR)
The rate at which plasma is filtered (ml/min)
Index of Kidney Function
74
What does GFR depend on?
Net filtration pressure
Surface area available for filtration
Membrane permeability
| GFR = Kf x net filtration pressure
## Footnote
Kf = Surface area + membrane permeabiity
75
What is the purpose of GFR?
| What does it tell us?
GFR is an index of kidney function
| Decrease in GFR can mean kidney disease
Increase GFR = Kidney recovery
76
What is the advatange of a high GFR?
Rapid control of body fluid volume and composition
77
What is used to measure GFR in clincial research? Why?
Inulin
It is the gold standard for measuring GFR
| Inulin is the exogenous marker
78
What is used to measure GFR in a patient? Why?
Creatinine
It is more convenient than inulin
| Endogenous marker
79
How is GFR measured?
We use the renal clearance of a substance that is freely filtered at the glomerulus, has a stable plasma concentration, is not reabsorbed, secreted, or metabolized by the kidney
| Measured exogenously by inulin and endogenously by creatinine
80
# GFR
Inulin
| Why is it the gold standard?
Filtered in the glomerulus, no tubular transport
But technically challenging and expensive
81
# GFR
Creatinine
| What is it? Why is it used?
Derived from the skeletal muscle creatine
production proportional to muscle mass and is constant
plasma concentration is stable unless there are changes in production (decrease in malnutrition, increase in rhabdomyolysis), or changes in excretion (decreased in acute kidney injury)
| Not gold standard because a small amount is secreted
82
The amount of creatinine excreted per min =
amount of creatinine filtered per minute
83
What is the relationship between GFR and plasma creatinine?
They are inversely related
Increasing GFR -> decreases creatinine
84
# Neurohumoral Control of GFR
What effects do the sympathetic nervous system have on GFR control?
Decreases RBF, Decreases GFR
Changes blood flow to kidneys
α1 activation -> vasoconstricton -> decreases BF -> decreases GFR
β1 activation -> renin release
## Footnote
vasoconstriction of afferent than efferent
85
# Neurohumoral Control of GFR
What effects does Angiotensin II have on GFR?
Decreases RBF, maintains GFR
Potent vasoconstrictor produced in response to descreases in AA pressure
AA and EA both constrict, EA more so
| The larger constriction of EA allows GFR to be maintained
86
# Neurohumoral Control of GFR
What effects do Prostaglandins have on GFR?
Increase RBF, Increase GFR
PGE2 and PGI2 cause dilation of arterioles -> increases RBF, GFR
| Effects afferent moreso than Efferent
## Footnote
Maintains GFR and RBF as we age due to increased production
87
# Equation
Blood flow through any organ is represented by...
Q = ΔP/R -> RBF = (Renal artery pressure - renal vein pressure)/ Renal vascular resistance (AA and EA)
## Footnote
Q = Blood Flow
ΔP = MAP - MVP
R = Resistance
88
Kidneys regulate their BF by _ in response to changes in _.
Adjusting Resistance
Arterial Pressure
89
# Regulating GFR
What are the three ways GFR is regulated by changing RBF?
Autoregulation
Hormonal (Ang II, Prostaglandins)
SNS
90
# Regulation of GFR: Autoregulation
Autoregulation
| What is its purpose? How does it work?
Feedback mechanisms intrinsic to the kidney
Operates to keep GFR steady over a wide range of blood pressure
Maintains BF over the range of 80-180
91
# Regulation of GFR: Autoregulation
What are the two types of autoregulation?
## Footnote
Both regulate AA tone
Myogenic Response
Tubuloglomerular Feedback
92
# Regulation of GFR: Autoregulation Mechanisms
Myogenic Response
| Define
Fast-acting constriction/dilation to Δ in arterial pressure
Initiated in muscle
When AA is stretched (increase in wall tension), smooth muscle contracts
| Pressure sensitive mechanism
## Footnote
Stretch of blood vessels allows Ca from ECF to enter cells and cause contraction
50% autoregulatory response
93
# Regulation of GFR: Autoregulation Mechanisms
Tubuloglomerular Feedback
| Define
Complicated signals that respond to Δ in tubular fluid flow rate
Increase GFR -> Increase NaCl in filtrate/Juxtaglomerular apparatus -> Increase AA resistance -> decrease GFR
| Flow dependent - Changes BF depending on Flow Rate through the nephrons
94
# Regulation of GFR: Autoregulation
What is the relationship between Arterial BP and GFR?
Arterial BP drives Glomerular Capillary pressure and thus GFR
| Increase arterial BP -> increases GFR
95
# Regulation of GFR: Autoregulation
Where is the Juxtaglomerular Apparatus located?
Where the tubule passes through the fork of AA and EA at the glomerulus
96
What is the structure of the JGA?
| What makes it up?
Granular Cells
Extraglomerular Mesangial Cells
Macula Densa
97
# Juxtaglomerular Apparatus
Granular Cells
| What are they? What do they?
Modified small muscle cells
Mechanoreceptors of the AA
Make, store, and secrete Renin
98
# Juxtaglomerular Apparatus
Extraglomerular mesangial cells
| What are they? What do they?
Holds capillaries together
Full of actin for contraction
contraction closes portion of filtering capillaries -> decreases SA -> decreases GFR
99
# Juxtaglomerular Apparatus
Macula Densa
| What is it? What does it do?
Chemoreceptors that detect NaCl
In contact with mesangial and granular cells
## Footnote
NaCl is proportional to rate of filtrate flow
Increase NaCl means Increase GFR -> AA constricts
Decrease NaCl means decrease GFR -> AA dilation
100
What happens to GFR when NaCl increases?
| During high flow rate
Increases in NaCl causes vasoconstriction and increases in GFR
| ↑ NaCl -> ATP -> Adenosine -> ↑ Ca -> contraction -> ↓ renin
101
What happens to GFR when there is Low flow rate?
↓Arterial Pressure → ↓Glomerular Hydrostatic Pressure → ↓GFR → ↓Macula Densa/NaCl → ↑ Renin → ↑ Ang II → ↑EA resistance → inhibits ↓Glomerular Hydrostatic Pressure → ↑GFR
↓Arterial Pressure → ↓Glomerular Hydrostatic Pressure → ↓GFR → ↓Macula Densa/NaCl → ↓ AA resistance → inhibits ↓Glomerular Hydrostatic Pressure → ↑GFR
102
# 3 most important points concerning Autoregulation
Autoregulation is absent when...
Arterial BP is < 80 mmHg
103
# 3 most important points concerning Autoregulation
Despite autoregulation, the RBF and GFR can be changed by...
| General
Certain hormones and changes in sympathetic nerve activity
104
# 3 most important points concerning Autoregulation
Autoregulation of GFR and RBF provides an effective means for...which ensures...
Autoregulation of GFR and RBF provides an effective means for uncoupling renal function from arterial pressure thus ensuring fluid and solute excretion remain constant
105
# GFR
What can override renal autoregulation?
Sympathetic Nervous System
106
# Extrinsic Sympathetic Control on GFR
Strong activation of renal sympathetic nerves can _ renal arterioles and _ RBF and GFR
Strong activation of renal sympathetic nerves can constrict renal arterioles and ↓ RBF and GFR
107
# Extrinsic Sympathetic Control on GFR
What effect does SNS have on renin and overall GFR?
↑ Renin → RAA →↑Na+ reabsorption (PT)
108
What would happen to GFR during a hemorrhage?
Hemorrhage →↓ECF Volume → ↓MAP → ↑SNS activation → ↓GFR
## Footnote
↓MAP - detected by carotid baroreceptors
↑SNS activation - Input to Afferent Arteriole (constriction)
109
Why would GFR need to be decreased?
Decrease GFR to hold onto important things
110
# Pathway of fluid flow
What is the sequence of fluid flow through the kidneys?
| General Overview
Kidney → Renal Pelvis → Ureter → Bladder → Urethra
111
# Pathway of fluid flow
What is the sequence of fluid flow through the arterial portion of the renal system?
Renal Artery → Afferent Arteriole → Glomerulus → Efferent Arteriole → Peritubular Capillaries → Renal Vein
112
# Pathway of fluid flow
What is the sequence of fluid flow through the filtrate pathway of the renal system?
Glomerulus → Bowman's Capsule → Proximal Tubule → Loop of Henle → Distal Tubule → Collecting Duct
113
Which of the following would cause the greatest decrease in GFR in a person with otherwise normal kidneys?
A. Decrease in renal pressure from 100 to 80 mmHg in normal kidney
B. 50% increase in glomerular capillary filtration coefficient
C. 5 mmHg increase in glomerular capillary blood pressure
D. 50% decrease in afferent arteriolar resistance
E. 50% decrease in efferent arteriolar resistance
F. 5 mmHg decrease in Bowman's Capsule pressure
E. 50% decrease in efferent arteriolar resistance
| Vasodilation of EA → ↓ GFR
114
# Would GFR increase or decrease if there is...
A rise in Bowman's Capsule pressure resulting from ureteral obstruction by a kidney stone
decrease
115
# Would GFR increase or decrease if there is...
A fall in plasma protein resulting from loss of these proteins from a large burned surface
Increase
116
# Would GFR increase or decrease if there is...
A dramatic fall in arterial blood pressure following severe hemorhage (<80 mmHg)
Decrease
117
# Would GFR increase or decrease if there is...
Afferent Arteriolar vasoconstriction
Decrease
118
# Would GFR increase or decrease if there is...
Tubuloglomerular feedback response to a decrease in tubular flow rate
Increase
119
# Would GFR increase or decrease if there is...
Myogenic response of an afferent arteriole stretched as a result of an increased driving BP
Decrease
120
# Would GFR increase or decrease if there is...
Sympathetic activity to the afferent arterioles
Decrease
121
# Would GFR increase or decrease if there is...
Contraction of the mesangial cells
Decrease
122
# Would GFR increase or decrease if there is...
Contraction of the podocytes
Decrease
