Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 41.5 Feedback Circuits Regulate Digestion, Energy Storage, and Appetite
1. Regulation of Digestion
- Enteric nervous system coordinates movement and secretion
- Hormones like gastrin, secretin, and CCK respond to food presence
- Gastrin stimulates gastric juice secretion
- Secretin and CCK trigger pancreatic enzyme and bile release
- Fatty meals slow digestion for more thorough processing
2. Energy Storage
- Excess energy stored as glycogen in liver and muscles
- When glycogen is full, surplus is stored as fat in adipose tissue
- During fasting, energy is drawn first from glycogen, then fat
- Fat yields more energy per gram than carbohydrates or proteins
3. Glucose Homeostasis
- Blood glucose is maintained between 70–110 mg/100 mL
- Insulin lowers blood glucose by promoting uptake and storage
- Glucagon raises blood glucose by stimulating glycogen breakdown
- Produced in pancreatic islets: insulin (beta cells), glucagon (alpha cells)
- The liver plays a central regulatory role
- Brain cells absorb glucose without insulin
4. Diabetes Mellitus
- Type 1 diabetes: autoimmune destruction of beta cells; needs insulin therapy
- Type 2 diabetes: insulin resistance; linked to diet, obesity, and inactivity
- Type 2 is more common and can often be managed with lifestyle changes
- Both types cause high blood glucose and long-term health risks
- Inflammation may contribute to insulin resistance
5. Regulation of Appetite
- Hormones signal the brain’s satiety center
- Ghrelin (from stomach) stimulates hunger
- Insulin, PYY (from intestine), and leptin (from fat) reduce appetite
- Weight loss increases ghrelin and decreases leptin—making hunger stronger
- Chronic overeating leads to obesity and higher disease risk
In a Nutshell
Digestive activity, energy reserves, and appetite are governed by feedback systems involving nerves and hormones. These circuits ensure that the body processes food efficiently, stores energy wisely, and maintains blood glucose levels. Hormones also regulate how hungry we feel, helping balance intake with energy demands.