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The right one looks like Napoleon's hat, while the left is a crescent moon. Each is surrounded by a thin fibrous capsule. Each gets flow from three named arteries which combine into a subcapsular plexus. The weight of the combined adrenal (suprarenal) glands is correctly given by Junqueira as 8 gm (4 gm each). You'll seldom see this. Only if a person's died without a few preceding stressful days (illness, crisis preceding homicide or suicide) will they be non-hyperplastic, which is why the older books give a heavier "normal" weight. The actual colors are:
zona glomerulosa and fascicula: bright yellow
zona reticularis: yellow-brown
medulla: pearly gray (NOT red-brown)
As you also know, the cortex comes from mesoderm, while the medulla comes from ectoderm (since it's really neurons). As in all endocrine glands, every business cell abuts a capillary. A few arteries ("medullary arteries") pierce through the cortex before they break up into capillaries, while most of them ("cortical arteries") break up into capillaries in the cortex and then penetrate the medulla. Most of the blood leaving the adrenal is by way of the single enormous vein ("athlete's vein", adrenalin) that passes across-and-out-of the medulla of each.
The cortex makes steroid hormones on demand, and secretes them into the bloodstream without any storage granules. It has three layers, which you can remember easily:
zona glomerulosa cells in clusters salt
zona fasciculata cells in cords sugar
zona reticularis cells in a network sex
"The deeper you go, the sweeter it gets." You can usually distinguish them microscopically by the arrangement of the cells, which is determined by their capillaries, i.e., the capillaries surround the clusters, run alongside the cords, and form a network within the network. Of these, the fasciculata is usually the thickest.
The zona glomerulosa is considered responsible for making aldosterone (your great mineralocorticoid, for hanging onto sodium and wasting potassium) under the influence of ACTH (corticotropin), angiotensin II, and probably a third yet-unknown hormone (I'll tell you why I believe this in "Path").
The zona fasciculata has cords ("fascicles" means "bundles", ask Mussolini or anyone using the word "fascist" in contemporary rhetoric) one or two cells thick ("can't be three, each cell needs to be adjacent to a capillary"). Glucocorticoids (cortisol mostly) are made here; you'll learn what these do elsewhere. The cytoplasm may or may not match Junqueira's description of lipid-(steroid-)laden, foamy-appearing. You can generally see the cell borders here, which is unusual for most organs.
The zona reticularis features cells in a sponge-like or net-like arrangement, and these cells have lots of lipofuscin for some reason. The zona reticularis is credited with producing dehydroepiandrosterone, a sex hormone that works much like testosterone, and is responsible for women's body-hair and libidos. Junqueira calls this "a negligible physiologic effect under normal conditions" (uh huh...) Dehydroepiandrosterone is the stuff that old guys are likely to be routinely supplemented with in the next few decades, and you can get it without a 'scrip from ads in workout magazines. Also unlike testosterone, the breakdown products don't contribute their distinctive musk to guy's-armpit-smell (which is women never get as stinky, qualitatively or quantitatively, as us men). Where the medulla isn't present (i.e., in the wings of the adrenals), reticularis folds over onto reticularis.
Not testable: Probably both reticularis and fasciculata make both glucocorticoids and sex steroids. As you get older, the cortex tends to acquire little bumps of endocrine cells. Bone marrow hamartomas are common here too.
The fetal ("provisional") zone, big liver-like cells present in the unborn child and the newborn, makes sex steroids that support the pregnancy. Nobody knows much about this, and anencephalic babies (who lack useful pituitary glands) lack this layer but get born anyway.
The medulla is a typical endocrine organ composed of clusters or cords of modified postganglionic sympathetic neurons ("pheochromocytes"). It's in direct contact with the zona reticularis, with no fibrous capsule of its own. Don't expect to be able to recognize it without a big hint or two (remember there's a huge vein down its middle.) The cells have uneven cytoplasm, variably blue, purple, pink, and/or vacuolated, and contain either epinephrine or norepinephrine in neurosecretory granules (150-350 nanometers); the granules also contain some enzymes and support proteins (notably "chromogranin"). Epinephrine granules are smaller than norepinephrine granules and stain paler for electron microscopy). They release their products just like neurons do, only into the blood rather than onto other excitable membranes. And they do so in response to stimulation from their cholinergic preganglionic sympathetic fibers. When you drop medulla into the old-fashioned chromic-acid-based tissues, the catecholamines the tissue brown ("chromaffin reaction"; "pheochromo-" means "ugly color"). "Sustentacular cells" (modified glia) supporting the pheochromocytes are undiscernible on H&E sections but can be seen with S100 staining.
If the kidney never forms, of course, the adrenal will be round. Nearby any adrenal, there will be some fat (often there's some brown, even in a grown-up). Here you may also see protruding and/or ectopic bits of cortex; you'll see the normal layers. Sometimes the capsules don't form quite right and some or all of the adrenal ends up under the renal or hepatic capsule or adjacent to the testis or ovary (which after all descended from here). There are bits of medulla at the origins of the great mesenteric arteries ("the organ of Zuckerkandl"; "extra-adrenal chromaffin tissue", etc., etc.)
Endocrine disease is easy to miss, but easy to treat IF you discover it!
Cortical hypofunction: Addison's disease and variants. Poor appetite, headache, malaise, and "psychiatric symptoms" are likely to precede the giveaway findings (hyperkalemia, others) by years, and there is a distressing tendency to drop over dead at times of slight stress.
Mineralocorticoid excess: Conn's syndrome and variants. High blood pressure, with an distressing tendency to drop dead when given potassium-wasting diuretics.
Glucocorticoid excess: Hungry, weight gain, diabetes, hypertension, infections, osteoporosis, weird mood swings, and a distressing tendency to commit suicide.
Adrenal androgen excess: Makes little girls into little boys, and little boys into little men. Makes grown women hairy and infertile. Gets missed, believe it or not.
Catecholamine excess: "Pheochromocytoma". Headaches, mood swings, labile hypertension, and a distressing tendency to be sent to psychiatrists until they die of brain hemorrhages.
15034 ADRENAL, NORMAL
15035 ADRENAL GLAND (ZONES), NORMAL
15036 ADRENAL GLAND (ZONES), NORMAL
15037 ADRENAL GLAND (CORTEX), NORMAL
15038 ADRENAL GLAND (CORTEX), NORMAL
15039 ADRENAL GLAND (CORTEX), NORMAL
15040 ADRENAL GLAND (CORTEX), NORMAL
15041 ADRENAL GLAND (CORTEX, LIPID STAIN)
15042 ADRENAL GLAND (CORTEX, LIPID STAIN)
15043 ADRENAL GLAND (MEDULLA), NORMAL
15044 ADRENAL GLAND (MEDULLA), NORMAL
15045 ADRENAL GLAND (MEDULLA, CHROMAFFIN STAIN)
15046 ADRENAL GLAND (MEDULLA, CHROMAFFIN STAIN)
15047 ADRENAL MEDULLA (CENTRAL VEIN), NORMAL
20701 ADRENAL GLAND WITH LAYERS LABELED
20702 ADRENAL GLAND WITH LAYERS LABELED
20703 ADRENAL GLAND WITH LAYERS LABELED
20704 ADRENAL GLAND WITH LAYERS LABELED
20705 ADRENAL GLAND, MEDULLA, NORMAL
20976 ADRENAL
20977 ADRENAL, GLOMERULOSA LAYER
20978 ADRENAL, FASCICULATA LAYER
20979 ADRENAL, RETICULARIS LAYER
20980 ADRENAL, MEDULLA
20981 ADRENAL, FASCICULATA
24712 ADRENAL, NORMAL
25393 ADRENAL CORTEX
48649 ADRENAL
48650 ADRENAL
In addition to its primary function of controlling extracellular fluid electrolyte composition and pH to allow excitable membranes (heart, brain) to continue to function, the kidney also makes the hormones renin (REE-nin, in spite of what anybody else might have told you), erythropoietin, and (not listed in Junqueira) calcitriol, the activated form of vitamin D.
In the unborn and newborn child, the kidney is still "under construction". Don't worry about the histology of "blastema", "the nephrogenic zone", little forming glomeruli, and so forth.
You probably know the gross anatomy of the kidneys. Easiest to forget: renal lobe is the mass of cortex drained by one pyramid-and-calyx (there are 8-18 in a normal kidney), renal lobule is the mass of cortex drained by one medullary ray (the "renal lobule" is a non-anatomic and non-functional, i.e., worthless concept), and the columns of Bertin are a just the masses of cortex of two lobes back-to-back because they curved around the pyramid. (Lobes at the superior and inferior renal poles may be incompletely separated, i.e., no columns of Bertin). Ignore anything anybody may tell you about subdivisions (gross or microscopic) of the medulla; they're real, but not worth knowing. Each kidney has about 1.4 million nephrons (howler in Junqueira "1-4 million"), and Junqueira's term uriniferous tubule for one nephron plus its (shared) collecting duct is artificial and I doubt you'll hear it again. The capsule around each kidney is tough, fibrous, and pain-sensitive.
You aren't going to understand what follows unless you know it already and/or focus on the pictures. Each kidney is perfused by one renal artery (sometimes paired), which branches extensively, first into the interlobar arteries between the pyramids, then the arcuate arteries at the corticomedullary junction, then the interlobular arteries within the cortex. From the interlobular arteries sprout a succession of afferent arterioles, which break up into a tuft (glomerulus; "renal corpuscle", 200 microns across) of 50-or-so glomerular capillaries (grouped into lobules of about ten each). These come back together while the pressure's still reasonably high to make the efferent arterioles. These quickly branch into the peritubular capillary network around the rest of the nephron, and if this is a nephron that sends a medullary loop down-and-back, a side branch will be the vasa recta. The capillaries join into venules which lead to the anastomosing stellate veins, which then empty into interlobular veins and follow the courses of those arteries. There must be no collateral circulation between arteries prior to reaching the glomeruli, or between individual nephrons (why not?) Lymphatics and nerves (sympathetic nerves for the renal parenchyma) follow the arterial supply.
The glomerulus also includes a sphere of simple squamous cells (parietal epithelium) which with their outer basement membrane are called Bowman's capsule which invest the capillaries. The afferent arteriole enters, and the efferent arteriole leaves, at the vascular pole of the glomerulus. The proximal convoluted tubule leaves at the urinary pole, which may be near the vascular pole or remote from it. The capillaries are surrounded, on the side of their basement membranes opposite their endothelium, by one-cell-thick layer of bizarre-looking epithelial cells called podocytes, or visceral epithelium. (Junqueira is unusual in considering these also to be part of Bowman's capsule.) The tubule, parietal epithelium, and visceral epithelium are all continuous. Each podocyte has several primary processes, from which sprout lots of secondary processes or pedicels, or foot processes, named because they look so much like fingers. Yeah. These encircle the capillaries, with fingers from adjacent podocytes interdigitating alternately and neatly. Each podocyte, in turn, may embrace more than one capillary. The spaces between the fingers are called filtration slits, 25 nanometers or so wide, and the slits are filled in turn with a thin membrane (5 nanometers, the "diaphragm") containing lots of holes (i.e., it's another chicken wire structure). Podocytes actually contain some actin, which makes them contractile, and are probably able to squeeze the capillaries shut or allow them to open. The glomerular basement membrane is only about 1/10 of a micron thick, but you can usually just distinguish it on photos since it's like a thin ribbon seen at an angle in sections which are usually 2-4 microns thick. Both endothelium and epithelium contribute to it. The "lamina dense" with a "lamina rara" on each side probably result from the tissue being tossed into fixative. The basement membrane is made mostly of type IV collagen and laminin with a generous admixture of heparan sulfate, the strongly-negatively-charged polyanion (charge barrier) which keeps (negatively-charged) albumin in the bloodstream. The endothelial cells feature huge (80 nanometers) fenestrae in a very thin cytoplasm. Between groups of capillaries, the mesangial cells (modified pericytes) sit surrounded by mesangial matrix which is the same stuff as basement membrane. These cells are phagocytic, have well-defined contractile actin-myosin equipment (Junqueira doesn't tell you, but they're famous for responding to atrial natriuretic factor, opening and closing capillaries), and probably do other stuff, and they send cytoplasmic processes up to and sometimes into the basement membrane around the capillaries; contrary to Junqueira, I've never seen or heard credible account of them "penetrating between endothelial cells to reach the lumen" in health, though they may do so in disease.
The proximal convoluted tubule is quite long, and a majority of cortical tubules in a random section will be proximal rather than distal. Their cytoplasm is cuboidal, with microvilli on their luminal side (for greater absorptive area), lots of mitochondria, lateral margins very interdigitated (to prevent leaks, I guess; this makes them look like tree stumps complete with the upper portions of roots), and an infolded membrane on their bottoms (because of the interdigitations). There are canaliculi at the bases of the microvilli to enable to proximal tubular cells to resorb the protein that does leak into the tubule, with their tips pinching off to produce pinocytotic vesicles (no, I don't know how the canaliculi know how to do this). These vesicles then fuse with lysosomes and the proteins (and whatever else) gets hydrolyzed. You probably already know that the proximal tubule reabsorbs, from the glomerular filtrate, the little molecules that you want to keep. With all the convolutions of the tubules in the cortex, you'll hear it called the "cortical labyrinth".
When the convoluted portion of the proximal tubule's completed, it dips down into the medulla and then returns to the cortex. This is "Henle's loop", for maintaining the medullary hypertonicity which is required for concentrating the urine. The basic loop has a thick descending limb (maybe; this is described by Junqueira but not by anybody else; most folks probably consider this part of the proximal tubule), a thin descending limb, a thin ascending limb, and a thick ascending portion. The ascendingand descending portions are called the two limbs. In the thin portions, the lumen is narrow (maybe 12 microns) and the cells are simple-squamous. Six-sevenths of nephrons are cortical nephrons (short-looped nephrons), which have only a tiny bit of thin descending limb, and no thin ascending limb, and which barely make it into the medulla. The other seventh are juxtamedullary nephrons (long-looped nephrons), which have full, long Henle's loops, and go deep into the medulla. Physiology: The thin descending limb is permeable to water but not to sodium chloride, the thin ascending limb is permeable to sodium chloride but not to water, and the thick ascending portion pumps sodium chloride into the interstitium and is of course impermeable to water. However it exactly works, the end result is to establish a gradient of hypertonicity within the medulla, with the papillary area the most hypertonic.
The distal convoluted tubule is easy to distinguish from its proximal counterpart, since its cells (which do much less) are smaller, lack a brush border (no microvilli or canaliculi), and have less active nuclei. This part of the nephron maintains sodium and potassium balance. The distal convoluted tubule joins its glomerulus of origin at its vascular pole.
The distal convoluted tubules join into anastomosing collecting tubules ("connecting tubules") which join to form collecting ducts (the ducts, though not the tubules, arise from the ureteric bud; hopefully you'll never hear them called the "papillary ducts of Bellini" again), which return through the medulla to reach the renal papillae, where they make a sieve-like area ("area cribrosa", 20-70 holes). The collecting tubules help out with bicarbonate balance. The proximal portions of the collecting ducts help out with potassium and pH balance. The distal collecting duct apparatus is where water, without salt, can be reabsorbed when hADH is in the bloodstream. The cytoplasm of all collecting duct cells stains very pale, and you can actually see the cell borders for once. You don't need to know about different cell subtypes in the ducts.
The interstitium, or stuff between the tubules, is inconspicuous in the cortex but prominent in the medulla. (Not testable, but a fun mystery: The medulla contains star-shaped lipid-laden cells in rows. They almost certainly produce a hormone which lowers blood pressure but which has escaped identification so far.)
Glomeruli: Cortical labyrinth
Convoluted portion of proximal tubule: Cortical labyrinth
Straight portion of proximal tubule: Medullary ray
Thick descending portion of loop: Medulla (Junqueira's the only authority describes this structure)
Thin descending portion of loop: Medulla
Thin ascending portion of loop: Medulla (only exists in juxtamedullary glomeruli)
Thick ascending portion of loop: Medulla
Straight portion of distal tubule: Medullary ray
Convoluted portion of distal tubule: Cortical labyrinth
Connecting tubules: Cortical labyrinth
Collecting ducts: Medullary ray and medulla
Any more-detailed breakdown should be ignored.
The juxtaglomerular apparatus is a physiologist's nightmare located at the vascular pole of the kidney. The smooth muscle cells of the afferent arteriole acquire PAS-positive granules full of renin, which they release if they sense low blood pressure or get certain other signals. The macula densa is a group of cells in the distal tubule which have very little cytoplasm (i.e., the nuclei are packed dense), because they're involved in sensing and reporting chloride ion concentration in the urine rather than sodium-pumping. The pole-cushion cells are mesangial cells at the vascular pole, and nobody knows what they do. (Not testable: they are also called "polkissen", "lacis" or "Goormaghtigh" cells.) You'll study this stuff in physiology; our understanding of all renal physiology remains incomplete.
Not testable, but worth knowing: In spite of Junqueira's silence, the key regulator of total-body water volume is probably atrial natriuretic peptide, produced when the right atrium feels some extra stretch.
03455 RENAL TUBULES COMPOSITE OF MICRO
03458 RENAL TUBULES COMPOSITE OF MICRO
11843 NEPHRON, MODEL
11844 NEPHRON, CLOSEUP, MODEL
11846 GLOMERULUS, RENAL, MODEL
11847 GLOMERULUS, CLOSEUP, MODEL
11850 KIDNEY, GROSS MODEL
11851 KIDNEY, CLOSEUP, MODEL
11852 KIDNEY, CLOSEUP, MODEL
11868 URINARY SYSTEM, MALE, MODEL
11870 KIDNEY AND URETERS, MODEL
11871 BLADDER, PROSTATE AND PENIS, MODEL
11872 URINARY AND REPRODUCTIVE, MALE, MODEL
11873 BLADDER AND URETHRA, MODEL
14919 KIDNEY, CORTEX & MEDULLA, NORMAL
14920 KIDNEY, CORTEX & MEDULLA, NORMAL
14921 KIDNEY, CORTEX & MEDULLA, NORMAL
14922 KIDNEY, CORTEX & MEDULLA, NORMAL
14923 KIDNEY, CORTEX, NORMAL
14924 KIDNEY, CORTEX, NORMAL
14925 KIDNEY CORTEX, (GLOMERULUS), NORMAL
14926 KIDNEY CORTEX, (GLOMERULUS), NORMAL
14927 KIDNEY, TUBULES (DISTAL & PROXIMAL)
14928 KIDNEY, TUBULES (DISTAL & PROXIMAL)
14929 KIDNEY, MEDULLA (COLLECTING TUBULES)
14930 KIDNEY, MEDULLA (COLLECTING TUBULES)
14931 KIDNEY, MEDULLA COLLECTING DUCT, NORMAL
14932 KIDNEY, MEDULLA COLLECTING DUCT, NORMAL
14933 JUXTAGLOMERULAR APPARATUS
14934 JUXTAGLOMERULAR APPARATUS, KIDNEY
14935 GLOMERULUS, (VASCULAR POLE), NORMAL
14936 GLOMERULUS, (VASCULAR POLE), NORMAL
15316 KIDNEY, CORTEX, NORMAL
15317 KIDNEY, MEDULLA, NORMAL
15318 KIDNEY, PAPILLA, AREA CRIBROSA, NORMAL
15319 KIDNEY, MEDULLARY RAY, NORMAL
15320 KIDNEY, MEDULLA, DISTAL AND COLLECTING, NORMAL
15321 KIDNEY, MACULA DENSA AND DISTAL TUBULE, NORMAL
15322 KIDNEY, AREA CRIBROSA, NORMAL
15323 KIDNEY, MEDULLARY RAY, NORMAL
15324 KIDNEY, CORTEX, MEDULLARY RAY, NORMAL
16657 KIDNEY, NORMAL
16726 KIDNEY, CORTEX HISTOLOGY, NORMAL
16729 GLOMERULUS, NORMAL
16730 GLOMERULUS, NORMAL
16743 GLOMERULUS, MESANGIUM, NORMAL
16748 GLOMERULUS, NORMAL
16955 KIDNEY, FETAL
16956 KIDNEY, FETAL
16957 KIDNEY, NEWBORN, PREMATURE
16958 KIDNEY, NEWBORN DEEP CORTEX
17149 KIDNEY, NORMAL
17150 KIDNEY, NORMAL
17258 BASEMENT MEMBRANES, KIDNEY
17335 KIDNEY, PARENCHYMA INTERSTITIUM
17534 KIDNEY, NORMAL
17576 KIDNEY, NORMAL REGION OF TUBULES
20924 KIDNEY, PAPILLA
20925 KIDNEY, MEDULLARY RAY
20926 KIDNEY, COLLECTING DUCT
20927 KIDNEY, DISTAL TUBULE
20928 THICK LOOP OF HENLE, KIDNEY
20929 KIDNEY, COLLECTING DUCT
20932 KIDNEY, MACULA DENSA
20933 KIDNEY, PARIETAL CELLS
20934 KIDNEY, PROXIMAL TUBULE
20935 KIDNEY, DISTAL TUBULE
20936 KIDNEY, COLLECTING DUCT
20937 KIDNEY, PROXIMAL TUBULE
20938 KIDNEY, DISTAL TUBULE
24033 KIDNEY, EMBRYONAL
29587 KIDNEY, NORMAL BIOPSY
34175 NORMAL GLOMERULUS, RETICULIN STAIN
39473 GLOMERULUS, NORMAL
44345 RENAL CORPUSCLE, GLOMERULUS
44346 RENAL CORPUSCLE, URINARY SPACE
44347 RENAL CORPUSCLE, BOWMAN'S SPACE
44348 RENAL CORPUSCLE, D=BOWMAN'S SPACE
44384 PELVIS, RENAL, KIDNEY
44385 PELVIS, RENAL, KIDNEY
44386 PELVIS, RENAL, KIDNEY
44387 RENAL PAPILLA, KIDNEY
44388 RENAL CORTEX, AFFERENT ARTERIOLE
44389 RENAL CORTEX, AFFERENT ARTERIOLE
44390 ARTERIOLE, AFFERENT RENAL
44391 ARTERIOLE, AFFERENT RENAL
44392 RENAL CORPUSCLE, AFFERENT ARTERIOLE
44393 RENAL CORPUSCLE, AFFERENT ARTERIOLE
44394 RENAL CORPUSCLE, AFFERENT ARTERIOLE
44395 RENAL CORPUSCLE, AFFERENT ARTERIOLE
44396 RENAL CORPUSCLE, MACULA DENSA, DISTAL TUBULE
44397 RENAL CORPUSCLE, MACULA DENSA, DISTAL TUBULE
44398 RENAL CORPUSCLE,THIN SECTION DISTAL TUBULE
44399 RENAL CORPUSCLE,THIN SECTION DISTAL TUBULE
45163 KIDNEY, MEDULLA, PYRAMID
45165 KIDNEY, MEDULLA, PYRAMID
45167 KIDNEY, MEDULLA, PYRAMID
45169 KIDNEY, MEDULLA, PYRAMID
46306 DIABETES, (TUBULAR GLYCOGEN)
47748 KIDNEY, RIGHT, CORONAL SECTION MODEL,
47749 KIDNEY, RIGHT, ADRENAL GLAND, MODEL,
47755 KIDNEY, MODEL, RIGHT, CORONAL SECTION, NEPHRON
47765 RENAL PYRAMID, MODEL, CLOSE-UP
47790 RENAL ARTERY AND BRANCHES, LATEX, DOG, URETER
48623 KIDNEY, MEDULLA
48624 KIDNEY, MEDULLA
48625 KIDNEY, MEDULLA
50410 KIDNEY, CROSS-SECTION, MODEL
50411 KIDNEY, CROSS-SECTION, MODEL
50412 KIDNEY, CROSS-SECTION, MODEL
50413 KIDNEY, CROSS-SECTION, NEPHRON MODEL
50414 KIDNEY, CROSS-SECTION, NEPHRON, CLOSEUP, MODEL
50421 KIDNEY, GLOMERULUS WITH SILVER STAIN, NORMAL
50426 KIDNEY, GLOMERULI, NORMAL
50427 KIDNEY, CORTEX WITH GLOMERULI, NORMAL
The renal pelvis (including the calyces), ureters, and bladder all have their inner mucosal surfaces covered with transitional epithelium, named because it appears to change from a two-layer stratified epithelium to an eight-layer stratified epithelium during the few seconds it takes to empty your bladder. In the empty bladder, the superficial cells are big and rounded, while in the full bladder, they are flattened and squamous. The term "umbrella cell" is apt. Older histology books describe a preposterous, obviously false mechanism by which transitional cells detach and reattach from each other as the organs fill and empty, changing the number of layers. What's actually happening, of course, is that most or all of these cells actually touch the basement membrane, the "layers" are merely nuclei at varying levels, and "transitional epithelium" is actually a subtype of pseudostratified epithelium. Transitional epithelium surface cells feature curious thickenings of the walls ("plates") which reinforce the osmotic barrier. (These slip into invaginations in the cell when the bladder empties.)
Here's how the smooth muscle is arranged in these organs:
Renal pelvis: Spirals
Ureter: Spirals; some people will tell you "three layers, the middle circular, the inner and outer longitudinal"; I could never see these
Ureter, within the bladder wall: Longitudinal only
Bladder: Crisscross, all directions ("the detrusor muscle")
Bladder neck: Three layers, the inner and outer longitudinal, the middle circular
Urethra: Both longitudinal layers continue to the bottom of a man's prostate, and the end of a woman's urethra; this is "the involuntary urethral sphincter"
A woman's urethra is lined mostly by stratified squamous epithelium, with perhaps some pseudostratified columnar and/or something else reasonable. The voluntary (external) sphincter is, of course, skeletal muscle. A man's urethra is divided into four portions. The prostatic urethra is lined by transitional epithelium, and has the verumontanum and its utricle on its backside, and the openings of the ejaculatory ducts on either side. The membranous urethra is lined by pseudostratified columnar and/or stratified squamous is surrounded by the voluntary (external) sphincter of skeletal muscle. The bulbous urethra and pendulous urethra, in the corpus spongiosum, are both lined with variable epithelium, most likely to be stratified squamous as they proceed distally. ("Pendulous" means "the part that hangs", go figure.) Littre's glands are mucous glands (some with ducts, some just acini) along the length of the urethra, most abundant in the pendulous part; these provide the mucus droplet on the glans for lubrication during intromission.
11870 KIDNEY AND URETERS, MODEL
11871 BLADDER, PROSTATE AND PENIS, MODEL
11873 BLADDER AND URETHRA, MODEL
14937 URETER (CROSS SECTION), NORMAL
14938 URETER (CROSS SECTION), NORMAL
14939 URETER (EPITHELIUM), NORMAL
14940 URINARY BLADDER, NORMAL
14941 TRANSITIONAL EPITHELIUM, NORMAL
15032 URETHRA, NORMAL
15033 URETHRA, NORMAL
15108 URETER, NORMAL
15109 URETER, NORMAL
15111 URETER, NORMAL
15112 URETER, NORMAL
15113 BLADDER, URINARY, NORMAL
15114 BLADDER, URINARY, NORMAL
15119 BLADDER, URINARY, NORMAL
15120 BLADDER, URINARY, NORMAL
15122 BLADDER, URINARY, NORMAL
15325 URETER, NORMAL
15326 BLADDER, NORMAL
15327 BLADDER, NORMAL
20719 EPITHELIUM, TRANSITIONAL
20930 URETHRA
20931 URINARY BLADDER
25172 URETHRA, NORMAL
25174 URETHRA, NORMAL
25266 BLADDER, NORMAL
44384 PELVIS, RENAL, KIDNEY
44385 PELVIS, RENAL, KIDNEY
44386 PELVIS, RENAL, KIDNEY
44400 EPITHELIUM, TRANSITIONAL, URINARY BLADDER
44401 URETHRA, PENILE, CORPORA
44402 URETHRA, PENILE, CORPORA
45123 TRANSITIONAL EPITHELIUM, URINARY BLADDER
45125 TRANSITIONAL EPITHELIUM, URINARY BLADDER
45127 TRANSITIONAL EPITHELIUM, URINARY BLADDER
45129 TRANSITIONAL EPITHELIUM, URINARY BLADDER