Homeostasis Flashcards
define a receptor (sensor)
a sensor/receptor responds specifically to the physiological variable (not other variables)
define an effector
a system acting to restore variable back to desired level (set point)
our body temperature fluctuates around a set point, what is this set point
37*C
(36.5-37.5)
what is the body temperature control center in the body?
(preoptic) hypothalamus= thermoregulation
define:
* conduction
* convection
* evaporation
* radiation
Conduction= heat loss through contact with solid surface
Convection= heat loss through local air currents - heat surrounding air, air moves along so heat new air
Evaporation= heat loss through evaporation of moisture on skin (sweat)
Radiation = heat loss from body to surrounding atmosphere through electromagnetic waves
what are catecholamines (e.g. adrenaline,noradrenaline,dopamine) and what is there role in thermoregulation?
catecholamines= a type of neurohormone (a chemical that is made by nerve cells and used to send signals to other cells). Catecholamines are important in stress responses. High levels cause high blood pressure which can lead to headaches, sweating, pounding of the heart, pain in the chest, and anxiety.
catecholamines stimulate thermogenesis in both skeletal muscle and brown fat; we shiver to break down the fat to generate heat not create (caloric) energy
where is glucagon + insulin secreted from
glucagon is released from pancreatic alpha cells from islets of Langerhan
insulin is released from pancreatic beta cellsfrom islets of Langerhan
pancreas; primarily an exocrine gland, secreting a variety of digestive enzymes, the pancreas has an endocrine function. Its pancreatic islets aka islets of Langerhans—secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide (PP).
define glycogenolysis
breaking down glycogen
liver glycogen is converted into glucose
define gluconeogenesis
making new glucose (glucagon stimulates glucose production from amino acids + glycerol through gluconeogenesis)
- a + β cells in pancreatic islets of Langerhans sense ______ via specialised membrane receptors - cells also effectors so called stimulus-secretion coupling
- a + β cells in pancreatic islets of Langerhans sense glucose via specialised membrane receptors - cells also effectors so called stimulus-secretion coupling
Describe term negative feedback loop
give example
once body gets to where it needs to be (e.g. blood glucose is normal) it inhibits whatever action it was doing
High blood glucose is most potent INHIBITORY signal of glucagon release - -ve feedback loop
explain thermoregulation in the body; when it gets too cold vs too hot
Too cold:
*vasoconstriction arterioles constrict to keep heat in
- hair effector muscles contract (piloerection) so hair stand up to create insulating layer round body
- Thermogenesis; muscles can produce heat by shivering.
- Hormonal thermogenesis: Your thyroid gland releases hormones to increase your metabolism. This increases the energy + therefeore produces heat
Too hot;
*Vasodilation arterioles dilate to keep heat in
*hair lies flat hair effector muscles relaxed
describe blood glucose regulation in body
norm blood glucose: 90mg/100ml
GLUCAGON
* Pancreatic α-cells are equipped with a specific set of channels that generate action potentials of Na+and Ca2+in the absence or at low levels of glucose
* This electrical activity triggers Ca2+signals and glucagon secretion. Glucagon will promote hepatic glycogenolysis because it wants to raise our blood sugar level
* In addition, glucagon drives hepatic and renal gluconeogenesis to increase endogenous blood glucose levels during prolonged fasting.
INSULIN:
* In contrast, insulin secretion from β-cells is stimulated by elevated exogenous glucose levels, such as those occurring after a meal.
* insulin enables the insulin-dependent uptake of glucose into these tissues and hence lowers blood glucose levels by removing the exogenous glucose from the blood stream.:
* circulating blood glucose is taken up by the facilitative glucose transporter GLUT2, which is located on the surface of the β-cells. Once inside the cell, glucose undergoes glycolysis, generating ATP, resulting in an increased ATP/ADP ratio. This altered ratio then leads to the closure of ATP-sensitive K+-channels (KATP-channels). Under non-stimulated conditions, these channels are open to maintain resting potential. Upon closure, the subsequent decrease in the magnitude of the outwardly directed K+-current elicits the membrane depolarization, followed by the opening of voltage-dependent Ca+-channels. The increase in intracellular calcium concentrations eventually triggers the fusion of insulin-containing granules with the membrane and release their content
* insulin promotes glycogenesis, lipogenesis and the incorporation of amino acids into proteins; thus, insulin is an anabolic hormone, in contrast to the catabolic activity of glucagon
n.b. Elevated glucose concentrations inhibit all these events.
- ATP-dependent K+(KATP) channels play a fundamental role in α-cells, such as they do in β-cells, since they couple variations in extracellular glucose concentrations to changes in membrane potential and electrical activity
explain positive feedback e.g. the release of oxytocin during pregnancy
a response triggers the body to send more of that response e.g. pushing a baby
- Oxytocin causes uterine contraction which causes increased oxytocin release which intensifies uterus smooth muscle contractions so uterus becomes more and more active at end stages of pregnancy - until bebe delivered
- Oxytocin increases contractions - amplified rather than kept in range
n.b. a stimulus always has an endpoint; so here the endpoint is the birth of the baby.
shortly after birth as contraction continues a bit to reduce blood loss - which stops +ve feedback and ends cycle - therefore -ve adjustments not needed and would be counter-productive (don’t wanna stop birth)
blood pressure can be adjusted/maintained by producing changes in which 2 variables
Blood pressure can be adjusted by producing changes in the following variables:
Cardiac output can be altered by changing stroke volume or heart rate.
Resistance to blood flow in the blood vessels is most often altered by changing the diameter of the vessels (vasodilation or vasoconstriction). Changes in blood viscosity (its ability to flow) or in the length of the blood vessels (which increases with weight gain) can also alter resistance to blood flow.
