Lecture 45 - Urinary System: Glomerular Filtration Flashcards
What are the 3 processes that occur within nephrons?
- Filtration - occurs at the glomerulus
- Reabsorption
- Secretion
Reabsorption and secretion occur in the renal tubule and the collecting duct
How and where does filtration occur?
It is due to hydrostatic pressure and it refers to the bulk flow of water and small solutes
It occurs at the glomeruli, which are found in the initial portion of each nephron
Define glomerulus
The blood vessels (capillary bed) between the afferent and efferent arterioles
Define renal capsule
The spherical epithelial structure at the beginning of each nephron which encapsulates the glomerulus
Define renal corpuscle
Glomerulus + capsule
Where are glomeruli found?
They are found at the renal cortex, at the ends of cortical radiate arteries. Glomeruli are the only location where blood vessels interact directly within the nephron
What does a glomerulus consist of? Describe them
An afferent and efferent arteriole, and a juxtaglomerular complex (JGA)
The afferent and efferent arterioles have different sizes and their smooth muscle layers can also be independently regulated by different factors
The JGA detects changes in the arteriole pressure and the flow of filtrate in the distal parts of the nephron
What does the renal corpuscle consist of?
It consist of a double-layered membrane (capsule) which encloses glomerular capillaries and a capsular space
What does the glomerular capsule (Bowman’s capsule) consist of?
Visceral layer (of the corpuscle) - contributes to filtration
Capsular layer - creates a space which contains the filtrate from the glomerular capillaries
What are the 4 components that make up the filtration membrane?
- Endothelial cells
- Basement membrane of the capillary - the main structure that prevents movement of large molecules
- Podocytes of the visceral layer have “feet” (pedicels) which wrap around the basement layer, leaving gaps known as “filtration slits”
- Glomerular capillaries - they are fenestrated with relatively large pores
What are the 4 factors that affect Net Filtration Pressure (NFP) in glomeruli?
Group A: pressure from the volume of fluid in enclosed tubes
1. Glomerular hydrostatic pressure (GHP)
2. Capsular hydrostatic pressure (CsHP)
Group B: osmotic pressure from large (ie. impermeable) solutes
3. Blood colloid osmotic pressure (BCOP)
4. Capsular colloid osmotic pressure (CsCOP)
NFP = (GHP + CsCOP) - (CsHP + BCOP)
How can glomerular filtration (and therefore GFR) pressure be altered? Name 2 examples
Physiological changes or diseases; alterations to the glomerular capillaries or arterioles, or to the filtration membrane or fluid within the nephron can alter the balance of the 4 forces, altering NFP and GFR
- Constricting the efferent arteriole will increase GHP
- Blocking the drainage of urine from the nephron will increase CsHP
What sensors affect the homeostatic regulation of GFR and where are they found?
Mechano- and chemo- sensory cells are found in the juxtaglomerular apparatus (JGA)
What are the main effectors for homeostatic regulation of GFR and where are they located?
Smooth muscle in arterioles and extra/intra-glomerular mesangial cells within the glomerulus
Is the kidney GFR primarily regulated by intrinsic or extrinsic mechanisms? Name 2 examples of how these mechanisms work
Intrinsic
- Changes in arteriole pressure are sensed by arteriolar smooth muscle, which respond with myogenic reflexes
- The distribution is also sensed by the JGA, which further alters the activity of effectors through paracrine signaling
