GI Anatomy & Physiology [McNeish] Flashcards
List the organisation of the gut wall
Serosa Longitudinal smooth muscle Circular smooth muscle Submucosa Muscularis mucosa Laminara propria Epithelium Lumen
What is the enteric nervous system?
Main control of motility in wall of GI tract
Integrates autonomic nervous system and local signals
Can function independently of any other signals
Which parts of the GIT wall are involved with the enteric nervous system?
The myenteric plexus = mainly motility
The submucosal plexus = mainly formation of secretions/blood flow
How does the parasympathetic nervous system affect the GI tract?
Increases motility and secretion
ACh acting on muscarinic receptors
Increased salivation and mucosa constriction
(via vagus nerve)
How does the sympathetic nervous system affect the GI tract?
The SNS reduces GI function
Noradrenaline relaxes smooth muscle in GIT
Which hormones regulate the GIT?
Endocrine hormones: Released into bloodstream Made in mucosal endocrine cells Paracrine hormones: Relatively short distance - local action Made in cell walls of GIT
How do hormones affect the GIT?
Often modulate nerve action
Affect secretion and motility
Give 2 examples of endocrine hormones which are present in the GIT
Gastrin
Cholesystokinin (CCK)
Give 2 examples of paracrine hormones which are found in the GIT
Histamine
Somatostatin
List 3 roles of saliva
Aids swallowing
Begins digestion
Kills bacteria
What effect does the parasympathetic nervous system have on saliva production?
Watery saliva
INcreased secretion and blood flow
What effect does the sympathetic nervous system have on saliva production?
Mixed response
Increased secretion, reduced blood flow
List the 3 stages of swallowing
1st step = voluntary
2nd step = peristalsis - distention triggered under autonomic control, mucous aids movement
3rd step = enters stomach via oesophageal sphincter
What is the role of gastric glands and where are they found?
Gastric glands are found in the stomach
They secrete gastric juice
Name the 2 types of gastric gland and their specific roles
Parietal cells = secrete acid
Chief cells = produce pepsinogens (and other digestive enzymes)
List 5 substances that gastric juice contains
Salts HCl Pepsinogens Water Intrinsic factor (glycoprotein necessary for the absorption of vitamin B12)
List 4 roles of HCl in the stomach
Aids breakdown of tissue
Activates pepsinogen and optimises pepsin function
Allows absorption of calcium and iron
Protects against micro-organisms/pathogens
How is stomach acid formed?
Parietal cell:
Carbonic anhydrase generates H+ and HCO3-
Cl- enters parietal cell in exchange for HCO3- and transported out via the K+/Cl- symport
Proton pump H+/K+ ATPase secretes H+ into stomach lumen
How is gastrin regulated?
Released from G cell in response to nerve, hormonal and food stimuli
Activates CCK2 receptors on ECL cells stimulating histamine release
How is acetylcholine regulated?
ACh released from cholinergic nerves
Stimulates parietal cells
How is histamine regulated?
Released from entero-chromaffin like (ECL) cells
Agonist on H2 receptor on parietal cells = stimulates acid secretion
What is the role of the gastric mucosa?
Protects stomach wall from acid and gastric enzymes
Gel-like and alkaline
What kind of cells does the gastric mucosa contain?
Secretory cells:
Epithelial cells
Neck cells of gastric pits
What is the role of prostaglandins in the GIT?
Promote mucosal secretion
by increasing blood supply
List 3 disorders associated with increased acid production
Gastro-Oesophageal Reflux Disease (GORD) - heartburn, acid reflux, indigestion
Gastric bleeding - often due to NSAID treatment
Ulceration - may be caused by stress
List 4 things that happen in the GIT during vomiting (emesis)
Respiration inhibited (larynx and nasopharynx closed) Stomach relaxes, duodenum contracts Diaphragm and abdominal muscles contract powerfully Gastro-oesophageal sphincter relaxes, gastric contents expelled
Which part of the brain controls vomiting?
The medulla of the brainstem
- The chemoreceptor trigger zone (CTZ)
- Vomiting centre
What is the main function of the pancreas?
Endocrine: Releases insulin and glucagon into the bloodstream
Exocrine: Releases alkaline fluid (reduces pH in duodenum) and digestive enzymes
Which 2 types of digestive enzyme which is released from the pancreas?
Proteolytic enzymes = aid breakdown of proteins
Lipolytic enzymes = aid fat digestion
How are monosaccharides and amino acids absorbed in the small intestine?
They are absorbed by Na-dependent co-transport
How are fats and fat-soluble vitamins absorbed in the small intestine?
They are absorbed by micelles and bile salts
How are water-soluble vitamins absorbed in the small intestine?
They are absorbed by facilitated transport
Name 2 disorders of absorption in the small intestine
Coeliac disease
Chrohn’s
What happens in the large intestine?
Indigestible food residues are stored before elimination
Mucous secretion aids motility of faeces
Absorbs water and electrolytes
Resident bacteria from some vitamins (riboflavin, vitamin K, vitamin B12)
How does dietary fibre increase motility/defecation?
Bulk stimulates movement
Dietary fibre hydrates the bulk allowing greater propulsion and softer faeces
