GI 1-6 Flashcards
What changes does digestion make to food?
Sterile
Neutral
Isotonic
What state does digestion change food to?
Solution of small sugars, amino acids, lipids in very small peptides and other small molecules
What does the body excrete?
Residues from food
Debris from the gut
Materials specifically excreted via liver to gut
How does the body break down food?
Physically to release large molecules
Chemically to release small molecules
Define chyme.
The semifluid mass of partly digested food expelled (slowly so as not to overwhelm) by the stomach into the duodenum. Generally sterile due to stomach acid.
Why must chyme be diluted?
Very hypotonic and acidic so must be made isotonic and neutral so as not to damage the rest of the GI tract.
What is mastication?
Chewing.
What is the purpose of saliva?
Protects mouth
Lubricates food for astication and swallowing - wet, mucus
Starts digestion - enzymes (esp. sugars)
How does saliva protect the mouth?
Wet
Bacteriostatic
Alkaline
High calcium
Why is the formation of a bolus important?
streamlined allowing for rapid, easy transport from mouth to stomach for storage.
How does the stomach accomodate storage and digestion?
Relaxes to accomodate food - receptive relaxation
Contracts rhymically and periodically to mix and disrupt - exposes chyme to secretions
Secretes acid and proteolytic enzymes to break down tissues and disinfect
What processes occur in the duodenum/jejunum?
Dilution and neutralisation - makes it safe to pass through the rest of the system
Osmotically draws water in from ECF to make it isotonic
Pancreas and liver secrete alkali (HCO3) to neutralise the acid
enzymes and bile salts to complete digestion
What are some of the products of digestion?
Amino acids from polypeptides
Monosaccharides from polypeptides
Break down and reform lipids
Break down nucleic acids
How is the surface area of hte intestine increased?
Brush border - villi
How are molecules absorbed in the small intestine?
Actively/passively
Often coupled to Na absorption
Where are absorbed molecules from the small intestine transported to?
Liver by hepatic portal vein
What is absorbed in the large intestine?
Water and some electrolytes
Very slow process
Where in the large intestine do faeces accumulate?
Descending and sigmoid colon
What are the 3 main processes of the GI system?
Secretion
Motility
Absorption
Why is it important to maintain a balance between secretion and absorption?
Imbalance will cause considerable loss of water and electrolytes - dehydration and electrolyte disturbance. Mostly from body fluids rather than ingested food adn water.
What are the 3 methods of control of the body for motility and secretion?
Neural
Paracrine
Endocrine
What is the neural control of the gut?
Somatic motor system for ingestion and excretion
Autonomic nervous system the rest - mostly parasympathetic. Coordinates both secretion and motility. Range of neurotransmitters. Gut is full of nerve cell bodies in the walls - plexuses
What is paracrine control? Give some examples in the gut.
Chemical messengers diffusing locally - NOT through blood
Histamine in stomach
Vaso-active substances to alter blood flow
How are hormones used in GI?
Secretion of stomach acid
Alali secretion from liver and pancreas
Enzyme secretion
All peptides in structurally related families