Digestive System Quiz 1 (AP)

Anatomy & Physiology FT 400/PT700

• Digestive System: A system of organs and accessory organs that take in, digest, and absorb food.

Chapter 24: Digestive System, Part 1

• Lecture Outline:
  • Functions of the digestive tract
  • Overview of the major organs of the digestive system
  • Layers of the GI tract
  • The peritoneum
  • Neural innervation of the GI tract
  • The GI tract: oral cavity, pharynx, and esophagus

Digestive System Anatomy

• Consists of:
  • 1. Gastrointestinal (GI) Tract:
    • Muscular tube (also called the digestive tract or alimentary canal)
    • Food passes from mouth to anus
  • 2. Accessory Organs:
    • Produce or store secretions that flow into the GI tract through ducts

Functions of the Digestive Tract

• Ingestion: Occurs when solid food and liquid enter the oral cavity

• Mechanical Digestion and Propulsion: Crushing and shredding of food in the oral cavity and mixing/ churning in the stomach

• Chemical Digestion: Chemical and enzymatic breakdown of food into small organic molecules for absorption by the digestive epithelium.

  • Secretion: Release of water, acids, enzymes, buffers, and salts by the digestive tract epithelium and accessory digestive organs.
  • Absorption: Movement of nutrients across the digestive epithelium and into the bloodstream
  • Defecation: Indigestible food is compacted into feces and eliminated.

Mechanical Digestion

• Includes all movements that help digest food.
  • Mastication (chewing)
  • Swallowing
  • Mixing
  • Peristalsis

Chemical Digestion

• Enzymes secreted by accessory organs and cells in the tract chemically break down food.
  • Mainly accomplished by using water to break down chemical bonds (hydrolysis)
  • Fats broken down into fatty acids and glycerol
  • Carbohydrates broken down into monosaccharides
  • Proteins broken down into amino acids

Digestive Tract Overview

• Muscular tube ~10 m (33 ft) long, from mouth to anus.
• Major Organs and their Functions:
  • Oral cavity (mouth) - Mechanical processing (teeth and tongue), moistening, and mixing with salivary secretions.
  • Pharynx- Muscular propulsion of food into the esophagus.
  • Esophagus- Transport of materials to the stomach.
  • Stomach- Chemical breakdown and mechanical processing.
  • Small intestine - Enzymatic digestion and absorption.
  • Large intestine- Dehydration and compaction of indigestible materials.

Accessory Organs Overview

• Salivary glands: Produce saliva (mucins and enzymes).
• Gallbladder: Stores and concentrates bile from the liver.
• Pancreas: Exocrine cells secrete buffers and digestive enzymes. Endocrine cells secrete hormones.
• Liver: Almost 200 known functions (various).

Layers of the GI Tract

• Four major layers from esophagus to anal canal:
  • Mucosa
  • Submucosa
  • Muscular layer
  • Serosa or adventitia

Mucosa (inner lining)

• Epithelium
• Lamina propria
• Muscularis mucosae

Submucosa

• Layer of dense irregular connective tissue.
• Contains blood vessels and lymphatic vessels.
• Exocrine glands in some regions.
• Secretes buffers/enzymes into the digestive tract
• Contains a nerve network (Meissner's plexus).

Muscular Layer

• Smooth muscle in two layers (inner circular layer, outer longitudinal layer).
• Involved in mechanical processing and movement along the tract.
• Myenteric plexus (Auerbach's plexus) between muscle layers.

Serosa

• Outermost covering of organs along the digestive tract (in abdominal cavity).
• Called the visceral peritoneum.
• No serosa in oral cavity, pharynx, esophagus, or rectum (Adventitia instead).

Peritoneum

• Largest serous membrane of the body.
• Divided into parietal (lines the inner surface of the peritoneal cavity) and visceral peritoneum (covers organs enclosed by the peritoneal cavity; also called the serosa).
• Space between is the peritoneal cavity and contains lubricating serous fluid.
• Serous membrane continuously secretes peritoneal fluid into peritoneal cavity (~7 liters/day).
• Thin layer separates parietal and visceral surfaces preventing friction and irritation.
• Rate of fluid accelerated by liver disease, kidney disease and heart failure, leading to abdominals swelling (ascites).
• Retroperitoneal: Some organs are retroperitoneal - the peritoneum only covers the anterior surface (kidneys, ascending/descending colon, duodenum, pancreas, ureters).

Peritoneal Folds: Mesentery

• Double sheets of peritoneal membrane.
• Areolar tissue lies between mesothelial layers (provides access route for blood/lymphatic vessels, nerves, and stabilizes the organs; prevents entanglement).
• Includes the mesocolon, mesentery of the colon.

Peritoneal Folds: Omenta

• Continuations of the mesentery, 2 types:
  • Greater Omentum: Large pouch attached to the stomach and transverse colon. Contains adipose tissue for padding, protection, blood vessels, and lymph tissue.
  • Lesser Omentum: Suspends the stomach and duodenum from the liver. Provides access route for blood vessels, hepatic portal vein, hepatic artery and common bile duct.

Peritoneal Folds: Falciform Ligament

• Connects the liver to the anterior body wall.
• Only digestive organ attached to the anterior abdominal wall.
• Remnant of umbilical vein.

The Oral Cavity

• Space containing tongue, teeth, gums

• Lined by oral mucosa (stratified squamous epithelium)

• Keratinized (areas exposed to abrasion)

• Thin, non-keratinized (cheeks, inferior tongue)

• Little to no nutrient absorption.

• Carbohydrate and lipid digestion begins here.

  • Boundaries: hard palate, soft palate, anterior and lateral boundaries (cheeks and lips), inferior boundary (tongue/floor of mouth), posterior boundary (uvula, Palatine tonsils, root of tongue, lingual tonsils).

• Salivary Glands (Parotid, Submandibular, Sublingual): Produce saliva to keep the mouth moist and clean, lubricate, and initiate chemical digestion.

  • Produce secretions (Saliva) containing water, mucins, lingual lipase, and salivary amylase.

Tongue

• Accessory digestive organ
• Skeletal muscle covered by mucous membrane.
• Extrinsic (move tongue) and intrinsic (shape tongue) muscles.
• Dorsum and lateral surfaces contain papillae with taste buds, touch receptors.

Swallowing (Deglutition)

• Initiated voluntarily, but proceeds automatically.
• Facilitated by secretions (saliva/mucus).
• Involves mouth, pharynx, and esophagus.
• Three phases:
  • Buccal phase
  • Pharyngeal phase
  • Esophageal phase

Pharynx

• Membrane-lined cavity posterior to the nose and mouth.
• Skeletal muscle.
• Plays a key role in swallowing.
• Continuous passageway for solid food, liquids, and air.
  • Three regions: (Nasopharynx, Oropharynx, Laryngopharynx).

Esophagus

• Hollow, muscular tube, (~25 cm; 10 in long, 2 cm;0.8 in. wide).

• Transports food and liquids to the stomach.

• No enzyme production, no absorption.

• Structures:

  • Upper esophageal sphincter.
  • Lower esophageal sphincter (cardiac sphincter)

• Histology:

  • Mucosa: Non-keratinized stratified squamous epithelium
  • Submucosa: Areolar connective tissue with blood vessels and mucous glands
  • Muscularis externa: Superior 1/3 skeletal muscle, middle 1/3 mixed skeletal/smooth, inferior 1/3 smooth muscle only
  • No serosa; Adventitia of connective tissue.

• GI Pathology: This section discusses disorders of the digestive tract, a key topic in anatomy and physiology.

  • Periodontal Disease: Inflammation of the gums and surrounding structures from bacterial activity; a common cause of tooth loss.

Review Questions

• Components of the GI tract
• Accessory digestive organs
• Most innermost layer of the GI tract
• Parasympathetic stimulation effect on digestion
• First enzyme acting on carbohydrates and its location.
• Place of lingual lipase origin and function
• Esophagus secretions