Overview
This lecture covers the structure and function of the body's organ systems, focusing on digestion, absorption, hormones, and the role of nutrients in supporting overall health.
Organization of the Body
- Cells are the basic units of life, forming tissues, organs, and body systems.
- Proteins are essential for building enzymes, hormones, muscles, and structural components.
- The cardiovascular and lymphatic systems transport nutrients and play immune system roles.
Hormonal and Nervous System Regulation
- Hormones are chemical messengers from glands, such as insulin and glucagon from the pancreas, regulating blood sugar.
- Hunger is a physiological need for food; appetite is a psychological desire for food.
- The hypothalamus in the brain regulates hunger via signals from gut receptors.
- The fight-or-flight response is triggered by hormones, increasing metabolism and suppressing digestion.
Digestive System Overview
- The digestive tract is a continuous tube from mouth to anus; digestion starts in the mouth.
- Main organs: mouth, esophagus, stomach, small intestine, large intestine (colon), rectum, anus.
- Accessory organs: salivary glands (release salivary amylase), liver (produces bile), gallbladder (stores bile), pancreas (makes digestive enzymes and bicarbonate).
- Mechanical digestion (chewing, churning) and chemical digestion (enzymes, acids) work together.
Digestion and Absorption
- Peristalsis is the muscular movement pushing food down the tract.
- Stomach uses hydrochloric acid (HCl) to begin protein digestion and create chyme.
- Small intestine is the primary site for digestion and absorption due to its large surface area (villi and microvilli).
- Unabsorbed components move to the large intestine, where water is reabsorbed and stool is formed.
Common Digestive Problems
- Constipation: infrequent or hard stools; treat with fluids, fiber, and activity.
- Diarrhea: frequent, watery stools; risk of dehydration; treat with the BRAT diet and fluids.
- Heartburn/GERD: stomach acid reflux into esophagus; avoid triggers, use antacids, stay upright after eating.
- Hemorrhoids: swollen rectal veins, often from constipation.
- IBS: alternating diarrhea and constipation, often stress- or diet-related.
- Ulcers: sores in the digestive tract, often caused by H. pylori bacteria.
Excretory System and Nutrient Storage
- Organs: lungs, liver, kidneys, bladder remove waste and maintain fluid balance.
- Liver stores glycogen for body-wide use; muscles store glycogen for local use.
- Excess nutrients are converted and stored as fat in adipose tissue.
- Frequent small meals help maintain blood sugar and metabolism.
Alcohol and Moderation
- Alcohol provides 7 kcal/gram, considered empty calories.
- Moderation: ≤1 drink/day for women, ≤2 drinks/day for men.
- Excess intake can harm liver, kidneys, and overall health; alcohol is a diuretic.
Key Terms & Definitions
- Hormones — chemical messengers regulating body processes.
- Insulin/Glucagon — hormones controlling blood glucose.
- Peristalsis — muscle contractions moving food along the digestive tract.
- Chyme — semi-liquid food mixture leaving the stomach.
- Villi/Microvilli — finger-like projections in the small intestine increasing surface area for absorption.
- BRAT Diet — bananas, rice, applesauce, toast; recommended for diarrhea.
- Glycogen — stored form of glucose in liver/muscle.
- Moderation — limiting alcohol intake as defined above.
Action Items / Next Steps
- Review digestive system organ structure and function.
- Highlight the roles of hormones and the nervous system in hunger regulation.
- Study accessory organ functions and main digestive enzymes.
- Memorize digestive disorders, their symptoms, and treatments.
- Read the alcohol section in your textbook for more details.