Anatomy Flashcards
Alimentary canal
The alimentary canal is a series of hollow organs running from the mouth to anus
Oral vs aboral directions
Oral - towards mouth, aboral - away from mouth
Structures of the alimentary canal
Mouth and oropharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus
Function of the mouth and oropharynx
Chops and lubricates food, stars carbohydrate digestion, delivers food to oesophagus
Function of the oesophagus
Propels food to the stomach by peristalsis
Function of the stomach
Stores/churns food, continues carbohydrate digestion, initiates protein digestion, regulates delivery of chyme to duodenum
What makes up the small intestine?
Duodenum, jejunum, ileum
Function of the small intestine
Principal site of digestion and absorption of nutrients
What makes up the large intestine?
Caecum, colon
Function of the large intestine
Colon reabsorbs fluids and electrolytes, stores faecal matter before delivery to the rectum
Function of the rectum and anus
Regulated expulsion of faeces
Accessory structures to the alimentary canal
Salivary gland, pancreas, liver and gallbladder
Structure of the digestive tract wall
Mucosa, submucosa, muscular externa, serosa
Layers of the mucosa
- Mucous membrane (epithelial, exocrine gland and endocrine gland cells)
- Lamina propria (capillaries, enteric neurones, gut-associated lymphoid tissue)
- Muscularis mucosae
Layers of the submucosa
- Connective tissue
- Larger blood and lymph vessels
- Glands
- Submucous plexus
Layers of the muscular externa
- Circular muscle layer
- Myenteric plexus
- Longitudinal muscle layer
What does the myenteric plexus produce?
Lubricant fluid
What is the serosa made from?
Connective tissue
Major functions of the alimentary canal
Motility, secretion, digestion, absorption
What is motility?
Mechanical activity mostly involving smooth muscle (skeletal at mouth, pharynx, upper oesophagus and external anal sphincter)
What is secretion required for?
Digestion, protection and lubrication
What is digestion?
Chemical breakdown by enzymatic hydrolysis of complex foodstuffs to smaller, absorbable units
What is absorption?
Transfer of the absorbable products of digestion (with water, electrolytes and vitamins) from the digestive tract to the blood or lymph
What happens in circular muscle contraction?
Lumen becomes narrower and longer
What happens in longitudinal muscle contraction?
Intestine becomes shorter and fatter
What happens in muscularis mucosae contraction?
Change in absorptive and secretory area of mucosa, mixing activity
What does muscular mucosae contraction ensure?
Ensures products for digestion in contact with the epithelium are thoroughly mixed
What is smooth muscle in the GI tract coupled by?
Gap junctions
What is spontaneous activity across coupled cells in the GI tract driven by and modulated by?
Driven by specialised pacemaker cells
Modulated by intrinsic and extrinsic nerves and numerous hormones
In the stomach, small and large intestine, what does spontaneous electrical activity occur as?
Very slow waves, rhythmic patterns of membrane depolarisation and repolarisation that spread from cell to cell via gap junctions
What is slow wave electrical activity driven by?
Interstitial cells of Cajal
Where are interstitial cells of Cajal located?
Pacemaker cells located largely between the circular and longitudinal muscle layers
Excitatory influences of the parasympathetic innervation of the GI tract
Increased gastric, pancreatic and small intestinal secretion, blood flow and smooth muscle contraction
Inhibitory influences of the parasympathetic innervation of the GI tract
Relaxation of some sphincters, receptive relaxation of stomach
Excitatory influence of the sympathetic innervation of the GI tract
Increased sphincter tone
Inhibitory influences of the parasympathetic innervation of the GI tract
Decreased motility, secretion and blood flow
What does the myenteric (Auerbach’s) plexus regulate?
Motility and sphincters
What does the submucous (Meissner’s) plexus modulate?
Epithelia and blood vessels
How does the enteric nervous system co-ordinate muscular, secretive and absorptive activities?
According to sensory neurones, interneurons, effector neurones
Peristalsis:
- What is it?
- What is it triggered by?
- What neurones coordinate the activity?
- A wave of relaxation, followed by contraction that normally proceeds a short distance along the gut in an aboral direction
- Distention of the gut wall
- Interneurones
What is segmentation?
Rhythmic contractions of the circular muscle layer that mix and divide luminal contents
Where does segmentation occur?
Small intestine and large intestine
Colonic mass movement
Powerful sweeping contraction that forces faeces into the rectum – occurs a few times a day
Migrating motor complex
Powerful sweeping contraction from stomach to terminal ileum
6 sphincters in the GI tract
Upper oesophageal sphincter Lower oesophageal sphincter Pyloric sphincter Ileocaecal valve Internal sphincter External sphincter
Upper oesophageal sphincter:
- What type of muscle is it comprised of?
- What does it relax to allow?
- When does it close?
- Skeletal muscle
- Swallowing
- Closes during inspiration
Lower oesophageal sphincter:
- What does it relax to allow?
- Why does it close?
- Permit entry of food to stomach
- To prevent reflux of gastric contents into the oesophagus
Pyloric sphincter:
- What does it do?
- What does it usually prevent?
- Regulates gastric emptying
- Duodenal gastric reflux
Ileocaecal valve:
- What does it do?
Regulates flow from ileum to caecum
Internal and external sphincters:
- What type of muscle makes up internal?
- What type of muscle makes up external?
- What are they regulated by?
- Smooth muscle
- Skeletal muscle
- Defecation reflex
