Renal & Urinary System histology
List the structural features that facilitate this massive resorption
Apical microvilli, basal membrane infolding with associated mitochondriaon (striated basal membrane).
How much of the urinary filtrate is resorbed in the PCT
Approximately 80%.
How does the JG complex work
Macula densa cells sense decreased NaCl levels in the DCT. This stimulates the JG cells to secrete renin to increase blood pressure. Pressure increases that dilate the wall of the afferent arteriole (hence the JG cells) is the negative feedback mechanism to shut down renin release and lower blood pressure.
What keeps it clean of debris/macromolecules?
Mesangial cells clean the filtration membrane.
List the component parts of a nephron and be able to label a representative diagram.
The renal corpuscle (glomerulus + Bowman's capsule), proximal convoluted tubule, loop of Henle, distal convoluted tubule. This diagram has also been used on previous exams.
What is the filtration slit?
The space between the pedicels of adjacent podocytes processes.
How do the PCT cells integrate with the function of this region of the nephron
Their microvillous apical border and striated basal border indicate an effective increase in surface area as well as basal membrane active-transport to exchange large volumes of fluid and electrolytes from the lumen into surrounding capillaries.
Be able to label a diagram indicating that you understand the morphology of the renal corpuscle and all its component parts
This is a comprehensive diagram and has been used on the exam before.
What is the function of the urinary bladder
To store urine prior to elimination from the body.
What specific type of epithelium lines the urinary passageways?
Transitional - a form of stratified epithelium
How many capillary beds are traversed in this pathway? Name them
Two
Why is this unusual
Usually arterioles lead to capillaries which lead to venules, NOT an efferent arteriole.
What specific function occurs in the region of the thin loop of Henle
Water, sodium ions and chloride ions are resorbed from the urinary filtrate in this segment of the nephron.
What is the function of the JG complex?
Regulate blood pressure within the glomerular capillary as well as body-wide.
What is the structural/functional unit of the kidney?
The nephron.
Which cell type secretes new BL to repair damage to the GBM?
The podocyte.
List three mechanisms that can trigger JG cell release of renin
1. Macula densa acts as an osmoreceptor and senses decreased sodium; 2. JG cells act as baroreceptors and sense decreased stretch (blood pressure) of the afferent arteriole; and 3. Sympathetic nerve stimulation of JG cells due to decreased sodium levels.
How do cross sectional profiles of the distal convoluted tubule differ from those of the proximal region?
1. PCT profiles are more numerous than those of DCT; 2. PCT stain darker with fewer visible nuclei; 3. PCT are higher cuboidal epithelium with a rough luminal microvillous border; 4. PCT exhibit striated basal regions due to basal infoldings and mitochondria required for active transport.
What other structure(s) have an intimate relationship with it the thin portion of the loop of Henle?
A coiled capillary bed.
What is the macula densa?
A crowded area (more epithelial cells per unit area) of the distal convoluted tubule wall.
What does excess protein in the urine indicate
A damaged filtration barrier.
Be able to label a diagram indicating that you understand the morphology of the filtration apparatus
A diagram like this has been used on the exam in the past (page 177).
What crosses the filtration slit
A filtration slit membrane extends across the filtration slit like a filter.
Where are mesangial cells located?
A stalk-like group at the vascular pole that extend out into the glomerulus (for supporting framework). They also extend out along the JG complex as lacis cells.
What is the implication of actin microfilaments in the podocyte pedicels?
Adds contractility as a function of the pedicels - allowing them to change the width of the filtration slit.
What other function(s) do these specific cells have
Also provide structural support for the glomerulus.
How are the smooth muscle layers of the ureter wall arranged
An inner longitudinal and outer circular layer of smooth muscle in the wall of the ureter.
What implication(s) does this have on their loops of Henle
Cortical have the shortest loops of Henle within the medulla as they are located furthest from it. The juxtaglomerular have the longest loops extending down into the medulla as they are closest.
What types of nephrons can be classified based on their location in the cortex
Cortical, juxtamedullary, intermediate.
What do the vesicles in the apical regions of the uppermost layer of epithelial cells in this epithelial lining represent
Extra thick portions of cell membrane that become exposed when the cells stretch.
How is efficient filtration accomplished in the renal corpuscle
Fenestrated glomerular capillaries (without diaphragms) and high hydrostatic pressure.
Where would the majority of the loop of Henle be located?
Generally, within the medulla.
What is the specific function of each of these two sets of capillaries
Glomerular capillaries function in effective filtration of the blood (loss of water and electrolytes); the peritubular capillaries surrounding the tubular portion of the nephron functions in resorbing the lost water and electrolytes.
Where might collecting tubules be located?
In addition to being in the medulla, they also extend up into the cortex as medullary rays.
Where are the collecting tubules located?
In the medulla as well as in medullary rays.
What happens to the urine as it passes through the collecting ducts
It becomes more concentrated. Water and electrolytes lost during filtration in the glomerulus are withdrawn by the capillary network surrounding the tubular portion of the nephron.
What is different about the cell membrane in these thick plates? It's supposed function
It contains a different type of membrane lipid - cerebroside which is the major component of the polar lipid fraction. Protects the epithelial cells from the acidic urine in the bladder lumen.
How does the release of renin result in increasing blood pressure
It converts plasma-bound angiotensinogen to angiotensin I which is in turn converted to angiotensin II which can cause vasoconstriction or aldosterone secretion from the suprarenal cortex. The latter causes sodium and water retention in the DCT. Both result in an increase of blood pressure.
What is the function of the glomerular basement membrane (GBM)?
It filters material from the lumen prior to its entering the filtration space as urinary filtrate.
Where does the newly formed urine go after it passes this location
It is collected by the funnel-like minor calyx. It is then funneled into a major calyx, then into the renal pelvis and out into the ureter proper.
By what other name are mesangial cells referred to elsewhere? Where is this
Known as lacis cells that extend out along the JG complex.
What are the distinguishing morphological features of the proximal convoluted tubule?
Large high cuboidal cells with indistinct lateral cell boundaries, ragged apical borders and a striated basal border. There are more PCT profiles than DCT profiles (as it is longer than the DCT).
Describe the appearance of the wall of this segment of the nephron.
Loops of Henle are composed of low to high squamous epithelial cells.
Does the ureter exhibit a submucosa?
No submucosa only a fibroelastic lamina propria.
Where do collecting tubules terminate?
On the renal papilla.
What is the function of each type and where is it specifically located
Podocytes form the filtration barrier; endothelial cells are fenestrated for effective filtration; mesangial cells support the glomerulus as well as clean the filtration barrier; simple squamous cells of the parietal layer of the capsule - line the outer aspect of the filtration (Bowman's) capsule.
What cell types would be found in a renal corpuscle?
Podocytes, endothelial cells, mesangial cells (all in the glomerulus) and simple squamous epitheliial cells of the parietal layer of Bowman's capsule.
What cells comprise the visceral layer of Bowman's capsule (glomerular epithelium)?
Podocytes.
Of what are collecting tubules composed?
Tall cuboidal to low columnar epithelium with distinct lateral cell membranes.
What are the specific components of the glomerular basement membrane?
The fused basement membranes of the podocyte and glomerular capillary. From the capillary lumen outward you encounter the lamina rara interna, the lamina densa, and the lamina rara externa.
What composes a renal corpuscle?
The glomerulus (capillary) and Bowman's capsule.
What specific portions of the GBM are responsible for the selective filtration of ions?, of macromolecules?
The lamina rara specifically filters out positively charged molecules. The collagen fibers of the lamina densa act as a physical barrier preventing molecules of more than 70,000 Daltons from entering the urinary filtrate.
How can you tell these two structures apart?
The loops of Henle do not have blood cells in their lumena.
Which other organ of the body is always involved in this process, why
The lung. It is the site of angiotensin conversion enzyme (ACE) within the endothelial cells of this organ needed to convert angiotensin I to angiotensin II.
Where is this structure located? be specific
The macula densa is found in the wall of the distal convoluted tubule in region of the vascular pole of the renal corpuscle.
What are the component parts of the J-G complex?
The macula densa of the distal convoluted tubule, JG cells (modified smooth muscle cells of the afferent arteriole wall) and extraglomerular mesangial (lacis) cells.
Where is the JG complex located
Within the wall of the afferent arteriole.