Urinary System Flashcards
Kidney - gross anatomy
retro-peritoneal organ
no mesentery
in a thin CT capsule (thick in cat)
cortex is adjacent to the capsule - darker area of fresh kidney
Kidney - medulla
deep to kidney
divided into pyramidal areas
striated base next to cortex
apex projects into renal pelvis of unilobar kidney or into minor calyx in multilobar kidney
parts of uriniferous tubules
parts of blood vessels arranged in parallel running from base to apex and back to base –> striated appearance
Zonation - due to location of different types of tubules w/in specific areas of the medulla
Kidney - cortex
adjacent to capsule
darker area of fresh kidney
contains renal corpuscles and many tubules
Kidney lobe
medullary pyramid + adjacent cortex
Renal columns
cortical tissue b/t medullary pyramids
Unilobar/unipyramidal kidney
has a single pyramid
true unilobar kidneys - in rodents
most have secondarily fused cortical and medullary areas = begin development as multilobar structures - e.g. small ruminants, dog, horse
Multilobar/multipyramidal
Two types:
cortical parts of lobes are fused while medullary pyramids remain separate (pig and human)
Cattle - both cortical and medullary parts of lobes are distinctly separated
Capsule
dense collagen and elastic fibersi
smooth muscle in all but the cat
Stroma
sparse and little internal CT
Parenchyma
divided into cortex and medulla
Nephron
blind-ended tubule
associated with capillary loops of renal corpuscle
continuous with a collecting duct
collecting ducts and nephron loops are in parallel clusters and form and are part of the cortex
Consists of:
thick descending limb (of proximal tubule) - both convoluted and straight
thin segment - descending and ascending part
thick ascending limb - of distal tubule
Most domestic animals: majority of nephron loops are short (don’t extend into medulla)
Long loops from juxtamedullary nephrons extend far into medulla and produce hypertonic urine
Most spp have both types
Cats and dogs - only long loops
renal/uriniferous tubule
nephron + arched collecting duct
=functional unit of the kidney
Medullary ray
straight collecting duct forms the central axis of this
continuous with tubules in the medulla
Renal blood supply
~25% of CO at rest renal artery interlobar arteries arcuate arteries interlobular arteries afferent arterioles Efferent arterioles peritubular capillaries vasa recta
Renal artery
enters kidney at the hilus and gives rise to interlobar aa.
Interlobar aa.
located b/t pyramids in renal columns
Arcuate aa.
parallel to capsule at the cortico-medullary junction and give off interlobular aa.
Interlobular aa.
found between medullary rays.
may give rise to short intralobular aa.
Afferent arterioles
supply glomerular capillary loops
larger than efferent arteriole
Efferent arterioles
drain glomerular capillary loops
smaller than afferent arteriole
Peritubular capillaries
in cortex
arise from efferent arterioles of superficial and middle cortical nephrons
drained by stellate/deep cortical vv.
All p.t. capillaries are fenestrated
Vasa recta
long, straight vessels
arise from efferent arterioles of juxtamedullary nephrons
descend into medulla as arterioles and return as venules to the arcuate vv.
descending vasa recta give rise to peritubular capillaries of medulla
Arterial portal system
afferent arteriole –> glomerular capillaries –> efferent arteriole
Renal corpuscle
glomerulus + glomerular capsule filtering structure of the kidney 3 components: indented end of the nephron (glomerular/bowman's capsule) cluster of capillary loops (glomerulus) mesangial cells b/t capillary loops
Glomerulus
cluster of capillary loops and associated cells
can be synonymus with renal corpuscle
capillary loops are supplied by afferent arteriole and drained by an efferent arteriole (arterial portal system)
Vascular pole
where arterioles enter and leave the renal corpuscle
location of juxtaglomerular apparatus
Urinary pole
opposite vascular pole
glomerular capsule becomes continuous with tubular part of the nephron
glomerular capsule
double walled
parietal layer of squamous cells
Capsular/urinary space
Between parietal and visceral layers of glomerular capsule
visceral layer: podocytes
thick basal lamina: b/t podocytes and endothelial cells - composed of collagen and glycosaminoglycans (- charged) produced by podocytes - 3x thicker than normal basal laminae
Podocytes
Support basement membrane of capsular/urinary space
elaborate, long, branching processes that enwrap glomerular capillaries
stabilizes glomerular architecture
counteract distentions of the glomerular basement membrane
maintain a large filtration surface through the slit diaphragms
responsible for ~40% of hydraulic resistance of the filtration barrier
filtration slit membrane - b/t tertiary processes of podocytes - similar to diaphragm of capillary fenestrations
Filtration
Glomerular capillaries: higher hydrostatic and osmotic pressure
Urinary space: lower hydrostatic and osmotic pressure
Filtration barrier = basal lamina
Water, ions, small proteins pass thru basal lamina by an entirely extracellular route - cells are held back by endothelium
Large molecules and negatively charged molecules are slowed/excluded by negatively charged basal lamina
Mesangial cells
both inside (intraglomerular) and outside (extraglomerular) the glomerulus
Intraglomerular mesangial cells are continuous w/the extraglomerular mesangium which forms the juxtaglomerular apparatus
Found in the center of the glomerulus
contain microfilaments
connected by gap junctions
Phagocytize worn out basal lamina and other debris
Provide structural support
Produce vasoactive agents
Mesangial cells and enothelial cells are on the same side of the basal lamina in the same basal lamina compartment
Intraglomerular mesangium
cluster of mesangial cells located b/t capillary loops of the glomerulus
proximal tubule
longest part of nephron
fills most of cortex
consists of convoluted and straight tubules
Straight segment = thick descending limb - found in medullary ray and outer stripe of medulla moph. similar to poximal convoluted tubules
apical/brush borders of lining cells have long microvilli - gives striated appearance
apical junctional complexes = terminal bars - join cells - leaky
pinocytotic and endocytotic vesicles form b/t bases of microvilli - take up protein from lumen of the tubule - 100% of protein is removed via endocytosis
protein is degraded in lysosomes
many basally enlarged mitochondria –> intense acidophilic stain and basal striation of proximal tubule cells - cells appear packed with organelles - mitoch provide ATP to drive glucose, AA, and NA+ active transporters
basal and lateral infoldings and projections of plasma membrane –> lateral cell boundaries are indistinct
specialization to ^ SA is characteristic of transport epithelia
Thin segment
simple squamous/low cuboidal epith
may resemble capillaries - but has larger diameter and more cells around periphery
nuclei bulge into lumen and appear round
pale, eosinophilic cytoplasm form a thin rim around the tubule
Distal tubule
convoluted and straight tubules
straight tubules return to renal corpuscle from which nephron arose
Comparison to prox. tubule:
Wider lumen
surrounded by cuboidal cells w/more distinct lateral borders
smaller cells (more in a xsxn)
smaller overall diameter
nuclei may bulge into tubule lumen
lighter acidophilic cytoplasm stain
apical tight junctions - impermeable to water
basal striations due to plasma membrane infoldings and aligned mitochondria
Collecting ducts
straight and arched segments
Arched collecting ducts merge to form a straight collecting duct
lining cells have distinct borders and bulge into lumen
cells are joined by complex apical tight junctions
two types of cells: light/principle cells, and dark/intercalated cells
Collecting ducts join to form papillary ducts
Light/principle cells
in collecting duct of nephron
cuboidal
stain pale, eosinophilic
function in Na+/K+ transport, water resorption
Dark/intercalated cells
contain many mitochondira (for acid production)
may be columnar
Papillary duct
formed by union of several collecting ducts
larger diameter than collecting ducts
columnar epith
light staining cytoplasm
near renal papilla, epith may be transitional (like in renal papilla/renal pelvis)
Juxtaglomerular apparatus
at point where distal straight tubule is adjacent to vascular pole of renal corpuscle (from which nephron arose)
adjacent afferent arteriole is part of JG apparatus
renin from JG cells initiates vasoconstriction
renin release is stimulated by several means, including macula densa and extraglomerular mesangial cells that communicate w/JG cells via gap junctions
Consists of 3 structures that are not separated by a complete basal lamina:
macula dens
JG cells
extraglomerular mesangium
Macula densa
in distal tubule walll
narrow tall columnar cells
nuclei appear crowded or overlapping
senses tubular Na+ and Cl- concentrations
Juxtaglomerular cells
located in the wall of the afferent (and maybe efferent) arteriole
adjacent to macula densa
modified sm. ms. cells w/round nuclei
few filaments and membrane bound granules containng renin (enzyme)
function as baroreceptors - release renin in response to a fall in luminal pressure
may also be ST by SNS or indirectly via macula densa and extracellular mesangium in response to ^ in distal tubule Na+ and Cl- concentrations
Extraglomerular mesangium
continuous with intraglomerular mesangium
composed of similar cells
located at vascular pole of renal corpuscle b/t the afferent and efferent arterioles and distal tubules
transmit information concerning tubular Na+ and Cl- [] to the JG cells (via gap junctions)
Kidney - overall functional anatomy
regulates volume and composition of body fluids by filtration, secretion, resorption, and excretion
depending on the physiological need, water molecules, and ions are either conserved or eliminated
Kidney - filtration functional anatomy
20% of renal blood volume crosses the glomerular filtration barrier to the urinary space
caliber of afferent arteriole deliver blood to glom. caps is greater than efferent arteriole draining them –> high pressure system to move blood fluids and solutes into urinary space
neg. charges on glomerular basal lamina repel anions and (-) charged molecules
molecules filtered out may be phagocytised by either mesangial cells or podocytes
mesangial cells regulate flow thru glom. caps. by their contractile properties
Kidney - resorption functional anatomy
2/3 to 3/4 of filtrate is resorbed in the proximal tubule
transit thru the rest of the renal tubule adjusts the final composition of the filtrate according to physiological requirements
hormones (ADH, aldosterone) act on renal tubules to regulate epithelial cells
Kidney - transcellular pathway functional anatomy
movement of substances thru epithelial cells may be active or passive
Kidney - paracellular pathway functional anatomy
movement b/t cells depends on the leakiness of tight junctions and is passive
Kidney - active processes functional anatomy
tend to occur in the more complex epithelia (e.g. the proximal and distal tubules)
cells have abundant mitochondria (energy) and expanded surface membrane (locations for transport protein)
Kidney - Passive processes functional anatomy
predominate in less complex epithelia
e.g. thin limb and collecting tubules/ducts
Anatomic basis of counter-current multiplier mechanism
In medulla
bundles of desc. and asc. tubules and collecting ducts are in proximity to bundles of descending and ascending vasa recta
=anatomical basis for counter current exchange that efficiently transfers ions and water from tubule to capillaries and back
Renal hormones
Erythropoietin - cortical interstitial cells
Prostaglandins - interstitial cells, mesangial cells, podocytes
Urinary passages
transitional epithelium throughout most passages
three or more apparent layers
all layers are actually attached to basal lamina, so it’s really a pseudostratified epithelium with:
basal small cuboidal germinal cells
intermediate layer of intermediate sized cells
luminal layer of often binucleate cells w/patches of thickened plasmalemma = plaques - prevent transcellular diffusion
junctional complexes b/t cells - prevent paracellular diffusion
intracellular membrane vesicles can guse w/surface membrane to accomodate rapid increases in size of organs
Renal pelvis/calyces
expanded origins of ureter that surround apex of medullary pyramid
wall contains smooth muscle
Renal pelvis/calyces & ureter: wall tructure
transitional epithelium
lamina propria-submucosa: loose CT
no muscularis mucosae
T. muscularis: 3 ill-defined layes (only 2 in cat)
Presence of T. serosa or adventitia depends on spp. location, and amount of fat present
Horse: mucous tubuloalveolar mucosal glands in upper 1/3 of ureter and in renal pelvis –> stringy, cloudy urine
Mucosa: in longitudinal folds which give a stellate cross-section
Ureters travel obliquely through the wall of the urinary bladder and are closed by valve-like mucosa flaps when bladder contracts = fnctnl sphincter that prevens reflux of urine during micturition
Urinary bladder - function
storage and some concentration of urine
Na+ is transported across [transport] epithelium
wall structure is greatly expandable
Urinary bladder - tunica mucosa
transitional epithelium
may find lymphocytes w/in epithelium
if thick with several layers of cells ==> contracted
if thin and flattened w/3 or less layers of cells ==> distended
L. propria - contains elastic fibers and lymphocytes maybe lymphatic nodules
muscularis mucosae - variable and may be incomplete - prominent in horse, thin in rums, dog, pig, absent in cat
Urinary bladder - tunica submucosa
contains elastic fibers, lymphocytes, and maybe lymphatic nodules
T. muscularis
=detrusor m.
composed of 3 ill-defined interweaving layers of smooth muscle
T. serosa
in dog and cat
T. adventitia
over part of urinary bladder in other domestic spp.
Urinary bladder - innervation
autonomic fibers and ganglia are located in T. submucosa and T. muscularis
coordinate contraction
ST by bladder distension
Female urethra - epithelium
transitional epithelium changes to stratified cuboidal or columnar then stratified squamous at/near external urethral orifice
goblet cells may be present near urinary bladder
may find intraepithelial lymphocytes
Female urethra - L. propria/submucosa
contains erectile tissue - characterized by endothelial lined cavernous spaces with lumens relatively large relative to thickness of delimiting wall structure
venous sinuses/cavernous spaces lined with endothelial cells and w/o smooth muscle in wall. Relavtively large caliber with an irregular outline
cavernous vv. - large caliber, irregular in shape, thin-walled w/patchy distribution of elastic fibers and smooth muscle in the wall
Lymphocytes may be present in L. propria
muscularis mucosae: sparse-absent
Female urethra - Tunica muscularis
3 ill-defined layers in most domestic spp
smooth muscle is replaced by skeletal muscle near the external urethral orifice (urethralis m.)
longitudinal muscle fibers contract to open lumen
elastic fibers close lumen
Female urethral mucosa
xsxn: appears to have longitudinal folds/forms a crest and thus the lumen of the urethra is irregularly stellate/crescent shaped
