The

Excretory System

Words To Know When Excreting

Contractile vacuoles: in cytoplasm of different protists and they collect water and merge with the plasma membrane to release the water to the outside

Flame Cells: found in platyhelminthes are along the branched tube system and this is where body fluids are filtered across.

Nephridia (or metanephridia: simple tube-shaped structure used to remove ammonia from the blood and release it from the body.

Malpighian tubules: are in arthropods and are tubes attached to the middle of the digestive tract and they collect body fluids of nitrogen waste and salt and water go to the midgut.

Kidney: organ that filters excess water, and other waste products from the blood and excretes them out of the body. Nephrons are filtering tubules in the kidney.

Ureter: tube that carries fluid from the kidney to the urinary bladder or cloaca.

Urethra: tube through which urine is released from the body.

Urinary bladder: saclike organ where urine is stored before being excreted.

Urine: waste fluids that are sometimes poisonous to the body

Getting rid of excess waste began with…

DiffusionIn the earlier life forms diffusion occurred when there were two layers of cells, an inner and an

outer layer.

PORIFERA• SUBSTANCE SECRETED: Ammonia

• STRUCTURE USED: Water serves as the primary component in the excretory system of Sea Sponges

• HOW: Water filters through the unspecialized cells where by-products of cellular respiration are released into the flowing water

CnidariaNo true excretory

system ~A simple organism in which all cells are in contact with the external aqueous environment.

~It uses simple diffusion to let waste get through the cell membrane.

As evolution took place a third layer of cells arose and they used…

ProtonephridiaOne step Up from diffusion

because now it is more difficult to get rid of excess waste.

Platyhelminthes• Substance secreted: excess water• Structure used: network of ducts (pores and canals); flame cells; Protonephridia

• How: Excess water eliminated by a network of ducts which contain flame cells. The flame cells enclose a tuft of beating cilia, moving the wastes into the ducts, through the excretory pores, and out of the body.

More time went on and a more sophisticated way to excrete excess

waste was needed so life forms developed…

Tubes that connected to the outside of the body or to

storage facilities within the body

Nematoda• SUBSTANCE SECRETED: Ammonia

• SYSTEM USED:Body walls

• HOW: Diffusion transports wastes created by cellular metabolism through the body walls of the roundworm and releases them.

Even more sophisticated was the…

Paired Metanephridia

MolluscaSubstance secreted: ammonia

Structure used: Paired Nephridia

How: The cellular metabolism produces nitrogen containing waste (ammonia) which is poisionous so they must remove it. It becomes urine and then is released via the nephridia through the mantle cavity.

Annelida• Substance secreted: urea

• Structure used: 2 pairs of nephridia in each body segment• How: Fluid from the circulatory system is filtered into fluid that fills the central body cavity. This fluid enters the nephridia tubules where some of it is secreted into the urine before it is excreted from a pore with the nitrogenous wastes

More sophistication took place and then came along the addition of…

Malpighian Tubules

Arthropoda• Substance secreted: solid uric acid crystals• Structure used: Malphigian tubules• How: The Malphigian tubules remove wastes from the blood, concentrate them, and then add them to undigested food before it leaves via the anus

Because the next group are Deuterostoma they are

considered more complex than the others yet they still use a form of diffusion to get rid of

waste

EchinodermaSUBSTANCE SECRETED: Ammonia

STUCTURE USED: Tube feet and Skin Gills

HOW: There is no systematic need to remove wastes, it leaks out through the tube feet and skin gills

Then the addition of Using the Kidney took place in

deuterosomes

Chondrichtyhes• Substance Secreted: Ammonia

• Structures Used: Kidneys and gills• Wastes diffuse either through the gills into the surrounding water or they are removed by the kidneys

The Most sophisticated structure of excretion are the….

Kidneys

Osteichthyes (bony fish)

Substance Secreted: Urine (ammonia)Structure Used: Kidneys

How it works: Nitrogenous waste can and some will diffuse through the gills of the fish.

…continuedFish in salt water loose water by

osmosis; their kidneys are able to concentrate waste and return as much water as possible to the fish.

Fish in fresh water pump out diluted urine because osmosis is always bringing in fresh water.

An example is salmon. Because of the way their kidneys function they can go from fresh water to salt water and vice versa

Amphibia• SUBSTANCE SECRETED:Urea through Urine

• STRUCTURE USED: Kidneys, Blood, Ureters, Cloaca, and Urinary Bladder

• HOW: The kidneys filter out wastes from the blood stream and and down the ureters and and into the cloaca where it is either released or sent to the urinary bladder where it can be held until excretion

Reptilia• Substance Secreted: Urine or uric acid

• Structure used: kidneys and they may have a urinary bladder

• How it works: Eliminate wastes in the form of urine, produced in their kidneys. Many excrete nitrogen-containing wastes in the form of uric acid rather than ammonia. This conserves water because uric acid doesn’t have to be diluted with water like ammonia does.

Aves (birds)Substance Secreted: Urine

Structure Used: Kidneys

How: Since a lot of birds live over or near salt water they have salt glands near their eyes that act like an extra pair of kidneys. This is how they get rid of excess salt.

…continuedThe urine of birds has uric

acid which flows to the cloaca through the ureters.

In the cloaca the water is reabsorbed so that the uric acid becomes crystals that are white and pasty-like (BIRD POOP!)

Mamalia• SUBSTANCE SECRETED: Urea, Water, Uric Acids, and other wastes through Urine

• STRUCTURE USED: Kidneys, Ureter,Urethra, and Urinary Bladder

• HOW: The kidneys are able to filter wastes from the blood stream while also retaining much needed nutrients that cannot afford to be lost. The removed wastes are sent down to the Urinary Bladder by way of the ureter where it is either held or excreted through the urethra.

The Kidney• The Kidney filters blood, controls the reabsorption of salts, glucose and amino acids, as well as collects and secretes NH3 in the less toxic form of urea

The Nephron

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• Filters blood through Glomerulus into Bowman’s Capsule

• Proteins and blood cells are too large to pass through, but Nitrogenous wastes and liquids enter easily

• The filtrate passes through the Proximal Convoluted Tube (PCT), the Loop of Henle, and the Distal Convoluted Tube (DCT); necessary molecules which diffused into the capsule are pumped back out into the Vasa Recta (thin walled blood vessels)

• The reabsorption of proteins, amino acids, sodium, and glucose into the blood stream begins at the PCT

Bowman’s Capsule and the Glomerulus**************************************************

• After the blood enters the dense ball of capillaries known as the Glomerulus, the small nitrogenous waste particles flow into Bowman’s capsule through diffusion

• The blood cells and other larger molecules return to the blood stream via a net-like system of blood vessels with thin walls

The Proximal Convoluted Tubule• The filtrate enters this tubule from Bowman’s Capsule

• necessary metabolites (glucose, sodium, amino acids, protein) are rescued by active transport which pumps them back into the blood stream by way of the Vasa Recta

The Loop of Henle~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• The end of the loop enters the center part of the kidney known as the medulla which is highly concentrated with sodium outside of the cells

• In the descending portion of the loop which is inside of the medulla, the sodium enters the loop through osmosis and mixes in with the filtrate

On the ascending portion of the loop, as it exits the medulla, the sodium is drawn back into the medulla along with water, making the filtrate more concentrated

The Distal Convoluted Tubule

• The Distal Convoluted Tubule is in charge of retaining water while sodium chloride and other inorganic salts are being absorbed

• It leads into the Collecting Duct

Collecting Duct˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚˚

• This is the main site for the reabsorption of water with the help of the Antidiuretic Hormone

• The Colleting Duct drains into the Renal Pelvis and from there into the Ureter and on to the Bladder

Antidiuretic Hormone

•A hormone secreted by the posterior pituitary gland and produced by the hypothalamus

• It causes the Collecting Duct to become more permeable to water to prevent it from leaving the body if the body were to be dehydrating

•A side affect of this hormone is that it leads to a rise in the volume of blood

Aldosterone• Aldosterone, a steroid hormone, is produced by the adrenal cortex in response to low levels of extra cellular sodium

• It works on the Distal Tubule stimulates the reabsorption of sodium and water by osmosis from the Urine (filtrate) as a means of conservation of water and sodium

• It reduces the volume of the extra cellular fluids while decreasing the urine volume

• Aldosterone leads to a rise in blood volume and pressure

And for Christy, because the Excretory System and Elimination are related

The End!

By Amanda Pouchot, Christy Titchenal, Alli Montana