Digestive system

What is the digestive system?

organ system that processes food, extracts nutrients, and eliminates residue

What are the five stages of digestion?

Ingestion, digestion, absorption, compaction, defecation

Ingestion

selective intake of food

Digestion

mechanical and chemical breakdown of food into a form usable by the body

Absorption

uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph

Compaction

absorbing water and consolidating the indigestible residue into feces

Defacation

elimination of feces

Mechanical digestion

the physical breakdown of food into smaller particles, chewing, churning action of stomach and small intestines

What is the main goal of mechanical digestion?

increase surface area of food so that digestive enzymes have more access to it

Chemical digestion

a series of hydrolysis reactions that breaks dietary macromolecules into their monomers (residues)

What is chemical digestion carried out by?

digestive enzymes produced by salivary glands, stomach, pancreas, and small intestine

What does chemical digestion turn polysaccharides into?

monosaccharides

What does chemical digestion turn proteins into?

amino acids

What does chemical digestion turn fats into?

monoglycerides and fatty acids

What does chemical digestion turn nucleic acids into?

nucleotides

What nutrients can be directly absorbed when they are ingested?

Vitamins, amino acids, minerals, cholesterol, and water

What are the two subdivisions of the digestive system?

digestive tract and accessory organs

What is part of the digestive tract?

alimentary canal, Mouth, pharynx, esophagus, stomach, small intestine, and large intestine, gastrointestinal tract

What is the gastrointestinal tract?

stomach and intestines

What are the accessory organs?

Teeth, tongue, salivary glands, liver, gallbladder, and pancreas

How many primary layers of the digestive tract are there and what are they?

4- mucosa, submucosa, muscularis externa, and serosa

what are the three sublayers of the mucosa?

Epithelium, Lamina propria, Muscularis mucosae

What are the two sublayers of the muscularis externa?

inner circular layer, and outer longitudinal layer

What are the two sublayers of the serosa?

areolar tissue, and mesothelium

Enteric nervous system

nervous network in esophagus, stomach, and intestines that regulates digestive tract motility, secretion, and blood flow, and can function independently of central nervous system, part of autonomic nervous system

What are the two networks of neurons that make up the enteric nervous system?

Submucosal plexus and myenteric plexus

Submucosal plexus

in submucosa, Controls glandular secretions of mucosa, Controls movements of muscularis mucosae

myenteric plexus

parasympathetic ganglia and nerve fibers between the two layers of the muscularis externa, Controls peristalsis and other contractions of muscularis externa

Mesenteries

connective tissue sheets that suspend stomach and intestines from abdominal wall

Functions of mesenteries

• Looseness allows stomach and intestines to undergo strenuous contractions with freedom of movement in the abdominal cavity

• Hold abdominal viscera in proper relationship to each other

• Prevent intestines from becoming twisted and tangled by changes in body position and by its own contractions

• Provide passage of blood vessels and nerves that supply digestive tract

• Contain many lymph nodes and lymphatic vessels

Parietal peritoneum

a serous membrane that lines the wall of the abdominal cavity

Functions of parietal perineum

• Turns inward along posterior midline

• Forms dorsal mesentery: a translucent two-layered membrane extending to the digestive tract

• The two layers of the mesentery separate and pass around opposite sides of the organ forming the serosa

• Come together on the far side of the organ and continue as another sheet of tissue, called the anterior (ventral) mesentery

  • May hang freely in the abdominal cavity

  • May attach to the anterior abdominal wall or other organs

Lesser omentum

a ventral mesentery that extends from the lesser curvature of the stomach to the liver

Greater omentum

• hangs from the greater curvature of the stomach (its left inferior margin)

  • Covers small intestine like an apron

  • The inferior margin turns back on itself and passes upward

  • Forming a deep pouch between its deep and superficial layers

  • Inner superior margin forms serous membranes around the spleen and transverse colon—mesocolon