chapter 25- urinary system

how many liters of fluid filtered from blood by kidneys every single day

about 200 liters

function of kidneys

maintaining the composition of the body’s extracellular fluids by filtering the blood.

what are the 5 things involved with kidneys performing their function?

• 1) Regulate total body water volume and concentration of solutes in water

• 2) Regulate concentration of ions in ECF
• 3) Acid-base balance

• 4) Remove toxins, metabolic wastes, & other foreign substances

• 5) Hormone production-EPO and renin

kidneys are ____ organs

retroperitoneal

do not have visceral peritoneum covering them

what does each kidney lie between?

the parietal peritoneum and dorsal body wall

medial portion of kidney is ??

concave: renal hilum

ureters, renal blood vessels, lymphatics enter at renal hilum

adrenal gland sits immediately ____ to each kidney

superior

• Supporting external structures of the kidneys:

1. renal fascia

2. perirenal fat capsule

3. fibrous capsule

renal fascia

dense connective tissue

renal fascia function

anchors kidneys to surrounding structures

perirenal fat capsule

fat mass surrounding kidneys

function of perirenal fat capsule

Cushions kidneys from physical trauma

fibrous capsule

thin, transparent capsule

fibrous capsule function

prevents disease from spreading to kidneys from other parts of body

3 major internal regions of kidneys:

1. renal cortex

2. renal medulla

3. renal pelvis

renal cortex functions

provides area for glomerular capillaries and blood vessel passage & EPO produced here

Renal Medulla contains several??

renal pyramids: packed with capillaries & urine-collecting tubules

function of renal medulla

allows for some water reabsorption, electrolyte balance, disposal of waste and H+ ions

Renal Pelvis

• Open space in center of each kidney

• Pelvis branches to form major

calyces (calyx)

• Major calyces lead into minor calyces at tip of each renal pyramid

Function of calyces and pelvis:

urine collection from renal medulla

blood supply to kidneys arteries

1. renal arteries

2. segmental arteries

3. interlobar arteries

4. arcuate arteries

5. cortical radiate arteries

renal arteries

deliver to kidneys: divide into smaller blood vessels to serve major regions of kidney

how many segmental arteries per kidney?

5

Interlobar arteries

travel between renal pyramids

Arcuate arteries

arc over bases of pyramids

Cortical radiate arteries

supply renal cortex

veins in kidneys trace arterial supply but in reverse:

1. cortical radiate veins (smallest)

2. arcuate veins

3. interlobar veins

4. renal veins (largest veins)

where do the renal veins dump into?

postcava

Renal plexus

autonomic nerve fibers & ganglia

What is the importance of changing blood flow to the kidneys?

change rate of filtration, you change rate of urine formation and you change blood volume

Sympathetic vasomotor fibers regulate blood supply to each kidney function

Adjusts diameter of renal arterioles to adjust blood flow to glomeruli

nephron

functional unit of the kidney

nephron function

Responsible for forming filtrate and eventually urine in the

kidneys

each nephron contains;

1. renal corpuscle

2. renal tubule

renal corpuscle

filters blood to form the filtrate

renal tubule

reabsorbs some substances from the filtrate and secretes other substances into the filtrate

What happens to anything that is secreted into filtrate or not reabsorbed from filtrate?

eventually forms urine which is disposed of

filtration

mass movement of solutes and water from plasma into the renal corpuscle and renal tubules

-kidneys filter blood

reabsorption

process by which nephrons remove water and solutes from the filtrate formed from filtration and return it to the blood

secretion

process by which excess ions (k and h, etc) and waste products are pumped back into the filtrate after it has been reabsorbed

renal corpuscle

• Located entirely within renal cortex

subdivisions of renal corpuscle

1. glomerulus

2. glomerular capsule

glomerulus

luster of capillaries

• Blood enters glomerulus via afferent arteriole, leave via efferent arteriole

significance of glomerulus

only set of capillaries that is fed and drained by arterioles, which have high pressures

makes it important to make filtrate

capillaries are very ?

porous: some fluid & substances in blood easily filtered out of capillary

filtrate

raw material used to produce urine

filtrate is not urine

Glomerular capsule

double-layered structure that completely surrounds glomerular capillaries

inner layer of glomerular capsule has 2 things;

1. podocytes

2. foot processes

podocytes function

maintain stability of glomerular capillaries

work with foot processes for filtration

foot processes function

overlaps with neighboring cells

important for filtering

Renal Tubules & Collecting Duct

• Begins in renal cortex, extends into renal medulla, then returns to renal cortex

what’s benefit of hairpin like structure of nephron loop

helps the kidneys to conserve water, concentrate urine, and regulate body fluid balance

subdivisions of renal tubule and collecting duct

1. proximal convoluted tubule

2. nephron loop

   -descending limb

   -ascending limb

3. distal convoluted tubule

4. collecting ducts

Proximal convoluted tubule (PCT):

leads immediately off from glomerulus

• Located in renal cortex

• Large cuboidal epithelial cells with dense microvilli

Nephron Loop (formerly Loop of Henle)

• Travel between renal cortex and renal

medulla

descending limb of nephron loop

• Leads off from PCT

• High permeability to H2O, impermeable to solutes

ascending limb of nephron loop

• Continuous with DCT

• High permeability to solutes, impermeable to H2O

Distal Convoluted Tubule (DCT)

• Located in cortex, composed of small

cuboidal epithelia

• Smaller diameter than PCT, contain no microvilli

what does the micro anatomy of the DCT indicate

by the time filtrate reaches DCT, most reabsoportion and secretion has already taken place in DCT

-it still happens in DCT but more fine tuning + hormonally controlled

• Important cell types in collecting ducts:

1. principal cells

2. intercalated cells

principal cells

maintain Na+ balance in body

-how much Na is absorbed influences how much water is absorbed too

Intercalated cells

help maintain acid-base balance

Each collecting duct receives filtrate from tubules of multiple nephrons and then…

• Collecting ducts fuse together, dump urine into minor calyces

• Types of Nephrons

• 1) Cortical Nephrons

• 2) Juxtamedullary Nephrons

Cortical Nephrons

• Located almost entirely in the cortex

• Small portion of nephron loop found in renal medulla

Juxtamedullary Nephrons

• Nephron loops deeply invade renal

medulla

• How does a change in nephron structure

affect urine formation?

better vary urine concentration

-best when need to form more highly concentrated urine

Glomerulus

• Maintains high pressure to increase filtrate production

Peritubular Capillaries

• Low pressure capillaries arising

from efferent arteriole

peritubular capillaries Cling to proximal & distal tubules of cortical nephrons function

Reabsorb water & solutes from tubule cells

peritubular capillaries empty into…

cortical radiate veins; filtered blood returns to circulation

vasa recta found only on…

juxtamedullary nephrons

• Run parallel to long nephron loop

• Help form concentrated urine

Juxtaglomerular complex

portion of nephron where portion of ascending limb lies against afferent & efferent arterioles

Juxtaglomerular complex overall function

Regulate blood pressure & filtration rate of the glomerulus

3 cellular modifications at this point of contact

• 1) Macula densa

• 2) Granular cells (Juxtaglomerular cells):

• 3) Extraglomerular mesangial cells

macula densa

chemoreceptor cells

function: Monitor NaCl content of

filtrate entering distal convoluted tubule

How does the rate of filtrate formation

affect NaCl concentration in the DCT?

What happens to the afferent arteriole to

“fix” this problem?

determine how quickly the kidneys are filtering blood and can make adjustments from there

too much: macula densa reverses this: decrease blood flow: vasoconstrict afferent arterioles and less blood to filter

Granular cells (Juxtaglomerular

cells):

specialized smooth muscle

cells

where are Granular cells (Juxtaglomerular

cells): found

• Found in arteriolar walls of afferent

arteriole

• Can sense blood pressure in afferent

arteriole

• Also stimulated by macula densa cells

Granular cells (Juxtaglomerular

cells) contain granules that secrete ?

renin

Renin mostly affects the efferent

arteriole!

Low NaCl concentration = ____

renin release

increased renin release

Extraglomerular mesangial cells

Packed between tubule and arterioles

function of extraglomerular mesangial cells

not sure

likely messenger cells telling granular cells when to contract based on macula densa cells

Renal Physiology & Urine Formation

(Diuresis) steps

• Step 1: Glomerular Filtration

•Step 2: Reabsorption

•Step 3: Secretion

• Step 1: Glomerular Filtration

production of a cell and protein-free

filtrate that serves as the raw material for urine

where does glomerular filtration occur

capillary walls

Pressure forces fluid out of glomerular capillary & into glomerular capsule

what does the filtration membrane allow?

passage of water, small solutes into glomerular capsule.

Foot processes of podocytes

foot processes create filtration slits

• Slits prevent passage of macromolecules/large-sized materials into filtrate

•Filtration Pressures:

pressures that

force fluid into or out of glomerulus

Outward Pressure

fluid moves from capillary into glomerular

capsule

promotes filtrate formation

includes hydrostatic pressure in glomerular capillaries

hydrostatic pressure in glomerular capillaries

blood pressure of the glomerular

capillaries that forces fluid out of

glomerulus and into the space of

the glomerular capsule

Remember: outward pressure here

is always ???? why?

HIGH

bc glomerulus is fed and drained by arterioles (high pressure), forcing stuff out, mostly comes in hydrostatic pressure, need to push material across this wall

Inward Pressure:

fluid moves from glomerular

capsule and into glomerular capillary

oppose filtrate formation

2 inward pressures:

1. hydrostatic pressure in capsular space

2. colloid osmotic pressure in glomerular capillaries

hydrostatic pressure in capsular space

pressure exerted by filtrate that

is already in the glomerular

capsule

Colloid osmotic pressure in

glomerular capillaries

(OPgc):

proteins that are still in

capillaries will “pull” water back in

•Glomerular Filtration Rate (GFR):

the total volume of filtrate

formed per minute for all nephrons in the kidneys

normal GFR

125 ml/min

factors affecting GFR

• 1) Net Filtration Pressure (NFP)

• 2) Surface area of capillaries

• 3) Filtration membrane permeability

• 1) Net Filtration Pressure (NFP)

increase NFP, more fluid forced out of beds, so you increase GFR