Gastrointestinal System Flashcards
What are the 3 main components of the digestive system?
- digestive tracts
- accessory organs
- cell lining and tissue components
What are the functions of the GIT?
- ingestion
- mechanical digestion and processing
- chemical digestions
- secretion (e.g. enzymes, acids, salts) by glandular organs
- absorption of vitamins, nutrients, water and minerals
- defecation (waste elimination through the anus)
- defence
What are the 7 components of the oral cavity?
- lips
- front 2/3 of tongue
- floor of the mouth
- buccal mucosa
- upper and lower gingiva
- retromolar trigone
- hard palate
What is the hard and soft palate respectively?
- hard = front part of roof of mouth
- soft = back part
What are functions of the oral cavity?
- mastication and lubrication to produce a bolus
- gustation (taste)
- limited chemical digestion of glucose and lipdis
What are functions of the uvula?
- secrete saliva to moisten the mouth and throat
- prevents food and liquid from going up the nose (along with soft palate)
What are functions of the tongue?
- mechanical digestion
- manipulation of food
- sensory taste and temperature
- lubrication via mucin, water and lingual lipase
What are teeth required for?
tearing and grasping food (mastication)
What do the major salivary glands do?
work together to keep the mouth moist and help with digestion
What are the 3 major salivary glands?
- parotid glands
- submandibular glands
- sublingual glands
Where are the parotid glands and what do they produce?
near the back of the jaw just in front of the ears and produce serous secretion to help with chewing and swallowing
Where are the submandibular glands and what do they produce?
under the jaw and produce a mix of mucus and saliva
Where are the sublingual glands and what do they produce?
under the tongue and produce saliva that is mostly mucus
What do minor salivary glands secrete?
mucous
What is the difference between serous and mucous cells?
- serous cells have spherical and vesicular nuclei and secrete a more watery substance
- mucous cells cytoplasm and nuclei are pushed against the basal cell membrane and secrete mucin
What are functions of saliva?
- lubricate and moisten the bolus
- dissolve chemicals for gustation
- act as a buffer
- control oral bacteria population via antibodies and lysozymes
- salivary reflex
What is the pharynx (throat)?
the muscle-lined space that connects the nose and mouth to the larynx and oesophagus
What is the larynx?
the upper opening into the trachea (windpipe)
What are the 4 phases of swallowing?
- buccal phase - voluntary phase where the tongue pushes the bolus to the back of the mouth towards the pharynx
- pharyngeal phase - involuntary phase begins when the bolus reaches the back of the throat which triggers a reflex that closes off the airway and moves the bolus down through the pharynx to the oesophagus
- oesophageal phase – involuntary phase where the bolus is pushed down the oesophagus towards the stomach by peristalsis
- bolus enters the stomach by triggering the opening of the lower oesophageal sphincter
What is mucosa?
the moist, inner linings of organs and body cavities
What are the 3 layers of mucosa?
- mucosal epithelium
- lamina propria
- muscularis mucosae (deepest and most active)
What parts of the digestive system have stratified squamous epithelium?
- oral cavity
- pharynx
- oesophagus
- anal canal
What parts of the digestive system have simple columnar epithelium?
- stomach
- small intestine
- large intestine
What is the muscularis mucosae made up of?
smooth muscle and elastic fibres that regulate contraction of the lumen
What are the 2 layers of the muscularis mucosae?
- inner – circular muscle
- outer – longitudinal
What is the submucosa?
a connective tissue layer that binds the mucosa and muscular layer
What does the submucosa contain?
- blood vessels, lymphatic vessels and nerve fibres
- exocrine glands that secrete buffers and enzymes in the lumen of digestive tracts
Why is the mucosa lined close to the muscular layer?
for protective functions, effective nutrient absorption and coordination of functions
What is the muscular layer movement of the mucosa coordinated by?
the enteric nervous system which innervates the myenteric plexus
What do pacesetter cells do?
spontaneously trigger action potentials and contractions in the muscle
What is peristalsis?
the rhythmic wave of contraction that propels the bolus
What is segmentation?
the back and forth movement caused by a local reflex in the small and large intestines required to churn, fragment and mix the stomach contents in no pattern or specific direction
What does the oesophageal submucosa contain?
- oesophageal glands that secrete mucous
- a muscular layer containing superior skeletal and inferior smooth muscle
What does the oesophageal adventitia do?
anchor the oesophagus to the posterior body wall
What do the upper and lower oesophageal sphincters do respectively?
- upper prevents air flowing into the oesophagus while breathing
- lower prevents food from flowing back up the oesophagus
What is the peritoneum?
the serous membrane that lines the abdominal cavity composed of mesothelial cells supported by a thin layer of fibrous tissue
What are mesenteries?
double sheets of peritoneal membrane that stabilise digestive tracts and prevent volvulus
What does the lesser omentum hold?
the liver and top part of the stomach
What does the greater omentum hold?
the bottom part of the stomach (pouch of adipose tissue)
What is the falciform ligament?
a thin, sickle-shaped, fibrous structure that connects the anterior part of the liver to the ventral wall of the abdomen
What is the mesentery proper?
the mesentery for the duodenum (small intestine) and pancreas
What is the mesocolon?
the mesentery for the colon (large intestine) and rectum that attaches to the abdominal wall
What are the 4 layers of the digestive tracts?
- mucosa
- submucosa
- muscular layer
- visceral peritoneum
What are functions of the stomach?
- storing food
- mechanical and chemical digestion
- site of chyme (digested bolus)
What are rugae?
ridges produced by folding of an organ wall present in the stomach for expansion
What are the 4 parts of the stomach?
- cardia – oesophagus entry; protects the oesophagus from stomach acids and enzymes
- fundus – superior region that forms many gastric secretions
- body – between fundus and pylorus
- pylorus – entry to duodenum (small intestine)
Does absorption happen in the stomach?
no
What are gastric pits?
indentations in the stomach which denote entrances to the tubular shaped gastric glands (deepest in the pylorus)
What do parietal cells secrete?
intrinsic factor (B12) and indirect HCl (kills microorganisms, denatures proteins and breaks down connective tissues in food)
What do chief cells secrete?
pepsinogen for protein digestion (require an acidic environment)
What do G (enteroendocrine) cells secrete?
gastrin which stimulates the gastric glands and contracts muscle wall
What do D cells secrete?
somatostatin to inhibit G cells
What is the pancreas?
a lumpy globular organ that delivers pancreatic secretion to the duodenum via the pancreatic duct
What are pancreatic islets?
cells in the pancreas that secrete insulin and glucagon
What are pancreatic acini?
the functional units of the pancreas formed of simple cuboidal epithelium
What is pancreatic juice secreted by?
pancreatic acini
What is the primary site of lipase production?
pancreatic juice
What happens when chyme reaches the duodenum?
secretin and CCK are released which trigger pancreatic secretion
What are the digestive enzymes in pancreatic juice?
- amylase
- lipase
- nucleases
- inactive proteolytic enzymes for small intestine protein digestion e.g. trypsin, chymotrypsin, carboxypeptidase and elastase
What is the liver made up of?
4 lobes
What is the porta hepatis/hilum of the liver?
a transverse fissure located in the inferior surface, where the major vessels and ducts enter or leave the organ
What is the blood supply to the liver?
1/3 hepatic artery and 2/3 hepatic portal vein to the inferior vena cava
What are the main functions of the liver?
metabolism, haematological and bile production and secretion
What are the metabolism functions of the liver?
- metabolises glucose, lipids and amino acids
- removes waste and toxins
- stores vitamins A, D, E, K and B12
- primary site of drug metabolism; enzymes convert active drugs to inactive forms
- mineral storage e.g. iron
What is the haematological function of the liver?
- largest blood reservoir
- synthesises plasma proteins
- removes old or damaged blood cells
What is the liver’s involvement in bile production and secretion?
- contains bile salts (bile acids conjugated with either taurine or glycine residues)
- emulsification of lipids to assist enzymes in the breakdown of lipids to fatty acids
Give examples of liver pathological conditions
hepatitis, liver cancer, cirrhosis
What are the functional units of the liver?
hexagonal lobules that consist of plates of hepatocytes arranged around a central vein
What are sinusoids?
blood-filled spaces between hepatocyte plates that allow close contact between the blood and liver cells
What are sinusoids lined with?
specialised cells like Kupffer cells (stellate macrophages) that help remove debris and old red blood cells
What is present at the corner of each liver lobule?
portal triads containing a branch of the hepatic artery, a branch of the portal vein, and a bile duct
Describe the pathway of bile secretion
- hepatocytes secrete bile into bile canaliculi regulated by CCK
- bile canaliculi merge to form larger ducts and eventually lead to liver bile ducts
- bile flows into the common hepatic duct and is stored temporarily in the gallbladder
- release of CCK by the duodenum triggers dilation of the hepatopancreatic sphincter and contraction of the gallbladder, which ejects bile into the duodenum through the duodenal ampulla
What does bile do?
aids in digestion, particularly in breaking down fats
What does the gallbladder do?
concentrate bile
What is bile made from?
recycled cholesterol, lipids, bilirubin, water and ions
What is the small intestine responsible for?
90% of absorption
What are the 3 parts of the small intestine?
duodenum, jejunum and ileum
What are the primary blood vessels of the small intestine?
superior mesentery artery and vein
What do the circular folds of the small intestine do?
slow the passage of the partly digested food and afford an increased surface for absorption
What are the circular folds of the small intestine covered in?
villi lined with simple columnar epithelium and microvilli
What does the brush border of the small intestine contain?
brush border enzymes that digest the products of luminal digestion to produce monosaccharides
What does the lamina propria of the small intestine contain?
capillaries that carry blood to the hepatic portal circulation
Where are chylomicrons produced?
in the epithelial cells of the small intestine
What is the function of chylomicrons?
transport of dietary triglycerides and cholesterol to peripheral tissues and liver
What is the main function of the duodenum?
receive chyme and neutralise acids to protect the lining
What are the 3 cells of the duodenum and what do they do?
- goblet cells - synthesise and secrete mucins
- intestinal crypt cells - solubilise chyme and neutralise gastric acid
- paneth cells - convey innate immunity via secretion of defensins and lysosomes
Where are Brunner’s glands and what do they do?
in the submucosa of the duodenum that secrete an alkaline fluid containing mucin, which protects the mucosa from the acidic stomach contents entering the duodenum
What does urogastrone do?
inhibit gastric acid secretion
What happens in the jejunum?
the bulk of chemical digestion and absorption
Describe the presence of circular folds throughout the small intestine
- duodenum - none
- jejunum - only in middle part
- lieum - only in proximal part
What does the ileum end with?
the ileocecal valve, which is a sphincter that controls entry into the cecum
What are Peyer’s patches?
specialised aggregates of lymphoid follicles in the lamina propria of the ileum responsible for recognising and processing antigens
What is the large intestine involved in?
- water absorption
- waste excretion
- vitamins K and B4 absorption (by microbiome)
What is the cecum?
the pouch that forms the first part of the large intestine and controls entry through the ileocecal valve
What does the colon contain?
- haustra - pouches that allow expansion and elongation of the colon
- teniae coli - smooth muscle bands in the colon wall that create haustra
- omental appendices - pouches of peritoneum filled with fat attached to the external surface of the large intestine
What is the rectum?
the last section of the large intestine that connects the colon to the anus (site of stool storage before bowel movement)
Where is the appendix?
between the small intestine (cecum) and large intestine (colon)
Describe the pathway of the colon
- ascends from the cecum and bends at the right colic flexure to become transverse colon
- transverse colon bends at the left splenic flexure
- descending colon reaches the iliac fossa and is firmly attached to the abdominal wall
What is the colon blood supply?
superior and inferior mesentery arteries and veins
What does the colon epithelium contain?
- large lymphoid nodules at the lamina propria
- muscular layer at the teniae coli to help with haustra-haustral churning
- no villi
- goblet cells that secrete mucus to lubricate faeces
How does colorectal cancer develop?
from polyps (growths) in the colon’s inner lining
What happens to the epithelium at the anal canal?
it transitions from columnar to stratified squamous
What does the anal opening have?
keratinised skin that has several folds while contracted
What are the 2 anal sphincters?
- internal - involuntary
- external - voluntary
