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Hormones of Hunger and Satiety - Coggle Diagram
Hormones of Hunger and Satiety
What is hunger?
Hunger (noun) - a feeling of discomfort or weakness caused by lack of food.
Hunger (verb) - have a strong desire or craving for
However from a scientific perspective we split the ‘need for food’ from the ‘desire for food’
Hunger is the need for food
Appetite is the desire for food
Hunger and appetite
Hunger
A physical reaction that includes chemical changes in your body related to a naturally low level of glucose in your blood several hours after eating.
An instinctive, protective mechanism that makes sure that your body gets the fuel it requires to function reasonably well.
Appetite
A sensory or psychological reaction (looks good! smells good)
A conditioned response to food.
Influenced by cravings, emotions, habits
How are hunger and appetite related to obesity?
The same amount of ENERGY IN (calories consumed) and ENERGY OUT (calories burned) over time = weight stays the same
More OUT than IN over time = weight loss
More IN than OUT over time = weight gain → OBESITY
The amount of ENERGY IN is controlled by hunger and appetite
The amount of ENERGY OUT can be varied:
Movement (motor activity)
Heat production (non-shivering thermogenesis)
Energy expenditure (RQ – fat vs carbohydrate as energy source)
Both hunger and appetite are tightly controlled in the brain, with input from hormones, the digestive tract and adipose tissue
Hormones keep hunger in check 'homeostasis'
Reciprocal control of hunger and therefore body weight
Where do these signals become integrated?
Hunger Hormone - Ghrelin
Short-term signal released from gastrointestinal system and within the brain
Fed Hormone - Leptin
Long and short-term signal released from adipose tissue
Fed Hormone - Insulin
Short-term signal released from pancreatic β-cells
The area of the brain that controls hunger and appetite is the hypothalamus
The part of the hypothalamus which controls hunger and satiety is called the:
Arcuate nucleus (ARC)
Ghrelin
28 amino acid peptide
released from the gastric epithelial cells and within the brain
Receptors (growth hormone secretagogue receptors) found in the arcuate nucleus of the hypothalamus on the NPY/AgRP neurons
Highest levels detected when fasting
Levels decrease when feeding
Growth-hormone secretagogue receptor (GHSR)
GHSR null mice (lacking ghrelin receptor) weigh less than wild type mice on high fat diet
Wild type mice, infused with ghrelin for 2 hours, food intake rose
GHSR-null mice (lack ghrelin receptor), infused with ghrelin for 2 hours, no rise in food intake
Ghrelin is key signal for feeding
Highest levels detected during fasting
Activates the Growth Hormone Secretagogue Receptor (GHSR)
receptors expressed in brain
Ghrelin receptors on both POMC and AgRP/NPY neurons in arcuate nucleus within the hypothalamus
Leptin
Hormone (adipokine)
Discovered in 1994 – quite new
166 Amino Acids long (Ob gene)
Produced primarily by fat cells but also in small quantities by stomach, mammary epithelium, placenta and heart
Activates the Leptin Receptor (LEPR)
1162 aa and composed of 18 exons and 17 introns
receptors are expressed in many tissues
Insulin
Pancreas: α-cells = glucagon
β-cells = insulin
Mostly act in the periphery on various tissues including liver, skeletal muscle, heart
BUT can also influence satiety in the brain
Peptide hormones
Insulin acts on various tissues to facilitate diffusion of glucose into cells and to increase conversion of glucose into glycogen (glycogenesis)
Also, binds to receptors on POMC and AgRP neurons in a similar way to leptin
Hunger is controlled by NPY/AgRP and POMC neurons
Stimulation of NPY/AgRP neurons has an orexigenic effect - stimulates hunger and appetite/promotes feeding
inc. ghrelin dec. insulin/leptin
Stimulation of POMC neurons has an anorexigenic effect - suppresses hunger and appetite/inhibits feeding
inc, insulin/leptin dec. ghrelin