MODULE 5 Flashcards
The digestive tract includes:
mouth, pharynx, oesophagus, stomach, small intestine and large intestine
Accessory organs include
teeth, tongue, salivary glands, gall bladder, liver and pancreas
The six processes of digestion
ingestion, propulsion, mechanical digestion, chemical digestion, absorption, defecation
Ingestion is… and involves…
taking food into the digestive tract… lips and tongue
Propulsion is…
moving food through the digestive tract, swallowing (voluntary).
Propulsion: peristalsis is…
alternate waves of muscle contraction and relaxation
Mechanical digestion is… and involves…
physically breaking the food up into smaller fragments so it can be chemically digested… mouth (chewing and mixing food with saliva), stomach (churning and mixing with gastric juice), small intestine (segmentation > mixes food with digestive juices and aids nutrient absorption
Chemical digestion is where…
enzymes break down complex food molecules into chemical building blocks. Begins in the mouth and ends in the small intestine
Absorption is the…
passage of digested end products from the digestive tract lumen into the blood or lymph
Defecation is the…
elimination of indigestible substances, in the form of faeces, from the body via the anus
The mucosa
innermost layer, rich in secretory cells, contains capillaries, contains smooth muscle layer, contains lymphoid follicles
The submucosa
external to the mucosa, contains elastic tissue, rich supply of: blood vessels, nutrient absorption lymphatic vessels, parasympathetic = increased motility and secretion. Sympathetic = decreased motility and secretion
The muscularis externa
surrounds the submucosa, contains two smooth muscle layers, inner circular, outer longitudinal the circular muscle can form sphincters (act as valves to control the passage of food)
The serosa
outermost layer, protection of the digestive tract, anchors the digestive tract within the peritoneal cavity
The oral cavity
Lined by stratified, squamous epithelium continually replaced due to abrasion
Digestive functions of the oral cavity
ingestion, mastication, mixing food with saliva, taste sensation, initiating chemical digestion of carbs by enzymes in saliva, propulsion (swallowing)
Salivary glands includes…
parotid, sublingual, submandibular
Saliva is
under parasympathetic control
Saliva consists of
water, mucin protein > mucous, enzymes, antimicrobial proteins (antibodies, lysozyme, defensins)
Functions of saliva
mucous moistens and lubricates food, aids in bolus formation, dissolves food chemicals and facilitates taste, contains enzymes (amylase) that begin chemical digestion of carbs
Function of the pharynx and oesophagus
propulsion of food to the stomach
Oblique muscle function
pummels the food and rams it into the small intestine
Stomach mucosa
Lining of simple columnar epithelium, mucosa contains gastric pits
Gastric pits contain cells which produce…
Hydrochloric acid (activates pepsin, denatures proteins), pepsin (chemical digestion of protein), mucous (protect mucosa from HCl), hormones (gut motility and secretion)
The mucosal barrier contains…
bicarbonate rich fluid under an insoluble mucous on the stomach wall, mucosal epithelial cells joined by tight junctions, damaged mucosal epithelial cells shed and quickly replaced
Functions of the stomach
storage of food, mechanical digestion, initiates chemical digestion of proteins, absorption, propulsion (to the small intestine).
Small intestine: duodenum
curls around the pancreas, receives bile and pancreatic juice for chemical digestion
Small intestine: jejunum
major site of mechanical and chemical digestion and absorption
Small intestine: ileum
ends at the large intestine
Small intestine functions
nutrient absorption, large surface area, circular folds and villi also increase surface area. Propulsion, mechanical digestion, chemical digestion, nutrient absorption.
Circular folds
deep, permanent folds of the mucosa and submucosa
Villi
finger-like projections of the mucosa, absorptive epithelial cells bound by tight junctions (nutrient and electrolyte absorption), contains a capillary bed and a wide lymph capillary, movement enhances absorption.
Microvilli
very small, densely packed villi on the surface of individual absorptive epithelial cells (form the brush border)
Brush border enzymes
Plasma membrane contains brush border enzymes that complete carbohydrate, protein and nucleic acid digestion
Segmentation (mechanical digestion)
breaks up the chyme (liquified food) into even smaller portions
Chemical digestion
chyme is delivered slowly, from the stomach and mixed with digestive juices and bile. Alkaline intestinal mucous and pancreatic juice help to neutralise acidic chyme. Brush border enzymes assist with digestion
Peristalsis
moves indigestible foodstuff into large intestine
Absorption
end products of digestion, water, vitamins and electrolytes are absorbed across the single epithelial cell layer of the mucosa and into the capillaries or lymphatic circulation within the villi
Nutrients (water soluble) absorbed into
blood, travel in the hepatic portal vein to the liver
Nutrients (lipid soluble) absorbed into
the lymphatic circulation, enter the blood at the thoracic duct
