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13-excretion and homeostasis - Coggle Diagram
13-excretion and homeostasis
excretion
it is a characteristic of all living organisms
it is the removal of waste products of metabolism from living organisms' bodies
for example, in humans urea, a waste product produced in the liver, is removed from the blood by the kidneys and mixed with other waste products to form urine
urea is produced thanks to the breakdown of proteins
they are broken down into amino acids to harvest the energy they contain in a process called "deamination", which leaves only the part of amino acids containing nitrogen to be excreted
they are then dissolved into blood plasma and transported to the kidneys
urine is stored in the bladder through the ureters and then flows out through the urethra
the kidney
it has two main parts
the cortex, the outer layer in a kidney
the medulla, the inner layer in a kidney
the ureter is a tube carrying urine from the kidney to the bladder
each kidney is made up of thousands of tiny tubules called "nephrons"
each nephron begins in the cortex, goes into the medulla, in the cortex again and out through the medulla to join up with the ureter
the renal artery, which carries blood into the kidneys, divides up to form little bundles of capillaries, called "glomeruli"
the blood passing through these glomeruli is filtered to remove water, urea, glucose and ions, which are then moved into the nephrons
nephrons and capillaries are closely bound, so some substances still needed by the body are reabsorbed before urine flows into the ureter
homeostasis
it is the mainteneance of a constant environment inside the body
thanks to it, temperature, water and glucose levels are kept constant to allow the cells to work as efficiently as possible
the values are not always the same, but instead they oscillate inside a range, which is called "set point"
glucose is very important for cell respiration
its level is controlled by the pancreas
when there is too much glucose in the blood, insulin is released
it causes the liver to absorb glucose from the blood and to convert it into glycogen, which is then stored
in type 1 diabetes, insulin-secreting cells are killed by the immune system, resulting in no control of blood glucose concentration
when there is too little glucose in the blood, glucagon is released
it causes the liver cells to break down glycogen to glucose and then release it into the blood
normally an ordinary gland that secretes pancreatic juice, it contains some isolated groups of cells, called "islets"
these islets detect changes in the glucose levels in the blood and act accordingly
this mechanism, which detects a change and works to bring it back to an original value, is called "negative feedback"
controlling body temperature
one of the most important organs in mammals involved in temperature regulation is the skin
under it there are sweat galnds, which extract water and ions from the blood to produce sweat, receptors, small blood vessels and a fatty tissue that insulates and acts as a energy reserve
the part of the brain dedicated to controlling body temperature is the "hypothalamus"
when a temperature change is detected, the hypothalamus sends signals to the liver, skin and muscles
when the temperature falls, muscles contract and relax quickly to produce heat that warms the blood ("shivering"), metabolism is increased to produce more heat and hairs stand up to prevent the body from losing heat
when the temperature rises, hairs lie flat so as to make heat disperse, sweat production is increased to reduce skin heat levels when it evaporates and capillaries near the skin get wider ("vasodilation") so that more blood goes there and more heat is lost