Control of Food Intake Flashcards
Define hunger
Discomfort caused by lack of food and desire to eat - Strong physiological craving/drive for food/ sensation of emptiness in stomach
Define appetite
Physiological desire/drive to satisfy body’s needs of food; a hunger stimulated response
Define satiety
State of being full after eating food
What is aphagia and hyperphagia?
Aphagia - Inability or refusal to swallow
Hyperphagia/polyphagia - Abnormal desire for food (unsatisfied extreme drive to eat)
How is satiety induced?
- Mechanical distension of the stomach wall - Afferent fibres to brain to induce satiety
- CCK potentiates/sensitises the vagal nerves to mechanical stimulation, and also reaches the brain where it inhibits feeding, has a catabolic effect. CCK is released by I cells in response to fatty chyme being within the intestines
- CCK acts locally to stimulate bile release as causes gallbladder to contract, nutrient absorption and promote gastric emptying
- The presence of nutrients in the intestine inhibits eating and gastric emptying
Describe the role of the vago-vagal reflex in accommodation of food
Food enters stomach, causes distension detected by stretch receptors, vagal afferents to dorsal medullary, vagal efferents secrete VIP/NO on fundus relaxing it, increasing area available for storage of food - Induces satiety
Distension of a full stomach inhibits appetite; contraction of an empty stomach stimulates appetite
What are the 3 types of relaxation of the fundus?
- Receptive relaxation - Mechanical stimulation of pharynx - mechanoreceptors, sight)
- Adaptive - Vagal innervation, NO/VIP
- Feedback - Nutrients, CCK
How does the hypothalamus control food intake?
Hypothalmus = Control centre for appetite and food intake
- Base of hypothalmus has several nuclei that regulate energy homeostasis
- These nuclei control appeptite, size of meal, ingestive behaviour
- Supraoptic nucleus (SON) contains neurosecretory ells that produce hormones (oxytocin, ADH)
- Prefrontal cortex - Food seeking behaviours
- Nucleus accumbens - Controls ingestion and swallowing
- Somatosensory cortex - Taste and perception
Describe the location of the satiety centre and its role in food intake
Satiety centre = Hypothalamus, ventromedial (wall of paraventricular) nuclei
- Stimulation of ventromedial nuclei → Aphagia (swallowing difficulty)
- Lesions of ventromedial nuclei → Hyperphagia (increased appetite or excessive hunger; weight gain)
Describe the location of the feeding/hunger/thirst centre and its role in food intake
Feeding/hunger/thirst centre = lateral hypothalamus (nuclei)
- Stimulation lateral hypothalmus - Increase feeding
- Lesion of lateral hypothalamus - Aphagia
What do orexigenic and anorexigenic neurotransmitters do?
Both found in hypothalmus:
- Orexigenic - Increase appetite
- Anorexigenic - Decrease appetite
NTs modulate feeding behaviour by binding to hypothalmic nuclei
Describe the role of the dorsomedial nucleus (DMN)
Modulates energy intake (hunger centre) - Release of NPY into DMN - Increases feeding
Describe the role of the paraventricular nucleus (PVN)
Modulates feeding behaviour - Paraventricular nucleus and perifornical hypothalamus:
- Control feeding behaviour
- NPY, opioids → Increase feeding
- Leptin → Decreases food intake
Describe the arcuate nucleus
Contains 2 neuronal populations with opposing effects:
- 1 population stimulates food intake and co-express orexigenic signals (NPY, AgRP, opioids, dynorphin, B-endorphin, galanin, glutamate)
- Another population suppresses feeding by co-expressing CART and POMC
Both types of neurons project to hypothalmic areas, which are involved in the control of appeptie including DMN, PVN and LHA
Describe the role of the suprachiasmatic nucleus
Location of human body clock
- Perception of the light-darck cycle (circadian rhythms), directly above optic chiasm
- Appetite or sensation of hunger → Mood/drive to eat
Describe the role of the medial amygadaloid complex
Sub-region of amygadaloid complex:
- Participates in regulation of food intake
- E.g 5-HT (serotonin) been shown to regulate appetite and food intake by binding to medial amygdaloid nucleus (Via 5-HT2C and 5-HT1A serotonin receptors)
Describe the role of the prefrontal cortex
Influences food-seeking behaviour:
- Integrates sensory information from inside and outside body
- Receives emotional and cognitive information from limbic system
- Helps one make choices by translating all of the homeostatic and environmental information into (adaptive) behavioural response
Describe the role of the limbic system
Complex system of nerves and networks in brain; areas concerned with instinct, learning, reproducitve behaviours; emotions/mood, pleasure (fear,anger, etc)
- Act of satiation of feeding behaviour associated with motor planning and execution
- Overall, cortico-limbic mechanisms of reward under executive control
Describe the role of higher functions in control of food intake
Signals from the periphery and CNS control nutrient intake
Modulate responses to both CNS and peripheral cues (e.g. gut; environment) → inhibition or stimulation of food intake
The activity of stomach nerves has a circadian rhythm, which may limit our food intake to certain times throughout the day
Higher functions can include:
- Food preference
- Emotions
- Environment - Cold = Want to eat, Hot = Don’t want to eat
- Lifestyle
- Circadian rhythms
- Executive function - Frontal cortex
These can all act directly on hypothalamus and change food intake
Describe the role of glucose in control of food intake
Blood glucose - Stimulates gluco-receptors in hypothalamus
Brain has glucostat:
- Low blood glucose - Induces hunger
- High blood glucose - Induces satiety
What are the central stimuli that increase food intake?
- NPY
- Orexin-A
- Cannabinoids
Stimulated by ghrelin, cortisol
What are the central stimuli that decrease food intake?
- POMC
- CART
- CCK
- NE/Noradrenaline (low dose) - Stimulation alpha-1 decreases eating, stimulation alpha 2 increases eating
- CRH
Stimulated by glucose, amino acids, FAs, CCK, PYY, Insulin, Leptin
Describe the role of ghrelin in control of food intake
- Secreted by stomach fundus, pancreas, adrenals in response to nutritional status
- Stimulates gastric emptying
- Increases sense of hunger
- Stimulates neuropeptide Y and AgRP neurones
- Lvls also increase during periods of fasting, stimulates food intake. Decreases after feeding. Gastric bypass supresses lvls of ghrelin
- Increases central orexins e.g. NYP and AgRP (hunger signals)
- Circulating lvls of ghrelin increase pre-prandial and decreases post-prandial (after meal)
- Leptin can inhibit the secretion of ghrelin
- Ghrelin suppresses the ability of leptin to stimulate anorexigenic factors
- Leptin and ghrelin act reciprocally on food intake
Describe the role of obestatin in control of food intake
Encoded by ghrelin gene, but opposes the effects of ghrelin on food intake
- Produced by epithelial cells of stomach
- Suppress appetite, decrease weight gain
- Regulate GI motility
- Antagonises ghrelin-induced food intake (and growth hormone secretion)
- Regulate insulin secretion
- Promoting proliferation
- Reducing inflammation and apoptosis
