Physiology- Grand Tour of the Alimentary Canal Flashcards
What 4 functions can the physiology of the digestive system be broken down into?
Digestion
Secretion
Absorption
Motility
How many salivary glands are found in the mouth and what are they called?
3 Salivary glands:
Parotid salivary gland on the roof.
Sublinguinal salivary gland under the tongue.
Submandibular salivary gland at the back of the jaw.
What are the two sphincters of the oesophagus?
Upper oesophageal sphincter (controls entry of food)
Lower oesophageal sphincter (prevents food leaving the stomach back into oesophagus)
What basic role does the mouth play in digestion?
Breaks foodstuffs down by chewing.
Saliva is added as lubricant
What basic role does the oesophagus play in digestion?
The oesophagus acts as a conduit between mouth and stomach
What basic role does the stomach play in digestion?
Stomach is the main start of digestion.
Specialises in the breakdown of proteins
Foodstuffs are reduced to liquid form.
Avid in the stomach helps to sterilise food.
Acts as a storage vessel.
How does the stomach act as a storage vessel?
Without the stomach to hold a large meal and slowly release the products into the GI tract there would be a massive influx of food.
Macromolecules would be broken down increasing the osmolarity of the intestines and large amounts of fluid would rush in. This causes a massive decrease in body fluid which causes shock and abdominal swelling.
This shock can be fatal and is called dumping syndrome.
What basic role does the pancreas play in digestion?
Produces digestive enzymes for digestion of fats, carbohydrates and proteins.
What basic role does the liver play in digestion?
Produces bile salts for digestion/ absorption of fats in small intestine
What basic role does the Gallbladder play in digestion?
Bile salts are produced all the time and stored in the gall bladder.
What role does the small intestine play in digestion?
The final stages of chemical digestion and nutrient absorption.
What role does the large intestine play in nutrient absorption?
Location of water absorption, bacterial fermentation and the formation of faeces.
What is the general structure of the Alimentary canal?
It is a continuous hollow tube of varying diameter.
From the oesophagus to the rectum its 8 meters long.
The tube wall has the same structural organisation throughout its length.
What are the 4 distinct histological layers of the alimentary canal?
- Mucosa (inside of the tube = basically outside the body)
- Submucosa (contains glands in oesophagus for mucous and glands in duodenum to cancel out stomach acid)
- Muscularis externa (the important muscular layer)
- Serosa/ adventitia (series below diaphragm, adventitia above the diaphragm)
What are the three layers of the alimentary mucosa?
- Epithelium
- Lamina Propria (next layer) = small layer of loose connective tissue (blood/ lymph vessels, glands)
- Muscularis mucosae (doesn’t really do much)
What are the two plexus in the wall of the alimentary canal?
Myenteric plexus: has both parasympathetic and sympathetic fibres. Motor control of the muscular externa.
Submucosal plexus: has only parasympathetic fibres which are derived from the myenteric plexus.
Where is stratified squamous and simple columnar epithelium found in the alimentary canal?
- Stratified squamous = mouth, oesophagus and anal canal.
2. Simple columnar = Stomach, small and large intestine
What function does the epithelial layer of the mucosa have?
- Barrier separating lumen of alimentary canal from body
- Synthesis and secretion of digestive enzymes, hormones and mucous.
- Absorbs products of digestion
What is the function of the submucosa?
This thick, irregular connective tissue supports the mucosa.
It contains neurones, blood vessels and lymphatic vessels.
has neurones which form an extensive network (Submucosal (Meissner’s) plexus)
tl;dr Supplies nutrients and control as well as structural support
What is the function of the serosa/ adventitia?
Connective tissue outer layer of alimentary canal.
Outside the peritoneal cavity the adventitia attaches the oesophagus and rectum to surrounding structures.
Inside the peritoneal cavity the series surrounds the stomach, small intestine and large intestine.
Describe the structure and function of the muscular externa
Two concentric thick layers of smooth muscle make up the muscular externa.
The inner layer = circular muscle (constricts lumen)
The outer layer = longitudinal muscle (shortens tube)
Together these produce motility by peristalsis and segmentation.
Where does the Myenteric (Auerbach’s) plexus lie?
Between the circular and longitudinal muscle of the muscular externa.
What makes up the enteric nervous system (ENS)?
Submucosal and myenteric plexuses.
These provide independent control of gut function. As in your gut functions without needing your brain. Like a snake inside of you.
Can peristalsis and segmentation happen at the same time?
No
How does the nervous system control alimentary function?
Autonomic control occurs through long (parasympathetic) and short (ENS) Reflexes.
The parasympathetic system stimulates secretion and motility through the vagus nerve. Salvation controlled through facial (VII) and glossopharyngeal (IX)
The sympathetic system inhibits secretion and motility through the splanchnic nerve.
What three arteries are branches of the descending (abdominal) aorta and supply the GI tract?
- Celiac Trunk
- Superior mesenteric artery
- Inferior mesenteric artery
What organs does the celiac trunk supply?
- Stomach
- Small intestine
- Pancreas
- Liver
What organs does the superior mesenteric artery supply?
- Small intestine
- Caecum
- Ascending colon
- Transverse colon
What organs does the inferior mesenteric artery supply?
- Descending colon
- Sigmoid colon
- Rectum
What organ does the splenic artery supply?
Spleen
What veins drain:
a) Stomach
b) Pancreas?
a) Gastric veins
b) Splenic veins
What organs do the superior mesenteric vein drain?
Small intestine
Caecum
Ascending colon
Transverse colon
What organs do the inferior mesenteric vein drain?
Descending colon
Sigmoid colon
Rectum
Into what vein do the gastric, splenic, superior and inferior mesenteric veins drain?
Hepatic portal vein
What vein does the hepatic portal vein drain into?
Hepatic vein.
From here the blood drains into the inferior vena cava.
