Digestive System Flashcards
What are the major and accessory organs?
Major: Food pipe, Gullet, oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine including rectum and anus
Accessory Organs: Teeth and tongue, salivary glands, liver, gallbladder, pancreas
Key functions of the digestive system?
Ingestion: The entry of foods/liquids into the digestive tract via the oral cavity
Mechanical digestion: Crushing/shearing of ingested food
Chemical digestion (extraction of nutrients): Enzymic breakdown of food into substances that can be absorbed
Absorption: Movement of nutrients into the bloodstream
Elimination: Indigestible food is compacted into feces and is excreted
What are the functional divisions of GIT:
Upper (food breakdown): Mouth/oral cavity, oesophagus, stomach, small intestine
Lower (absorption, waste compaction and excretion): Small intestine, large intestine including rectum and anus
What tissue types are included in the GIT?
Peritoneal tissue: Holds organs in place
Retroperitoneal: behind the peritoneal, outside the peritoneal cavity
What is the gut brain axis? What is its anatomy?
A part of the Autonomic Nervous System and Enteric (second brain/gut brain). It is a segment of our gut that has its own brain and can operate independently.
Muscularis: Circular muscle, longitudinal muscle, myenteric plexus
Mucosa: Epithelium, lamina propria, muscularis mucosae
Serosa: Areolar connective tissue, epithelium
What is the process of digestion?
- Oral cavity: Mechanical digestion (mastication) and mixing of food with saliva, enzymes in saliva begin chemical digestion
- Oesophagus: A fibromuscular tube that transfers food (bolus) into the stomach
- Chemical digestion: Bolus mixed with gastric juices (hydrochloric acid and digestive enzymes), mechanical churning facilitated digestion, bolus is converted into chyme
- Small intestine (duodenum): Chemical digestion, aided by digestive juices from the pancreas and gallbladder
- Small intestine (jejenum and ileum)
- Large intestine: Cecum, ascending colon, transverse colon, descending colon, reabsorption of water and some nutrients, compacts waste (faeces) for elimination
- Rectum and anus: Stored and eliminates waste (faeces)
What is the general structure of the GIT wall?
From inside out:
Mucosa: Mucous epithelium, lamina, propria, muscularis mucosae
Submucosa: Gland in submucosa, Duct from gland
Muscularis Externa:
Serosa/Adventitia
What is the function of the GIT wall?
Protection from abrasion: Stratified squamous epithelium in the oesphagus and anus
Vigorous mixing (mechanical disruption): Oblique muscle layer within the stomach
Efficient absorption: Simple columnar epithelium with microvilli (cellular membranes that help diffusion and increase surface area)
Structure and function: Oesophagus
Muscular tube that transports food (bolus) from mouth to stomach, needs peristalsis to squeeze, runs posteriorly to the trachea
Upper: at junction of pharynx and oesophagus, prevents airflow into the oesophagus and also reflux of food into the airway
Lower: At gastro-oesophageal junction, controls entry of bolus into the stomach and prevents backflow of gastric juices
Structure and function: Stomach
Expandable muscular organ that stores food and mechanically and chemically breaks down food. Wants to contain acid in the stomach. Contains rugae (folds of mucosa and submucosa to allow expansion)
Contains two sphincters:
Lower gastro-intestinal sphincter, control of entry into the stomach and prevents backflow of gastric juices
Pyloric sphincter: Distal end of the stomach, prevents early discharge of stomach contents
Four regions: Cardia, Fundus, Body, Pylorus
Mucosa: Simple columnar epithelium, contains numerous secretory cells that produce gastric secretions
Submucosa
Muscularis externa: Inner oblique layer: responsible for creating churning motion to aid mechanical breakdown
Middle layer
Outer longitudinal layer: Moves bolus towards pylorus
Serosa
Function: Stomach Gastric Glands
Gastric glands open into the stomach through gastric pits in the mucosa, they secrete most of the acid and enzymes required for chemical digestion in the stomach, contains specialized calls
Structure and function: Small intestine
Longest portion of the GIT, 3-5 meters, site of enzymatic digestion and absorption. 3 regions;
Duodenum (5%)
Jejunum (40%)
Illeum (60%)
Mucosa: Simple columnar epithelium
Produces a layer of mucous for protection against acidic chyme and defense. Contains a series of finger-like projections called villi
Submucosa:
Muscularis Externa: Inner circular layer, outer longitudinal layer
Serosa
What are the small intestines movement types?
Segmentation:
Local mixing of chyme with intestinal juices, repeated involuntary/ contraction/ relaxation (sloshing) of the inner circular muscularis externa layer, increases exposure time of chyme to absorptive surface
Peristalsis: Involuntary contraction/relaxation of both muscularis externa layers, propels chyme onwards through the tract
Small intestine surface area:
Plica Circularis:
Permanent folds within the mucosa and submucosa, present only until the mid-section of the ileum, cant stretch out like rugae (stomach)
Villi: The surface of the plicae circulares contains small vascularized projections of mucosa called villi
Microvilli: Cell surface feature sometimes referred to as a brush boarder
Structure and function: Large intestine
1.5 Meters, absorbs water and salt and chyme is converted into faeces. 90% water within chyme is reabsorbed.
Large bowel obstruction: Fecal vomiting as they cannot move anything through, sepsis, dehydration. Blockage of appendix causes it to become inflamed and infected and cause pain/nausea/ fever.
Ascending colon on the right side takes a turn (hepatic flexure) as it moves across (transverse colon), then another turn before downwards descent and heads down towards rectum and anus
