urinary system i

Question 1

urinary system organs

Answer 1

Kidneys - major excretory organs
Ureters - transport urine from kidneys to urinary bladder
Urinary bladder - temporary storage reservoir for urine
Urethra transports urine out of body

Question 2

Kidney Main Functions

• water
• endocrine
• vitamin
• glucose

Answer 2

1. regulate water volume/ solute concentration
2. regulate ECF ion concentration
3. ensure long-term acid-base balance
4. remove metabolic waste/toxic drugs
5. renin to regulate BP
6. erythropoeitin to regulate RBC production
7. activation of vit D: calcitriol
   8 gluconeogenesis during fasting

Question 3

Internal anatomy (cortex and medulla)

Answer 3

Renal cortex
-Granular-appearing superficial region

Renal medulla

• -Composed of cone-shaped medullary (renal) pyramids
• Pyramids separated by renal columns (Inward extensions of cortical tissue)

Question 4

Papilla, lobe, and pelvis

Answer 4

Papilla
-Tip of pyramid; releases urine into minor calyx

Lobe
-Medullary pyramid and its surrounding cortical tissue; ~ 8/kidney

Renal pelvis
-Funnel-shaped tube continuous with ureter

Question 5

calyces

Answer 5

Minor calyces
-Drain pyramids at papillae

Major calyces

• Collect urine from minor calyces
• Empty urine into renal pelvis

Question 6

urine flow

Answer 6

Renal pyramid  minor calyx  major calyx  renal pelvis  ureter

Question 7

kidney blood supply

Answer 7

• Rich blood supply
• arteries deliver 25% of cardiac output to kidneys each min
• arterial flow into and venous flow out of kidneys along similar path

Question 8

nerve supply to kidneys

Answer 8

sympathetic fibers from renal plexus

NO parasympathetic innervation

Question 9

blood flow path

Answer 9

aorta
renal artery
segmental artery
interlobar artery
arcuate artery
cortical radiate artery
afferent arteriole
glomerulus capillaries
efferent arteriole
peritubular capillaries or vasa recta
cortical radiate vein
arcuate vein
interlober vein 
renal vein
inferior vena cava

Question 10

how many nephrons per kidney?

Answer 10

over a million

Question 11

tubular parts of nephron

Answer 11

Glomerular (Bowman’s) capsule
Proximal convoluted tubule (PCT)
Nephron loop (loop of Henle)
Descending limb →  Ascending limb
Distal convoluted tubule (DCT)
Multiple nephron tubules drain into Collecting Duct (CD)

Question 12

blood vessel components of nephron

Answer 12

Afferent arteriole
Glomerulus
Efferent arteriole
Peritubular capillaries
Vasa recta (if juxtamedullary nephron)

Question 13

two parts of renal corpuscle

Answer 13

Glomerulus
-Tuft of capillaries; fenestrated endothelium  highly porous  allows filtrate formation

Glomerular capsule (Bowman's capsule)
-Cup-shaped, hollow structure surrounding glomerulus

Question 14

glomerular capsule anatomy

Answer 14

Parietal layer - simple squamous epithelium

Visceral layer - branching epithelial podocytes

• Extensions terminate in foot processes that cling to basement membrane
• Filtration slits between foot processes allow filtrate to pass into capsular space

Question 15

proximal convoluted tubule
cells
function
location

Answer 15

Cuboidal cells with dense microvilli (brush border –> high surface area); large mitochondria

Functions in reabsorption and secretion

Confined to cortex

Question 16

nephron loop

Answer 16

Descending and ascending limbs

Proximal descending limb continuous with proximal tubule

Distal descending limb = descending thin limb; simple squamous epithelium

Thick ascending limb
-Cuboidal to columnar cells; thin in some nephrons

Question 17

distal convoluted tubule
cell
function
location

Answer 17

Cuboidal cells with very few microvilli
Function more in secretion than reabsorption
Confined to cortex

Question 18

Collecting duct’s cells

Answer 18

Principal cells

• Sparse, short microvilli
• Maintain water and Na+ balance

Intercalated cells
-Cuboidal cells; abundant microvilli; two types –>A and B; both help maintain acid-base balance of blood

Question 19

collecting duct func

Answer 19

receive filtrate from many nephrons

run thru medullary pyramids –> look stripy

fuse together to get urine thru papillae into minor calyces

Question 20

2 types of nephrons

Answer 20

Cortical nephrons—85% of nephrons; almost entirely in cortex
–have peritubular capillaries

Juxtamedullary nephrons

• Long nephron loops deeply invade medulla
• Ascending limbs have thick and thin segments
• Important in production of concentrated urine
• Have vasa recta

Question 21

Nephron capillary beds (2 kinds)

Answer 21

glomerulus = all renal tubules (specialized for filtration)

Peritubular capillaries (for cortical nephrons) or vasa recta (for juxtamedullary nephrons)

Question 22

why is bp high in glomerulus

Answer 22

• afferent arterioles larger in diameter than efferent arterioles
• arterioles are high-resistance vessels

Question 23

peritubular capillaries

Answer 23

Low-pressure, porous capillaries adapted for absorption of water and solutes

Arise from efferent arterioles

Cling to adjacent renal tubules in cortex

Empty into venules

Question 24

vasa recta

Answer 24

Long, thin-walled vessels parallel to long nephron loops of juxtamedullary nephrons

Arise from efferent arterioles serving juxtamedullary nephrons
-Instead of peritubular capillaries

Function in formation of concentrated urine

Question 25

Juxtaglomerular complex

Answer 25

-one per nephron Involves modified portions of - distal portion of ascending limb of nephron loop (some references say it involves the first part of the distal convoluted tubule) - afferent arteriole Important in regulation of rate of filtrate formation and BP includes macula densa cells, granular cells, and extraglomerular mesangial cells

Question 26

macula densa cells

Answer 26

Tall, closely packed cells of ascending limb (or first part of DCT) Chemoreceptors; sense NaCl content of filtrate

Question 27

granular cells

Answer 27

Enlarged, smooth muscle cells of arteriole Secretory granules contain enzyme renin (so now we do not just say renin comes from the kidney! We know exactly where it comes from.) Mechanoreceptors; sense blood pressure in afferent arteriole

Question 28

extraglomerular mesangial cells

Answer 28

Between arteriole and tubule cells Interconnected with gap junctions May pass signals between macula densa and granular cells

Question 29

how much urine is produced per day vs the amount of fluid processed? What are the 3 processes of urine formation

Answer 29

180 L processed/day --> 1.5 L urine/day 1. glomerular filtration 2. tubular reabsorption 3. tubular secretion

Question 30

definitions of the 3 processes

Answer 30

glomerular filtration = produces cell-and protein- free filtrate Tubular reabsorption = selectively returns 99% of substances from filtrate to blood in renal tubules and collecting ducts Tubular secretion = selectively moves substances from blood to filtrate in renal tubules and collecting ducts

Question 31

* how many times a day do the kidneys filter the body's plasma volume? * how much of the body's oxygen do the kidney's use at rest? * from what is the urine produced?

Answer 31

60 times 20-25% From filtrate (from glomerular filtration) = blood plasma minus proteins Urine = <1% of oringinal filtrate --> contains metabolic wates and inneeded substances

Question 32

energy requirements of glomerular filtration

Answer 32

- passive - no metabolic energy required - hydrostatic pressure forces fluids and solutes thru filtration membrane - no reabsorption into capillaries of glomerulus

Question 33

Filtration membrane | definition and layers

Answer 33

Porous membrane between blood and interior of glomerular capsule -Water, solutes smaller than plasma proteins pass; normally no cells pass 1. Fenestrated endothelium of glomerular capillaries 2. Basement membrane (fused basal laminae of two other layers) 3. Foot processes of podocytes with filtration slits; slit diaphragms repel macromolecules

Question 34

Filtration membrane: what can pass and what can't

Answer 34

Macromolecules "stuck" in filtration membrane engulfed by glomerular mesangial cells Allows molecules smaller than 3 nm to pass (Water, glucose, amino acids, nitrogenous wastes) Plasma proteins remain in blood  maintains colloid osmotic pressure  prevents loss of all water to capsular space Proteins in filtrate indicate a filtration membrane problem. Protein in urine is abnormal!

Question 35

pressures that affect filtration

Answer 35

Outward: hydrotatic pressure in glomerular capillaries = glomerular bp -chief force pushig water and solutes out of blood -high (55 mm Hg) --> most capillary beds = 26 mm Hg ``` Inward: Hydrostatic pressure in capsular space -pressure of filtrate in capsule (15 mm Hg) Colloid osmotic pressure in capillaries -"pull" of proteins in blood (30 mm Hg) ``` Sum: Net filtration pressure -outward force of 10 mm Hg -resposible for filtrate formation and glomerular filtration rate

Question 36

Glomerular filtration rate

Answer 36

Volume of filtrate formed per minute by both kidneys (normal = 120–125 ml/min) GFR directly proportional to * NFP – primary pressure is hydrostatic pressure in glomerulus * Total surface area available for filtration – glomerular mesangial cells control by contracting * Filtration membrane permeability – much more permeable than other capillaries

Question 37

regulation of glomerular filtration: intrinsic

Answer 37

Intrinsic controls (renal autoregulation) - act locally within kidney to maintain GFR - if glomerular hydrostatic pressure falls by only 18%, GFR = 0 - maintains constant GFR w/in MAP of 80-180 - 2 methods: myogenic mechanism and tubuloglomerular feedback mechanism

Question 38

Myogenic Mechanism

Answer 38

smooth muscle contracts when stretched high BP = smooth muscle stretch --> constriction of afferent arterioles = restricted blood flow into glomerulus (protects from damage) low bp --> dilation of afferent arterioles

Question 39

Tubuloglomerular Feedback Mechanism

Answer 39

Flow dependent mechanism directed by macula densa cells --> respond to filtrate NaCl concentration If GFR is high --> filtration flow rate is high --> there's a shorter reabsorption time --> there's high filtrate NaCl levels --> there's constriction of afferent arteriole --> decreases NFP and GFR --> more time for NaCl reabsorption opposite for low GFR

Question 40

Extrinsic controls of glomerular filtration

Answer 40

Extrinsic controls maintain systemic blood pressure - sympathetic NS and Renin-Angiotensin-Aldosterone mechanism --> can negatively affect kidney func - takes precedence over intrinsic controls if systemic BP <80 or >180 mm Hg

Question 41

Extrinsic controls: sympathetic NS

Answer 41

If extracellular fluid volume extremely low (bp is low) - NE released by SNS and Epitnephrine released by adrenal medulla - systemic vasoconstriction and higher bp - constriction of afferent arterioles --> lower GFR --> increased blood volume and pressure

Question 42

Extrinsic Controls: Renin-Angiotensin- Aldosterone Mechanism

Answer 42

Main mechanism for increasing blood pressure –Three pathways to renin release by granular cells 1. Direct stimulation of granular cells by sympathetic nervous system 2. Stimulation by activated macula densa cells when filtrate NaCl concentration low 3. Reduced stretch of granular cells in afferent arteriole