digestive Flashcards
Digestive system process
ingestion digestion (mechanical and chemical) absorption secretion (into lumen, paracrine signaling, into blood (hormones)) motility (mixing and propulsion) excretion defense mechanisms regulation - hormones and ANS
Digestive system= 2 groups of organs
- Alimentary canal (GI tract)
- mouth to anus
- digests food and absorbs fragments
- mouth, pharynx, esophagus, stomach, small intestine, and large intestine - Accessory digestive organs
- teeth, tongue, gallbladder
- digestive glands : salivary glands, liver, gallbladder, pancreas
Digestion (2 kinds) and objective
Mechanical: chewing, mixing, segmentation
Chemical - enzymes
- carbs, prots, lipids, nucleic acids
- dif enzymes are active in dif organs
Objective: breakdown of foodstuffs into smaller pieces that the cell can use
Absorption
movement of substances from lumen, across intestinal epithelium, into blood or lymph
can be active or passive
Secretion
release of substances from glandular epithelium of digestive tract and accessory organs into the lumen
release of hormones into the blood that affect target cells that regulate digestive functions
release of paracrines for local control
Motility
movement as a result of contraction of smooth muscle in walls of digestive organs
- segmental = mixing
- propulsion = peristalsis = forms bolus
mechanical digestion
Defense mechanisms
- Important bc it’s open to outside world –> mucus membrane
- mucus is secreted by epithelium
- enzymes (lysozymes)
- acidity of stomach
- Lymphoid tissue (MALT) = collections of lymphocytes along digestive tract
Excretion
removal of wastes, unabsorbed and undigested products via defecation in form of feces
GI Regulation: mechanoreceptors and chemoreceptors
-Respond to stretch, changes in osmolarity and pH, and presence of substrate and end product of digestion
- initial reflexes that either
1. activate/inhibit digestive glands or
2. stimulate smooth muscle to mix and move lumen contents
GI regulation: intrinsic and extrinsic controls
Short refleces = enteric nerve plexuses (gut brain) respond to stimuli in GI tract
Long relexes = respond to stimuli inside or outside GI tract –> involve CNS centers and autonomic nerves
Hormones from cells in stomach and small intestine stimulate target cells in same or dif organs to secrete or contract
Peritoneum and peritoneal cavity
Peritoneum = serous membrane of abdominal cavity
- visceral peritoneum on external surface of most digestive organs
- parietal peritoneum lines body wall
Peritoneal cavity
- bt two peritoneums
- fluid lubricates mobile organs
Mesentery = double layer of peritoneum
- routes for blood vessels, lymphatics, and nerves
- holds organs in place and stores fat
retroperitoneal organs are posterior to peritoneum
Intraperitoneal organs ARE surrounded by peritoneum
Blood supply: splanchnic circulation
Branches of aorta serving digestive organs
- hepatic/splenic/left gastric arteries
- inferior/superior mesenteric arteries
Hepatic portal circulation
- drains nutrient-rich blood from digestive organs
- delivers it to the liver for processing
Histology of alimentary canal
4 layers/tunics
Mucosa
submucosa
muscularis externa
serosa
Mucosa (func and layers)
lines the lumen
Functions: dif layers perform 1 or all 3
- secretes mucus, digestive enzymes, and hormones
- abdorbs end products of digestion
- protects against infectious disease
3 sublayers: epithelium, lamina propria, and muscularis mucosae
Mucosa epithelium
simple columnar epithelium and mucus secreting cells (most of the tract)
-mucus protects digestive organs from enzymes and eases food passage
may secrete enzymes and hormones (e.g. stomach and small intestine)
Mucosa: lamina propria and muscularis mucosae
Loose areolar CT
- capillaries for nourishment and absorption
- lymphoid follicles (part of MALT) –> defend against microorganisms
Muscularis mucosae = smooth muscle –> local movements of mucosa
submucosa
areolar CT
- blood and lymphatic vessels
- lymphoid follicles
- submucosal nerve plexus
Muscularis externa
- responsible for segmentation and peristalsis
- inner circular and outer longitudinal layers
- circular layer thickens in some areas –> sphincters
- myenteric nerve plexus b/t two muscle layers
Serosa: (tissue and func)
Visceral peritoneum
- areolar CT covered with mesothelium in most organs
- replaced by fibrous adventitia in esophagus
- retroperitoneal organs have both an adventitia and serosa
Func
- secrete fluid - decrease friction
- part of peritoneum –> binds organs to surrounding structures and body wall (visceral layer, peritoneal cavity, and parietal layer)
- extensions provide support to abdominal organs, blood vessels, nerves
Folds of serosa
Lesser omentum = bt stomach and liver
Falciform ligament = attach liver to abdominal wall
greater omentum = extends below stomach
mesentery proper = small intestine and pancreas to posterior wall
mesocolon = large intestine to posterior wall (also transverse and sigmoid mesocolon)
Enteric NS definition what it supplies plexuses how it's linked to NS
- Intrinsic nerve supply of alimentary canal –> enteric neurons (more than spinal cord)
- major nerve supply to GI tract wall: control motility and secretions
- submucosal nerve plexus regulates glands and smooth muscle in mucosa
- myenteric nerve plexus controls GI tract motility
Linked to CNS via afferent visceral fibers
Long ANS fibers synapse with enteric plexus
-sympathetic impulses inhibit digestive activities
-parasympathetic impulses stimulate digestive activities
Mouth
oral (buccal) cavity
- bounded by lips, cheek, palate (hard and soft), and tongue
- oral orifice is anerior opening
- lined with stratified squamous epithelium
- begins posterior to teeth
Lips and cheeks
- contain orbicularis oris and buccinator muscles
- oral vestibule = recess internal to lips (labia) and cheeks, external to teeth and gums
- oral cavity proper lies within teeth and gums
- labial frenulum = medun attachment of each lip to gum
Palate
Hard palate = palatine bones and palatine processes of maxillae
-slightly corrugated to help create friction against tongue
Soft palate = fold fomed mosly of skeletal muscle
- closes of nasopharynx during swallowing
- uvula projects downward from its free edge
tongue
skeletal muscle
Func:
-repositioning and mixing food during chewing
-form bolus
initiate swallowing, speech, and taste
intrinsic muscles change shape of tongue
extrinsic muscles alter tongues position
Lingual frenulum = attachment to floor of mouth
Lingual lipase
- secreted by serous cells beneath foliate and vallate papillae
- fat-digesting enzyme functional in stomach –> must be activated by acid in stomach
Salivary glands
Major salivary glands:
- produce saliva and lie outside oral cavity
- parotid, submandibular, and sublingual
Minor salivary glands
-scattered thoughout oral cavity –> augment slightly
Functions of saliva
cleanse mouth
dissolve food chems for taste
moistens food –> compacts into bolus
begins breakdown of starch with enzymes
Submandibular gland and Sublingual gland
Submandibular
- medial to body of mandible
- duct opens at base of lingual frenulum
- secretes mixture of enzyme and mucous saliva
Sublingual gland
- anterior to submandibular gland uner tongue
- opens via 10-12 ducts into floor of mouth
- secretes a more mucous rich saliva
Parotid gland
- anterior to ear –> external to masseter muscle
- parotid duct opens into oral vestibule next to second upper molar
- mumps is inflammation of parotid glands
- secretes a more watery, enzyme rich saliva
Composition of saliva
97-99.5% water; slightly acidic
- electrolytes = Na, K, Cl, PO4, HCO
- salivary amylase and lingual lipase
- mucin
- metabolic wastes: urea and uric acid
- lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms
control of saliva
1500 ml/day
-intrinsic glands continuously keep mouth moist
major salivary glands activated by parasympathetic nervous system when:
- ingested food stimulates chemoreceptors and mechanoreceptors in mouth
- salivatory nuclei in brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX
Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)
Digestive processes that happen in the mouth
ingestion mechanical breakdown (chewing) propulsion (deglutition = swallowing) digestion (salivary amylase and lingual lipase) NO ABSORPTION (except for a few drugs)
Pharynx
food passes from moth to oropharynx to laryngopharynx
- allows passage of foods, fluids, and air
- stratified squamous epithelium lining; mucus producing glands
- skeletal muscle layers: inner longitudinal and outer pharyngeal constrictors
Oropharynx = digestive and respiratory func Laryngopharynx = digestive and respiratory func Nasopharynx = just respiratory; no digestion
Esophagus
Secretes mucus, transports food –> no enzymes and no absorption
Mucosa = protection against wear and tear: stratified squamous epithelium
Submucosa secretes mucous
Muscularis divided in thirds
- Superior 1/3 = skeletal muscle
- Middle 1/3 = skeletal and smooth muscle
- Inferior 1/3 = smooth muscle
- 2 sphyncters = upper esophageal (regulates movement into esophagus) and lower esophageal (regulates movement into stomach)
Adventitia - no serosa - attaches to surroundings
Deglutition
involves tongue, soft palate, pharynx, and esophagus
- requires coordination of 22 muscle groups
- Buccal phase = voluntary contraction of tongue
- Pharyngeal-esophageal phase = involuntary (primary vagus erve) –> control center in medulla and lower pons
Actual steps of deglutition
- buccal phase: UES is contracted and tongue presses against hard palate, forcing food bolus into oropharynx
- pharyngeal-esophageal phase starts as uvula and larynx rise to prevent food from entering respiratory passageways–> tongue blocks moth and UES relaxes to let food into esophagus
- constrictor muscles of pharynx contract, forcing food through esophagus –> UES contracts after food has entered
- peristalsis moves food through esophagus to stomach
- LES, surrounding cardinal oriface opens and food enters stomach
