Ameen Khan

Homeostasis and Thermoregulation

Homeostasis mean “same state” and refers to the process of keeping the internal body in the same state when the external environment is changed. Homeostasis is mainly achieved through negative feedback which is when the body automatically tries to return the body to its normal state. The hormone system and the autonomic nervous system play a big role in homeostasis and are coordinated by the hypothalamus.

Humans are endotherms which means they have a constant internal body temperature. (35-40 C)

Body temperature is controlled by the thermoregulatory center in the hypothalamus.

The thermoregulatory center usesReceptors in hypothalamus which measure

temperature of the blood as it passes through the brain

Skin receptors that monitor outside temperatureThe thermoregulatory system uses these receptors

to send signals to other parts of the body to maintains temperature.

Temperature Homeostasis(Thermoregulation)

response Response to low temperature

Response to high temperature

Smooth muscles in skin

Muscles contract and less heat is carried to the surface of the body. Extremities turn blue. (frostbite)

Muscles relax and heat is carried to the surface of the body. This is when skin turns “red”.

Sweat glands No sweat is produced Glands secrete sweat onto the surface of the skin. The water takes heat with it and evaporates into the air.

Erector pilli muscle Muscles contract and raise the skin hair which keeps a layer of warm air on the skin. (goosebumps)

Muscles relax and lowers skin hair. This allows for more evaporation.

Response to Low temp.

Response to high temp.

Skeletal muscles Muscles contract and relax repeatedly which generates heat from friction and from metabolic reactions. (shivering)

No shivering

Adrenal and Thyroid Glands

Glands secrete adrenaline and thyroxine which increases metabolic rate in different tissues, mainly the liver. This generates heat.

The glands stop secreting adrenaline and thyroxine.

The thermoregulatory center usually keeps temperature in the 35-40 C range but sometimes it increases temperature in humans. In a fever, white blood cells release chemicals which increase body temperature by 2-3 C to kill off bacteria and other viruses.

Glucose is a very important carbohydrate in animals, and its concentration in the blood affects all the cell in the body. Very high or low levels of glucose can lead to death.

Glucose concentration in the blood is controlled by the pancreas which has glucose receptor cells which monitor glucose levels and secrete hormones if needed. The α-cells secrete the hormone glucagon, while the β-cells secrete the hormone insulin.

Blood Glucose Homeostasis

When Glucose Level Is Too High (After a meal)Insulin from β-cells - makes cells use up extra

glucose through respiration and makes the liver convert glucose to glycogen . Insulin decreases blood glucose level.

When Glucose Level is Too LowGlucagon from α-cells: causes the liver to break

down glycogen to glucose, which diffuses into the blood. Glucagon increases blood glucose level.

Homeostasis is also maintained by the excretions of organs to get rid of wastes in our body.

Skin- sweat ( water, ions, urea)Lungs- carbon dioxide and waterKidneys- excrete urine which consists of urea

and many other substances that the blood doesn’t need.

Excretions

controlled by the hypothalamus which contains osmosreceptor cells, which detect changes in the water potential of the blood.

When water levels are low, the hypothalamus makes us feel thirsty, and it also secretes the hormone ADH.

ADH targets kidney cells and causes water channels in the cells to open so more water is reabsorbed from urine.

Blood Water Homeostasis

JGA is a special tissue that supplies blood to the glomerulus (which is near the kidneys).

When blood pressure becomes too low, JGA releases an enzyme called renin.

Renin converts angiotensinogen to angiotensin II in the blood.

Angiotensin II increases blood pressure by causing arterioles to constrict, and it also signals nephrons to reabsorb more NACl and water.

Blood Pressure

Medulla controls respiration rate as well as the heart rate.

The amount of carbon dioxide in the blood is one of the main things that determines whether the breathing rate needs to be changed.

Medulla- Breathing and Heart rate

If carbon dioxide in the blood stream increases, then chemoreceptors send messages to the medulla .

Medulla sends nerve impulses down to the rib muscles and the diaphragm which causes them to contract and relax more quickly .

This increases the breathing rate to get more oxygen to the blood stream and bring back equilibrium of oxygen and carbon dioxide levels in the blood stream.

Breathing

Special receptors located within the muscles send impulses to the medulla.

The medulla secretes epinephrine and norepinephrine.

The two chemicals reach the Sino-atrial node, which acts like a pacemaker.

These chemicals arouse the Sino-atrial node, which increases heart rate.

This also occurs in times of stress or danger.

Faster Heart Rate (exercising)

Muscles send additional impulses to the medulla.

Medulla then secretes the hormone acetylcholine.

Acetylcholine decreases the heart rate by slowing down the electrical impulses from the Sino-atrial node.

Slowing down heart rate

http://www.biology-online.org/articles/introduction-homeostasis.html

http://www.biologymad.com/resources/A2%20Homeostasis.pdf

Biology book