Week 9 Lecture 2 Flashcards
What is the functional unit of the kidney?
Nephron
The nephron filters blood and modifies the filtrate to form urine.
What two main parts consist of the nephron?
Glomerulus and Bowman’s capsule
These are crucial for blood filtration.
What are the structures included in the nephron?
- Glomerulus and Bowman’s capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting tubules and ducts
These structures work together in urine formation.
What are the two types of nephrons?
- Cortical nephrons
- Juxtamedullary nephrons
They differ in the depth of the Loop of Henle in the medulla.
What is the primary function of the glomerulus and Bowman’s capsule?
Site where blood is filtered through a specialized membrane, forming an ultrafiltrate
This ultrafiltrate is then modified to become urine.
What is the main role of the proximal convoluted tubule?
Reabsorb the majority of solutes and water, and all important filtered nutrients
It is also a key site for waste secretion.
What is the function of the Loop of Henle?
Crucial for concentration of urine
It utilizes countercurrent exchangers and multipliers to limit water loss.
What happens in the distal convoluted tubule and collecting system?
Urine composition is finalized based on hormonal presence
Principal and intercalated cells play roles in ion and pH homeostasis.
What does kidney clearance refer to?
The volume of plasma from which a substance is completely removed by the kidneys per unit of time
It measures the kidney’s ability to clear substances from the bloodstream.
True or False: If half of the substance is removed in one pass through the kidney, the other half will also be removed in the next pass.
False
The same proportion is removed, not the remaining half.
What are the three ways the kidney handles substances?
- Filtration
- Secretion
- Reabsorption
These processes can occur for some substances or only one of them.
What does ‘filtered’ refer to in kidney filtration?
The process by which substances are selectively removed from the blood and transported into the kidney’s tubular system
This primarily occurs in the glomerulus.
What is the role of the glomerular capillaries in filtration?
Allow for the passage of water, ions, small molecules, and waste products from blood into Bowman’s capsule
They have fenestrations that facilitate this process.
Fill in the blank: The initial filtrate formed in the glomerulus is called _______.
glomerular filtrate
This filtrate contains substances that will eventually become urine.
What is the renal blood flow in terms of cardiac output?
1 L of blood/min (about 20% of the cardiac output)
This indicates that the kidneys receive a significant portion of the heart’s output, which is essential for their function.
What percentage of renal blood flow is filtered at the glomerulus?
Approximately 20%
This means that out of the renal plasma flow, only a fraction is actually filtered into the Bowman’s space.
What is the renal plasma flow (RPF) available for filtration?
600 ml/min
This is the volume of plasma that is available for filtration after accounting for the hematocrit.
What is the glomerular filtration rate (GFR) for most people with good renal function?
120 ml/min
This is a rough approximation based on the renal plasma flow.
What does eGFR stand for?
Estimated glomerular filtration rate
This is a measure used to estimate kidney function.
What does GFR represent?
The volume of fluid filtered from the kidney’s glomerular capillaries into the Bowman’s capsule per unit time
GFR is a key indicator of kidney function.
What is considered a normal eGFR value?
Above 90 mL/min/1.73m²
Values below this indicate decreased kidney function and may suggest kidney disease.
What are the components of the filtration barrier in the glomerulus?
- Fenestrations in glomerular capillaries
- Basement membrane
- Filtration slits between podocyte pedicels
These components work together to filter blood effectively.
What is the role of charged ions in the filtration process?
Charged ions contribute to the selective permeability of the glomerular filtration barrier
Ions such as Na⁺, K⁺, Cl⁻, and Ca²⁺ pass through the barrier, while larger charged molecules like proteins are retained.
What is the equation for net filtration pressure (NFP) across the glomerulus?
NFP = Kf · (PGC – PBC – πGC)
This equation factors in the leakiness of the filtration membrane and pressures affecting filtration.
How does the constriction of the afferent arteriole affect GFR?
Decreases GFR
Constriction reduces blood delivery to the glomerulus, lowering the pressure needed for filtration.
How does the constriction of the efferent arteriole affect GFR?
Increases GFR
This constriction causes blood to back up in the capillary, increasing the pressure for filtration.
What is the significance of arteriole tone in regulating GFR?
It regulates both NFP and renal blood flow
The relative constriction or dilation of afferent and efferent arterioles is crucial for maintaining GFR.
What does the glomerular filtration barrier selectively retain?
Larger molecules like proteins and blood cells
This selectivity is important for preventing the loss of vital proteins in urine.
True or False: The glomerulus is less leaky than most continuous capillaries.
False
The glomerulus is hundreds of times leakier than most continuous capillaries.
Fill in the blank: The glomerular filtration barrier is permeable to _______ but not to larger charged molecules like proteins.
ions
This permeability is crucial for maintaining electrolyte balance.
What happens to net filtration pressure as fluid moves along the length of the capillary?
It decreases.
What is the oncotic pressure of blood affected by?
The amount of protein-free fluid filtered into the Bowman’s capsule.
What happens to hydrostatic pressure the further fluid flows along a tube?
It decreases.
What is the usual pressure in Bowman’s capsule?
Very low.
What does autoregulation of GFR involve?
Intrinsic mechanisms that maintain a constant GFR despite changes in systemic blood pressure.
What are the two main mechanisms involved in the autoregulation of GFR?
- Myogenic response
- Tubuloglomerular feedback
What does the myogenic response refer to?
Contraction and relaxation of smooth muscle cells in the afferent arteriole in response to blood pressure changes.
What does tubuloglomerular feedback regulate?
Filtration based on feedback from the tubules to the glomerulus.
What are the main components of the juxtaglomerular apparatus involved in tubuloglomerular feedback?
- Macula densa
- Granular cells
- Extraglomerular mesangial cells
What happens when ‘too much’ solute is delivered to the macula densa?
ATP or adenosine is released, resulting in reduced renin secretion and decreased GFR.
What is the effect of prostaglandins when ‘too little’ solute is delivered to the macula densa?
Increased renin release and vasodilation of the afferent arteriole.
What is the role of angiotensin II in GFR regulation?
Constricts the efferent arteriole more than the afferent arteriole, increasing GFR.
What effect does epinephrine have on GFR?
It constricts afferent and efferent arterioles, decreasing renal blood flow and GFR.
What is the role of endothelin in GFR regulation?
It is a powerful vasoconstrictor that reduces blood flow to the nephron and GFR.
What is the function of natriuretic peptides (ANP, BNP) in relation to GFR?
They inhibit renin release and relax the afferent arteriole, which increases GFR.
Fill in the blank: The glomerulus filters approximately ______ liters of water per day.
180
True or False: The myogenic mechanism is the most important mechanism by itself in autoregulation.
False.
