Digestive System: Functions and Organs

• The digestive system functions in five stages: ingestion, mechanical breakdown, chemical digestion, absorption, and elimination.
• Mechanical digestion involves the physical breakdown of food.
• Chemical digestion involves enzymatic breakdown.
• Macronutrients include carbohydrates, proteins, and fats.
• Micronutrients include vitamins and minerals.

Accessory Organs vs. Alimentary Canal Segments

• Accessory organs aid digestion, while the alimentary canal is the direct pathway food travels.

Accessory Digestive Organs/Structures Functions

• Teeth are for mastication.
• Salivary glands secrete saliva.
• The liver produces bile.
• The gallbladder stores bile.
• The pancreas produces enzymes.

Digestive Tract Layers Functions

• The serosa is the outermost layer.
• The longitudinal muscle layer is for peristalsis.
• The circular muscle layer is for segmentation.
• The submucosa contains blood vessels and nerves.
• The Muscularis Layer is responsible for movement.
• The Plexuses of the enteric nervous system regulate digestive activity.
• The Lumen the the open space in the intenstine.

Retroperitoneal Organs Examples

• Examples include the kidneys, pancreas, and parts of the duodenum and colon.

Omenta Function

• Omenta support abdominal organs and store fat.

Connective Tissue Structures of Abdomen Locations

• The lesser omentum attaches the stomach to the liver.
• The greater omentum hangs from the stomach, covering the intestines.
• The falciform ligament attaches the liver to the anterior abdominal wall.
• The mesentery suspends the small intestine from the posterior abdominal wall.

Oral Cavity Functions

• The oral cavity functions in ingestion, taste, mastication, and initial digestion.

Palatine Tonsils

• Palatine tonsils are located in the lateral walls of the oropharynx and function in immune response.

Oral Cavity Boundaries

• Anterior boundary: lips, Lateral boundary: cheeks, Superior boundary: hard and soft palates, and Inferior boundary: tongue.

Tongue Tie

• The frenulum is implicated in "tongue tie."

Lingual Papillae Location & Function

• Lingual papillae are on the tongue's surface and contain taste buds.

Tongue Papillae With Taste Buds

• Fungiform, foliate, and circumvallate papillae contain taste buds.

Tongue Papillae Without Taste Buds

• Filiform papillae lack taste buds.

Teeth in Deciduous vs. Permanent Sets

• Deciduous teeth: incisors, canines, molars.
• Permanent teeth: incisors, canines, premolars, molars.

Autonomic Nervous System Control of Salivation

• Parasympathetic stimulation increases salivation; sympathetic decreases it.

Salivary Enzymes Function

• Salivary amylase breaks down carbohydrates.
• Lingual lipase breaks down fats.

Deglutition (Swallowing) Phases

• Voluntary, pharyngeal, and esophageal phases.

Voluntary Control of Deglutition

• Only the voluntary phase is consciously controlled.

Air, Food, or Both Movement

• Oropharynx: Both.
• Laryngopharynx: Both.
• Nasopharynx: Air.
• Esophagus: Food.
• Trachea: Air.

Sphincter Definition

• A sphincter is a circular muscle that constricts a passage or opening.

Anatomical vs. Physiological Sphincters

• Anatomical sphincters are structural, while physiological sphincters are functional.

Sphincters Function

• Lower Esophageal Sphincter: Prevents stomach acid reflux (physiological).
• Pyloric Sphincter: Regulates stomach emptying (anatomical).
• Ileocecal Sphincter: Controls flow into the colon (anatomical).
• Anal Sphincter: Controls defecation (anatomical).

Stomach Cell Types Secretions

• Epithelial Cells: Mucus.
• Parietal Cells: Hydrochloric acid and intrinsic factor.
• Chief Cells: Pepsinogen.

Pepsin Activator

• Hydrochloric acid activates pepsin.

Active Pepsin Production

• Parietal cells secrete HCl, and chief cells secrete pepsinogen.

Advantages of Acidic Stomach Environment

• Kills bacteria, denatures proteins, and activates pepsin.

Digestive Enzymes Inactive Form

• Digestive enzymes are secreted in an inactive form to prevent self-digestion.

Duodenum Parts

• Four parts include the superior, descending, horizontal, and ascending portions.

Liver Function Categories

• Metabolic Functions: nutrient processing, storage.
• Secretory Function: bile production.
• Endocrine Functions: hormone regulation.
• Filtering Functions: detoxification.

Liver vs. Gallbladder Roles in Bile

• The liver produces bile, and the gallbladder stores it.

Digestive System Ducts Contents

• Cystic Duct: Bile.
• Hepatic Duct: Bile.
• Pancreatic Duct: Pancreatic enzymes and bicarbonate.
• Hepatopancreatic Duct: Bile and pancreatic secretions.

Bile Components

• Bile salts, cholesterol, and bilirubin are bile components.

Emulsification Definition

• Emulsification is the breakdown of large fat globules.

Jaundice Pathology & Treatment

• Jaundice is caused by bilirubin buildup; treatment varies based on the cause.

Pancreas Functions

• Endocrine: insulin and glucagon secretion.
• Exocrine: digestive enzyme secretion.

Pancreatic Enzymes for Micronutrients

• Amylase for carbohydrates, proteases for proteins, and lipase for fats.

Enteropeptidase Function

• Enteropeptidase activates trypsinogen to trypsin.

Pancreatic Bicarbonate Function

• Pancreatic bicarbonate neutralizes acidic chyme.

Jejunum vs. Ileum Characteristics

• Jejunum: thicker walls, larger diameter, longer villi, more circular folds.
• Ileum: more Peyer's patches.

Jejunum/Ileum & Colon Features for Absorption

• Jejunum and Ileum: Villi and microvilli increase surface area.
• Colon: Primarily absorbs water and electrolytes.

Intestinal Villi Structures Functions

• Lacteals: Absorb fats.
• Goblet Cells: Secrete mucus.
• Blood Capillaries: Absorb most nutrients.
• Microvilli: Increase surface area.

Small Intestine Microanatomy

• Includes villi, microvilli, and crypts of Lieberkühn.

Microanatomy Significance

• Increases surface area for absorption.

Small Intestine Organization Structures

• Circular folds, villi, columnar enterocytes, and goblet cells.

Macromolecule Absorption

• False: Fats are absorbed into lacteals, while proteins and carbohydrates are absorbed into blood capillaries.

Peristalsis & Segmentation

• Peristalsis: Propulsive movements.
• Segmentation: Mixing movements.

Macronutrient Chemical Digestion

• Carbohydrates: Begins in the mouth with salivary amylase, continues in the small intestine with pancreatic amylase.
• Proteins: Begins in the stomach with pepsin, continues in the small intestine with pancreatic proteases.
• Lipids: Begins in the small intestine with pancreatic lipase.

Nutrient Absorption in Small Intestine

• Carbohydrates: Glucose and galactose are actively transported.
• Proteins: Amino acids are actively transported.
• Lipids: Absorbed as micelles, then reassembled into triglycerides in the cells.

Enterohepatic Circulation

• The enterohepatic circulation recycles bile salts.

Large Intestine Structures

• Teniae Coli: Longitudinal muscle bands.
• Haustra: Pouches.
• Epiploic Appendages: Fat-filled pouches.

Disease States & Defecation

• Diarrhea: Increased frequency and fluidity of bowel movements.
• Constipation: Infrequent or difficult bowel movements.

Digestive Tract Segment Features

• Stomach: Rugae, gastric pits.
• Duodenum: Brunner's glands.
• Jejunum: Long villi and plicae circulares.
• Ileum: Peyer's patches.
• Cecum: Appendix attachment.
• Sigmoid Colon: S-shaped curve.

Mechanical & Chemical Digestion in Colon

• Mechanical: Haustral churning.
• Chemical: Bacterial fermentation.

Defecation Structures Relaxing

• Only the external anal sphincter relaxes under voluntary control.

Colon Sphincters

• Proximal: Ileocecal valve.
• Distal: Internal and external anal sphincters.

Dietary Component Not Digested

• Fiber is not digested.

Defecation Steps

• Feces move into the rectum, rectal wall distension initiates signals to the brain, and voluntary relaxation of the external anal sphincter.

Food Path

• Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus.

Smooth Muscle Layers

• Stomach: Three.
• Small Intestine: Two.
• Colon: Two.

Enteric Nervous System

• Regulates digestive system activity independently; the brain refers to as the "gut brain".