Excretion.docx

The Excretory System in the Human (3) Excretion is the removal of the waste products of metabolism from the body There are three organs of excretion - Skin: Excretes water, salt, and small amounts of urea in sweat produced by the sweat glands. It plays a major role in the controlling the temperature...

The Excretory System in the Human (3) Excretion is the removal of the waste products of metabolism from the body There are three organs of excretion - Skin: Excretes water, salt, and small amounts of urea in sweat produced by the sweat glands. It plays a major role in the controlling the temperature - Lungs: Excrete both Carbon dioxide and water - Urinary system: Excretes water and urea and is the main organ of excretion and homeostasis, in terms of solution concentrations Kidney Structure and Location (4) - Located on either side of the spine, at the rear of the upper abdominal cavity, just below the diaphragm - Has three main layers: The medulla (middle layer), the cortex (outer layer), and the pelvis (inner layer) - The pelvis narrows to a thin tube called the ureter which connects to the bladder - When full, the bladder contracts and empties the urine through the urethra - Adrenal gland located on top of each kidney - Kidney receives blood through the renal artery which branches from the aorta - Filtered and purified blood leaves the kidney through the renal vein and enters through the inferior vena cava Kidneys control the concentration of bodily fluids. - If you drink a lot of water, bodily fluids are diluted, causing all chemical reactions to slow down. The body responds by producing lots of weak, watery pale urine to increase the concentrations back to their proper levels. This is called diuresis - If you sweat a lot, do not drink enough, or eat a salty meal, the fluids in the body will become too concentrated. This causes the production of dark-coloured, strong, concentrated urine. Thirst will increase, which is the body’s way of informing that more water needs to be drank to bring the concentration of body fluids back to normal Nephron Structure and Formation of Urine (5) Nephrons are thousands of structures in the kidney which produce urine. The formation of urine by nephrons - Blood containing impurities, such as urea, enters the kidneys from the aorta through the renal artery - The pressure in the afferent arteriole and the glomerulus increases greatly due to the narrowing of these blood vessels, especially in the efferent arterioles - High pressure and large surface area of capillaries causes ultrafiltration of blood plasma through the pores in the glomerulus wall, into the lumen of the Bowman’s capsule, forming a liquid called the glomerular filtrate. Both walls are one cell thick. The filtrate does not contain proteins and blood cells as they are too large for the pores - Glomerular filtrate contains glucose, amino acids, vitamins, salt, and water. It collects here before passing into the proximal convoluted tubule where all useful substances are reabsorbed - Water is absorbed by osmosis. The other substances are absorbed by diffusion and active transport depending on their concentrations - The cells of the proximal convoluted tubes have many mitochondria because they use a lot of energy when they carry out active transport - More water is absorbed in the loop of Henle and in the distal convoluted tube - Final water balance happens in the collecting duct, under the influence of anti-diuretic hormone, which is produced by the pituitary gland - Urine passes to the pelvis of the kidney and then through the ureter in the bladder for storage. A sphincter muscle prevents the bladder from leaking - When the bladder is full it empties through the urethra Anti-diuretic Hormone (ADH) Action ADH conserves water. - ADH makes the collecting duct more permeable, so more water is reabsorbed from urine - Diuresis is the production of large quantities of water. ADH is an anti-diuretic because it stops diuresis - When you drink a lot of water, the blood becomes more dilute, and this is monitored by the hypothalamus. The hypothalamus tells the pituitary gland to stop producing ADH, which causes the collecting ducts to become less permeable, so less water is reabsorbed and large volumes of watery urine pass into the bladder - If your blood concentration increase, ADH production increases and makes the collecting ducts more permeable, so more water is reabsorbed into the blood. This means that urine contains less water, is more concentrated, and results in small amounts of strong urine Temperature Control Temperature regulation is vital to maintain life. Temperature is the most important factor in determining the rate of chemical reactions. Animals can be split into two groups depending on how they regulate their body temperature. Ectotherms – Referred to as poikilothermic, obtain the heat they require from the environment. For example, fish, reptiles, and amphibians. Although many ectotherms are adapted to live in cold places, they can only occupy areas with a limited temperature range. In many cases, a sudden change in temperature can kill them Endotherms – Referred to as homoeothermic, e.g., birds and mammals. Require three mechanisms to keep their temperature constant; a. Monitor the temperature of the body b. Get rid of their heat if temperature is too high c. Produce and retain heat if their temperature is too low Temperature is monitored and controlled by the hypothalamus, the body’s thermostat. Cooling mechanisms of the body - Sweat: Produced in the sweat glands, reaches the surface of the skin through sweat ducts. Sweat evaporates on the surface of the skin. It has a high latent heat of vaporisation, so it cools the skin - Blood: Carries heat from the liver and other organs. Blood is diverted towards the skins surface when arterioles dilate allowing more blood to flow through capillary beds near the surface of the skin. This allow more heat to escape by radiation - Hair: Hair lies flat on the skin because the erector muscle is relaxed, thus, no layer of insulating air is trapped. This allows heat to escape When the body is too cold - No sweat is produced - Blood flow is kept away from the surface of the skin - Hairs stand erect and trap a layer of insulating air - The brain causes a rapid contraction and relaxation of muscles (shivering) which produces heat Endotherms can occupy a wider range of temperature zone than ectotherms.