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

Cortex The outer tissue region of the kidney Medulla The inner tissue region of the kidney Pyramids Medulla is divided into fan-shaped regions Papilla Where the pyramids terminate Casts 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 formation filtration 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 diffusion A molecule-specif “helper” or carrier acts as a tunnel and speeds the molecule along and through the membrane i.e. Glucose When 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 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

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