digestive system Flashcards
digestive system
- also called gastrointestinal system
- composed of alimentary canal(gi tract)
- and accessory organs
alimentary canal
extends from the mouth to anus through ventral cavity
-9m or 30ft long
accessory organs
- teeth
- tongue
- salivary glands
- liver
- gallbladder
- pancreas
digestive system(functions)
- ingestion
- secretion
- digestion(chemical and mechanical)
- mixing and propulsion
- absorption
- defecation
metabolic processess
-gi tract and accessory organs like the liver and pancreas are responsible for facilitating the boys metabolic processes
mechanical digestion
- all movements that facilitate catabolic processes:
- mastication
- swallowing(deglutition)
- mixing:increase contact of food with digestive chemicals
- peristalsis: movement of muscles within the GI tract that facilitates movement of food.
chemical digestion
- mainly accomplished by using water to break chemical bonds(hydrolysis)
- fats are broken down into fatty acids and glycerol
- carbohydrates are broken down from polysaccharides into monosaccharides
- proteins are broken down into polypeptides and amino acids
walls of gi tract from lower esophagus to anal canal
- four basic layers
- deep - superficial
- mucosa, submucosa,muscularis,serosa/adventita
Mucosa
has epithelium, lamina propria, and muscularis mucosae
lamina propria
-mucous membrane made of various types of epithelium sitting on loose connective tissue
muscosa
-nonkertinized stratified squamous epithelium(for protection) lines the pharynx, esophagus, and anus.
mucosa
-simple columnar epithelium(for secretion/absorption) lines the stomach and intestines
mucosa
-located among the epithelial cells are various glandular cells that secrete muscus and fluid into the lumen of the tract(exocrine).
muscosa
- lamina propria contains a prominent lymphoid tissue (mucosa-associated lymphatic tissue or MALT) that protects against disease.
- underneath it is the muscularis
mucosae
-thin layer of smooth muscle that throws the lining of the stomach and small intestines into tiny folds(increase surface area to aid digestion/absorption)
submucosa
- composed of loose connective tissue the binds the mucosa to the muscular
- contains blood and lymph vessels(to receive absorbed substances)
- and an extensive network of neurons known as the submucosal plexus(plexus of messier)
- motor neurons of the submucosal plexus supply the secretory cells of the organs of GITq
muscularis
- of the mouth,pharynx,superior&middle parts of the esophagus,external anal sphincter contain skeletal muscle that allows for voluntary swallowing and control of defecation.
- rest of tract, it is smooth muscle
- arranged in inner circular and outer longitudinal sheets w/ myenteric nerve plexus continuing between them
- these plexus mostly control GI tract motility
- particulary frequency and strength of contraction of the muscular
- neurons of the ENS(enteric nervous system, brain of the gut are arranged in 2 plexuses explained above meissner and auerbach plexuses.
serosa/adventitia
- outermost layer
- if attached to surrounding tissue(around the esophagus) called adventitia
- if contained in the peritoneal cavity it is called series, which has a slippery mesotheliem layer
- serosa covers the intra abdominal organs as the visceral peritoneum
adventita
fibrous connective tissue arranged around the organ which it supports
peritoneum
- bodys largest serous membrane and it wraps around most abdominal pelvic organs
- the visceral peritoneum forms the series of the alimentary canal and covers other intra-abdominal organs
- it then continues around the abdominal wall as the parietal peritoneum
5 major peritoneal folds
- greater omentum
- falciform ligament
- lesser omentum
- mesentery
- mescolon
falciform ligament
-attaches the liver to the anterior abdominal wall and diaphragm
greater omentum
- largest peritoneal fold
- drapes over the transverse colon and the anterior coils of the small intestine like a fatty apron
- contains many lymph nodes that help combat and contain infections of the gi tract
- large amount of adipose tissue can greatly exapnd(as seen in people with beer bellies)
lesser omentum
- peritoneal fold that suspends the stomach and duodenum from the inferior edge of the liver
- forms a pathway for blood vessels(hepatic portal vein and common hepatic artery to enter the liver and it contains the common bile duct
mesentery(of the small intestine)
mesocolon(large intestine)
-attach the bowel to the posterior abdominal wall holding the intestine loosely in place as muscular contractions mix and move the luminal contents along the GI tract
organs in retroperitoneal space
- kidnerys-ureters
- pancreas
- adrenal gland
- aorta and inferior vena cava
- duodenum
- ascending and descending colons of the large intestine
Neural innervation of the gi tract
1-enteric nervous system
2-autonomic nervous system
3-gastrointestinal reflex pathways
enteric nervous system
1-submucosal plexus(plexus of meissner) is one network of neurons
a-it regulates movement of the mucosa, vasoconstriction of blood vessels, and innervates secretory cells of mucosal glands
2-the myenteric plexus(plexus of auerbach) consists of fibers from both divisions of the ANS
a-plexus mostly controls gi tract motility
autonomic nervous system
1-stimulation of the parasympathetic nerves that innervate the gi tract causes an increase in gi secretions and motility by increasing the activity of ENS neurons
2-sympathetic nerves that supply the gi tract cause a decrease in gi secretion and motility by inhibiting the neurons of the ENS
gastrointestinal reflex pathways
-made up of plexuses that regulate gi secretions and motility in response to stimuli within the gi tract
digestive activities of the gastrointestinal tract occur in three overlapping phases:
- cephalic phase
- gastric phase
- intestinal phase
cephalic phase
- smell,sight,thought,initial taste of food activates neural centers int he cerebral cortex, hypothalamus, and brain stem to prepare for digestion
- brain stem activates the facial(7) and glossopharyngeal(9) nerve to stimulate secretions of saliva, while vagus nerves stimulate secretions of gastric juice
gastric phase
- once food reaches the stomach gastric phase begins
- neural and hormonal mechanisms(HORMONE GASTRIN OF G-CELLS) promote secretions of gastric juice and increase gastric motility. stomach distention and high pH stimulate stretch receptors and chemoreceptors leading to peristalsis and gastric juice secretion.
intestinal phase
- begins once food enters small intestine
- neural(distention of duodenum due to chyme causes enterogastric reflex) and hormonal responses promote the continued digestion of food that have reached the small intestine.
2 major hormones secreted by the small intestine
1) cck(cholecystokinin) from cck cells of small intestine crypts of lieberkuhm and secretin from S cells of small intestinal crypts of lieberkuhn mediate intestinal phase of digestion.
2) secretin promotes secretion of bicarbonate ions into pancreatic juice and bile. it inhibits secretion of gastric juice and promotes normal growth and maintenance of the pancreas. enhances the effects of CCK. causes buffering of acid in chyme. CCK stimulates secretion of pancreatic juice rich in digestive enzymes and ejection of bile into duodenum. also shows gastric emptying
other hormones of small intestine
1) motilin,substance p,bombesin: stimulate intestinal movement
2) VIP(vasoactive intesintal peptide): stimulated secretion of ions and water by intestines and inhibits gastric secretions
3) Gastrin-releasing peptides-stimulates gastrin release
4) somatostatin: inhibits gastrin release
cephalic phase
- consist of reflexes initiated by sensory receptors in the head.
- stimulates gastric secretion and motility
gastric phase
a. can be regulated by neural and hormonal mechanisms
b. neural regulation begins when the stomach walls are distended or when pH increases because proteins have entered the stomach and buffered some of the stomach acid, the stretch receptors and chemoreceptors are activated resulting in waves of peristalsis and continual flow of gastric juice
c. hormonal negative feedback also regulates gastric secretions during the gastric phase
- chemo receptors and stretch receptors stimulate the ANS to release acetylcholine which stimulates the release of gastrin by G-cells
- gastrin stimulates growth of the gastric glans and secretion of large amounts of gastric juice it also strengthens contraction of lower esophageal sphincter
- increases motility of the stomach, and realizes the pyloric and ileocecal sphincters
intenstinal phase
-intestinal phase begins when partially digested food enters the small intestine
neural regulation
-neural regulation is stimulated by distention of duodenum
-distention triggers the enterogastric reflex which reduces gastric emptyin
hormal regulation
- secretin: promotes secretion of bicarbonate ions into pancreatic juice and bile
- inhibits secretion of gastric juice and promotes normal growth and maintenance of the pancreas. enhances the effects of CCK. causes buffering of acid in chyme - cck stimulates secretion of pancreatic juice rich in digestive enzymes and ejection of bile into the duodenum.(slows gastric emptying)
d. other hormones secreted by and having effects on the Gi tract. they include motion,substance p, bombazine,vasoactive intestinal polypeptide, gastrin-releasing peptide, and somatostatin.
oral / buccual cavity
- formed by the cheeks,
- hard and soft palates and
- the tongue
mechanical digestion
-food through mastication(chewing) enables it to be mixed with saliva to form a soft flexible bolus that can be easily swallowed
saliva starts the process of chemical digestion of food
- saliva is 99.5% water
- tiny amounts of dissolved ions, gases, uric acid, lga,lysozyme, and salivary amylase(digestive enzyme that acts on starch)