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
What forms H+ and Cl- ions in the gastric lumen?
HCl
What are the three parts of the small intestine?
Duodenum
Jejunum
Ileum
What are the functions of the small intestine?
Receive secretions from liver and pancreas
Mechanical and chemical digestion; absorption of nutrients
Transportation of undigested material to large intestine; absorption of nutrients
Transportation of undigested material to large intestine
What is the role of the small intestine?
Mechanical breakdown and propulsion
Digestion
Absorption
How does the small intestine breakdown and propel food?
Involved in segmentation and peristalsis
How is the small intestine involved in digestion?
Digestive enzymes delivered from pancreas
Brush border enzymes embedded in microvilli membranes
Bile produced by liver emulsified fats and enhances digestion
How is the small intestine involved in absorption?
Breakdown products of CHO, protein, fat and nucleic acid digestion
Water, vitamins and electrolytes
What is the first and shortest part of the small intestine?
The duodenum
C-shaped tube around head of the pancreas
What are the 4 parts of the duodenum?
D1: Superior part
- Direct continuation of pyloric region
Only part that is intraperitoneal
D2: Descending part
- Runs between sup. and inf. duodenal flexures
D3: Horizontal part
- Runs between sup. and inf. duodenal flexures
D4: Ascending part
- Runs along lt side of aorta
- Angles sharply at L2 (duodenojejunal flexure)
What are some special features of D2?
Common bile duct and pacreatic duct unite to form the hepatopancreatic ampulla/duct
Enters D2 at the major duodenal papilla
Muscular valve: heptaopancreatic sphincter (of Oddi)
Also entering D2 is the accessory pancreatic duct at the minor duodenal papilla
Where do the jejunum and ileum extend between?
The duodenaljejunal flexure to the ileocecal junction
How long are the jejunum and ileum?
6-7m long combined
Which quadrants are the jejunum and ileum found?
Most jejunum in LUQ
Most ileum RLQ
Are the jejunum and ileum intra or retro peritoneal?
intra-peritoneal
- Attached to post abdominal wall by fan shaped small bowel mesentery
What does the mesentery provide?
A pathway for neurovascular structures and is site for fat storage
What is the arterial supply of the small intestine?
Branches of the superior mesenteric artery
What is the venous drainage of the small intestine?
Superior mesenteric vein
- Unites with the splenic vein to form portal vein
What is the nerve supply of the small intestine?
Intrinsic nerve: ENS
Extrinsic:
PNS - CNX Vagus
SNS - Greater and Lesser splanchnic nerve T5-9
Visceral afferents
What histological features are found in the small intestine?
Specialised for absorbing nutrients
- Circular folds
- Villi
- Microvilli
What are the circular folds in the small intestines?
Mucosa and submucosa arranged in permanent folds
Force chyme to spiral through lumen
What are the villi of the small intestine?
‘Shaggy hair’ fingerlike projections of the mucosa
In the core of each villus: dense capillary bed and a lymphatic capillary (lacteal)
Between villi are tubular glands (intestinal crypts)
What are the microvilli of the small intestine?
Cytoplasmic extensions of the mucosal absorptive cells
Brush border enzymes (embedded in membrane) perform the final digestion
How many functions does the liver have?
More than 500
What can happen to the liver with some pathologies?
Can become harder and bigger
What quadrants are the liver in?
Right upper and part of the left upper
Which of the 9 divisions is the liver found?
Right hypochondrium, most of epigastrium and some of left hypochondrium
What separates the liver from the thoracic cavity?
Diaphragm
What separates the two surfaces of the liver?
Anterior by sharp inferior border
What are the two surfaces of the liver?
Diaphragmatic and visceral
Difference between two surfaces of the liver?
Diaphragmatic: smooth, dome shaped, convex
Visceral: inferior and posterior aspect
What are both surfaces of the liver covered in?
Diaphragmatic: Peritoneum except posteriorly where the bare area of the liver lies in contact with the diaphragm
Visceral: Peritoenum except near the gall bladder and porta hepatis
What is the porta hepatis?
Hepatic portal or portal fissure
Transverse fissure on the visceral surface of the liver between the caudate and quadrate lobes
What does the porta hepatis give passage to?
Portal vein
Hepatic artery
Hepatic nerve plexus
Hepatic ducts
Lymphatic vessels
What are the peritoneal relations of the liver?
Lesser omentum
How does the lesser omentum connect to the liver?
Double fold of peritoneum which connects the lesser curvature of the stomach and the proximal duodenum to the liver
What is the heptoduodenal ligament?
A thickened region on the free edge
What encloses the portal triad?
The hepatoduodenal ligament
- Along with lymph nodes, lymphatic vessels and the hepatic plexus of nerves
What is the hepatogastric ligament?
The remaining, sheet-like aspect of the lesser omentum
What is the calciform ligament?
Connects liver to anterior abdominal wall and diaphragm
What is the round ligament of the liver?
Contained within the free edge of the falciform ligament
Fibrous remnant of the umbilical vein (carried well-oxygenated, nutrient-rich blood from placenta to foetus)
What is the ligamentum venosum?
Fibrous remnant of the ductus venosus
In foetus, connects left umbilical vein to IVC (allows blood to bypass the liver)
What do the falciform lig., round lig. and ligamentum venosum divide the liver into?
Right and left lobes
What is the coronary ligament of the liver?
Peritoneal reflection from liver to diaphragm
Demarcates the bare area of the liver
What are the triangular ligaments?
Peritoneal folds that connect the liver to the diaphragm
Rt triangular: situated at the rt extremity of the bare area
Lt triangular: continuous with falciform lig anteriorly
What is the blood supply to the liver?
Portal vein 70%
Hepatic artery 30%
What is the portal vein of the liver?
Formed by superior mesenteric vein and splenic vein just posterior to the neck of the pancreas
Conveys nutrient-rich blood from stomach to intestines
What is the hepatic artery of the liver?
Branch of the celiac artery - provides oxygenated blood
At or close to porta hepatic, both vessels divide into lt and rt branches (supply corresponding part of the liver)
What is the venous drainage of the liver?
Hepatic veins (open into the IVC just inf. to diaphragm)
What is the nerve supply of the liver?
Sympathetic fibres (T5-9 via celiac plexus)
Parasympathetic fibres (CNX Vagus)
Visceral afferent fibres
What is the role of the liver?
Synthesis
Detoxification
Metabolism and storage
Excretion
Immune function
What is the liver’s role in synthesis?
Bile (1L daily)
Plasma proteins e.g. clotting factors, albumin
Hormones e.g. angiotensinogen, erythropoietin
Haemopoiesis (foetal development)
What is the liver’s role in detoxification?
Drugs, alcohol
Conversion of ammonia to urea
What is the liver’s role in metabolism and storage?
Fat, carbohydrates, amino acids, vitamins and minerals (iron, vitamins A, B12, D)
What is the liver’s role in excretion?
Bilirubin in bile (erythrocyte breakdown)
What is the liver’s role in immune function?
Phagocytic activity (Kupffer cells)
What are the components of bile?
Bile salts, phospholipids (lecithin)
Bile pigments (bilirubin)
Cholesterol, triglycerides, electrolytes
What is the role of bile?
Assist in digestion and absorption of fats
Where are most of the bile salts reabsorbed?
95% by the ileum and returned to the liver (portal vein) and resecreted in newly formed bile
What are the functional units of the liver?
Liver lobules
- Size of a sesame-seed and hexagonal shaped
What are featured on each lobule?
hepatocytes that radiate outward from a central vein
Where are portal tracts found?
At the corner of each lobule
- Branch of the hepatic artery
- Branch of the hepatic portal vein
- Bile duct
What is the direction of flow of the liver?
Blood flows from portal tract to central vein (via sinusoids)
Bile flows from central areas to portal tracts (via bile canaliculi)
What is the structure of the biliary tree?
Blood passing into central vein eventually enters hepatic vv -> IVC
Bile entering the bile ducts eventually enters the lt and rt hepatic ducts which drain the lt and rt lobes of the liver respectively. These unite to form the common hepatic duct
Common hepatic duct merges with the cystic duct of the gall bladder to form the bile duct (Formerly called the common hepatic duct)
What forms the hepatopancreatic ampulla?
Union of bile duct and major pancreatic duct
What is the function of the gallbladder?
Storage and concentration of bile
Where does the gallbladder lie?
In the gallbladder fossa on visceral surface of liver
What are the three parts of the gallbladder?
Fundus: wide end, projects from the inferior border of the liver
Body: contacts the visceral surface of the liver
Neck: narrow tapered region, makes an S-shaped bend and is continuous with the cystic duct
What is the arterial supply of the gallbladder?
Cystic artery (off hepatic artery)
What is the venous drainage of the gallbladder?
Cystic vv directly into liver or into portal vein
What is the lymphatic drainage of the gallbladder?
Cystic nodes -> hepatic nodes -> celiac nodes
What is the nerve supply to the gallbladder?
Parasympathetic: CNX Vagus
Sympathetic: Splanchnic nn T5-9 (via celiac plexus)
Sensory: Rt phrenic n
Where is the pancreas?
Found in epigastric and lt hypochondriac regions
Stretches transversely behind stomach, in between spleen and duodenum
Is the pancreas intra or retro peritoneal?
Retro-peritoneal
Does the pancreas have a fibrous capsule?
No - instead has a very thin capsule that invaginates into gland (forms septae)
What is the function of the pancreas?
Both an exocrine and endocrine organ
What are the regions of the pancreas?
Head
Neck
Body
Tail
What are the two pancreatic ducts?
Main
Accessory
What is the main pancreatic duct?
Begins in the tail of the pancreas and runs to the head
Found more in the posterior aspect of the pancreas
Unites with bile duct to form hepatopancreatic ampulla (opens into D2: major duodenal papilla)
What is the accessory pancreatic duct?
Drains the inferior part of the head
Opens into the duodenum (minor papilla)
IN 60% of people, it communicates with the main pancreatic duct
What are the sphincter of the pancreas?
Sphincter of the pancreatic duct
- Around the terminal part of the pancreatic duct
Sphincter of the bile duct
- Around terminal part of the bile duct
Hepatopancreatic sphincter (sphincter of Oddi)
- Around hepatopancreatic ampulla
What do the sphincters of the pancreas control?
Smooth mm sphincter control flow of bile and pancreatic juice
When are pancreatic sphincters closed?
When no digestion is occurring (bile secreted by liver gets stored in GB)
What is the arterial supply of the pancreas?
Mainly branches of splenic artery
Anterior and posterior superior pancreaticduodenal aa (from gastroduodenal a)
Anterior and posterior inferior pancreaticoduodenal aa (from SMA)
What is the venous drainage of the pancreas?
Pancreatic veins (most tributaries of the splenic being, some of the superior mesenteric vein)
What is the nerve supply of the pancreas?
Parasympathetic: CNX Vagus
Sympathetic: Abdominopelvic splanchnic nerves (T5-9) via celiac ganglion
What is the make-up of the exocrine portion of the pancreas?
Acinar cells - form the bulk of the pancreas
- Possess abundant rough ER and zymogen granules
- Secrete enzyme-rich pancreatic juice into ductal system
Ductal cells
- Secrete water and HCO3-
What is the make-up fo the endocrine portion of the pancreas?
Pancreatic islets are scattered among th eacinar cells
Contain hormone producing cells
What is the composition of pancreatic juice?
1200-1500ml produced daily
Key contents: enzymes, water and electrolytes
What are the pancreatic enzymes?
Proteases: digest proteins
Amylase: digests starch
Lipases: digest emulsified fats
Nucleases: digest nulceic acids
