Urinary System II

Question 1

urinary system reabsorption and secretion

Answer 1

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

Question 2

urine

Answer 2

a collection of substances that are not reabsorbed during glomerular filtration or tubular reabsorption

Question 3

renal tubules

Answer 3

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

Question 4

proximal convoluted tubule (PCT)

Answer 4

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

Question 5

PCT structure

Answer 5

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

Question 6

PCT histology

Answer 6

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

Question 7

distal convoluted tubule (DCT)

Answer 7

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

Question 8

DCT histology

Answer 8

lined by simple cuboidal epithelium
- cells are small with a short and sparse microvilli, no brush border
- pale cytoplasm due to fewer organelles

Question 9

DCTs vs PCTs

Answer 9

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

Question 10

juxtaglomerular apparatus

Answer 10

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

Question 11

juxtaglomerular apparatus function

Answer 11

regulates blood pressure and volume by activating renin-angiotensin-aldosterone system, a hormone system that regulates blood pressure and fluid and electrolyte balance

Question 12

macula densa cells

Answer 12

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

Question 13

macula densa cell function

Answer 13

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)

Question 14

juxtaglomerular cells

Answer 14

modified smooth muscle cells found in the wall of the afferent arteriole

Question 15

juxtaglomerular cell function

Answer 15

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

Question 16

connecting tubules

Answer 16

join the DCT to the collecting ducts
- located in the renal cortex

Question 17

connecting tubules histology

Answer 17

AKA collecting tubules
- lined by simple cuboidal epithelium that lacks a brush border
- connect the DCT with the collecting duct in the medulla

Question 18

renal medulla

Answer 18

consists largely of the loops of Henle, collecting ducts, and an extensive vascular (vasa recta) network, which courses in parallel with the various tubules

Question 19

loop of Henle

Answer 19

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

Question 20

thin limb

Answer 20

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

Question 21

thick limb

Answer 21

located in the renal medulla
- lined by simple low cuboidal epithelium that contains no brush border
- lateral cell walls are not visible
- acidophilic cytoplasm

Question 22

collecting duct

Answer 22

DCT passes near to the renal corpuscle, and then leads to a collecting duct
- located in the renal medulla

Question 23

collecting duct histology

Answer 23

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

Question 24

2 distinct regions of the kidney

Answer 24

cortical labyrinth and medullary rays

Question 25

medullary rays

Answer 25

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

Question 26

cortical labyrinth

Answer 26

tissue containing the renal corpuscles and the convoluted portions of the tubules