Is a fibromuscular tube, approximately 25cm in length and 2cm in diameter, that transports food from the pharynx to the stomach.

Ends at the cardiac orifice of the stomach.

Food is transported through the esophagus by peristalsis- rhythmic contractions of muscles which propagate down the esophagus.

Hardening of these muscular layers can interfere with peristalsis and cause difficulty in swallowing (dysphagia)

STRUCTURE

It has four layers; from outside

Adventitia

Muscle layer

Submucosa

Mucosa

Outer layer of connective tissue, elastic fibrous tissue.

NB: The very distal and intraperitoneal portion of the esophagus has an outer covering of serosa, instead of adventitia.

There are two layers

The inner is circular

The outer is longitudinal

The external layer is composed of different muscle type in each third

Superior third – voluntary striated muscle

Middle third – voluntary striated and smooth muscle

Inferior third – smooth muscle

Made up of non-keratinized stratified squamous epithelium

There are two sphincter

Upper esophageal sphincter

Lower esophageal sphincter

This is an anatomical, striated muscle sphincter at the junction between the pharynx and esophagus

It is produced by the cricopharyngeus muscle

Normally, it is constricted to prevent the entrance of air into the esophagus

Is located at the gastro-esophageal junction

This sphincter is classified as a physiological (or functional) sphincter.

VASCULATURE

Arterial blood supply is through oesophageal arteries, branches of thoracic aorta, inferior phrenic arteries and the left gastric branch of the coeliac artery

Venous drainage is through the azygos and hemiazygos veins, and left gastric vein

Home work

Innervation

Lymphatic drainage of esophagus

Is the expanded part of the alimentary tract between the esophagus and the small intestine.

Situated in the epigastric, umbilical and left hypochondriac regions of the abdominal cavity.

It is intraperitoneal digestive organ located btn the esophagus and duodenum.

In most people, the shape of the stomach resembles the letter J.

The stomach has

Two openings

Cardiac orifice

Pyloric orifice

Two curvatures

Greater curvature

Lesser curvature

Two surfaces

Anterior surface

Posterior surface

The stomach is divided for descriptive purposes into four regions by arbitrary lines drawn on its external surface

The cardia, which surrounds the opening of the esophagus into the stomach

The fundus of stomach, which is the area above the level of the cardial orifice

The body of stomach, which is the largest region of the stomach

The pyloric part, which is divided into the pyloric antrum and pyloric canal and is the distal end of the stomach

Serosa

Muscle layer

An outer layer of longitudinal fibres

A middle layer of circular fibres

An inner layer of oblique fibres.

Submucosa

Mucosa: simple columnar epithelium

Mechanical function

Storage function

Chyme formation

Digestive function

Protective function

Hemopoietic function

Excretory function

Arterial supply: branches of coeliac artery

venous drainage is into the portal vein.

Nerve supply

The sympathetic supply to the stomach is mainly from the coeliac plexus

The parasympathetic supply is from the vagus nerves.

Sympathetic stimulation reduces the motility of the stomach and the secretion of gastric juice

vagal stimulation has the opposite effect

It is highly adapted for digestion and absorption

The walls of small intestine are composed of four layers of tissues and there are some modifications of the peritoneum and mucous membrane

The surface area of the mucosa is greatly increased by permanent circular folds, villi and microvilli

It consists of three parts

The duodenum

The jejunum

The ileum

Is a C-shaped tube surrounding the head of the pancreas and is the shortest (25 cm long) but widest part of the small intestine.

It begins with the duodenal bulb and ends at the ligament of Treitz

Secretions from the gall bladder and pancreas are released into the duodenum through the hepatopancreatic ampulla, and the opening into the duodenum is guarded by the sphincter of Oddi

Is divided into four parts

Superior (First) Part

Descending (Second) Part

Transverse (Third) Part

Ascending (Fourth) Part

Is the middle section of the small intestine

In adult humans, the small intestine is usually between 5.5-6m long, 2.5m of which is the jejunum

The inner surface of the jejunum, its mucous membrane, is covered in projections called villi, which increase the surface area of tissue available to absorb nutrients from the gut contents

The ileum is the final section of the small intestine

It is separated from the cecum by the ileocecal valve

The function of the ileum is mainly to absorb vitamin B12 and bile salts and whatever products of digestion which were not absorbed by the jejunum

Onward movement of its contents which is produced by peristalsis

Secretion of intestinal juice

Completion of chemical digestion of carbohydrates, protein and fats in the enterocytes of the villi

Protection against infection by microbes that have survived the antimicrobial action of the hydrochloric acid in the stomach, by the solitary lymph follicles and aggregated lymph follicles

Secretion of the hormones cholecystokinin (CCK) and secretin

Absorption of nutrients.

Its length is about 1.5 metres long, which is about one-fifth of the whole length of the intestinal canal

Its subdivisions include

The cecum

Colon

Rectum

Anal canal

Is a pouch, connecting the ileum with the ascending colon of the large intestine

It is separated from the ileum by the ileocecal valve is considered to be the beginning of the large intestine

It is also separated from the colon by the cecocolic junction

The vermiform appendix is a fine tube, closed at one end, which leads from the caecum.

It is usually about 13 cm long and has the same structure as the walls of the colon but contains more lymphoid tissue

Has four parts

Ascending colon

Transverse colon

Descending colon

Sigmoid colon

This is a slightly dilated section of the colon about 13 cm long.

It leads from the sigmoid colon and terminates in the anal canal.

This is a short passage about 3.8 cm long in the adult and leads from the rectum to the exterior.

Two sphincter muscles control the anus

The internal sphincter, consisting of smooth muscle fibres, is under the control of the autonomic nervous system

The external sphincter, formed by skeletal muscle, is under voluntary control

The four layers of tissue described in the basic structure of the gastrointestinal tract are present in the large intestine.

The arrangement of the longitudinal muscle fibres is modified in the colon.

They do not form a smooth continuous layer of tissue but are collected into three bands, called taeniae coli, situated at regular intervals round the colon.

The anal sphincters are formed by thickening of the circular muscle layer

Absorption

Microbial activity

Temporary storage of feces

Lubrication of feces by mucus

Accessory organs of gastrointestinal tract: The organs which are not directly part of gastrointestinal tract but their products are essential for the digestive system to accomplish its primary function

These organs include

The liver

Gallbladder and bile duct

Pancreas

These are essential for the digestive system as they either produce or store secretions essential the digestion to take place

Is the largest gland in the body, weighing between 1 and 2.3Kg

In adults the liver weighs 2% of body mass

It is situated in the upper part of the abdominal cavity occupying the greater part of the right hypochondriac region, part of the epigastric region and extending into the left hypochondriac region.

Is divided, based on hepatic drainage and blood supply, into the right and left lobes by the fossae for the gallbladder and the IVC.

Diaphragmatic surface, the convex upper surface of the liver which is molded to the undersurface of the domes of the diaphragm. 

Visceral surface or posteroinferior surface, is uneven and concave. It is covered in peritoneum apart from where it attaches the gallbladder and the porta hepatis

Two main lobes

right lobe(larger)

left lobe(smaller)

They are separated by the falciform ligament.

The right lobe is further divided lobe by the presence of the GB, the fissure for the ligamentum teres, IVC, and the fissure for the ligamentum venosum into:

quadrate lobe (anteriorly and inferiorly)

caudate lobe (posteriorly and superiorly).

Caudate and quadrate lobes are functional part of the left lobe.

Glisson’s capsule: The capsule of the liver. A layer of connective tissue surrounding the liver and ensheathing the hepatic artery, portal vein, and bile ducts within the liver.

The liver is made up of liver lobules. These are the structural functional units of the liver.

Each lobule is drained by a central vein which is a tributary of the hepatic vein. 

In the spaces between the lobules are the portal canals. These contain branches of the hepatic artery, portal vein and a tributary of a bile duct (the three together known as the portal triad).

The arterial and venous blood passes btn the liver cells by means of sinusoids.

Fissure for the round ligament (ligamentum teres hepatis), located between the lateral portion of the left lobe and the quadrate lobe.

Fissure for the ligamentum venosum, located between the caudate lobe and the lateral portion of the left lobe.

Fossa for the gallbladder, located between the quadrate lobe and the major part of the right lobe.

Fissure for the IVC, located between the caudate lobe and the major part of the right lobe.

Porta hepatis. This transverse fissure on the visceral surface of the liver between the quadrate and caudate lobes lodges the hepatic ducts, hepatic arteries, branches of the portal vein, hepatic nerves, and lymphatic vessels

The bare area of the liver (nonperitoneal area) is a large triangular surface of the liver devoid of peritoneal covering.

The coronary ligaments represent reflections of the visceral peritoneum covering the liver onto the diaphragm.

Boundaries of bare area of liver

Superior coronary ligament

Inferior coronary ligament

Left triangular ligament

Right triangular ligament

Dual Blood Supply

Artery: The hepatic artery (30%), a branch of the celiac artery, divides into Rt and Lt terminal branches that enter the porta hepatis.

Vein: The portal vein (70%) divides into Rt and Lt terminal branches that enter the porta hepatis behind the arteries.

Venous Drainage

The hepatic veins (3 or more) emerge from the posterior surface of the liver and drain into the IVC.

The liver produces a large amount of lymph (~ 1/3 – 1/2) of all body lymph.

The lymph vessels leave the liver and enter a number of lymph nodes in the porta hepatis.

The efferent vessels pass to the celiac nodes.

A small number of vessels pass from the bare area of the liver thru the diaphragm to the posterior mediastinal lymph nodes.

Nutrient and vitamin metabolism and storage

Glucose and other sugars

Amino acids (Deamination of amino acids),the end product is urea which is then excreted in the urine)

Lipids o Fatty acids

Cholesterol

Lipoproteins

Fat-soluble vitamins

Water-soluble vitamins

Breakdown of erythrocytes and defense against microbes

Detoxification of drugs and noxious substances

Inactivation of hormones such as Steroids

Production of heat

Formation and Secretion of bile

Synthesis of plasma proteins

Acute-phase proteins

Albumin

Clotting factors

Steroid-binding and other hormone-binding proteins

Immunity; by Kupffer cells

The system of organs and ducts that create and store bile and release it into the duodenum.

It is also known as the biliary, or bile, tract.

Bile is secreted(produced) by the liver cells. It is stored, and concentrated in the Gall Bladder; later it is delivered to the duodenum.

The bile ducts of the biliary system consist of

Rt and Lt hepatic ducts

Common hepatic duct

GB and Cystic duct

Common Bile duct

The right and left hepatic ducts join to form the common hepatic duct just outside the portal fissure.

The hepatic duct passes downwards for about 3 cm where it is joined at an acute angle by the cystic duct from the gall bladder.

The cystic and hepatic ducts together form the common bile duct which passes downwards behind the head of the pancreas to be joined by the main pancreatic duct at the hepatopancreatic ampulla.

The opening of the combined ducts into the duodenum is controlled by the sphincter of Oddi.

The common bile duct is about 7.5 cm long and has a diameter of about 6 mm.

The gallbladder is a pear-shaped sac lying on the visceral surface of the right lobe of the liver in a fossa between the right and quadrate lobes attached the liver by connective tissue.

The gallbladder has the following structures

Fundus of gallbladder: A rounded end, which may project from the inferior border of the liver

Body of gallbladder: A major part in the fossa, which may be against the transverse colon and the superior part of the duodenum

Neck of gallbladder: A narrow part, with mucosal folds forming the spiral fold

The walls of the gallbladder is formed by three tunics which are

Inner mucous layer which folded into reggae and this allows it to expand

The muscular layer which contains smooth muscles that allows the gallbladder to contract

The outer covering layer of the serosa

It stores and concentrates the bile which is secreted by the liver

Concentration of the bile by up to 10 or 15 fold by absorption of water through the walls of the gall bladder

Release of stored bile

The pancreas is a pale grey gland situated in the epigastric and left hypochondriac regions of the abdominal cavity weighing about 60 grams and it is about 12 to 15 cm long.

The pancreas consists of

Head

Neck

Uncinate process

Body

Tail

The pancreas is both an exocrine and endocrine gland.

Exocrine portion

Makes up majority of pancreas

Has a compound acinar arrangement and tiny ducts which unite to form the main pancreatic duct, which empties into the duodenum

It secretes pancreatic juice which consists of pancreatic enzymes

Endocrine portion

embedded between exocrine units; called pancreatic islets; constitute only 2% of the total mass of the pancreas; made up of alpha cells and beta cells which produce glucagon and insulin respectively and pass its secretions into capillaries

The arterial supply is through pancreatic arteries the branches of splenic artery, gastro-duodenal and superior mesenteric arteries

VENOUS DRAINAGE

Follows arterial supply