Urinary System

Four major structures Kidneys Ureters Urinary bladder Urethra

Kidneys Organ that produces urine Performs other functions Contains nephrons

microscopic structure that produces urine

Left kidney lies in the upper ABD behind the spleen

Right kidney lies behind the liver Located at what we call the flank area Hilum

Where the renal artery, nerves, lymphatic vessels, and ureter pass into the kidney

Nephrons In a young adult there are aprox. One million We loose 10% per decade after age 40

CortexThe outer tissue region of the kidney MedullaThe inner tissue region of the kidney PyramidsMedulla is divided into fan-shaped regions PapillaWhere the pyramids terminateCasts into the renal pelvis a hollow space

The spaces of the pelvis come together at the derivation of the ureter

Urine forms in the cortex and medulla and leaves the kidney through the renal pelvis and the ureter

Nephron Functional unit of the kidney Forms urine Consists of a tubule Each tubule is divided into parts of a different

structure and capillaries which form a complex net of vessels that covers the surface of the tubule

Glomerulus

Capillaries that filter blood into a nephron Bowman’s capsule First part of the nephron tubule that is a cup-

shaped, hollow structure

Water and chemical substances enter the tubule through the bowman’s capsule and after passing through the successive parts of the tubule proximal tubule

descending loop of henley

ascending loop of henley

distal tubule

Urine drips in the collecting duct before entering the renal pelvis and ureter

Nephron Physiology

Major functions of the kidneys

forming urine

eliminating urine

Entails Maintaining blood volume with proper balance

of water,electrolytes and pH Retaining glucose while excreting waste such

as urea

Controlling arterial blood pressure

relies both on urine formation and another mechanism that does not involve formation of urine

Kidney cells regulate erythrocyte development ; does not involve urine formation

First step in urine formationfiltration of blood

Blood flows through the capillaries of the glomerulus and water and numerous chemical materials are filtered out into the Bowman’s Capsule

Blood cells and plasma proteins are not filtered as they are too large to pass through into the capsule

Filtrate

Fluid after the filtration process Blood is filtered at a rate of 180L/day Thus urea and drug metabolites can be filtered

so quickly that they don’t accumulate in the blood

The process of reabsorption and secretion maintain homeostatis of the body

Reabsorption and Secretion Intracellular transport

simple diffusion

facilitated diffusion

active transport

Simple diffusion Molecules small enough to permiate the cell

membrane randomly move in and out of the cell

Requires no energy Higher [ ] to lower [ ] equalizes both sides

Osmosis

the movement of water to equalize [ ] on both sides of the membrane

Osmolarity

When particles are dissolved in water they move so that the [ ] is equal on both sides

Facilitated diffusionA molecule-specif “helper” or carrier acts as a

tunnel and speeds the molecule along and through the membrane

i.e.GlucoseWhen insulin binds to a glucose-specific carrier,

it can pass 10x quicker than without insulin

Active transport {“uphill”} Net movement of lower to higher [ ]. Requires E Essential for homeostasis by handling

electrolytes and glucose as well as other substances

Water and Electrolytes

Electrolytes

Na+

K+

H+

Cl-

The handling of water and electrolytes is the footing for control of blood volume and electrolyte balance

Maintaining blood volume Na+ is the main cation in extracellular fluid

whereas K+ is the main cation in intracellular fluid

Appropriate retention of Na+ along with osmotic retention of water

Electrolyte and pH balance Retention of K+ and Cl-

So. . . . . . . .

Filtrate formed in the Bowman’s capsule enters the proximal tubule.

65% of Na+ and Cl- is reabsorbed as well as osmotic reabsorption

At the same time H+ is secreted which through a process determines the pH of venous blood leaving the kidneys as well as the excreted urine

20% of water in the filtrate is reabsorbed

Diuresis

Formation and passage of a dilute urine, decreasing blood volume

Handling of Glucose Freely filtered into the Bowman’s capsule Reabsorbed before filtrate enters the proximal tubule Retained to a certain level then glucose is lost in

urine When there is so much glucose in the filtrate

reabsorption becomes insufficient so not only is glucose lost in but large amounts of water as well

Control of arterial blood pressure The balance of water and electrolytes thus

maintaining blood volume Juxtaglomerular cells respond to low blood

pressure by releasing the enzyme renin Renin then produces the hormone angiotensin

I Angiotensin I flows through the lungs and by

process produces Angiotensin II

Angiotensin II acts on both kidney tubular cells and on adrenal cells

Adrenal cells produce aldosterone

So how do these all come into play. . . .?

Aldosterone

Target tissue; distal tubule

collecting duct

Effects increases reabsorption of Na+, Cl- and water

Angiotensis II

Target Tissue; Proximal tube

Effects: increases reabsorption of Na+, Cl- and water

increases secretion of H+