resources week01 scigast 2.2

Endocrine control

• Glucose levels has a lot to do with feeling hungry and satiety

Hungry and satiety (fullness): chemical input

Some time since last

food intake

Decline in blood

glucose level

Glucostats detect fall in glucose level

Glucostats fire rapidly

Animals feel hunger and seek food

• Expt. 1. lower glucose level leads to a sense of hungry/weakness

• Expt. 2. infusion of glucose to

duodenum (gut) speeds up the sense of satiety.

Hungry and satiety (fullness): chemical input

• Insulin level vs hunger and satiety – Low level: Hungry, an urge for

eating – High level: Cessation of eating

Hunger and satiety: an integrated hormonal control

Hunger and satiety: an integrated hormonal control Insulin is produced by our pancreas

↓ proteins, lipids and carbohydrates breakdown ↑ glycogen and fatty acid synthesis ↑ amino acids uptake and DNA synthesis Cells store energy and grow

Leptin (made by fat cells, i.e.,

adipose tissues)

Acts on receptors in the Hypothalamus of the brain

- to inhibit food intake

ob/ob or db/db +/+

Absence of leptin or its receptors leads to un-controlled food intake and obesity.

Leptin • When the body does not receive enough calories

(energy), leptin production is decreased to signal the body that it needs energy.

• This “low” signal is sent directly to the Hypothalamus in the brain which is responsible for appetite control, sort of like a fuel gauge with an alarm on it.

• Fuel gets low and the alarm goes off, telling you to add fuel.

• Hormones are designed to trigger a response in the body and the body will always respond to that trigger in a delay but systemic way.

Ghrelin • Grehlin is a "hunger" hormone, and is

responsible in letting your body know it does not have enough food.

• Ghrelin is increased when there is an energy shortage and its production site is at the gastro-intestinal tract (fundus of stomach)

20th U.S. edition of Gray's Anatomy of the Human Body

Ghrelin • So when energy intake is low, the increase in

ghrelin production works to trigger hunger.

• When ghrelin is increased, satiety is decreased leading to that ravished feeling.

• At this point, satisfaction cannot be reached no matter how large the amount of food ingested (more than you should eat).

[Recall how hormone works in the system –

time delay. What happens then?]

Solution to ghrelin control • High levels of ghrelin during a fasting

state promote increased food intake

• Lower levels of ghrelin are observed after eating a meal. (Kravitz, 2005).

So it makes sense to eat more frequently throughout the day to help reduce the

release of the hormone and control appetite (i.e., no overdose).

Ghrelin (Stomach)

Ghrelin receptor (hypothalamus)

Leptin (fat cell)

Insulin (pancreas)

Leptin receptor (hypothalamus)

Energy (Circulating Glucose)

appetite

Endocrine control of hunger

(liver)