Urinary System Flashcards
what is the urinary system composed of?
the urinary system is compoesd of a pair of kidneys, a pair of ureters, the urinary bladder and the urethra
what is the general structure of the kidney?
the kidney is a bean-shaped organ enveloped by a thin capsule of connective tissue.
each kidney is divided into an outer cortex and an inner medulla
each kidney contains ~2 millions nephons. a nephron and a collecting tubule form a uriniferous tubule
what is the renal himum?
the renal hilum is a concavity on the medial border of the kidney. it houses arteries, veins, lymphatic vessels, nerves and the renal pelvis.
what is the renal pelvis?
the renal pelvis is a gunnel shaped expansion of th upper end of teh ureter. it is continuous with the major renal calyces, which in turn have several small branches, the minor calyces.
what does the renal medulla contain?
the renal medulla lies deep to the cortex but sends extensions (medullary rays) into the cortex.
the medulla contains the renal pyramids and renal papilla
what are renal pyramids?
renal pyramids are conical structures that compose the bulk of the renal medulla.
- each kidney contains 10-18 renal pyramids - each pyramid consists primarily of the thin limbs of loops of henle, blood vessels, and collecting tubules.
what are renal papilla?
renal papilla is located at the apex of each renal pyramid. it has a perforated tip (area cribrosa) that projects into the lumen of a minor calyx.
what does the renal cortex contain?
the renal cortex is the superficial layer of the kidney beneath the capsule. it consists primarily of renal corpuscles and convoluted tubules
also contain renal columns of Bertin and medullary rays
what are renal columns of Bertin?
they are extensions of cortical tissue between adjacent renal pyramids
what are medullary rays?
medullary rays are groups of straight tubules that extend from the base of each renal pyramid into the cortex.
what does a renal lobe consist of?
each renal lobe consists of a renal pyramid and its closely associated cortical tissue.
what does a renal lobule consist of?
a renal lobule consists of a central medullary ray and the closely associated cortical tissue on either side of it, extending as far as an interlobular artery. its many nephrons drain into the collecting tubules of the medullary ray.
what is the renal interstitium?
- when cell types are present?
the renal interstitium is the connective tissue compartment of the kidney. it consists primarily of fibroblasts and mononuclear cells.
in the medullary, it consists of two additional cell types:
- pericytes - interstitial cells
what are interstitial cells found in the kidney?
interstitial cells are found in the renal interstitium of the medulla. interstitial cells have long processes that extend toward capillaries and tubules in the medulla. these cells manufacture medullipin I, a vasodepressor hormone that is converted to medullipin II in the liver.
Medullipin II is a vasodilator that acts to reduce blood pressure.
what is medullipin II?
medullipin II is a vasodilator that acts to reduce blood pressure.
it is derived from medullipin I, a vasodepressor that has been produced by interstitial cells of the medulla of each kidney.
what does each nephron consist of?
renal corpuscle, proximal convoluted tubules, loop of henle and distal convoluted tubule.
describe the passage of filtrate from the urinary space of a renal corpuscle to the ducts of Bellini…
- bowman (urinary space) of a renal corpuscle
- proximal convoluted tubule
- loop of henle
- descending thick limb
- thin limb (loop)
- ascending thick limb - distal convoluted tubule
- cortical.medullary collecting tubules
- papillary collecting tubule (ducts of Bellini)
how are the nephrons classified?
nephrons are classified into cortial or juxatmedullary nephrons.
classification depends of location of the renal corpuscle.
juxtamedullary nephrons possess longer loops of henle than cortical and are responsible for establihing the interstitial concentration gradient in the medulla.
what does a renal corpuscle consist of?
a renal corpuscle consists of the glomerulus and the bowman capsule and is the structure on which the filtration of blood occurs.
what does the bowman capsule consist of? (5)
- parietal layer - simple squamous epithelium
- visceral layer - composed of podocytes
- bowman space - cavity between the two layers
- vascular pole - site where arterioles enter and leave
- urinary pole - site proximal convoluted tubule leaves
what does the parietal layer of the bowman capsule consist of?
the parietal layer is the simple squamous epithelium tht lines the outer wall of the bowman capsule.
what does the visceral layer of the bowman capsule consist of?
the viseral layer (glomerular epithelium) is the modified simple squamous epithelium composed of podocytes that lines the inner wall of the bowman capsule and envelopes the glomerular capillaries.
what is the space between the parietal layer and the visceral layer of the bowman capsule?
the urinary or bowman space is a narrow cavity between the two layers into which the ultrafiltrate passes.
what are the poles of a bowman capsule?
- vascular pole - the site on the bowman capsule where the afferent arterioles enters and the efferent glomerular arteriole leaves the glomerulus
- urinary pole - the site on the bowman capsule where the capsular space becomes continuous with the lumen of the proximal convoluted tubule
what are podocytes?
podocytes form the viseral layer of the bowman capsule.
podocytes are highly modified epithelial cells. they have complex shapes and possess several primary processes that give rise to many seconday processes called pedicels.
what is the purpose of pedicels on podocytes?
pedicels are secondary processes on podocytes.
- pedicels embrace the glomerular capillaries and interdigitate with pedicels arising from other primary processes
- their surfaces facing the urinary space are coated with podocalyxin, a protein that is thought to maintain their organisation and shape.
- filtration slits are elongated spaces between adjacent pedicels.
what is the renal glomerulus?
- structure
the renal glomerulus is the tuft of capillaries that extends into the bowman capsule.
the renal glomerulus is formed from glomerular endothelial cells, a basal lamina and the mesangium.
what do the glomerular endothelial cells form?
- structure
the glomerular endothelial cells form the inner layer of the capillary walls.
they have a thin cytoplasma that is thicker around the nucleus, where most organelles are located.
glomerular endothelial cells possess large fenestrae (60-90nm in diameter) but lack the thin diaphragms that typically span the openings in other fenestrated capillaries.
what is the structure of the basal lamina found in the renal glomerulus?
- zones
the renal glomerulus possess a basal lamina between the podocytes and the glomerular endothelial cells, manufactured by both cell populations.
it is unusually thick (0.15-0.5um) and contains 3 distinct zones:
- the lamina rara externa - podocyte side
- the lamina densa - amorphous material
- the lamina rara interna - endothelial side
what is the mesangium?
- location
- composition
the megangium is the interstitial tissue between glomerular capillaries. it is composed of mesangial cells and an amorhous extracellular matrix.
what are mesangial cells?
- location
- function
mesangial cells are found within the mesangium located bewteen the glomerular capillaires.
- they phagocytose large protein molecules and debris that accumulate during filtration.
- they can contract, decreasing the surface area available for filtration
- they possess receptors for angiotensin II and atrial natriuretic peptide.
what is the structure of the renal filtration barrier?
the renal filtration barrier is composed of fenestrated glomerular endothelial cells of the capillaries, the basal lamina and filtration slits with diaphragms between the pedicels of podocytes.
what is the function of the renal filtration barrier?
the renal filtration barrier permits passage of water, ions and small molecules from the bloodstream into the urinary space but prevents passage of large molecules (and negatively charged proteins), thus forming an ultrafiltrate of blood plasma in the urinary space.
- laminae rarae contain heparan sulphate (restrict negatively charged proteins) - laminae densa contains type IV collagen, acts as a selective macromolecular filter.
what is the structure of the proximal convoluted tubule?
- epithelial lining - structures found in epithelial cells
the proximal convoluted tubule is lined by a single layer of irregularly shaped epithelial cells that have microvilli forming a prominent brush border
1. apical canaliculi, vesicles and vacuoles, which function in protein absorption 2. prominent interdigitations along their lateral borders, which interlock adjacent cells with one another. 3. compartmentalised mitochindria in basal plama membrane infoldings, which supply energy for active transport of Na ions out of the tubule
what are the functions of the proximal convoluted tubule?
- the proximal convoluted tubule drains the bowman space at the urinary pole of the renal corpuscle
- it resorbs all of the glucose, amino acids and small proteins and 80% of water and NaCl from the glomerular filtrate
- it exchanged hydrogen ions in the interstitium for HCO3- in the filtrate.
- it secretes orgains acids and bases and certain foriegn substances into the filtrate.
what are regions of the loop of Henle?
- the descending thick limb
- the thin limb
- the ascending thick limb
what is the descending thick limb of the loop of henle?
- structure
- function
the descending thick limb is also known as the straight portion of the proximal tubule
it is lined by simple cuboidal epithelium and contains a brush border.
it functions to resorb, exchange and secrete in a manner similar to the proximal convoluted tubule
- resorb: glucose, amino acids, NaCl and water
- exchange: H+ for HCO3-
- secrete: organic acids and bases
what is the thin limb of the loop of henle?
- structure
the thin limb of the loop of henle is composed of a descending portion, a loop and an ascending portion, all of which is lined with simple squamous epithelium possessing few short microvilli. the nuclei bulge into the lumen.
what is the ascending thick limb of the loop of henle?
the ascending thick limb of the loop of henle is also know as the straight portion of the distal tubule.
it is lined by cuboidal epithelial cells that posses a few microvilli, an apical nucleus and mitochondria compartmentalised in the basal plasma membrane infoldings.
the ascending thick limb returns to the renal corpuscle of origin, where it is in close association witht eh afferent and efferent arterioles. in this region the wall of the tubule is modified, forming the macula densa (part of the juxtaglomerular apparatus)
what is the juxataglomerlular apparatus?
- components
the juxtaglomerular apparatus is located at the vascular pole of the renal corpuscle.
it is composed of:
1. JG cells
2. macula densa cells
3. extraglomerular mesangial cellswhat are juxtaglomerular cells?
JG cells are modified smooth muscle cells that exhibit characteristics of protein-secreting cells.
they are primarily located in the wall of the afferent arteriole.
secretes renin into the bloodstream
what are macula densa cells of the JG apparatus?
macula densa cells are tall, narrow, closely pakced epithelial cells of the distal tubule.
they have elongated, closely pakced nuclei that appear as a dense spot.
the macula densa monitor the osmolarity and volume of the fluid in the distal tubule and transmits this information to th JG cells via gap junctions.
how does JG apparatus maintain blood pressure? (3 steps)
the JG apparatus maintains blood pressure by:
- a decrease in extracellular fluid volume stimulates JG cells to release renin into the bloodstream
- renin acts of angiotensinogen in the plasma, converting it to angiotensin I. in capillaries of the lung angiotensin I to converted to angiotensin II by ACE. angiotensin II is a potent vasoconstrictor that stimulates release of aldosterone in the zonula glomerulous of the andrenal cortex.
- aldosterone stimulates the epithelial cells of the distal convoluted tubule to remove Na and Cl ions. water follows ions, thereby increasing the fluid volume in the extracellular compartment, leading to increase in blood pressure.
what is the structure of the distal convoluted tubule?
the distal convoluted tubule is much shorter than the proximal convoluted tubule and has a wider lumen. it also lacks a brush border.
the distal convoluted tubule is continuous with the macula densa and is similar to the ascending thick limb of the loop of henle.
what is the function of the distal convoluted tubule?
the distal convoluted tubule resorbs Na ions from the filtrate and actively transport it into the renal interstitium; this process is stimulated by aldosterone.
it also transfers K+, NH4+ and H+ ions into the filtrate from the interstitium.
