Chapter 23- The digestive system Flashcards
Functions of the digestive system (6)
- Ingestion
- Movement
- Mechanical breakdown
- Digestion
- Absorption
- Defecation
How does movement occur in the digestive system?
Food propelled through digestive system by peristaltic movement. Peristaltic movements are wavelike contractions moving food in one direction- uses smooth muscle tissue
How does mechanical breakdown occur in the digestive system?
Food broken down into smaller pieces to increase efficiency of digestion. Increases the surface area of food that’s exposed to digestive substances
Membranes of the digestive system (2)
- Peritoneum
2. Mesentery
Peritoneum
Serous membrane that covers organs of the abdominopelvic cavity. The visceral peritoneum covers organs, while the parietal peritoneum clings to body wall
Peritoneal cavity
Fluid filled space between visceral and parietal peritoneum. Function- prevents friction form organ/organ or organ/body wall contact
Mesentery definition
Double layer of peritoneum extending from digestive organs to body wall
Mesentery functions (3)
- Holds organs in place
- Providing passage for blood/lymphatic/nerve supply to digestive organs
- Fat storage
Alimentary canal (6 organs)
Portion of digestive system that forms one long tube in- out of the body. Includes- mouth, pharynx, esophagus, stomach, small intestine, large intestine. Has associated accessory glands
4 basic layers of the alimentary canal organs
- Mucosa- innermost layer
- Submucosa- lies external to mucosa
- Muscularis externa
- Serosa- outermost layer is the visceral peritoneum
3 subdivisions of the mucosa
- Epithelia
- Lamina propria
- Muscularis mucosa
Epithelia of the mucosa
Epithelia is mostly simple columnar. Function- secretes mucus, digestive enzymes, hormones. Exceptions- mouth, esophagus, and anus- stratified squamous
Lamina propria
Vascularized loose areolar connective tissue. Allows absorption of nutrients. Lymph supply (MALT)- tonsils and appendix- protection from infectious disease
Muscularis mucosa
Has smooth muscle cells, creates movement to increase digestion and secretion. Digestive enzymes that break down food molecules and hormones are secreted. Not the most important layer for creating movement
Submucosa
Lies external to mucosa. Areolar connective tissue with elastic fibers- organs can stretch. Rich supply of blood and lymphatic vessels, lymphoid follicles, nerve fibers- serve surrounding layers of GI tract. BV keep the submucosa healthy, but also provides blood supply to surrounding layers
Muscularis externa
Muscular layer that generates peristaltic movement of GI tract. Thickenings in muscularis externa form sphincters. Functions- controls movement from one alimentary organ to another and prevents back movement of ingested food. The 2 layers can’t contract at the same time since they have opposite functions. To produce movement, the layers contract asynchronously
2 layers of the muscularis externa
- Circular layer- contraction causes tube to constrict
2. Longitudinal layer- contraction causes tube to become wider
Serosa
Outermost layer is the visceral peritoneum. In organs not found in abdominopelvic cavity (esophagus), the serosa is replaced by adventitia. Dense connective tissue that binds organ to surrounding structures- tougher and more fibrous than visceral peritoneum
Splanchnic circulation
Blood supply to digestive organs. Arteries that branch off aorta and hepatic portal circulation
Arteries of splanchnic circulation
Arteries- branches of celiac trunk that serve spleen, liver, and stomach. Hepatic artery, left gastric, splenic arteries. Splenic artery not part of digestive system
Hepatic portal circulation
Collects nutrient rich blood draining from digestive organs and transports it to the liver. In portal circulation, the blood skips the heart and goes to another organ. The digestive organs bring in new nutrients- don’t want the heart or the brain to be exposed to unstable conditions. Blood goes to the liver so it can be processed and toxins can be removed
2 major intrinsic nerve complexes of the enteric nervous system
- Submucosal nerve plexus- found in submucosa
2. Myenteric nerve plexus- found between circular and longitudinal muscle layers
Function of ENS nerve plexuses
Function- both plexuses supply walls of entire GI tract and help regulate motility through it
ENS long reflex
Initiated by stimuli inside and outside the GI tract. Involves CNS and extrinsic autonomic nerves- sympathetic and parasympathetic. Sympathetic stimulation inhibits gastric activity, while parasympathetic stimulation enhances gastric activity