urinary system

Kidney Functions

Regulating total water volume and total

solute concentration in water

• Regulating ECF ion concentrations

• Ensuring long-term acid-base balance

• Removal of metabolic wastes, toxins,

drug

Renin hormone

regulation of blood pressure

Erythropoietin hormone

regulation of RBC

production

Ureters

transport urine from kidneys to

urinary bladder

Urinary bladder -

temporary storage

reservoir for urine

Urethra

transports urine out of body

Kidney Anatomy location

Retroperitoneal, in the superior lumbar

region; ~ T12 to L5

Adrenal (suprarenal) gland

atop each kidney

Renal fascia-kidney

Anchoring outer layer of dense fibrous connective

tissue

Perirenal fat capsule - kidney

fatty cushion

Fibrous capsule-kidney

Prevents spread of infection to kidney

Renal cortex-kidney

Granular-appearing superficial region

Renal medulla -kidney

Composed of cone-shaped medullary (renal)

pyramids

Pyramids separated by

renal columns

• Inward extensions of cortical tissue

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

Minor calyces-kidney

Drain pyramids at papillae

Major calyces-kidney

Collect urine from minor calyces

– Empty urine into renal pelvis

Urine flow

Renal pyramid  minor calyx  major calyx

 renal pelvis  ureter

Kidneys cleanse

blood; adjust its

composition  rich blood supply

Renal arteries deliver

¼ (1200 ml) of

cardiac output to kidneys each minute

Arterial flow into

venous flow out of

kidneys follow similar path

Nerve supply via sympathetic fibers from

renal plexus

Path of blood flow through renal blood vessels (arteries)

Aorta, renal artery, segmental artery, interlobar artery, arcurate artery, Cortical radiate artery, Afferent arteriole, Glomerulus (capillaries), and Efferent arteriole

after efferent arteriole

Peritubular capillaries or vasa recta, Cortical radiate vein, Arcuate vein, Interlobar vein, Renal vein, and Inferior vena cava

Nephrons

Structural and functional units that form

urine more than 1 million per kidney

Two main parts of nephron

Renal corpuscle

– Renal tubule

glomerulus of renal corpusle

Tuft of capillaries; fenestrated endothelium 

highly porous  allows filtrate formation

Glomerular capsule of renal corpusle

Cup-shaped, hollow structure surrounding

glomerulus

Glomerular capsule of Renal Tubule Parietal layer

- simple squamous epithelium

Glomerular capsule of renal tube Visceral layer

branching epithelial podocytes

What are podocytes?

ranching epithelial cells in the visceral layer of the glomerular capsule that help form the filtration barrier.

What are foot processes in podocytes?

Extensions of podocytes that wrap around capillaries and attach to the basement membrane.

What are filtration slits?

Small gaps between foot processes of podocytes that allow filtrate to pass into the capsular space.

What is the function of the glomerular capsule structure?

it filters blood and allows water and small solutes to pass into the capsular space while keeping larger molecules (like proteins and cells) in the blood.

The Filtration Membrane site

Porous membrane between blood and

interior of glomerular capsule

the filtration membrane function

Water, solutes smaller than plasma proteins

pass; normally no cells pass

What are the three layers of the glomerular filtration barrier?

• Fenestrated endothelium of glomerular capillaries

• Basement membrane (fused basal laminae)

• Podocyte foot processes with filtration slits

What is the function of the fenestrated endothelium in the glomerulus?

It allows water and small solutes to pass through while preventing blood cells from leaving the capillaries.

What is the basement membrane in the glomerulus?

A fused layer of basal laminae from the capillary endothelium and podocytes that acts as a selective filtration barrier, blocking most proteins.

What is the role of podocyte foot processes in filtration?

They wrap around capillaries and create filtration slits that allow filtrate to pass while restricting large molecules

What are filtration slits and slit diaphragms?

• Filtration slits: gaps between podocyte foot processes

• Slit diaphragms: thin structures that span the slits and help repel macromolecules (like proteins)

What is the overall function of the glomerular filtration barrier?

To filter blood so that water and small solutes enter the filtrate while cells and large proteins stay in the bloodstream.

Renal Tubule three parts

proximal convoluted tubule (closest to renal capsule) , nephron loop, and distal convoluted tubule (farthest from renal corpuscle)

Proximal convoluted tubule (PCT) anatomy

Cuboidal cells with dense microvilli (brush

border  surface area); large mitochondria

proximal convoluted tubule functions

Functions in reabsorption and secretion

– Confined to cortex

Nephron loop Distal descending limb

descending thin

limb; simple squamous epithelium

Thick ascending limb nephron loop

Cuboidal to columnar cells; thin in some nephrons

Distal convoluted tubule (DCT) nephron loop

Cuboidal cells with very few microvilli and confined to cortex

distal convoluted tubule

Function more in secretion than reabsorption

Principal cells of collecting ducts

Sparse, short microvilli

• Maintain water and Na+ balance

Intercalated cells of collecting ducts

Cuboidal cells; abundant microvilli; two types

– A and B; both help maintain acid-base balance of blood

Collecting Duct receive

Receive filtrate from many nephron

Where do collecting ducts run in the kidney?

They run through the medullary pyramids, contributing to the kidney’s striped appearance.

Why do the medullary pyramids look striped?

Because the collecting ducts and other tubular structures run in parallel through them.

What happens to collecting ducts as they descend in the kidney?

They fuse together into larger ducts.

Where does urine go after leaving the collecting ducts?

It flows through the renal papillae into the minor calyces.

What is the pathway of urine from collecting ducts?

Collecting ducts → renal papillae → minor calyces → (then major calyces → renal pelvis → ureter)