Objectives:1.13.0 Identify structures and functions of

the urinary system 2.13.1 Tracing the filtration of blood from

the kidneys to the urethra 3.13.2 Recognizing diseases and disorders

of the urinary system

Urinary System:removes salts and nitrogenous wastes from the blood.

helps maintain normal concentrations of water and electrolytes of bodily fluids

regulates pH and volume of bodily fluids

helps control RBC production and blood pressure

Organs of the Urinary SystemKidneysUrinary bladderThey are connected by the ureters.The urethra takes urine from the bladder

to the outside of the body.

KidneysLocated on either side of the vertebral column, on the posterior wall of the abdominal cavity.

Left is 1.5-2.0 cm higher than the right

Where do people feel kidney pain?

Kidney Structure Lateral surface is convex; medial side is deeply concave.

Medial depression leads to hollow chamber called the renal sinus.Entrance to sinus is called hilum, and it is also the passage for blood vessels, nerves, lymphatic vessels, and the ureter.

Kidney Structure, continued…..Superior end of the ureter forms the renal pelvis (funnel-shaped sac inside the renal sinus)

Renal pelvis subdivides into major calyces (tubes, which divide into minor calyces.

Renal papillae project into the renal sinus.

Kidney Structure, continued…..Two distinct regions in the kidneys:Renal medulla (inner)

Composed of conical masses (renal pyramids) that appear striated

Renal cortex (outer)Forms a shell around medullaProjects into medulla between renal

pyramids, forming renal columns

Kidney FunctionsRegulate composition and volumes of extracellular fluids

Secrete hormone erythropoietin (???)

Role in activation of vitamin DHelp maintain blood pressure

Extracellular fluid volumeSecrete enzyme renin

NephronsThe kidneys’ functional unitsAbout 1 million in each kidneyEach nephron consists of:

Renal corpuscleRenal tubule

Nephron, continued…..Renal corpuscle composed of:

Glomerulus – tangled cluster of capillaries that filter fluid

Glomerular capsule – sac-like structure surrounding the

glomerulusLocated at the proximal end of the

renal tubuleReceives the fluid filtered by the

glomerulus

Nephron, continued…..Renal tubule:

Transports fluid from the glomerular capsule to a minor calyx

Proximal convoluted tubule: Dips down toward the renal pelvis

and becomes the descending limb of the nephron loop (“loop of henle”)

Curves back up (ascending limb of the nephron loop)

Becomes coiled again (distal convoluted tubule)

Nephron, continued…..Distal convoluted tubules from several nephrons will merge in the renal cortex to form a collecting duct

In the renal medulla, several collecting ducts will merge before emptying into a major calyx through an opening in a renal papilla.

Renal Blood FlowRenal arteries branch off the _________, and enter the kidneys through the ____.

Renal arteries give off several branches:Interlobal arteries → arcuate arteries → interlobular arteries → afferent arterioles

The afferent arterioles enter the nephrons and form the glomerulus.

Renal Blood Flow, continued…..Blood leaves the glomerulus through efferent arterioles.

The efferent arteriole branches into a network of capillaries, called the peritubular capillary system.

Blood then enters the venous system of the kidney and enters the __________ through the renal vein.

Renal Blood Flow SummaryAbdominal aorta → renal artery →

interlobular arteries → afferent arteries → glomerulus → efferent arteries → peritubular capillaries → renal vein → inferior vena cava

Movements Through Cell MembranesPassive mechanisms:

Diffusion – EX: exchange of O2 and CO2 in the lungs

Facilitated diffusion – uses carrier molecules; EX: movement of glucose through cell membrane

Osmosis – movement of water…..Filtration – EX: water molecules leaving blood capillaries

Movements Through Cell Membranes, continued…..Active mechanisms:

Active transport - moves molecules from areas of lower concentration to areas of higher transportation

Endocytosis – cell membrane engulfs substances, bringing them into the cell

Exocytosis – a vesicle fuses with the cell membrane to “expel” a substance

Urine Formation1. Glomerular filtration:

Glomerular capillaries filter blood plasma

Produces 180 L of fluid daily! (more than 4x total body fluid)

2. Tubular reabsorption: kidneys reclaim water, electrolytes, and glucose needed by the body

3. Tubular secretion

1. Glomerular FiltrationGlomerular capillaries contain many tiny openings, making them more permeable than capillaries in other tissues.

Glomerular capsule receives the glomerular filtrate (mostly water and same components as plasma)

Filtration is driven by pressure differences (net filtration pressure).

2. Tubular ReabsorptionComposition of glomerular filtrate entering renal tubule is different than that of urine leaving the tubule:Glucose – present in glomerular filtrate, absent in urine

Urea and uric acid – more concentrated in urine than in glomerular filtrate

Tubular Reabsorption, continued…..Some substances pass out of the tubular fluid, through the epithelium of the renal tubule, and into the interstitial fluid.

These substances diffuse into the peritubular capillaries.

Reabsorption occurs throughout the renal tubule, but mostly in the proximal convoluted tubule.

Tubular Reabsorption, continued…..Different parts of the tubule are designed to reabsorb specific substances, using different transport modes:

Substance Transport Mechanism

Portion of Tubule

Glucose Active transport

Proximal tubule

Water Osmosis Throughout tubule and collecting duct

Amino acids Active transport

Proximal tubule

Protein Endocytosis Proximal tubule

Various chemicals

Active transport

Proximal tubule

Sodium ions Active transport

Throughout tubule and collecting duct

Cl-, PO4-3, and

HCO3- ions

Passive transport

Throughout tubule (w/Na+ ions)

3. Tubular SecretionCertain substances move from the peritubular capillaries into the renal tubule.

As Na+ is reabsorbed, they may “trade places with” K+ or H+ ions

Urine Formation Recap1. Glomerular filtration of plasma2. Tubular reabsorption of

substances into the interstitial fluid: water, glucose, sodium, potassium, calcium, proteins, amino acids, etc.

3. Tubular secretion of substances into urine: hydrogen and potassium ions, etc.