Lecture 38 - Glomerular Filtration Flashcards
The three processes involving the nephrons, collecting ducts, and their blood supply formation in urine formation are
Glomerular filtration, tubular reabsorption, and tubular secretion
An _____________ of urine is formed in the cortex and is modified during its course through the medulla
Ultrafiltrate
What drives filtration?
The structures within the cortex, primarily the glomeruli
The tubules within the medulla are responsible for
Reabsorbing, excreting, and concentrating the urinary filtrate
Our kidneys filter ________ of blood every minute, which works out to be 45 gallons of blood per day
Half a cup of blood
Kidneys filter all blood in your body ________ times a day
50 - this keeps blood’s components stable
How much blood volume do kidneys Reabsorb?
99%
What is ultrafiltration
The first of 3 processes by which metabolic wastes are separated from the blood and urine is formed. Nonspecific filtration of the blood under high pressure
Where does ultrafiltration occur
Renal corpuscle of the nephron
What facilitates ultrafiltration?
The ultrastructure of the glomerulus and Bowman’s capsule
The glomerulus is made up of
Many capillaries
Blood flows into capillaries through a ___________ & leaves through ________________
Wider afferent arteriole, narrower efferent arteriole
The change in diameter of arteriole going/leaving the glomerulus maintain
A high filtration pressure which is essential for filtration
What forces molecules through the glomerular filtration barrier
High filtration pressure
What is the glomerular filtration barrier responsible for
Selectively filtering the blood forming the glomerular filtrate
The Bowman’s capsule surrounds the
Capillaries of the glomerulus and has 2 layers of cells separated by the urinary space
The inner cells of bowman’s capsule are called
Podocytes
Podocytes have cellular extensions called _______
Pedicels
What do pedicels wrap around
Blood vessels of the glomerulus
Where is filtrate collected before entering the proximal tubule
Urinary space
The major players of the glomerular filtration barrier include
Endothelium, glomerular basement membrane, and podocytes
Glomerular endothelial cells are characterized by
Numerous fenestrations
Glomerular endothelial cells have fenestrations to allow
Water & non-cellular components of blood to pass through
Glomerular endothelial cells act as a barrier to
Cells in the blood
The glomerular basement membrane is a product of fusion of the basement membranes produced by
Endothelial cells and podocytes
What secretes proteins to make up the basement membrane
Podocytes and endothelial cells
What is the main barrier to proteins
Glomerular Basement membrane
Does the glomerular basement membrane have a lower permeability to anions or cations
Anions ! This allows for further selective filtration
Podocytes are what kind of cell
Epithelial
What do podocytes do
- provides structural & functional stability to the glomerulus
- vital part of glomerular filtration barrier
Podocytes are located on
The opposite side of capillary lumen and cover the outer part of the glomerular basement membrane
Podocyte cell bodies and major processes float in
Bowman’s space in primary urine
Podocytes have numerous
Processes, similar to tentacles that surround the capillaries
Each podocyte process has many
Smaller processes (foot processes or pedicels) that attach to the underlying basement membrane
The foot proceses of podocytes interdigitate with
Foot processes of adjacent podocytes (let them dogs out)
The space between the foot processes forms the
Slit diaphragm
The slit diaphragm is a
Molecular sieve, and it provides an additional filtration barrier based mainly on size exclusion
Blood that is travelling through the capillary is selectively filtered across
The glomerular filtration barrier to form an ultrafiltrate of the plasma
This filtration barrier permits passage of small and some medium sized molecules while blocking the passage of
Large molecules
The glomerular filtrate is called an ultrafiltrate of plasma because
The larger components (platelets and blood cells) and not filtered
Glomerular filtrate is similar to plasma and interstitial fluid, except that it has
A lower protein concentration than either of them
Glomerular filtrate is similar to plasma and interstitial fluid, except that
It has a lower protein concentration than either of them
Glomerular filtration barrier filter molecules bigger than
7000 DA
Small molecules with a molecular weight <7000 Da are filtered without restriction. These include:
Water
Cl
Creatinine
Urea
Uric acid and Phosphate are filtered in isotonic levels (same conc as plasma)
Larger molecules with a molecular weight > 7000 Da such as myoglobin are filtered
Less
Plasma proteins with molecular weights up to 70 000 Da are heavily restricted from
Passing through the glomerulus
However, small amounts of albumin do make it across the membrane. These are completely reabsorbed in
The proximal tubules
Normal filtrate is basically ______ free
Protein
Glomerular filtration rate (GFR) is the measure that describes
The total amount of filtrate formed by all the renal corpuscles in both kidneys per minute
GFR is influenced by
Both the hydrostatic pressure and the colloid osmotic pressure (oncotic pressure) on either side of the capillary membrane of the glomerulus
The blood inside the glomerulus creates a
Hydrostatic pressure which is the force to move fluid out of the glomerulus into the lumen of Bowman’s capsule. Thus, net fluid movement will be into the Bowman’s capsule
Glomerular filtration will occur when the
Glomerular hydrostatic pressure exceeds the luminal hydrostatic pressure of the Bowman’s capsule. Thus, net fluid movement will be into the Bowman’s capsule
Increased blood volume with its higher blood pressure will go into the afferent arteriole and into the glomerulus, resulting in
Increased GFR
Low blood volume due to dehydration will cause a
Decreased GFR
Other than blood pressure, what can impact GFR
Pressure changes within the afferent and efferent arteriole that go into and out of the glomerulus
Arteriole pressure can be varied by
Changes in the diameter of the afferent or efferent arteriole
Dilation of the afferent arteriole increases the blood flow to the glomerulus, which in turn increases
The pressure and potential for filtration
Constriction of the efferent arteriole increases
Glomerular pressure
The Bowman’s capsule space exerts hydrostatic pressure of its own that pushes
Against the glomerulus
Increased Bowman’s capsule hydrostatic pressure will
Decrease GFR
Decreased Bowman’s capsule hydrostatic pressure will
Increase GFR
What could cause bowman’s capsule hydrostatic pressure to rise?
Ureter obstruction to the flow of urine that gradually causes a fluid build up in the nephrons.
The renal corpuscle filters the blood to create a filtrate that differs from blood mainly
By the absence of cells and large proteins
From the renal corpuscle to the ends of collecting ducts, the filtrate of forming urine is undergoing
Modification through secretion and reabsorption before true urine is produced
Tubular reabsoprtion involves transport of water and solute from
Tubular fluid to peritublar capillaries
Tubular secretion is associated with
Transport of solute from peritubular capillaries to the tubular fluid
Selective reabsorption is
The second of 3 processes by which blood is filtered and urine formed. When filtrate passes through nephron, much of its contents are reabsorbed into the body
Reabsorption is a finely tuned processes that is altered to
Maintain homeostasis of blood volume, blood pressure, plasma osmolarity, and blood ph
Reabsorbed fluids, ions, and molecules are returned to the bloodstream, through
The peritubular capillaries and are not excreted as urine
Substances important to body function, such as Na+, glucose, and amino acids enter tubular fluid by
Filtration at the glomerulus
Because of Na+, glucose, and amino acids’ relatively small molecular size, they pass easily through
The glomerular membrane, and their concentration in the glomerular filtrate is about equal to their concentration in plasma
The majority of selective reabsorption occurs in
The proximal convoluted tubule, which extends from the Bowman’s capsule
The proximal tubule is located in the
Cortex
The proximal tubule selectively reabsorbs
Useful substances (electrolytes, nutrients, and fluid) via multiple mechanisms of transport
The proximal tubule is composed of
A simple columnar epithelium joined together by tight junctions
The apical brush border is a
Characteristic and distinguishing feature of the proximal tubule
The luminal surface of the epithelial cells of this segment of the nephron (proximal tubule) is covered with
Densely packed microvilli forming a border readily visible under the light microscope giving the brush border its name
The microvilli greatly increase the
Luminal surface of the cells, presumably facilitating their re absorptive function
The cytoplasm of the cells of proximal tubules are densely packed with
Mitochondria
Mitochondria of proximal tubule epithelial cells are needed to
Supply the energy for the active transport of sodium ions out of the cells to create a concentration gradient
In order for Na+, glucose, and amino acids from the tubular fluid to be returned to the blood, energy is supplied by
The Na+/K+-ATPase pump (sodium pump) on the basal and lateral surfaces of the tubular epithelial cells
Na+K+-ATPases constantly pump
Na+ out of the cell, maintaining a strong electrochemical gradient for Na+ to move into the cells from the tubular lumen
Sodium is actively pumped into the interstitial spaces between cells and diffuses down
It’s concentration gradient into the peritubular capillary
On the apical surface of proximal tubule, a Na+/glucose cotransporter protein assists
Both Na+ and glucose movement into the cell
The cotransporter moves glucose into the cell against
It’s concentration gradient, where it then diffuses across the basal membrane by facilitated diffusion into the interstitial space and from there into peritubular capillaries
Na+ moves down the electrochemical gradient created by
The basal membranes Na+/K+ ATPases
Simultaneous transport of two or more compounds on the same carrier in the same direction is called
Cotransport. Ex Na+/glucose
Water will follow Na+/glucose passively to
Maintain an isotonic fluid environment inside the capillary
Movement of water into the peritubular capillaries is influenced mainly by
Osmolarity and concentration gradients
The proximal tubules secrete retained organic solutes and drugs directly into the urine to
Remove substances that are not easily filtered. This achieves waste removal, disposes of end products that have been reabsorbed passively, such as urea and uric acid, and acid-based balance
The tubular secretion of H+ from the blood into the tubular fluid is involved in
Blood pH regulation
The typical pH of urine is about
6.0, much lower than blood which is 7.35-7.45
The secretion of H+ is mainly a result of
The Na/H exchanger, which is an antiporter in the apical membrane
Energy for H+ secretion is provided by
The Na/K ATPase in the basolateral membrane. This allows it to drive H+ against its concentration gradient
Urine is formed via the three processes of
Filtration, reabsorption, and secretion
Urine leaves the kidney through
The ureter & is stored in bladder before being removed through the urethra
Right before peeing, urine is only approximately ______ % of the originally filtered volume
1
Urine is made up of highly diluted amounts of
Urea, creatinine, and variable concentrations of ions
Do the kidneys reabsorb creatinine
No
A build up of creatinine in the blood can be a sign of
Impaired kidney function. This can lead to chronic kidney disease
Kidney diseases are conditions that
Incapacitate the kidney’s ability to filter waste products from the blood
Individuals with kidney diseases will demonstrate a(n) ___________________GFR
Decreased
If untreated, kidney diseases can lead to
Kidney failure
What can be used as an indicator of kidney disease
Kidneys prevent the excretion of blood cells and proteins during ultrafiltration as well as glucose (selective reabsorption). Presence of these materials in urine can be used as indicator of disease
The presence of glucose in urine is a common indicator of
Diabetes (high blood glucose = incomplete reabsorption)
The presence of blood in urine can indicate
A variety of diseases, including certain infections and cancer
High quantities of protein in urine may indicate
Disease or hormonal conditions (hCG= pregnancy)
Under normal conditions, albumins cannot be filtered into the
Bowman’s capsule
In certain kidney diseases, the basement membrane may be damaged which makes it
Leaky to proteins
Many drugs pass through the body into urine and can be
Detected (ie performance enhancing drugs)
Glomerular diseases are a leading cause of
Chronic kidney disease (CKD) in dogs and less often in cats
In dogs, the two major causes of proteinuric renal disease are
Glomerular nephritis and renal amyloidosis
Glomerular nephritis
Inflammation of the glomeruli
Renal amyloidosis
Deposition of amyloid fibrils in glomeruli, vessels, and/or interstitium
If glomeruli are damaged, what leaks into urine
Protein from the blood (check protein to creatinine ratio)
How to determine the specific glomerular disease present in any animal
Renal biopsy
Human glomerular disease is routinely defined following
-Examination light microscopic sections with a specific panel of histochemical stains
-Immunofluorescence to detect presence of immunoglobulins and complement proteins
-Transmission electron microscopy
Clinical signs associated with urinary protein loss are usually non specific:
Mild: weight loss, lethargy
Severe: edema, abdominal fluid collection
Extensive: renal failure, anorexia, Nausea, and vomiting
Most important treatment for glomerular diseases is
Identification and correction of any underlying disease processes
For glomerulonephritis, immunosuppressive drugs, antiplatelet therapy, and supportive therapy are done to
Decrease hypertension, edema, and the tendency for thromboembolism
