• Bladder: A hollow organ that stores urine.
• Bowman’s capsule: A cup-shaped structure around the glomerulus that collects the filtered substances; part of the nephron.
• Dialysis: A medical procedure in which blood is filtered with the help of a machine.
• Excretion:The process of removing wastes and excess water from the body.
• Filtration: The process of filtering substances from blood in the glomerulus.
• Glomerulus: Part of the nephron; a cluster of arteries that filters substances out of the blood.
• Homeostasis: The ability to maintain a stable internal environment despite external changes.
• Kidney: Organ that filters the blood and forms urine.
• Kidney stones: Crystals of dissolved minerals that form in urine inside the kidneys.
• Nephrons: The structural and functional units of the kidneys; includes the glomerulus, Bowman’s capsule, and renal tubule.
• Reabsorption: The return of needed substances in the filtrate back to the bloodstream.
• Renal tubule: A long, narrow tube surrounded by capillaries that reabsorbs many of the filtered substances and secretes other substances; part of the nephron.
• Urea: The main waste nitrogen in the urine of mammals. It is produced in the metabolism of proteins.
• Ureter: Tube-shaped structure that brings urine from the kidneys to the urinary bladder.
• Urethra: A muscular tube that carries urine out of the body.
• Urinary system: The organ system that makes, stores, and gets rid of urine.
• Urine: The liquid waste product of the body that is excreted by the urinary system.

Formation of Urine

In the last post about the nephron function we studied how urine is produced, but in this new post we are going to explain very carefully all the process. I hope you'll be able to understand it.
The process of urine formation is as follows:
1. Blood flows into the kidney through the renal artery. The renal artery branches into capillaries inside the kidney. Capillaries and the nephrons lie very close to each other in the kidney.
2. In the nephron, the blood pressure within the capillaries causes water and solutes (small soluble molecules) such as salts, sugars, and urea to leave the capillaries and move into the Bowman’s capsule. (GLOMERULAR FILTRATION).
3. The water and solutes move along through the tubules of nephrons. At this point most of the water and solutes are returned to the capillaries that surround the nephron (TUBULAR REABSORPTION). Some chemicals are secreted in the las part of the tubules (TUBULAR SECRETION).
4. The fluid that remains in the nephron at this point is called urine.
5. The blood that leaves the kidney in the renal vein has much less waste than the blood that entered the kidney.
6. The urine is collected in the ureters and is moved to the urinary bladder where it is stored.
Nephrons filter 125 ml (about ¼ cup) of body fluid per minute. In a 24-hour period nephrons produce about 180 liters of filtrate, of which 178.5 liters are reabsorbed. The remaining 1.5 liters of fluid forms urine.
Urine enters the bladder through the ureters. Similar to a balloon, the walls of the bladder are stretchy. The stretchy walls allow the bladder to hold a large amount of urine. The bladder can hold about 400 to 620 ml of urine, but may also hold more if the urine cannot be released immediately. Urination is the process of releasing urine from the body. Urine leaves the body through the urethra.
Nerves in the bladder tell you when it is time to urinate. As the bladder first fills with urine, you may notice a feeling that you need to urinate. The urge to urinate becomes stronger as the bladder continues to fill up.
In this table it is possible to compare plasma and urine composition.

	plasma g/100ml	urine g/100ml	concentration in urine
water	90-93	95
protein	7 - 8.5	0
urea	0.03	2	x60
uric acid	0.002	0.03	x15
glucose	0.1	0

Nephrons

A single kidney may have more than a million nephrons. Nephrons are the structural and functional units of the kidneys. The diagram represents an individual nephron and shows its main structures and functions. The structures include the glomerulus, Bowman’s capsule, and renal tubule.
Nephron structures.

• The renal corpuscle that consists of two structures:

• The glomerulus is a cluster of capillaries that filters substances out of the blood.
• Bowman’s capsule is a cup-shaped structure around the glomerulus that collects the filtered substances.

• The renal tubule is a long, narrow tube surrounded by capillaries that reabsorbs many of the filtered substances and secretes other substances. It is divided into three parts: the proximal tubule, the Loop of Henle, and the distal tubule.

Tubules of several nephrons join to form a single collecting tubule.
Nephron function.
The nephron function is to produce urine. In this process we can consider two stages
FILTRATION
Filtration is the process of filtering substances from blood in the glomerulus. The renal arteries, which carry blood into the kidneys, branch into the capillaries of the glomerulus of each nephron. The pressure of blood moving through these capillaries forces some of the water and dissolved substances in the blood through the capillary walls and into Bowman’s capsule.
The fluid that collects in Bowman’s space is called filtrate. It is composed of water, salts, glucose, amino acids, and urea. Larger structures in the blood—including protein molecules and blood cells—do not pass into Bowman’s space. Instead, they return to the main circulation.
REABSORPTION AND SECRETION.
From the space inside the Bowman’s capsule the filtrate passes into the renal tubule. The main function of the renal tubule is reabsorption. Reabsorption is the return of needed substances in the filtrate back to the bloodstream.
At the beginning, in the proximal tubule, salts, glucose and amino acids are picked up from the filtrate. In the rest of the tubule the main reabsorbed substance is water. Before the tubule arrives to the collecting tubule, some substances can be secreted in the distal tubule.
The collecting tubule reabsorbs water from tubular fluid and return it to the blood. The remaining fluid, called urine, has a smaller volume and a greater concentration than tubular fluid. From the collecting ducts, urine enters a ureter and is eventually excreted from the body.

The Urinary system

The urinary system is the organ system that makes, stores, and gets rid of urine. It includes two kidneys, two ureters, the bladder, and the urethra. The main function of the urinary system is to filter waste products and excess water from the blood and remove them from the body. Urine is the liquid waste product of the body that is excreted by the urinary system. Recall that in the excretion process, other organs as skin and lungs take part in it.Organs of the urinary system
Kidneys
The kidneys are a pair of bean-shaped, reddish brown organs about the size of a fist. They are located just above the waist at the back of the abdominal cavity, on either side of the spine. Located on top of each kidney is an adrenal gland.
The kidney has three layers, the outer layer is the renal cortex, and the middle layer is the renal medulla. The inner layer, the renal pelvis is urine is collected and is funnelled into the ureter
From the aorta, the renal arteries carry blood to the kidneys to be filtered, then the renal veins carry the filtered blood away from the kidneys to the inferior vena cava.
Ureters
From the kidneys, urine enters the ureters, which carry it to the bladder. Each ureter is a muscular tube about 25 centimeters long.
Bladder
The bladder is a hollow organ that stores urine. It can stretch to hold up to 500 milliliters. When the bladder is about half full, the stretching of the bladder sends a nerve impulse to the sphincter that controls the opening to the urethra. In response to the impulse, the sphincter relaxes and lets urine flow into the urethra.
The urethra is a muscular tube that carries urine out of the body. Urine leaves the body through another sphincter in the process of urination. This sphincter and the process of urination are normally under conscious control.
As in other organ systems here you have a video for kids but it is very clear.

New findings

Allways it's possible to find out new webpages or videos when you browse in internet. In this post there are several videos about the organ systems we have already studied. I found them when I was looking for a video of the urinary system to the last post. I advice you watch them. You'll improve your knowledge.

The circulatory system


The digestive system

The respiratory system


Another good finding is this other video of Tom and Moby about the digestive system:

The excretory process

We have to finish the nutrition function with the excretory system. As we saw in previous posts, in the nutrition process your body takes nutrients from food in the digestive system and oxygen in the respiratory sytem. Both pass to circulatory system and blood transports them to all the cells of the body. Cells obtain energy from nutrients and also produce waste products. Wastes go to the bloodstream and must be removed from the body. This process is called excretion. The excretory system is where it carries it out. But the excretory system not only releases wastes from the body, it maintains homeostasis by keeping the correct balance of water and salts in your body.
Homeostasis is the body’s attempt to maintain a constant internal environment. It involves keeping many internal factors at more or less constant levels. The factors include body temperature and properties of the blood as the right levels of acidity, salts, glucose,... in order for cells to function normally.For instance homeostasis of temperature. According to body temperature detected by receptors, the brain sends appropriate orders to return the body temperature to normal. If temperature is too higher, the body reacts to decrease that temperature (negative feedback control). Maybe you will learn better with this video of the sympathetic tim and Moby (with subtitle):

A little secret, you can see in spanish in this link
The kidneys are the main organs in excretion of wastes from the blood, but several other organs are also involved in this process as liver, skin, and lungs.
• The liver breaks down excess amino acids in the blood to form ammonia, and then converts the ammonia to urea, a less toxic substance. The liver also breaks down other toxic substances in the blood, including alcohol and drugs.
• The skin eliminates water and salts in sweat.
• The lungs exhale water vapor and carbon dioxide.
Those organs can be considered part of the excretory system but, in the study of excretion process we are going to refer only to the urinary system
Finally, a second video fron HEATINCca where is explained the Urinary system and the homeostasis

Valentine's day

Last week I found this Valentine's Day love song. It's a little different but with charm.


HAPPY VALENTINE'S DAY

The lymphatic system

The lymphatic system consists of a fluid (lymph), vessels that transport the lymph, and organs that contain lymphoid tissue. It is often called the secondary circulatory system. The lymphatic system has three primary functions:
• The removal of excess intresticial fluids from body tissues.
• The absorption of fats from the small intestine and transport of those fats to the cardiovascular system.
• The third and probably most well known function of the lymphatic system is defense against invading microorganisms and disease. Lymph nodes and other lymphatic organs filter the lymph to remove microorganisms and other foreign particles.
Lymph
Lymph originates as blood plasma that leaks from the capillaries of the cardiovascular system. This blood plasma fills the space between individual
cells of tissue where it becomes part of the interstitial fluid. Most of the interstitial fluid is returned to the capillaries. The excess interstitial fluid is collected by the lymphatic system into lymph capillaries, and is processed by lymph nodes before to being returned to the circulatory system. Once within the lymphatic system the fluid is called lymph, and has almost the same composition as the original interstitial fluid. Returning the fluid to the blood prevents edema and helps to maintain normal blood volume and pressure.
Lymphatic vessels
Lymphatic vessels, unlike blood vessels, only carry fluid away from the tissues. The smallest lymphatic vessels are the lymph capillaries, which begin in the tissue spaces as blind-ended sacs. There isn’t a central pump, lymph movement occurs slowly with low pressure due to the squeezing action of skeletal muscles. Lymph travels through lymp vessels that are similar to capillaries and veins. Lymph moves in one direction only, due to valves in lymph vessels that are similar to the valves found in veins, shown in Figure above. The lymph is transported to progressively larger lymphatic vessels that drain into the circulatory system at the right and left subclavian veins.
Lymphatic organs
Lymphatic organs are characterized by clusters of leukocyte. When the body is exposed to microorganisms and other foreign substances, the leukocytes proliferate within the lymphatic organs and are sent in the blood to the site of the invasion. This is part of the immune response that attempts to destroy the invading agent.
The four types of lymphatic organs :
.Lymph Nodes
Lymph nodes are small bean-shaped structures that are usually less than 2.5 cm in length. They are widely distributed throughout the body along the lymphatic vessels where they filter the lymph before it is returned to the blood.
Tonsils
Tonsils are clusters of lymphatic tissue just under the mucous membranes that line the nose, mouth, and throat (pharynx).
Spleen
The spleen is located in the upper left abdominal cavity, just beneath the diaphragm, and posterior to the stomach. The spleen filters blood in much the way that the lymph nodes filter lymph. The spleen, along with the liver, removes old and damaged erythrocytes from the circulating blood. Like other lymphatic tissue, it produces leukoocytes, especially in response to invading pathogens
Thymus
The thymus is located anterior to the ascending aorta and posterior to the sternum. It is relatively large in infants and children but after puberty it begins to decrease in size so that in older adults it is quite small. Thymus is where the lymphocytes are processed.
In this link you can complete the description of the lymphatic organs.

Vocabulary of circulatory system

Anemia: The condition of not having enough hemoglobin in the blood to carry oxygen to body cells.
Antibodies: Proteins that identify pathogens or other substances as being harmful; flow in blood; can destroy pathogens by attaching to the cell membrane of the pathogen.
Arteries: Blood vessels that carry blood away from the heart.
Atrioventricular (AV) valves: Valves that stop blood from moving from the ventricles back into the atria.
Atrium: One of the two small, thin-walled chambers on the top of the heart that blood first enters.
Blood: A body fluid that is a type of connective tissue; moves oxygen and other compounds throughout the body.
Blood clotting: The complex process by which blood forms solid clots.
Blood pressure: The force exerted by circulating blood on the walls of blood vessels.
Capillaries: The smallest and narrowest blood vessels in the body.
Cardiovascular system: The organ system that is made up of the heart, the blood vessels, and the blood.
Heart attack: Event that occurs when the blood supply to a part of the heart is blocked.
Hemophilia: A group of hereditary diseases that affect the body's ability to control blood clotting.
Hypertension: Also called high blood pressure; a condition in which a person’s blood pressure is always high;
Leukemia: Cancer of the blood or bone marrow; characterized by an abnormal production of blood cells, usually white blood cells.
Lymphatic system: A network of vessels and tissues that carry a clear fluid called lymph; includes lymph nodes, lymph ducts, and lymph vessels.
Plasma: The golden-yellow liquid part of the blood.
Platelets: Fragments of larger cells that are important in blood clotting.
Pulmonary circulation: The part of the cardiovascular system which carries oxygen-poor blood away from the heart to the lungs, and returns oxygen-rich blood back to the heart.
Red blood cells (RBCs) : Flattened disk-shaped cells that carry oxygen, the most common blood cell in the blood. Mature red blood cells do not have a nucleus.
Semilunar (SL) valves: Found in the arteries leaving the heart; prevents blood flowing back from the arteries into the ventricles.
Sickle cell disease: A blood disease that is caused by abnormally-shaped blood protein hemoglobin.
Stroke: A loss of brain function due to a blockage of the blood supply to the brain.
Systemic circulation: The portion of the cardiovascular system which carries oxygen-rich blood away from the heart to the body, and returns oxygen-poor blood back to the heart.
Veins: Blood vessels that carry blood back to the heart.
Ventricle: One of the two muscular V-shaped chambers that pump blood out of the heart.
White blood cells (WBCs): Nucleated blood cells that are usually larger than red blood cells; defend the body against infection by bacteria, viruses, and other pathogens.