Intro to GI tract Flashcards
What are the functions of the GI tract
Describe each one
Digestion-The processes by which foodstuffs are degraded to produce smaller molecules that can be absorbed
Finishes at small intestine
Absorption- The processes by which nutrient molecules are absorbed by cells that line the GI tract and enter the bloodstream Starts at small intestine
Protection- The processes by which the lining of the GI tract is protected from damage during digestion of foodstuffs
Describe the gastrointestinal tract proximal to distal
Mouth- Pharynx- Oesophagus- Stomach - Duodenum- Jejunum- Ileum- Colon- Rectum- Anus
What are the associated organs of the GI tract and what do they associate with
Salivary glands - mouth
Liver, Gallbladder, Pancreas- Small intestine
What is the exocrine pancreas
part of the pancreas that produces enzymes
What is the common structure layers of the GI tract starting proximal to the lumen
Mucosa
Submucosa
Muscularis externa
Serosa- closest to abdomen
What is the regional specialisation of the stomach
Gastric pits
Gastric glands- responsible for acid secretion
What is the regional specialisation of the large intestine
Flat surface
Crypts coming of surface- mucus secreting cells
Where are crypts found
Small and large intestine
What are the three layers of the mucosa?
Epithelium- Single layer
Lamina propria- Most of the mucosa
Muscularis mucosae- Muscular layer
What is lamina propria
Loose connective tissue made up a fibroblast predominantly
made of muscle nerve blood cells
What is the function of the muscularis mucosae
Local movement E.g squeezing glands
What is the submucosa made of?
Connective tissue made of fibroblasts
made of muscle nerve blood cells
What are the two layers of the muscularis externa?
How are they positioned?
Inner Circular muscle- wraps around tube
Outer Longitudinal muscle -along the length of the tube
What is serosa made of
Connective tissue made of fibroblasts
made of muscle nerve blood cells
What things are found in the wall of the GI tract? Where?
Lymph node(GALT) - mucosa
Glands- Submucosa
Network of neurons
What does GALT stand for?
Gut associated lymphoid tissue
What is the function of GALT
To recognise food stuffs so body doesn’t initiate immune response against them
So protects GI Tract
Where do you find glands in the submucosa? Names?
In two places
Bottom of oesophagus - submucosal gland
Top of small intesstine(Duodeum)- Brunners gland
What are the network of neurones found in the GI tract?
Function?
Two
Submucosal plexus
(Meissner’s plexus)
Myenteric plexus
(Auerbach’s plexus)
regulating gastrointestinal tract function
Where are the network of neurones found in the GI tract?
Submucosal plexus (Meissner's plexus)- Found in between muscularis externa and submucosa- Only found in small and large intestine
Myenteric plexus
(Auerbach’s plexus)- found in between the two layers of muscularis externa
Starts at oesophagus and ends at rectum. Completely throughout
What are the levels of amplification of surface area of the GI tract
Circular or spiral folds
Villus
Microvilli
What is special about the epithelial cells of the GI tract?
Polarised
What is meant by polarised?
Two distinct membranes
What are the membranes of the epithelial cells
Apical membrane
Basolateral membrane
What is an apical membrane?
Facing the lumen of the gastrointestinal tract
What is a basal lateral membrane?
Facing the rest of the gastrointestinal tract that isn’t the lumen
What membrane makes up most of the epithelial cells?
basolateral membrane
What separates the membranes of the epithelial cells
Tight juctions
What is the function of tight juctions in the epithelial cells?
Sorting different transport proteins to the two membranes. Preventing proteins entering apical membrane frim travelling to the basolateral membrane
What is vectorial transport
Cells can transport in a specific direction
What is transcellular transport
Transporting through cells
What is paracellular transport/pathway?
Transport between cells
What are parietal cells function?
Acid secretion
What are the major sites of GI secretion in the GI tract? 4
Salivary glands
Gastric glands
Exocrine pancreas
Liver-biliary system Small Intestine
What is the total GI secretion per day
6 ~ 7 l
What does GI secretion contain?
enzymes, ions, water and mucus
What is the function of secretion
breakdown large compounds
regulate pH
dilute and protect
What is the blood supply to the GI tract
Splanchnic circulation
Describe how arteries positioned in the Splanchnic circulation
Branching from abdominal aorta Arteries goes to Intestines Pancreas Spleen Stomach Liver
Describe how veins positioned in the Splanchnic circulation
Veins branching from Intestines Pancreas Spleen Stomach join together to form Portal vein and pass through the liver ( where liver absorbs nutrients FIRST) and join the hepatic vein which joins into the inferior vena cava
Microvasculature of the Villus
Central arteriole goes through middle of villi then goes to top of the villi to form rich capillary network and then through central venule
Central lacteals
What happens to nutrients absorbed by the villi
Arterioles and Venules take in absorbed amino acids and sugars to take to the liver
Lacteals take in reassembled fats that were fatty aids and monoglyceride where they join with intestinal lymph and then into circulation at the thoraxic duct
difference in blood supply to the gastrointestinal tract between the fasting state and the fed state after a meal
Eight times increases
sequential blood delivery- doesnt happen all at once
What regulates the blood supply of the GI tract?
Vagus nerve increases digestion
cholecystokinin CCK
vasodilator metabolites
What is cholecystokinin
Peptide hormone
How does absorbing via vili affect metabolism
Metabolically expensive
Example of vasodilator metabolites
CO2
Regulatory Mechanisms
Control Gastrointestinal Function
Endocrine:
Peptide hormone released by a specialised cell
Release of a transmitter (e.g. peptide) into blood for delivery to distant target cell.
Paracrine:
Release of a transmitter from a sensor cell to affect adjacent target cells without entering blood or activating neurons
Neuronal:
Electrical signalling via neurons
Where do you find endocrine cells
In the mucosa of the stomach. intestine and pancreas
What cells produce gastrin?
G cells
What cells produce cholocystokinin
I cells
What cells produce secretin?
S cells
What cells produce Glucose-dependent insulinotropic peptide (GIP)?
K cells
What cells produce Somatostatin?
D cells
Where are G cells located?
Stomach
Where are I cells located?
Small Intestine
Where are S cells located?
Small Intestine
Where are K cells located?
Small Intestine
Where are D cells located?
Stomach, Pancreatic islets, Small Intestine
What is Glucose-dependent insulinotropic peptide (GIP) also known as?
Gastric inhibitory peptide
What opposes the role of Gastrin?
Somatostatin
What is special about the Somatostatin hormone
Dual role
Endocrine and Paracrine factor
What is the function of Gastrin
Gastric secretion
Gastric motility
What is the function of CCK
Gallbladder contraction
Pancreatic secretion
Stimulates blood flow
What is the function of GIP
Stimulates insulin release
What is the vagovagal reflex
Intrinsic mervous system interacting with the autonomic nervous sytem and parasymthetic nerves to make change
Long range reflex
Explain what happens in the Intrinsic nervous system?
Chemo/ Mechanoreceptors detect change
Submucosal/ Myenteric plexus
carry signals through to effectors (smooth muscle/ Secretory cell/ blood vessel)
Explain what happens in the Vagovagal reflex
Chemo/ Mechanoreceptors detect change
Submucosal/ Myenteric plexus
carry signals through to parasympathetic which get signals to brain and then signals to effectors (smooth muscle/ Secretory cell/ blood vessel)
What are the three phases of gastrointestinal control
Cephalic phase
Gastric phase
Intestinal phase
