D3.3 Homeostasis Flashcards
Define homeostasis
Maintaining a constant internal environment at preset values despite fluctuations from the external environment.
What are examples of external stimuli?
Body temperature, blood glucose concentration, blood pH, blood ion concentration
Why is negative feedback more common than positive feedback?
Negative feedback counteracts changes of various properties from their target values to bring it back to set values. However, positive feedback amplifies the initiating stimuli hence, amplifying any change happening.
How are blood glucose concentrations adjusted?
By balancing the amount of glucose removed from the blood with the amount that is added. This is done with the help of hormones insulin and glucagon through negative feedback loops.
Describe the process of blood glucose regulation
- Endocrine gland: the islets of Langerhans have glucagon-secreting α-cells and insulin-secreting β-cells, secreting these hormones into the bloodstream.
When the blood glucose levels fall below the set point, α-cells will synthesize and secrete glucagon, stimulating the breakdown of glucose concentration.
When blood glucose levels rise above the set point, β-cells synthesize and secrete insulin, stimulating the uptake of glucose by many target cells in multiple tissues, especially in the skeletal muscles and liver, and the conversion of glucose into glycogen. These cells use glucose instead of fats in cell respiration. Skeletal muscle and liver are particularly active in glucose uptake and in these tissues, decreasing the blood glucose concentration.
Outline Type 1 Diabetes
- Inability to produce sufficient insulin caused by the destruction of beta cells in the Islets of Langerhans by the body’s immune system.
- Usually diagnosed more often in children and young adults
- Treatment involves injecting insulin when blood glucose becomes too high or likely to become too high. Timing is important because insulin is easily broken down. A permanent cure may be achievable by coaxing stem cells to become fully functional replacement beta cells.
Outline Type 2 Diabetes
- Inability to process insulin due to a deficiency of insulin receptors or glucose transporters on target cells.
- Happens in people who are older, obese, or lack exercise.
- Treated by adjusting diet:
- eating frequent small amounts of foods rather than infrequent large meals in encouraged
- high sugar content should be avoided
- low glycaemic index and high-fibre foods are good
- strenuous exercise is beneficial
How is negative feedbacking brought upon?
Body temperature is regulated by two types of thermoreceptors: peripheral receptors in the skin, which are sensitive to external temperatures, and central thermoreceptors located within the body’s core and hypothalamus. The hypothalamus processes information from both sets of thermoreceptors. When it detects hypothermia or hyperthermia, it initiates the appropriate response.
How does the hypothalamus function as an effector
- Regulates secretion of a hormone called thyrotropin-releasing hormone
- Thyrotropin-releasing hormone stimulates the pituitary gland to release thyroid-stimulating hormone
- Thyroid-stimulating hormone stimulates the thyroid gland to release thyroxin
- Thyroxin increases metabolic rate
Altering the level of thyroxin alters heat generation by cell metabolism, aiding regulation of body temperature
How does muscle tissue function as an effector?
Shivering in the muscles raises the metabolic rate of muscle cells, releasing heat energy.
How does adipose tissue function as an effector?
White adipose tissue: stores lipids in a layer beneath the skin and around internal organs, providing insulation that aids temperature regulation.
Brown adipose tissue: generates heat energy before shivering begins in the muscles.
Describe vasoconstriction
Muscles in the arteriole walls contract, causing the arterioles near the skin to constrict, allowing less blood to flow through capillaries. Instead, the blood is diverted through shunt vessels, which are deeper in the skin and therefore do not lose heat in the environment. The reduction in blood flow to the skin surface means that less heat energy is lost by radiation.
Describe shivering
Many, small involuntary muscle contractions and relaxation are carried out at a rapid rate solely to generate heat.
Describe uncoupled respiration in adipose tissue
All the energy released by the oxidation of fat is transformed into heat and no ATP is produced.
Describe hair erection
Hair erector muscles in the skin contract, causing hairs to stand on end. This forms insulating layer over the skin’s surface by trapping air between the hairs and prevents heat from being lost by radiation.
