Homeostasis
Learning objectives The human body needs to maintain and regulate a steady state in order to function correctly Homeostasis involves interactions between various systems of the body
Homeostasis “the tendency of a system, esp. the physiological system of higher animals, to maintain internal stability, owing to the coordinated response of its parts to any situation or stimulus tending to disturb its normal condition or function” - Dictionary.com Unabridged (v 1.1) “The ability or tendency of an organism or a cell to maintain internal equilibrium by adjusting its physiological processes.” - American Heritage Stedman's Medical Dictionary
Homeostasis There are several examples of homeostasis and the processes involved We have already looked at the reproductive hormones and how oestrogen and LH are linked through NEGATIVE FEEDBACK – i.e. as one gets more it causes the other to get less Here are 3 more commonly used examples
Temperature Control Also known as THERMOREGULATION The enzymes in our bodies work best at around 37°C we need to be able to keep our bodies as close to this temperature as possible The body will react if it gets too hot or if it gets too cold It will adjust the temperature back to where it should be
Thermoregulation Involves receptors linked to the HYPOTHALAMUS located in the brain Nerve impulses are sent from here to the SKIN Skin reacts to change body temperature
Too Hot…? VASODILATION – blood vessels near the skin get wider This allows more warm blood to flow near the surface and lose heat, cooling you down Muscles controlling the hairs on your skin relax – causing the hairs to lie flat Sweat is secreted from sweat glands – as it evaporates, this cools you down
Too Hot…?
Too Cold…? VASOCONSTRICTION – blood vessels near the skin get smaller Less blood flows near the surface, keeping the heat closer to your body core Erector muscles contract, pulling your hairs up on end This traps warm air close to your skin Sweat glands no longer secrete sweat Shivering also helps to warm you up – your muscles generate more heat through respiration
Water Control Also known as OSMOREGULATION Controlled by the hypothalamus using negative feedback Involves the pituitary gland and the kidneys
Osmoregulation Water is very important to the body, but it must maintain the right amount If there is a problem, it is spotted by OSMORECEPTORS in the hypothalamus A message is sent through nerve impulses to the pituitary gland This changes the amount of a particular hormone it releases The change in hormone level causes the kidneys to react
Not Enough Water..? Hypothalamus signals the pituitary gland Pituitary increases its release of the hormone ADH (ANTI-DIURETIC HORMONE) More ADH enters kidney, stimulating it to reabsorb more water Smaller amounts of more concentrated urine are produced
Osmoregulation
Too Much Water..? Hypothalamus signals the pituitary gland Pituitary slows down its release of the hormone ADH Less ADH enters kidney, which then absorbs LESS water More urine is produced Urine is LESS concentrated
Blood Sugar levels When food is digested, sugar – glucose – is produced It is important that blood sugar levels do not get too high – HYPERGLYCEMIA – or too low – HYPOGLYCEMIA It involves the hormone INSULIN
Too much glucose Receptors in the blood sense high levels of glucose Nerve impulses sent to the PANCREAS Insulin is released into the blood Triggers an increase in glucose being converted in glycogen by the LIVER Glucose levels drop to normal Insulin no longer produced and degrades
Not Enough Glucose Receptors in the blood sense low levels of glucose Nerve impulses sent to the pancreas Insulin stops being released into the blood Less glucose is converted in glycogen by the liver Less glucose absorbed by the cells Glucose levels return to normal
Glucose Regulation Insulin crystals
Glucose Regulation People who cannot naturally control their blood sugar levels are called DIABETIC They must control their blood sugar manually by controlling their diet, and by injecting themselves regularly with insulin