Microscopic anatomy of the urinary tract Flashcards
Water is actively pumped in the kidneys, true or false?
False
Briefly, how does water move in the kidneys?
Na is moved and water follows by osmosis
The _____ is the functional unit of the kidney
Nephron
What constitutes a nephron?
The Bowmans capusle, PCT, Loop of Henle, DCT, collecting tubules and ducts
Were do the collecting ducts drain to?
Renal pelvis
Where does urine pass after it enters the renal pelvis?
Ureter
Where does urine pass after the ureter?
Bladder
Where does urine pass after the bladder?
Urethra
What are the two different types of nephron?
Cortical
Juxtamedullary
What is the difference between cortical and juxtamedullary nephrons?
Cortical nephrons glomeruli are in the outer cortex, LOH only enters the outer medulla, whereas juxtamedullary nephrons have glomerulus in the inner cortex and LOH enter the inner medulla
The gross structure of the kidney is directly related to its appearance. The amount of _____ present in the medulla regions gives the variation in colour seen on histology and in life. The _____ medulla has th most tubules within, hence the darker colour, whereas the _____ has less, accounting for the paler colour.
Tubules
Outer
Inner
The greater the amount of nephrons in the kidney, the greater the _____ _____ for the exchange of fluid and the formation of urine.
Surface area
The glomerulus is also known as the _____ _____.
Renal corpuscle
The glomerulus is a vascular tuft or capillary bundle that enters the _____ _____.
Bowmans capsule
Outline the blood supply of the glomerulus.
Afferent arteriole to the glomerulus
Exits via efferent arteriole
Passes to the peritubular capillaries (i.e. surrounding the PCT, LOH and DCT)
What structure results in the fenestrations seen on the surface of the glomerulus?
Podocytes
What is the function of the podocytes covering the glomerulus?
Prevents proteins from leaving the blood, ensures filtration of fluids only
What makes up the visceral layer of the Bowmans capsule?
The podocytes covering the glomerulus.
What makes up the parietal layer of the Bowmans capsule?
Epithelial cells
The glomerulus is made up of lots of parallel capillaries with lots o interconnections, true or false?
True
Where are the glomeruli found within the kidney?
The cortex
Exchange of substances between the peritubular capillaries and the _____ _____ are important in determining the concentration and volume of _____.
Collecting ducts
Urine
What structure do the peritubular capillaries empty into?
Venules
What structure do the peritubular capillaries empty into?
Venules
What is the spaces between the two layers of the Bowmans capsule called?
Urinary space or Bowmans space
What are the peritubular capillaries that follow the course of the LOH in juxtamedullary nephrons called?
Vasa recta
What cells are found between the endothelium and basal lamina of capillaries of the glomerulus?
Mesangial cells
What are the three main properties of mesangial cells?
1.
2.
3.
Contractile smooth muscle cells
Immune functions
Structural support
How can mesangial cells influence the diameter of the glomerular capillaries, rate of blood flow through the glomerular capillaries and filtration rate?
They can contract, increasing the diameter of the capillaries, thus increasing flow rate and filtration rate
How do mesangial cells contribute to immune functions?
They can take up immune complexes and participate in inflammatory processes through the production of cytokines and phagocytose foreign material to help clean the glomerular basal lamina
What makes up the filtration apparatus in the nephron?
Fenestrated capillary endothelium
Glomerular basement membrane
Podocytes
The fenestrations in the endothelium allow fluids and ions to pass through, but not _____
Cells
The glomerular basal lamina is made up of collagen and glycoprotein fibres restricts the passage of _____ _____.
Plasma proteins
Podocytes are found within the inner epithelial layers of the Bowmans capsule. They are in contact with the _____ _____.
Basal lamina
Anions are not able to pass into the filtrate because the basal lamina of the glomerulus is _____ _____.
Negatively charged
Outline the three different stages fluid in the glomerular capillaries have to pass through to get to the urinary space.
1.
2.
3.
Through the fenestrations in the endothelial cells of the capillaries
Through the basal lamina of the capillaries
Through the spaces between the pedicels of the podocytes
Podocytes have primary and secondary process known as _____ that act as filtration slits.
Pedicles
The PCT is very _____ as lots of pumping of solutes and solution occurs here.
Active
Name the two different segments of the PCT.
Convoluted (S1 and S2)
Straight (S3)
In what region does the majority of transport of materials occur?
PCT
Why are there lots of different mitochondria present in this region?
Very active region that uses oxidative process for the transport of materials to occur
What structures aids bulk absorption in the PCT?
Brush border cells
Basal striations
How does a brush border aid in bulk absorption?
Increases the SA for absorption
What are basal striations?
In-folding of the basal cell membrane that increases surface area
What does the basal membrane face?
The peritubular fluid, i.e. the space around the PCT
What is present on the basal membrane of the PCT to aid absorption of Na and K?
Na/K ATPases
Are transport pumps present on just the basal membrane?
No, also see transport pumps on the apical membrane
What happens when the PCT is overloaded, i.e. if the rate of flow of fluid exceeds the ability of the PCT to transport molecules out of the tubule?
Osmotially active substances flow into the LOH which will disrupt the absorptive processes that occur here. Water will be held in the tubules due to the high osmolarity of the water in the tubules, therefore more dilute urine will be produced.
PU/PD in diabetes mellitus is caused by what?
Glucose is not reabsorbed in the PCT, therefore it remains in the LOH, which causes the osmolarity of the fluid in the tubules to increase, so water follows by osmosis, leading to PU compensatory PD
What are the three different segments of the LOH?
Thin descending limb
thin segment of loop
Thick ascending limb
The countercurrent multiplier is a mechanism utilised to reabsorb water from the tubular fluid. A _____ _____ is generated which allows water to be _____ from the tubular fluid and _____ _____ to be generated.
Concentration gradient
Reabsorbed
Concentrated urine
Countercurrent multiplication in the LOH if the juxtamedullary nephrons is largely responsible for generating the osmotic gradient required for _____ _____ to be produced.
Concentrated urine
Apart from the countercurrent multiplication in the LOH, what else is important for concentrating urine?
The vasa recta
There is an increasing gradient of osmolarity from the _____ to the _____ as you pass down the LOH. This osmotic gradient allows urine the is _____ _____ than plasma to be produced.
Cortex
Medulla
The thin ascending limb of the LOH is passively permeable to _____ only.
Water
Active reabsorption of solutes from the _____ _____ increases the concentration gradient within the _____. Water and solutes move down their concentration gradient until they equilibriate, so water moves out of the descending tubule, and ions move into the interstitium.
Ascending limb
Interstitium
The thick ascending limb is impermeable to ______ but actively reabsorbs Na, K and Cl.
Water
Countercurrent multiplication essentially moves NaCl from the tubular fluid into the interstital space within the kidneys. This generates a concentration gradient that _____ will follow.
Water
There are two things that contribute to the development and maintenance of a countercurrent multiplier system.
One is the _____ _____ of NaCl out of the tubular fluid in the _____ limb and into the interstitium. The second is that new _____ is constantly being produced, which pushed the fluid at a _____ osmolarity down the tubule. The difference in osmolarity across the epithelial cells of the ascending limb created by the separation of ions and water has been multiplied in the interstial fluid, i.e. is higher, hence the same countercurrent multiplier. Countercurrent comes from the fact that the flow direction in the ascending and descending limbs are opposite.
Active transport
Ascending
Fluid
Higher
The length of the LOH determines the size of the osmotic gradient, so the longer the loops, the ____ the osmotic gradient.
Greater
Absorption of water to the circulatory system occurs via the _____ _____ capillary system
Vasa recta
The absorption of water and solutes in the vasa recta is very similar to what happens in the nephron, except that the portion of the capillary near the PCT is permeable to _____, and the portion near the DCT is permeable to water, hence the water _____ into the circulation.
Ions
Reabsorption
What is the process called involving the vasa recta and the maintenance of the high osmolarity in the intersitium?
Countercurrent exchange
Species that have a short LOH are usually _____ at conserving water. This is because they live in an environment where water is _____.
Poor
Abundant
Species that have a long LOH are usually _____ at conserving water. The longer the LOH the greater the _____ of the medulla, therefore the more _____ can be reabsorbed.
Good
Osmolarity
In terms of structure, what does the DCT lack that the PCT has.
Brush border
The DCT has a straight portion from the _____ _____ _____ and a convoluted portion for _____ _____.
Loop of Henle
Ion transfer
The initial part of the distal tubule passes between the _____ arterioles of its own glomerulus.
Efferent
The cells in contact with the efferent arteriole are known as the _____ _____.
Macula densa
What is the function of the macula densa?
Function of chemosensors that register the concentrations of Na and Cl in the tubular fluid
Probably also sense the volume of fluid flowing past this part of the tubule.
What makes up the juxtoglomerular apparatus?
Juxtomedullary cells
Macular densa
What is the function of the juxtamedullary cells?
Renin synthesising, storing and secreting cells
Register the blood pressure in the afferent arterioles
What is the function of the juxtoglomerular apparatus?
Regulation of renal function
The cells of the distal part of the distal tubule and the collecting ducts have nearly identical properties. There are two cell types in these parts of the nephron, what are they called?
1.
2.
Intercalated cells
Principle cells
What is the function of principle cells?
Absorb Na and Cl, secrete K
What is the function of intercalated cells?
Reabsorb K
Involved in acid-base balance
Where are the collecting ducts found?
Inner medulla
Each individual collecting ducts coalesces to form a _____ which opens into the _____ _____ that then opens into the renal pelvis and then ureter.
Duct Renal papilla (area cribosa)
Collecting duct cells are sensitive to _____ which is able to open or close aquaporin channels.
ADH
a-intercalated cells secrete _____ while B-intercalated cells secrete _____.
H+
HCO3-
What structures are found within the outer renal medulla?
Straight parts of PT, thick ascending limb of the LOH, LOH, collecting ducts, thin parts of the tubules, vasa recta
What structures are found in the inner renal medulla?
Collecting ducts, thin parts of tubules, vasa recta
What type of epithelium do the ureters have?
Transitional epithelium
The ureters have a _____ lamina propria. This and the _____ epithelium acts as a protective layer.
Fibroelastic
Transitional
What is transitional epithelium?
Epithelium that has multiple layers of cells that can expand and relax.
What is the function of the smooth muscle layer found in the ureter?
Peristalsis of urine down the ureter
The upper ureter has _____ layers of smooth muscle.
Two layers
How are the smooth muscle layers in the upper ureters arranged?
Inner layer is arranged longitudinally
Outer layer is circularly arranged
How many smooth muscle layers does the lower ureter have and how are they arranged?
Three
Inner layer longitudinally arranged
Middle layer circulalry arranged
Outer layer is longitudinally arranged
Ureters enter the bladder _____ preventing backflow of urine to the kidneys.
Obliquely
When the bladder wall stretches, the _____ are compressed, preventing backflow of urine to the kidneys. When this does not occur, urine can travel back to the kidneys and _____ can develop.
Ureters
Hydronephrosis
How many layers of smooth muscle are there in the bladder?
Three
What kind of epithelium is found in the bladder?
Transitional
Why is transitional epithelium found in the bladder?
To allow the bladder to stretch when filling
What autonomic control is the bladder under?
SNS and PSNS
Why is the equine renal pelvis different from other species?
The renal pelvis contains mucus glands. This accounts for the constant turbidity of horses urine.
What are the three histological layers of the ureter (and renal pelvis)?
Inner mucosa
Middle muscular layer
Outer adventitia
What type of epithelium does the urethra have?
Transitional, but parts stratified
Erectile tissue in the urethra is found in both sexes, true or false?
True
What are the erectile tissues found in the urethra?
Endothelial vascular spaces
The renal pyramids are found in the _____.
Medulla
Outflow of blood from the glomerulus does not go into venous drainage. Instead, it passes to the _____ _____
Vasa recta
The kidney is split into _____ by the position of the interlobar arteries.
Lobes
What are end arteries?
Blood vessels that are the only supply of oxygen to a specific area.
Cortical glomeruli have _____ capillaries, and juxtaglomerular glomeruli have _____ _____.
Peri-tubular
Vasa recta
Why is the concept of end arteries important with regards to the kidney?
The kidney has end arteries within it, therefore if the blood supply is cut off to one area of the kidney, it will not be perfused at all because it will only have one blood supply.
What difference is there in the renal capsule of cats compared to other species?
Cats have subcapular veins that run towards the hilum of the kidney
What is meant by the renal portal system?
Blood from the glomeruli does not enter the venous drainage, instead it passes to the vasa recta
