Urinary Histology Flashcards
What is the kidney composed of?
Hilum
Renal sinus
Capsule
Cortex
Medulla
Minor calyx
Major calyx
Kidney lobe
Kidney lobule
Uriniferous Tubule = Nephron + Collecting duct
What is the hilum?
A depression in the kidney’s concave surface that is the main inlet/outlet for all the tubes
Opens into renal sinus
Where vessels, nerves, and ureter pass into or leave the kidney
Renal pelvis in the expanded, proximal end of the ureter
What is the renal sinus?
Fat filled cavity enclosing the renal artery(ies), veins, and lymph vessels
Encloses the ureter and nerve fibers
What are the inner and outer layers of the capsule of the kidney?
Outer layer - collagen and fibroblasts
Inner layer - collagen and myofibroblasts
What is the cortex?
Outer region of the kidney
90-95% of blood flowing through the kidney is in the cortex where it is filtered through the glomeruli
What does the cortex consist of?
Consists of alternating regions of cortical labyrinth and medullary rays
What does the cortical labyrinth contain?
Renal corpuscles
Convoluted tubules (PCT, DCTS)
Connecting tubules
“Curly” structures
What does the medullary rays contain?
Medullary tissue that extends from the base of the pyramid into the cortex and consists of
Straight tubules (proximal and distal)
Collecting ducts
What is the medulla?
Inner region of the kidney
5-10% of blood flowing through the kidney is in the medulla and consists of renal pyramids and renal columns
What are renal pyramids?
Within medulla
8-18 per kidney
Apex (renal papilla) - area cribrosa that consists on about 20 openings of the papillary ducts (of Bellini). Projects and empties into minor calyx
Base at corticomedullary border
What are the renal columns of Bertin?
Peninsulas of cortical tissues that are in medulla
Consists of straight tubules and collecting ducts
What is the minor calyx?
Receives urine from one renal pyramid
What is the major calyx?
Receives urine from multiple minor calices
What is the kidney lobe?
Human kidney is multi-lobar ad consists of:
Renal pyramid (number of pyramids = number of lobes)
Associated renal columns
Associated cortical tissue at the base of the pyramid
What is the kidney lobule?
Consists of central medullary ray and surrounding cortical tissue
Each lobule contains:
a collecting duct and all nephrons that empty into the collecting duct
What is the uriniferous tubule?
Nephron + Collecting Duct
Consists of epithelium and is covered by basal lamina on its exterior, includes the papillary ducts
What is the nephron and what is it composed of?
Structural and functional unit of the kidney
Composed of:
Renal corpuscle
Glomerulus
Bowman’s Capsule
Bowman’s Space
Vascular Pole
Urinary Pole
Filtration barrier
Proxima Tubule
Distal Tubule
Connecting Tubules
What brings blood in and out of renal corpuscle and what does fluid diffuse into?
Afferent arteriole bring blood to capillary bed (larger lumen)
Efferent arteriole takes blood away (smaller lumen)
Fluid diffuses out of the capillary system into the urinary space
What is the glomerulus?
Cluster of fenestrated capillaries
Surrounded by Bowman’s capsule
Ultrafiltrate oozes out of the glomerulus by passing through the filtration barrier
What is Bowman’s Capsule and what doe sit consist of?
Proximal end of the nephron
Visceral layer of capsule - covers capsule and is made of podocytes and pedicels. Filtration slits covered by diaphragm made of nephrin
Parietal layer - simple squamous epithelium, covered by basal lamina
What is Bowman’s space?
Urinary space
Space between visceral and parietal layers of Bowman’s capsule
Contains ultrafiltrate
What is the vascular pole?
Site where afferent glomerular arteriole enters the renal corpuscle and site where efferent glomerular arteriole leaves the renal corpuscle
What is the urinary pole?
Contains the initial part of proximal convoluted tubule (PCT)
What is the filtration barrier?
Consists of endothelial surface layer of glomerular capillaries
Fenestrated endothelium of glomerular capillary
Basal lamina
Subpodocyte space
Visceral layer of Bowman’s capsule
What is part of the proximal tubule?
Proximal Convoluted Tubule
Proximal Straight Tubule
Thin Limbs of the Loop of Henle
What is the structure of the proximal convoluted tubule?
Composed of simple cuboidal epithelium
Intensely acidophilic
Contains microvilli
What is the structure of the proximal straight tubule?
Thick descending limb of the loop of Henle
Similar to PCT
What are the thin limbs of the loop of Henle?
Includes thin descending limb, Henle’s loop, and thin ascending limb (lined with simple squamous epithelium)
What is part of distal tubule?
Distal Straight Tubule
Macula Densa
Distal Convoluted Tubule
What is the structure of the distal straight tubule?
=Thick ascending limb of the Loop of Henle
Low cuboidal epithelium with few microvilli
More mitochondria than cells of PCT
Similar to DCT
What is the macula densa?
Modified segment of the distal tubule located next to the afferent arteriole, between afferent and efferent arterioles
What is the structure of the distal convoluted tubule?
Much shorter and less tortuous than the PCT
Wide, clear lumen
Smaller cells, more cells
What is the cortical collecting duct?
Part of uriniferous tubules but not the nephron
DCT empties into a connecting tubule that drains into a cortical collecting duct or a medullary collecting duct
What is the Papillary Ducts of Bellini?
Continuation of the medullary collecting ducts
Open in the area cribrosa
Lined with tall columnar epithelium
What does the Juxtaglomerular Apparatus consist of and control?
Consists of the macula densa, the JG cells, and the extraglomerular mesangial cells
Controls blood pressure by activating the renin-angiotensin-aldosterone system
What are the JG cells?
Cells of the afferent glomerular arteriole
Modified smooth muscle cells in the tunica media of the afferent glomerular arteriole
Contain renin
What are the extraglomerular mesangial cells?
Reside in the interval bordered by the afferent arteriole, maculas densa, efferent arteriole, and the vascular pole of the renal corpuscle
Cells play a role in blood pressure regulation
What is the renal interstitium?
Contains a small amount of connective tissue, fibroblasts, macrophages
What is the blood supply of the kidney?
Renal artery
Anterior and posterior division
Segmental arteries
Lobar arteries
Interlobar arteries
Arcuate arteries
Interlobar arteries
Afferent glomerular arteries
What occurs to the macula dense if there is a drop in blood pressure and sodium concentration or filtrate volume falls too low?
- Causes dilation of the afferent glomerular arterioles, increasing blood flow into the glomerulus
- Instructs the juxtoglomerular cells to release renin
What occurs when blood pressure falls too low and renin is released?
Renin converts angiotensin to angiotensin 1 (mild vasoconstrictor)
Angiotensin converting enzyme (ACE) converts angiotensin 1 to angiotensin 2
Angiotensin 2 increases blood pressure
How does Angiotensin 2 increase blood pressure?
Potent systemic vasoconstrictor
Increases thirst
Synthesis and release of aldosterone (resorbs NaCl)
Release of ADH - resorbs water from the lumen of CT
Inhibits renin release - feedback inhibition
Release of prostaglandins - targeted vasodilation of afferent glomerular arteriole
What lines the minor calices, major calices, ureter, urinary bladder, and proximal segment of the urethra?
Transitional epithelium
What is the uroepithelium facing the lumen coated in?
Rigid urothelial plaques with hinge regions between them
Plaques consists of uroplakins, transmembrane proteins that with tight junction make an impermeable barrier on surface of urothelium
What is the structure of the major and minor calices and renal pelvis?
Minor Calyx- covered by transitional epithelium, lamina propria, and smooth muscle layer
Major Calyx - receives urine from minor calices, same structure as minor
Renal pelvis is similar structure
What is the ureter and its layers?
Delivers urine to the urinary bladder via peristaltic waves produced by the muscular layers of the ureter
Composed of:
Mucosa - contains folds when ureter empty, transitional epith, basal lamina, lamina propria with dense irregular fibroelastic CT
Muscularis - upper 2/3 has an outer circular layer and inner longitudinal. lower 1/3 has an extra longitudinal layer, middle circular, inner longitudinal
Fibrous CT covering
What are the layers of the urinary bladder?
Mucosa - has folds when empty, transitional epith, lamina propria with superificial (dense irreg collag CT) and deep layer (loose layer of collager and elastic fiber CT)
Muscularis - 3 layers of smooth muscle, middle layer forms internal sphincter
Adventitia - dense irregular collagenous CT, elastic fibers
Serosa - covers part of bladder
What are the layers of the female urethra?
Mucosa - transitional epith near bladder. rest is stratified squamous nonkeratinized, lamina propria is fibroelastic with glands of Littre
Muscularis - inner longitudinal layer and outer circular
External urethral sphincter - skeletal muscle where urethra comes through the UG diaphragm
What are the layers of the male urethra?
Prostatic urethra - in prostate, transitional epith
Membranous urethra - through UG diaphragm, lined by stratified columnar epithelium
Spongy urethra - through corpus spongiosum, most lined by pseudostratified columnar epithelium with stratified squamous nonkeratinized near glans
Lamina propria - loose fibroelastic tissue, vascular, glands of Littre
Muscularis:
Prostatic + Membranous have two layers of smooth muscle, inner long and outer circ
Muscularis of membranous urethra surrounded by external urethral sphincter
Spongy urethra has 3 layers - inner long, middle circ, outer long
