Homeostasis is the state of steady internal physical and chemical conditions maintained by living systems.
Homeostasis maintains the optimal functioning conditions of the organism and includes many variables:
- thermoregulation
- blood sugar regulation
- osmoregulation
- pH of extracellular fluid
- concentrations of sodium, potassium and calcium ions
- fluid balance
stimulus
- Negative feedback loop - when a variable changes, an opposite change directs it back to the equilibrium value.
- Stimulus-response model - stimulus noticed by receptor, so tell the effector to create a response.
response
Structural adaptations are physical constructions of an organism that help homeostasis. For example, fat and fur helps to stay warm. In contrast, behavioral responses are voluntary actions.
thermoregulation
Thermoregulation (also homeothermy) is the ability of an organism to keep its body temperature within narrow limits.
In humans, your body temperature is measured with thermoreceptors on the skin and in the hypothalamus part of the brain.
- if temperature is too high, signals via nerves are sent to the sweat glands and blood vessels in the skin and the brain, causing sweating and vasodilation of the arterioles (a small-diameter blood vessel).
- If temperature is too low, signals via nerves are sent to blood vessels and muscles in the skin, causing vasoconstriction of blood vessels and shivering. also, a hormone called thyroid hormone is signaled to be released, traveling to cells and causing energy to be burned, increasing the basal metabolic rate.
Organisms that are poikiloterms don’t have physiological mechanisms to maintain homeostasis temperature. Rather, they allow their body temperature to fluctuate and use behaviours to voluntarily change the temperature.
blood sugar regulation
Blood sugar regulation (also glucose homeostasis), is the process by which the levels of blood sugar are maintained in the body within a narrow range.
The blood sugar level is the measure of glucose concentrated in the blood..
Glucose causes osmosis, so it cannot be simply be stored in water. So instead, cells store glucose in the form of glycogen (an insoluble polymer of glucose), which can be broken down to quickly release glucose into the blood.
The islets of Langerhans is an endocrine (creating hormones) tissue in the pancreas that measure blood glucose concentration. It can release two hormones, insulin using beta cells, and glucagon using alpha cells.
- Insulin stimulates liver, skeletal muscle and other cells to take glucose from the blood and store it as glycogen.
- Glucagon stimulates just the liver to release more glucose.
Both the alpha and beta cells detect the blood sugar levels, and the cells produce less of one hormone and more of another to work together.
Diabetes is a condition when the mechanisms to lower the blood glucose don’t work properly. Symptoms of diabetes include frequent urination, fatigue, increased thirst and hunger.
- Type 1 diabetes (also juvenile diabetes) is caused by an autoimmune disorder in which cytotoxic T cells inappropriately target and kill the beta cells. This means you need to take injections insulin.
- Type 2 diabetes develops over a long period of time, as liver cells and other cells become resistant to insulin. Not exactly sure about the causes.
Hypoglycaemia is a blood sugar level that is below normal. Symptoms include clumsiness, trouble talking, confusion and stuff. The most common cause of hypoglycaemia is the medication for diabetes.
osmoregulation
Osmoregulation maintains the fluid balance and the concentration of electrolytes to keep the body fluids from becoming too diluted or concentrated.
Osmoregulation is the active regulation of the osmotic pressure of an organism’s body fluids, detected by osmoreceptors, to maintain water content.
The purpose of water in the body is to dissolve things - proteins, sugars, salts…
The body lacks a way to measure how much total water the body contains so instead it measures how much stuff is dissolved in the water.
The amount of solute present in water is called osmolarity.
- If osmolarity is high, cells in the hypothalamus increases the release of anti-diuretic hormone which acts of the cells of the kidney to increase the retention of water from urine, producing more concentrated urine and prevents water loss.
- If osmolarity is low, the hypothalamus decreases the release of anti-diuretic hormone.
Kidneys play a large role in human osmoregulation by regulating the amount of water reabsorbed from the glomerular filtrate in kidney tubules, which is controlled by hormones such as antidiuretic hormone (ADH) and aldosterone.
ADH is released from the pituitary gland in response to high blood tonicity (high amount of solute). It targets the collecting tubules in the nephron, where it stimulates insertion of aquaporine into the membrane. This increases the amount of water reabsorption in the nephron.
For more about kidneys, see excretory system.