Digestive System - Anatomy and Physiology LAB - Lecture Slides, Slides of Physiology

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The Digestive System

Digestive System: Overview

• The alimentary canal or gastrointestinal (GI)

tract digests and absorbs food

• Alimentary canal – mouth, pharynx,

esophagus, stomach, small intestine, and

large intestine

• Accessory digestive organs – teeth, tongue,

gallbladder, salivary glands, liver, and

pancreas

Digestive Process

• The GI tract is a “disassembly” line
  • Nutrients become more available to the body in each step
• There are six essential activities:
  • Ingestion, propulsion, and mechanical digestion
  • Chemical digestion, absorption, and defecation

Digestive Process

docsity.com Figure 23.

GI Tract

• External environment for the digestive

process

• Regulation of digestion involves:
  • Mechanical and chemical stimuli – stretch receptors, osmolarity, and presence of substrate in the lumen
  • Extrinsic control by CNS centers
  • Intrinsic control by local centers

Receptors of the GI Tract

• Mechano- and chemoreceptors respond to:
  • Stretch, osmolarity, and pH
  • Presence of substrate, and end products of digestion
• They initiate reflexes that:
  • Activate or inhibit digestive glands
  • Mix lumen contents and move them along

Nervous Control of the GI Tract

• Intrinsic controls
  • Nerve plexuses near the GI tract initiate short reflexes
  • Short reflexes are mediated by local enteric plexuses (gut brain)
• Extrinsic controls
  • Long reflexes arising within or outside the GI tract
  • Involve CNS centers and extrinsic autonomic nerves

Nervous Control of the GI Tract

Figure 23.

Peritoneum and Peritoneal Cavity

Figure 23.5a

Blood Supply: Splanchnic

Circulation

• Arteries and the organs they serve include
  • The hepatic, splenic, and left gastric arteries: Spleen, liver, and stomach
  • Inferior and superior mesenteric arteries: Small and large intestines
• Hepatic portal circulation:
  • Collects nutrient-rich venous blood from the digestive viscera
  • Delivers this blood to the liver for metabolic processing and storage

Histology of the Alimentary Canal

docsity.com^ Figure 23.

Mucosa

• Moist epithelial layer that lines the lumen of

the alimentary canal

• Its three major functions are:
  • Secretion of mucus
  • Absorption of the end products of digestion
  • Protection against infectious disease
• Consists of three layers: a lining epithelium,

lamina propria, and muscularis mucosae

Tongue

Figure 23.

Salivary Glands

• Produce and secrete saliva that:
  • Cleanses the mouth
  • Moistens and dissolves food chemicals
  • Aids in bolus formation
  • Contains enzymes that break down starch
• Three pairs of extrinsic glands – parotid,

submandibular, and sublingual

• Intrinsic salivary glands (buccal glands) –

scattered throughout the oral mucosa