lecture 1- overview of digestion Flashcards
Most common viral or food-borne bacteria
Gastroenteritis (Gastro)
Gastroenteritis symptoms
Diarrhoea, abdominal pain, vomiting and fever
Digestive systems primary function
Transfer nutrients, water & electrolytes from food into bodes internal environment
Digestive system=
Digestive tract + accessory digestive organs
Basic digestive function- 1. Motility
Muscular contractions that propel and mix the food (smooth muscle contractions)
Basic digestive function- 2. Secretion
Exocrine glands secrete digestive juices. Endocrine glands secrete hormones
Basic digestive function- 3. Digestion
Food is both mechanically and biochemically broken down into small units
Basic digestive function- 4. Absorption
The small units (with water and electrolytes) are transferred into the blood and lymph
Mouth
Mastication (breaking food into smaller pieces and a little carb digestion) (saliva, mucus, amylase, lysozyme)
Pharynx and Oesophagus
Swallowing and transporting food from the mouth to stomach (mucus)
Stomach
Mixing, churning and digestion (no absorption of foodstuffs) making of chyme, gastric juices, HCI, pepsin
Small Intestine
Digestion and most absorption (with help from secretions from liver and pancreas)
Large Intestine
Completes absorption of water and electrolytes (faeces remain)
Accessory Organs- Salivary glands
Secretions help in lubrication, antibacterial and begin digestion
Accessory Organs- Pancreas
Vital for digestion, enzymes for all food categories and alkaline sol.
Accessory Organs- Liver
Secretes bile continuously, biliary system, bile salts storage and concentration
Accessory Organs- Gallbladder
Secretes bile continuously, biliary system, bile storage and concentration
Mucosa
highly folded, lining the luminal surface of the digestive tract (3 layers)
Mucous membrane
protective surface barrier, epithelial tissue with exocrine, endocrine and ‘absorptive’ cells
Lamina propria
thin middle layer of connective tissue containing the gut-associated lymphoid tissue
Muscularis mucosa
sparse layer of smooth muscle which upon contraction can expose different areas of surface folding
Submucosa
connective tissue containing larger blood and lymph vessels and a nerve network- the submucosal plexus
Muscularis externa
major smooth muscle coat, contains the myenteric plexus
Serosa
outer connective tissue secretes a serous fluid and is continuous with the mesentery
Propulsive movements (peristalsis)
forward movement
Mixing movements (segmentation)
mix in with digestive juices, expose to absorptive surfaces
Digestion- Hydrolysis
is used in the digestion of proteins, fats and carbs
Regulation 4 factors
1 Autonomous smooth muscle function, 2 Intrinsic nerve plexuses, 3 extrinsic nerves, 4 gastrointestinal hormones
Extrinsic nerves
sympathetic and parasympathetic systems act on intrinsic nerves, hormone secretion
Gastrointestinal hormones
Enteroendocrine cells in the mucosa of the GIT release hormones into the blood where they exert excitatory or inhibitory effects on smooth muscle and exocrine cells
Swallowing 3 stages
Oral (voluntary phase), Pharyngeal (involuntary phase), Oesophageal stage (involuntary phase)
Pharyngo-oesophageal (upper sphincter)
prevents excess air from entering GIT
Gastro-oesophageal (lower sphincter)
keeps out stomach contents, otherwise ‘heart burn’
Primary peristalsis
preceded by pharyngeal phase, controlled by swelling centre
Secondary peristalsis
can occur without pharyngeal phase if oesophagus distended e.g. if food is stuck, pressure receptors trigger intrinsic nerve plexus leading to stronger force
Swalling disorder
Dysphagia (disordered eating- leads to aspiration, pneumonia, malnutrition, dehydration, airway obstruction)
Gastrointestinal tract major functions
ingestion, digestion, absorption, and defaecation
