Chapter 24.1-24.6 Flashcards
list the major digestive organs
oral cavity
pharynx
oesophagus
stomach
small intestine
large intestine
rectum
anus
list the accesory digestive organs
salivary glands
liver
gall bladder
pancreas
name the 3 regions of the small intestine
duodenum
jejunum
ileum
what are the six major functions of the digestive system
ingestion and mastication
propulsion and mixing
secretion
digestion
absorption
elimination
why is it important for solid foods to be mechanically broken down by mastication
- digestive enzymes only effective on outer surface of food particles
- to increase total surface area for digestion
define propulsion
the movement of food from one end of the digestive tract to another
define mixing
the movement of food back and forth in the digestive tract without forward movement
what is the correct order of propulsive movement
swallowing
peristalsis
mass movements
what are peristaltic waves
muscular contractions
- wave of relaxation of the circular muscles in front of the mass of undigested food (chyme)
followed by
-wave of strong contraction of the circular muscles behind the chyme forcing bolus along the digestive tract
what are mass movements
contractions that move material in the distal parts of the large intestine to the anus
what are mixing waves
gentle stomach contractions that churn food with gastric secretions
then released to small intestine as chyme
what are segmental contractions
mixing of food particles with digestive secretions in the small intestine
describe the process of segmental contraction
-mass of chyme begins at one location
-segments of digestive tract alternate between contraction and relaxation
-mass of chyme spreads out in both directions
what is the role of secretions
-lubricate (food)
-liquefy (food)
-buffer (food)
-digest (food)
Define digestion
the breakdown of large organic molecules into their individual components
Define absorption
the movement of molecules out of the digestive tract and into the blood or lymphatic system
-depending on molecule, they may pass out by diffusion, facilitated diffusion, active transport, symport or endocytosis
Define elimination
the process by which the waste products of digestion are removed from the body
What are the 3 major types of glands associated with the digestive tract?
- unicellular mucus glands in mucosa
- multicellular glands in mucosa and submucosa
- multicellular glands outside digestive tract
What is the innermost tunic of the GI tract (in contact with the lumen)
the mucosa
What does the mucosa consist of
- mucous epithelium
- lamina propria
- muscularis mucosae
Describe the structure and function of the mucous epithelium
- non-keratinised stratified squamous epithelium in mouth, pharynx, oesophagus and anal canal
- simple columnar epithelium in remainder of GI tract
- layer of epithelial cells- absorbs material into capillaries/lymph lacteals
- protects from gut abrasion and exocrine/endocrine and enteroendocrine secretions
Describe the structure and function of the lamina propria
- loose connective tissue
- contains Peyer’s patches
- contains capillaries and lymph vessels
- involved in inflammatory response
Describe the structure and function of the muscularis mucosae
- thin outer layer of smooth muscle
- controls folding of GI wall
What are the 2 types of specialised cells in the mucosa
-mechanoreceptors
-chemoreceptors
List the tunica of the GI tract from innermost to outermost
-mucosa
-submucosa
-muscularis externae
-serosa/adventitia
Describe the structure and function of the submucosa
- thick layer of connective tissue
- network of neurons and glial cells form submucosal plexus of the ENS (directly in contact with mucosa)
- oesophagus and stomach lack submucosal plexus
- sensory function and regulation of secretory activity
Describe the structure and function of the muscularis externae
-inner layer of circular smooth muscle
-outer layer longitudinal smooth muscle
-between 2 layers : myenteric plexus
-myenteric plexus: more extensive than submucosal and controls GI tract motility
-exceptions: upper oesophagus (skeletal) and stomach (3 layers)
-responsible for peristalsis and segmentation
Describe the structure and function of the serosa/adventitia
-outermost layer
-loose connective tissue
-forms visceral peritoneum and is continuous with parietal peitoneum
-simple squamous epithelium
-protects GI tract when it moves
How is most nervous regulation of the GI tract controlled
-by the enteric nervous system (ENS)
-submucosal and myenteric plexuses
-also autonomic (ANS) innervation (mostly parasympathetic) through vagus nerves
What is the ENS capable of controlling in the digestive tract?
- peristaltic and mixing movements
- blood flow to tract
What is Hirschprung disease?
-painful developmental disorder
-caused by absence of enteric neurones in distal large intestine
-loss of function mutation in RET gene
-results in poor intestinal motility and severe constipation
Describe the chemical regulation of the digestive system
-acetylcholine (stimulates GI activity)
-norepinephrine (inhibits GI activity)
-serotonin (stimulates GI motility)
-95% body serotonin found in GI tract
-gastrin and secretin (regulates GI function)
-local chemical regulators eg. histamine
What is the peritoneum
-continuous serous membrane
-lining the walls and organs of the abdominal cavity
Describe the structure of the peritoneum
-serous membrane: smooth and secretes lubricating serous fluid
- membrane and fluid reduce friction as organs move
-portion that covers organs: visceral peritoneum
-portion that covers interior surface of abdominal cavity wall: perietal peritoneum
What is peritonitis?
-potentially life-threatening inflammation of the peritoneum
-resulting from chemical irritation (bile escape from damaged GI tract or infection
What are the main symptoms of peritonitis?
-acute abdominal pain and tenderness worsened by movement
-ascites can occur (accumulation of excess serous fluid in peritoneal cavity)
-ascites also present in starvation, alcoholism and liver cancer
Describe the regions of the oral cavity
-vestibule (space between lips or cheeks and teeth)
-oral cavity proper (lies medial to teeth)
Which type of epithelium is present in the oral cavity?
- non-keratinised stratified squamous
- protects against abrasion
Name the 2 dental arches
-maxillary arch
-mandibular arch
Describe the protective functions of saliva
- large volume of saliva (continually washes oral surface preventing bacterial infection)
- HCO3- (acts as buffer to neutralise acids produced by oral bacteria)
- lysozyme and immunoglobulin A (prevents bacterial infection)
-mucus protects GI tract from physical abrasion
Describe the action of salivary amylase
breaks covalent bonds between glucose molecules in starch and other polysaccharides to produce disaccharides maltose and isomaltose
Name the secretions released from the oral cavity
-serous saliva
-salivary amylase
-mucus
-lingual lipase
Name the salivary glands
-submandibular gland
-sublingual gland
-parotid gland
Identify the structures of the digestive tract that are lined with stratified squamous epithelium
- oropharynx
- mouth
- oesophagus
- anal canal
Name the structures through which a bolus enters and exits the stomach
- enters through lower oesophageal sphincter
- exits through pyloric sphincter
