Oesophagus, stomach, small intestine and accessory digestive organs Flashcards
What is the digestive system composed of?
Gastrointestinal tract
Accessory digestive organs
What are the four basic layers of the GIT?
Mucosa (innermost)
Submucosa
Muscularis
Serosa or adventitia (outermost)
What is the intrinsic supply of the GIT?
Submucosal n. plexus
Myenteric n. plexus
- In between the circular and longitudinal layers of the muscularis
What does the ENS participate in?
Short and long digestive reflexes
What are short reflexes?
Mediated entirely by the ENS in response to stimuli in the GIT
What are long reflexes?
Involve integration with the CNS and extrinsic autonomic nn
What are the processes of the digestive system?
Ingestion
Propulsion
- Deglutition and peristalsis
Mechanical breakdown
- Chewing, churning, segmentation
Digestion
- Enzymatic breakdown
Absorption
- Passage of nutrients through GIT mucosal cells into blood or lymph
Defecation
What process does digestion involve?
Hydrolysis
- Water is added to each molecular bond that is broken
Where are digestive enzymes produced?
By various organs of the GIT
What are most digestive enzymes synthesised by?
Zymogens
What is the oesophagus?
A muscular tube extending between the pharynx and the stomach
- 25cm long, 2cm diameter
- Collapsed when not involved in food propulsion
What are the three portions of the oesophagus?
Cervical
Thoracic
Abdominal
- Retroperitoneal
What is the role of the oesophagus?
Propulsion
- Conveys food to stomach
What are the two major deglutition phases?
Buccal phase (voluntary)
Pharyngeal-oesophageal phase (involuntary)
What is involved in the pharyngeal-oesophageal phase of deglutition?
Foods moves from pharynx into oesophagus
Requires blocking or trachea (epiglottis) and relaxation of UOS
Peristaltic waves propel food distally
Relaxation of LOS allows food to enter stomach
What are other names for the lower oesophageal sphincter?
Gastroesophgeal or cardiac sphincter
What type of sphincter is the lower oesophageal sphincter?
Functional
- Only slight thickening of circular m.
- Reinforced extrinsically by the diaphragm
What type of epithelium is in the oesophagus and what layer is it in?
Mucosa
Stratified squamous epithelium
*Gastroesophageal junction = simple columnar
What type of glands are located in the submucosa of the oesophagus?
Mucous-secreting glands
What type of muscle is found in the muscularis of the oesophagus?
Sup. 1/3: skeletal
Mid. 1/3: Mix
Inf. 1/3: smooth
What is the outer layer of the oesophagus?
Adventitia
What is the nerve supply of the oesophagus?
Upper 1/3 cervical
- Recurrent laryngeal nn (branch of CNX)
Rest of oesophagus
- Nerves of the enteric nervous system and: Autonomic nerves
*Parasympathetic: CNX Vagus
*Sympathetic supply: cardiopulmonary splanchnic, abdominopelvic splanchnic (greater and lesser)
* Visceral afferents
What is the purpose of the stomach?
Food blender and reservoir (4L capacity)
What shape is the stomach?
Generally J shaped
- Varies with respiration, contents and posture
What are the main functions of the stomach?
Mechnical brekadown and propulsion
Digestion
Absorption
Food reservoir
HCl contributes to immunity
Intrinsic factor
How many part and curvatures are in the stomach?
4 part and 2 curvatures
What are the 4 part of the stomach?
Cardia
Fundus
Body
Pyloric part
Where is the cardia of the stomach found?
Surrounds the cardial orifice
- B/w abdominal oesophagus and stomach
Where is the fundus found?
Dilated superior region
Relates to the left dome of the diaphragm
What does the fundus of the stomach correspond with?
5th intercostal space
Where is the cardiac notch found in the stomach?
B/w fundus and oesophagus
Where is the body of the stomach?
Region b/w fundus and oesophagus
Where is the pyloric part of the stomach and where does it lead into?
Funnel part of the stomach
Widest part is the pyloric antrum
- Leads into narrowest part, pyloric canal
What is the pylorus?
Thickened sphincteric region
What is the pyloric sphincter?
Controls movement of stomach contents through the pyloric orifice into the duodenum
What are the two curvatures of the stomach?
Greater
- Longer concave border
Lesser
- Shorter concave border
What is the angular notch and which curvature is it found on?
Junction between body and pyloric region
- Lesser curvature
Is the stomach intra or retro peritoneal?
Intra-peritoneal
What two omentum are present with the stomach and which structures do they connect?
Lesser omentum
- Connected lesser curvature of stomach and proximal duodenum to liver
Greater omentum
- Attached to greater curvature of stomach and proximal duodenum
What happens to the greater omentum after descending?
Folds back and attaches to transverse colon and transverse mesocolon
What is the intrinsic nerves supply to the stomach?
The two plexuses of the enteric nervous system
What extrinsic autonomic nerves supply the stomach?
Parasympathetic: CNX Vagus
Sympathetic: T6-T9 greater splanchnic
Visceral afferents
What is the arterial supply to the stomach?
Branches of the celiac trunk
- Lt gastric (directly off celiac trunk)
- Rt gastric (from common hepatic)
- Lt gastro-omental (from splenic)
- Rt gastro-omental (from gastroduodenal)
- 4-5 short gastric (from splenic)
What is the venous drainage of the stomach?
Veins run w/ arteries
- Rt and lt gastric —> portal vein
- Short gastric & lt gastro-omental v —> splenic
Rt gastro-omental —> SMV
- SMV and splenic unite to form portal
What are the longitudinal ridges of the stomach when it contracts?
Rugae
What type of epithelium is in the mucosa of the stomach?
Simple columnar epithelium
What stimulate mucous production in the mucosal layer of the stomach?
Prostaglandins (PGE2)
What is dotted all over the mucosa of the stomach?
Gastric pits that lead into tubular gastric glands (produce gastric juice)
What is the additional layer in the muscularis of the stomach?
Oblique layer of smooth muscle
What does the extra oblique layer of the stomach help with?
Helps stomach to perform specialised functions; grinding, churning, mixing
What are the three gastric gland cells of the stomach?
Mucous neck cells
Parietal cells
Chief cells
Enteroendocrine cells
What do the parietal cells of the stomach do?
Secrete HCl: contributes to the acidity of gastric juice
Also produces intrinsic factor: required for absorption of vitamin b12 in terminal ileum
What do the chief cells of the stomach do?
Produce pepsinogen and gastric lipase
Low pH required for conversion of pepsinogen to pepsin
What do the enteroendocrine cells of the stomach do?
Secrete hormones and chemical mediators
What hormones and chemical mediators do the enteroendocrine ells secrete?
Gastrin (from G cells): controls secretory activity of stomach
Histamine (secretion)
Serotonin (contractility)
What are the important properties of parietal cells in the stomach in regards to the mechanism of HCl secretion?
Receptors for gastrin, histamine and Ach
Mmebrane bound pumps: H+/K+ ATPase pump (proton pump) and a HCO3/Cl- antiporter
What is the process of HCl secretion?
H2CO3 formed by H2O formed by H2O and CO2 (requires carbonic anyhydrase)
H2CO3 readily dissociates into H+ and HCO3
The binding of what activates second messenger systems?
Binding of gastrin, histamine and ACh receptors
What does the activation of second messenger systems drive?
Action of membrane-bound pumps