Urinary System Flashcards
Anatomy of kidney
Lobe: a pyramid + associated cortex
Describe the arteries of the kidney
- Renal artery enters the kidney and divides into segmental arteries
- Interlobar arteries between the lobes
- Arcuate arteries run on the horizontal aspect of the lobes, between cortex and medulla
- Interlobular artery betwen the lobules.
- Afferent arterioles is where the blood enters the glomerulus (loose not of capillaries) for filtration
- Efferent arterial network (where nutrients get reabsorbed):
- Peritubular capillaries in the cortical nephron
- Vasa recta capillaries in the medulla
Renal corpuscles vs Nephron
-
Renal corpuscle (red blob)
- Glomerular capsule: podocytes, parietal epithelium, urinary space
- Glomerulus: fenestrated capillaries, arterioles, mesangial cells
- Filtration apparatus: fenestrated endothelium, basal lamina, filtration slits between pedicles
-
Nephon (bigger circles)
- renal corpuscle
- proximal tubule
- loop of Henle
- distal tubule
- collecting tubule/duct
Describe the venous system of hte kidney
Interlobular
- > arcuate
- > interlobar
Functions of the kidney
- Remove cellular wastes from the blood
- Filtration, selective reabsorption of water and solutes, excretion of wastes & excess water
- Regulates blood pressure
- Regulates cid-base balance
- Produce hormones (e.g. Epo)
- Assists in vitamin D production
Are renal corpuscles in the cortex or medulla?
- Cortex
- Renal corpuscles
- Convoluted tubules, straight tubules, collecting tubules
- Medulla
- Collecting ducts
- Straight tubules
Lobe vs Lobule
- Lobe: pyramid + associated cortical tissue
- Lobule: medullar ray (collection of straight tubules in cortex) + associated cortical tissue
- Nephron: functional unit of the kidney
How to find a lobule on a histology slide?
- First find the medullary ray (in the middle)
- Then find an interlobular artery (blue arrow)
Wheres the medullary ray?
What is the bottom blue arrow pointing to in this singular lobe?
Arcuate artery because it’s between the cortex (left arrow) and the medulla (right arrow)
Wheres the medulla?
Where the rays are draining into
Identify a lobule
The white blood vessels in the cortex are interlobular arteries. the distances between two of them that contain a medullar ray are a lobule (horizontal line)
Point out the arcuate artery
between cortex and medulla
the glomerular capsule has how many layers of epithelial cells?
two.
Parietal layer (yellow) is simple squamous epithelium.
Visceral layer (yellow on the glomerulus) is a podocyte, which has a lot of processes that divide into pedicles that wrap around the capillaries, forming a filtration barrier.
What kind of capillaries make up the glomerulus?
fenestrated
Glomerular Mesangial cells
Pericytes associated with the endothelial cells; they turn over basal lamina, control capillary diameter, secrete vasoactive compounds.
Only podocytes’ foot processes actually attach to the capillary; whereas, mesangial cells do share a basal lamina w it.
How can you differentiate betwen proximal and distal tubule cells on a slide?
Proximal tubule cells are thicker and taller cells than the distal, which are smaller and flatter.
How do collecting ducts appear in the medulla?
The cells’ nuclei don’t have a consistent color; it’s light and dark, kinda alternating
Podocytes
- visceral epithelial cells of Bowman’s capsule
- pedicles/foot processes of podocytes with filtration slits
- synthesizes nephrin
Two poles of a renal corpuscle
Urinary pole (lighter): filtrate leaves glomerulus and leaves via this pole to the proximal convoluted tubule
Vascular pole (darker) blood comes in, leaves via efferent arteriole
Describe the layers of the filtration apparatus
-
Fenestrated endothelium
- Only proteins that can pass are albumin and anything smaller than that
-
Glomeruluar basement membrane
- collagen IV*
- fibronectin, laminin, heparin sulfate
- charge barrier against anions
-
Podocytic filtration slits between podocyte processes (pedicles)
- nephrin-containing diaphragms
Which side is the urinary space and which side is the capillary? How do you know?
- Podocytes project into the urinary space and are grounded to a nephrin-containing diaphragm (the right blue arrow)
- Fenestrae (the left blue arrow) belong to the capillary side
Congenital nephrotic syndrome
Mutation in nephrin –> absence / malfunction of the podocyte’s slit filtration diaphragm
- Proteinuria, hypoalbuminemia, hyperlipidemia, edema
- Low albumin in your blood –> less osmotic pressure –> edema
Alport’s syndrome / Hereditary glomerulonephritis
Gene for collagen IV is faulty
- proteinuria
- RBCs in urine
- thinner glomerular basement membrane
Describe the passage of filtrate from blood capillaries in the glomerulus through the filtration apparatus
- Fenestration
- Basal lamina of endothelial cell and the podocyte
- Filtration slit of the podocyte
- Filtration diaphragm of podocyte
- Bowman’s space
What cell’s nucleus is this?
Podocyte. You can see its pedicles sent to the capillary
What cell’s nucleus is the bottom blue arrow pointing to?
Mesangial cell.
Unlike podocytes, the nucleus is actually within the basement membrane
The bottom right is the most abnormal: the pedicles are weird and meshed together, which would block filtration
the proximal straight tubule is also known as
the thick limb of the descending loop of henle
Characteristics of proximal tubules on a slide
- In renal cortex or medullary ray
- Simple cuboidal cells with brush border (for reabsorption) & microvilli
- Luminal debris
- Indistinct cellular outlines due ot numerous infoldings of plasma membrane
- Eosinophilic bc mitochondria
What happens in the proximal tubule?
Reabsorb 60-65% of water via passive diffusion
Reabsorb ions, amino acids, glucose
What is this an EM of?
Proximal tubule because
- microvilli
- mitochondria
- membrane infoldings
Luminal proteins are absorbed via
endocytosis to form endosomes and lysosomes
Polycystic Kidney Disease
Cysts from nephrons grow and compress interstitial tissue
- Enlargement of kidney –> back pain
- High blood pressure
- Renal failure -> decreased RBCs -> anemia
- Complications: infection of cysts, renal stones
Erythropoietin is a ___ hormone produced by ___ in the kidney in close association with the __ and __
glycoprotein hormone produced by interstitial fibroblasts in close association w peritubular capillary and proximal convoluted tubule
1-alpha hydroxylase
What part of the kidney produces and processes it?
What is it important for?
Proximal tubules
Performs Vitamin D hydroxylation (25-OH-D3 to 1,25(OH)D3) in the mitochondria of proximal tubule cells; turns pro-vitamin D into its active form
What symptom will result from decreased vitamin D production in patients with CKD or end-stage kidney disease since the proximal tubules can’t make 1-alpha hydroxylase?
Osteoporosis
What is the funciton of activated vitamin D?
- Activates bone osteoblasts
- Causes Ca2+ absorption in intestine to help bone mineralization
Identifying the loop of Henle
- Located primarily in medulla and also in inner cortex
- Simple squamous* epithelia
- Differentiated from capillaries (vasa recta) by the absence of blood cells
Sodium pumps in the cell membranes of the ___ limb of the loop of Henle pumps sodium into/out of the tubule?
Sodium pumps in the thick ascending limb pump Na+ out of the tubule
After _____, all water and ion regulation is determined by hormonal action
After loop of Henle
Distal tubule identification
- Located in renal cortex & medullary rays
- Simple cuboidal (brush border not visible)
- Smaller, flatter (nuclei closer together) than PCT
- Fewer and smaller microvilli
- Membrane infoldings
- Little luminal debris
- Indistinct cellular outlines due to infolding sof plasma membrane
- Eosinophilic bc mitochondria
Compare the top arrow (PCT) to the bottom arrow (DCT)
What are each these EM slides of?
The left is an EM of PCT because the mcirovilli are long and therse a lot of vesicles
The right is an EM of DCT becuase the microvilli are sparse
The flow of filtrate in nephron is regulated according to..
- the speed and concentration of sodium in the returning flow in the distal tubule
Describe the juxtaglomerular apparatus: macula densa cells, JG cells, extraglomerular mesangial cells
-
Macula densa cells in the DCT epithelium can sense sodium concentration in the DCT
- Ex) If it senses a high [NaCl], then that means the flow of the filtrate is too fast because more NaCl should have been rebasorbed earlier.
- Sends signals to juxtaglomerular cells: smooth muscle cells in the walls of the afferent arterioles to release vasoconstrictors or vasodilators
- Extraglomerular mesangial cells are outside the renal corpuscle
Which arteriole does the macula densa associate with- afferent or efferent? Why?
Afferent arteriole
In this photo of a DCT, which cells are the macula densa cells?
What is that pink triangle in the center?
The ones at the bottom (more columnar) are the macula densa cells
The pink triangle in the center are extraglomerular mesangial cells
Idnetify the macula densa, the arteriole, and the extraglomerular mesangial cells and a podocyte.
How does the juxtaglomerular apparatus respond when there is a decrease in renal perfusion (e.g. hypovolemia or hypotension)?
- Juxtaglomerular cells release renin, which will turn angiotensinogen to angiotensin I
- ACE (in lung and kidney) will turn angiotensin I to angiotensin II
-
Angiotensin II will cause water & salt retention to increase the effective circulating volume –> increased perfusion of the juxtaglomerular apparatus
- Increase sympathetic activity (general vasoconstriction)
-
Increase NaCl & H2O retention via
- <strong>Aldosterone</strong> for NaCl & H2O retention
- <strong>ADH</strong> from pituitary for H2O reabsorption in the collecting duct
- Increase K+ excretion
- Arteriole vasoconstriction
Effects of angiotensin II
- Increase sympathetic activity (general vasoconstriction)
- Increase NaCl & H2O retention via
- Aldosterone for NaCl & H2O retention
- ADH from pituitary for H2O reabsorption in the collecting duct
- Increase K+ excretion
- Arteriole vasoconstriction
How to identify collecting tubules and ducts
- Simple cuboidal (gets taller approaching the papilla)
- Light-staining principal cells w ADH-regulated aquaporins
-
Dark-staining intercalated cells secrete H+ and absorb HCO3-
- Much fewer than the light-staining; may not even be present
- Cellular outlines are clear
ADH is produced by ___ and affects ___
Produced by posterior pituitary gland
Affects the principal cells of the late distal tubule & collecting duct to increase water reabsorption
Label these
1: collecting duct
- nothing in it
- cuboidal
- clear cell borders
2: loop of henle
- nothing in it
- simple squamous
3: capillary
If the right side is a calyx and we magnified right in the center of this image, what would we see?
Renal papilla: projects into the calyx; large collecting ducts of Bellini (green arrows) open into the surface of the renal papilla.
3 most common causes of kidney disease
- Diabetic nephropathy: damage to glomerular filtration barrier due to excessive sugar entering urine
- Hypertensive nephropathy: sclerosis of glomerular arterial wall
- Glomerulonephritis: inflammation of glomerulus leading to nephrotic or nephritic syndrome
Alport syndrome
- Genetic mutation in collagen type IV synthesis –> glomerular basement membrane is thin and leaky, allowing blood and protein in the urine
- Type IV collagen is also in the eye and ear
Goodpasture syndrome
Antibodies to type IV collagen affects basement membrane in the lung
- Cough, chest pain, shortness of breath
- Blood & protein in urine
- High blood prssure
What is urothelium? Where do you find it?
Transitional epithelium surrounded by smooth muscle + connective tissue
Found in ureter, urinary bladder, urethra
Luminal epithelial layer of urothelium consists of umbrella cells
Purpose of umbrella cells
Forms a seal of uroplatin protein so urine does not enter the tissue
Senses distension
What is the middle arrow pointing at? What is the big arrow outside pointing at?
The middle arrow: lamina propria
Big arrow: 2 layers of smooth muscle (circular & longitudinal for peristalsis)
Bladder on a slide
looks pretty similar to ureter, except its not in a perfectly enclosed star shape
Contrast the female vs male urethra
- Female
- Shorter,
- Covered in urothelium, but transitions to nonkeratinized stratified squamous as you get more external
- Male
- Longer
- 3 types:
- Prostatic
- Membranous
- Penile urethra
- Also stratified squamous as it approaches the external surface
