Digestive System Overview and Functions

Digestive System Overview

• The digestive system is a disassembly line, breaking down nutrients into usable forms for the body and absorbing them.
• Most food cannot be directly used, necessitating breakdown into smaller components like amino acids and monosaccharides.
• These smaller components are universal to all species.

Digestive System Functions

• Ingestion: The selective intake of food.
• Digestion: Mechanical and chemical breakdown of food into usable forms.
• Absorption: Uptake of nutrients into the blood and lymph.
• Compaction: Absorbing water and consolidating indigestible residue into feces.
• Defecation: Elimination of feces.

Digestive System Anatomy

• Digestive tract: A muscular tube from mouth to anus (also known as the alimentary canal or gut).
  • Includes: mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
  • The stomach and intestines constitute the gastrointestinal (GI) tract.
• Accessory organs: Teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

Oral Cavity (Mouth)

• Also known as the buccal cavity.
• Ingestion(food intake), taste, chewing (mastication), swallowing, and respiration occur here.
• The mouth is enclosed by lips, palate, and tongue.

Salivary Glands

• Two types: intrinsic (small glands dispersed in oral tissues) and extrinsic (three pairs of larger glands).
  • Intrinsic glands include lingual, labial, and buccal glands.
  • Extrinsic glands are the parotid, submandibular, and sublingual glands.
• Saliva secreted constantly, moistening the mouth and inhibiting bacterial growth.

Pharynx

• A muscular funnel connecting oral cavity to esophagus and nasal cavity to larynx.
• A point of intersection between the digestive and respiratory tracts.
• Swallowing occurs by tongue and palate action.

Esophagus

• A muscular tube (25-30 cm long) posterior to the trachea.
• Connects pharynx to the stomach.
• Superior opening is between vertebra C6 and cricoid cartilage of the larynx.
• Its inferior end is located where the stomach begins.

Stomach

• A muscular sac in the upper left abdominal cavity, inferior to the diaphragm.
• Primarily a food storage organ.
• Mechanically breaks down food, liquefies it, and begins chemical digestion (proteins, fats).
• Chyme is the soupy mixture of semidigested food forming in the stomach.

Pylorus and Pyloric Sphincter

• Pylorus is the end of the stomach.
• A thick ring of smooth (pylorus circular muscle) that regulates chyme passage into the duodenum (first part of the small intestines).

Small Intestine

• A coiled mass within the abdominal cavity, inferior to the stomach.
• Divided into three segments: duodenum, jejunum, and ileum.
• Primary site for nutrient absorption.
  • The surface area for absorption is increased by extensive folding of the mucosa and great length of the small intestine.
• Chyme is fully digested and almost all nutrients are absorbed here.

Ileocecal Valve and Large Intestine

• The ileocecal valve separates the ileum (small intestine) from the cecum (large intestine).
• It regulates food residue passage into the large intestine and prevents feces from backing up into the ileum.
• The large intestine receives undigested residue, reduces it to approximately 150mL of feces by absorbing water and electrolytes, then eliminates the feces.
  • Divided into the cecum, colon (ascending, transverse, descending, and sigmoid), rectum and anal canal.

Liver

• The body's largest gland, located immediately inferior to the diaphragm (right upper quadrant).
• Contributes to digestion by secreting bile.
• Bile emulsifies fat (breaks down fat into smaller droplets), greatly enhancing fat digestion.
• Also plays essential roles in detoxifying, processing various substances, and synthesizing numerous molecules.

Pancreas

• A spongy gland posterior to the stomach (retroperitoneal).
• Both endocrine (secreting hormones) and exocrine glands (secreting digestive enzymes).
  • Secretes pancreatic juice(an alkaline fluid).
• Pancreatic juice is a mixture of water(a solvent), bicarbonate(neutralise acidic chyme) and enzymes (digest carbohydrates and proteins) into the duodenum.

Explore the intricacies of the digestive system, including its essential functions like ingestion, digestion, absorption, compaction, and defecation. Understand the anatomy of the digestive tract and the role of accessory organs in nutrient breakdown and absorption.