Anabolism

nutrients are used as raw materials for synthesizing essential compounds

Catabolism

decomposes substances to provide energy cells need to function

Catabolic Reactions

-requires two essential ingredients

1. Oxygen
2. Organic molecules ( such as carbohydrates, fats, and proteins) broken down by intracellular enzymes

The Digestive Tract

• aka the gastrointestinal (GI) tract or alimentary canal
• is a muscular tube
• includes the mouth, pharynx, esophagus, stomach, and small and large intestines
• extends from the oral cavity to the anus

Accessory Digestive Organs

• teeth
• tongue
• salivary glands
• liver
• gallbladder
• pancreas

6 Functions of the Digestive System

1. Ingestion
2. Mechanical Processing
3. Digestion
4. Secretion
5. Absorption
6. Excretion

Ingestion

• takes place when materials enters the oral cavity

Mechanical Processing

• crushing and shearing, making materials easier to move along the digestive tract

Digestion

• the chemical breakdown of food into small organic fragments for absorption by digestive epithelium

Secretion

• the release of water, acids, enzymes, buffers, and salts by the epithelium of the digestive tract & glandular organs

Absorption

• the movement of organic substrates, electrolytes, vitamins, and water across digestive epithelium and into interstitial fluid of the digestive trace

Excretion

the removal of wastes from the body

*defecation

Defecation

ejection of wastes from the digestive tract eliminating them as feces

Serosa or Visceral Peritoneum

covers organs within peritoneal cavity

Parietal Peritoneum

lines inner surfaces of body wall

Peritoneal Fluid

• produced by the serous membrane lining
• provides essential lubrication
• separates parietal and visceral surfaces, allowing sliding without friction or irritation

Ascites

• excess peritoneal fluid causing abdominal swelling

Mesenteries

• double sheets of peritoneal membrane
• suspend portions of the digestive tract within the peritoneal cavity by sheets of serous membrane that connect parietal and visceral peritoneum
• stabilize positions of attached organs
• prevent intestines from being entangled

Areolar Tissue Between Mesothelial Surfaces

-provides an access route to and from the digestive tract for passage of blood vessels, nerves, and lymphatic vessels

The Lesser Omentum

• fat skin
• stabilizes the position of the stomach
• provides an access route for blood vessels and other structures entering or leaving the liver
• attaches stomach to liver

The Falciform Ligament

• helps stabilize the position of the liver, relative to the diaphragm and abdominal wall

The Dorsal Mesentery

• enlarges to form an enormous pouch, called the greater omentum

The Greater Omentum

• extends inferiorly between the body wall and the anterior surface of the small intestine
• hangs like an apron, from the inferior and lateral borders of the stomach

Adipose Tissue in the Greater Omentum

• conforms to shapes of surrounding organs
• provides padding & protection
• insulates to reduce heat loss
• stores lipid energy reserves

The Mesentery Proper

• suspends all but the first 25 cm of small intestine
• thick mesenterial sheet
• provides stability, but permits SOME independent movement
• associated with the duodenum and pancreas
• fuses with posterior abdominal wall, locking structures in position

Four Layers of the Digestive Tract

1. mucosa
2. submucosa
3. muscularis externa
4. serosa

The Mucosa

• the inner lining of digestive tract
• mucous membrane
• consists of epithelium, moistened by glandular secretions
• lamina propria of areolar tissue

The Digestive Epithelium

• mucosal epithelium is either simple or stratified depending on the location, function, and stresses

Lined with Stratified Squamous

• oral cavity
• pharynx
• esophagus

Lined with Simple Columnar Epithelium

• for absorption
• stomach
• small intestine
• most of the large intestine
• contains mucous cells

Enteroendocrine Cells

• scattered amongst columnar cells of the digestive tract
• secrete hormones that coordinate the activities of the digestive tract

Lining of the Digestive Tract

• appears as longitudinal folds, which disappears as the tract fills
• folding increases the surface area available for absorption

The Lamina Propria

• layer of areolar tissue
• contains:
  1. blood vessels
  2. sensory nerve ending
  3. lymphatic vessels
  4. smooth muscle cells
  5. scattered areas of lymphoid tissue

The Muscularis Mucusae

• narrow sheet of smooth muscle and elastic fibers in lamina propria
• cells are arranged in two concentric layers

The Submucosa

• layer of dense irregular connective tissue
• binds the mucosa to the muscularis externa
• has numerous blood and lymphatic vessels
• some regions contains exocrine glands that secrete buffers and enzymes into the lumen of the digestive tract

Submucosal Plexus

• aka Meissner plexus
• network of intrinsic nerve fibers and scattered neurons
• contains sensory neurons, parasympathetic ganglionic neurons, and sympathetic postganglionic fibers

The Muscularis Externa

• smooth muscles dominates this region
• cells are arranged in circular layer and outer longitudinal layer