digestion - lecture 1 Flashcards
what is the gastrointestinal tract
alimentary canal
continuous tube from mouth to anus
what makes up digestive system
gastrointestinal tract and accessory digestive organs
what are accessory digestive organs
salivary glands
pancreas
liver
gallbladder
secretions into tract to help with digestion
what are git functions
conveys food along git
allows it be broken down into small molecules which can be absorbed into circulation
while moving down tract - used for energy needed by all cells of body
name the 6 activities of digestive system
- ingestion - chew
- secretion
- motility
- digestion - muscular and secretory
- absorption
- defecation
describe secretion
glandular activity - exocrine and endocrine
leads to chemical breakdown
describe motility
propulsion and physical breakdown - muscular activity of git
moves through
describe absorption
transfer to blood circulation and to all cells of body
what are most important git functions
secretion
motility
absorption
describe homeostasis
git is an important contributor
fundamental principle in physiology
at all levels of organization, body activities are directed at maintaining optimal and relatively constant internal conditions - in nutrient concentrations in body
what is gits role in homeostasis
provide nutrients to body
from external environment = food, git breaks food down into absorbable molecules and then processed to all cells = energy and raw materials for growth and repair, function and regulation
describe git capacity
digestive and absorptive capacity
git is exquisitely efficient = digest and absorb almost all the food we eat
carbs = 99%
fat = 95%
protein = 92%
name activities for git and integration
propulsive, secretory and absorptive activities highly coordinated and integrated for high functional efficiency by neural and hormonal mechanisms
the efficiency of git is due to this
describe git structure
tubular structure
communicates with external environment at both ends = lumen contacts, central lumenal cavity = considered as extracellular space
good for function - if toxins or bacteria = wont get into blood stream, but also must be able to absorb nutrients and molecules we need
name parts of git
mouth –> stomach –> si –> li –> anus
what is git length
4.5 m in living adult = longer than human (1.5 meters)
in cadaver = 10 m since humans have lots of muscle tone = always contracts while alive
describe growth of git - sa
increase in total internal sa
adult = 200-250 m^2
600x larger than external sa due to = invaginations and fingerlike projections - in and out pushings
FORM FOLLOWS FUNCTION
describe differentiation of git
tube into alimentary canal and all accessory organs near canal
describe wall of gi tract
4 main layers =
mucosa (secretory and absorptive cells)
submucosa (lymphatics and circulation = absorb nutrients and provide nutrients to cells in git)
muscularis externa
serosa
describe mucosa of git
3 layers =
epithelial layer = epithelial and glandular cells - exocrine and endocrine secretory cells and absorptive cells
lamina propria = loose ct
Muscularis mucosae = smooth muscle
describe submucosa of git
loose ct with lymphatics and bvs and neuronal networks
describe muscularis externa of git
2 diff layers of muscle =
Inner layer circular fibers - decrease aperture of lumen when contracts
outer layer longitudinal fibers - along lenght of git = if contract it shortens
striated muscle at beginning of git (oral cavity, pharynx and upper 1/3 eso and external anal sphincter) then majority smooth (involuntary) and then striated at anus again
describe serosa of git
thin tough layer of ct
in some places = serosa acc continuous with peritoneum (abdominal mesentery) (lining of abdominal cavity) (holds git in place)
what is ens
Enteric nervous system
controls secretion and motility
neurons reside within wall of git
Billions of neuron’s
