carbohydrate digestion, absorption and blood sugar homeostasis Flashcards
what are the two forms of starch
amylose and amylopectin
what are the differences between the two forms of starch
branched in amylopectin due to the 1,6 glycosidic bond whereas amylose only has 1,4
what enzyme digests the amylose and amylopectin
salivary and pancreatic amylase
which bond is broken by the salivary and pancreatic amylase
1,4 bond
describe amylose
STRAIGHT linear chain containing 1,4 glycosidic bonding
describe amylopectin
branched structure of alpha glucose and contains 1,4 and 1,6 glycosidic bonding
describe cellulose
a polysaccharide which is made out of b glucose monomers joined together by b1,4 glycosidic bonding. it is largely indigestible in the SI and therefore excreted
describe glycogen
polysaccharide of a glucose which is bonded by 1,4 and 1,6 glycosidic bonding. highly branched structure
how is carbohydrates digested in the oral cavity
mechanical and chemical digestion( salivary amylase)
how is the carbohydrates digested in the gastro intestinal tract
chemical
what is an exocrine gland
a gland that secretes enzymes into a duct
what is an endocrine gland
secretes its hormones into the blood stream to get to the site of action
where does salivary amylase come from
secreted by serous acini of the parotid and submandibular glands
what is the optimal ph of salivary amylase
6.7
what does salivary amylase break down polysaccharides into
mixture of disaccharides and trisaccharides
how long does salivary amylase work for in the stomach
for 1-2 hours before being deactivated by the gastric acids
where is pancreatic amylase secreted from
the pancreatic exocrine acini into the duodenum through the pancreatic duct
what is the optimum ph of pancreatic amylase
6.7-7
WHAT BOND DOES PANCREATIC AMYLASE DIGEST
1,4 glycosidic bond
what does pancreatic amylase break down
more complex carbohydrates that take longer to break down to disaccharides or oligosaccharides
which enzymes are brush border enzymes or disaccharidases
maltase
sucrase and lactase
what is the optimal ph of disaccharidases
7-8
what do disaccharidases hydrolyse
disaccharides into monosaccharides
why do some people suffer from lactose intolerance
due to a lack of the lactase enzyme therefore lactose cannot be broken down and the water potential in the gut in reduced therefore water moves out via osmosis and the patient suffers from diarrhoea
where does carbohydrate absorption occur
occurs in the SI
why is the villi folded
to increase surface area
what is the most absorbable form of carbs
monosaccharides
how do glucose and galactose enter the enterocytes
via active transport using the sodium dependant co transport (SGLT1)
how do glucose and galactose leave the enterocyte
via facilitated diffusion and glucose co transported (GLUT2)
how does fructose enter the enterocyte
glut5
how does fructose leave the enterocyte
leaves via GLUT2 and facilitated diffusion
which mode of transport requires energy in the form of ATP
active transport
what factors will affect carbohydrate absorption
faster through intact mucosa- can be damaged due to lactose intolerance cus of inflammation
thyroid hormones increase the absorption
mineralocorticoid eg aldosterone
Na+ conc- higher the conc the more absorption
what is mineralocorticoid
corticosteroid hormone, which is synthesized by the adrenal cortex.
what does aldosterone do
regulation of salt and water in the body
how many k calories does glucose produce
3.75K calories of energy/gm
what is insulin
a hormone secreted by b cells in the islets of langerhans in the pancreas
what does insulin do
regulates the level of glucose when glucose levels are high
what is glucagon
it is a hormone secreted by a cells in the islets of langerhans in the pancreas
what does glucagon do
it is stored in the liver to glucose and released when blood glucose is low
what is a homeostatic level of glucose
90mg/100ml
what is the structure of insulin
2pp chains A&B linked by disulphide bonds
how is insulin synthesised
- proinsulin with 1 pp chain enters through ER
- ER adds 2 chains so there’s 3 PP chains A-C-B
- packaged at the golgi and the c structure is cut by endopeptidases and TGN releasing insulin
what is the molecular weight of insulin
small protein 6000
how does insulin work
- insulin attaches to the insulin receptors on cell membrane, stimulating GLUT-4
- causes GLUT-4 receptor to bind to the membrane and glucose enters the cell through GLUT-4
- glucose is converted into pyruvate and fatty acids stored in adipose tissue
what is the co transporter that transports glucose into the cell
GLUT4
what are the normal glucose levels when fasting
80-90mg/100ml
what are the normal glucose levels when after a meal
120-140/100ml
what does intracellular hypoglycaemia lead to
glucogenesis and gluconeogensis
what are the symptoms of diabetes
fatigue blurred vision slow healing sores unusual weight loss yeast infections polyuria itching in groin and vagina nausea xerostomia
what are the macrovascular complications of diabetes
brain: stroke TIA cognitive impairment heart: coronary syndrome MI congestive heart failure extremities: diabetic foot skin ulcers amputation
what are microvascular complications of diabetes
eye:retinopathy cataract glaucoma kidneys: renal failure nephropathy microalbuminemia
what are the two hypothesis of vascular damage
damage to the blood vessel due to high glucose level causing oxidative stress in the lining affecting mitochondria
or glycated products and the glucose glycates fsatty acids which build up on the vessels
what are dental complications of diabetes
xerostomia gum and perio disease loss of teeth impaired and delayed healing infections
how should we manage diabetic patients
regular visits maintenance of OH regular checks antibiotic coverage controlled blood sugar mouth wash artificial saliva
