Urinary System Presentationyorkville College 1203376567476185 2

1. Urinary System Presented By: Milani, Mandeep, Karthiga, Gladyz, Elisa

Although many believe that the kidneys are located in the lower back, this is not their location.

These small, dark red organs with a kidney bean shape lie against the dorsal body wall in a retroperitoneal position (beneath the parietal peritoneum) in the superior lumbar region.

The kidneys extend from the T12 to the L3 vertebra; thus they receive some protection from the lower part of the rib cage.

Right kidney is slightly lower then the left

It is convex laterally and has a medial indentation called the renal hilus.

Atop each kidney is an adrenal gland, which is part of the endocrine system and is a distinctly separate organ functionally.

A fibrous, transparentrenal capsuleencloses each kidney and gives a fresh kidney a glistening appearance.

The adipose capsule, surrounds each kidney and helps hold it in place against the muscles of the trunk wall.

When a kidney is cut lengthwise, three distinct regions become apparent, as can be seen in this picture.

The outer region, which islightin color, is therenal cortex.

Deep to the cortex is a darker reddish-brown area, therenal medulla.

The broader base of each pyramid faces toward the cortex; its tip, the apex, points toward the inner region of the kidney.

The pyramids are separated by extensions of cortex like tissue, therenal columns.

Medial to the hilus is a flat, basinklike cavity, the renal pelvis

Pelvis is continuous with the ureter leaving the hilus.

Extension of the pelvis, calyces (calyx), form cup-shaped areas that enclose the tips of the pyramids.

The calyces collect urine, which continuously drains from the tips of the pyramids into the renal pelvis.

Urine then flows from the pelvis into the ureter, which transport it to the bladder for temporary storage.

The kidneys continuously cleanse the blood and adjust its composition, so it is not surprising that they have a very rich blood supply

One-quarter of the total blood supply of the body passes through the kidneys each minute.

The arterial supply of each kidney is therenal artery

As the renal artery approaches the hilus, it divides intoSegmental arteries .

Once in side the pelvis, the segmental arteries break up intolobar arteries

Each of which gives off several branches calledinterlobar arteriesthen branch off the arcuate arteries and run outward to supply the cortical tissue.

The venous blood draining from the kidney flows through veins that trace the pathway of the arterial supply but in a reverse direction-interlobular veinstoarcuate veinstointerlobar veinsto therenal vein , which emerges from the kidney hilus

Each kidney contains over a million tiny structures called nephrons.

Nephrons are the structural and functional units of the kidneys and, as such, are responsible for forming urine.

Each nephron consists of two main structures: aglomerulus , which is a knot of capillaries, and arenal tubule .

The cup- shaped of the renal tubule is called the glomerular, or Bowmans, capsule.

The inner layer of the capsule is made up of highly modified octopus- like cells calledpodocytes

Extends from the glomerular capsule, it coils and twists before forming a hairpin loops and then again becomes coiled and twisted before entering a collecting tubule called thecollecting duct. (these different regions of the tubule have specific names)

These different regions of the tubule have specific names.

Most nephrons are calledcortical nephronsbecause they are located almost entirely within the cortex.

Thecollecting ducts , each of which receives urine from many nephrons, run downward through the medullary pyramids, giving them their striped appearance.

Theafferent arteriole , which arises from an interlobular artery, is the feeder vessel, and theefferent arteriolereceives blood that has passed through the glomerulus.

The glomerulus, specialized for filtration, is unlike any other capillary bed in the entire body.

The second capillary bed, theperitubular capillaries , arises from the efferent arteriole that drain the glomerulus.

Unlike the high-pressure glomerulus, these capillaries are low- pressure, porous vessels that are adapted for absorption instead of filtration.

The peritubular capillaries drain into interlobular veins leaving the cortex.

It is a result of three processes:

FILTRATION

TUBULAR REABSORPTION

TUBULAR SECRETION

Glomerulus Acts as a Filter

Water and solutes smaller than proteins are forced through the capillary walls and pores of the glomerular capsule into the renal tubule.

Both proteins and blood cells normally too large to pass through the filtration membrane and when either one of these appear in urine it is evident there is a problem with the glomerular filters

Also, systemic blood pressure has to be normal in order for filtration to happen

If the arterial blood pressure falls too low, the glomerular pressure becomes inadequate to force substances out of the blood and into the tubules, and filtrate formation stops

Oliguria: an abnormal low urinary output if it is between 100 and 400 ml/day

Anuria if it is less than 100ml/day

Low urinary output indicates that glomerural blood pressure is too low to cause filtration

However, Anuria may also result from transfusion reactions and acute inflammation or from crush injuries of the kidneys

Blood from afferent arteriole flows into the glomerulus (capillaries)

Due to blood pressure in the glomerulus, filtration occurs

Water and small molecules (such as salts, amino acids, urea, uric acid, glucose) move from the blood plasma into the capsule

Small molecules that escape being filtered and the nonfilterable components leave the glomerulus by the Efferent arteriole

This produces a filtrate of blood, called glomerular filtrate

Filterable Blood Components

Nutrients

Nitrogenous Waste

Nonfilterable Blood Components

Formed elements (blood cells and platelets)

Plasma Proteins

As the filtrate moves along the tubule some of the molecules and ions are actively and passively (by diffusion) reabsorbed into the capillary bed from the tubule

Active transport: transport of molecules against a concentration gradient (from regions of low concentration to regions of high concentrations) with the aid of proteins in the cell membrane and energy from ATP

About 99% of filtered water and many useful molecules (such as salts, urea, nutrients, glucose, amino acids, sodium Ion Na+, chloride ion Cl-) returned to the blood

Reabsorption of water is by osmosis

Most of the reabsorption occurs in the proximal convoluted tubules, but the distal and the collecting duct are also active

More substances such as ions (hydrogen ion, creatinine, some drugs (penicillin), toxic substances, are actively secreted from the capillary network to tubules

The fluid (urine), from filtration that was not reabsorbed and from tubular secretion, then flows into the collecting duct, then renal pelvis

Substances found in urine are water, salts, urea, uric acid, ammonia, creatinine (NOT large molecules (proteins, blood cells), glucose

Also, if all those substances weren't reabsorbed by tubules (glucose, water, salts, urea) than the body would continually lose water, salt and nutrients

Nephrons filter 125 ml of body fluid per minute; filtering the entire body fluid component 16 times each day

In a 24 hour period nephrons produce 180 liters of filtrate, of which 178.5 liters are reabsorbed.

The remaining 1.5 liters forms urine

Freshly voided urine is generally clear and pale to deep yellow

The more solutes are in a urine, the deeper yellow its color; whereas dilute urine is a pale, straw color

When formed, urine is sterile,and its odor is slightly aromatic

Ph is slightly acid (around 6)

Urine weight more than distilled water (because it has water plus solutes)

It is a slender tube each 25-30 cm long and 6mm in diameter

Each tube descends beneath the peritoneum, from the hilum of a kidney, to enter the bladder at its dorsal surface

The ureters is a passageway that carry urine from the kidneys to the bladder

Although it may seem like urine may drain to the bladder by gravity, but the uretersdoplay an active role in urine transport

Smooth muscle layers in their walls contract to propel urine into the bladder by peristalsis (even if a person is laying down)

Once urine has entered the bladder, it is prevented from flowing back into the ureters by small valvelike folds of bladder mucosa that flap over the ureter openings

When urine becomes extremely concentrated, solutes such as uric acid salts form crystals that precipitate in the renal pelvis

These crystals are called renal calculi, orkidney stones

The crystals may grow into a stone ranging in size from a grain of sand to a golf ball. Most stones form in the kidneys.

Very small stones can pass through the urinary system without causing problems. However, larger stones, when traveling from the kidney through the ureter to the bladder, can cause severe pain called colic.

Most stones (70 to 80 percent) are made of calcium oxalate. A smaller number are made of uric acid or cystine

For treatment, surgery is a choice

However, a newer noninvasive procedure (lithotripsy) may be used

Uses ultrasound waves to break the stones into small fragments (about the size of grain of sand)

They then can be eliminated painlessly in the urine

The urinary bladder stores urine until it is expelled from the body

The bladder is located in the pelvic cavity, behind the public symphysis and beneath the peritoneum

The bladder has three openings---two for the ureters and one for the urethra, which drains the bladder

The smooth triangular region of the bladder base outlined by these three openings is called the tridone

The trigone is important clinically because infections tend to persist in this region

In males the prostate gland surrounds the neck of the bladder were it empties into the urethra

The bladder wall contains three layers of smooth muscle called the detrusor muscle and its mucosa is a special type of epithelium: transitional epithelium

When the bladder is empty it is collapsed, 5-7.5 cm long at most and its walls are thick and thrown into folds

As urine accumulates, the bladder expands and rises superiorly in the abdominal cavity Fig 15.7

Its muscle wall stretches and the transitional epithelial layer thins, allowing the balder to store more urine without substantially increasing its internal pressure

A full bladder is about 12.5 cm long and hold about 500 ml of urine, but it is capable of holding more than twice that amount

When the bladder is really distended, or stretched by urine, it becomes firm and pear shaped and may be felt just above the public symphysis

Although urine is formed continuously by the kidneys, it is usually stored in the bladder until its release is convenient

The epithelium of the urethra starts off as transitional cells as it exits the bladder. Further along the urethra there are stratified columnar cells, then stratified squamous cells near the external meatus (exit hole).

There are small mucus-secreting urethral glands, that help protect the epithelium from the corrosive urine

Female urethra

In the human female, the urethra is about 1 1/2-2 inches (3-5 cm) long and opens in the vulva between the clitoris and the vaginal opening.

Because of the short length of the urethra, women tend to be more susceptible to infections of the bladder (cystitis) and the urinary tract.

The female urethra is a narrow membranous canal, extending from the internal to the external urethral orifice.

It is placed behind the symphysis pubis, imbedded in the anterior wall of the vagina, and its direction is obliquely downward and forward; it is slightly curved with the concavity directed forward.

Its lining is composed of stratified squamous epithelium, which becomes transitional near the bladder.

The urethra consists of three coats: muscular, erectile, and mucous, the muscular layer being a continuation of that of the bladder.

The release of urine is controlled by two sphincters.

Internal urethral sphincter

External urethral sphincter

Themale urethraextends from the internal urethral orifice in the urinary bladder to the external urethral orifice at the end of the penis.

It presents a double curve in the ordinary relaxed state of the penis.

Its length varies from 17.5 to 20 cm.; and it is divided into three portions, theprostatic, membranous,andcavernous,the structure and relations of which are essentially different.

Except during the passage of the urine or semen, the greater part of the urethral canal is a mere transverse cleft or slit, with its upper and under surfaces in contact; at the external orifice the slit is vertical, in the membranous portion irregular or stellate, and in the prostatic portion somewhat arched.

1.Theprostatic portion( pars prostatica ), the widest and most dilatable part of the canal, is about 3 cm. long.

2. Themembranous portion( pars membranacea ) is the shortest, least dilatable, and, with the exception of the external orifice, the narrowest part of the canal It extends downward and forward, with a slight anterior concavity, between the apex of the prostate and the bulb of the urethra, perforating the urogenital diaphragm about 2.5 cm. below and behind the pubic symphysis.

3. Thecavernous portion( pars cavernosa; penile or spongy portion ) is the longest part of the urethra, and is contained in the corpus cavernosum urethr. It is about 15 cm. long, and extends from the termination of the membranous portion to the external urethral orifice.

The structure of the urethra (tube) itself is a continuousmucous membranesupported bysubmucous tissueconnecting it to the other structures through which it passes.

Themucous coatis continuous with the mucous membrane of the bladder, ureters and kidney. In the membranous and spongy sections (2. and 3. above), the mucous membrane is arranged in longitudinal folds when the tube is empty.

Thesubmucous tissueconsists of a vascular (i.e. containing many blood vessels) erectile layer surrounded by a layer of smooth (involuntary) muscle fibers

These muscle fibres are arranged in a circular configuration that separates the mucous membrane and submucous tissue from the surrounding structure - which is the tissue of the corpus spongiosum (labeled simply "penis" in the diagram above).

Unlike the female urethra, the male urethra has a reproductive function in addition to it's urinary function - it conveys semen out of the body at ejaculation. For further information about this function red the section about the male reproductive system.

Gender differences:

The females only carries urine.

The males carries urine and is a passageway for sperm cells.

Both sphincter muscles must open to allow voiding.

The internal urethral sphincter is relaxed after stretching of the bladder

Activation is from an impulse sent to the spinal cord and then back via the pelvic splanchnic nerves.

The external urethral sphincter must be voluntarily relaxed.

Blood composition depends on three major factors:

Cellular metabolism

Urine output

In general, thekidneyshave four major roles to play, which help keep the blood composition relatively constant.

Excretion of nitrogen containing wastes

Maintaining water in the blood

Maintaining electrolyte balance in the blood, and

Ensuring proper blood pH

Body Fluids and Fluid Compartments:

Of the hundreds of compounds present in your body, the most abundant is water.

Males weighing 154 pounds will have an average of 60% of their body weight, nearly 40L, as water.Females about 50%. (based on nonobese individuals).

The more fat present in the body, the less total water content per kg of body weight .

Female body contains slightly less water per kg of weight because it contains slightly more fat than the male body.

In a newborn, water may account for up to 80% of body weight. That percentage increases if the infant is born premature.

The percentage of body water decreases rapidly during the first 10 years of life.

In elderly individuals, the amount of water per kg of body weight increases (because old ages is often accompanied by a decrease in muscle mass -65% water- and in increase in fat -20% water-)

Water is the universal body solvent within which all solutes (including the very important electrolytes) are dissolved.

Body Fluid Compartments:

Total body water can be subdivided into two major fluid compartments called extracellular and intracellular fluid compartments.

Extracellular : consists mainly of the liquid fraction of wholeblood called the plasma, found in the blood vessels and the interstitial fluid that surrounds the cell.In addition, lymph, cerebrospinal fluid, humors of the eye, and the specialized joint fluids are also considered extracellular fluid.

Intracellular : largest volume of water by far. Located inside of the cells.

3 sources of fluid intake: the liquids we drink, the water in the food we eat, and the water formed by catabolism of foods.

Fluid output from the body occurs through four organs: the kidneys, lungs, skin, and intestines.The fluid output that changes the most is that from the kidneys.

The body maintains fluid balance mainly by changing the volume of urine excreted to match changes in the volume of fluid intake

When fluid loss from the body exceeds fluid intake, salivary excretion decreases, producing a dry mouth feeling, and the sensation of thirst.The individual then drinks water, thereby increasing fluid intake and compensating for previous fluid losses. This tends to restore fluid balance.

Water is continually lost from the body through expired air and diffusion through the skin.

Although the body adjusts fluid intake, factors that adjust fluid output, such as electrolytes and blood proteins, are far more important.

Electrolyte is a "medical/scientific" term for salts, specifically ions. The term electrolyte means that this ion is electrically-charged and moves to either a negative (cathode) or positive (anode) electrode:

ions that move to the cathode (cations) are positively charged

ions that move to the anode (anions) are negatively charged

For example, your body fluids -- blood, plasma, interstitial fluid (fluid between cells) -- are like seawater and have a high concentration of sodium chloride (table salt, or NaCl). The electrolytes in sodium chloride are:

sodium ion (Na+) - cation

chloride ion (Cl-) - anion

As for your body, the major electrolytes are as follows:

sodium (Na+)

potassium (K+)

chloride (Cl-)

calcium (Ca2+)

magnesium (Mg2+)

bicarbonate (HCO3-)

phosphate (PO42-)

sulfate (SO42-)

Electrolytes play indispensible roles in transmitting nerve impulses, contracting muscles, and keeping proper fluid levels in the body

Electrolytes also:

Serve as essential minerals

Control osmotic pressure between body fluid compartments

Maintain acid base balance in the body

Very small changes in electrolyte balance (solute concentrations in various fluid compartments) cause water to move from one fluid compartment to another.This alters blood volume and blood pressure, but it can also severely impair the activity of irritable cells like the nerve and muscle cell.

A variety of electrolytes have important nutrient or regulatory roles in the body.

For example, Iron required for hemoglobin production.Iodine must be available for synthesis of thyroid hormones.

Electrolytes are also needed for many cellular activities such as nerve conduction and muscle contraction.

The most abundant of electrolytes aresodium , potassium, and chloride.

Electrolytes are important because they are what your cells (especially nerve, heart, muscle) use to maintain voltages across their cell membranes and to carry electrical impulses (nerve impulses, muscle contractions) across themselves and to other cells.

Your kidneys work to keep the electrolyte concentrations in your blood constant despite changes in your body. For example, when you exercise heavily, you lose electrolytes in your sweat, particularly sodium and potassium. These electrolytes must be replaced to keep the electrolyte concentrations of your body fluids constant. So, many sports drinks have sodium chloride or potassium chloride added to them. They also have sugar and flavorings to provide your body with extra energy and to make the drink taste better.

The kidney acts as the chief regulator of sodium levels in body fluids.

When blood volume drops for any reason (ie excessive sweating or diarrhea), arterial blood pressure drops, which in turn decrease amount of filtrate formed in the kidneys

Highly sensitive cells in the hypothalamus called osmoreceptors react to change blood composition (less water and more solutes) by becoming more active. Result is the nerve impulses are sent to the posterior pituitary, which releases anti-diuretic hormone (ADH)

ADH travels in the blood to its main target, the kidneys collecting ducts, whiere it causes the duct cells to reabsorb more water. As more water is returned to the blood stream, blood volume and blood pressure increase to normal levels, and only a small amount of very concentrated urine is formed.

ADH is released more or less continually unless the solute concentration of the blood drops too low. When this happens, the osmoreceptors become quiet and excses water is allowed to leave the body in the urine.

A second hormone helps to regulate blood composition and blood volume by acting on the kidney : ALDOSTERONE

Aldosterone is the major factor regulating sodium ion content of the ECF and in the process helps regulate the concentration of other ions (calcium, potassium, and magnesium) as well.

Sodium ion is responsible osmotic water flow. When too little sodium is in theblood, the blood becomes too dilute. Consequently, the water leaves the bloodstream and flows out into the tiusse spaces, causing edema and possibly a shutdown of the cirulatory system.

For each sodium ion that is reabsorbed in the kidney, a chloride ion follows and a potassium ion is secreted into the filtrate. Thus, as the sodium content of the blood increases, potassium concentration decreases, bringing the two ions back to their normal balance in the blood.

Another effect of aldosterone is to increase water reabsorption. Because as sodium is reclaimed, water follows it passively back into theblood (WATER FOLLOWS SALT)

Reabsorption of water and electrolytes by the kidney is regulated primarily by hormones.

When blood volume drops for any reason, (ie due to hemorrhage or excessive water loss sweating or diarrhea), arterial blood pressure drops, which in turn decreases amount of filtrate formed by kidneys. In addition, highty sensitive cells in the hypothalamus called somoreceptions react to the change in blood composition. (That is. Less water and more solutes.)

Fluid Imbalances:

Dehydration:the fluid imbalance seen most often. In this potentially dangerous condition, IF volume decreases first, but eventually, if treatment has not been given, IFC and plasma volumes also decrease below normal levels. Prolonged diarrhea or vomiting may result in dehydration due to the loss of body fluids.

Overhydration:much less common that dehydration.Giving IV fluids too rapidly or in too large of an amount, or consuming an extremely high amount of liquid can put too heavy a burden on the heart.

Electrolyte Imbalances:

Any disruption in a homeostatic mechanism controlling the level or normal checmical activity of a particular electrolyte in any of the different body fluids produces an electrolyte imbalance. Such imbalances are widespread and often very serious and sometimes fatal, preventing electrolytes to do their job.

For the cells of the Body to function, blood pH (potential of Hydrogen) must be maintained between 7,35 and 7.45.

When the pH rises above 7.45, a person is said to have alkalosis.

A drop in arterial pH to below 7.35 results in acidosis.

Because a 7 is neutral, 7.35 is not acidic, chemically speaking; however, it represents a higher than optimal hydrogen ion concentration for the functioning of most body cells.

Therefore, any arterial pH between 7.35 and 7.45 is called physiological acidosis

Although some acidic substances enter the body through ingestion, most hydrogen ions originate as by-products of cellular metabolism, which continually adds substances to the blood that tend to disturb its acid base.

Ie phosphoric acid, lactic acid, and many types of fatty acids.

Carbon dioxide, which is released during energy production, forms carbonic acid.

Ammonia and other basic substances are also released to the blood as cells go about their usual business.

Although the chemical buffers in the blood can temporarily tie up excess acids and bases, the lungs have the chief responsibility for eliminating carbon dioxide from the body, the kidneys assume most of the load for maintaining accid base balance of the blood.

There are two pH controlling systems: Blood buffers and respiratory system.

Chemical buffers are systems of one or two molecules that act to prevent dramatic changes in hydrogen ion concentration when acids or bases are added.

They bind to hydrogen ions whenever the pH drops and by releasing hydrogen ions when the pH rises.

Chemical buffers are the first line of defense in resisting pH changes.

How does a chemical buffer system work??

Acids are proton (H+) donors, and that the acidity of a solution reflects only the free hydrogen ions, not those still bound to anions.

Strong acids dissociate completely and liberate all their H+ in water.

Weak acids dissociate only partially and have a slighter effect.

(weak acids are very effective at preventing pH changes since they are forced to dissociate and release more H+ when the pH rises).

Bases are proton or hydrogen ion acceptors.

Strong bases like hydroxides dissociate easily in water and quickly tie up H+

Weak bases are slower to accept H+ (however, as pH drops, weak bases become stronger and begin to tie up more hydrogen ions).

There are 3 major chemical buffer systems of the body:

Bicarbonate system

Phosphate system

Protein buffer system

They all maintain pH balance in one or more fluid compartment.

They all work together, and anything that causes a shift in H+ concentration in one compartment also causes changes in the others.

The respiratory system eliminates carbon dioxide (CO2) from the blood while it loads oxygen into the blood.

When CO2 enters the blood from the tissue cells, most of it enters the red blood cells where it is converted to bicarbonate ions for transport in the plasma.

In healthy people, carbon dioxide is expelled from the lungs at the same rate as it is formed in the tissues. Thus, the H+ released when carbon dioxide is loaded into the blood is not allowed to accumulate because it is tied up in water when CO2 is unloaded in the lungs. So, under normal conditions, the hydrogen ions produced by carbon dioxide transport have no effect on blood pH.

However, when Carbon dioxide accumulates in the blood (ie during restricted breathing), the chemoreceptors in the respiratory control centers of the brain are activated. As a result, breathing reate and depth increase, the excess H+ is blown off as more CO2 is removed from the blood.

On the other hand, when blood pH begins to rise (alkalosis), the respiratory center is depressed. The respiratory rate begins to fall, allowing carbon dioxide (hence, H+) to accumulate in the blood. Again, blood pH is restored.

Chemical buffers can tie up excess acids and bases only temporarily, but they cannot eliminate them from the body. While the lungs can dispose of carbonic acid by eliminating carbon dioxide, Only the KIDNEYS can rid the body of other acids generated. (although the kidneys act slowly and require hours or days to bring about changes in blood pH, they are the most potent of mechanisms for regulating blood pH).

To maintain acid base balance, the kidneys:

Excrete bicarbonate ions and

Conserving (reabsorbing) or generating new bicarbonate ions

As blood pH rises, bicarbonate ions are excreted and hydrogen ions are retained by the tubule cells. Conversely, when blood pH falls, bicarbonate is reabsorbed and hydrogen ions are secreted. Urine pH varies from 4.5-8.0, which reflects the ability of the renal tubules to excrete basic or acid ions to maintain blood pH homeostasis.

Thedevelopment of the urinary and reproductive organsis a part of the prenatal development, and concerns the urinary system and sex organs. The latter is a part of the stages of sexual differentiation. The urinary and reproductive organs are developed from the intermediate mesoderm. The permanent organs of the adult are preceded by a set of structures which are purely embryonic, and which with the exception of the ducts disappear almost entirely before the end of fetal life. These embryonic structures are on either side; the pronephros, the mesonephros and the metanephros of the kidney, and the Wolffian and Mllerian ducts of the sex organ. The pronephros disappears very early; the structural elements of the mesonephros mostly degenerate, but the gonad is developed in their place, with which the Wolffian duct remains as the duct in males, and the Mllerian as that of the female. Some of the tubules of the metanephros form part of the permanent kidney.

Intermediate mesodermis a type of mesoderm that is located between the paraxial mesoderm and the lateral plate. It develops into the part of the urogenitasystem (kidneys and gonads)

forms of urogenital system

series of short evaginations from each segment grows dorsally caudally

vestiges of the future kidney, the pronephros briefly appears.

pronephric duct arises in the intermediate mesoderm just ventral to the anterior somites

grows caudally until it becomes the cloaca

it is distinct from the lateral mesoderm, as it is not influenced by the secretion of BMP-4 by the ectoderm, possibly due to the lack of receptors.

Pronephrosthe most primitive of the three excretory organs that develop in vertebrate, corresponding to the first stage of kidney development.

The pronephros develops in the anterior nephrotomes of all vertebrates. It is a paired organ, consisting of a series of nephrons filtering urine from both the pericardium fluids via openings called nephrostomes and blood from the glomerulus.

The organ is active in adult forms of some primitive fish, like lampreys or hagfish. It is present at the embryo of more advanced fish and at the larval stage of amphibians. In human beings, it is rudimentary, appears at the end of the third week (day 20) and replaced by mesonephros after 3.5 weeks.

Themesonephros(Latin for "middle kidney") is one of three excretory organs that develop in vertebrates. It serves as the main excretory organ of aquatic vertebrates and as a temporary kidney in higher vertebrates

TheWolffian duct(also known asarchinephric duct ,Leydig's duct ,mesonephric duct , ornephric duct ) is a paired organ found in mammals including humans during embryogenesis.

It connects the primitive kidney Wolffian body (ormesonephros ) to the cloaca and serves as the anlage for certain male reproductive organs.

In both the male and the female the Wolffian duct develops in to the trigone of urinary bladder, a part of the bladder wall. However, further development differentiates between the sexes in the development of the urinary and reproductive organs.

In the female, in the absence of testosterone support, the Wolffian ducts develop and wither.

TheMllerian ducts(orparamesonephric ducts ) are paired ducts of the embryo which run down the lateral sides of the urogenital ridge and terminate at the mullerian eminence in the primitive urogenital sinus. In the female, it will develop to form the fallopian tubes, uterus, and the upper portion of the vagina. It is tissue of mesodermal origin.

Thegonadis the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes. Although medically the gonad term can refer to either male gonads (testicles) or female gonads (ovaries), the vernacular, or slang use of "gonads" (or "nads") usually only refers to the testicles.

Mader, S.S (2006)Inquiry into Life

Marieb, E.N (2006)Essentials of Human Anatomy & Physiology

http://www.kidney.ca/page.asp?intNodeID=22132

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Urinary System Presentationyorkville College 1203376567476185 2