Purpose The digestive system prepares food for use by hundreds of millions of body cells. Food when eaten cannot reach cells (because it cannot pass through the intestinal walls to the bloodstream and, if it could would not be in a useful chemical state. The gut modifies food physically and chemically and disposes of unusable waste. Physical and chemical modification (digestion) depends on exocrine and endocrine secretions and controlled movement of food through the digestive tract. Mouth Mouth Food enters the digestive system via the mouth or oral cavity, mucous membrane lined.
The lips (labia) protect its outer opening, cheeks form lateral walls, hard palate and soft palate form anterior / posterior roof. Communication with nasal cavity behind soft palate. Floor is muscular tongue. Tongue has bony attachments (process, hyoid bone) attached to floor of mouth by frenulum. Posterior exit from mouth guarded by a ring of palatine / lingual tonsils. Enlargement sore throat, tonsillitis.
Food is first processed (bitten off) by teeth, especially the anterior incisors. Suitably sized portions then retained in closed mouth and chewed or masticated (especially by cheek teeth, premolars, molars) aided by saliva Ducted salivary glands open at various points into mouth. This process involves teeth (muscles of mastication move jaws) and tongue (extrinsic and intrinsic muscles).
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Mechanical breakdown, plus some chemical (ptyalin, enzyme in saliva).
Taste buds allow appreciation, also sample potential hazards (chemicals, toxins) Swallowing In leaving the mouth a bolus of food must cross the respiratory tract (trachea is anterior to oesophagus) by a complicated mechanism known as swallowing or which empties the mouth and ensures that food does not enter the windpipe. Swallowing involves co-ordinated activity of tongue, soft palate pharynx and oesophagus.
The first (buccal) phase is voluntary, food being forced into the pharynx by the tongue. After this the process is reflex. The tongue blocks the mouth, soft palate closes off the nose and the larynx rises so that the epiglottis closes off the trachea. Food thus moves into the pharynx and onwards by peristalsis aided by gravity. If we try to talk whilst swallowing food may enter the respiratory passages and a cough reflex expels the bolus. Oesophagus The oesophagus (about 10′) is the first part of the digestive tract proper and shares its distinctive structure.
Basic tissue layers of the gut are 1. mucosa. Innermost, moist lining membrane. Epithelium (friction resistant stratified squamous in oesophagus, simple beyond) plus a little connective tissue and smooth muscle. 2. sub mucosa.
Soft connective tissue layer, blood vessels, nerves, lymphatics 3. Muscular externa. Typically circular inner layer, longitudinal outer layer of smooth muscle 4. Serosa l fluid producing single layer.
Stomach shaped, left side abdominal cavity (because liver is on right).
Cardio esophageal sphincter guarding entrance from oesophagus is of doubtful anatomical integrity (though functionally the diaphragmatic pinch cock serves).
Pyloric sphincter guarding the outlet is much better defined. Fungus, body and pylorus recognized as distinct regions.
Stomach secretes both acid and mucus (for self protection).
Surface area increased by rug… Serves as a temporary store for food which is also churned by muscular layers (three here) to form chyme, creamy substance voided via pyloric sphincter to duodenumDuodenumFirst part of small intestine. C shaped 10′ long and curves around head of pancreas and entry of common bile duct (accessory organs of digestion, pancreas, liver see below).
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Britt ni Philpot 8 th Grade Health Introduction How does the Digestion System Work? The digestive system is a series of hollow organs joined in a long tube that starts at the mouth and ends at the anus. Inside the tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food. Two solid organs, the liver and ...
Chemical degradation of small controlled amounts of food controlled by pyloric sphincter begins here, enzymes secreted by pancreas and duodenum itself aided by emulsifying bile (which also lowers pH).
Duodenal ulcers caused by squirting of acid stomach contents into duodenal wall opposite sphincter.
small intestine Jejunum (8 feet) and ileum (12 feet) continue degenerative process. Surface area increased by plica circulars (circular folds) carrying: cells of carry micro villi. Each villus has a capillary and a lacteal (lymphatic capillary) Absorption of digested foodstuffs is via these to the rich venous and capillary drainage of the gut. Towards the end of the small intestine accumulations of lymphoid tissue (Peyer’s patches) more common. Undigested residue of food is rich in bacteria. Large Intestine Jejunum terminates at caecum.
Caecum is small sack like examination, important in some animals as a repository for bacteria / other organisms able to digest cellulose. A blind ending appendix may give trouble (appendicitis) if infected. The large intestine has three longitudinal muscle bands (taenia coli) with bulges in the wall between them. These may emarginate in the elderly to become diverticulitis and infected in diverticulitis. The large intestine resolves water then eliminates drier residues as feces.
Regions recognized are the ascending colon, from appendix in right groin up to a flexure at the liver, transverse colon, liver to spleen, descending colon, spleen to left groin, then sigmoid (S-shaped) colon back to midline and anus. Anus has voluntary and involuntary sphincter and ability to distinguish whether contents are gas or solid. No villi in large intestine, but many goblet cells secreting mucus. Accessory digestive organs Salivary glands Three pairs, parotid, sub mandibular, sublingual. Mumps begins as infective parotitis in the parotid glands in the cheek. The others open into the floor of the mouth.
Saliva is a mixture of mucus and serous fluids, each produced to various extent in various glands. Also contains salivary amylase, (starts to break down starch) (antibacterial) and antibodies. In some mammals (and snakes! ) saliva may be poisonous, quieting down living prey. Pancreas Endocrine and exocrine gland. Exocrine part produces many enzymes which enter the duodenum via the pancreatic duct. Endocrine part produces insulin, blood sugar regulator.
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The Problems Most Frequently Encountered by Small Businesses Small business is defined as a kind of business, with a relatively small staff. The definition of the word small, related to legal sphere is various in different countries, it also depends upon branch of industry and country or region, but the general number of employers doesnt exceed 100 employers. Small business enterprises usually ...
Liver and gallbladder Bile, a watery greenish fluid is produced by the liver and secreted via the hepatic duct and cystic duct to the gall bladder for storage, and thence on demand via the common bile duct to an opening near the pancreatic duct in the duodenum. It contains bile salts, bile pigments (mainly bile rubin, essentially the non-iron part of hemoglobin) cholesterol and phospholipids. Bile salts and emulsify fats, the rest are just being excreted. Gallstones are usually cholesterol based, may block the hepatic or common bile ducts causing pain, jaundice.
Liver Multi functional: important in this context since the capillaries of the small intestine drain fat and other nutrient rich lymph into it via the hepatic portal system.
