Animal+Systems


 * Animal Systems **



**A Common Misconception Animals Cells:** Animal cells have a cell wall. **The Truth:** Unlike plant cells, animal cells do not have a cell wall that can regulate water intake. The **cell membrane** surrounds the cell and is semi-permeable, which means it controls the movement of substances in and out of the cells. Animal cells have a cell membrane that is made up of a special type of fat molecule called **phospholipids**. The fat phospholipids have a polar head, meaning that it attracts water and a non-polar double tail, which means it hydrophobic (does not like water). The cell membrane also contains some carbohydrates and proteins. A good way to think about the cell membrane is like a plastic bag with tiny holes. The bag holds all of the cell parts and fluids inside the cell and keeps the unwanted things outside of the cell. The little holes are there for letting some things move in and out of the cell.

The phospholipids make up this bag and the proteins are found around the little holes that help in moving molecules the cells need in and out of the cell. **Osmosis** is the diffusion of water through this semi-permeable membrane. It is a physical process in which a solvent moves, without energy, across the semi-permeable membrane. The cell membrane is selectively permeable, so only necessary materials are let into the cell and waste left out. For example, salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This may be why you can get really thirsty after eating something that is very salty. Diffusion and Osmosis are both types of passive transport, which means that no energy is required for the molecules to move into or out of the cell. Anytime energy is required for movement of molecules across the cell membrane, and then it is called **active transport** . The liquids inside and outside of cells have different substances. Sometimes a cell has to work and use some energy to maintain a proper balance of ions and molecules. Macromolecules broken into their most simple state would be diffused into the cell through active transport because they are larger molecules that need energy to be taken into the cell.

The way cells gain this useful energy coming into the cell through the cell membrane is a process called **cellular respiration** . The process of cellular respiration takes place in an organelle inside the cell called the **mitochondria** . The mitochondria is known as the powerhouse of cells because they act like a digestive system that takes nutrient, breaks them down and creates energy for the cell, which is cellular respiration. The inside of the mitochondria is filled with water and protein/enzymes. The proteins take food molecules and combine those with oxygen. After the oxygen is added, the material can effiecently be digested. The mitochondrion produces  **ATP (adenosine triphosphate)** using the energy from food, which is important because ATP fuel’s all of life’s activities.. The chemical energy of food molecules are released and partially captured in the form of ATP. Carbohydrates, fats, and proteins can all be used as fuels for cellular respiration, but glucose is the more actively used.

**Ribosomes** are the sites of protein synthesis, where RNA is translated into protein. When cells need large numbers of proteins, they must first build numerous ribosomes. Ribosomes release and hold energy for the cell. (Chiras, 1993). (http://upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Ribosome_mRNA_translation_en.svg/651px-Ribosome_mRNA_translation_en.svg.png)
 * Translation ** is the process of building protein in our cells. Proteins are the building blocks and workers of our cells. It might seem simple that DNA's long sequence, made up of only 4 letters, get converted into the 100,000 or so different kinds of protein molecules that perform the daily work for our body. This is accomplished through translation.

The **Nucleus** is the “control center” of a cell. It contains most of the genetic material of a cell in the form of DNA. The DNA is responsible for telling the cell what kind of cell it is; such as a muscle cell or a liver cell. The other job of the nucleus is to control the functions of the cell and the different parts of the cell. **DNA replication** is the process of the nucleus making exact copies of its DNA. The double helix of the DNA unwinds and each of the strands acts as a template. Then the enzyme DNA polymerase “reads” the DNA template and uses it to synthesize a new strand. This result of this process is two identical DNA molecules. **Transcription** i s the process of creating an equivalent RNA copy of a sequence of DNA. A DNA sequence is “read” by RNA polymerase which then produces a complementary RNA strand. Different than DNA replication, transcription results in a RNA compliment that has uracil (U) wherever there is a thymine (T) in the DNA molecule. <span style="font-family: Arial,Helvetica,sans-serif;">

** CIRCULATORY SYSTEM: ** The Circulatory System is a big name for one of the most important systems in the body. It is a cooling and delivery system made up of your heart, blood, and blood vessels. Blood moving from the heart delivers oxygen, water, and nutrients to every part of the body. On the return trip, the blood picks up waste, such as carbon dioxide, so that your body can get rid of it. It is like a highway that connects all of the body's cells **A Common Misconception about the Heart:** Your **heart** is on the left side of your body. **The Truth:** It is actually located in the center of your chest, only slightly to the left. It's job is to __pump the blood__ and keep it moving throughout your body. Your heart is the size of a clenched fist. It is a two sided, four chambered muscle that contracts and relaxes about 70 to 80 times a minute (which adds up to about 3 billion times during the average lifetime!) while resting or doing normal, everyday activities and even more when exercising. It squeezes and pumps blood through its chambers to all parts of the body, and it does this through a collection of **blood vessels**. Inside the blood, there are many things at work. **Red blood cells**, for example, are responsible for carrying oxygen and carbon dioxide. The __carbon dioxide__ is gathered up and taken back to the lungs where it is removed from the body when we exhale. There are about 5,000,000 red blood cells in one drop of blood! There are also **white blood cells**, which help the body fight off germs by attacking and destroying them when they enter the body. When you have an infection, the body will produce more white blood cells to fight it off. And don't forget about the platelets. **Platelets** are blood cells that stop bleeding. When we cut ourselves, we have broken open a blood vessel, and the blood leaks out. In order to __plug__ up this opening, the platelets stick to the opening of the damaged blood vessels. As is sticks, more platelets, fibers, and other blood cells help form a plug to seal it. When the plug is completely formed, the wound stops bleeding. The rest of the blood is made up of **plasma**.

The blood is pumped into the right side of the heart, which is the low pressure side. It pushes the red blood cells up to the lungs so that they can get recharged with __oxygen__. The blood enters this side of the heart through a chamber called the **Right Atrium**. Then the blood is pushed back through into the **Right Ventricle**. **Valves** prevent the blood from being sucked back up into the Right Atrium. The Right Ventricle then begins pushing the non-oxygenated blood into the lungs through the **Pulmonary Artery**. **Arteries** are larger blood vessels that lead away from the heart to push the blood into the **veins**, blood vessels that lead into the heart. When the blood leaves the artery, it enters the **capillaries**, very small blood vessels that __act as connectors__ between veins and arteries. They are located around the **alveoli**, which are air sacs that __increase the surface area__ of the lungs. When the blood travels past these air sacs in the capillaries, the red blood cells pick up oxygen. The newly oxygenated blood continues to blood vessels known as cardiac veins, which empties into the **Left Atrium** of the heart. Since the left side of the heart is the high pressure side, it's job is to push the oxygenated blood out to the rest of the body's circulation. The blood is sent to the **Left Ventrical** where there is enough __pressure produced__ to push it into the **Aorta**. As soon as it enters the Aorta, the blood begins its journey throughout the body by way of the veins. Clearly, the heart is the hardest working muscle in the body.

Exertion on the body causes the need for blood to be __circulated__ at a faster rate - thus the heart rate increases to make this happen. Your fast breathing is causing a more rapid exchange between oxygen and carbon dioxide. When you exercise, your heart has to pump more blood to supply oxygen to your muscles because muscles require oxygen when in use so the heart has to deliver oxygen-rich blood to them (after stopping at the lungs to re-oxygenate of course!) The volume of blood that your heart pumps in a minute depends on the **heart rate** (the number of beats per minute) and the **stroke volume** (the blood volume pumped by each ventricle of your heart with each beat). When you exercise, your heart beats faster and __contracts__ more forcefully, pushing out more blood and increasing the blood volume pumped by each ventricle. This is why exercising makes your heart stronger! Remember, your heart is a muscle... the more you use it, the stronger it becomes!



There are so many blood vessels in your body that they could circle the globe almost 2 1/2 times! These veins and blood vessels carry the blood up to your heard first, __distributing the oxygen and other nutrients__ in blood to your brain. After that is taken care of, since the brain is such an important part of our survival, then the blood can continue on to nourish the rest of the body's __cells__. The circulatory system is what connects the other systems of the body, because the vessels and veins reach almost every part we could think of. We already know how it connects to our respiratory system, but it also connects to the urinary and digestive system, both in getting rid of the wastes that are produced and taking in more nutrients from the food we eat.



A lot of people donate their own blood to save lives. A lot of people also donate plasma. **Plasma** is essentially the liquid part of your blood, yellowish in color. Comprised primarily of water and various proteins (92% water, 7% plasma proteins, and 1% other), it helps carry important substances throughout your body, including hormones and vitamins. The red blood cells, white blood cells, and platelets are all suspended in blood plasma so they can circulate. Plasma is extracted from blood by a process called **plasmapheresis**, during which a machine spins the collected product to separate the liquid from the blood cells.

Fainting and that dizzy feeling is usually caused by a reduction of circulating blood flow to the brain. After donating usually just a little under a pint of blood, it takes your heart a little while to replenish your body with a fresh supply of blood to replace the blood you donated. We know that the presence of __carbon dioxide in the blood stimulates breathing__. Donating blood decreases your blood amount, which contains CO2, and contributes the imbalance of it in your brain which causes you to feel woozy. Eating food immediately after helps tremendously with this problem. Every cell in your body requires an energy supply in order to live and function efficiently. They get this energy from the food you eat, which reaches all of the cells via the blood.



<span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">** A Common Misconception About The Respiratory System: ** We breathe in oxygen, and breathe out carbon dioxide.
 * RESPIRATORY SYSTEM: **

<span style="color: #800080; font-family: Arial,Helvetica,sans-serif;">**The Truth:** We actually breathe in oxygen and some carbon dioxide everytime we breathe in and breathe out carbon dioxide and some oxygen every time we breathe out. This oxygen and carbon dioxide enter and exit through the Respitory System. <span style="font-family: Arial,Helvetica,sans-serif;">The Respiratory System is a fancy way of saying all the parts of the body that help get the oxygen necessary for life into the body and help expel carbon dioxide. There are many important parts that have specific tasks every time you take a breath. The first is the ** diaphragm **; this is the organ that contracts downward when you inhale. The contraction of the diaphragm decreases the pressure in the lungs, causing air to flow into the lungs. When you exhale, the diaphragm raises back up which puts pressure on the lungs, causing the air to flow out of the lungs. When you take a breath of air, the oxygen makes a very long journey through your body. The trip starts with the contracting of the diaphragm and air coming in though the nose and mouth. The air then travels down the ** trachea **which is a large air tube that goes down the throat and to the lungs. The trachea and esophagus are both in the throat; you can tell which one is the trachea because it has rings of cartilage that keep it from collapsing. The trachea then branches into each lung, these two tubes are called the <span style="color: #800080; font-family: Arial,Helvetica,sans-serif;">**bronchial tubes** <span style="font-family: Arial,Helvetica,sans-serif;">. Once the bronchi are in the lungs, the tubes start to branch into smaller tubes. These tubes are called <span style="color: #800080; font-family: Arial,Helvetica,sans-serif;">**bronchioles** <span style="font-family: Arial,Helvetica,sans-serif;"> and they branch out all over the lungs. The bronchioles end with clusters of air sacs called <span style="color: #800080; font-family: Arial,Helvetica,sans-serif;">**alveoli** <span style="font-family: Arial,Helvetica,sans-serif;">. After traveling through the bronchial and bronchiole tubes the alveoli are where the oxygen will be transferred to our cells through the capillaries.



The capillaries contain blood cells with CO2 (Carbon Dioxide) on them from the cells throughout the body. The CO2 is a bi-product of the cellular respiration going on in the cells throughout the body. The red blood cells containing CO2 travel through the capillaries in the alveoli and as they pass through, they drop off their CO2 and pick up some of that oxygen that has made its journey through the respiratory system. The alveoli have a very large surface area to volume ratio so there is more opportunities for the oxygen to "get on" the cells and travel throughout the body. This oxygen still has more travel ahead though; it will travel through the blood stream to a cell that needs oxygen so it can perform cellular respiration. Like in the lungs, the CO2 will load onto the red blood cell and the oxygen will get off and will be put to use in the cell!



DIGESTIVE SYSTEM: ** Macromolecules are made by combining many monomers together in chemical reactions. One of the most important of these reactions is hydrolysis. Hydrolysis means to break up with water, meaning that hydrolic reactions occur any time a bond is broken with the addition of H20. A lot of the food we eat consists of polymers (proteins and polysaccharides) which are far too large for us to be absorbed the cells in the our small intestine. There are enzymes inside the intestinal tract that break down the polymers by catalyzing the addition of water across the bonds that hold the monomers together. The most common types of monomers are amino acids, glucose, nucleotides, and fatty acids. The monomers that are released during the digestion of food are used to make the physical structure of the body.

__Amino Acids:__ organic molecules made of sugars and their polymers __Fatty Acids:__ include fats, oils, waxes, and cholesterol; repel water; serve as both structure (the cell membrane) and an energy source Proteins: polymers made of up 20 different amino acids; structural components like the cell skeleton; catalysts of cell reactions; provide support to tissues, transport molecules; assist is muscle contractions __Nucleotides__: hold all genetic information; includes ATP (the energy currency of a cell) The generalized reaction for chemical digestion is: **macromolecule + water --> (enzyme) basic units**. Every cell needs matter and energy. Cellular respiration is breaking bonds of glucose because these broken bonds release energy. This process occurs in the mitochondria in the cell. The energy is stored in ATP. The formula for cellular respiration is: **CH20 + O2 --> CO2 + H2O.**

When we consume these macromolecules, they provide matter and energy for our cells. Food provides a supply of energy and building material for the cell. We consume macromolecules... but then what happens? ...Digestion! ** A Common Misconception About The Digestive System: ** As you eat your food, it goes straight into your stomach so that you feel full and satisfied. The digestive system is very complex and has many different organs that all play extremely important roles in digesting the food!
 * The Truth **:

So where exactly does your food go? And how does it leave your body?

The **mouth** is the site of the physical breakdown of food. Even before you eat the delicious lunch, your digestive system is already at work. When you can smell the food, or even see it, saliva starts for form in your mouth. This watery secretion is released by the salivary glands. Saliva liquefies the food (which makes it easier to swallow), kills or neutralizes some of the bacteria through the enzymes and antibodies it contains, and dissolves substances so that they can be tasted. Saliva also breaks down starch molecules with the help of the **enzyme amylase**. The tongue pushes the food to the back of the throat to the opening of the esophagus. (http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/8880.jpg)

The **esophagus** is a muscular tube like structure that transports food to the stomach. The esophagus transports the food through a process called peristalsis. It is so powerful that it allows you to swallow by hanging upside down! Inside the **stomach**, the food is liquefied by acidic secretions of tiny glands that are against the stomach wall. They are called gastric glands. They produce a watery secretion called gastric juice. It contains Hydrochloric acid (HCI) and the **enzyme pepsin** - an enzyme released by the gastric glands of the stomach that breaks down proteins into large peptide fragments. You can think of the stomach has a mixer - it churns and mashes up the small balls of food with the gastric juice which helps break it down even more. (http://www.mayoclinic.com/images/image_popup/ans7_esophagus.jpg)

(http://www.acm.uiuc.edu/sigbio/project/digestive/middle/stomach2.jpg)



The broken down food becomes a thin watery substance known as __chyme__. The body can hold 2 to 4 liters of chyme which is gradually released into the small intestine at a rate suitable for digestion and absorption. Very little enzymatic digestion occurs in the stomach but an exception is protein. Proteins are denatured (rendering it digestible) by HCI. Pepsin catalyzes the breakdown of proteins into large pieces, where they are further broken down in the small intestine.

Chyme leaves the stomach and enters the ** small intestine **. It is digested into the stomach by peristaltic muscle contractions. Even after all the chyme enters the small intestine, peristaltic muscle contractions still take place. These are known as hunger pains. When the wave of contraction reaches the end of the stomach, the __pyloric sphincter__ opens and essentially squirts the chyme into the small intestine. As chyme leaves the stomach, the presence of protein is removed. Acid and pepsin release decline, shutting down the stomach until the next meal needs to be digested. The small intestine serves as a site for food digestion and absorption. It is a coiled tube that is about 20 feet long in adults. It consists of three parts: the __duodenum__, the __jejunum__, and __ileum__. Inside the small intestine, macromolecules are digested with the aid of numerous enzymes. Digestion of food molecules inside the small intestine requires enzymes produced from two distinctly different sources: the pancreas (an organ located beneath the stomach) and the lining of the small intestine itself. The following enzymes are produced in the lining of the small intestine: (http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19221.jpg)
 * **Maltase** - breaks maltose into glucose subunits
 * **Sucrase** - breaks sucrose into glucose and fructose subunits
 * **Lactase** - breaks lactose into glucose and galactose subunits
 * **Aminopeptidase** - breaks down peptides into amino acids

The **pancreas** is formed by the first portion of the small intestine, the duodenum. It is a dual-purpose organ: it has endocrine and exocrine functions. As an exocrine gland, it produces enzymes and sodium bicarbonate which is essential for the digestion of foodstuffs in the small intestine. Its endocrine function by producing hormones that help regulate blood glucose levels and thus maintaining homeostasis. The following enzymes are produced in the pancreas: The digestive enzymes of the pancreas are produced in small glandular units. These glands are emptied into many small ducts that come together to form the pancreatic duct. The pancreatic duct joins with a duct draining the gall bladder and liver and then empties into the small intestine. (http://www.gopetsamerica.com/anatomy/illustrations/pancreas.jpg)
 * **Trypsin** - cleaves peptide bonds of polypeptides and proteins
 * **Chymotrypsin** - exact same as trypsin
 * **Carbozypeptidase** - cleaves peptide bonds on carboxy end of polypeptides
 * **Phospholase** - breaks fatty acids from phosphoglycerides to form monoglycerides
 * **Lipase** - breaks two fatty acids from triglycerides
 * **Ribonuclease** - breaks RNA into smaller nucleotide chains
 * **Deoxyribonuclease** - breaks DNA into smaller nucleotide chains

The **liver** performs many functions essential for homeostasis. It stores glucose and fats, synthesizes key blood proteins, stores iron and certain vitamins, detoxifies certain chemicals, and plays an important role in producing bile which is key to the process of digestion. __Bile__ is a fluid containing water, ions, and molecules such as cholesterol, fatty acids, and bile salts. Bile salts are steroids that break fat globules into smaller ones. This process is essential for dietary lipid digestion (digestion of fats), because lipid-digesting enzymes in the small intestine do not work well on larger fat globules. Bile is first transported to the **gall bladder**, a sac attached to the underside of the liver. It concentrates bile by removing water from it. When chyme is in the gall bladder, it contracts, causing the bile to flow out through the duct system into the small intestine. On the surface of the small intestine, there are many finger-like projections called villi, which increase the surface area available for the absorption of food molecules. (http://www.clarian.org/ADAM/doc/graphics/images/en/8848.jpg) (http://www.uphs.upenn.edu/surgery/graphics/images/GI-gallbladder.jpg)

Now we are the **large intestine**. It is only about 5 feet long. The large intestine is the site of water absorption. Most of the large intestine consists of the colon. The colon is made up of three portions: the ascending colon, the transverse colon, and descending colon. The colon empties into the rectum. The large intestine receives materials from the small intestine. These materials consists of a mixture of water, undigested food molecules, and indigestible food resides (like cellulose). It also contains sodium and potassium ions. The colon absorbs 90% of the water and sodium and potassium ions. The contents of the large intestine (after the water and salt have been removed) are known as the feces. The feces consist of undigested foods, indigestible materials, and bacteria. The feces are propelled by peristaltic contractions along the colon until they reach the __rectum__ where they are deposited through the __anus__. (http://www.sjhsyr.org/sjhhc/hidc07/graphics/images/en/19220.jpg) (http://www.aboutincontinence.org/nf/uploads/Image/rectum_analcanal_anatomy.gif)

**Water’s Role In Digestion:** When water is consumed, it is immediately passed into the intestine and absorbed. The water is secreted into the stomach through its glandular layer in the mucosa swelling from underneath, readying the stomach for food breakdown. The act of digestion of solid foods depends on this action. When the acid in the stomach is poured onto incoming food, enzymes are activated, food is broken down, and the fluid mass formed (chyme) can be passed along into the next phase. Mucus covers the glandular layer of the stomach, which is the inner most layer of the stomach. Mucus consists of 98% water and 2% “scaffolding” that helps trap water. The cells secrete sodium bicarbonate in the water layer. As the acid tries to go through this protective layer, the bicarbonate neutralizes it. The efficiency of this process depends solely on water. There must be enough water in our bodies to hydrate the mucus glands, otherwise there would be no protection from the strong stomach acids. (http://www.liquidsculpture.com/images/water/water-drop-a.jpg)

The digestive system is the process that enables us to physically break down the essential nutrients that are imperative for our body’s growth and energy. The circulatory system absorbs, transports, and distributes the broken down nutrients (thanks to the digestive system) to our tissues and cells. Without the digestive process our tissues and c​ells would not receive the essential material that enables us to move, grow, and live. Our cells need food too. They need to be able to perform cellular respiration so that our bodies keep moving. They also participate in their own digestion with the help of **lysosomes** in the process of **hydolysis**. Lysosomes are organelles that are made in the __Golgi Apparatus__ and contain about 50 different enzymes, but the most important one used for digestion are the hydrolytic enzymes. These enzymes break down the organelles and it's molecular contents until it is fully digested. The digestive system works interdependently with other systems and processes so that we are able to live a healthy life. (Chiras, 1993).

Drawing by: Angie

**URINARY SYSTEM:** All living organisms create waste material after their systems have taken what they need from the food. The next step is the getting rid of those wastes from our blood and bowel. Solid waste is excreted through the digestive system and liquid waste through the urinary system. The urinary system works together with the lungs, skin, and intestines in the balance of chemicals and water in our bodies. The **urinary system** removes a type of nitrogen waste that is produced in from the breaking down of proteins (meat, poultry, and some vegetables). This waste is made from the combination of an amino group and a hydrogen ion to form ammonia. Ammonia is quite toxic so the body converts to something called **urea**, which is carried in the bloodstream into the kidneys to be filtered.

**A Common Misconception about Kidneys:** Kidneys are part of the digestion system **Truth:** The ** kidneys ** are actually part of the urinary system, which is also called the excretory system, though the urinary system is closely tied to both the digestive system and the circulatory system. The urinary system is an organ system that has the function of producing, storing, and eliminating waste in the form of urine. The human urinary system consists of two kidneys, two ureters, a bladder, a urethra, and in males, the penis. <span style="font-family: Arial,Helvetica,sans-serif;">The kidneys have quite a few tasks being done in the urinary system, those being: the concentrating of urine, regulation of blood volume and blood pressure triggering the formation of red blood cells, regulation of electrolytes and the maintenance of acid-base balance in our bodies. The kidney re-absorbs and excretes electrolytes, which is sodium, potassium, and calcium from the influence of hormones. The kidneys are the essential organs for the maintenance of ** salt and water balance. ** One of the functions of the kidneys is to control the water and salt balance in the body. That is why it is referred to as the main organ of homeostasis. Too much or too little salt in cells is bad for the cell and must be maintained around 1% or they will shrink or bust. If the cell is places in a saltier solution is will shrink and if placed in pure water, it will swell and burst. This is why your skin becomes pruny when you are in the bathtub or swimming in the pool for too long.

Eating salty foods like potato chips or popcorn will make you thirsty. As we said above, the body struggles to maintain a constant level of salts as well as water for proper functioning. As the saltier blood circulates through the body, it makes the fluid outside of our body cells saltier than the fluid inside the cells.The cells notice the change right away. That’s because the extra salt outside acts like a magnet, pulling water out of the cells. The cells try to hold in the water and they send chemical messengers to the brain, protesting the saltiness of the fluid around them. There are also sensors in the thirst center in the brain that keep tabs on the saltiness of the blood. When the thirst center goes on alert because things are too salty and the body needs water to dilute the salt, that’s when you start to feel thirsty.The kidneys help dilute the salt too by slowing down urine production and conserving water. The constant balancing of salt and water in the body helps maintain the right amount of water in our cells and in the bloodstream.



The kidneys are two organs that about the size of your fist and are bean-shaped. They are in the abdomen, below the ribcage. The vena cava vein and aorta artery are connected to the two kidney’s by the renal artery (coming from the aorta) and the renal vein (coming from the vena cava) that transport blood in and our of the kidneys. Like said before, the kidneys main role is to filter out the water-soluble waste products from our blood. The kidney’s filter urea from our blood through tiny filtering parts called **nephrons**. Each one of these nephrons is a ball that is formed of small blood capillaries (a glomerulus) and a little tube that is called the renal tubule. The urea together with other wastes substances and water forms the waste produce urine as it passes through these nephrons and down into the renal tubules of the kidney.

From there the urine travels down the **urters** **,** which are two tubes that connect the kidney to the bladder. Muscles constantly contract and relax in the ureter walls to force the urine down the tubes away from the kidneys. If the urine stays in one place or returns to the kidney, an infection can occur in the kidneys. There are small amounts of urine that about every 10 to 15 seconds is emptied into the **urinary bladder.**

The bladder is a trangle-muscular organ that is hollow and looks like a balloon. The bladder sits in your pelvic region and is held in its place be ligaments that are attached to other organs and the bone in pelvis. When it is full it is a round swollen shape and when it empties it gets smaller. A healthy bladder can hold 2 cups or 16 ounces of urine for about 2 to 5 hours.

There are muscles that are circular called sphincters to help the urine from leaking. The sphincter muscles close tightly almost like a rubber band around the opening of the bladder into the tube that allows the urine to pass out of the body called the **urethra**. The brain signals the bladder muscles to tighten ultimately squeezing the urine out of the bladder and eventually out of the body. The brain also signals the sphincter muscles to relax letting the urine leave the bladder through the urethra. The bladder has nerves that alert the person when it is time to empty the bladder, a process called **urination.**

Drinks containing caffeine and alcohol will cause you to urinate more often. This is because alcohol and caffeine are diuretics. This means it encourages the body to lose more water than it takes on by halting the production of the body's anti-diuretic hormone, resulting in you needing to go to the bathroom excessively and so speeding up the loss of fluid from your body, leading to dehydration.

All of these processes are necessary to rid the waste created during cellular activity.

<span style="color: #2a5d7a; display: block; font-family: Arial,Helvetica,sans-serif; font-size: 160%; text-align: center;">**BIBLIOGRAPHY:**

<span style="font-family: Arial,Helvetica,sans-serif;">Chiras, Daniel (1993). "Biology: The Web of Life." West Publishing Company: St. Paul, MN.

Krogh, David. Biology: A Guide to the Natural World. Second Edition. Upper Saddle River, NJ: Prentice Hall, 2002. Print.

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">Stein Carter, J. "Excretory/Urinary System." <span style="font-family: verdana,helvetica,sans-serif; font-size: 10px; letter-spacing: 1px; line-height: normal;">//<span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">Your Body // <span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">. 1996. University of Cincinnati, Web. 26 Oct 2009. <http://biology.clc.uc.edu/courses/Bio105/kidney.htm>.

Johnson, Delos. "The Circulatory System." //The Circulatory System//. Global Classroom, Web. 28 Oct 2009. <http://www.globalclassroom.org/hemo.html>.

"Cardiovascular System." //Your Gross and Cool Body: Circulatory System//. Discovery Kids, Web. 28 Oct 2009. <http://yucky.discovery.com/flash/body/pg000131.html>.