The structure and function of the renal system

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TABLE OF CONTENTS

Pass

Organs in the lymphatic system2-3

Position of the Lymph nodes3-5

Position of the blood vessels5

Merit

Macrophages6

Role of macrophages, t cells and b cells6-7

Role of antibodies and antigens8

Distinction

The Lymphatic system in a healthy and diseased state9-10

http://www.highlands.edu/academics/divisions/scipe/biology/labs/cartersville/2122/diagrams/urinarydiagram1.jpg

kidney structure

http://www.dorenarode.com/anatomy/images/kidney3_model.jpg

Nephron structure

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importance of fluid balance

Fluid balance occurs when the amount of fluid we lose from our bodies equals the amount of fluid that is taken in by our bodies. Electrolytes are present in the blood, urine and other bodily fluids. These electrolytes can help the bloods chemistry, the movement of muscles and processes. The levels of these electrolytes can become too high or too low. When bodily fluids are lost from the body through vomiting, diarrhea and sweating can cause a lot of problems to the body as the fluids become imbalanced. Bodily fluids are distributed around the body in three main compartments, the intracellular fluid, which is the fluid within the cells of the body and the extracellular fluid which is found outside of the cells, which is the body’s internal environment and the cells external environment. The fluids are also distributed inside of blood vessels I the blood plasma. Around 5% is found in the plasma, 15% in the extracellular compartment, and 40% in the intracellular compartments. Bodily fluids move from each compartment in a variety of ways. Electrolytes and water move through cell membranes and walls. Fluids move through the compartments using diffusion; where ions and molecules flow from an area of high concentration to an area of low concentration. This can also occur through filtration, where the amount of pressure can cause the water molecules and also ions to move from high pressure areas to low pressure areas. Active transport is another way that water molecules and ions can be moved between the compartments, Active transport occurs when these molecules are carried by a larger molecule or a vacuole on a cell wall, using certain enzymes to cause the effect of a pump through the different concentration ranges. For example, potassium and phosphate ions would require active transport as the high concentration means that diffusion wouldn’t be able to occur. Transport also occurs through osmosis, where water flows from a dilute solution to a concentrated solution. The water flows from a hypotonic solution to a hypertonic solution. Each electrolyte has a different way of moving through the different compartments. The kidneys help to maintain the body’s water concentration in the blood plasma, which helps to maintain the concentration of water in the blood plasma. Water is taken in from foods and drinks, and it is lost in our sweat, bodily excretions and even when we exhale. Our water levels need to be kept balanced for all of the cells in the body to work properly, the amount of water taken in and given out needs to be at equal amounts. This mainly occurs due to the kidneys, where blood is filtered and the water and salts from the blood are reabsorbed into the blood plasma to maintain the fluid balance of our bodies. Electrolytes are ions that are present in the blood, urine and other bodily fluids of human beings. These ions can help with the chemistry of the blood, the movement of muscles and other bodily processes.

process of materials in the nephron

Each of the kidneys contains around 1 million nephrons that help to reabsorb different types of substances back into the blood, so that they are not lost during excretion. There are many stages to the full filtration of the urine, and it each takes part in different sections in the nephron. The glomerulus is a section of the nephron that consists of knotted capillaries, and is surrounded by the Bowman’s capsule. The afferent and efferent arterioles have cells called granular cells on them. These cells are mechanoreceptors that secrete a hormone called renin that will help to maintain blood pressure. The arterioles also consist of meningeal cells that secrete actin which is important for the contraction of the vessels, which help to maintain blood flow and pressure which is important as the kidneys have high blood supply. If there is very high blood pressure, more glucose will be forced out of the blood into the proximal tubules. If too much is forced out, not enough becomes reabsorbed which could cause high contents of glucose in the urine which could be because of diabetes. It can also cause more sodium and potassium to be forced out of the blood. If Not enough is reabsorbed back into the blood it will cause more sodium and potassium in the urine, or less of these in the blood. This is normally an indication of kidney failure which they will then need the use of kidney dialysis or a transplant. The capillaries in the glomerulus are covered in cells called podocytes, which wrap around the capillary and consist of ‘finger like’ projections – called major projections that are very important in the filtration of the substances from the blood. The glomerulus consists of two arteries; an afferent arteriole, and an efferent arteriole. These both differ in size as the afferent arteriole is a lot larger than the efferent arteriole. Not only is this because when the blood leaves the efferent arteriole it has a lesser volume of blood, the afferent arteriole needs to create a higher blood pressure, so that the substances can be forced out efficiently and can therefore become filtrate. The glomerulus allows everything but blood cells to be passed out of the blood vessels and into the glomerulus. The glomerulus doesn’t allow proteins to diffuse through the basement membrane, as it is a fine mesh of collagen fibers and glycoproteins. This acts as a filter as large molecules cannot pass, and is also negatively charged, as are the protein molecules. The capillary consists of endothelium cells that have narrow gaps for the substances and blood plasma to diffuse through easily. The filtrate that is taken from the glomerulus and into the Bowman’s capsule, are then transported down the rest of the nephron where reabsorption can take place. Reabsorption mostly takes place in the proximal convoluted tubule, where glucose, sodium and water are mainly reabsorbed. A sodium ion moves into the cell through diffusion, and moves with a glucose molecule also, by the use of a co-transported protein, which carries both of the molecules into the cell. The concentration of glucose in the proximal convoluted tubule cell then increases. The glucose molecule continues out of the cell and back into the blood. There are two ways that substances can pass through the nephron to the blood; passive transport and active transport. Active transport is where ATP is used to help substances (amino acids, glucose and sodium) to move through the membrane. Passive transport is where the substances are moved between the tubules and capillaries due to a difference in concentration. This is usually urea, water and chlorine. In the proximal convoluted tubule the concentration between blood plasma are equal, in the descending loop of Henle the filtrate concentration is higher, and in the ascending loop of Henle the blood plasma has a higher concentration. In the distal convoluted tubule the blood plasma has a higher concentration. The sodium is pumped out of the cell into the blood through active transport, and is then binded with ATP to cause a conformational change. The sodium is then released into the blood, and potassium is secreted and binded, so that is can return to the nephron to continue as excretion. The potassium is also needed as there is a low concentration of sodium in the nephron, another positive ion such as potassium can take its place. Water passes through the cells via osmosis; therefore most of the water is sent straight back to the blood from the proximal convoluted tubule. After all the reabsorption has occurred in the tubules, some substances need to be secreted back from the blood into the nephron to be excreted. Potassium ions and hydrogen ions are secreted from the distal convoluted tubule, so that these ions are decreased in the body and are not too high. Creatinine and histamine and penicillin are secreted into the proximal convoluted tubule. These hormones are produced continuously and need to be removed from the body, as an excess can cause issues.

It is important that all of the water is reabsorbed back into the blood, however not all areas of the nephrons are permeable. The proximal tubule and descending limb of the loop of Henle are always permeable, the distal tubule and the colleting duct are sometimes permeable, however the ascending limb of the loop of Henle are not permeable at all times. Permeability can respond to large levels of ADH (anti-diuretic hormone). A lack of ADH can be detected in the part of the brain called the hypothalamus, which then sends a message to the pituitary gland so that more of this hormone can be produced. This hormone then affects the walls of the tubules and allows the water to be able to pass through them back into the blood capillaries. After the full filtration of the blood and the formation of urine, the filtrate will next go down the collecting duct, where it is connected to the calyx, which takes the urine to the ureter and is then carries to the bladder, where it is stored for excretion.


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