Gastro Flashcards
What is the overall purpose of the GI tract and system?
The body lacks the ability to take in the larger and complex molecules in the diet straight to the cells and use them for energy. The GI tract has to aid in the cutting up of the macromolecules and get the sub-macro molecules into the blood. This process is absorption and digestion.
What 3 properties does the end product of digestion possess?
Isotonic (stop water movement inappropriately) to surrounding solution, correct pH and sterile.
What protection mechanisms does the stomach have against it’s own digestion mechanisms?
c
What is contained within excrement?
Residue, dead cells and waste products in the body.
What is the consequence of rate of digestion being lower than the rate of the eating?
Humans need a place to store food as the food is digested. Held and then released gradually from the stomach.
What are the two mechanisms that food is digested by?
Physical and chemical disruption (mastication, acid and enzymes)
What are the main roles of the stomach
Production of chyme, acid kills pathogens, storage of food, receptive relaxation to accommodate food, enzymic reactions for chemical reactions and muscular contractions for physical disruption and churning.
What needs to happen to chyme when it leaves the stomach and why?
It needs to be neutralised and made isotonic. THis is to protect the lower GI tract from the acidity of the stomach.
How does saliva aid digestion?
Lubricates the food and enables bolus formation. contains ptyalin (amalase) for breaking down starch and also contains salivery lipase which is key in new borns.
How does saliva act as a disinfectant?
Human saliva (although lacking nerve growth factor) contains several anti-microbials agents. these include IgA, lactoferrin and peroxidase.
Properties of saliva
Wet to protect the mucosa in the oral cavity,
Bacteriostatic
Alkaline and high calcium to protect the teeth
What induces saliva production?
Both sympathetic and parasympathtic stimulation.sympathetic increase secretions of mucosal composition and parasympathetic induces production of the enzyme rich serosal fluid.
Where and why does dilution and neutralisation of chyme occur?
Entry of acid into the duodenum induces the release of Secretin from s cells there. Secretin is released at a pH of 4.5. They induce the secretion of HCO3 and also fluid from the pancreas. The duodenum has it’s own intrinsic HCO3 production but it’s limited to the proximal portion of. This intrinsic mechanism involves the Anion exchanger and the CFTR in the apical membrane.
What are the 3 processes of movement in the stomach?
Propulsion
grinding
retro-propulsion
What mechanisms are in place to ensure the intragastric pressure remains lower?
receptive relaxation and gastric accommodation.
How is the intestine designed to optimize absorption?
Slow movement of chyme, massive surface area from microvilli and villi. Hepatic portal vein allows to maintain the steep concentration gradient.
Describe the fluid absorption and secretion in the GI tract.
Food- 1 litre in saliva- 1.5 litres in Gastric secretions- 2.5 litres in Water and alkali- 9 Litres in Small intestine- 12.5 litres out Large intestine- 1.35 Litres Faeces- 0.15 Litres
Describe the parotid gland
Develops in the 6th week of gestation and is the first salivary gland to be formed. They grow towards the ears and are closely associated with the mandibular ramus.
They are mainly serous glands and are anterior and inferior to the acoustic meatus.
Surrounded by a dense capsule the gland has short striated ducts and long intercalated ducts from which it contributes only 25% total salivary volume (which is high in alpha amylase)
Its blood supply is from the external carotid and innervation is entirely autonomic coming from the glossopharyngeal nerve.
Describe the composition of saliva
99.5% water Low Na High K plasma conc Ca Low Cl high HCO3 Mucos (mucopolysaccharides and glycoproteins) Anti microbial agents various enzymes Haptocorrin.
What is the role of haptocorrin?
Binds strongly to Vit B12 to protect it from being denatured in the stomach by HCL.
What are the 3 mechanisms of control of the GI tract?
Neural
Paracrine
Endocrine.
Describe the divisions of the ENS
Meissner’s/submucosal plexus- sub mucosa of the small and large intestine,
Mysenteric plexus- between the circular and longitudinal muscle,
Why is the ENS considered to be a mini brain?
As it can function almost in isolation of any autonomic input from the CNS
What are the neurotransmitters used in the ENS?
Ach is the most common
Vasoactive intestinal peptide has a role in the inhibition of intestinal smooth muscle and stimulation of intestinal fluid and electrolyte secretion. VIP can also be found in the CNS.
What two hormones induce the secretion of HCL from parietal cells?
Histamine and gastrin.