Digestive Glands

Digestive Glands:

1. Salivary Gland

-Three pairs in man, secrete saliva into oral cavity.

-Saliva is slightly Acidic (pH 6.8)

-Everyday 1 to 1.5 liter of saliva is secreted in man

i)Parotid Gland

-Largest and situated near the ears.

-Their ducts open into the oral cavity near the upper second Molar teeth.

-The duct of Parotid Gland is called Stenson’s Duct.

ii)Sublingual Gland

-Situated beneath the tongue.

-Their ducts are called Sublingual ducts or duct of Rivinus.

-Their ducts open into the floor of oral cavity.

iii)Submandibular(Submaxillary) Gland

-Located at the angle of lower jaw.

-Their ducts open into the oral cavity near the lower central Incisor.

-Their ducts are called Whartson’s Duct.

-In few mammals including man and Pig, saliva contains starch digesting enzyme(Salivary Amylase also called Ptyalin)

-The Parotid Salivary Glands secrete much of salivary amylase.

-Sublingual and Submandibular salivary glands secrete salivary amylase and mucus.

NOTE:The disease Mumps is a viral infection that may involve one or more of the Parotid salivary gland.

2.Gastric Gland:

-Four types of gland cells are found in the gastric gland.

i)Peptic(Chief or Zymogenic) Cells

-Secrete proenzyme(Pepsinogen and Prorenin)

ii)Oxyntic(Parietal)

-Secrete HCl and Castle intrinsic factor.

iii)Mucous Cell

-Secrete watery substance, the mucus, which has some protein-like material called mucin.

iv)Argentaffin Cells

-May produce Somatostatin, 5-Hydroxytryptamine(a powerful stimulant) and Histamine.

Gastric Juice is composed of these all cells secretion(pH 2-3.7)

Infant’s gastric juice ph is 5.0

2 to 3 liter of Gastric Juice is secreted everyday.

3.Liver(Heper):

-Largest gland of the body.

-Heavier in male(1.4-1.8 Kg) than in female(1.2-1.4Kg).

-Covered by two sheaths

i)Serous Capsule(outer) consists of visceral peritoneum.

ii)Glisson’s Capsule(inner) consists of thin layer of dense connective tissue.­

-The Liver is divided into two main lobes(Right and Left Lobe)separated by the

  Falciform Ligament.

The Right Lobe of the Liver is differentiated into Right Lobe Propria, a Quadrate Lobe and a Caudate Lobe on the posterior surface.

-Gall Bladder found in the Liver stores bile secreted by the Liver.

-Rat and Horse do not have Gall Bladder.

-Right and Left Hepatic duct arises from the corresponding lobes and join to form the

  Common Hepatic duct. Common Hepatic duct joins with Cystic duct of Gall Bladder and form Bile duct.

-Bile duct passes downwardly and joins with Pancreatic duct forming Hepatopancreatic Ampulla(Ampulla of Vater).

-Ampulla of Vater opens into the Duodenum and the opening is guarded by Sphincter of Oddi.

-The sphincter of Boyden surrounds the opening of Bile duct before it is joined with pancreatic duct.

-Hepatic lobules are found in the Liver which are the functional and structural unit of the Liver.

-At the periphery of the lobule the bile canaliculi empty intoHering’s canals which are walled by cuboidal epithelium.

-Hepatic sinusoids are wide capillary like blood vessels lined by incomplete endothelium.

-Kupffer cells(hepatic macrophages or stellate cells) are also present in the Liver.

Kupffer cells are phagocytic in nature which eat bacteria and foreign substances.

-Liver has high power of regeneration.

-Blood enters the Liver through the Hepatic Artery and Hepatic Portal Vein.

Function of Liver:

1. Production of Bile (pH 8.6) -about 500ml to 1000ml bile is secreted everyday. Bile is stored in the Gall Bladder.

2. Deamination-It is a process by which the amino group(-NH₂) is removed from the amino acids resulting in the production of ammonia which is converted into Urea.Deamination is carried out by Liver cells.

3. Excretion-Liver synthesizes Urea with the help of Ammonia and Carbon dioxide.The bile contains bile pigments(billirubin-yellow and biliverdin-green) the are excretory product.Liver also eliminate certain other wastes like cholesterol, metal ions and waste product of haemoglobin.

4. Glycogenesis- It is the conversion of excess of Glucose into Glycogen by Liver cells with the help of Insulin secreted by the Pancreas.

5. Glycogenolysis- It is the conversion of glycogen into glucose by the liver cells with help of glucagons secreted by the pancreas.

6. Lipogenesis- Conversion of excess of glucose and amino acid into fats.

7. Gluconeogenesis- It is the formation of glucose or glycogen from non-carbohydrate sources.It also occurs in the kidneys and striped muscles.

8. Detoxification- Liver converts toxic substance into harmless substance eg.harmful prussic acid, formed during metabolism in all body cells, is neutralized and rendered harmless by Liver cells.

9. Haemopoiesis-Process of formation of blood corpuscles.Liver produces red blood corpuscles (RBC) in the embryo.

10.Synthesis of Blood Proteins-Liver produces blood proteins such as prothrombin and fibrinogen that help in the clotting of blood.

11.Secretion of Heparin(anticoagulant)

12.Lymph formation

13.Synthesis of Vit. A -Liver synthesizes Vitamin A from β-carotene(orange-yellow substance of carrot)

14.Secretion of Enzyme-Liver secretes certain enzymes which play important roles in the metabolism of proteins, fats and carbohydrates in the body.

15.Destruction of RBC- Old RBCs are broken down and haemoglobin is changed into bile pigment.

16.Phagocytosis- The Kupffer’s cells of Liver engulf the disease causing micro-organism,dead cells and foreign matter.

17.Osmoregulation-Liver produces angiotensinogen(a protein) which helps kidneys in maintaining body fluid osmoregulation.

18.Production of Heat- due to high metabolic activities enough heat is generated which is essential for maintaining the optimum body temperature.

19.Storage-It stores glycogen, fats, Vitamins(A,D,E,K and B₁₂), bile in the gall bladder, blood, water, iron, copper and potassium.

Function of Bile:

1.Neutralization of HCl-Its sodium bicarbonate neutralizes HCl of chyme(semi fluid food found in stomach)

2.Emulsification-sodium glycocholate and sodium taurocholate break the large fat droplets into the smaller ones.

3.Absorption of fat and fat-soluble vitamins-its salts help in the absorption of fat(fatty acids and glycerol) and fat-soluble vitamins(A,D,E and K)

4.Excetion-Bile pigments(bilirubin and biliverdin) are excretory products.

5.Prevention of decomposition-Bile is alkaline hence it prevents the decomposition of food by preventing the growth of bacteria on it.

6.Stimulation of Peristalsis-Bile increases peristalsis of the intestine.

7.Activation of Lipase-Bile contains no enzyme but activates the enzyme Lipase.

4.Pancreas:

-Soft,lobulated,grayish-pink gland weighs about 60grams.

-2.5 cm wide 12 to 15 cm long.

-Located posterior to the stomach in the abdominal cavity.

-The main pancreatic duct (duct of wirsung) opens into the hepatopancreatic ampulla(ampulla of vater).

-an accessory pancreatic duct(duct of santorini) is also present in the pancreas and opens directly into the duodenum.

-It is a mixed type of gland.

-Consists of two parts:   Exocrine part and Endocrine part

i)Exocrine Part

-consists of rounded lobules(acini) that secret an alkaline pancreatic juice with pH 8.4

-500ml to 800ml of pancreatic juice is secreted daily and is carried by main pancreatic duct into duodenum through hepatopancreatic ampulla.

-The accessory pancreatic duct directly pours the pancreatic juice into duodenum.

-The pancreatic juice contains NaHCO₃ ,three proenzymes; trypsinogen, chymotrypsinogen and procarboxypeptidase and some enzymes such as elastase, pancreatic α-amylase, DNAase, RNAase and pancreatic lipase.

-The pancreatic juice helps in the digestion of starch, protein, nucleic acids and fats.

ii)Endocrine part

-Consists of Islets of Langerhans.

-The human pancreas has about 1 million islets.Most numerous in the tail of pancreas.

-Each Islets of Langerhans consists of the following types fo cells which secret hormones to be passed into the circulating blood.

a)Alpha cells(α-cells)-more numerous towards the periphery of islets. Constitute 15% of islets of langerhans. Produce Glucagon hormone.

b)Beta cells(β-cells)-More numerous towards the middle of the islet.Constitute 65% of islets of langerhans.Produce insulin hormone.Dificiency of insulin causes diabetes mellitus.

c)Delta cell(δ-cells)-Constitute 5% of islets of langerhans.Secret Somatostatin(SS) hormone.Its secretion inhibits the secretion of glucagons and to a lesser extent secretion of insulin.It also inhibits the secretion of growth hormone by anterior pituitary gland.

d)Pancreatic polypeptide cells(PP cells or F cells)-It constitute 15% of islets.Secretes pancreatic polypeptide which inhibits production of pancreatic juice.

-Pancreas performs two main function ,i.e. secretion of pancreatic juice(digestive enzyme) and production of hormones.

5.Intestinal Glands:

-These are of two types; Crypts of Lieberkuhn and Brunner’s Glands.

i)Crypts of Lieberkuhn

-occurs throughout the small intestine between the villi.

-secrete digestive enzymes and mucus.

ii)Brunner’s Gland

-found only in the duodenum and are located in the submucosa.

-secrete a little enzyme and mucus.

The secretion of intestinal glands is called intestinal juice or succus intericus with pH 7.6.About two to three liters of intestinal juice is secreted daily.The intestinal juice contains many enzymes –maltase,isomaltase,sucrase,lactase,α-dextrinase,enterokinase,aminopeptidase,dipeptidases,nucleotidases,nucleosidases and intestinal lipase.