Urinary System I Flashcards
the urinary system
consists of the paired kidneys and ureters, the bladder, and the urethra
the kidneys
paired bilateral organs located on the posterior abdominal wall. the ureters are tubes that carry the urine from the kidneys to the urinary bladder
- the kidney is a regulatory organ
regulatory functions of the kidney
- filtration: water and solutes in the blood leave the vascular space and enter the lumen of the nephron
- regulation: regulates the balance between water and electrolytes, regulates acid-base balance
- modification: modification of the filtrate through selective resorption and specific secretion by the tubules
- endocrine: kidneys synthesize and secrete erythropoietin (regulates RBC production) and renin (controls blood volume and pressure)
gross anatomy of the kidneys
kidneys are composed of an outer renal cortex and an inner renal medulla
- medulla is composed of renal pyramids
- kidneys contain renal columns, which are medullary extensions of the renal cortex between the renal pyramids
excretory passages of the kidneys
urine is produced in the kidneys are transported out by the ureter into the bladder through a series of excretory passages
- renal pyramid: urine is produced here
- minor calyx: renal calyces are chambers of the kidney which urine passes through. Minor calyces surround the renal papillae of renal pyramids
- major calyx: formed by the union of the seven minor calyces
- renal papilla: location where the renal pyramids empty urine into the minor calyx
- renal pelvis: two to three major calyces unite to form the enlarged renal pelvis which continues as the ureter
- ureter: eventually drains into the urinary bladder
blood supply to the kidney
the arterial supply of blood to the kidneys is substantial and complex
- the renal artery, a branch of the aorta, enters the hilum of the kidney. the renal artery branches into interlobular arteries, which travel between the pyramids through the renal columns
- interlobular arteries branch laterally to form the arcuate arteries, which mark the boundary between the cortex and medulla
the nephron
basic structural and functional unit of the kidney
- functions to remove wastes from the blood and balance the constituents of the circulation through the process of filtration, reabsorption, and excretion
- each kidney contains one million nephrons that consist of a simple epithelium along their entire length
structural components of the nephron
- renal corpuscles
- cortical and medullary tubular system
each nephron consists of a blood supply and a specialized network of ducts called tubules
renal corpuscle
filtering component of the nephron
composed of a tuft of high pressure capillaries called the glomerulus, which is surrounded by Bowman’s capsule
- for each nephron, an afferent arteriole feeds a high pressure capillary bed called the glomerulus
- blood is filtered by the glomerulus to produce filtrate, which is caught in Bowman’s space
major divisions of the nephron
renal corpuscle, proximal tubules, loop of Henle, and distal tubule, collecting duct
glomerulus arteriole supply
interlobular arteries travel through the centre of the cortex, where they give off afferent arterioles, which supply the glomerulus
proximal convoluted tubule
continues from Bowman’s capsule
- long twisted tubules fill most of the cortex and the kidney
- lined by tall cuboidal epithelium with a brush border
proximal straight tubule
after the proximal convoluted tubule enters the medulla, it becomes the proximal straight tubule
- this segment is continuous with the nephron’s loop of Henle
Loop of Henle
U-shaped structure consisting of a thick descending limb, a thick ascending limb, and a thin looped segment (thin limb), which interconnects the two
- the ascending limb of the nephron is straight as it enters the cortex and forms the macula densa, and then becomes twisty as the distal convoluted tubule
distal convoluted tubule
short and twisty nephron segment
- empties into the collecting system, which empties into the minor calyx
- has low cuboidal lining with irregularly spaced nuclei
collecting system components
consists of the connecting tubule, collecting duct, and papillary duct
collecting duct
the last part of each nephron which carries the filtrate into a collecting system that transports it to a minor calyx
- a connecting tubule extends from each nephron, and when several tubules join together, they form collecting ducts
- in the apex of the renal pyramid, several collecting ducts merge and deliver urine to the minor calyx
classification of nephrons
there are two types of nephrons in the kidney cortex that are classified based on the location of their renal corpuscles:
- juxtamedullary nephrons
- cortical nephrons
juxtamedullary nephrons
have their renal corpuscles located near the junction of the cortex and medulla
- they possess long loops of Henle that penetrate deep into the medulla
cortical nephrons
have their renal corpuscles located closer to the outskirts of the cortex
- they have short loops of Henle
renal corpuscles composition
at the beginning of each nephron is a renal corpuscle, which is comprised of the glomerulus, housed within the Bowman’s capsule
renal corpuscle filtration
filtrate from the blood in the glomerulus is collected in the Bowman’s capsule. the filtrate is then further processed as it travels through the nephron to form urine
- successful filtration depends on the specific flow of filtrate and blood through the renal corpuscle
filtrate flow in the renal corpuscle
- afferent arteriole
- glomerulus
- Bowman’s capsule
- urinary pole
- efferent arteriole
- vascular pole
filtrate flow in the afferent arteriole
blood enters the glomerulus through the afferent arteriole
filtrate flow in the glomerulus
the glomerulus is the capillary bed between the afferent and efferent arterioles
- it is suspended within Bowman’s capsule
- glomerular capillaries filter blood based on particle size
filtrate flow in Bowman’s capsule
bowman’s capsule is double walled and encloses the glomerulus. it has an inner visceral layer of podocytes, which surrounds the glomerulus and serves as part of the filtration barrier. the outer parietal layer is simple squamous epithelium, which is continuous with the proximal convoluted tubule
- the glomerular filtrate accumulates between these two layers
filtrate flow at the urinary pole
the continuation of the parietal layer of Bowmans capsule, with the epithelium forming the proximal convoluted tubule
- at the urinary pole, the filtrate accumulating in Bowman’s space enters the first tubular part of the nephron, the proximal convoluted tubule
filtrate flow at the efferent arteriole
after passing through the renal corpuscle, the capillaries form a second arteriole, the efferent arteriole
- blood exits the glomerulus through the efferent arteriole, which then forms a capillary network around the more distal portions of the nephron
filtrate flow at the vascular pole
the junction with the afferent and efferent arterioles is the vascular pole of the renal corpuscle
- the visceral and parietal layers of Bowmans capsule is continuous at the vascular pole
the juxtaglomerular apparatus
a regulatory structure formed by the distal convoluted tubule and the afferent arteriole
- located near the vascular pole of the renal corpuscle
- functions to regulate blood pressure and filtration rate
juxtaglomerular apparatus composition
- modified cells in the wall of the distal convoluted tubule
- macula densa cells, modified cells in the distal convoluted tubule wall
- juxtaglomerular cells: cells in the wall of the afferent arteriole
macula densa cells
modified cells in the wall of the distal convoluted tubule
- monitor sodium concentration in the filtrate, whereas juxtaglomerular cells monitor blood pressure
glomerular filtration
involves the transfer of soluble components, such as water and waste, from the blood into the glomerulus
- during filtration, blood enters the afferent arteriole and flows into the glomerulus where filterable blood components (ex: water and waste) will move into bowmans capsule. filterable components accumulate in the glomerulus to form the glomerular filtrate
- non-filterable components (cells and proteins) will exit through the efferent arteriole
glomerular filtrate barriers
glomerular filtrate is produced in the corpuscle when blood plasma is forced under pressure through three barriers:
1. fenestrated capillary endothelium
2. glomerular basal lamina
3. filtration slits diaphragms
fenestrated capillary endothelium
endothelium of glomerular capillaries is fenestrated with large pores, and these fenestrations block blood cells and platelets
- filtrate is produced in the corpuscles when blood plasma is forced under pressure through the capillary fenestrations, across the filtration membrane surrounding the capillary, and through the filtration slits located between the podocyte pedicels
glomerular basal lamina
the pedicels of a podocyte contact the thick, combined basal laminae of the endothelial cell and the podocyte
- the thick combined basal laminae between the podocytes and endothelium restricts large proteins and some organic anions
filtration slit diaphragms
filtration slits are the spaces between adjoining pedicels and are spanned by a membrane that also regulate filtration
- restricts some small proteins and organic anions
podocytes
each renal corpuscle has a simple squamous parietal layer of the Bowman’s capsule, continuous with the proximal tubule, and a specialized visceral layer of podocytes surrounds glomerular capillaries
- the podocytes, together with the capillary endothelial cells, compose the apparatus for renal filtration
nucleus of podocytes
together with the endothelial cells of the glomerular capillary and the glomerular basement membrane, they form a filtration barrier
podocytes primary process
podocytes extend large, primary processes that curve around a capillary and extend short, interdigitating secondary processes called pedicels
- between the pedicels are narrow spaces called filtration slits
blood supply to the nephron
after passing through the renal corpuscle, the capillaries form a second arteriole, the efferent arteriole
- efferent arterioles will next form a capillary network around the more distal portions of the nephron tubule (the peritubular capillaries and vasa recta) before returning to the venous system
- as the glomerular filtrate progresses through the nephron, these capillary networks recover most of the solutes and water, and return them to the circulation
vasa recta
surrounds the loops of Henle, which are located in the medulla of the kidney
- goes into the medullar to approach the loop of Henle
peritubular capillaries
tiny blood vessels, supplied by the efferent arteriole that travel alongside the nephrons, allowing reabsorption and secretion between blood and the inner lumen of the nephron
- peritubular capillaries surround the cortical parts of the proximal and distal tubules
