11. structure and function of digestive system

organs that form alimentary canal/ tract

• propel food from mouth to anus

• fundamental for ingestion and digestion of food

  • absorption of nutrients

  • formation and excretion of fecal matter

organs that function as accessory digestion glands

• produce secretions that flow into alimentary tract thru ducts

• these secretions aid chemical breakdown of food

oral cavity

• mouth = mucosal lined cavity that contains teeth, tongue, salivary glands and ducts

functions of oral cavity

1. ingestion, mastication, salivation, physical and chemical breakdown of food to form bolus, deglutition (swallowing)

2. ventilation, speech

regions of oral cavity

openings of oral cavity

walls of oral cavity

pharynx - auditory/ Eustachian tube

• osteocartilaginous canal that links nasopharynx (/upper throat) to middle ear

• equalises air p on both sides of tympanic membrane (eardrum)

pharynx - soft palate

• highly mobile and mucosal lined musculoponeurotic structure that extends from hard palate into pharynx

• distal tip = uvula

• moves whenever we speak, swallow, cough, sneeze, gag

pharynx - tonsils

• collections of lymphatic tissue (pharyngeal, tubal, palatine, lingual) in mucosa of pharynx that protects organism against ingested/ inhaled pathogens

• together, tonsils form Waldeyer’s ring

pharynx - fauces

• small space (between arches) in anterior oropharynx

• immediately behind oral cavity

muscles of pharynx

• constrictor muscles of pharynx

• longitudinal muscles

• muscles of soft palate

esophagus

• 25cm long mucosal lined tube

• walls of smooth muscle that traverses neck, mediastinum and diaphragm (at oesophageal hiatus) to reach abdominal cavity

• (oesophageal hiatus = openning in diaphragm)

function of oesophagus

transports bolus to stomach thru peristaltic contractions

stomach

mucosal lined sac with walls of smooth muscle in upper L quadrant of abdomen

small intestine

• 6m long mucosal lined tube with walls of smooth muscle

functions of small intestine

1. mixes chyme with intestinal juices, pancreatic juices and bile from liver/ gallbladder

2. physical and chemical breakdown of chyme

3. absorbs 90% of nutrients and water

4. propels chyme to large intestine

large intestine (colon)

• 1.5m long mucosal lined tube with walls of smooth muscle

• ends in anal canal that crosses pelvic diaphragm to open onto anus

(hepatic → liver)

functions of large intestine

1. houses most of gut microbial flora

2. absorbs water, ions and vit

3. forms and stores fecal matter in rectum prior to evacuation

layers of walls of gastrointestinal tract

endoscopies

walls of GI tract

sphincters in walls of GI tract

• control progression of food

• formed by smooth muscle (involuntary) except for 1st and last (skeletal (vol) muscle)

peritoneum

• continuous double layered serous membrane that surrounds many abdominal organs

• encloses peritoneal cavity

arteries of GI tract

veins of GI tract

aortic nerve plexus of GI tract

salivary glands

• include 3 pairs of major salivary glands + minor salivary glands in oral mucosa

(parotid = beside ear)

liver

• largest internal organ of body

• located in upper R quadrant in abdomen

functions of liver

1. metabolises/ stores macronutrients (carbohydrates, proteins, lipids)

2. removes/ inactivates/ destroys toxins, drugs, metabolites, hormones, pathogens, aged cells from bloodstream

3. synthesises molecules and compounds

4. prod and secretes bile into duodenum

   1. bile = excretory product which contains bile salts that emulsify lipids

gallbladder

• stores bile continuously produced by liver

porta hepatis

pancreas and pancreaticobiliary tree

• pancreas = mixed endocrine and exocrine gland

functions of pancreas

1. prod and secretes pancreatic juices (with digestive enzymes) to duodenum

2. produces and secretes hormones (e.g. insulin and glucagon) to bloodstream

pancreaticobiliary tree