Whats the functions of the digestive system?
Digestion
Secretion
Absorption
Motility
What comprises the Alimentary system?
- Mouth
- Sublingual salivary gland
- Submandibular salivary gland
- Parotid salivary gland
- Pharynx
- Trachea
- Oesophagus
- Stomach
- Liver
- Pancreas
- Gallbladder
- Small intestine
- Colon
- Large intestine (Colon, Cecum, Rectum )
- Anus
Whats the function of
the mouth, oesophagus, stomach, pancreas, liver, gallbladder, small intestine, large intestine?
Mouth: Breaks down and lubricates food with teeth and saliva
Oesophagus: Conduit between mouth and stomach
Stomach: Digestion of proteins: foodstuffs reduced to liquid form; storage; sterilization
Pancreas: Digestive enzymes for digestion of fats, carbohydrates and proteins.
Liver: Bile salts for digestion/absorption of fats in small intestine
Gallbladder: Stores and concentrates bile
Small intestine: Final stages of chemical digestion and nutrient absorption
Large intestine: Water absorption, bacterial fermentation and formation of faeces
Describe the general structure of the alimentary canal?
Continious hollow tube with varying diameter
Oesophagues to rectum is around 8 meteres long#
Tube wall has same structural organisation throughout length
Whats the four distinctive layers (tunics)?
Mucosa: epithelium , lamina propria, muscularis mucosae
- Submucosa
- Muscularis externa
- Serosa/adventitia
List the 4 tunics in order deep to superficial.
Mucosa;
- Mucosa epithelium
- Lamina propria
- Muscularis mucosae
Submucosa
Muscularis;
- Circular muscle layer
- Longitudinal muscle layer
Serosa;
- Connective tissue layer
- Peritoneum
Explain the Mucosas function and role?
Epithelium
- Mouth, oesophagus, anal canal = stratified squamous
- Barrier separating lumen of alimentary canal from body
- Synthesis and secretion of digestive enzymes, hormones, mucus
- Absorbs products of digestion
- Epithelium differs along length of gut tube to adaptation for function.
Lamina propria
- Loose connective tissue ( glands, blood/lymph vessels)
Muscularis mucosae
- Thin smooth muscle layer
Describe Submucosa?
- Thick, irregular connective tissue -> Supports mucosa
- Contains neurones, blood vessels (-> mucosa, muscularis externa, serosa), lymphatic vessels
- Neurones form extensive network -> submucosal ( Meissner’s) plexus ( parasympathetic)
- Submucosal glands in oesophagus and duodenum
Describe Serosa/Adventitia?
- Connective tissue outer layer of alimentary canal
Outside peritoneal cavity:
- Adventitia attaches oesophagus and rectum to surrounding structures
Inside peritoneal cavity:
- Serosa surrounds stomach, small intestine and large intestine
Describe Muscularis Externa?
- Two concentric thick layers of smooth muscle
Inner layer= circular muscle (constricts lumen)
Outer layer= longitudinal muscle (shortens tube) - Produce motility -> peristalsis, segmentation
- Myenteric ( Auerbach’s) plexus between circular and longitudinal muscle
- Subcostal + myenteric plexuses = enteric nervous system (ENS) => Independent control of gut function
Nervous control of alimentary function
Autonomic control:
Long (parasympathettic) and short (ENS) reflexes
Parasympathetic => vagus nerve (X)
(except salivation => facial (VII) and glossopharyngeal (IX))
Stimulatory
Increases secretion
Increases motility
Sympathetic => Splanchnic nerve
Inhibitory (except salivation)
Decreases secretion
Decreases motility
Arterial supply to GI tract
Descending (abdominal) aorta ;
- Celiac trunk: Stomach, Small intestine, Pancreas, Liver.
- Superior mesenteric artery: Small intestine, Caecum, Ascending colon, Transverse colon.
- Inferior mesenteric artery: Decending colon, Sigmoid colon, Rectum.
Arterial supply to GI tract;
Name the arteries
Splenic- spleen
Celiac trunk- Foregut
Superior mesenteric- midgut
Inferior mesenteric- hindgut
Venous drainage from GI tract
4 stages
Stomach drains to Gastric veins
Pancreas drains to splenic vein
Small intestine, Caecum, Ascending colon and Transverse colon all drains to superior mesenteric vein.
Decending colon, sigmoid and Rectum all drains to Inferior mesenteric vein.
The Gastric vein, Splenic vein, Superior mesenteric vein and Inferior mesenteric vein all drains to Hepatic portal vein.
The hepatic portal vein drains to the Hepatic vein.
The Hepatic vein drains to the Inferior vena cava.
Describe the Hepatic Portal Circulation
Aorta travels to Digestive tract arteries and Hepatic artery. Which then goes to the Liver capillaries.
Digestive tract arteries travel through the capillaries of digestive tract: stomach, intestines, pancreas and spleen. Which goes to Hepatic portal vein then the Liver capillaries.
The Liver blood supply then goes from the capillaries of liver then to Hepatic vein which drains to Inferior vena cava.
