MCQ 4 - Gastrointestinal System (stomach + Intestines) Flashcards
Define gastrointestinal system
Human digestive system
Primary functions of the gastrointestinal system
Regulate intake food + water Convert food to nutrients Absorb nutrients + water Energy store Waste excretion Protect against toxins + bacteria
Processes in gastrointestinal system
Sensory inputs = appetite, taste, smell, sight
Mechanical + chemical food breakdown
Secretion
Absorption
Excretion
Regulated = nerves, hormones, local factors
Gastrointestinal structure top to bottom
Oral cavity, teeth, tongue Pharynx esophagus Stomach Small intestine Large intestine
Internal structure of gastrointestinal system inner to outer layer
Mucosa = epithelium, lamina propria (connective tissue), muscularis mucosa (smooth, thin muscle layer can contract)
Sub-mucosa = loose connective tissue, exocrine glands, nerves,blood + lymphatic vessels
Muscularis propria/externa = inner circular smooth muscle, outer longitudinal smooth muscle
Serosa = outer connective tissue
Enteric nervous system
Autonomic nerves in gut (parasympathetic = rest + digest // sympathetic = fight or flight) para+sympa nerves control
Have ganglia at myentric + submucosal plexus
Control smooth muscle contractions + exocrine/endocrine gland secretions
Controlling gut motility
Interstitial cells of canal (pace-setter cells)
Specialised smooth muscle cells
Pacemaker activity
Determine frequency of slow waves
Responsible for spontaneous depolarisation spreading to smooth muscle cells
(Pace maker cells to smooth muscle cells)
Circulation of gastrointestinal system
Collectively = splanchnic circulation
Contains = 15% total blood volume
Transports absorbed nutrients + waste for excretion
Portal circulation between GI tract + liver
Adjustable resistance + reservoir of blood
Vasodilation = parasympathetic
Vasoconstriction = sympathetic
List phases of digestion
Cephalic
Gastric
Intestinal
Cephalic phase of digestion
Head
Anticipation of feeding
Sensory input from food - thought, smell, sight, taste
Mediated by a vagal parasympathetic nerves
Activating vagus nerve in head
Gastric phase of digestive system
Presence of food in stomach
Sensory input from food = stretch + chemicals
Mediated via parasympathetic + enteric nerve reflexes, hormones (gastrin)
Intestinal phase of digestive system
Presence of food in intestines
Sensory input from food - stretch, chemicals
Mediated via parasympathetic + enteric nerve reflexes, hormones (secretin + CCK)
Oral cavity: initial digestion + sensory input
Mechanical breakdown = teeth, tongue, muscles
Chemical breakdown = amylase, lipase - in saliva
Swallowing reflex to move food from bolus into pharynx + oesophagus
Sensory input = chemical stimulation of olfactory receptors in nose + taste buds in tongue
Define olfaction
Nasal cavity structure
Sensation of smell
Olfactory epithelium = long form sensory receptors - axons all the way up to brain = long
Nerves only apart of sensory nervous system are capable of regeneration
Define gustation
Sensation of taste
Primary taste sensations = sweet, salty, sour, bitter, umami, water
Secretion of lingual lipase
Structure of a taste bud
Pore exposes microvilli
Support cell made of receptor cells = connected to different taste afferents
Surrounded by stratified epithelial cells = protection
Functions of saliva
Maintain oral hygiene
Wash out bacteria
pH = 6-7 = neutralise bacterial acids
Anti-bacterial agents = lysozyme, lactoferrin, thiocyanate, antibodies
Initial digestive stage = chewing, form food bolus, lubricant swallowing, amylase digest starch to oligosaccharides, lingual lipase to digest lipids into triglycerides + fatty acids
Enables speech + taste
Salivary glands - serous
Watery secretion
Contains enzymes + electrolytes
Salivary glands - mucous
Thick secretion
Contain mucus + glycoproteins
State whether it’s serous or mucous:
Submandibular
Parotid
Sublingual
Submandibular = serous, mucous, mainly serous Parotid = entirely serous Sublingual = mucous, serous, mainly mucous
Controlling saliva secretion
Parasympathetic nerves = cephalic phase, large volume of aqueous rich amylase spit, contraction myoepithelial cells, increased spit blood flow by vasodilation
Sympathetic nerves = anxiety + fear, small volume viscous mucous spit, contraction of myoepithelial cells, decrease spit blood flow vasoconstriction
Structure + function of oesophagus
Deliver food to stomach
Mucosa + sub-mucosa folds accommodate food bolus
Stratified squamous epithelium to protect oesophagus
Skeletal muscle in muscularis propria = facilitate swallowing
Functions of the stomach
Food mechanical breakdown
Chemical breakdown = gastric acid, pepsin, lipase
Protect against bacteria + toxins
Produce intrinsic factor for intestinal absorption - vitamin B12
Food storage reservoir
Regulated input to duodenum
Regulate appetite - stretch of stomach + ghrelin
Control of gastric secretions
Stimulation = acetylcholine from parasympathetic (vagal) nerve endings, gastrin, histamine
Inhibition = low gastric pH, secretin, somatostatin,cholecystokinin (CCK), gastric inhibitory polypeptide (GIP)
