Excretion

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EXCRETIONIt’s not only to get rid of wastes, it’s the maintenance of

constant equilibrium to preserve health.


How do we keep ourselves in equilibrium?HOMEOSTASIS: Includes the processes by which organisms maintain their internal environment within a narrow range of conditions necessary for cells to function properly under changing conditions.These changes include• Temperature• Water and salt concentrations• Glucose concentrations• pH• Oxygen and carbon dioxide concentration


Excretion=filteringCell membranes in excretory structures serve as filters for extracellular fluids. In animals it helps filtering blood too.

Through this process, the system keeps osmolarity which means proper concentration of substances in cells and their environment (water balance)


Urinary systems remove wastes from cellular metabolism • Water and small molecules are filtered both from blood

or extracellular fluids.• Nutrients are selectively reabsorbed back from the

filtered fluid.• Excess of water, nutrients and disolved wastes are

excreted from the body in urine.


EXCRETION IN ANIMALS

Protonephridia Malphigian tubules Nephridia


HUMAN URINARY SYSTEM

What kidneys are for…• Regulate blood levels of ions such as Na, K, Cl and Ca.• Maintain pH of blood by regulating H and H2CO3• Regulate water contents.• Retain important nutrients such as glucose and

aminoacids.• Eliminate cellular waste such as urea.• Secreting hormones


HUMAN URINARY SYSTEM


STRUCTURE FUNCTIONRENAL ARTERY

Transports blood with wastes from the inferior Aorta.

KIDNEY Filter blood and produces urine.RENAL VEIN Transports filtered blood from the kidneys to

the Vena Cava.URETER Transports urine from kidneys.URINARY BLADDER

Stores urine from ureters.

URETHRA Tube by which urine is expulsed from the body.


In the inside… Renal Capsule: A smooth semitransparent membrane

that adheres tightly to the outer surface of the kidney. Renal Cortex: The region of the kidney just below the capsule. Renal Medulla: The region deeper into the kidney, beneath the cortex layer. It is segregated into triangular regions called the renal pyramids, which should be striated (or striped) in appearance due to the collecting ducts running through them, and columnar regions between the pyramids called the renal columns in which arteries are located.Renal Pelvis: A cavity within the kidney that is continuous with the ureter, which exits from the hilus. The pelvis has portions that extend towards the apexes of the renal pyramids. The primary (large) extensions are the major calyces and the smaller extensions are the minor calyces.


Within the pyramids FILTRATION: Blood enters the Bowman’s capsule under relatively high pressure. 1/5 of plasma is filtered (water, glucose, vitamins, salts and urea). REABSORPTION: Many substances are reabsorbed selectively in the walls of the proximal tubule and the distal tubule by osmosis and active transport. The Loop of Henle keeps the high concentration of Cl and Na ions to ensure reabsorption of water in the distant tubule.


Blood vessels make a clustered network by which blood is filtered. Inside the Bowman’s capsule, a tangle of capillaries called glomerulus press blood to help plasma to be filtered. Venules collect filtered plasma and reabsorbed nutrients into the bloodstream.Some arterioles secrete substances from plasma with wastes and toxic materials into the distal tubule to be dismissed.


ELIMINATION: All collecting tubes from the pyramids meet at the renal pelvis where they transport urine. Then, it goes through a narrow tube called ureter that goes downwards to a sac-like structure called urinary bladder. Contractions of ring-like muscles called sphincters force urine out of the body through a tube called urethra.

Usually an adult eliminates from 1.5 to 2.3 L of urine every day. At least 500 mL of urine must be eliminated daily.

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Excretion