What are columns of Bertin?
Interlobar cortical tissue and CT → separates the lobes of the kidney
Extends the renal cortex between the renal pyramids
Has renal corpuscles, blood vessels, etc.
What are the different sections of the nephron?
- Renal corpuscule (contains glomerular tuft)
- Proximal convoluted tubules (in medullar, very eosinophilic)
Loop of Henle: - Thick straight descending limb (medulla, crosses cortico-medullary junction)
- Thin limb (mostly descending, cortex)
- Thick straight ascending limb (cortex)
End of loop of Henle - Distal convoluted tubule (stained paler, medulla)
*DCT drains into the collecting system
What are the 2 parts of the Uriniferous tubule?
- Nephron
- Collecting system:
- Collecting tubules in the cortex
- Collecting duct in the medullar (larger)
*Uniniferous tubules = functional uni of the kidney
- Both parts differ in embryological origin
- Ends in the papillary duct of Bellini which opens the renal papilla in the area cribrosa
What are the different structures of the renal corpuscule?
Glomerulus (fenestrated capillaries) + Bowman’s capsule
Bowman’s capsule has 2 epithelial layers:
- Visceral layer (podocytes)
- Parietal layer (squamous cells resting on BM, with reticular fibers on the outside)
In between there is a capsular space in which the ultrafiltrate goes before entering the urinary pole → Proximal convoluted tubule
Each renal corpuscule has a vacular pole (afferent and efferent arteriole + macula densa) and urinary pole (PCT starts)
What is the epithelium in the parietal layer of the renal corpuscule and how does it change at the urinary pole?
Parietal layer → Simple squamous epithelium
At urinary pole → PCT → simple cuboidal to columnar epithelium with brush border
What are pedicels?
They are the 2ndary processes of the podocytes (from visceral layer of renal corpuscule)
- Interdigitated with pedicels from adjacent podocyte
- Form filtration slits (25nm wide) → bridged by very thin diaphragm
- Touch BM (only part of podocytes that do)
- Cell bodies of podocytes are poor in mitochondria
- Processes contain actin filaments for contractility
What type of capillaries are found in the glomerulus?
What are features of the BM the endothelial cells rest on?
Fenestrated capillaries (with diaphragm)
Endothelial cells share a thick BM with pedicels
BM contains type IV collagen, laminin, fibronectin, proteoglycans rich in heparan sulfate
What is the problem of diabetes mellitus at the level of the kidney?
The BM around the capillaries is damaged → more permeable to proteins
*BM also acts as a filter
Where are mesengial cells found?
- Extraglomerular mesangial cells
- At the vascular pole, outside the glomerulus, between the afferent and efferent arterioles - Intraglomerular mesangial cells
- Between capillary loops inside glomerulus
- Likely phagocytic + involved in digestion of BM
- Maybe also contractile → reducing blood flow in glomerulus
- Provide structure
What is the macula densa?
It is composed of specialized epithelial cells in the distal convoluted tubule that detect the Na concentration of the fluid in the tubule.
These cells are involved in the production of Nitric Oxide (vasodilator) and other factors
What are the different circulation vessels in the kidney?
- Renal artery/vein
- Interlobar artery/vein → in renal columns of Bertin
- Arcuate artery/vein → at the cortico-medullary junction
- Lobular artery/vein → in cortex in between medullary rays towards capsule
- Afferent arteriole → going into the renal corpuscle → capillaries (in glomerulus) → efferent glomerular arterioles
6a. Efferent arteriole from cortical nephrons (shorts) branch to form peritubular capillary network → supplies cortical tubules
6b. Efferent glomerular arteriole of juxtamedullary nephrons → Vasa Recta (long capillaries that penetrate deep into medulla, form loop following limbs of loop of Henle)
*Vasa recta drain into Arcuate veins
Peritubular capillaries / vasa recta → Interlobular veins → Arcuate veins → Interlobar veins → Renal vein → Inferior vena cava.
Under the capsule another capillary network → peritubular capillaries draining into Stellate veins → interlobular veins…
What is the process of glomerular filtration?
- Fluid leaves blood through fenestrae in capillaires
- Crosses the basement membrane (molecules over 69 kDa (ex: albumin) are trapped by the BM + negatively charged molecules are prevented from crossing by anions present in BM
- Fluid enters the capsular/urinary space → glomerular ultrafiltrate
- To prevent clogging of the BM by larges trapped molecules, the BM is continuously renewed through phagocytosis by mesengial cells and de novo synthesis by podocytes and endothelial cells
What are features the Proximal Convoluted Tubules?
- Continuous with the urinary pole of Bowman’s capsule
- In the cortex
- Longer than DCT (and larger cells)→ more often found in histological sections
- Lined by simple cuboidal → columnar epithelium
- Acidophilic cytoplasm because of numerous mitochondrias
- Brush border (mircovilli) on apical surface
- Basal surface has invaginations and lareral interdigitations with adjacent cells (w/ Na/K pumps + Mitochondrias)
- Absorption of 85% of water, solute and proteins (Na, Cl, Ca)
- Secretes creatine into the lumen (generated by M-line in muscles)
- Water passes freely across the apical membrane, but active reabsorption across basolaterla membrane (NA/K ATPase)
- Fluid leaving PT is the same as initial glomerular filtrate (isotonically)
Which nephrons have the long loops of Henle that penetrate deep into the medulla?
Juxtamedullary nephrons → the ones that have the corpuscle near the cortico-medullary junction
- Important nephrons!
- Share capacity of filtration, absorption and secretion with all other nephrons + unique capability of contributing (with the blood vessel loops) to the establishement of the gradient of hypertonicity in the medulla → for urine concentration (couter-current exchange system)
*Urine concentration
*Thin descending limb = permeable to water, but entire ascending limb is not
What are some features of the Distal Convoluted tubule?
- Much shorter than PCT (also in the cortex)
- Simple cuboidal epithelium, no microvilli
- Rich in mitochondria (ion transport)
- Absorbs Na+ and secretes K+
- Secretes protons (H+) and absorb bicarbonate (or vice versa depending on pH)
- Primary site of site of hormone (Aldosterone) based regulation of Ca2+ (Na/Cl apical symport + permeable)
Modified DCT → Macula Densa:
- Cells become elongated (columnar) and nuclei seem packed together
What are the main differences between the DCT and the PCT?
- Cells are smaller and flatter in the DCT
- Lumens are larger in DCT
- Brush border only in PCT
- Apical nuclei in DCT vs central in PCT
- more cells (more nuclei)/cross section in DCT
*Can’t really see the lateral membrane in both
What are the 3 different components of the juxtaglomerulus apparatus?
- Macula Densa
- Juxtaglomerual cells → modified smooth muscle cells which secrete renin
- Extraglomerular Mesangial cells
What is the role of the Parathyroid hormone (PTH)?
- Increase concentration of Calcium in the blood by acting upon the PTH1receptor (expressed in bone and kidney) → in DCT
Increases Ca rabsorption in the DCT
- Binds to its receptor on DCT cells → activates calcium channel
What is the effect of Calcitonin?
Calcitonin → hormone produced by parafollicular cell (C cells) of the thyroid gland.
Lowers blood Ca2+ levels in 4 ways:
- Inhibits Ca2+ absorption by the intestines
- Inhibits osteoclast activity in bones
- Stimulates osteoBlastic activity in bones
- Inhibits renal tubular cell reabsorption of Ca2+ → allows excretion in the urine
What is the range of the human body pH?
7.35 - 7.45
- Slightly alkaline pH → important for oxygenated blood
What structure give its structure to the Brush border of PCT cells?
Actin filaments in the microvilli
What are the diameters of the Proximal convoluted tubules, the thin limb, the distal convoluted tubule?
PCT → 60 um (packed lumen)
Thin limb → 12 um
DCT → 60 um (clear lumen)
What is the role of Aldosterone?
Secreted by the Adrenals and stimulate the incorporation of Na and Chloride
What are the diameters of the Collecting tubules vs Collecting ducts vs Collecting duct of Bellini?
Where are they found?
Collecting tubules → 40-50um
- Found in cortex + medullary rays
Collecting duct → 200 um
- Found in medulla
- The end is called collecting duct of Bellini
- Site of ADH action (Antidiuretic hormone/vasopressin) → males the collecting ducts permeable to H2O (for water retention/urine concentration)
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Labs21
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Lab3 - CT14
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Lab4 - Bones16
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Lab5 - Muscle11
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Lab7 - Respiratory System6
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Lab8_OralCavity10
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Lab9_GItract9
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Lab10_SalivaryGlands, Liver & Pancreas5
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Lab12_Nervous Tissue3
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Histology21
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Epithelial tissue66
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Connective tissue43
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Bones32
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Muscle48
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Blood vessels34
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Respiratory system39
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Oral cavity40
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Esophagus, Stomach, Small and Large intestine32
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Liver & Pancreas34
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Renal30
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Nervous Tissue18
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Vocabulary63
