The Digestive System - Human Anatomy and Physiology 2

functions of the digestive system

the organ system that breaks food into molecules the body can use and removes solid waste

digestion

breaking food down, 2 types: digestion and absorption

mechanical digestion

physical breakdown: chewing, churning, mixing

chemical breakdown

hydrolysis. enzymes and secretions break macromolecules into smaller monomers

absorption

transporting nutrients. moving digested molecules from the GI tract into blood or lymph for transport to cells

components of the digestive system

the alimentary canal (GI tract), as well as accessory organs

alimentary canal (GI tract)

food travels through and makes contact with one long tube

the alimentary canal (GI tract) order

mouth - pharynx - esophagus - stomach - small intestine - large intestine - rectum - anus

accessory organ function

organs that help digestion by adding secretions, but food does not pass through them

accessory organs location

salivary glands, pancreas, liver, gallbladder

tissue membranes

when epithelial tissues combine with connective tissues, a membrane is formed. membranes cover and protect in a variety of ways

4 types of tissue membranes

mucous, serous, cutaneous, synovial

4 layers of the alimentary canal wall

mucosa, submucosa, muscularis, serosa *each layer has a specialized function

mucosa location

the innermost layer of the canal

mucosa function

protection: provides a barrier from enzymes, acids, and microbes. secretion: of mucus and enzymes. absorption: of nutrients and water (varies by organ)

mucosa histology

simple columnar epithelium: a common “lining” tissue for absorption and secretion. goblet cells: secrete mucus for protection of the epithelium and lubrication. lamina propria: underlying connective and smooth muscle tissue

circular folds, villi, microvilli

the small intestine portion of the GI tract is specialized for absorption. these 3 structures allow for increased surface area:

submucosa

a “supply and control” layer - supports the mucosa by nourishing surrounding tissues and transporting absorbed materials.

submucosa contains

blood vessels for carrying away absorbed sugars and amino acids. lymphatic vessels for carrying away absorbed lipids. nerves for regulating secretion and movement

submucosa histology

loose connective tissue and submucosal glands

(ENT) enteric nervous system - innervation of the submucosa

GI activity is strongly influenced by the autonomic nervous system

parasympathetic nervous system function in digestion

generally promotes digestive activity - increased motility and secretion

sympathetic nervous system function in digestion

generally inhibits digestive activity - decreased motility and secretion

muscularis

the muscular layer which allows for mixing and propulsive, wave-like, movements to push food through the lumen (inside) of the canal

muscularis histology

two layers of smooth muscle: circular layer inner, longitudinal layer outer

peristalsis

wave-like propulsion that moves contents forwards (caudally) through the tube. primarily in the esophagus.

segmentation

back-and-forth contractions that mix and segment contents, increasing contact with mucosa and optimizing absorption. primarily in the intestines.

serosa

the protective outer covering that secretes serous fluid for lubrication

serosa histology

serous membrane = simple squamous epithelium and loose connective tissue. also described as visceral peritoneum in abdominal regions