Excretion

All organisms produce waste in the process of metabolism. If the waste is allowed to accumulate, it will cause a problem for the organism

Excretion: is the process of removing waste products of metabolic processes.

Summary of metabolic wastes….

Large Intestine – removes waste from the digestive system

Liver- transforms toxins such as alcohol, drugs, heavy metals and products of protein metabolism into soluble compounds that can be eliminated by the kidneys

The Kidney and Urinary System

Humans have 2 kidneys, located low in the abdominal cavity

Function of Urinary Systemremove waste, balances blood pH, and

maintains water balance.

The average adult loses ~2L of water every day through urine, perspiration, and exhaled air – and even more under physical activity.

To maintain water balance, adults should drink ~2L of fluids (~8 glasses) daily to replenish lost water.

Nitrogenous WasteProteins are very important in your diet because

they maintain tissues, promote cell growth, and direct cell processes

Excess proteins are often converted into carbohydrates.

Unlike proteins, carbohydrates don’t have nitrogen – so the nitrogen component is a waste component that needs to be removed from your body.

Nitrogenous WastesDuring deamination (break down of proteins),

ammonia (NH3) is formed.Ammonia is toxic – even in small amounts In the liver, ammonia combines with CO2 to

produce UREA.UREA is much less toxic.Uric acid is also produced (from breakdown

of nucleic acids).Both are released in urine.

Urinary System – Basic Summary

Blood flows to the kidneys (via the renal artery)

Wastes are filtered from the blood by the kidneys (the filtered blood leaves the kidneys via the renal vein)

These waste products form urine.

Urine leaves the kidney via the ureter and goes to the bladder for temporary storage

When the bladder is full, a signal is sent to the brain (to give you the urge to urinate)

Urine leaves the bladder via the urethra

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The NephronThe functional unit of the kidney is a slender

tubule called a nephron

There are ~ 1 million nephrons in a single kidney.

Urine is formed inside the nephron

~1 million slender tubules called NEPHRONS make up the kidney

Fluid Flow through the KidneysBlood is brought to the kidneys via the renal

artery

The renal artery branches into the afferent arterioles

The afferent arterioles branch into a capillary bed called the glomerulus

Blood leaves the glomerulus via the efferent arterioles

Blood then flows through the peritubular capillaries (which are entwined around the nephron) and joins a venule and then the renal vein to leave the kidney (and eventually return back to the heart for recirculation)

The glomerulus is surrounded by a portion of the nephron called the Bowman’s Capsule.

Here, fluids that will be processed into urine enter the Bowman’s capsule from the blood.

Fluids then flow through a thinner tubule called the proximal tubule to the loop of Henle to the distal tubule to the collecting ducts where urine from many nephrons merge.

The collecting ducts all merge at the renal pelvis which delivers urine to the ureter

FORMATION OF URINE

Includes: filtration, reabsorption, and secretion

FILTRATION: fluids moved from the blood to the bowman’s capsule.

(Also referred to as *ultrafiltration)

Too large to diffuse through the walls of the glomerulus. Only smaller molecules can pass through.

ReabsorptionREABSORPTION: Transfer of essential solutes

and water from the nephron back to the blood.

~600mL of fluid flows through kidneys every minute

20%/~120mL is filtered into the nephrons.

If none of that was reabsorbed, you would form 120mL of urine every minute.

ReabsorptionIn reality, about 119mL is reabsorbed and

1mL of urine is formed (for every 120mL)Active and passive transport are both used.Numerous mitochondria in the surrounding

cells provide energy for active transport.Reabsorption occurs until the threshold level

of a substance is reached.Excess NaCl remains in the nephron to be

excreted with urine

Secretion

SECRETION: movement of materials from the blood back into the nephron

These are wastes such as nitrogen-containing wastes, excess H+ ions, minerals (K+), drugs

Cells with lots of mitochondria line the distal tubule to provide energy for active transport.