64: Urinary System I (Histo) Flashcards
What parts make up Urinary System?
Bladder
Kidneys
Urethra
Ureters
Functions of the Urinary System
Important excretory system
Formation of urine
Monitoring of blood pressure
Functions of Kidneys
Regulation of acid base balance
Maintain composition and volume of extracellular fluid
Excretion of metabolic waste & drugs
Regulation of blood pressure
Endocrine functions of Kidneys
hydroxylation of 25-OH vitamin D3 to active 1,25- (OH)2 vitamin D3
erythropoietin ( EPO) : acts on bone marrow to regulate RBC formation in low blood oxygen concentration
secretion of renin- enzyme involved in blood pressure regulation
Paired bean shaped, retroperitoneal organs derived from intermediate mesoderm
Kidneys
the point of entry of
neurovascular supply and origin of ureter (renal pelvis)
Hilum of kidneys
space around the hilar
structures, filled with loose connective tissue
Renal sinus
granular in appearance
consists most of the components of the nephron
extends between medullary pyramids as renal columns
(Columns of Bertin)
Cortex
striated appearance
arranged as discrete pyramids
apical portion of pyramid
(renal papilla) projects into
minor calyx
consists mainly straight
portion of uriniferous tubules and straight blood vessels
Medulla
composed of renal corpuscle and
associated tubular structures
Renal cortex
Regions of Renal Cortex
Medullary rays: straight
tubules of the nephron and
collecting ducts
Cortical labyrinth: convoluted tubules of the nephron
medulla and
associated cortex
Renal lobe
medullary rays and
adjacent cortical tissue
consists of a collecting duct and the nephrons
it drains
Renal lobule
predominantly consists rounded structures –> renal
corpuscles, PCT, DCT, peritubular capillaries
Pars convoluta
predominantly consists straight structures ->
loop of Henlé, collecting ducts
Pars recta (medullary rays)
Consists predominantly straight tubules:
proximal straight tubule thin loop of Henlé distal straight tubule collecting ducts vasa recta (blood vessels)
Medulla
Kidney blood supply
Renal artery (main)
Interlobar artery
Arcuate artery
Interlobular artery
arise from interlobular
arteries to form glomerular capillary tuft
Afferent arterioles
Capillary tuft leaves the corpuscle as?
Efferent arterioles
in corticcal nephrons, efferent arterioles
give rise to?
peritubular capillary
network
In Juxtamedullary nephrons: efferent arterioles descend into medulla to become?
Vasa Recta
( arteriolae and venulae
rectae) are involved in the countercurrent exchange of ions in the medulla, run
parallel to loops of Henlé
Vasa Recta
functional unit of the
kidney
Nephron
Glomerulus and
Bowman’s capsule
Renal corpuscle
Tubules
Proximal convoluted tubule
Loop of Henlé: • proximal straight tubule • Thin descending limb • Thin ascending limb • Distal straight tubule
Distal convoluted tubule
Nephron + connecting tubule
Uriniferous tubule
Three types of Nephrons
Cortical: short loops of
Henle (hairpin turn by
distal straight)
Intermediate (mid cortical)
Juxtamedullary: long loops
of Henle, these are crucial
for concentrating urine
Renal corpuscle components
Glomerulus : blood enters via afferent arteriole and leaves as efferent
arteriole : both are found at the vascular pole of renal corpuscle
Bowman’s capsule surrounds glomerulus
Mesangium: mesangial cells (intra-glomerular)
Ultra-filtrate
collects in urinary space and is directed to the PCT
at the urinary pole
Visceral layer (glomerular) of Bowman’s Capsule
podocytes (modified squamous cells) which invests glomerular
capillaries
Parietal layer (capsular) of Bowman’s Capsule
outer layer of simple squamous epithelium which is continuous
with the proximal convoluted tubule
Urinary space (Bowman’s space or capsular space)
lies between the
two layers where the ultra-filtrate collects and is channeled to the proximal convoluted tubule (PCT)
Consists of mesangial cells (contain actin
filaments) and the matrix they produce
Mesangium
Phagocytosis of residue along the GBM
Structural support-> secretes ECM
Secretion of inflammatory substances:
IL-1, prostaglandin E2, PDGF
Contractile cells: may regulate glomerular
distension in high blood pressure (in response to angiotensin II & ANF (atrial natriuretic factor))
Mesangium functions
Numerous fenestrations
No diaphragms
Produces nitric oxide and
prostaglandins (PGE2)
Abundant aquaporin-1 receptors
Endothelium of glomerular capillaries
Thick 300-370 nm
Fused basal lamina of endothelial cells and podocytes
Type IV collagen
Predominantly contains heparan sulphate
Glomerular basement membrane (GBM)
Structural arrangement of GBM
I. Lamina rara interna: (of the capillary)
II. Lamina densa: Type IV
collagen – physical barrier
III. Lamina rara externa: (of thepodocyte) rich in heparan sulphate to repel [-} charged molecules
Modified epithelial cells, called podocytes with primary/secondary processes, and pedicels
Filtration slits b/n pedicels covered by slit diaphragm (zipper like sheet w/ nephrin transmembrane protein, anchored to filaments w/in pedicels of podocytes)
Visceral layer of Bowman’s Capsule
Factors affecting filtration
charge: [-} charged repelled
size: upper limit of 70 KiloDaltons
shape: upper limit of 3.6 nm
Filtrates
water, glucose, small amino acids, ions, urea, hormones, Vit. B & C, ketones
most abundant
tubular profiles in the cortex
receive ultrafiltrate from urinary space and reabsorbs 65% of it including 100% of glucose,
98% amino acids, small
polypeptides
Proximal convoluted tubules
What type of cells are in the proximal convoluted tubules?
Simple cuboidal epithelium
specialized for absorption
Large cells result in large spaces b/n adjacent cellular nuclei
Structure of proximal convoluted tubules
Apical surface : long microvilli forming brush border
•Lateral:
– Tight junctions and zonula adherens
– Plicae: folds which interdigitate w/ adjacent cellular processes
Basal interdigitations
Basal striations associated w/ elongated mitochondria
Which part of nephron has Na +/ K+ pumps on lateral folds that create osmotic gradient for water
reabsorption?
Proximal convoluted tubules
Which processes are actively involved in protein absorption and recycling in the proximal convoluted tubules?
Endocytic complex (vesicles, endosomes, lysosome)
contains enzymes for
absorption of glucose, peptides & stained with PAS
Glycocalyx
