Serves many crucial functions relating to homeostasis

And performs excretion of wastes

Blood is filtered to remove water and

small dissolved molecules

Then nutrients are reabsorbed from the

filtrate

Remaining water and dissolved wastes

are excreted

Protonephridia= the first specialized excretory structure that arose during evolution

Still used by flatworms› Regulates water balance

› Which consists of tubes that branch throughout the body

End in flame cells (single celled bulbs) Named for the cilia that extends into the bulb

Water is filtered into the bulbs › The continuously beating cilia conduct the fluid

through the tubes

› More waste is added and some nutrients are reabsorbed

› Then it reaches a pore and leaves through diffusion

cilia

nucleus

flame

cell

fluid

eyespot

tubule

extended

pharynx

excretory

pores

Earthworms, mollusks, and several others

have simple kidney like structures

(nephridia)

› Fluid fills the body cavity (coeluom) and

surrounds the organs collecting wastes

› Flows through the nephrostome that

reabsorbs salts and nurtients into the blood

› Leaves behind water and wastes that is

stored in a bladder area of the nephridium

Then waste is excreted through the excretory

pores (an opening in the body wall)

› Each segment of an earthworm has its own

nephridia

coelom

(contains

coelomic fluid)

nephridia

intestine

ventral nerve cord nephrostomeexcretory pore

Excretory systems must eliminate dissolved

wastes without losing too much water in the

process

› Water may also still contain nutrients

Kidneys collect and absorb extra nutrients

from blood and other bodily fluids

› At the same time wastes and dangerous

chemicals, to be excreted, are also filtered out

Regulating blood levels of ions such as

sodium, potassium, chloride, and calcium

Regulates water content of blood

Maintains pH of blood

Retains nutrients like glucose and amino acids

Secretes hormones such as erythropoietin

which stimulates red cell production

Eliminates cellular waste such as urea

Urea is a product of amino acid

metabolism

› Digestive system breaks proteins into

amino acids

Those are absorbed

Some used for new proteins

Others lose their amino groups (-NH2) and used for

energy or to synthesize new molecules

The amino groups are released as ammonia

(NH3) which is toxic

This travels in blood to the liver where it is

converted to urea (far less toxic)

The Urea is then filtered from the blood by the

kidneys

› Excreted in urine (fluid containing water, dissolved

wastes, and excess nutrients)

Mammals avoid ammonia’s dilapidating

effects by excreting it in water

› But then we lose water

› Reptiles excrete it in uric acid with little loss of

water

1 In cells, amino acids are brokeninto simpler molecules, releasingammonia.

NH2 CH C

O

R

OH

ammonia

(NH3)

carried in

blood

2 In the liver, ammonia is combined

with CO2 to produce urea.

urea

carried in

blood

NH2CNH2

O

3 In the kidneys, urea and otherwater soluble wastes are converted into urine.

excreted in

urine

amino acid

The Urinary System Consists of the: Kidneys- paired organs located on either side of the spinal column

and extending slightly above the waist where blood carrying cellular waste enters to be filtered.

Renal Artery- The artery which blood enters each kidney.

Renal Vein- The vein which blood exits each kidney.

Ureter- Muscular tube through which urine leaves each kidney to reach the bladder.

Bladder- Hollow, muscular chamber which collects and stores urine.› Muscles contained in the walls of the bladder are capable of considerable

expansion.

Urine is retained in the bladder by two sphincter muscles located at its base.

Urethra- Through this narrow tube, urine exits the body. 1.5 inches long in females and 8 inches long in males.

Renal Artery/Vein

Urinary System

Structure of the Kidneys: Each kidney contains a sold

outer layer where urine is

formed, which consists of

the renal cortex overlying

the renal medulla, and a

subdivided inner chamber

called the renal pelvis, that

collects urine and funnels it

into the ureter.

More the one million tiny,

Individual filters called

Nephrons are pack into the

Outer layer of each kidney.

The three major parts of the nephron are the glomerulus, the

tubule, and the collecting ducts.

With the help of these three structures. Each individual nephron is

able to filter the blood and produce urine to be excreted.

GLOMERULUS: Within a cup-shaped portion of the nephron- Bowman’s Capsule-

the arteriole, which supplies each nephron with blood and branches

from the renal artery, branches further into the microscopic

capillaries that intertwine in a mass called the glomerulus.

Within its water permeable walls, pressure is created through

difference in diameter between the larger incoming arteriole and

the smaller outgoing arteriole. This process is termed filtration, and

the resulting fluid is called filtrate. This fluid

collects into the Bowman’s Capsule and

through the nephron.

Blood after passing through the

glomerulus is more concentrated.

Tubule: Through the processes of tubular reabsorption, which occurs

primarily in the proximal tubule and tubular secretion, which occurs

primarily in the distal tubule, the tubule of the nephron will restore

needed nutrients and most of the water to the blood to the filtrate in

the Bowman’s Capsule. This will be done while retaining wastes for

elimination, maintaining a balance required for homeostasis.

Loop of Henle/Collecting Ducts: Urine can become concentrated because there is an osmotic

concentration gradient of salts and urea in the interstitial fluid that

surrounds the loop of Henle and the collecting ducts.

As filtrate passes through this area, additional water may leave the

filtrate through walls of the collecting ducts, while wastes are left

behind. This filtrate, as is passes through the ducts, is now called

urine.

It is important to produce concentrated urine when water is scarce,

and to produce dilute, watery urine when there is excess water in

the blood. All this depends on the permeability of the collecting

duct to water, which is, in turn, controlled by the amount of

antidiuretic hormone.

Loop of Henle

Disorders of this system include:› Gout, also known as gouty arthritis, is incredibly common and

painful. People with gout usually first experience pain in the joint

of the big toe.

› A kidney stone, also known as a renal calculus is a solid

concretion or crystal aggregation formed in the kidneys from

dietary minerals in the urine.

› Pyelonephritis is an ascending urinary tract infection that has

reached the pyelum or pelvis of the kidney. It can lead to kidney

failure and death.

The kidneys regulate the water content

of the blood

Human kidneys filter out about half a

cup of fluid from blood each minute

Without reabsorption of water, your body

would produce 50 gallons of urine daily

The amount of water reabsorbed is

controlled by an antidiuretic hormone

(ADH)

Kidneys produce two hormones that are

essential to regulating blood

When blood pressure fails, the kidneys

release renin into the bloodstream

› Renin is an enzyme that speeds up the

formation of the second hormone,

angiotensin

› Angiotensin is a protein that causes arteries

to constrict, raising blood pressure

In response to low oxygen levels, the

kidneys release erythropoietin

Erythropoietin travels to the bone

marrow, where the marrow is

stimulated to produce more red

blood cells

Kidney failure leads to anemia

, because the kidneys do not produce

enough erythropoietin to make the minimal number of red blood cells

Different types of mammals have

different kidney structures depending on

the availability of water in their habitat

The longer the Henle, the more

concentrated the urine is, which means

more water is conserved

A loop of Henle is what recycles water,

the longer the loop, the less diluted the

urine is

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