Chapter 25 - The Urinary System & Renal Physiology

Filtration

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

Reabsorption

The process by which nephron removes water and solutes from filtrate formed from filtration and return it to blood

Secretion

The process by which excess ions (K+, H+, etc). and waste products are pumped back into the filtrate after it has been reabsorbed

Fluid filtering in kidneys rate

200 liters of fluid filtered from blood by kidneys every day

Function of kidneys

Maintaining the composition of the body’s extracellular fluids by filtering blood

Maintaining the composition of the body’s extracellular fluid involves…

1.) Regulating total body water volume and concentrations of solutes in water

2.) Regulate concentration of ions in ECF

3.) Acid base balance

4.) Remove toxins, metabolic wastes, and other foreign substances

5.) Hormone production-EPO and renin

Where do kidneys lie

Between the parietal peritoneum and dorsal body wall

Kidneys are what types of organs

Retroperiotoneal organs

Medial portion of the kidney is

Concave

What lies in the medial portion of kidney

Renal hilum

Renal hilum

Urters, renal blood vessels, lymphatics, and something else enter here

Adrenal gland

Sits immediately superior to each kidney

Supporting external structures of kidneys

1.) Renal fascia

2.) Perirenal fat capsule

3.) Fibrous capsule

Renal fascia is made of

Dense connective tissue

Renal fascia function

Anchors kidneys to surrounding structures

Perirenal fat capsule

Fat mass surrounding kidneys

-Cushions kidneys from physical trauma

Fibrous capsule

Thin, transparent capsule that prevents disease from spreading to kidneys from other parts of body

3 major interal regions of kidneys

1.) Renal cortex

2.) Renal medulla

3.) Renal pelvis

Renal cortex functions

Filtration

Provide area for glomerular capillaries and blood vessel passage and EPO produced here

Renal medulla contain

Several renal pyramids

Renal pyramids

Packed with capillaries and urine collecting tubules

Renal medulla functions

Reabsorption and secretion

Allow for some water reabsorption, electrolye balance, disposal of waste, and H+ ions

Renal pelvis

Open space in center of each kidney

Renal pelvis branches to form

Major calyces (calyx)

Major calcyes lead into

Minor calyces at tip of each renal pyramid

Function of calyces and pelvis

Urine collection from renal medulla

Blood supply to kidneys include

1.) Renal arteries

2.) Segmental arteries (5)

3.) Interlobar arteries

4.) Arcuate arteries

5.) Cortical radiate arteries

All are branch into each other

Renal arteries deliver to

The kidneys; divide into smaller blood vessels to serve major regions of kidney

Interlobar arteries travel…

Between renal pyramids

Arcuate arteries travel where

Arc over bases of pyramidsC

Cortical radiate arteries

Supply renal cortex

Kidney veins trace…

Arterial supply, but in reverse

1.) Cortical radiate veins

2.) Arcuate veins

3.) Interloblar veins

4.) Renal veins

Combines into larger veins from 1 —> 4 (opposite of arterial)

Renal plexus

Autonomic nerve fibers and ganglia

-Provide sympathetic vasomotor fibers that regulate blood supply to each kidney

Renal plexus

Adjusts diameter of renal arterioles to adjust blood flow to glomeruli

What is the importance of changing blood flow to the kidneys

Increases or decreases filtering function —> changes urine volume —> changes blood volume/pressure

Nephron

Functional unit of the kidney

-Responsible for forming filtrate and eventually urine in the kidneys

General structure of nephron

Contains a renal corpuscle and renal tubule

Renal corpuscle

Filters blood to form the filtrate

Renal tubule

Rebasorbs some substances from filtrate and secretes other substances into filtrate

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

Forms filtrate and leaves body

Renal corpuscle is located entirely…

Within renal cortex

Subdivisions of renal corpuscle

1.) Glomerulus

2.) Glomelular capsule

Glomerulus

Cluster of capillaries where blood enters via afferent arteriole and leaves via efferent arteriole W

What is the significance of efferent and affarent arterioles

“pushes away” - it is unique because it is fed and drained by arterioles on both side —> increases pressure in arterioles —> keeps high pressure in capillary bed`

High pressure in capillary bed will do what to fluid

Drives fluid out to form filtrate

Capillaries are very porous, allowing what?

Some fluid and substances in blood easily filtered out of capillary (filtrate)

Filtrate

Raw material used to produce urine (NOT URINE)

Glomerular capsule

Double layered structure that completely surrounds glomerular capillaries

Inner layer of glomerular capsule has…

1.) Podocytes

2.) Foot processes

Podocytes and foot processes function

Form a filter to prevent passage of important large molecules outside glomerular capsule

Renal tubules and collecting duct pathway

Begins in renal cortex —> extends into renal medulla —> returns to renal cortex

“Hairpin structure”

What is the benefit of the “hairpin structure” of renal tubules and collecting duct

Large surface area that allows for most reabsorption and secretion

Subdivisions of renal tubules and collecting ducts

1.) proximal convoluted tubule (PCT)

2.) Nephron loop

3.) Distal convoluted tubule

4.) Collecting ducts

The proximal convoluted tubule (PCT)

1.) Leads immediately off glomerulus

2.) Located in renal cortex

3.) Large cuboidal epithelial cells with dense microvilli

Nephron loop

Travel between renal cortex and renal medulla

Descending limb of nephron loop

1.) Leads off from PCT

2.) High permeability to H₂O, impermeable to solutes

Ascending limb of nephron loop

1.) Continuous with DCT

2.) High permeability to solutes impermeable to H₂O

Distal convoluted tubule

1.) Located in cortex, composed of small cuboidal eputhelia

Diameter and feature of DCT vs PCT? Indicates?

Smaller diameter with no microvilli

-Has less surface area - by time filtrate reaches DCT, reabsorption and secretion are almost complete

Important cell types in collecting ducts

1.) Principal cells

2.) Intercalated cells

Principle cells

Maintain Na+ balance in the body that influences absorption of other substances (ex. too much Na+ —> increase in H₂O reabsorption)

Intercalated cells

Help maintain acid base balance through reabsorption of bicarbonate and H+ ions

Each collecting duct receives…

Filtrate from tubules of multiple neurons

What happens to the collecting ducts?

They fuse together and dump urine into minor calyces

Type of nephrons

1.) Cortical nephrons

2.) Juxtamedullary nephrons

Cortical nephorns location

Located almost entirely in the cortex in the small portion of nephron loop found in renal medulla

Juxtamedullary nephrons location

Deeply invade renal medulla

How does a change in nephron structure affect urine formation

Changes concentration of urine to form highly concentrated urine that is goof for H₂O reabsorption

What is same/different from previous nephrons and cortical/juxtamedullary nephrons?

Same structures, but slight modifications

Glomerulus

Filtration

-Maintains high pressure to increase filtrate production

Peritubular capillaries

1.) Low pressure capillaries arising from efferent arteriole

2.) Cling to proximal and distal tubules of cortical nephrons

Peritubular capillaries - function

Reabsorption and secretion

-Reabsorb water and solutes from tubule cells

-Empty into cortical radiate veins

After peritubular capillaries emtpy fluid in cortical radiate veins, what happens to this “fluid”

Fluid (filtered blood) returns to circulation

Vasa recta is only found where

Found only on juxtamedullary nephrons that run parallel to long nephron loop

Vasa recta function

Help form concentrated urine

Juxtaglomerular complex

Portion of nephron where portion of ascending limb lies against afferent and efferent arterioles

Overall function of juxtaglomerular complex

Regulate blood pressure and filtration rate of the glomerulus

3 cellular modifications at Juxtaglomerular complex

1.) Macula densa

2.) Granular cells (juxtaglomerular cells)

3.) Extraglomerular cells

Macula densa

Chemoreceptor cells

-Monitor NaCl content of filtrate entering distal convoluted tubule

How does the rate of filtration formation affect NaCl concentration in the DCT? What happens to the afferent arteriole to “fix” this problem?

Decreases filtrate formation by putting less blood in glomerular capillaries —> will vasoconstrict afferent arterioles so less blood goes into capillary

Granular cells

Specialized smooth muscle cells found in arteriolar walls of afferent arteriole

Function of granular cells

Can sense blood pressure in afferent arteriole

Granular cells are stimulated by…

Macula densa

Granular cells have granule that…

Secrete renin (which affects the efferent arteriole)

Low NaCl concentrations means what for renin?

Increase renin release

Extraglomerular mesangial cells

Packed between tubule and arterioles that possibly allow message between macula cells and granular cells

Diuresis (urine formation) steps

1.) Glomerular filtration

2.) Reabsorption

3.) Secretion

Glomerular filtration

Production of a cell and protein-free filtrate that serves as the raw material for urine

-Pressure forced fluid out of glomerular capillary and into glomerular capsule

Filtration membrane

Allows passage of water and small solutes into glomerular capsule

Foot processes of podocytes

Create filtration slits which prevent passage of macromolecules/large sized materials into filtrate

Filtration pressures

Pressures that force fluid into/out of glomerulus

Outward pressure

Promotes filtration formation

-Hydrostatic pressure in glomerular capillaries (HPgc)

Hydrostatic pressure in glomerular capillaries (HPgc)

Blood pressure of the glomerular capillaries that force fluid out of glomerulus and into space of the glomerular capsule

Outward pressure that forced fluid into or out of glomerulus is always

HIGH

Inward pressure

Oppose filtrate formation

1.) Hydrostatic pressure in capsular space (HPcs)

2.) Colloid osmotic pressure in glomerular capillaries (OPgc)

Hydrostatic pressure in capsular space (HPcs)

Pressure exerted by filtrate that is already in glomerular capsule

Colloid osmotic pressure in glomerular capilarries (OPgc)

Proteins that are still in capillaries will “pull” water back in

Positive net filtration pressure

Forming more filtrate (outward pressure>inward)

Glomerular filtration rate (GFR)

Total volume of filtrate formed per minute for all nephrons in the kidneys

Factors that affect GFR

1.) Net filtration pressure

2.) Surface area of capillaries

3.) Filtration membrane permeability