2 - Histology of the Kidney and Urinary Tract Flashcards
What are the three main functions of the kidneys?
- Excretory: produce ultrafiltrate from blood passing through. Excess water and ions, some drugs, toxins, and metabolites are excreted in urine.
- Homeostatic: regulating and maintaining EC fluid volume and composition. Maintaining acid-base balance.
- Endocrine: monitoring O2 carrying capacity of the blood via erythropoietin and regulating BP through RAA system.
What are the components of the nephron? What is it’s function?
Components: renal corpuscle and renal tubule
Function: filter and fluid modifier - kidney makes an ultrafiltrate of the blood, but also recycles many components that are in the filtrate.
What are the three main macroscopic components of the kidney?
Cortex: granular appearance. Linear arrays of tubules called medullary rays extending into the cortex.
Medulla: striated appearance; consists of 6-18 renal pyramids. The apex or tip of each pyramid is called a renal papilla.
Kidney lobe: consists of a renal pyramid and it’s surrounding cortex. Indisctint externally in adults.
What is a kidney lobule? What is the capsule?
Lobule = medullary ray + cortical tissue (primarily nephrons) on either side
The tubules of these nephrons connect with the collecting ducts within the medullary rays
The capsule consists of mainly fibrous connective tissue and surrounds the kidney.
How much blood goes to the kidney? What much is extracted/filtered?
Recieves 20-25% of the total cardiac output/minute. The total blood volume of the body passes through the kidneyts every 4-5 minutes.
125 mL of fluid is extracted fromthe blood each minute as filtrate, and 124 mL is reabsorbed in the tubules while only 1mL is excreted as urine.
What are the 2 capillary systems of hte kidney’s microvasculature?
Tubular plexus - supplies tubules of the cortical nephron
Vasa recta - long capillary loops that supply tubules of juxtamedullary nephrons
What is located in the space between the renal tubules?
The innerstitial (stromal) tissue is found in the renal cortex and medulla - the stroma is finer in the cortex.
- It’s made of interstitial connective tissue and interstitial cells (fibroblasts)
- interstitium is where ultrafiltrate goes before it’s taken up by the BVs
What are the four components of the renal corpuscle?
- Glomerulus
- Visceral layer of the Renal Capsule (Bowman’s)
- Parietal layer of the Renal Capsule
- Mesangium
What is the renal corpuscle? What are the poles? In what part of the kidney are these found?
Spherical, double layered sac that surrounds a network of capillaries (glomerulus)
Has a vascular pole where the arterioles enter and exit and a urinary pole that’s continuous with the proximal convoluted tubule.
Renal coerpuscles are found only in the cortex.
What is the glomerulus? What supplies and drains it?
A network of capillary loops supplied by the afferent arteriole and drained by the efferent arteriole. The afferent arteriole is large in diameter, which creates a pressure differential that drives glomerular filtration.
What is Bowman’s Capsule? What are the different layers and what cells make them up?
Double-layered epithelial sac around the glomerulus.
- The outer parietal layer is simple squamous epithelium.
- The visceral layer is also simple epithelium composed of cells called podocytes.
- The space between the two layers is the urinary space and is continuous with the proximal tubule; glomerular filtrate enters this space
What are the components of the glomerular filtration barrier (ie the filtration membrane of the kidney)?
Capillary endothelium - discontinuous with numerous 70-100 nm pores that are permeable to water and solutes 6-8 kD or less and moderatly permeable to molecules 8-16 kD. The luminal surface has a negative charge because it’s coated with glycocalyx made of proteoglycans.
Basement membrane - primary barrier that prevents proteins from entering filtrate
Podocytes - with foot processes make basement membrane
What is the structure and function of the glomerular mesangium?
Functions: physical support and regulation of glomerular blood flow
Cells and ECM that abut the inner surface of the glomerular basement membrane.
- ECM contains fibronectin and collagen and specialized pericyte/smooth muscle cells
What is the function of the convoluted portion of the proximal tubule? What type of cells are present?
(Green in picture) Begins at the urinary pole. Glucose, aas, and proteins are reabsorbed through facilitated transport.
- Cuboidal/columnar cells with granular cytoplasm and basal nuclei.
- Apical brush border with glycocalyx obscures lumen.
- Lysosomes, apical vescicles, and mitiochondria.
- Complex lateral interdigitations between epithelial cells make lateral cell membranes indistinguishable.
What cells are located in the straight portion of the proximal tubule?
Cuboidal epithelium (Purple in picture)
Also found inthe thick descending limb of henle.
What are the four parts of the loop of henle? Where is the loop of henle located?
- Straight portion of the proximal tubule (thick descending limb)
- Thin desxending limb
- Thin ascending limb
- Straight portion of the distal tubule (thick ascending limb)
Located in the medulla.
Describe the two different types of nephrons and their loops?
Cortical nephrons: located external to the juzxtamedullaruy zone; they have short loops that only have a descending thin limb
Juxtamedullary nephrons: are long looped and have ascending and descending thin limbs
What types of cells are found in the loop of henle? What about cell junctions?
Thick portions of the loop are lined with cuboidal epithelium, but thin segments are lined with simple squamous epithelium.
Thin descending limb is permeable to water.
Cell membranes in the ascending thin limb between epithelial cells are interdigitated, resulting in water impermeability.
What is the cell type and structure of the straight portion of the distal tubules (thick ascending limb)? What is the function of this region?
- Lined with cuboidal epithelium, scant microvilli, efficient tight junctions.
- Lateral and basal membrane interdigitations.
- Abundant mitochondria.
- Impermeable to water, Na and Cl resorbed. H+ secreted.
What is the cell type and structure of the convoluted portion of the distal tubule (early distal tubule)? What is the function of this region?
Lined with cuboidal eithelium, scant microvilli, fewer basal interdigitations and fewer mitochondria than the straight portion.
Na+, CL-. and K are secreted.
What cells makes up the collecting tubules (late distal tubule) And the dollecting ducts?
Cuboidal cells (principle - light, intercalated - dark)
Distinct cell borders
What are the collecting tubules (late distal tubule)? What is the structure and function?
Transitional segment between the nephron and the collecting duct.
Anti-diuretic hormone (ADH) dependent segment where Na+ is reabsorbed and K+ is sescreted.
Epithelium contains principal cells.
What are the componants of hte juxtaglomerular apparatus (JG)?
Renin-producing JG cells: specialized SMCs in the wall of the afferent arteriole.
Extraglomerular mesangial (lactis) cells: connected to JG cels via gap junctions
Macular densa: columnar cells of the DCT that detect Na and Cl concentration for the JG cells, resulting in alterations of the filtration rate and auto-regulation of blood volume via the RAA system.
What are the three layers of the calyces, pelvis, and ureters?
- Mucosa: transitional (uro)epithelium; lamina propria contains abundant elastic tissue
- Muscularis: smooth muscle. ~2 layers in the upper 2/3 of the ureter, 3 layers in the lower 1/3
- Adventitia - fibrous connective tissue
What is the cellular structure of the urinary bladder?
Transitional epithelium
- appears pseudostratified when empty
- appears stratified when filled
3 layers of smooth muscle.
How does the urethra differ in men and women?
Men:
- 15-20 cm, 3 parts (prostatic, membranous, and penile)
- Transitional - pseudostratified squamous epithelium
- Shared urinary and reproductive systems
Women:
- 3-5 cm
- Transitional - pseudostratified squamous epithelium
- Urinary system only
What is the cell type, lumen characteristics, cell borders, nuclei location, cytoplasmic staining in the proximal tubule?
Cell type: cuboidal
Lumen: occluded
Cell borders: indistinct
Nuclei: few, basally located
Cytoplasmic staining: eosinophilic granular
What is the cell type, lumen characteristics, cell borders, nuclei location, cytoplasmic staining in the distal tubule?
Cell type: cuboidal
Lumen: open, wide, smooth contour
Cell borders: indistinct
Nuclei: many, centrally located
Cytoplasmic staining: pale
What is the cell type, lumen characteristics, cell borders, nuclei location, cytoplasmic staining in the collecting duct?
Cell type: cuboidal to columnar
Lumen: open, scalloped edge because cells buldge inward
Cell borders: distinct
Nuclei: many, centrally located
Cytoplasmic staining: pale
How are the collecting tubules distinguished from proximal tubules and distal tubules?
By their large lumens and the distinct borders between adjacent cells:
- cuboidal to columnar cells have pale cytoplasmic staining and centrally located nuclei
- lumen will have scalloped edges because apical lumen buldges into the lumen
What are the three tunics of the ureter? Describe the middle layer in the upper 2/3 of the ureter?
Mucosa, muscularis, and adventitia.
In the upper 2/3 of the ureter, the muscularis layer has an inner longitudinal layer and an outer circular layer.
- Another outer longitudinal layer is present int he bottom 1/3 of the ureter (so it goes longitudinal-circular-longitudinal)
This is the opposite arrangement to what is found in the tubular organs of the GI tract.
Because the bladder is a saccular organ, it has ___ layers of smooth muscle in its wall.
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