HUBS192 Lecture 20 - Gastrointestinal System I: The Basic Structure of the GI System Flashcards
what is the primary function of GI system?
bring nutrients (from the external environment e.g food) into the internal environment so that they can be transported to all body cells to be utilised for growth and energy
what are the 4 things the GI system needs to be specialised for to perform its primary function?
1) motility
2) secretion
3) digestion
4) absorption
what is the function of motility in the GI system?
movement of things through the tract at an appropriate rate
what is the function of secretion in the GI system?
can be related to the:
- secretion of enzymes
- secretion of acid for digestion
- secretion of mucous for protection
- secretion of serous fluid for lubrication
what is the function of digestion in the GI system?
refers to the process of breaking things down into smaller particles
- mechanical digestion
- chemical digestion
what is mechanical digestion?
physically breaking things down into smaller parts to increase surface area
what is chemical digestion?
process that involves breaking down by enzymes
what is the function of absorption in the GI system?
absorb the smaller particles across the intestinal epithelium and into the blood for transport the cells
what are the 6 major organs of the digestive tract?
1) oral cavity (mouth)
2) pharynx
3) oesophagus
4) stomach
5) small intestine
6) large intestine
what are the 6 accessory structures of the digestive system?
1) teeth
2) tongue
3) salivary glands
4) liver
5) gallbladder
6) pancreas
what is the GI system in simple terms?
a long tube with outgrowths lined with epithelium that is closed off at both ends
-the accessory organs into the system via a duct system
what are sphincters?
bands of smooth muscle that regulate the passage of lumen content from one region to another and parties the GI tract into different functional compartments
what is the process of ingesting food material in terms of the structures it passes down?
- ingested into the oral cavity (mouth)
- then moves down to the pharynx when we swallow
- firstly into the oropharynx and then down into the laryngopharynx
- then moves down into the oesophagus
- then to the finally into the stomach (where it can be stored for up to 2 hours)
- moves down to the small intestine (nutrient absorption)
- moves down to the large intestine and then is excreted through the rectum
what is the start and end of the GI tract?
from the oral cavity to the anus
what is the type of epithelium in the mouth/oral cavity and the oesophagus? and what is the function of this epithelium?
- stratified squamous epithelium
- protects from abrasion
what is the type of epithelium in the stomach, small intestine, and large intestine? and what is the function of this epithelium?
- simple columnar epithelium
- secretion and absorption
what is the type of epithelium in the anal canal? and what is the function of this epithelium?
- stratified squamous epithelium
- protects from abrasion
what is the simplest form of a gland?
unicellular gland
what is the only unicellular gland in the body?
goblet cell
what are the 4 features that make up a goblet cell?
- columnar epithelium
- goblet shape
- apical mucous granules
- basal nucleus
what are multicellular glands?
epithelium that has invaginated to form glands
what are the 2 types of multicellular glands and what are they?
1) simple: gland with a single duct (e.g stomach an small intestine)
2) compound: gland with 2 or more ducts (e.g salivary glands)
- increased SA
what are the 4 layers of the gut tube?
1) mucosa (deep)
2) submucosa
3) muscularis (externa/proper)
4) adventitia (superficial)
what does the mucosa layer of the gut tube consist of?
- epithelium
- lamina propria (FCT)
- muscularis mucosae (muscle layer of the mucosa)
- lymphatics
- blood vessels
what does the submucosa layer of the gut tube consist of?
contains:
- glands
- blood vessels
- connective tissue
how is secretion regulated in the submucosa layer?
regulated by the submucosal nerve plexus which is part of the enteric (gut) nervous system (ENS)
what does ENS stand for?
enteric nervous system
what is the relationship between the enteric nervous system (ENS) and the central nervous system (CNS) input?
the ENS can act independently from CNS input
what does the muscularis layer of the gut tube consist of?
consists of smooth muscle in 2 main layers and the myenteric plexus
1) inner CIRCULAR layer (muscle cells arranged around the outside in circles of the tube)
2) outer LONGITUDINAL layer (muscle cells arranged parallel to the length of the tube)
what is the myenteric plexus and what is its function?
part of the enteric nervous system (ENS) located in-between muscle layers
- function is to regulate motility
what does the adventitia layer of the gut tube consist of?
layer of connective tissue (FCT) the helps to maintain the structure of the tube and adhere to outside structures
what is the serosa?
additional outer covering of the peritoneal cavity
-not one of the 4 layers of the gut tube
what is the peritoneum?
the peritoneum is a serous membrane (a layer of epithelial cells that secrete a watery serous lubricant fluid)
what is a serous membrane?
a layer of epithelial cells that secrete a watery serous lubricant fluid
what is the peritoneum composed of?
a parietal layer that lines the body wall (superficial) and a visceral layer that lines the organs (deep)
-between these layers is a fluid filled space
what is retroperitoneal?
posterior to the peritoneum
what is the function of the peritoneum?
allows the organs to move in a frictionless environment
what is the pancreas?
an important source of digestive enzymes which secretes into the small intestine
-does not peritoneum
what is an example of a retroperitoneal organ?
the pancreas
what is a mesentery?
double layer of visceral peritoneum that connects organ to body wall
what is the function of a mesentery?
connects an organ to the body wall
what is the omenta?
double layer of visceral peritoneum that connects an organ to another organ
what are the 2 types of omenta?
1) lesser omenta
- connects the liver to the stomach
2) greater omenta
- attachs to the stomach and folds up to attach to the transverse colon
what is the epithelium in the oral cavity and why?
stratified squamous epithelium because it needs to protect against abrasion
what does digestion require in the oral cavity?
requires enzymes and lubrication
what is a fauce?
an opening at the back of the oral cavity where the tongue forces food down when we swallow
what are the 3 pairs of salivary glands connected to the oral cavity via ducts?
1) parotid - secretes a serous fluid with amylase
2) sublingual - secretes mucous only
3) submandibular - secretes a mixture of serous fluid with amylase and mucous
what is the total volume of salivary secretions?
1L per day
what is an acinus?
cells in clusters
what are salivary glands?
compound secretory glands
what do acinar cells secrete?
secrete enzymes (amylase)
what do duct cells secrete?
secrete bicarbonate (for buffering)
what is the oesophagus?
long muscular tube (approx. 25cm) located posterior to the trachea, extends from the pharynx to the stomach
what is the function of the epiglottis in terms of the oesophagus?
epiglottis ensures that food enters the oesophagus, NOT the trachea
what is the function of the highly folded submucosa and mucosa?
gives the oesophagus to expand as food travels down to the stomach
what type of epithelium is mucosa?
stratified squamous epithelium
what is a modification that occurs to the muscularis externa?
modified to propel food down to the stomach via a motility pattern called peristalsis
how does the oesophagus change as you go down in terms of muscle?
1) first 1/3 = skeletal muscle
2) middle 1/3 = a mixture of skeletal muscle and smooth muscle
3) last 1/3 = smooth muscle
how does the oesophagus remain lubricated if it does not have goblet cells in the top layer of the stratified squamous epithelium?
has mucous secreting glands that produce mucous from ducts that produce mucous at the surface
