Anatomy & Physiology Flashcards
What is the esophagus
- The third organ of digestion after the mouth and the pharynx
- Serves as the channel for food from the mouth to the stomach
- Located posterior to the trachea and larynx
- Goes through the diaphragmatic hiatus to reach the stomach
What is the primary function of the esophagus
The conduction of food from the pharynx to the stomach; accomplished by peristalsis
What is peristalsis
A distally progressive band of circular muscle contractions
When is primary peristalsis initiated in the esophagus
By swallowing
Where and how does secondary peristalsis begin
- Begins in the pharynx, below the hypopharynx
- It begins without antecedent swallowing movement
- It’s elicited by esophageal distention and moves distally at 3-5cm per second
How fast does food move through the esophagus
3-5cm per second
What nerves control peristalsis
Vagal reflexes
How long is the tubular structure of the esophagus and what is the diameter
9-10 inches long (25 cm)
1 inch wide (2.5 cm)
Where does the structure of the esophagus begin
Just below the cricoid
What muscles make up the esophagus
The upper 5% of the esophagus is striated muscle
The transition zone of the esophagus is 30-40% striated muscle
The lower 50-60% of the esophagus is smooth muscle
How many layers does the esophagus have
3
What are the three layers of the esophagus
- Mucosa layer
- Submucosa layer
- Muscularis layer
What layer does the esophagus lack that the rest of the GI tract has
The serosa layer
What makes up the mucosa layer of the esophagus
- It’s covered with squamous epithelium
- Lamina propria
- Muscularis mucosa
What is the lamina propria that is in the mucosa layer of the esophagus
A thin layer of fibrous tissue that lies immediately beneath the epithelium
What is the muscularis mucosa that is in the mucosa layer of the esophagus
A thin band of smooth muscle that separates the lamina propria from the underlying submucosa
What is in the submucosa layer of the esophagus (the middle layer)
Connective tissue
Blood vessels
Nerve fibers
What is the muscularis layer of the esophagus
Outermost layer of the esophagus
Inner layer of circular muscle responsible for squeezing the esophagus
Outer layer of longitudinal muscles that contracts to shorten the esophagus
Auerbach’s plexus (myenteric plexus)
What is Auerbach’s plexus (myenteric plexus) located in the muscularis layer of the esophagus
Sympathetic nerve fibers located between the longitudinal and circular muscles
Where are the mucus glands located in the esophagus
They line the upper and lower end of the esophagus for lubrication
What are the two sphincters located in the esophagus
Upper esophageal sphincter (UES)
Lower esophageal sphincter (LES)
What is another name for the upper esophageal sphincter
The hypopharyngeal sphincter
What muscles make up the upper esophageal sphincter
Striated muscle
Cricopharyngeal muscle
Where is the upper esophageal sphincter located
Between the pharynx and the beginning of the esophagus, separating the pharynx from the esophagus
It’s anterior border is the cricoid cartilage
What is the function of the upper esophageal sphincter when open
Allow the passage of food into the esophagus
What is the function of the upper esophageal sphincter when closed
It keeps inspired air from entering the esophagus
What is another name for the lower esophageal sphincter
Cardiac sphincter
Gastroesophageal sphincter
Where is the lower esophageal sphincter located
About 5 cm above the Gastroesophageal (GE) junction
Directly above the angle of His
What is the angle of His
Demarcates the junction between the tubular esophagus and the stomach
What type of muscle makes up the lower esophageal sphincter
Smooth muscle
What is the size of the lower esophageal sphincter
2-4cm in length
What is the function of the lower esophageal sphincter when open
Controls the passage of food into the stomach
What is the function of the lower esophageal sphincter when closed
Inhibits the reflux of stomach contents into the esophagus and pharynx
Is the lower esophageal sphincter physiological or anatomical
Physiological
What arteries supply blood to the esophagus
Esophageal arteries of the aorta
Inferior thyroid artery
Left gastric artery
What arteries supply blood to the GE junction
Left gastric artery
Inferior phrenic arteries
What veins carry blood out of the esophagus
Azygos vein
Thyroid vein
Left gastric vein
What nerves control swallowing
Starts at the swallowing center in the medulla
What nerves initiates peristalsis
The vagus nerve
What nerves initiates secondary peristalsis in response to esophageal distention
The sympathetic nerves
It’s derived from cervical and thoracic ganglia, and from preganglionic fibers of the greater and lesser splanchnic nerves
What nerves innervate the lower esophageal sphincter
Sympathetic and parasympathetic
Why is GERD sometimes misdiagnosed as heart-related
The same sympathetic and parasympathetic nerves are involved in the lower esophageal sphincter are also involved in myocardial infarctions
What is the stomach
A j-shaped distensible organ located just below the diaphragm between the esophagus and duodenum
What are the important physiological purposes of the stomach that are achieved through complex combination of exocrine secretory mechanisms and smooth muscle contraction and relaxation
- Maintains relatively low levels of microbes in the upper digestive tract
- Serves as a reservoir for swallowed food, drink, and digestive secretions
- Originates signals for hunger and satiety
- Digests food and prepares nutrients for absorption
- Mixes and delivers chyme to the small intestine for further digestion and absorption
What is the primary function of the stomach
To initiate digestion using both chemical secretions and mechanical movement
What are functions of the stomach
- Initiate digestion using both chemical secretions and mechanical movement
- Temporary storage of food
- Mixes food with gastric secretions forming a semi fluid mixture called chyme
- Mixing and grinding motion breaks food into smaller particles to prepare for digestion
What glands are located in the stomach
Cardiac, oxyntic, pyloric
Where are the cardiac glands located and what do they secrete
Located just distal to the gastroesophageal junction
They secrete mucus and pepsinogens, which are converted into pepsin by hydrochloric acid
What is another name for oxyntic glands and where are they located
Fundus glands
Located in the proximal two-thirds of the stomach
How many types of cells have been identified in the oxyntic glands
4
What are the 4 cells that have been identified in the oxyntic glands
Zymogen cells - also called chief cells
Oxyntic cells - also called parietal cells
Mucous neck cells
Endocrine or endocrine like cells
What does zymogen cells of the oxyntic glands secrete
Pepsinogens
What do oxyntic cells of the oxyntic glands secrete
Hydrochloric acid
Intrinsic factor - necessary for the absorption of B12
What do mucous neck cells of the oxyntic glands secrete
Mucous
Where are the pyloric glands located and what cells do they contain
Located in the antrum and pylorus
Mucus cells - that secrete mucus and pepsinogens
G cells - that secrete gastrin
What do pyloric and oxyntic glands both have
Enterochromaffin cells that secrete serotonin
How many different types of endocrine cells do the cardiac, oxyntic and pyloric glandular mucosa contain and what do they secrete
9
They secrete hormonal products such as somatostatin and glucagon
What do both the parietal glands and pyloric glands secrete
Bicarbonate
What is the pH of the gastric secretions produced by the cardiac, oxyntic and pyloric glands
PH 1.0-4.0
What are the different gastric secretions produced by the cardiac, oxyntic and pyloric glands
Pepsin
Gastric amylase
Gastric lipase
Hydrochloric acid
Intrinsic factor
What does the secretion pepsin do
Breaks down protein into polypeptides
What does the secretion gastric amylase do
Breaks down carbohydrates
What does the secretion gastric lipase do
Breaks down fats and lipoproteins
What is hydrochloric acid and what is its function
Major component of gastric secretions
Lowers pH and is bactericidal
Where is intrinsic factor produced and what is its function
Produced by the parietal cells
Promotes the absorption of vitamin B12 in the ileum
How fast are gastric secretions produced
0.5ml/minute when the stomach is at rest
3ml/minute with food ingestion
Approximately 1,500-3,00cc/day
What is the function of the pyloric sphincter
It regulates emptying of chyme into the small bowel based on proper consistency and acidity
How small must a particle be to pass through the pyloric sphincter into the duodenum
1mm or less
What is the size of the stomach
Approximately 10-12 inches long and 6 inches wide at its widest point
What are the different parts of the stomach
Cardia
Fundus
Body
Antrum
Pyloric region
Lesser curvature
Greater curvature
What is the cardia of the stomach
The part of the stomach that immediately adjoins the esophagus
What is the fundus of the stomach
The dome-shaped part of the stomach that extends to the left above the cardia
What is the body of the stomach
It’s below the fundus and extends to the incisura angular is, a notch-like indentation located on the upper, lateral border of the stomach
It is the reservoir that stretches to accommodate the quantity of content
What is the antrum of the stomach
It’s below the incisura angularis and extends to the narrow, tubular pylorus
It moves food toward the pylorus with intense waves
What is the pyloric region of the stomach
The gateway to the small bowel at the distal end of the stomach, with a thick, muscular wall that forms the pyloric sphincter
What is the lesser curvature of the stomach
The upper lateral border of the stomach
What is the greater curvature of the stomach
The lower lateral border of the stomach
How many layers does the stomach have
4
What are the four layers of the stomach
- Outer serosa
- Muscularis propria
- Submucosa
- Gastric mucosa
What is the outer serosa layer of the stomach
Layer of visceral peritoneum that covers the exterior of the stomach
It includes both the greater omentum and lesser omentum
Subserosa is support tissue for the serosa
What is the greater omentum in the serosa layer of the stomach
It hangs in a double layer from the greater curvature over the anterior side of the abdominal viscera
What is the lesser omentum of the serosa layer of the stomach
It connects the lesser curvature to the underside of the liver
What is the muscularis propria layer of the stomach
Outer layer of longitudinal muscle fibers and inner layer of transverse fibers that contract to produce the peristalsis of the stomach while it churns and compresses food during digestion
A three-tired muscular layer also known as muscularis external
Outer layer - longitudinal muscle fibers
Middle layer - circular smooth muscle fibers
Inner layer - oblique fibers
What is the submucosa layer of the stomach
Lies below the muscular layer
Composed mainly of areolar connective tissue
Contains the gastric blood vessels, lymphatics and nerves
What is the mucosa layer of the stomach
The interior lining of the stomach that forms a series of ridges called rugae that allows the stomach to distend to hold a large quantity of food
It contains several types of epithelial cells
What arteries supply the stomach
Celiac axis - supplies lesser and greater curvature
Left and right gastric artery - left flows down from the cardia and joins with the right
Common hepatic
Gastroepiploic artery - greater curvature
Splenic artery
What veins carry blood away from the stomach
Portal vein
Left and right gastroepiploic veins - the greater curvature
Right gastric vein - lesser curvature
Coronary vein - lesser curvature
What nerves stimulates acid secretion and motility in the stomach
The vagus nerve
What is the liver
The largest organ in the body, weighing 1200-1600 grams
And is extremely vascular
Where is the liver located
The right upper quadrant of the abdomen, immediately below the diaphragm
A small portion extends into the left upper quadrant
What percentage of total body weight does the liver make up
2-3% of the average body weight
How quickly do liver cells regenerate and how long does it take for normal liver function to be restored if part of it is removed
Cells can regenerate themselves within 3 weeks
It can be restored to full function within 4 months
How much liver is needed to function
The liver can function even with damage to 90% of its mass
Only 10% is needed to function
How long can someone live after removal or total destruction of the liver
10 hours
What is the function of the liver
- Bile formation and secretion
- Vitamin storage
- Coagulation
- Metabolism
- Detoxification
How is the bile transported from the liver after it is produced
Transported from the liver through the biliary system into the duodenum
What vitamins are stored in the liver
Vitamins: A, B2, C, D, E, and K
How does the liver effect coagulation
- The liver have both clotting and anticoagulant properties
- Clotting factors and anticoagulant heparin are produced in the liver
- It produces vasopressor substances after hemorrhage
- All coagulation factors should be monitored
What is metabolized in the liver
Carbohydrates
Protein
Fat
Steroid
How does the liver aide in detoxification
Hepatocytes attempt to make medications and toxic substances more water soluble so they can be eliminated in urine or in bile
The mechanisms of detoxification include reduction; hydrolysis; conjugation; oxidation; excretion in the bile; degradation; and storage of certain substances such as morphine, curare, and strychnine to be released at a later time into the circulation
Through these processes, the hepatocytes protect the body from drug-related hepatic injury
How can the liver be described
Morphological anatomy
Functional anatomy
What is the morphological anatomy of the liver
The external appearance
What is the functional anatomy of the liver
The internal features of the liver
How many main lobes of the liver are there
2
Which lobe contains the falciform ligament
The left lobe
Who came up with the classification system of the liver that divides it into eight segments
French surgeon and anatomist Claude Couinaud in 1957
Each segment has its own vascular inflow and outflow and its own biliary drainage
What is the Glisson’s capsule of the liver
A thick capsule of connective tissue containing blood vessels and lymphocytes and it covers the entire surface
What covers the Glisson’s layer of the liver
A layer of serosa
Where does the falciform ligament that divides the liver connect to
It attaches the liver to attach to the abdominal wall and diaphragm causing the liver to move with respiration
What is another name for the mass of the liver
Parenchyma
Which lobe of the liver is large
The right lobe is 6 times larger than the left
What makes up the parenchyma of the liver
Lobules
Hepatocytes
Sinusoids
Canaliculi
Kupffer cells
What do the lobules of the parenchyma of the liver consist of and what do they do
- Ongoing process of division occurs that continues to divide the right and left lobe into many small lobes called lobules
- Approximately one million small lobules make up the mass of the liver
- Small hepatic lobules act as the functioning unit of the liver
- Each small lobule contains its own hepatic artery, portal vein and bile duct
- Each lobule consists of numerous rows of liver cells known as hepatocytes
What is another name for the combination of hepatic artery, portal vein and bile duct
The portal triad
What are the hepatocytes of the liver
- Each row of liver cells are one cell thick with finger-like projections call microvilli
- They radiate from central veins called terminal hepatic venules toward a thin layer of connective tissue that separates each lobule
What are sinusoids of the liver
They are lined by thin endothelial cells that have openings through which the microvilli and hepatocytes extend
This allows the hepatocytes direct access to the bloodstream of the sinusoids
What are the canaliculi of the liver
They are small channels that are the farthest end of the biliary system
They receive bile from the hepatocytes
The bile canaliculi branch and combine eventually forming the right and left hepatic ducts which merge to form the common hepatic ducts
The common hepatic duct joins the cystic duct of the gallbladder form to create the common bile duct
What are Kupffer cells of the liver
The other major cells of the liver that adhere to the wall of the sinusoid and project into the lumen
They function as phagocytes - cells that engulf and destroy foreign material of other cells
They remove amino acids, sugars, old erythrocytes, bacteria, debris and toxic substances
What arteries supply the liver
The portal vein - supplies 75% of the livers blood bringing 50% of its oxygen supply and nutrients that are absorbed from the GI tract
The hepatic artery - supplies the other 25% of the blood flow and the remaining 50% if the oxygen to the liver
What veins carry blood away from the liver
The hepatic veins
The inferior vena cava
What nerves are involved with the liver
The vagus nerve and thoracolumbar system
The sympathetic nervous stimulation - may cause hepatic artery and portal vein vasoconstriction and a dull pain over the area of the liver
The bile ducts receive sensory nerves as well as sympathetic and parasympathetic innervation
How does the liver metabolize carbohydrates
The liver cells convert glucose, fructose and galactose to glycerin ( glycogenesis) for storage in the liver
They break down glycogen to glucose (glycogenolysis) to maintain blood glucose levels when there is a decrease in carbohydrate intake
They synthesize glucose from noncarbohydrate nutrients (gluconeogenesis) to maintain blood glucose levels ( synthesizing glucose from proteins or fats)
How does the liver metabolize protein
The liver cells deaminate amino acids to produce ketoacids and ammonia, from which urea is formed and excreted in urine
They synthesize about 50g of new protein daily, including most of the plasma proteins such as albumin, fibrinogen, transferrin, ceruloplasmin, haptoglobin and the lipoproteins
How does the liver metabolize fat
Digested fat is converted in the intestine to triglycerides, cholesterol, phospholipids, and lipoproteins
The substances are taken up by the liver and hydrolyzed to glycerol and fatty acids through a process known as ketogenesis
What steroids are metabolized by the liver
Adrenocotrical steroids
Glucocorticoids
Estrogens
Testosterone
Progesterone
Aldosterone
What makes up the biliary system
- The gallbladder and its associated ductal systems
- Hepatic, cystic, common bile and pancreatic duct
What is the anatomy of the gallbladder
A pear-shaped, sac-like bile storage structure that is attached to the undersurface of the liver by connective tissue, peritoneum and blood vessels
What is the size of the gallbladder
Approximately 3 inches long and 1 inch wide
How much bile can the gallbladder hold
50mls
How many anatomical divisions make up the gallbladder
4
What are the four anatomical divisions of the gallbladder
Fundus
Funnel-shaped body
Infundibulum
Neck
What is the fundus of the gallbladder
The distal blind sac
What is the funnel-shaped body of the gallbladder
Connects the fundus and the infundibulum
what is the infundibulum of the gallbladder
The transitional region between the body and the neck
Occasionally has a shallow diverticulum known as Hartmann’s pouch, present on the inferior surface
Gallstones may become impacted within the pouch causing cystic obstruction and acute Cholecystitis
What is the neck of the gallbladder
It narrows into the cystic duct
What duct emerges from the gallbladder
The cystic duct
What duct merges with the cystic duct to form the common bile duct
The hepatic duct
What joins the common bile duct to form the ampulla of Vater
The pancreatic duct
When the common bile duct and pancreatic duct pass through the duodenal wall they are surrounded by smooth muscle known as
The sphincter of Oddi
How many layers does the gall bladder have
3
What are the three layers of the gallbladder
Outer serosa
Fibromuscular layer
Inner mucosa
What does the outer serosa layer of the gallbladder consist of
Derived from the peritoneum
What does the fibromuscular layer of the gallbladder consist of
Contains longitudinal and spiral smooth muscle and fibrous tissue
What does the inner mucosa layer of the gallbladder consist of
Made up of simple columnar epithelium and arranged in folds, or rugae, similar to those of the stomach
What is the function of the biliary system
Collects bile from the small lobules within the liver, concentrates it, and sends it through the biliary system to be stored in the gallbladder
Releases bile into the duodenum when needed to aid in the digestion of food
What is the function of the gallbladder
Stores and concentrates bile
Releases bile into the duodenum when stimulated by the hormone cholecystokinin (CCK)
What is the function of bile
It is an alkaline, greenish-yellow fluid that is secreted continuously by the liver
It is made up of water 97% bile salts, fatty acids, lipids (mainly cholesterol and lecithin) inorganic electrolytes, conjugated bilirubin and other organic substances
When bile leaves the liver it is 97% water, by the time it is stored in the gallbladder 90% of the water is absorbed to create concentrated bile
Emulsification of undigested fats
Facilitation of the absorption of fat-soluble vitamins
Activation of intestinal and pancreatic enzymes
Provision of a route for the excretion of bilirubin; cholesterol; and certain sex, thyroid, and adrenal hormones
Helps neutralize gastric acid in the duodenum
What happens when the biliary ducts are obstructed and are unable to allow the passage of bile
A build up of bile can cause jaundice which can be shown in the skin, sclera
Jaundice can also result from destruction of red blood cells or from liver dysfunction
How does bile move through the biliary system and into the GI tract
The sphincter of Oddi normally remains slightly opened to allow a continuous minuscule amount of bile to pass into the duodenum
During normal digestion when food enters the duodenum the hormone cholecystokinin-pancreozymin (CCK-PZ) is released causing the gallbladder to contract, which in turn pushes increased amounts of bile into the duodenum
Other factors that may cause contraction of the gallbladder includes:
Certain drugs, sensory input, disease, and emotional state
What arteries supply blood to the biliary system
The hepatic arteries
What veins drain blood from the biliary system
The cystic vein
What nerves innervate the biliary system
Sympathetic stimulation - derived from the splanchnic unreversed and 7th-10th thoracic segments
- inhibits smooth muscle gallbladder contraction
Parasympathetic stimulation - derived from the right branch of the vagus nerve
- causes the gallbladder to contract
- the sphincter of Oddi muscle to relax and the duodenal junction
What is the pancreas
- A fished shape, lobulated gland that lies behind the stomach and duodenum and in front of the spine
- Approximately 6-8 inches in length and 2 inches wide
- The average weight is less than 4 ounces
- Divided into three segments - head, body and tail
What is the head of the pancreas
The widest part of the pancreas and is found in the right side of the abdomen.
The head lies over the vena cava in the c-shaped curve of the duodenum
What is the uncinate process in relation to the pancreas
The part of the head of the pancreas that hook toward the back of the abdomen
The uncinate hooks around two very important blood vessels
- the superior mesenteric artery and
- the superior mesenteric vein
What is the neck of the pancreas
The thin section of the gland between the head and the body of the pancreas
What is the body of the pancreas
The middle part of the pancreas, which lies behind the duodenum and extends across the abdomen, behind the stomach and across the spine
The superior mesenteric artery and vein run behind this part of the pancreas
What is the tail of the pancreas
The thin tip of the pancreas in the left side of the abdomen in close proximity to the spleen
What are the cell types that make up the layers of the pancreas
Endocrine cells
Exocrine cells
What are exocrine cells of the pancreas
They are pyramidal acinar cell that make up the majority of the pancreatic tissue
Groups of acinar cells form an acinus and groups of acini form grape-like lobules
The lobules are joined together by connective tissue into lobes; which unite to form the entire gland
The acini are arranged around a small central lumen into which they drain their enzymes
The central lumina - of which the most proximal portion is lined by clear, cuboidal cells called centroacinar cells - is drained by means of ductules - they drain into multiple intralobular ducts - which in turn drain into the duct of Wirsung
They produce 500-1000ml of pancreatic juices daily
Controlled by hormones - cholecystokinin (CCK-PZ) stimulates the release of pancreatic enzymes when chyme is made up predominately of proteins and fats to break down the amino acid bonds of protein
What is the duct of Wirsung in relation to the pancreas
The main pancreatic duct
Runs the length of the pancreas
Joins the common bile duct, emptying into the duodenum at the ampulla of Vater
What is the duct of Santorini
It leads from the head of the pancreas and drains into the duodenum at an accessory or minor papilla that lies just proximal and anterior to the papilla of vater
What is the main function of the exocrine cells of the pancreas
Produces enzymes and juices that digest food
What are the pancreatic secretions produced by the exocrine cells
Secretin
Amylase
Lipase
Trypsin
Protease
What is the pancreatic enzyme secretin
It stimulates the release of pancreatic juice rich in bicarbonate and water when the chyme is comprised mainly of acid
The production occurs in four phases
What are the four stages of production of the pancreatic enzyme secretin
- At rest - mild secretion
- Cephalic phase caused by the sight and smell of food - modest secretion
- Gastric phase caused by distention of the stomach - moderate secretion
- Intestinal phase caused by delivery of food into the duodenum - maximum secretion
What are the three major types of digestive enzymes that are secreted by exocrine cells
- Amylases - hydrolyzes carbohydrates into glucose and maltose
- Lipases - hydrolyzes fat into glycerol and fatty acids
- Trypsin and chymotrypsin - digest proteins by breaking down amino acid bonds
What is protease in relation to pancreatic secretions
- includes trypsinogen, the precursor of trypsin
What is the function of endocrine cells of the pancreas
Islets of Langerhans secrete the hormones insulin and glucagon into the bloodstream to normalize blood sugar
Where can endocrine cells of the pancreas be found
They make up 1% of pancreatic cells and are found in the islet of Langerhans which is embedded in the loose connective tissue between the lobules, mainly in the tail
What are the three types of endocrine cells
Alpha cells
Beta cells
Delta cells
What do the alpha endocrine cells of the pancreas do
They produce glucagon
When the blood sugar level falls below normal, the alpha cells are stimulated to secrete glucagon which accelerates the conversion of glycogen to glucose in the liver
What do beta endocrine cells do
They produce insulin
When the blood sugar level is above normal, the beta cells secrete insulin, which promotes both the metabolism of glucose by the tissue cells and the conversion of glucose to glycogen, which is then stored in the liver and muscles
What do delta endocrine cells do
Produce the hormone somatostatin
Somatostatin secretion inhibits insulin and glucagon secretion as needed
How much blood flow do islet cells receive
Despite only being 1% of pancreatic mass they receive 10-15% of the pancreatic blood flow
This allows for hormones secreted by the cells close access to the circulation
What arteries supply blood to the pancreas
Branches of the:
Splenic artery
Superior mesenteric artery
Celiac artery
What veins carry blood away from the pancreas
Carried away from the pancreas into the portal or splenic circulation by the:
Superior mesenteric vein and
Splenic vein
What nerves innervate the pancreas
Sympathetic nerves control:
- pain sensation
- blood flow
- enzyme secretion
Parasympathetic nerves control:
- exocrine function
- endocrine function
What is the small intestine
A tubular structure that extends from the pyloric sphincter of the stomach to the cecum of the large intestine
It consists of three parts
Approximately 9 feet long in the neonate
Approximately 22-23 feet long in the adult and about 1.5 inches in diameter
What are the three parts of the small intestine
Duodenum
Jejunum
Ileum
What is the duodenum of the small intestine
The first 30cm (1ft) section of the small intestine
It is the c-shaped muscular section that begins at the pyloric sphincter and ends at the ligament of
Treitz
Lies retroperitoneal and attaches to the posterior abdominal wall
The common bile duct empties into the duodenum at the ampulla of vater
What is the jejunum of the small intestine
The section located after the duodenum and is the proximal two-fifths of the small intestine
Suspended by the mesentery from the posterior abdominal wall
Most of the intestinal villi are located in this section
What is the ileum of the small intestine
The distal three-fifths of the small intestine and extends from the jejunum to the ileocecal valve
The terminal ileum connects to the large bowel
Suspended by mesentery from the posterior abdominal wall
Contains fewer villi
What is the function of the ileocecal valve and where is it located
Controls the flow of chyme into the large intestine and prevents reflux from the large intestine into the ileum
Located at the junction of the terminal ileum and cecum
How many layers make up the small intestine wall
4
What are the four layers of the small intestinal wall
Outer serosa
Muscularis
Submucosa
Mucosa
What does the outer serosa layer of the small intestine wall consist of
Mesothelial cells that overlie loose connective tissue
Is arranged in circular folds called the plicae circulares which provide a greater surface area for secretion and absorption during the 3-6 hours the chyme remains in the small intestine
What does the muscularis layer of the small intestine wall consist of
It has an outerlongitudinal and inner circular muscles that are separated by a nerve network of ganglion cells and nerve fibers (myenteric plexus or Auerbach’s nerve plexus)
What does the submucosa layer of the small intestine wall consist of
Comprised of connective tissue that contains blood vessels, lymphatics and autonomic nerves called the Meissner’s plexus which communicated with Auerbach’s plexus
What does the mucosa layer of the small intestine wall consist of
Simple columnar epithelium known as the lamina propria
Thin sheet of smooth muscle known as the muscularis mucosae that separates the mucosa and submucosa
The mucosa forms an estimated 4-5 million small, finger-like villi that project into the intestinal lumen
Each villus is lined with simple columnar epithelial cells
A brush border consisting of multiple microvilli covers the surface of each columnar cell
The presence of the folds increases the absorptive capacity of the small intestine nearly 600-fold
What lies in the circumvillar basin (between the villi).
Crypts of Lieberkuhn
Paneth cells
Brunner’s glands
What are crypts of Lieberkuhn
Small tubular glands
Cells that replace the epithelium
- entire intestinal epithelial surface is replaced every 32 hours
What are Paneth’s cells
Located at the base of the crypts
Regulate intestinal flora
Secrete antimicrobial and growth protein substances
What are Brunner’s glands
They lie in the proximal duodenum
Elaborately branched acinar glands
Contain mucus and secretory cells
Secrete clear viscous alkaline fluid to neutralize entering gastric acid
They empty into the Crypts of Lieberkuhn
What is lymphoid tissue of the small intestine
Makes up about 25% of the intestinal mucosa
There are three distinct types
What are the three types of lymphoid tissue in the small intestine
Peyer’s patches
Lymphocytes and plasma cells
Intraepithelial lymphocytes
What are Peyer’s patches located in the small intestine
Circular aggregated lymph nodes that lie in the mucosa and submucosa of the ileum
They participate in antibody synthesis and in the bodies immune response
What are lymphocytes and plasma cells in relation to the small intestine
Located in the lamina propria
Approximately 70-80% of these cells produce immunoglobulin A (IgA) which is the major immunoglobulin in intestinal secretions
This secretory IgA plays an important role in the resistance of mucous membranes to pathological microorganisms and dietary antigens
What are intraepithelial lymphocytes in relation to the small intestine
Another type of lymphocyte
Lie between the intestinal epithelial cells
A large portion of these Intraepithelial lymphocytes are T cells
What is the function of the small intestine
Digestive
Absorptive
Secretory
Barrier
Immunologic
What is the primary function of the small intestine
Digestion and absorption of nutrients, electrolytes and vitamins from the chyme
Receives up to 8L of fluid per day and passes only 500-1000cc into the large intestine
7L of fluid is reabsorbed by columnar cells of the villous epithelium in the mucosal layer of the small intestine
Maintains intestinal fluid and electrolyte balance
What is absorbed in the different parts of the small intestine
Duodenum - the primary site of iron and calcium absorption
Jejunum - absorbs most of the fats, proteins, and carbohydrates
Terminal ileum - absorbs most of the B12 and bile acids
Where are the digestive juices and a variety of hormones secreted from and what secretions are received from the liver and pancreas
- Microvilli secretions contain peptidases and disaccharidases required to digest proteins and carbohydrates
- Brunner’s glands secrete an alkaline (pH 8.2-9.3), viscous fluid that protects the duodenal mucosa from gastric acid secretions
- Goblet cells located on and between the villi secrete a protective mucus
- The crypts of Lieberkuhn secrete 2-3L of watery fluid per day to supply a carrier substance for absorption of nutrients when the villi come in contact with the chyme
- Ten different types of endocrine cells located in the crypts produce peptides and gastric hormones
- Secretin, Cholecystokinin (CCK), Gastrin, Somatostatin, Neurotensin, Serotonin, Gastric inhibitory peptide, vasoactive intestinal peptide, enteroglucagon, motilin
What are the three types of movements that contribute to the mixing of chyme
- Concentric segmenting contractions - mix secretions of the small intestine with the chyme particles in the jejunum
- Short propulsive contractions (peristaltic) waves - push the chyme in the direction of the colon and occur in the first portions of the duodenum and jejunum
- Continuous shortening and lengthening of the villi - stir the intestinal contents
What arteries supply blood to the small intestine
Hepatic artery - supplies the duodenum
Superior mesentery artery - supplies the remainder of the small bowel
What veins carry blood away from the small intestine
Superior mesenteric vein
What nerves innervate the small intestine
The vagus nerve
- increases the tone of the small bowel
- increases the frequency, strength and velocity of the smooth muscle contractions
- enhances motor and secretory activities
Sympathetic stimulation via spinal nerves from T6-T12
- reduce peristalsis
- inhibit GI activity
What is the large intestine
- 4-5 feet long (120-150cm) and 2 inches (4-6cm) in diameter
- Extends from,the ileocecal valve to the anus
- Colon is the portion of the large intestine extending from the cecum to the rectum
- At the distal end of the small intestine there is a flap like valve known as the ileocecal valve that acts as a sphincter
What is the function of the ileocecal valve
Controls the passage of intestinal contents from the ileum to the colon
Prevents reflux of bacteria from the colon back into the small intestine, preserving the relative sterility of the small intestine
What are the different parts of the large intestine
Cecum
Ascending colon
Hepatic flexure
Transverse colon
Splenic flexure
Descending colon
Sigmoid colon
Rectum
What is the cecum in relation to the large intestine
- The first section of the large intestine to receive fecal material from the small bowel
- A short blind sac where the appendix is attached
- The appendix is a tubular structure from 2-20cm in length and about 8mm in diameter with no known digestive role
What is the ascending colon in relation to the large intestine
- The right colon
- It passes up the right side of the abdomen to the lower border of the liver
- It bends to the left at the right colic flexure - also known as the hepatic flexure
What is the transverse colon in relation to the large intestine
- The portion of the bowel that crosses the abdomen from the hepatic flexure to the splenic flexure (left colic flexure)
What is the descending colon (left colon) in relation to the large intestine
- Runs down the left side if the abdomen from the spleen to the iliac crest
- It then makes an s-curve at midline
What is the sigmoid colon in relation to the large intestine
- An s-shaped structure at the midline
What is the rectum in relation to the large intestine
- The last portion of the large intestine 8-13cm (4-6 inches)
- Follows the curvature of the lower sacrum and coccyx
- Distal portion forms the anal canal
- Movement of feces through the anal canal is controlled by
- internal sphincter of involuntary smooth muscle
- external sphincter of voluntary striated muscle
How many layers make up the large intestine wall
4
What are the four layers of the large intestine wall
- Serosa
- Muscularis
- Submucosa
- Mucosa
What does the serosa layer of the large intestine wall consist of
- Formed by the visceral peritoneum (the rectum does not have a serosa layer)
What does the muscularis layer of the large intestine wall consist of
- The inner circular and outer longitudinal bands (tenia coli) which form the hautstra
- Auerbach’s nerve plexus is located between the circular and longitudinal muscle layers
- A prominent extracellular matrix contains increased amounts of collagen and elastin than is present in the small bowel
- the amount of collagen and elastin increases with advancing age
What is the haustra that is located in the muscularis layer of the wall of the large intestine
The Tania coli are shorter than the intestine, thus causing it to pucker and form small sacs
The size and shape of the haustra vary with the state of contraction of the circular and longitudinal muscle layers
What does the submucosa layer of the large intestine wall consist of
- Comprised of loose connective tissue that contains arteries, veins, lymphatics and nerve fibers
- The nerve fibers and ganglion cells form the Meissner’s plexus
- The submucosa is separated from the mucosa by the muscularis mucosae, a layer of smooth muscle cells
What does the mucosa layer of the large intestine wall consist of
- Smooth surfaced and arranged in folds called plicae semulunares
- As in the small intestine the tubular crypts of Lieberkuhn open into the lumen of the large intestine
- Intestinal villi are absent from the large bowel
- The absorptive surface is flat and lined by columnar epithelial cells and a number of goblet cells
- There are fewer microvilli on the colonic columnar cells than in the small intestine
- The epithelium in the lower half of the crypts is composed of proliferative undifferentiated columnar cells, mucus-secreting goblet cells and a few endocrine cells
- The mucus membrane that lines the rectum is arranged in longitudinal rows called rectal or anal columns
- each rectal column contains an artery and a vein
- these rectal columns end about 2cm from the anal orifice where they join transverse tissue folds
- at the anorectal line, also known as the mucocutaneous border or the denate line, the colonic mucosa meets the external anal canal
- the anorectal line also marks a change on nerve supply and venous drainage
What is the function of the large intestine
- Absorption
- Absorption of electrolytes
- Excretion
- Storage and movement of intestinal contents
How is the function of absorption in the large intestine carried out
- Absorption of water is accomplished mainly in the large intestine
- 1,000-2,000cc of liquid chyme enters the colon daily
- 150-250 is evacuated
- The colon removes 80-90% of the water
What electrolytes are absorbed in the large intestine
- Absorbs sodium and chloride
- Most of the absorption is done in the ascending colon
What is excreted from the large intestine
- Minimum amount of secretion
- Mucus, water, potassium, and bicarbonate
- Goblet cells secrete alkaline mucus to lubricate and protect the mucosa from bacteria
- Metals such as lead, mercury, bismuth, silver and calcium are excreted through the large bowel
What does the function of storage and movement of intestinal contents of the large intestine consist of
- Elimination is accomplished in stool that contains intestinal bacteria that break down and decompose waste
- Normal stool is brown in color due to the metabolism of bile pigments to sterobilin. The odor is the result of indole, skatole, mercaptan, hydrogen sulfide and the breakdown products of cystine
- Contains gram-negative anaerobic bacteria to:
- break down waste material
- synthesize vitamin K
- control overgrowth of harmful bacteria
- destroy pancreatic enzymes
- Three basic patterns of movement
What bacteria is found in the large intestine
- An estimated 500 species of 100 trillion organisms live in the healthy colon
- The normal adult colon contains approximately 109-1,011 organisms per gm of stool, which consist primarily of both gram-negative anaerobic cocci and aerobic bacterium
- gram-negative anaerobic cocci - such as bacteroides, lactobacillus, eubacterium, bifidobacterium, veillonella and fusobacterium
- aerobic bacterium - such as Escherichia, enterococcus, streptococcus, bacillus, citrobacter, and klebsiella
- gram-negative anaerobic cocci - such as bacteroides, lactobacillus, eubacterium, bifidobacterium, veillonella and fusobacterium
What are the three basic patterns of movement found in the large intestine
- Periodic - uncoordinated contractions of the longitudinal and circular muscles forming the haustra
- Phasic - random, non-propulsive contractions that mix stool material and help absorb the liquid contents
- Spontaneous mass movements when the colon becomes filled and distended
- mass movements from the sigmoid into the rectum stimulate the urge to defecate
- results in peristaltic waves in the rectum and relaxation of the internal and external anal sphincters
What arteries supply blood to the large intestine
- The superior mesenteric artery - right half of the large intestine
- The inferior mesenteric artery - left half of the large intestine
- The hemorrhoidal artery ( a branch of the inferior mesenteric artery) - rectum and anal canal
- Branches of the hypogastric artery - rectum
What veins carry blood away from the large intestine
Venous blood from the colon is drained mainly through the inferior and superior mesenteric veins
Above the anorectal line - venous blood drains upwards to the superior hemorrhoidal veins and from there the portal veins
Below the anorectal line - venous blood drains downward to the inferior hemorrhoidal veins
What nerves innervated the large intestine
- Parasympathetic innervation of the right portion of the colon is derived from the vagus nerve
- The remaining portion of the colon receives parasympathetic innervation through the branches of the sacral nerves
- in general parasympathetic nerves increases intestinal contraction and mucus secretion and inhibits the rectal sphincter - Sympathetic innervation through the spinal nerves
- stimulation of sympathetic fibers inhibits colonic motility and secretions and stimulates the rectal sphincter
