WHAT IS THE DIGESTIVE SYSTEM? BMLT

Digestive system


The gastrointestinal tract (digestive  tract, digestional tract, GI tract, GIT, gut,or alimentary canal) is an organ system within  humans and other animals which takes in food, digests it and absorb energy and nutrients, and  expels the remaining waste as feces.

  • The major organs of the digestive system:
  • Mouth.
  • Pharynx.
  • Esophagus.
  • Stomach.
  • Small Intestine.
  • Large Intestine.
  • Rectum
Accessory digestive organs:
liver gallbladder pancreas.
Salivary gland
Functions of GI tract
  • Ingestion: taking of food into the alimentary tract.
  • i.e. eating & drinking.
  • Propulsion:mixes & moves the contents along the alimentary tract.
  • Digestion:consist of:
  • Mechanical breakdown of food e.g. mastication (chewing)
  • Chemical digestion of food into small molecules by enzymes.
  • Absorption:this is the process by which digested food substances pass through the walls of some organs of the walls of some organs of the alimentary canal into the blood for circulation.
  • Elimination:food substances that have been eaten but cannot be digested & absorbed are excreted from the alimentary canal as faeces by the process of defaecation. 

MOUTH

The mouth is the first portion of the alimentary canal that receives food and produces saliva.
  • Relations:
  • Anteriorly-lips
  • Posteriorly-continue with the oropharynx
  • Laterally-muscles of cheeks
  • Superiorly-bony hard palate
  • Inferiorly-muscular tongue & the soft tissues of the floor of the mouth

  • The palate forms the roof of the mouth & is divided into the anterior hard palate & posterior soft palate.
  • The uvula is a curved fold of muscle covered with mucous membrane,hanging down from the middle.
TONGUE
  • The tongue is a muscular organ in the mouth, that manipulates food for mastication, and is used in the act of swallowing.
  • It is of importance in the digestive system and is the primary organ of taste in the gustatory system.
  • The tongue's upper surface (dorsum) is covered
  • by taste buds housed in numerous lingual papillae.
  • The human tongue is divided into two parts,
  • an oral part at the front and a pharyngeal part at the back.
  • BLOOD SUPPLY
  • lingual artery
  • external carotid artery
  • VENOUS DRAINAGE
  • lingual veins
  • internal jugular vein
  • NERVE SUPPLY
  • hypoglossal nerve
  • Taste and sensation: glossopharyngeal nerve


  • FUNCTIONS
  • Mastication (chewing)
  • Deglutition (swallowing)
  • Speech
  • Taste
  • TEETH
  • The human teeth function to mechanically break down items of food by cutting and crushing them in preparation for swallowing and digesting. Humans have four types of teeth: incisors, canines, premolars, and molars, each with a specific function.



PARTS
ENAMEL

  • Enamel is the hardest and most highly mineralized substance of the body.
  • It is one of the four major tissues which make up the tooth, along with dentin, cementum, and dental pulp.
  • 96% of enamel consists of mineral, with water and organic material comprising the rest.
  •  The normal color of enamel varies from light yellow to grayish white.
  • DENTIN
  • Dentin is the substance between enamel or cementum and the pulp chamber.
  • The porous, yellow-hued material is made up of 70% inorganic materials, 20% organic materials, and 10% water by weight
  • Dentin is a mineralized connective tissue with an organic matrix of collagenous proteins.

  • CEMENTUM

  • Cementum is a specialized bone like substance covering the root of a tooth.
  • Its coloration is yellowish and it is softer than dentin and enamel.

  • DENTAL PULP

  • The dental pulp is the central part of the tooth filled with soft connective tissue.
  • This tissue contains blood vessels and nerves that enter the tooth from a hole at the apex of the root.

FUNCTIONS OF TEETH

  • Two incisor -for cutting
  • One canine -for tearing
  • Two premolar-for crushing
  • Three molar-for grinding
  • ERUPTION
  • Tooth eruption in humans is a process in tooth development in which the teeth enter the mouth and become visible.
  • Primary teeth erupt into the mouth from around six months until two years of age.

BLOOD SUPPLY

Maxillary arteries  VENOUS DRAINAGE  Internal jugular veins  NERVE SUPPLY  Maxillary nerves  Mandibular nerves.

SALIVARY GLANDS

  • The salivary glands in are exocrine glands that produce saliva through a system of ducts.
  • Humans have 3 paired major salivary glands:
  • Parotid
  • submandibular and
  • Sublingual
  • as well hundreds of minor salivary glands.
  • Parotid glands
  • The two parotid glands are major salivary glands wrapped around the mandibular ramus in humans.
  • The largest of the salivary glands.

  • They secrete saliva to
  • facilitate mastication and swallowing,
  • and amylase to begin the digestion of starches.
  • It enters the oral cavity via the parotid duct.

  • Submandibular glands

  • The submandibular glands are a pair of major salivary glands located beneath the lower jaws, superior to the digastric muscles.
  • The secretion produced is a mixture of
  • both serous fluid and mucus, and enters the oral cavity via the submandibular duct.

  • Sublingual glands

  • The sublingual glands are a pair of major salivary glands located inferior to the tongue, anterior to the submandibular glands.
  • Approximately 5% of saliva entering the oral cavity comes from these glands.
  • The secretion produced is mainly mucous in nature

  • Minor salivary glands

  • There are 800 to 1,000 minor salivary glands located throughout the oral cavity within the submucosa of the oral mucosa in the tissue of the buccal,and lingual mucosa

  • BLOOD SUPPLY

  • External carotid artery
  • VENOUS DRAINAGE
  • Jugular veins
  • COMPOSITION OF SALIVA
  • About 1.5 litres of saliva is produced daily & it consists of:
  • Water
  • Mineral salts
  • An enzyme
  • Mucus
  • Lysozyme
  • Immunoglobulins

  • FUNCTION OF SALIVA

  • Saliva contributes to the digestion of food and to the maintenance of oral hygiene.
  •  Without normal salivary function the frequency of dental caries, gum disease and other oral problems increases significantly.
  • Lubricant
  • Saliva, coats the oral mucosa, mechanically protecting it from trauma during eating, swallowing and speaking.
  •  In people with little saliva soreness of the mouth is very common, and the food (especially dry food) sticks to the inside of the mouth.

Digestion

  • The digestive functions of saliva include moistening food and helping to create a food bolus.
  • This lubricative function of saliva allows the food bolus to be passed easily from the mouth into the esophagus.

Role in taste

  • Saliva is very important in the sense of taste.
  •  It is the liquid medium in which chemicals are carried to taste receptor cells (mostly associated with lingual papillae).
  • Other Function
  • Saliva maintains the pH of the mouth. Saliva is supersaturated with various ions.

THE PHARYNX

  • The pharynx is the part of the throat that is behind the mouth and nasal cavity and above the esophagus and the larynx, or the tubes going down to the stomach and the lungs.
  • The pharynx is the portion of the digestive tract that receives the food from your mouth.
  •  Branching off the pharynx is the esophagus, which carries food to the stomach,

THE ESOPHAGUS

  • The esophagus or oesophagus,commonly known as the food pipe or gullet, The esophagus is a muscular tube connecting the throat (pharynx) with the stomach.
  • The esophagus runs behind the windpipe (trachea) and heart, and in front of the spine.
  • Length :25 cm
  • Diameter:2 cm

STRUCTURE
  • The wall of the esophagus from the lumen outwards consists of mucosa, submucosa (connective tissue), layers of muscle fibers between layers of fibrous tissue, and an outer layer of connective tissue.
  • The mucosa is a stratified squamous epithelium of around three layers of squamous cells, which contrasts to the single layer of columnar cells of the stomach.
  • Most of the muscle is smooth muscle although striated muscle predominates in its upper third.
  • It has two muscular rings or sphincters in its wall, one at the top and one at the bottom.
  •  A sphincter is a circular muscle that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning.
  • The lower sphincter helps to prevent reflux of acidic stomach content.

FUNCTIONS

  • Formation of a bolus
  • Swallowing
  • Food is ingested through the mouth and when swallowed passes first into the pharynx and then into the esophagus.
  • Reducing gastric reflux
  • Constriction of the upper and lower esophageal sphincters help to prevent reflux (backflow) of gastric contents and acid into the esophagus, protecting the esophageal mucosa.

Blood supply

  • Oesophageal arteries
  • Inferior phrenic arteries
  • Venous drainage
  • Left gastric vein

STOMACH

  • The stomach is a muscular organ located on the left side of the upper abdomen. The stomach receives food from the esophagus.
  • As food reaches the end of the esophagus, it enters the stomach through a muscular valve called the lower esophageal sphincter.

  • Relations:

  • Anteriorly-left lobe of liver & anterior abdominal wall
  • Posteriorly-abdominal aorta,pancreas,spleen,left kidney
  • Superiorly-diaphragm,oesophagus & left lobe of liver
  • Inferiorly-transverse colon & small intestine
  • Left side-diaphragm & spleen
  • Right side-liver & duodenum
  • A pouch-like organ primarily designed for food storage (for 2-4 hours) , some mechanical and chemical digestion also occur .
  • Contains two sphincters at both ends to regulate food movement :
  • cardiac sphincter near the esophagus ,
  • pyloric sphincter near the small intestine .
  • Divided into 4 regions :
  • cardiac stomach (or cardiac),
  • fundic stomach (or funded) ,
  • body of stomach
  • pyloric stomach (or Pylorus).
  • Contain thick folds called rugae at its layer , for providing
  • larger surface area for expansion , secretion , digestion , and some absorption.

  • FUNCTIONS

  • Digestion

  • The stomach releases proteases (protein-digesting enzymes such as pepsin) and hydrochloric acid, which kills or inhibits bacteria and provides the acidic pH of 2 for the proteases to work.
  • Food is churned by the stomach through muscular contractions of the wall called peristalsis

Absorption

  •  some absorption of certain small molecules nevertheless does occur in the stomach through its lining

GASTRIC JUICE

  • Gastric acid, gastric juice or stomach acid, is a digestive fluid formed in the stomach and is composed of hydrochloric acid (HCl), potassium chloride (KCl) and sodium chloride (NaCl).
  • The acid plays a key role in digestion of proteins, by activating digestive enzymes, and making ingested proteins unravel so that digestive enzymes break down the long chains of amino acids.

Gastric Secretory Cells

  • Chief cells: secrete pepsinogen (an inactive enzyme).
  • Parietal cells: secrete hydrochloric and (HCl) and "intrinsic factor" (which helps absorption of vitamin B12 in the intestines).
  • Mucous cells: secrete mucus and alkaline substances to help neutralize HCl in the gastric juice .
  • G cells: secrete a hormone called gastrin , which stimulates the parietal cells and overall gastric.

Blood supply

  • right gastroepiploic artery
  • left gastroepiploic artery
  • gastric artery
  • Venous drainage
  • gastric vein

Pancreas

  • The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates.
  •  It is located in the abdominal cavity behind the stomach.
  •  It is an endocrine gland producing several important hormones, including insulin, glucagon, somatostatin, and pancreatic polypeptide, all of which circulate in the blood.
  • Length: 15 cm or 6 inch



Structure
  • Anatomically, the pancreas is divided into the head of pancreas,
  • the neck of pancreas,
  • the body of pancreas,
  • and the tail of pancreas.
  • The neck is about 2.5 cm or 1 inch long and lies between the head and the body
  • The body is the largest part of the pancreas and lies behind the pylorus.
  • The tail ends by abutting the spleen.