Lecture 8: The Digestive System Flashcards
what does the digestive system do
-acquires nutrients from the environment
-anabolism: essential compounds
-catabolism: yield energy for cells
what is anabolism
a biochemical process in metabolism where the simple molecules combine to generate complex molecules
what is catabolism
breaking down body tissues and energy stores to get more fuel for body functions
what are the categories of components of the digestive system (DS)
- Gastrointestinal (GI) tract: alimentary canal (AC)
-continuous muscular tube that runs from the mouth to anus
-digests food: breaks down into smaller fragments
-absorbs fragments through lining into blood - Accessory Organs: teeth, tongue, gall bladder and various glandular organs (salivary glands, liver, pancreas)
what are the 6 primary functions of the digestive system
- ingestion
- secretion
- motility
- digestion
- absorption
- defecation
what is ingestion
eating: occurs when food enters oral canal
what is secretion
-release of water, acids, enzymes, buffers, and salts
-by epithelium of GI tract, glandular organs, and gallbladder
what is motility
-food mixed; peristaltic movement of food along the GI tract
-food is propelled to the anus
what is digestion and the two types of breakdown mechanisms
-digestion: breakdown of ingested food into smaller pieces that are useable by body tissue
-mechanical breakdown: mastication (chewing) and shearing of food, churning food, bolus formation
-chemical breakdown: catabolic processes mediated by digestive enzymes, macromolecules are hydrolyzed into small fragments for absorption by digestive epithelium
what is absorption
-movement of digested products across digestive epithelium into interstitial fluid and lymph
-some absorbed with digestions- organic molecules, electrolytes, vitamins, minerals, and water
what is defecation
elimination of wastes (indigestible substances), microbes, cells sloughed from GIT wall, from body
how many layers are there in the GI tract
-four layers from inside-out: mucosa, submucosa, muscular layer (muscularis externa), and serosa/adventitia
-lining of AC varies by region: empty stomach= longitudinal folds, small intestine= permanent transverse fold (circular folds)
what are the different parts (3 sublayers) of the mucosa layer
inner lining of DT, made up of three sub layers:
1. digestive epithelium (moistened by glandular secretions)
2. lamina propria of alveolar tissue
3. muscularis mucosae
describe the digestive epithelium (in mucosa layer)
-epithelium is simple or stratified: depends on location, function, and stresses
a) oral cavity, pharynx, esophagus, anal canal: stratified squamous epithelium
b)stomach, small intestine, most of large intestine: simple columnar epithelium
-enteroendocrine cells which are disperesed among the columnar cells: secrete hormones that coordinate activities of GIT
describe the lamina propria (in the mucosa layer)
a layer of areolar tissue containing:
-blood vessels, lymphatic vessels, sensory nerve endings
-binds epithelium to overlying muscularis mucosae
-has mucosa-associated lymphatic tissues (MALT) for protection
describe the muscularis mucosae (in the mucosa layer)
-deep to lamin propria
-a narrow sheet of smooth muscle and elastic fibers
-give rise to folds-increase surface area for digestion and absorption
what is the submucosa layer of the GIT
-connects mucosa to muscular layer
-numerous blood and lymphatic vessels
-contain exocrine glands which secrete enzymes
-contains the submucosal neural plexus which innervates mucosa and submucosa
what is the muscular layer (muscularis) of the GIT
-mainly smooth, and some skeletal muscle cells: inner circular and outer longitudinal layers
-involved in mechanical disgestion and peristalsis
-between two muscle layers is myentric plexus
-movements coordinated by enteric nervous system (ENS)
what is the serosa- visceral peritoneum layer of the GIT
serous membrane of areolar CT covering the muscular layer
what does the enteric nervous system (ENS) do in the digestive system
enteric neurons make up bulk of the two interconnecting intrinsic nerve plexuses
-submucosal plexus: glands and smooth muscle in mucosa
-myenteric plexus: between circular and longitudinal smooth muscle layers of the muscularis- GI tract motility
what does the autonomic nervous system (ANS) do in the digestive system
-parasympathetic: vagus and sacral nerves
-sympathetic: thoracic and upper lumber segments
what is the protective function of the lining of the GI tract
-safeguards surrounding tissues against: corrosive effects of digestive acids and enzymes, mechanical stress such as abrasion, and bacteria either ingested with food or that reside in the tract
what is the peritoneum
-largest serous membrane in the body
-parietal and visceral peritoneum form the peritoneal cavity
-ascites: acculumation of fluid in the peritoneal cavity
-retroperitoneal organs: kidneys, pancreas, duodenum, ascending and descending colon
-peritonitis:
what are the 5 peritoneal folds
greater omentum, falciform ligament, lesser omentum, mesentery, and mesocolon