BIOL 347 - Chapter 25 - The Urinary System & Renal Phyisology

What are the suffixes associated with the urinary system & renal physiology (3)?

1) "renal"
2) "nephr-"
3) "nephro"

How many mL of fluid is filtered from the kidneys every single day?

About 200L

What is the function of the kidneys?

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

What does filtering the blood involve (5)?

1) Regulating total body water volume & 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 & renin

What are the functions of EPO and renin?

EPO increases RBC production and renin increases the BP

Where is the kidney located?

Between the parietal peritoneum & the dorsal body wall

What type of organ is the kidney? How is this different from other body organs?

It's a retroperitoneal organ, which means its developed within the parietal peritoneum, instead of being outside of it, thus being attached the to body cavity instead of "floating"

What vertebrate does the kidneys extend from?

T12 to L3

Renal Hilum

Medial portion of the kidney that is concaved and allows the ureters, renal blood vessels, lymphatics, and renal nerve supply to enter

Where is the adrenal gland located in regards to the kidney?

Immediately superior

What are the supporting external features of the kidneys (3)?

1) Renal fascia
2) Perirenal fat capsule
3) Fibrous capsule

Renal Fascia

Consists of dense connective tissue that anchors kidneys to surrounding structures

Perirenal Fat Capsule

A fat mass surrounding the kidneys that cushions the kidneys from physical trauma

Fibrous Capsule

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

What are the major internal parts of the kidney (3)?

1) Renal cortex
2) Renal medulla
3) Renal pelvis

Renal Cortex

Provides area for glomerular capillaries and blood vessel passage along with producing EPO

Glomerular Capillaries

Where filtering occurs

What is contained within the renal medulla?

Renal pyramids

Renal pyramids

Packed with capillaries & urine-collecting tubules

How many renal pyramids are there per kidney? What are they separated by?

We have 7 per kidney, with each being separated by renal columns

What does a kidney lobe consist of?

Renal pyramid + surrounding columns

Renal Pelvis

Funnel-shaped tubes continuous with ureter

What does the renal pelvis branch to form? What does this lead to?

The major calyces (calyx), thus leading to the minor calyces

What is the function of the major & minor calyces?

Urine collection & emptying into the pelvis

What are the arteries of the kidneys (5)?

1) Renal arteries
2) Segmental arteries
3) Interlobar arteries
4) Arcuate arteries
5) Cortical radiate arteries

Renal Arteries

Deliver blood to the kidneys then divide into small blood vessels to serve major regions of the kidneys

How many segmental arteries do we have?

5

Interlobar Arteries

Travel between kidney lobes

Arcuate Arteries

Arch over the base of the pyramids

Cortical Radiate Arteries

Supply cortical tissue

What are the veins of the kidneys (4)?

1) Cortical radiate veins
2) Arcuate veins
3) Interlobar veins
4) Renal veins

Where are these veins located in respect to the arteries within the kidney?

They trace arterial supply but in reverse

Renal Plexus

Automatic nerve fibers & ganglia that regulate blood supply to each kidney

Which one of the automatic nervous systems has influence over the kidneys?

Sympathetic division

What is the function of the renal plexus?

Adjusts diameter of renal arterioles, and influences nephron activity

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

By changing blood flow to the kidneys you also change all the kidney functions that maintain homeostasis

Filtration

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

Reabsorption

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

Secretion

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

Nephron

Functional unit of the kidney that is responsible for forming filtrate and eventually urine in the kidneys

What is the importance of nephrons?

They ensure waste products are properly disposed of & that we have proper water/ion balance

What is the general structure of a nephron (2)?

1) Renal corpuscle
2) Renal tubule

Renal Corpuslce

Filters blood to form the filtrate

Renal Tubule

Reabsorbs what is needed by the by from the filtrate & secretes more substance into the filtrate

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

Leaves the body in urine

Where is the renal corpuscle located?

Entirely within the renal cortex

What are the subdivisions of the renal corpuscle (2)?

1) Glomerulus
2) Glomerular capsule

Glomerulus

Cluster of blood vessels that enter via the afferent arteriole and exit via the efferent arteriole

What is the significance of arterioles in the glomerulus?

It is the only capillary system that is well feed and drained

What is the benefit of the glomerulus being very porous?

Fluid passes from glomerular capillaries and into the surrounding empty space

What is this fluid called? What is this fluid used for?

It's called filtrate and is the raw material that's used to produce urine

Glomerular Capsule

Double-layered structure that completely surrounds glomerular capillaries

What is the function and importance of podocytes?

Ensure that only tiny things will only pass through such as H2O and ions

What does the inner layer of the glomerular capsule consist of?

Podocytes with foot processes

Where are the renal tubules & collecting ducts located?

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

What is the benefit of this hairpin-like structure (renal tubules & collecting ducts)?

Increases surface area to allow more reabsorption & secretion

What are the subdivisions of the renal tubules (4)?

1) Proximal convoluted tubule (PCT)
2) Nephron loop
3) Distal convoluted tubule (DCT)
4) Collecting ducts

Proximal Convoluted Tubule (PCT)

Leads immediately off from glomerulus

What does the PCT consist of?

Large cuboidal epithelia cells with dense microvilli

Nephron Loop

Has descending and ascending limbs that invade renal medulla

Descending Limb

Portion that is continuous with PCT

Ascending Limb

Continuous with DCT

What is the permeability regarding H2O and solutes in the descending and ascending limbs?

Descending - High permeability of H2O and low permeability for solute
Ascending - Low permeability of H2O and high permeability for solute

Distal Convoluted Tubule (DCT)

Located in cortex and has a small diameter than the PCT

What is the DCT composed of?

Small cuboidal epithelia and no microvilli

What does the microanatomy of the DCT indicate?

Not a lot of secretion & absorption occurs here

Collecting Ducts

Pass through cortex and medulla

What are the important cell types of the collecting ducts (2)?

1) Principal cells
2) Intercalated cells

Principal Cells

Maintain Na+ balance in the body

Would this influence absorption of any other substances? How?

It would impact H2O content because H2O follows Na+

Intercalated Cells

Helps maintain acid-base balance

What does each collecting duct receive? What do the collecting ducts dump into?

They receive filtrate from tubules of multiple nephrons & they fuse together to dump urine into the minor calyces

What are the types of nephrons (2)?

1) Cortical nephrons
2) Juxtamedullary nephrons

Cortical Nephrons

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

Juxtamedullary Nephrons

Nephron loops deeply invade renal medulla

How do cortical and nephron differ? How are they similar?

They consist of all the same structures previously discussed, but they have slight modifications

How does a change in nephron structure affect urine formation?

An increase in surface area, will increase the amount of water crossing, thus increase the amount of concentrated urine

Why/When is concentrated urine beneficial?

When we have a lack of H2O

What are the capillary beds of nephrons (3)?

1) Glomerulus
2) Peritubular capillaries
3) Vasa rectsa

Glomerulus

Maintains high pressure to increase filtrate production

Peritubular Capillaries

Low pressure capillaries arising from efferent arterioles & cling to renal tubules

What is the importance behind clinging to renal tubules?

They can reabsorb water & solutes from tubule cells

What do the peritubular capillaries empty into? Where does it go from here?

They empty into venules, in which filtrated blood returns to circulation

Vasa Recta

Efferent arterioles of juxtamedullary nephrons that run parallel to the nephron loop

What does the vasa recta help with?

Forming concentrated urine

Juxtaglomerular Complex

Portion of nephron where distal ascending limb lies against arterioles

What is the overall function of the juxtaglomerular complex?

Regulate blood pressure & filtration rate of the glomerulus

What are the cellular modifications at the juxtaglomerular complex (3)?

1) Macula dense
2) Granular (Juxtaglomerular) cells
3) Extraglomerular mesangial cells

Macula Densa

Chemoreceptor cells that monitor NaCl content of filtrate entering distal convoluted tubule

What effect does Na+ concentration have on afferent arterioles?

Na+ concentration causes afferent arterioles to constrict in order to slow the blood flow to increase reabsorption of Na+

What occurs in regards to reabsorption to Na+ concentration is too high?

The blood flow is going to be moving too fast, thus no Na+ will be able to be reabsorbed

Granular (Juxtaglomerular) Cells

Specialized smooth muscle cells that are found in arteriolar walls of afferent arterioles

What are granular cells stimulated by? What do they sense?

They are stimulated by macula densa cells and they sense blood pressure in afferent arterioles

What do granular cells secrete?

Renin

How does renin secretions increase?

Low NaCl concentration and low pressure in arterioles

What occurs due to low NaCl concentration and low pressure?

It indicates low filtrate formation

Extraglomerular Mesangial Cells

Packed between tubules and arterioles

What is the function of extraglomerular mesangial cells?

Unknown, but it is believed to regulate communicate between granular cells & the macula densa

What is urine formation called?

Diuresis

What is step one of diuresis? What is involved in this process?

Glomerular filtration, which is the production of a cell and protein-free filtrate that serves as the raw material for urine