Homeostasis: Active Regulation of the Internal Environment Flashcards
Define the terms homeostasis and motivation. How are they related?
Homeostasis: the maintenance of a relatively constant internal environment. Includes variables such as: water level, oxygenation, temperature, energy availability, saltiness, and acidity.
When we deviate from our optimum state, our motivation is affected. Motivation is the psychological process that induces or sustains a particular behaviour. The more we deviate from the optimum state, the more our motivation increases.
How does negative feedback work in homeostatic systems? What is the difference between set points and set zones?
negative feedback is when a system monitors its own output and reduces its activity when the set point or zone is reached.
A set point is the point of reference on a feedback system. It is the point the feedback system waits to reach before it is signaled to reduce it’s activity
A set zone is similar to a set point but instead of being a specific point, it is a range that the system can reach. So
What is thermoregulation and what are different types?
Thermoregulation is the active process of maintaining a relatively constant internal temperature through behavioural and physiological adjustments.
Endotherms are when body temperature is regulated internally. Mammals are endotherms
Ectotherms are animals that regulate their body temperature externally. Reptiles are ectotherms
Define redundancy. Why do homeostatic systems have so much redundancy?
Redundancy means that the system is monitored by more than one mechanism.
It is important because it ensures that critical needs are met, even if one mechanism is malfunctioning.
Describe the basic elements of mammilian thermoregulatory systems.
Mammals use the skin surface, body core, and hypothalamus (POA) as receptors for body temperature.
These receptors report to the spinal cord, brain stem and POA of the hypothalamus.
When the optimal state is not in place, the system will induce behavioural responses like shivering and heat seeking or avoiding behaviour. It will also induce physiological responses such as the restriction or dilation of the blood vessels, sweating, respiration, and thyroid hormone secretion.
What is allostasis?
The varying behavioural and physiological adjustments that an individual makes in order to maintain optimal functioning of a regulated system in the face of changing environmental stressors.
Define nutrients?
chemicals required for effective functioning and growth/maintenance of the body.
What is glucose? How is it stored in the short term? in the long term?
A simple sugar, the main fuel for all cells of the body.
Glucose is stored in the short term as glycogen. Glycogen is a complex carbohydrate that is stored in the liver and muscles. Insulin initiates glycogenisis: the conversion of glucose to glycogen. Glucagon (also from the pancreas) initiates glycogenolysis: the conversion of glucogen to glucose.
Glucose is stored in the long term as lipids in the adipose tissue. Under prolonged food deprivation, lipids get converted into glucose (through gluconeogenesis) and into ketones (another secondary form of fuel)
What is Basal Metabolism? is it fixed?
Basal metabolism is the use of energy for basic life sustaining functions like heat production and maintenance of membrane potentials. It is not fixed, basal metabolism is under homeostatic control, it adjusts with dietary changes which is why weight loss can be challenging.
What is the role of insulin besides converting glucose into glycogen?
glucose transporters require insulin to function, these transporters bring glucose into the cell from the blood.
What is diabetes mellitus?
Is a result of a lack of insulin production (type-I) or a reduced sensitivity to insulin (type-II)
What triggers the release of insulin during mealtimes?
There are several mechanisms that trigger the release of insulin during mealtimes
- Cephalic phase: Insulin is triggered by the sights, smells, and tastes associated with food.
- Digestive Phase: Insulin is triggered by food entering the digestive tract
- Absorptive phase: insulin is triggered by food being absorbed into the bloodstream. Glucodetectors detect glucose in the blood and trigger the release of the insulin.
What is the duel centre hypothesis?
The original school of thought for the role of the hyothalmus in eating behaviour.
The Ventromedial hypothalamus was believed to control satiety becasue lesions here led to obesity (the animals didn’t know when to stop eating.
The lateral hypothalamus was believed to control appetite becasue lesions here led to a refusal to eat, the animals didn’t know when they needed food.
Later research demonstrated that animals with such lesions do eventually exhibit satiety and appetite behaviour, suggesting that other areas are part of the process too.
What is the arcuate nucleus?
The arcuate nucleus is in the hypothalamus. It is the key element in our appetite network because it integrates peptide hormone signals from several sites on the body (the pancreas, digestive organs, and fat tissues)
Besides insulin, what are the four main hormones that interact with the arcuate nucleus?
Leptin: Comes from fat cells. Tells the brain information about our long term energy storage. Defective leptin production or impaired leptin sensitivity can lead to overeating due to false under reporting of of body fat.
Ghrelin: Tells the brain about short term energy balance; namely the presence or absence of food in the stomach. When you fast, Ghrelin is released, it is an appetite stimulant.
PYY3-36 is released in the intestine when food is ingested. It stimulates appetite suppression.
Glucagon-like Peptide 1 (GLP 1) is released by the intestine when food is ingested, especially if that food is high in fats and carbs. It suppresses appetite and signals the rewarding aspect of food.
What are the two types of neurons in the arcuate nucleus? How do the five main hormones in the appetite system interact with these neurons?
The two neurons in the arcuate nucleus have opposite effects.
The NPY neurons: hunger neurons, they stimulate appetite and reduce metabolism when activated.
POMC neurons: satiety neurons. They inhibit appetite and increase metabolism.
- Leptin: stimulates POMC neurons and inhibit NYP neurons. Overall effect: suppresses appetite.
- Ghrelin: Stimulates NYP neurons. Overall Effect: stimulates appetite
- PYY3-36: Inhibits NYP neurons. Overall Effect: inhibits appetite
- GLP 1: Stimulates POMC neurons. Overall effect: suppresses appetite
- Insulin: Inhibits NYP neurons. Overall effect: inhibits appetite.
What happens to the net activity of NYP and POMC systems?
The net activity is projected to two areas:
- the Orexigenic neurons in the lateral hypothalamus. These neurons coordinate increased appetite and feeding behaviour.
- Anorexigenic neurons in the paraventriculer nucleus coordinate decreased appetite and feeding behaviour
These appetite signals converge from the hypothalamus to the nucleus of the solitary Tract in the Brainstem (NST).
What two neurotransmitters are predominant in the control of feeding behaviour?
Orexin: produced by neurons in the hypothalamus and increases feeding behaviour.
Endocannabinoids: regulate appetite and feeding
What is Cholecytokinin (CCK)
A peptide released by the gut after eating. It acts on the vagus nerve to inhibit appetite.
What are some strategies to address obesity?
Appetite control: drugs to dampen the hypothalamic appetite controller (not very effective)
Increased Metabolism: cause the bodies metabolic rate to increase and burn more calories
Inhibition of Fat tissue: interfere with the formation of new fat tissue
Reduced absorption: drugs that interfere with the absorption of fat (Not very effective)
Reduced reward: drugs that reduce the rewarding capacity of food
Anti-obesity surgery
LIFESTYLE CHANGES: Most effective
What are three different eating disorders?
Anorexia Nervosa: Distorted body image. Patients have no appetite and other side effects. Treated with family based treatment often.
Bulimia: binging and purging, distorted body image.
Binge Eating: binging without the purging behaviour. Can sometimes be a pre-curser to bulimia.
