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Associated glands And Histology

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MAJOR GLANDS ASSOCIATED WITH ALIMENTARY CANAL  .


  1. Salivary glands 

 It is an exocrine gland associated in the buccal cavity. Major  salivary glands are :

  • Parotid gland :  largest salivary gland located between skin of cheeks and masseter muscle.

 Its duct is  called  stenson’s duct that innervates the buccinator muscle above the second molar.

 Its secretion is purely serous   of about 20% of saliva.

 Myxo virus affect this gland mainly in babies  to cause Mumps .

  •  Sub -mandibular gland :  second largest salivary gland ; located just below mandibular angle .

 Its duct is called Wharton's duct opening behind lingual frenulum.

Mixed salivary glands  producing equal serous as that of mucous secretion; which is the most; 70% of the total saliva,

  • Sub lingual gland:

 Located on the floor  of the buccal cavity.

Duct of rivinus is called for it’s duct . 

Mucous  secretion ; of about 5% ;the least of 3.


 Other minor salivary glands contribute rest shares in saliva formation. They are vital to moist your mouth in an idle state of buccal cavity; no food in the cavity.

 Saliva :

  • Seromucinous liquid  of Ph 6.2 acidic in idle state.

  • Consists 99.5% water, the rest are enzymes  like ptyalin ( lingual  amylase), lipase, electrolytes like Na,cl ions and many others  and immunoglobulin A.

  • 1600 ml of it is secreted per day

  • FUNCTIONS : lubrication and digestion of food,lysogenic role,dissolving solid foods for taste buds reception and immunity too.

  1. Liver 

  • Largest visceral organ but  second largest organ after skin in case of humans.

  •  Weighs about 1.5 kg  in a healthy adult.

  • Location : below diaphragm in abdominal pelvic  cavity. 

  •  Divided unequally into right and left lobe  divided by falciform ligament, anatomically.  Left  is smaller ; one sixth the total while the right  lobe is  the remaining ones. But looking dorsally we can further divide right one to 3 sub parts called right proper, caudate, quadrate. So humans have 4 lobes functionally  while frogs have 3 lobes and rabbits have 5.

  • Intraperitoneal organ but truly covered by fibrous connective tissue called Glisson’s capsule .

  • 27% of  CARDIAC OUTPUT reach this organ  which is the most of all.

 Histology of liver : 


  • Functional  unit of the liver is hepatic lobules.

  • Each lobule is hexagonal with a centrally located vein. Lines of polyhedral cells in intra locular space are called hepatic cord.

  • In each hepatic cord spaces are called canaliculi while spaces in between  2 hepatic cords are called  hepatic sinusoids.

  • Each vertex of lobules are with a portal triad  whose transverse view is with hole of portal vein, artery and bile duct.

  • 80% of total supply are of hepatic portal vein and rest of hepatic arteries.

  • Cells in lobules can be ito/stellate  cells ; which stores fat  or kupffer cells ; which are phagocytic or normal bile secreting or storage or producing cells .

 Functions of liver : 


  • Main role is production of bile juice secretion.

 Short note to bile juice :

  • An alkaline fluid  that is bitter in taste and golden yellow  colour .

  • 500 ml per day .

  • Composition : 86% water and rest  14% includes bile salts of glycolic and taurocholic acids, bile pigment like bilirubin and biliverdin, cholesterol , lecithin , inorganic salts of chlorides and essential component ; carbonates making fluid alkaline.

  •  Functions :  

  1. Bile salts here;

  •  emulsifies fat ; which is breaking large globules to smaller ones which is  mechanical digestion.

  • Neutralizes acidic chyme .

  • Increases peristaltic movement .

  • Absorption of fat soluble vitamins.

  • Bile acids coat the  emulsified fats.

  1. Metabolic function : 

  •  Glycogenesis : conversion of excess glucose to glucagon in presence of insulin.

  • Glycogenolysis : reverse of glycogenesis in  presence of glucagon.

  • Gluconeogenesis : formation of glucose from non-carbohydrates source 

  • Lipogenesis : excess protein and fats convert to lipids .

  1. Deamination of acid ;  excess of protein  gains a lot of ammonia which is converted to urea.

  2. Detoxification  of toxins .

  3. Thermogenesis : thermal homeostasis  condition in the body.

  4.  Synthesis of RBC in babies, blood proteins, heparin, glycogen, fat soluble vitamins. Vitamin B12,angiotensinogen, iron, copper, vitamin A from beta carotenes.

  5. Destruction of RBC and converted  it’s protoporphyrin portion to bilirubin and biliverdin.

  6. Immunological role by kupffer ‘s cells.


  All the hepatic ductules  from each side  meet to form the right and  left hepatic duct. The sides  from both  join to form a common hepatic duct  which further join with bile  duct from gallbladder to form common bile duct . This again joins with a pancreatic duct called duct of wirsung and    forms a swollen common hepatic pancreatic   ampulla called “ ampulla of vater”.

Sphincter of boyden  lies guarding  on junction joining with duct of wirsung

 While a sphincter of oddi guards the  end of ampulla of vater.

 Another supplementary duct called the duct of santorini arises from pancreas only, opening  right of  opening of common hepatic pancreatic   ampulla. 


  1. Pancreas 

  •  Soft , lobulated and retroperitoneal , endodermal  and pale greyish pink in colour.

  • 2nd largest gland  about 12 -15 cm in length and 60 gm in weight.

  • Located :  behind and below stomach in concavity of duodenum so called, romance of duodenum.

  • It  can be divided into 4 parts : 

  1. Bulky head :  it is   positioned on a curve  and exocrine in nature. It posses extra growth off called uncinate portion.

  2. Neck : this is also exocrine  part

  3. Body : also exocrine 

  4. Tail : this is the endocrine part  secreting  hormones. This part is in fact  intraperitoneal .

 Histology : 

  •  Lumen  are connective tissues and pancreatic lobules .

  • Each pancreatic lobule is  with many columnar granulated cells .

  • Their secretions are thrown off the lumen  and are connected with the pancreatic duct.

  • Types of  enzymes  secreted  by those acinar  cells : pancreatic amylase, trypsinogen,  pancreatic lipase . 

  • Duct cells are responsible to produce bicarbonates under action of secretin hormones.

  •  Lumen of mostly tails, possess endocrine cells  called islets of langerhans.   This consists of four types of cells : 

  1. ∝ cells : secretes glucagon 

  2. ᵝ cells : secretes insulin .

  3. ઠ cells : inhibits abovementioned cells .

 Pancreatic  juice  : 

  • Alkaline of Ph 8   includes  enzymes like pancreatic amylase, trypsinogen,  pancreatic lipase and bicarbonates ,sodium, calcium, magnesium, potassium ions .

  • 1500 ml per day secretion.

 Functions of pancreas: 

  • Secretes enzymes for digestion. 

  • Hormones for glucose humoral control.

  • Neutralize acidic chyme .


Histology of alimentary canal :

Tissues from oesophagus to anal canal more or less are similar posssesing 4 layers : 

  1. Serosa 

  2. Muscularis externa 

  3. Sub mucosa 

  4. Mucosa : 

  • Muscularis interna 

  • Lamina propria 

  • Mucosa epithelium 

  •   Serosa : this is the outermost layer made up of squamous epithelium .  However , this layer is made up of elastic  fibrous  connective tissue in the oesophagus called tunica adventitia. Because they lie out of coelom .


  • Muscularis externa  :  in general there is outer longitudinal muscle and inner  circular muscle. But  in the stomach there is an extra middle oblique layer. Here there  is myenteric/Auerbach’s plexus  to create peristaltic waves .


  • Sub mucosa : this layer possesses connective tissues like areolar ,lymphatic vessels and blood vessels.  In the small intestine’s ileum there are wandering cells called peyer’s patch .Meissner's  plexus is here to control secretion of glands here. sub mucosa and mucosa both extend inward , fold to form plica circularis/valve of kerckring (but not a valve) . While only mucosa fold to form villi; to fullfill the purpose of effective and more absorption of digested food.


  • Mucosa : 

  • Muscularis interna : outer longitudinal and inner circular muscles like muscularis externa .

  • Lamina propria: this is a layer of connective tissues  and  the speciality in duodenal histology is presence of brunner’s gland.

  • Mucosal epithelium :   buccal cavity,oesophagus and anus have stratified squamous epithelium and rest are with simple  columnar epithelium.

 Extra : 

 Gross look to retroperitoneal part of the system : 

  1. Pancreas except tail.

  2. Duodenum  except 1st part that excludes ampulla of vater . the  intraperitoneal  region is also a common site for peptic ulcer.

  3. Colons.


Diagram of histology discussed below :

                    

 fig : common histology.