Test 3 - Quiz 8 - Renal Physiology (Colombo) Flashcards
Kidneys manage both the __________ of urine and the ___________ or expulsion of various components of the serum.
Outflow
Retention
The kidneys are regulators of three things. Name them.
BP
Blood plasma constituents
pH
The fluid in the body is distributed across 4 compartments. Name them and roughly how much is in each.
Plasma - 3 L - Least
Interstitial - 11 L
Transcellular (ECF) - 14 L
Intracellular - 28 L - Most
How is fluid volume disposed of and about how much per day for each mechanism?
Kidneys - 0.5-20 L/day
Skin/Respiratory - 700 mL/day
Sweat - 100 mL/day (1-2 L/hour in heavy exercise)
Poop - 100 mL/day
Increased volumes of blood means what for blood pressure?
How is this alleviated via the kidneys?
Increased blood pressure
By controlling urine volume, they can rapidly shed excess pressure
*The opposite is also true, urine volume can be restricted in dehydration, preserving pressure
__________ _____________ is regulated by the kidney, which also serves to regulate tonicity.
Electrolyte balance
The kidneys excrete metabolic __________ products and ____________ chemicals.
Waste
Foreign (Pharmaceuticals)
*They also excrete systemic hormones
Waste products are highly ____________ and poorly ____________.
Filtered
Reabsorbed
What are 4 metabolic wastes?
Urea
Uric acid
Creatinine
Bilirubin
What are 4 foreign substances?
Pesticides
Food additives
Toxins
Drugs
Excreting 1 HCO3- is basically the same as adding what?
1 H+
What are three important “other” renal functions?
Production of erythropoietin (RBCs)
Gluconeogenesis
Adrenal glands
The kidney can be divided into 2 basic parts. Name and describe them.
Renal cortex - Outer section
Renal medulla - Innermost section
In the renal medulla, what are the specialized regions of tissues and what make up those tissues?
Renal pyramids
-Nephrons
What is the renal pelvis and how are the pyramids connected to it?
Urine drainage tube
Papilla
*Pic on slide 11 of his presentation, if needed
Where are the capillary beds located in the kidneys?
Renal pyramids (nephrons)
**THIS IS WHERE FILTRATION OCCURS
What are the 3 processes of the kidney?
Filtration - What gets there and how it is taken into the nephron
Modification - What is done to filtrate in the nephron
Excretion - Micturition
What is the vessel that supplies blood to the kidneys?
Renal a.
Renal arteries then branch into what 3 aa.?
Interlobar a.
Arcuate a.
Radial a.
The 3 arteries after the renal artery then lead to what?
Afferent arterioles
Afferent arterioles lead to what?
Glomerular capillaries
The glomerular capillaries lead into what?
Nephron
AND
Efferent arterioles
Filtration occurs here
The efferent arterioles lead to what?
Peritubular capillaries
This is where reabsorption/secretion occurs
Peritubular capillaries send their blood where?
Renal vein
What is the part of the kidney where vessels go in and out?
Hilum
What is the basic functional unit of the kidney?
Nephron
How many nephrons are in a single kidney?
1 million
Each nephron is fed by glomerular capillaries that are referred to as what?
Glomerulus
The glomeruli are covered by what?
Epithelial cells and encased in Bowman’s capsule
What is the route plasma takes going from glomerulus to ureter?
Glomerulus -> Bowman’s capsule -> Proximal tubule -> Loop of Henle (concentrates urine) -> Distal tubule -> Collecting duct (part the body can control) -> Renal pelvis -> ureter
Cortical nephrons are different than juxtamedullary nephrons how?
More common (70% of nephrons)
Found in cortical region primarily
Loop of Henle only penetrating the medulla
More superficial
Juxtamedullary nephrons differ from cortical nephrons how?
Less common (30% of nephrons)
Primarily w/in medulla
Long loops of Henle that penetrate deep into the medulla
*These nephrons are very good at concentrating the urine
What is the vasa recta?
In juxtamedullary nephrons, efferent arterioles extend part of the way down the Loop of Henle and form special peritubular capillaries (called the vasa recta)
Urinary excretion rate is equal to what?
Filtration rate - reabsorption + secretion
(Out of proximal tubule minus what’s taken back by peritubular capillaries plus what comes out of the peritubular capillaries
Example of a substance filtered but not reabsorbed at all?
Waste
Example of a substance filtered and partially reabsorbed?
H20, Na+
*Most things are this
Example of a substance filtered and totally reabsorbed?
Glucose
*In a healthy state. Diabetes is a different story
Example of a substance filtered and added to via secretion?
H+
Example of a substance not filtered?
Proteins
A high glomerular filtration rate (GFR) ensures what?
Rapid removal of waste from the blood
What is a normal GFR?
180 L/day
*3 L of blood plasma. So, all the plasma in the body is filtered about 60 times per day.
The glomerular capillary membrane is permeable to what types of molecules and impermeable to what types of molecules?
+ small molecules (enter filtrate)
- big molecules (stay in blood)
The glomerular capillary membranes have 3 layers. Name and describe them.
Endothelium - Fenestrated - (-) charge (this repels the big negative molecules)
Basement membrane - Collagen/proteoglycan mesh - (-) charge
Specialized epithelial cells - “Podocytes” (foot cells that form slit pores)
GFR = what?
Kf x net filtration pressure
Kf- which is the glomerular capillary filtration coefficient
Net filtration pressure - Sum of colloid and hydrostatic pressures across the glomerular capillaries
- Net filtration - pushing stuff out
- Colloid - pressure from proteins
- Hydrostatic - blood pressure
Net filtration pressure would be what if the following:
Glomerular hydrostatic pressure = 60 mmHg
Bowman’s capsule pressure = 18 mmHg
Glomerular oncotic pressure = 32 mmHg
10 mmHG
**Net filtration = glomerular hydrostatic pressure - Bowman’s capsule pressure - glomerular oncotic pressure
Constriction of afferent arterioles will _________ pressure on glomerulus.
Decrease
*This forces blood out of Bowman’s capsule and decreases GFR
**Dilatation has the opposite effect
More afferent pressure = Decreased GFR
Minor constriction of efferent arterioles ____________ resistance of blood to leave Bowman’s capsule, _________ GFR.
Increases
Increases
Major constriction of effect arterioles results in what?
Trapping of protein in Bowman’s capsule, raising colloid osmotic pressure, and DECREASING GFR.
Dilatation of efferent arterioles results in what to GFR?
Decreased GFR
A sympathetic response would do what to the kidneys and renal arterioles?
Clamp aff and eff arterioles and less blood is sent to the kidneys.
Sympathetics do what to Ra (afferent restriction), Re (efferent restriction) and that results in what to GFR and RBF (renal blood flow)?
SLIDE 21
Ra - greatly increased
Re - increased
GFR - decreased
RBF - greatly decreased
Catecholamines (norepi) does what to Ra, Re, GFR, RBF?
Ra - greatly increased
Re - increased
GFR - increased
RBF - greatly increased
Angiotensin II does what to Re, GFR, and RBF?
Re - increases
GFR - constant
RBF - decreases
Prostaglandins/Endothelial-Derived Nitric Oxide does what to Ra, Re, GFR, and RBF?
Ra - greatly decreases
Re - decreases
GFR - increases
RBF - greatly increases
What is the macula densa?
Salt sensor
What does the macula densa do?
Initiates dilatation in the afferent arterioles and causes increased release of renin -> Increases angiotensin I and II -> constriction of efferent arterioles.
THIS RESTORES THE GFR
In the proximal tubule, what percentage of the filtrate is reabsorbed?
80%
In the Loop of Henle, what percentage of the filtrate is reabsorbed?
6%
In the distal tubule, what percentage of the filtrate is reabsorbed?
9%
In the collecting tubule, what percentage of the filtrate is reabsorbed?
4%
Urine volume is what percent of the filtrate?
1%
The Na/K ATPase is what kind of transporter?
Primary active transporter
The Na/K ATPase sets up gradients for what?
Secondary active transport
What type of transport with Na brings glucose into the cell from the tubule?
Co-transport
The glucose then diffuses into the blood on the other side
How are H+ ions excreted into the filtrate?
Counter-transport with Na+
The ___________ tubule is heavily involved with the reabsorption of water (linked to active Na+ gradients).
PROXIMAL
As the filtrate proceeds along the proximal tubule, the amount of Na+ decreases, but concentration doesn’t follow suit. Why?
H20 follows Na+, so relative concentration stays the same, even though the amount of Na+ is decreasing.
The Loop of Henle has 2 distinct regions. Name them.
Thin descending
Thick ascending
The thin descending segment is highly permeable to water via what?
Water
Aquaporins
~20% of filtered water is reabsorbed here.
The thick ascending is ____________ to water, but has a ton of active transporters for what ions?
Impermeable
Na, Cl, K, also Ca, Mg, HCO3
Since the thick ascending segment is impermeable to water, what happens as the filtrate moves further down the loop of Henle and eventually gets to the ascending segment?
Filtrate gets more and more concentrated
What is the main function of the loop of Henle?
Generally, the longer the loop the ___________ concentrated the urine may become.
Control the concentration of the urine.
MORE
The thin descending segment working with the thick ascending segment form what?
The renal counter-current exchange
200 mOsm/L difference
Explain the loop of Henle countercurrent exchange principle.
As filtrate comes into the loop from the PCT, it is around 300 mOsm/L. As filtrate moves from the descending to the ascending loop, it will want to equilibrate with the concentration of the interstitium which is 400 mOsm/L. So, in the ascending part, ions are pumped out to achieve that, however, the water in the descending part will want to equilibrate, and water will be pumped out. As the filtrate goes further into the medulla, the concentration of the filtrate in the descending loop and the interstitium gets progressively higher, but equal, while the ascending loop does not match the interstitium, but is also at a higher conc lower in the loop. All of this allows H2O to be pulled out of the collecting duct if needed, and concentrates the urine very effectively.
The proximal part of the DISTAL TUBULE is impermeable to what?
Water, just like the ascending part of the loop of Henle.
The distal part of the distal tubule contains 2 distinct cell types. Name them.
Principal
Intercalated
What do principal cells do?
Reabsorb Na and H20 and secrete K. Favors outward Na flow
What do intercalated cells do?
Reabsorb K and HCO3 and secrete H ions into the tubule. This can regulate pH.
The permeability of H2O in the late distal tubule is controlled by what?
ADH
*In the absence of ADH, tubule becomes impermeable to H2O, causing urine to be more dilute.
**In the presence of ADH, tubule becomes permeable to H2O, causing urine to be more concentrated.
Where is the bulk of water reclamation?
Loop of Henle
*However, late distal tubule does fine tuning of concentration/dilution of urine via ADH amount.
T/F - collecting ducts are regulated by ADH in similar manner to the distal tubules.
TRUE
The cortical collecting ducts are very __________ in function to the late ________ tubules, and have the ____________ cells.
Similar
Distal
Same
The medullary collecting duct cells are very efficient at pumping out what ions?
B/c of this, these cells are particularly important for what regulation?
H ions
pH
The medullary collecting ducts are ___________ to urea.
Permeable
This creates more osmotic pressure
When ADH levels are high (concentrated urine), the collecting duct is permeable to water, and more ________ enters the renal medulla (urine).
UREA
*This allows max urea excretion with minimal water loss.
Urea is concentrated in the urine in what way?
The distal tubule and PCT reabsorb water, but the tubule walls here are not permeable to urea. This concentrates the urea.
What role does the vasa recta play?
Long U-bend shape allows it to have a role in the countercurrent exchange mechanism by maintaining the steep concentration gradient.
When ADH is increased, what happens to the urea concentration in the urine?
It is increased as well
What is a normal GFR?
180 L/day
