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