Week 11 Digestive or GI System Physiology
digestive secretions
consist of water, electrolytes, and specific organic constituents secretions are released into digestive tract lumen on appropriate neural or hormonal stimulation normally reabsorbed in one form or another back into blood after their participation in digestion
longitudinal layer(muscularis externa)
outer layer, contraction shortens the length of the tube
endocrine gland cells
secrete blood-born gastrointestinal hormones
exocrine gland cells
secrete digestive juices
Serosa
secretes serous fluid(lubricates and prevents friction between digestive organs and surrounding viscera), continuous with mesentery throughout much of the tract
Submucosa
thick layer of loose connective tissue, provides digestive tract with distensibility and elasticity, contains larger blod and lymph vessels, contains nerve network known as submucosal plexus
Digestive motility and secretion are regulated by
Autonomous smooth muscle function, Intrinsic nerve plexuses, Extrinsic nerves, Gastrointestinal hormones
mesentery (serosa)
attachment provides relative fixation, supports digestive organs in proper place while allowing them freedom for mixing and propulsive movements
digestion
biochemichal breackdown of structurally complex foodstuffs into smaller, absorbable units accomplished by enzymatic hydrolysis complex foodstuffs and their absorbable units carbohydrated into monnosaccaharides proteins into amino acids fats into glycerol and fatty acids
Mucosa
highly folded surface greatly increases absorptive area, three layers(mucous membrane, lamina propria, muscularis mucosa )
lamina propria
houses gut-associatied limphoid tissue(important in defence against diseasse-causing intestinal bacteria)
circular layer(muscularis externa)
inner layer, contraction decreases diameter of lumen
muscularis externa
major smooth muscle coat of digestive tube, in most areas consists of two layers(circular layer, longitudinal layer), contractile activity produces propulsive and mixing movements, mycentric plexus (lies between the two muscle layers)
absorption
most absorption is completed in the small intestine small units resulting from digestion, allong with water, vitamins, and electrolytes are transferred from digestive tract lumn=en into blood or lymph
the digestive system performs these functions
motility, secretion, digestion and absorption
digesrive tract
mouth, pharynx, esophagud, stomach, small intestine (duodenum, jejunym, ileum), large intestine (cecum, appendix, colon, rectum), anus
wall of the digestive tract (esophagus to anus)
mucosa(innermost layer), submucosa, muscularis externa, serosa (outer layer)
motility
muscular contractions that mix and move forward the contents of the digestive tract
propulsive movements(motility)
push contents forward through the digestive tract
accesory digestive organs
salivary glands, exocrine pancreas, bilary system(liver, callbladder)
mucous membrane
serves as protective serface, modified ofr secretion and absorption, contains(exocrine gland cells, endocrine gland cells, epithelial cells)
mixing movements(motility)
serves two functions: mixing food with digestive juices promotes digestion of foods, facilitates absorption by exposing all parts of intestinal contents to absorbing surfaces of digestive tract
muscularis mucosae
sparse layer of smooth muscleq
epithelial cells
specialized for absorbing digestive nutrients
primary function of the digestive system
transfer nutrients, water, and electrolytes from ingested food into body's internal environment