Digestive System Review

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