List the salivary glands and their function@
Parotid - Sublingual - Submandibular
They coat the mouth in saliva which acts as a lubricant and begin digesting starch through salivary amylase
What are the functions of the stomach?
- Digests Proteins
- Reduces food to a liquid
- Stores food during digestion
- Sterilizes food
What is the digestive function of the pancreas?
Produces digestive enzymes (to break down fats, carbs and proteins) and passes them to the duodenum via the pancreatic duct
What is the digestive function of the liver?
- Produces bile salts for digesting and absorbing fats in small intestine
- Also stores fat and sugar delivered from the small intestine via the portal vein
Whats the function of the gall bladder?
Stores & concentrates up to 50ml of bile
Whats the function of the small intestine?
Performs the last bit of chemical digestion and the vast bulk of nutrient absorption
Whats the function of the large intestine?
- Absorbs water
- Forms faeces
- Bacterial fermentation
What are the layers of the GI tract?
- Mucosa (Epithelium - Lamina Propria - Muscularis Mucosae)
- Muscularis Externa
Do glands exist in the submucosa?
Only in two places:
- The esophagus where they make mucous to aid motility
- The duodenum where they make bicarbonate to neutralize stomach acid
What are the layers of the muscularis externa?
Inner circular layer which contracts the tube
Outer longitudinal layer which shortens the tube
Together they produce GI motility by peristalsis & segmentation
What are the serosa and adventitia?
The connective tissue sheath surrounding the GI tract.
Inside the peritoneal cavity its called serosa
Outside its called Adventitia (Oesophagus & Rectum)
What makes up the enteric nervous system?
The neural plexus that makes up the bulk of the enteric nervous system.
Its split in two:
- Submucosal plexus on the submucosa
- Myenteric plexus between layers of the muscularis externa
What type of epithelium is found in the mucosa?
Two different types based on location.
- Stratified squamous at the ends (mouth, esophagus & anal canal) to protect against solids
- Simple columnar in the middle (stomach & intestines) to reduce absorption/secretion time
Whats the function of the epithelium in the mucosa?
- Absorbing digestive products
- Synthesising & secreting digestive enzymes, hormones and mucous
What makes up the lamina propria?
Loose connective tissue
What else is found in the lamina propria?
What is the muscularis mucosae?
A thin layer of smooth muscle on the mucosa which does very little.
What makes up the submucosa?
- A thick band of irregular connective tissue
- It also supplies blood, lymph and neurones.
- Topped with the submucosal plexus
What kind of nervous control is the gut under?
What nerves supply the gut with parasympathetic stimulation and what effect do they have?
- Parasympathetic control comes via the Vagus nerve.
- The exception is the salivary glands which are supplied by the facial & glossopharyngeal nerves
- When stimulated they increase gut secretion and motility
What nerves supply the gut with sympathetic stimulation and what effect do they have?
- The thoracic Splanchnic nerves. Split into the Greater (T7-T9), Lesser (T10-T11) and least (T12)
- Mainly inhibitory, decreasing secretion & motility. Except in the salivary glands which are stimulated by sympathetic innervation.
How is sympathetic stimulation of the salivary glands different to parasympathetic?
They produce different types of saliva
Explain the arterial supply of the gi tract?
Descending abdominal aorta feeds into the:
- Celiac Trunk which supplies the foregut
- Sup. Mesenteric artery which supplies the midgut
- Inf. Mesenteric artery which supplies the hindgut
Whats fucking annoying about the arterial supply of the duodenum?
Half by the celiac trunk and half by the superior mesenteric
Explain the venous drainage of the Gi tract:
Hindgut -> Inf. mesenteric
Midgut -> Sup. mesenteric
stomach -> gastric veins
Pancreas & spleen -> Splenic vein
All of the above feed into the hepatic portal vein
Then the hepatic vein via the liver
Finally into the IVC
What is the purpose of filtering all blood from the GI tract through the liver first>
- It screens the blood for nasty stuff you dont want to absorb from the gut
- Also stores any excess nutrient and sugar.
Whats the difference between symp and parasymp salivation?
Symp salivation - thick (for facilitating resp)
Parasymp Salivation - watery (for facilitating digestion)