Digestive System Flashcards
What is the digestive system?
Mouth Oesophagus Stomach Duodenum Jejunum Ilium Large intestine (colon) Rectum
What is the order of the large intestine?
Caecum, ascending colon, transverse colon, descending colon, sigmoid colon
What is the peritoneum?
Serosa double membrane surround the organs of the GI tract in the abdomen (except the duodenum). Connects to the abdomen wall by the mesentery
What are the 4 layers of the gut wall
Mucosa
Submucosa
Muscularis externa
Serosa
What are the three layers of the gut mucosa?
Epithelium
Lamina propria - connective tissue, mucosal glands, peyers patches
Muscularis mucosae - smooth muscle
What does the submucosa of the gut contain?
Connective tissue with glands, arteries, veins and nerves.
What does the muscularis externa?
Two layers of smooth muscle - inner circular layer and outer longitudinal layer
What is digestion?
Conversion of what we eat (by physical and chemical disruption) into a solution of neutral pH, relatively sterile and isotonic from which we can absorb nutrients
What is the physical disruption occurring in the mouth?
Action of the teeth, tongue and muscles of mastication act to break down food
What are four functions of saliva?
Salivary amylase and lipase - start breakdown of food
Bacteriostatic - contain immunoglobulin A
High calcium - protects teeth
Protects mouth and assists swallowing - forms a food bolus
Alkaline
Food moved through the oesophagus by ___________
Peristalsis
What nerves are present in the muscularis externa of the oesophagus?
Submucosal plexus
Myenteric plexus
(Part of autonomic nervous system - post ganglionic neurones form plexuses - use a range of neurotransmitters)
What are the physical and chemical functions of the stomach?
Physical - churning, three layers of muscle and rugae, contracts rhythmically to mix and disrupt stomach content
Chemical - acid (HCL) and proteolytic enzymes (e.g. Pepsin) breakdown food and disinfect
What part of the GI tract acts as a primary food store?
Stomach (we eat faster than we digest)
How is the stomach itself protected from degradation?
Contain mucous secreting cells, thick layer of mucus - resistant to pepsin degradation, contains bicarbonate (neutralise H+) protects stomach lining
What is the product of stomach digestion (transported to the duodenum)?
Produces hypertonic chyme (partially digested stomach content) slowly (controlled) to duodenum
What happens in the duodenum? (4)
Walls contain brunners glands - secret bicarbonate rich mucus to neutralise acidic chyme
Water drawn in from extracellular fluid - dilutes chyme
Liver secrets bile (via gallbladder) contains water, alkali and bile salts (emulsify fats)
Pancreas, liver and intestine secrete specific enzymes (act with bile) to complete digestion of chyme
What three things are required for absorption?
Active process (lots of ATP)
Large surface area
Good blood supply/drainage
What occurs in the jejunum?
Most of the absorption - most sugars, amino acids and fatty acids
What are plicae circulares?
Circular folds of mucosa and submucosa that project into the gut lumen (present in the jejunum)
What happens in the ilium?
Absorbs vitamin 12, bile acid and remaining nutrients
What happens in the large intestine?
Water recovery
Electrolyte absorption
Crypts of lieberkuhn secrete a lot of mucus (goblet cells)
What are three functions of bacteria in the colon?
Synthesis of vitamins K, B12, thiamine and riboflavin
Breakdown of bile acids
Conversion of bilirubin to non-pigmented metabolites
Competition for pathogenic bacteria - physical barrier
What are some of the defences the colon has against pathogens?
Mucus layer Immunoglobulin A Tight junctions High turnover of cells Peyers patches
What is the function of histamine in digestion and what type of signalling does it show?
Paracrine signalling - acts locally controlling the production of stomach acid
What is secretin?
Peptide hormone - promotes bicarbonate secretion from the pancreas and promotes bile production in the liver. Also inhibits the secretion of acid by parietal cells of the stomach
What is cholecystokinin (CCK)?
Peptide hormone synthesised and secreted by entero-endocrine cells of the duodenum. Promotes release of digestive enzymes from the pancreas and release of bile from the gallbladder (stimulates it to contract). Acts as a hunger suppressant.
What is gastrin?
Peptide hormone released by G cells of pyloric antrum of stomach, pancreas and duodenum. Promotes production of gastric acid (HcL) by parietal cells of the stomach.
What are the three phases of swallowing?
Oral phase - chewing, makes bolus, soft pallet stays down to protect nose. Epiglottis sits over trachea to prevent food down windpipe (upper oesophageal sphincter closed)
Pharyngeal phase - upper oesophageal sphincter opens
Oesophageal phase - upper oesophageal sphincter closes
What is harder to swallow - liquids or solids?
Liquids are harder- move with gravity, harder to coordinate by muscle
What is aspiration?
When swallowing goes wrong.
Food, saliva, liquids etc goes into lungs
