Urinary System II Flashcards
urinary system reabsorption and secretion
after glomerular filtration, the next step is reabsorption during which molecules and ions will be reabsorbed into the circulatory system
- as the filtrate passes through the nephron, water and ions are removed from the filtrate
- this reabsorption is made possible because of changes in the fluid osmolarity
- as the filtrate passes through the collecting duct, secretions are added before it leaves through the ureter in the form of urine
- end product of these processes is urine
urine
a collection of substances that are not reabsorbed during glomerular filtration or tubular reabsorption
renal tubules
the proximal convoluted tubule, distal convoluted tubules, and connecting tubules are located in the renal cortex
the loop of Henle and collecting ducts are found in the renal medulla
proximal convoluted tubule (PCT)
cells of the PCT are specialized for both reabsorption and secretion
- over half of the water, electrolytes, and all of the organic nutrients that are filtered from the blood in the renal corpuscle are normally reabsorbed in the PCT
- these molecules are transported directly across the tubular wall for immediate uptake into the blood stream, specifically into the peritubular capillaries
PCT structure
long and twisty
- due to its length, secretions of the PCT are more numerous in the renal cortex compared to the DCT
- located in the renal cortex
PCT histology
lined by simple cuboidal epithelium
- epithelial cells contain microvilli that form a brush border
- as a result of the brush border, the lumen of the PCT appear filled
- cells have a central nuclei, and an acidophilic cytoplasm due to an abundance of mitochondria
distal convoluted tubule (DCT)
plays a critical role in a variety of homeostatic processes, including sodium chloride reabsorption, potassium secretion, and calcium and magnesium handling
- located in the renal cortex
DCT histology
lined by simple cuboidal epithelium
- cells are small with a short and sparse microvilli, no brush border
- pale cytoplasm due to fewer organelles
DCTs vs PCTs
DCTs have no brush border, and are therefore have a larger and more clearly defined lumen
- DCT sections are shorter in length and less numerous than PCT sections
- cells of the DCT have fewer mitochondria than PCT, making them less acidophilic
juxtaglomerular apparatus
an exocrine structure located at the vascular pole of each renal corpuscle
- formed by an afferent arteriole and the DCT of the same nephron
- has two specialized cells: macula densa and juxtaglomerular cells
juxtaglomerular apparatus function
regulates blood pressure and volume by activating renin-angiotensin-aldosterone system, a hormone system that regulates blood pressure and fluid and electrolyte balance
macula densa cells
each DCT returns to the vascular pole of the renal corpuscle where it contacts the afferent arteriole
- at this site, the cells of the DCT become more columnar and densely packed, forming the macula densa
macula densa cell function
monitor the osmolarity and volume of the filtrate
- when there is a drop in sodium concentration, macula densa cells stimulate the juxtaglomerular cells to release renin (hormone)
juxtaglomerular cells
modified smooth muscle cells found in the wall of the afferent arteriole
juxtaglomerular cell function
synthesize renin in response to a drop in blood pressure detected by stretch receptors in the vascular walls, or when stimulated by macula densa cells
connecting tubules
join the DCT to the collecting ducts
- located in the renal cortex
connecting tubules histology
AKA collecting tubules
- lined by simple cuboidal epithelium that lacks a brush border
- connect the DCT with the collecting duct in the medulla
renal medulla
consists largely of the loops of Henle, collecting ducts, and an extensive vascular (vasa recta) network, which courses in parallel with the various tubules
loop of Henle
descends into the medulla, and turns back up to return to the cortex
- its main function is to create a concentration gradient in the renal medulla
- U shaped and has a thin limb and a thick limb
thin limb
located in the renal medulla
- lined by simple squamous epithelium (thicker than capillary epithelium)
- has a pale staining cytoplasm
- lateral cell walls are usually not visible
thick limb
located in the renal medulla
- lined by simple low cuboidal epithelium that contains no brush border
- lateral cell walls are not visible
- acidophilic cytoplasm
collecting duct
DCT passes near to the renal corpuscle, and then leads to a collecting duct
- located in the renal medulla
collecting duct histology
epithelial cells compose collecting ducts
- they have a homogenous cytoplasm, lack a brush border, and display conspicuous lateral cell boundaries
- nuclei are regularly spaced around the lumen, usually located close to the basal surface of the cell
2 distinct regions of the kidney
cortical labyrinth and medullary rays
medullary rays
portions of the medulla extend into the cortex as the medullary rays
- these are collections of straight portions of the proximal and distal tubules, as well as portions of the collecting ducts
- they travel perpendicular to the renal capsule, and extend into the medulla from the cortex
cortical labyrinth
tissue containing the renal corpuscles and the convoluted portions of the tubules
