Dynamics of Glomerular Filtration Flashcards
What does the term “Freely Filtered” mean?
A substance is present in the filtrate at the same concentration as it is in the plasma
What does filtrate consist of?
Mainly inorganic ions and low molecular-weight organic solutes
What is the “Hose Analogy?”
A hose with a bunch of holes in it is a Capillary
A bucket is the Bowman’s Capsule
Water slowly filling the bucket is Filtrate
Substances that freely move into the bucket are “Freely Filtered” substances
What are some examples of Freely Filtered Substances?
- Ions (ClaNK and Bicarb)
- Neutral Organics (glucose and urea)
- Amino Acids
- Peptides (Insulin and ADH)
What is normal Glomerular Filtration Rate (GFR)?
125 mL/min which translates into 180 L/day
(All other capillaries in the body only accomplish 4L/day)
Average Plasma Volume in human is 3L so the kidney filters plasma about 60 times a day
What does Glomerular Filtrate consist of?
- Freely Filtered Substances
- Limited Plasma Proteins
- NO RBCs
What are the different cell types of the Glomerulus? What is their purpose?
- Podocytes
- Endothelial Cells
- Mesangial Cells
Form Glomerular Filtration Barrier which determines the size of the “Holes” in the capillaries and what can be filtered and make it into Bowman’s Space
Where are the Endothelial Cells of the Glomerulus located and what is their function?
- Located right next to the blood
2. Filter by SIZE (due to fenestrations)
What is the function of the Podocyte cells of the Glomerulus?
Form Filtration Slits that filter by SIZE
Foot processes interdigitate with the foot processes of other Podocytes to form the Filtration Slits
What are the Mesangial Cells of the Glomerulus?
- Filter by CHARGE because they lay down the negative extracellular proteins that repel the negative cells and proteins from entering the Nephron
- Modified Smooth Muscle cells that can contract
What is Net Filtration Pressure? What is the formula?
- Pressures associated with the Glomerulus and Bowman’s Space that are pushing fluid into the Nephron
- NFP= HPG - (HPBS - piG)
What causes Oncotic Pressure? Where does Oncotic Pressure not exist?
- The proteins and cells in a certain space wanting to retain fluid to surround the proteins and cells
- Oncotic Pressure does NOT exist in Bowman’s Space because it has no proteins or cells
What are normal NFP values
HPG= 45 mmHg piG= 0 mmHg HPBS= -10 mmHg piBS= -25 mmHg NFP= 10 mmHg
What would happen if normal Hydrostatic Pressure of the Glomerulus were to drop 10 mmHg?
Since HPG is the only force that favors filtration, if it were to drop from 45 to 35, NFP would be NONEXISTENT, meaning filtration would not happen
What is Glomerular Filtration Rate (GFR)? What is the formula?
The rate of filtration in the Glomerulus
GFR= Kf x NFP
OR
GFR= KF x (HPG - HPBS - piG)
Kf is a constant that stands for the surface area/amount of Glomeruli
What are the 4 forces that play a role in GFR?
- Surface Area (Kf)
- Hydrostatic Pressure of the Glomerulus (HPG)
- Hydrostatic Pressure of the Bowman’s Space (HPBS)
- Oncotic Pressure of the Glomerulus (piG)
What is Kf and what are some ways that it can be changed?
- Kf is Surface Area of the Kidney
2. It can be decreased via: A. Diabetes B. Kidney Disease C. Hypertension D. Kidney Donation E. Drugs causing Mesangial cells to constrict
Describe Hydrostatic Pressure of Bowman’s Space:
- Very constant
- ONLY changed if there were to be an obstruction of flow through the Nephron such as a Kidney Stone
- Increased HPBS would decrease GFR
Describe Oncotic Pressure of Glomerulus:
- Opposes Filtration
- Increases with an increase in proteins found in the blood
- Increased piG decreases GFR
Describe Hydrostatic Pressure of Glomerulus:
- Comes from Blood Pressure
- Can be regulated via the Afferent Arteriole and Efferent Arteriole
- Constricting Afferent Arteriole lowers HPG and GFR
- Constricting Efferent Arteriole raises HPG and GFR
- Dilating Afferent Arteriole raises HPG and GFR
- Dilating Efferent Arteriole lowers HPG and GFR
How could you significantly raise the Hydrostatic Pressure of the Glomerulus and ultimately the GFR?
By Dilating the Afferent Arteriole and Constricting the Efferent Arteriole
What is Filtered Load? What is its equation?
The amount of a substance that gets into a Nephron and is filtered per unit time
FL=GFR x Plasma Concentration
What is a normal Filtered Load value for Na?
17.5 mEq/min
This comes from:
GFR x Plasma Concentration
125 mL/min x 140 mEq/L
What are the Autoregulatory Mechanisms essential to keeping GFR constant?
- Myogenic Response (smooth muscle contraction/dilation of blood vessels) SHORT TERM
- Tubuloglomerular Feedback (Renin-Angiotensin-Aldosterone System) LONG TERM
