Lecture 29: Neurocircuitry of Metabolism 1 Flashcards
What is energy balance?
when energy intake is equivalent to energy expenditure
Why have complex internal regulatory mechanisms evolved to store energy in the body?
to store energy in the body so that it is available when needed
Why are we motivated to eat?
to keep reserves at a sufficient level to ensure there will be no energy shortfall
What are the three main components of energy balance?
energy intake, energy expenditure and storage
What does energy intake include?
three major macronutrient groups which are carbohydrate, protein, and fat
What does faecal loss amount to?
2-10%
What does energy expenditure involve?
absorbed carbohydrates, proteins, and fats are transformed in vivo to substrates that can ultimately either be oxidized to produce metabolically useful energy that drives biological processes or they may be stored
Which compounds are stored in the body?
triglycerides and glycogen
What is energy used for?
basal metabolic rate; digestion, growth, reproduction
work/exercise; non-exercise activity thermogenesis
shivering and non-shivering thermogenesis
How are triglycerides stored?
stored in adipose tissue
How are carbohydrates stored?
mainly in the form of intracellular glycogen in skeletal muscle and liver
What happens when there is an imbalance between the intake and utilisation of macronutrients?
this will lead to an alteration in body composition
How much glycogen is there in the body?
the total mass of glycogen is relatively small, several hundred grams, and turnover is rapid; maximal amounts are observed in the post meal state
What occurs during anabolism?
the body’s energy stores are replenished during and immediately after consuming a meal
What is the condition in which blood is filled with nutrients?
the prandial state
Where is glycogen and triglycerides found in the body?
glycogen is found in the liver and skeletal muscle
triglycerides are found in the adipose tissue
What is the assembly of macromolecules such as glycogen and triglycerides from simple precursors known as?
anabolism or anabolic metabolism
What occurs during catabolism?
the stored glycogen and triglycerides are broken down to prove the body with a continuous supply of the molecules used as fuel for cellular metabolism
What is the process of breaking down complex macromolecules called?
catabolism or catabolic metabolism
What will happen when underfed and overfed animals are given the ability to eat whenever they want?
overfed animals will lose weight and underfed animals will gain weight and both groups will match that of the controls
What is the set point for body mass determined by?
physiological responses that regulate both food intake and energy expenditure -> seek to maintain an appropriate fat mass and can counteract even modest imposed changes in energy intake and fat mass
Where is the hypothalamus located?
sits below the thalamus, along the walls of the third ventricle and is connected via a stalk to the pituitary gland, which dangles below the brain just above the roof of the mouth
What is the role of the hypothalamus?
regulates temperature, hunger, satiety, thirst, sexual development, fight or flight stress response, and sleep
What is the hypothalamus made up of?
several distinct divisions or nuclei which are bilateral
What does each nuclei of the hypothalamus contain and coordinate?
each nuclei contains different cell types and coordinates different physiological functions
What does each nuclei of the hypothalamus receive input from?
each nuclei receives input from different brain regions and in turn output to different parts of the brain
Why is the neurocircuitry of the hypothalamus incredibly complex?
because there is significant intra-nuclei connectivity
What is the role of the arcuate nucleus of the hypothalamus?
plays a critical role in
feeding behaviour, energy expenditure and is capable of sensing metabolic hormones in the blood
What is the role of the ventral medial hypothalamus?
plays a critical role in feeding behaviour, energy expenditure and reproduction
What is the role of the dorsomedial hypothalamus?
plays a key role in adaptive thermogenesis and feeding behaviour
What is the role of the lateral hypothalamus?
plays a role in sleep and arousal and acts as a critical reply between the Arc and VMH and higher centres of the brain involved in motivation and reward
What is the role of the paraventricular hypothalamus?
important autonomic control centres in the brain, with neurons playing essential roles in controlling stress, metabolism, reproduction and gastrointestinal, renal and cardiovascular functions
What is the role of the median eminence?
circumventricular organ which has permeable capillaries and serves as an interface between the neural and peripheral endocrine systems
What did lesions in the lateral hypothalamus result in?
caused anorexia and weight loss
leaves the animal inappropriately satiated so they don’t eat
What did lesions in the ventral medial hypothalamus result in?
caused hyperphagia and obesity
leaves the animal insatiable so they over eat
What are the two main cell types contained in the arcuate nucleus of the hypothalamus?
AgRP / neuropeptide Y neurons and proopiomelanocortin neurons
What is the role of AgRP neurons?
are orexigenic (increase food intake) and decrease energy expenditure
What is the role of POMC neurons?
are anorexigenic (decrease food intake) and promote energy expenditure
What do AgRP neurons promote?
positive energy balance
What did ablation of AgRP neurons in adult mice lead to?
profound weight loss, loss of feeding and death within 10 days unless force fed
What did ablation of POMC neurons in adult mice lead to?
profound weight gain, increased adiposity and enhanced food intake
What are tanycytes?
a subtype of ependymal cells with long processes that extend into the hypothalamic parenchyma
What is the role of tanycytes?
their tight junctions prevent the diffusion of blood-borne molecules into the adjacent CSF
What do tanycytes share some features with?
glia/astrocytes and express GABA receptors like neurons
Where are alpha 1 and alpha 2 tanycytes found and where do they project?
found along the ependymal surface of the VMH and ARC
project to adjacent hypothalamic regions and contact blood vessels and neurons
Where do beta 1 tanycytes reside?
in the lateral extensions of the infundibular recess whereas beta 2 tanycytes line the floor of the ventricle
What do tanycytes play a crucial role in?
controlling energy balance and regulating the access of peripheral metabolic signals to the ARC
