Anatomy and Functions of Accessory Glands of GIT
The gastrointestinal tract has several accessory organs that assist in the breakdown and digestion of ingested food. These include:
- Teeth
- Tongue
- Salivary glands
- Gall bladder
- Pancreas
- Liver
1) Teeth
Teeth are embedded in the alveoli of the mandible and maxilla. Humans have two sets of teeth: deciduous (temporary) and permanent. Deciduous teeth (20) erupt between 6–24 months. Permanent teeth (32) replace deciduous teeth starting from the 6th year and complete by the 21st year.
Functions of Teeth
- Incisors and canines: cutting and biting food
- Premolars and molars: grinding and chewing food
Structure of a Tooth
- Crown: protrudes from gum
- Root: embedded in bone
- Neck: region connecting crown and root
- Pulp cavity: contains blood vessels, lymph vessels, and nerves
- Dentine: hard ivory-like layer surrounding pulp
- Enamel: covers crown
- Cementum: covers root and secures tooth in socket
Blood and Nerve Supply
Arterial supply: branches of maxillary arteries. Venous drainage: internal jugular veins. Nerve supply: branches of trigeminal nerve (maxillary for upper teeth, mandibular for lower teeth).
2) Tongue
The tongue is a voluntary muscle attached to the hyoid bone and floor of the mouth via the frenulum. The superior surface has papillae with taste buds.
Blood Supply
Lingual branch of external carotid artery; venous drainage via lingual vein to internal jugular vein.
Nerve Supply
- Hypoglossal nerve (12th cranial nerve) – voluntary muscles
- Lingual branch of mandibular nerve (5th cranial nerve) – somatic sensation
- Facial (7th) and glossopharyngeal (9th) nerves – taste
Functions
- Chewing (mastication)
- Swallowing (deglutition)
- Speech
- Taste
3) Salivary Glands
Salivary glands release saliva into the mouth via ducts. Major glands include:
- Parotid: below the external acoustic meatus; opens near 2nd upper molar
- Submandibular: under the jaw; ducts open near tongue frenulum
- Sublingual: under mucosa of floor of mouth; multiple ducts
Structure
Each gland is lobulated with acini lined by secretory cells. Secretions flow into ducts opening in the mouth.
Blood Supply
Branches of external carotid arteries; venous drainage into external jugular veins.
Composition and Function of Saliva
- Water, mineral salts, mucus
- Salivary amylase – begins starch digestion
- Antimicrobial substances – immunoglobulins, lysozyme
- Lubricates and cleans mouth, aids taste and swallowing
Secretion Control
Autonomic nervous system controls saliva: parasympathetic – watery, enzyme-rich; sympathetic – small, organic-rich. Reflexes triggered by food, sight, or thought of food.
4) Gall Bladder
Pear-shaped sac on the posterior liver surface; consists of fundus, body, and neck connecting to cystic duct.
Blood Supply
Cystic artery (branch of hepatic artery); cystic vein drains into portal vein.
Functions
- Reservoir for bile
- Concentration of bile by absorption of water
- Release of bile into duodenum via contraction, stimulated by CCK and fat in chyme
5) Pancreas
A 12–15 cm gland in epigastric and left hypochondriac regions. Head in duodenal curve, body behind stomach, tail near spleen. Functions as both exocrine and endocrine gland.
Exocrine Pancreas
Acini secrete digestive enzymes into pancreatic duct, joining bile duct at hepatopancreatic ampulla, controlled by sphincter of Oddi.
Endocrine Pancreas
Pancreatic islets secrete insulin and glucagon directly into blood for glucose regulation.
Blood Supply
Splenic and mesenteric arteries; veins drain into portal vein.
6) Liver
Large, smooth organ (1–2 kg) in right upper quadrant under diaphragm; eight segments with left and right lobes. Tissue can regenerate up to two-thirds.
Blood Supply
- Portal vein: 70% nutrient-rich blood from gut
- Hepatic artery: 30% of blood supply
- Hepatic veins: drain into vena cava
Functions
- Processing nutrients
- Bile production for fat digestion
- Excretion of bilirubin and cholesterol
- Metabolism of carbohydrates, proteins, and fats
- Synthesis of plasma proteins and clotting factors
- Glucose homeostasis
- Drug and hormone metabolism
- Detoxification
- Storage of minerals, vitamin B12, and fat-soluble vitamins
- Destruction of worn-out red blood cells
Bile
Produced by liver (~1 litre/day); contains water, bile salts, bilirubin, and cholesterol. Emulsifies fats, aids absorption of fat-soluble vitamins, and colors faeces. Transported via hepatic ducts to duodenum via sphincter of Oddi in response to food, especially fats.
Detailed Notes
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