Digestive system Flashcards
what are the functions of the digestive system?
ingestion, digestion, propulsion, absorption and defecation
ingestion
taking food in, occurs in the mouth
digestion
breaking down food into smaller particles to release nutrients
propulsion
movement of food along the digestive tract
absorption
transport of nutrients from the lumen of the gastrointestinal tract to the blood
defecation
elimination of waste and indigestible substances from the gastrointestinal tract as feces that passes through the anal canal
alimentary canal
aka gastrointestinal or GI tract, tube extending from the proximal opening of the mouth to the distal opening of the anus
mouth
functions include ingestion, mastication, mixes food with saliva, forms a bolus
pharynx
functions include the pharyngeal phase of deglutition
esophagus
functions include the esophageal phase of deglutition
stomach
functions include secretion of acidic gastric juice leading to formation of chyme (semi-fluid composed of partially digested food) from a bolus
small intestine
primary location of chemical digestion and nutrient absorption, has three major regions-duodenum, jejunum, and ilium
duodenum
short proximal segment that receives chyme from stomach and exocrine secretions from the pancreas and liver/gall bladder, responsible for most chemical digestion and some nutrient absorption
jejunum
long middle segment responsible for most nutrient absorption. surface is highly folded with large circular folds called plicae circulares covered in smaller folds called villi
ilium
longest and most distal segment responsible for some nutrient absorption, drains into the large intestine, contains numerous peyer’s patches (lymphoid tissue)
large intestine (colon)
absorbs most of remaining water and some nutrients, forms feces, eliminates feces in the process of defecation
accessory organs that assist with digestion
- salivary glands-produce saliva that lubricates food and contains enzymes
- pancreas-produces digestive enzymes and bicarbonate
- liver-produce bile salts which emulsify lipids
- gall bladder- stores concentrates and releases bile salts
what is the function of teeth?
mastication begins mechanical digestion by breaking down food into smaller pieces
deciduous teeth
20 teeth-emerge from ages 6 to 24 months
permanent teeth
32 teeth, most emerge from ages 6-12 years, 3rd molar 17-25 years
incisors
2 per quadrant
canine
1 per quadrant
premolars
2 per quadrant replace the deciduous molars
molars
3 per quadrant
crown
exposed portion of tooth covered in enamel (hardest substance in the body)
neck of tooth
contacts the gingiva (gums)
Root of tooth
connected to dental alveolus (tooth socket) by periodontal ligament
dentin
deep to the enamel, consists of calcified CT and gives tooth its shape
pulp cavity of tooth
blood vessels and nerves, root canal extend into the root
cementum
surrounds the dentin in the roots, attaches root to the periodontal ligament
Parotid salivary gland
superficial to the masseter muscles, duct opens near 2nd upper molar
submandibular salivary gland
lies on the medial aspect of the mandible, duct opens near base of the lingual frenulum (fold of mucous membrane connecting the tongue to the floor of the oral cavity)
sublingual salivary gland
lies under the tongue, 10-12 ducts open to the floor of the oral cavity
What is the organization of the esophagus?
Mucosa
Submucosa
Muscularis externa
Adventitia
Mucosa of esophagus
innermost layer lining lumen, mucus membrane epithelium
*non keratinized stratified squamous epithelium
Submucosa of esophagus
second layer, dense irregular CT layer, contains nervous tissue, large blood vessels, and large lymphatic vessels
Muscularis externa of esophagus
third layer, layers of muscle and nervous tissue surrounding submucosa. Composed of skeletal muscle in the proximal region and smooth muscle through the middle and distal portions
Adventitia of esophagus
superficial sheath of dense irregular CT
What is the organization of the stomach?
Mucosa Lamina propria Muscularis interna Submucosa Muscularis externa Serosa
Mucosa of stomach
innermost layer lining the lumen, mucus membrane epithelium
*simple columnar epithelium, folds in to form gastric pits (glands) that contain the cells that secrete gastric juice
Lamina propria of stomach
layer of areolar CT, contains numerous blood and lymphatic vessels that transport nutrients following absorption
Muscularis interna of stomach
layer of smooth muscle in the stomach and intestines that forms the border between mucosa and submucosa and contracts to produce folds that increase surface area
Submucosa of stomach
dense CT layer, contains nervous tissue, large blood vessels, and large lymphatic vessels
Muscularis externa of stomach
layers of muscle and nervous tissue surrounding the submucosa. Composed of smooth muscle arranged in three laters- oblique layer(deepest), circular layer (middle) and longitudinal layer (superficial)
Serosa of stomach
aka visceral layer of peritoneal membrane this serous membrane forms outermost lining and attaches to the mesentery (folds of peritoneal membrane)
Lesser omentum (mesentery of the stomach)
between the liver and the lesser curvaturenof the stomach, Contains the left and right gastric arteries
Greater omentum (mesentery of stomach)
extends from the greater curvature of the stomach and drapes inferiorly over the anterior of the intestines folding up to attach to the transverse colon
Duodenum
first portion of small intestine- contains numerous brunner’s glands
Jejunum
second portion of small intestine- largest plicae circulares and longest villi in mucosa
ilium
contains peyer’s patches
Right and left lobes of liver
right is larger lobe, separated by falciform ligament
caudate lobe of liver
on the posterior along the right side of the inferior vena cava
quadrate lobe of liver
rectangular shaped lobe immediately to the left of the gallbladder
Lobule
structural units of the liver, consisting of plates of hepatoctyes situated around a central vein
portal triad
branch of hepatic portal vein, hepatic proper artery, and bile duct
*blood from hepatic portal veins and hepatic arteries empty into sinusoids then drains through the central vein to hepatic veins exiting the liver
hepatocytes
liver cells lining the sinusoids, absorbs and secrete materials into the blood, produce bile
bile canaliculi
narrow channels that carry bile away from the hepatocytes empty into bile ducts at the portal triad
What is the path of bile from the liver?
- Right and left hepatic ducts merge to form common hepatic duct
- Common hepatic duct merges with the cystic duct to form the common bile duct
- common bile duct merges with the main pancreatic duct to empty into the duodenum
pancreas
posterior to stomach and parietal layer of the peritoneal membrane (retroperitoneal)
pancreatic acini
clusters of exocrine cells producing the pancreatic juices containing bicarbonate (a base that neutralizes acidity raising the pH of the chyme from the stomach)
*pancreatic juice is excreted through the pancreatic ducts into the duodenum
Organization of colon
mucosa
muscularis externa
serosa
mucosa of colon
simple columnar epithelium with a brush border of microvilli, contains numerous goblet cells, infoldings form indentations called intestinal crypts but there are no villi
muscularis externa of colon
longitudinal layer-contractions decrease the length of alimentary canal-forms three narrow parallel bands called the tenia coli that produce haustra (bulging segments)
Serosa of colon
aka visceral layer, transverse mesocolon-connects transverse colon to the posterior wall of the abdomen, contains the middle colic artery
