Alimentary canal
organs that food (or waste) pass through
Organs of alimentary canal
mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus
Accessory organs
organs that secrete substances that aid the digestive process
Accessory digestive organs
teeth, tongue, salivary glands, gallbladder, liver, pancreas
Mechanoreceptors/stretch receptors
upregulates the digestive process if the stomach stretches
Intrinsic gut influences
the gut brain; a plexus of nerves in the wall in the GI tract allow organs to communicate; coordinate physical digestion
Extrinsic gut influences
hormones can be secreted by stomach and small intestine that will affect other digestive organs; come from outside the gut
Peritoneum
membrane of connective tissue
Visceral
surrounds organs
Parietal
lines inside of abdominal cavity
Peritoneal cavity
houses organs, produces peritoneal fluid that allows organs to move easily during digestion
Peritonitis
bacteria from a burst appendix leak into the abdominal cavity, causing infection and inflammation
Mesentery
double layer of peritoneum that extends from the digestive organs to the parietal peritoneum; provides a pathway for blood vessels and nerves to reach digestive organs
Splanchnic circulation
arterial blood from aorta that serves the digestive organs
Mucosa
innermost layer of epithelium; secretes mucus, digestive enzymes, provides barrier to pathogens and enzymes
Soft palate
rises to close nasopharynx during swallowing
Tongue
interlacing bundles of muscles; grips and tastes food, assists in mechanical digestion; papillae add roughness to the tongue and house taste buds
Saliva
moistens food, begins digestion of complex carbs, dissolves chemicals, cleanses the mouth; contains enzymes and electrolytes and immune-related chemicals
Esophagus
muscular tube superior to the stomach; propels food into the stomach via peristalsis
Gastroesophageal Sphincter
connects the esophagus to the stomach; keeps stomach contents in the stomach
Stomach
has oblique muscles that allow for more movement, ie churning of food; contains parietal and chief cells; held in place by the omentum; muscles run in 3 diff directions to be able to squish food around
Rugae
stretch in the stomach when eating to make space for more food
Omentum
attaches curvatures of stomach to parietal peritoneum
Parietal cells
secrete HCl that gives the stomach contents a pH between 1.5-3.5; secrete intrinsic factor that helps absorb B12 in the small intestine which helps with erythrocyte production
Chief cells
produces pepsin in the acid of the stomach which digests proteins
HCl
denatures proteins into simpler shape, making it easier for enzymes to catabolize them
Pepsin
enzyme that degrades proteins; chops off individual amino acids so that they can be easily absorbed into your capillaries
Cephalic reflex
sensory input from nose, eyes, thoughts, etc increases gastric secretion rates (prepares for food)
Gastric (regulation of gastric secretion)
distension of stomach (stretching), partially digested proteins, and increases in pH stimulate secretion; feedback loop because the more you eat, the more acid is produced
Intestinal (regulation of gastric secretion)
when intestines receive process food from the stomach, the pyloric sphincter will close and decrease gastric secretion rates
Pyloric Sphincter
connection between the stomach and small intestine; opens and closes to allow chyme in at a small amount at a time so that stomach has time to process food before sending it down; prevents too much acid from going down at a time that’d burn the intestine
Motility
serves to mix food and create chyme; stomach will relax when anticipating food; only small amounts of chyme are allowed into the small intestine by the sphincter; more stretch = more mixing
Small Intestine
digestion is completed here; extends from pyloric sphincter to ileocecal valve; roughly 7-13 ft in living people but longer in the dead because muscles relax; wall includes intestinal crypts, enteroendocrine cells, and immune cells
Duodenum
receives chyme from stomach, bile from liver, and pancreatic juice; bile and pancreatic juice are controlled by the hepatopancreatic sphincter
Jejunum
extends from duodenum to ileum
Ileum
extends from jejunum to the large intestine
Intestinal crypts
cells that secrete intestinal juice which facilitates absorbing nutrients from chyme
Enteroendocrine cells
release hormones for communication with other organs
Pancreas
lies deep to the greater curvature of the stomach; produces pancreatic juice; main pancreatic duct delivers juice to the duodenum by fusing with bile duct
Pancreatic Juice
high pH helps neutralize stomach acid; contains enzymes to break down all organic macromolecules
Liver
largest gland in the body; under the ribcage, superior and anterior to stomach; produces bile which is exported to the duodenum to aid digestion; filters and processes blood to remove dead cells, toxins, and metabolites
Portal triad
hepatic artery, bile duct, hepatic portal vein
Hepatic artery
brings oxygenated blood to the cells
Hepatic portal vein
brings deoxygenated blood from the digestive system to the liver to detox the germs you could’ve eaten; run through multiple times to detox; ultimately delivers to the heart
Bile duct
put into the gallbladder bile made from the liver cells
Gall Bladder
located under the ventral surface of the liver; stores bile not immediately needed for digestion and concentrates bile by removing water
Large Intestine
frames the small intestine on three sides; removes water from the food to reduce water loss; stores feces prior to defecation; water is being removed as it travels and put back into the blood via the mesentery; has a huge bacteria population because they’re symbiotic bacteria
Rectum
holds feces until defecation; stretch receptors initiate muscle contraction; muscles in rectal walls flex, internal anal sphincter is relaxed; external (voluntary) anal sphincter is allowed to open, allowing excretion
Salivary glands
produces saliva; scattered throughout the oral cavity
Peristalsis
movement of food or waste through the system; automatic wave-like movement
Hepatocytes
cells in the liver that produce bile
Bile
alkaline (high pH) emulsifier produced by the liver and exported via common hepatic duct; neutralizes pH with pancreatic juice of the stomach acid; makes it so that fat can be broken down into smaller pieces and able to get to the water soluble enzymes in the small intestine to be absorbed
Emulsifier
takes fat and breaks it up into smaller pieces to allow it to mix with water easier
Why does the stomach need acid and enzymes?
the acid denatures the proteins while the enzymes actually digests them and makes them into smaller pieces for the small intestine
How are digestive processes regulated?
sensors (mechano and chemo) are present in the walls of the alimentary canal; stretch and pH receptors; stimulation of receptors causes changes in the function of the digestive system (can cause hormone release and peristalsis)
Why does the stomach need a low pH?
acts as an immune barrier to bacteria; denatures proteins to allow enzymes to get in and break them down
Why do you need to produce amylase in your pancreas if it's already in your mouth?
When you swallow saliva, the amylase becomes denatured because the pH goes from 7 (its optimal pH) to lower; if you have any carbs left, you need to produce more amylase which is why its also in the pancreas to digest in the small intestine; constantly make new enzymes on the trip because it’s getting destroyed as it goes down
What is the structure of the small intestine and why?
circular folds slow food down for efficient absorption; villi increase surface area and contain microvilli that also release enzymes for digestion
Why should the pH in the small intestine be high?
it doesn’t contain the mucus of the stomach so it’d be burned by acid; if a coating of mucus is present in the SI, you can’t really absorb anything
How do you know that you should stop eating?
The stretch receptors in your stomach are stimulated the more the rugae are stretched out
How does one part of your alimentary canal communicate with the other?
the hormones released by different organs in the body communicate with each other in the blood stream and the nerves signal them
How are the layers of tissue organized in the organs of the alimentary canal? What are their functions?
made of connective tissue, epithelial, and muscle; connective tissue provides a barrier to bacteria, epithelial tissue Produces mucus which lubricates food and protects cells and produces enzymes and hormones, the muscle allows for peristalsis to happen
What regulates peristalsis?
Pacemaker cells set the rhythm of peristalsis in combination with neural and hormonal factors
What controls salivation?
food ingestion, Mechano and chemoreceptors in the brain send messages to the salivatory nuclei, neural input
How does the liver “filter” the blood?
blood from the gut goes to the liver cells and as they go through, it removes dead cells, toxins, and metabolites
Why are there such drastic changes in pH during digestion? How is pH influenced?
as more food is put into the stomach, the pH increases because the food doesn’t have a low pH; it’s influenced by the amount of food in your stomach, sensory input which increases gastric secretion
What is the role of enzymes in digestion?
enzymes break down proteins and digests them to make them smaller and allow for absorption
Why do you harbor so many bacteria in you large intestine?
Symbiotic bacteria; the bacteria further breaks down the waste as it waits to be excreted and gets the nutrients
What produces the enzymes in your stomach?
chief cells produce pepsin which breaks down/digests proteins