Unit III: Endocrine & Digestive Systems

Chapter 16: Endocrine System

The endocrine system is a major regulatory system in the body, responsible for producing and secreting hormones that regulate various physiological processes.

• Functions of the Endocrine System: Regulates metabolism, growth, development, tissue function, sexual function, reproduction, sleep, and mood through hormone secretion.

Comparison: Endocrine vs. Nervous System

• Endocrine System: Uses hormones, slower response, longer-lasting effects, widespread influence.

• Nervous System: Uses neurotransmitters, rapid response, short-lived effects, localized influence.

Hormone Classifications

• Hormone: A chemical messenger secreted by endocrine glands, transported by the bloodstream to target organs, where it regulates physiology and behavior.

• Peptide/Protein Hormones: Made of amino acids (e.g., insulin, growth hormone).

• Steroid Hormones: Derived from cholesterol (e.g., cortisol, estrogen).

• Amine Hormones: Derived from amino acids (e.g., epinephrine, thyroxine).

Hormone Transport Mechanisms

• Free Hormone: Circulates unbound in the blood; usually water-soluble hormones.

• Protein-Bound Hormone: Circulates bound to plasma proteins; usually lipid-soluble hormones (e.g., steroid and thyroid hormones).

Hormone Receptors

• Cell Membrane Receptors: For water-soluble hormones (peptides/proteins); activate second messenger systems (e.g., cAMP, IP3).

• Intracellular Receptors: For lipid-soluble hormones (steroids, thyroid hormones); directly affect gene transcription.

Feedback Mechanisms

• Negative Feedback: The most common mechanism; hormone secretion is inhibited by its own effects (e.g., insulin lowers blood glucose, which then inhibits further insulin release).

• Positive Feedback: Less common; hormone secretion is stimulated by its own effects (e.g., oxytocin during childbirth).

Anatomical & Functional Relationships: Hypothalamus and Pituitary Gland

• Infundibulum: The stalk connecting the hypothalamus to the pituitary gland.

• Hypophyseal Portal System: Blood vessel network connecting hypothalamus and anterior pituitary, allowing hormone transport.

• Differences: The hypothalamus produces releasing/inhibiting hormones; the anterior pituitary (adenohypophysis) produces its own hormones; the posterior pituitary (neurohypophysis) stores and releases hypothalamic hormones.

Major Endocrine Organs & Hormones

• Hypothalamus

• Pituitary gland (anterior and posterior)

• Pineal gland

• Thyroid gland

• Parathyroid glands

• Adrenal glands (cortex & medulla)

• Pancreas (islets of Langerhans)

• Ovaries / Testes

• Heart

• Kidney

Hormone Classification Table

The following table summarizes the classification, site of production, target cells (organ), and function of key hormones:

Digestive System

The digestive system is responsible for the breakdown and absorption of nutrients, as well as the elimination of waste.

Organic Molecules in Digestion

• Proteins: Broken down into amino acids.

• Carbohydrates: Broken down into monosaccharides (e.g., glucose).

• Lipids/Triglycerides: Broken down into fatty acids and glycerol.

Digestive Processes

• Ingestion: Taking in food.

• Digestion: Mechanical and chemical breakdown of food.

• Absorption: Uptake of nutrients into the bloodstream.

• Elimination: Removal of indigestible substances.

Histology of the Digestive Tract

• Mucosa: Innermost layer; secretion and absorption.

• Submucosa: Connective tissue with blood vessels and nerves.

• Muscularis externa: Smooth muscle for peristalsis.

• Serosa: Outermost layer; protection.

Peritoneum and Mesenteries

• Peritoneum: Serous membrane lining the abdominal cavity.

• Mesentery: Double layer of peritoneum supporting the intestines.

• Lesser and greater omentum, mesocolon, falciform ligament: Specific mesenteries supporting organs.

Digestive Enzymes and Secretions

• Salivary amylase: Starch digestion in mouth.

• Pepsin: Protein digestion in stomach.

• Trypsin, chymotrypsin: Protein digestion in small intestine.

• Pancreatic lipase: Fat digestion.

• Brush border enzymes: Final digestion of carbohydrates and proteins.

• Lingual lipase: Fat digestion in mouth.

Phases of Digestion

• Cephalic phase: Initiated by sight, smell, or thought of food.

• Gastric phase: Food in stomach stimulates secretion.

• Intestinal phase: Chyme enters small intestine, regulating further digestion.

Motility and Control

• Peristalsis: Wave-like muscle contractions moving food.

• Segmentation: Mixing contractions in the intestine.

• Defecation: Elimination of feces.

• Neural control: Vagus nerve, submucosal and myenteric plexuses.

Digestive Hormones

• Gastrin: Stimulates gastric acid secretion.

• GIP (Gastric inhibitory peptide): Inhibits gastric motility.

• Secretin: Stimulates bicarbonate secretion from pancreas.

• Cholecystokinin (CCK): Stimulates bile and pancreatic enzyme release.

• Leptin & Ghrelin: Regulate appetite and satiety.

Absorptive vs. Post-Absorptive States

• Absorptive State: Nutrients are absorbed and stored (glycogenesis, lipogenesis).

• Post-Absorptive State: Stored nutrients are mobilized (glycogenolysis, gluconeogenesis).

Metabolic Rate and Energy Balance

• BMR (Basal Metabolic Rate): The rate of energy expenditure at rest.

• ATP: Main energy currency of the cell.

• Aerobic respiration, deamination, urea cycle: Key metabolic pathways for energy production and nitrogen disposal.

Vitamins

• Major Vitamins: A, Thiamine, Riboflavin, Niacin, B6, B12, Vitamin C, Vitamin D, Vitamin E, Folate, Vitamin K.

• Functions: Coenzymes, antioxidants, bone health, blood clotting, energy metabolism.

Additional info: Some details, such as specific hormone mechanisms and vitamin functions, were expanded for academic completeness.