Endocrine System, Digestive System, and Metabolism: ANP Study Guide (Chapters 16, 23, 24)

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Endocrine System

Overview of Endocrine Glands

The endocrine system consists of glands that secrete hormones directly into the bloodstream to regulate various physiological processes. Understanding the location and function of each gland is essential for grasping endocrine regulation.

Pineal gland: Located in the brain; produces melatonin.
Hypothalamus: Links nervous and endocrine systems; controls pituitary gland.
Pituitary gland: Master gland; anterior and posterior lobes release different hormones.
Thyroid gland: Located in the neck; produces thyroid hormones.
Parathyroid glands: Four small glands on the thyroid; regulate calcium.
Thymus: Located in the chest; involved in immune function.
Adrenal glands: On top of kidneys; cortex and medulla produce different hormones.
Pancreas: Both endocrine and exocrine functions; regulates blood glucose.
Gonads: Ovaries and testes; produce sex hormones.

Hormones and Their Functions

Hormones are long-distance chemical messengers that travel in blood or lymph and bind to specific receptors on target cells, causing physiological responses.

Autocrines: Local chemical signals acting on the same cell that secretes them (e.g., prostaglandins).
Types of stimuli: Hormone release is triggered by humoral (blood levels of ions/nutrients), neural (nerve impulses), or hormonal (other hormones) mechanisms.

Hypothalamus and Pituitary Gland Interaction

The hypothalamus controls the pituitary gland via blood (anterior) and nerve (posterior) connections.

Anterior pituitary hormones: GH, TSH, ACTH, FSH, LH, PRL
Posterior pituitary hormones: Oxytocin, ADH

Key Hormones and Homeostatic Imbalances

Oxytocin: Causes uterine contractions and milk ejection.
ADH (Antidiuretic hormone): Decreased ADH leads to diabetes insipidus (excess urine, dehydration).
GH (Growth hormone): Decreased GH causes pituitary dwarfism; increased GH causes gigantism (children) or acromegaly (adults).
TSH (Thyroid-stimulating hormone): Increased TSH causes hyperthyroidism (Graves’ disease, exophthalmos); decreased TSH causes hypothyroidism (myxedema).
Iodine deficiency: Causes goiter due to impaired thyroid hormone synthesis.
ACTH (Adrenocorticotropic hormone): Increased ACTH causes Cushing’s disease (high glucose, tissue swelling).
FSH (Follicle-stimulating hormone): Maturation of oocyte (female), sperm (male).
LH (Luteinizing hormone): Ovulation (female), sperm production (male).
PRL (Prolactin): Stimulates milk production.

Calcium Regulation

Calcitonin: Produced by thyroid C cells; inhibits osteoclasts, lowers blood calcium.
PTH (Parathyroid hormone): Increases blood calcium by stimulating osteoclasts.

Adrenal Gland Structure and Hormones

Zona glomerulosa: Produces aldosterone (mineralocorticoid).
Zona fasciculata: Produces cortisol (glucocorticoid).
Zona reticularis: Produces androgens.
Adrenal medulla: Produces epinephrine and norepinephrine (fight/flight response).

Adrenal Gland Table

Layer	Hormone	Main Function
Zona glomerulosa	Aldosterone	Regulates sodium and potassium
Zona fasciculata	Cortisol	Stress response, increases glucose
Zona reticularis	Androgens	Sex hormone precursors
Adrenal medulla	Epinephrine/Norepinephrine	Fight/flight response

Pancreatic Hormones and Glucose Regulation

Glucagon: Secreted by alpha cells; increases blood glucose via glycogenolysis and gluconeogenesis.
Insulin: Secreted by beta cells; decreases blood glucose by promoting uptake and storage.
Diabetes mellitus: Type 1 (no insulin), Type 2 (insulin ineffective or insufficient).

Digestive System

Alimentary Canal and Accessory Organs

The digestive system consists of the alimentary canal (GI tract) and accessory organs that aid in digestion.

Alimentary canal: Mouth → pharynx → esophagus → stomach → small intestine → large intestine
Accessory organs: Teeth, tongue, gallbladder, salivary glands, liver, pancreas

Digestive Processes and Terminology

Chemical digestion: Breakdown of food by enzymes.
Absorption: Passage of nutrients from GI tract to blood/lymph.
Peristalsis: Wave-like muscle contractions propelling food.

GI Tract Layers

Mucosa (innermost)
Submucosa
Muscularis externa
Serosa (outermost)

GI Tract Layers Table

Layer	Location	Main Function
Mucosa	Inner lining	Secretion, absorption, protection
Submucosa	Below mucosa	Support, blood vessels, nerves
Muscularis externa	Middle layer	Peristalsis, segmentation
Serosa	Outer layer	Protection

Peritoneum and Receptors

Visceral peritoneum: Covers external surface of digestive organs.
Parietal peritoneum: Lines body wall of peritoneal cavity.
Receptors: Mechanoreceptors, chemoreceptors, osmoreceptors in GI tract wall.

Nervous System Control of Digestion

Parasympathetic nervous system: Controls digestive processes (salivation, peristalsis, enzyme production).

Digestive Secretions and Phases

Saliva: Contains enzymes for carbohydrate and lipid breakdown.
Bicarbonate ions: Released from pancreas to neutralize stomach acid.
Gastric secretion phases: Cephalic (before food enters), gastric (food in stomach), intestinal (food in intestine); controlled by neural and hormonal mechanisms.

Stomach and Liver Functions

Stomach: Stores and mechanically breaks down food; initiates protein digestion.
Chief cells: Produce pepsinogen (precursor to pepsin).
Parietal cells: Produce HCl and intrinsic factor.
Liver: Hepatocytes secrete bile, process nutrients, store vitamins, detoxify blood.

Gallbladder and Bile

Gallbladder: Stores bile; contraction triggered by cholecystokinin.
Bile absence: Leads to abnormal fat digestion and absorption.

Small Intestine Structure and Function

Plicae circularis and villi: Increase surface area for absorption.
Cell types: Enterocytes (absorption), goblet cells (mucus), enteroendocrine cells (hormones), Paneth cells (antibacterial), stem cells (renewal).
Lacteals: Specialized lymphatic vessels in villi for fat absorption.

Small Intestine Cell Types Table

Cell Type	Main Function
Enterocytes	Absorption of nutrients/electrolytes
Goblet cells	Mucus secretion
Enteroendocrine cells	Hormone secretion (secretin, CCK)
Paneth cells	Antibacterial activity
Stem cells	Cell renewal

Digestion of Nutrients

Carbohydrates: Digested in mouth (salivary amylase), small intestine (pancreatic amylase, brush border enzymes).
Proteins: Digested in stomach (pepsin), small intestine (pancreatic enzymes, brush border enzymes).
Lipids: Digested in mouth (lingual lipase), stomach (gastric lipase), small intestine (bile, pancreatic lipase).
Most digestion: Occurs in small intestine.
Pancreas: Produces enzymes for carbohydrate, protein, and lipid digestion.

Large Intestine Subdivisions

Cecum
Appendix
Colon
Rectum
Anal canal

Metabolism

Metabolic Reactions

Metabolism is the sum of all chemical reactions in the body, divided into anabolic (building up) and catabolic (breaking down) reactions.

Anabolic reactions: Monomers are joined to form polymers (e.g., glucose to glycogen, amino acids to proteins).
Catabolic reactions: Polymers are broken down into monomers (e.g., glycogen to glucose, lipids to fatty acids and glycerol).

Monomers and Polymers

Carbohydrates: Monomer = glucose; polymer = glycogen/starch
Lipids: Monomer = fatty acids and glycerol; polymer = triglycerides
Proteins: Monomer = amino acids; polymer = proteins (e.g., hemoglobin, insulin)
Nucleic acids: Monomer = nucleotides; polymer = DNA, RNA, ATP

Cellular Respiration

Cellular respiration is the process by which cells produce ATP from nutrients. It consists of three main phases:

Glycolysis: Occurs in cytoplasm; converts glucose to pyruvic acid.
Kreb’s cycle: Occurs in mitochondria; processes pyruvic acid.
Electron transport chain: Occurs in mitochondria; produces most ATP.

Main product: ATP

Aerobic glycolysis: Produces pyruvic acid and CO2 as byproduct.

Anaerobic glycolysis: Produces lactic acid.

Cellular Respiration Equation

Glucose Metabolism

Gluconeogenesis: Formation of glucose from non-carbohydrate sources.
Glycogenolysis: Breakdown of glycogen to glucose.
Glycogenesis: Formation of glycogen from glucose (storage).

Lipid Metabolism

Chylomicrons: Fatty-protein droplets for lipid transport in lymph.
Beta oxidation: Catabolic; fatty acids converted to acetyl CoA for Kreb’s cycle.
Lipogenesis: Anabolic; formation of lipids from acetyl CoA and glyceraldehyde-3-phosphate.
Lipolysis: Catabolic; breakdown of lipids to fatty acids and glycerol.

Protein Metabolism

Proteins: Examples include fibrinogen, gamma globulins, hemoglobin, insulin, glycogen, myelin.

ATP Production

Electron transport system: Produces maximum ATP during cellular respiration.

Example: During intense exercise, anaerobic glycolysis produces lactic acid, while aerobic respiration produces ATP and CO2.

Additional info: The electron transport chain is the final stage of cellular respiration and is responsible for the majority of ATP generation in cells.