digestive system (anatomy) Flashcards
digestive system=
alimentary canal (GI tract) and accessory organs
general functions of the digestive system include
ingestion- eating
digestion- mechanical and chemical
absorption- nutrients absorbed by epithelial cells into blood and lymph
egestion- defecation (excretion of undigested foods)
in the alimentary canal there is the muscularis externa, what are the two layers
longitudinal layer
circular layer
which layer is outermost in canal of muscularis externa
longitudinal (O for outer)
which layer is innermost in canal of muscularis externa
circular layer (I for inner)
what is inner to the circular layer
submucosa (connective tissue)
the mucosa is made up of?
muscularis mucosa (smooth muscle) lamina propria (connective tissue) epithelium
how is food propelled throughout the alimentary canal
contraction of smooth muscle fibers in muscularis externa
what happens when the longitudinal muscle contracts?
the canal shortens
what happens when the circular muscle contracts?
canal lengthens and narrows
what are the 2 movements produced by contraction of smooth muscle in muscularis externa?
peristalsis and segmentation
what is peristalsis?
food is propelled toward anus (unidirectional)
what is the peristaltic reflex?
stretching of smooth muscle by food triggers reflexive contraction proximal to bolus and relaxation distally
what is segmentation?
back and forth movement (mixing)
what are mesenteries?
double layer of visceral peritoneum extending from organ surface to body wall
what to mesenteries hold in place?
intraperitoneal organs
what do mesenteries provide a network for?
blood/lymph vessel/ nerve attachment
what organs are retroperitoneal (outside peritoneal cavities)
rectum, duodenum, pancreas, ascending/descending colon
which mesenteries are considered ventral mesenteries
- falciform ligament
- lesser omentum
what is the falciform ligament
attaches liver to diaphragm and ventral wall
what is the lesser omentum
attaches lesser curvature of stomach to liver
what mesenteries are considered dorsal mesenteries
- greater omentum
- mesentery proper
- mesocolon
what is the greater omentum
drapes over coils of small intestine; attaches greater curvature of stomach to the dorsal wall
what is the mesentery proper
links coils of jejunum and ileum and binds to dorsal wall
what is the mesocolon
large sheet of tissue attaches transverse and sigmoid colon to dorsal wall
mouth (oral/buccal cavity) hold:
tongue, teeth, salivary glands
what is the tongue
glossal muscles manipulate food to form a bolus
what is the tongue anchored to the floor of buccal cavity by
frenulum
what are papillae
bumps, grip food; associated with glands that secrete fat digesting enzyme linguinal lipase
what are taste buds
sensory chemoreceptors located in the pits between the papillae
how many adult teeth and of which kind
32 adult teeth
- 8 incisors
- 4 canines (cuspids)
- 8 premolars
- 12 molars
what are the incisors for
biting and griping
what are the canines for
tearing
what are the premolars and molars for
chewing and grinding
what are salivary glands
exocrine glands that secrete saliva (1-1.5L per day)
what are the functions of saliva
moistens, dissolves food antimicrobial (lysozyme and IgA antibodies) digests starch (salivary amylase) buffers acid (alkaline) lubricates bolus (mucins)
three pairs of salivary glands
parotid (in cheeks)
sublingual (under tongue)
submandibular (floor of mouth, secrete 70% of saliva)
what is the esophagus
a muscular tube that conveys food to stomach (approx 25 cm long)
what tissue is the esophagus
epithelium, non-keratinized stratified squamous
what glands are in the esophagus that lubricate the bolus
submucosal mucus glands
what regulates the passage of food into the stomach
the cardiac/esophageal sphincter
what is swallowing initiated by
voluntarily initiated, but proceeds automatically
what is the swallowing reflex
triggered when bolus of food contacts the uvula (pharyngeal muscles contract to push food into esophagus, peristalsis moves food toward stomach)
what is the stomach
a storage organ, rugae (folds) expand so that there is a 4L capacity
gastric pits in the stomach house?
gastric glands, gastric gland cells
what kind of epithelial cells are in the gastric pit
simple columnar
in the gastric gland there are 4 cells..?
mucous neck cells
parietal cells
chief cells
G cells
mucous neck cells
secrete mucus
parietal cells
secrete HCl and intrinsic factor (required for absorption of B12)
chief cells
secrete pepsinogen, activated by HCl- become pepsin (protein digesting enzyme)
G cells
secrete hormone gastrin
gastric juice?
very acidic, pH is about 2, kills bacteria
stomach peristalsis “churning” to form..
acid chyme (acidic food paste) moves through pyloric sphincter
what additional layer in the muscularis externa facilitates churning
oblique muscle
what is the small intestine
19 feet of convoluted tube, small diameter
what are the 3 subdivisions of the small intestine
- duodenum
- jejunum
- ileum
what is the duodenum
proximal 5%
-main site of chemical digestion
-receives pancreatic juice (from pancreas)
and bile (from gallbladder)
what is the jejunum
middle 40%
what is the ileum
distal 55%
what are the jejunum and ileum good for
huge surface area specialized for absorption of water and nutrients; cells here secrete digestive enzymes
microanatomy of the small intestine- there are 3 main structures?
- pilcae circularis
- villi
- microvilli
what are the pilcae circularis
large folds of mucosal membrane
what are the villi
finger like projections of mucosal surface
what are the microvilli
folds in apical surface of epithelial surface- form “brush border” membrane
all 3 micro structures of small intestine..
increase surface area
what are the 3 specialized cells in the small intestine and there function
goblet cells- secrete mucus
crypt cells- secrete digestive enzymes
Brunner’s glands- produce alkaline secretion
what is the large intestine (structurally)
large diameter, but short in length (1.5 m)
functions of the large intestine
- water reabsorption
- compaction/ storage of feces
- absorption of some vitamins
- many bacteria (non-pathogenic- coliforms)
what are coliforms
non-pathogenic bacteria in large intestine, protect, digest, stimulate immune system, produce vit K and some B vitamins
what is the histology of the l.i
simple columnar, no villi, lots of goblet cells
structures of the large intestine
ileocecal valve, cecum, ascending colon, transverse colon, descending colon, sigmoid colon
what are taenia coli
3 longitudinal bands of smooth muscle; strong, slow contractions
what is the anus
large intestine terminates in rectum, 6 inches long and expandable.. it stores feces which goes to the anus
what are the two anal sphincters and their tissue
internal anal sphincter (smooth muscle)
external anal sphincter (skeletal muscle)
what is the liver
largest visceral organ in the body, has some ability to regenerate
functions of the liver (6)
- metabolic factory (receives nutrients and metabolizes)
- produces bile from cholesterol (bile acids which emulsify fats)
- inactivation of drugs, toxins, hormones
- storage of iron & fat soluble vitamins
- breaks down RBC’s/hemoglobin/antibodies
- synthesis of plasma proteins (ex. clotting factors, albumin, complement)
blood supply to the liver?
receives 25% of cardiac output
blood arrives by 2 routes
-hepatic artery
-hepatic portal vein
where is blood from hepatic artery from
oxygen rich blood from heart
where is blood from hepatic portal vein from
nutrient rich blood from digestive system
what are liver cells called
hepatocytes
functional unit= lobules, approx 100000
what is each lobule of the liver structurally like?
hexagonal- 6 portal triads connected by sinusoidal capillaries to a central vein
what is a portal triad
bile ductule + portal venule + hepatic arteriole
as blood passes through the sinusoids, what do the hepatocytes do?
absorb and secrete materials into bloodstream
what is the gallbladder function
store and concentrate bile (up to 70ml)
the liver continously synthesizes bile and the gallbladder fills when the sphincter is?
closed
what is the pancreas
both and exocrine and endocrine gand
what are pancreatic acini
they house exocrine cells, secrete pancreatic juice
what are the characteristics of pancreatic juice
- alkaline solution
- lipase digests lipids
- nucleases digest RNA/DNA
- amylase digests starch
- proteases digest proteins
pancreatic duct delivers pancreatic juice to?
hepatopancreatic sphincter- duodenum
