overview of digestion Flashcards
what is the name given to involuntary muscle contractions ?
peristalsis
what is the primary driving force of digestion ?
peristalsis
where are digestive enzymes secreted from ?
mucosae
what do locally produced hormones do and give some examples ?
affect the physiological activity of the GI tract
- gastrin
- cholecystokinin
where does the primary absorption of nutrients occur ?
the small intestine
what type of fluid secretions are largely reabsorbed ?
salivary
gastrointestinal
how is undigested material eliminated ?
by combined activity of involuntary and voluntary muscles
what 4 major organs does the digestive tract differentiate into ?
- esophagus
- stomach
- small intestine
- large intestine
how are organs separated ?
by muscular valves / sphincters
what lines the inner surface of the digestive tract ?
mucosal layer
where is digestion of carbohydrates initiated and by what ?
in the mouth
by amylase
where does the majority of digestion + absorption of carbs + amino acids occur ?
across the muscosae of the stomach + small intestine
what does the pancreas secrete and where does it pass into ?
HC03
lumen of small intestine
what does the liver secrete and what does it pass into ?
bile salts
lumen of small intestine
what are the 4 layers of muscle that make up the GI tract ? (deep to superficial)
- mucosa
- submucosa
- muscularis
- adventitia of the serosa
what makes up the mucosa ?
- epithelium
- stroma
- vascularised loose connective tissue
- immunocompetent cells (lamina propria)
- smooth muscle (muscularis mucosae)
what is the outer layer of smooth muscle in mucosa subdivided into ?
- inner circular
- outer longitudinal
what does contractions of the muscularis do ?
throws mucosa into folds + ridges
what is present in the submucosa ?
- large blood vessels
- lymphatic vessels
- nerves (messners plexus)
where do the nerve fibres of messners plexus go ?
mucosa
muscularis
how many layers of muscle exist in the muscularis externa ? and where is an exception found ?
- 2 both smooth
- in upper esophagus + anal sphincter there is striated fibres
what is the arrangement of muscle in the muscularis ?
inner circular layers surrounded by outer longitudinal layers
circular constricts the lumen
longitudinal constricts the digestive tube
describe the structure of adventitia / serosa :
several layers of loose connective tissue
alternately collagenous + elastic
covered by layer of mesothelial cells
where are the largest arteries found?
longitudinally in submucosal layers
where are smaller branches of arteries found ?
in serosal layer
how do capillaries run in the muscularis layer ?
parallel to muscle fibres
describe the blood supply in the mucosa
arteries supply an irregular capillary plexus around glands
sends terminal branches to mucosal villi (lumen of intestine)
what is the general pattern of capillaries ?
fenestrated in the intestinal + exocrine epithelium
describe the movement of veins :
veins arising in the mucosa anastomose in the submucosa and pass out of intesine alongside arteries
how do lymphatic vessels arise ?
as blind tubes in the mucosa
known as lacteal vessels
what do lymphatic vessels contain ?
what do they do ?
contain pinocytotic vesicles
shuttle macromolecules + chyclomicrons from the interstitial space into the lymphatic circulation
how are lymph vessels found in the submucosa ?
large lymphatics branch freely
cross muscle layers
spread into the intermuscular tissue + serosa
what do vascular + lymphatic vessels help do ?
aid nutrient absorption
what fibres are found in the gastrointestinal tract ?
autonomic motor
sensory
describe the formation of nerve fibres
ramify throughout GI tract
form a plexus in each layer
where does the intramural parasympathetic ganglia innervate ?
submucosal plexus (meissner) between 2 layers of muscularis externa in myenteric plexus of auerbach
what does innervation of the intramural parasympathetic ganglia do ?
stimulates motor + secretory activity of the gut
where do the sympathetic fibres of the GI tract terminate ?
in the submucosal + myenteric plexus
what does sympathetic innervation of the GI tract cause ?
cause constriction of blood vessels
inhibits contraction of muscularis externa
constrict muscularis mucosae
where do gut hormones influence ?
alimentary tract
neurocrine
paracrine
endocrine
where are endocrine cells distributed ?
epithelia of stomach small intestine large intestine appendix distal esophageal glands ducts of liver + pancreas
