Ćarbohydrates and glucose metabolism Flashcards
1
Q
Monosaccharides are (3)
A
glucose, fructose, galactose
2
Q
Disaccharides are (3)
A
lactose (galactose + glucose),
maltose (glucose + glucose),
sucrose (fructose + glucose, non-reducing)
3
Q
The brain CANNOT - relationship between brain and glucose (3)
A
- Synthesize glucose
- Store glucose in significant amounts
- Metabolize substrates other than glucose and ketones
4
Q
Entry of glucose in the brain is not facilitated by _______
A
insulin
5
Q
Normal glucose plasma conc.
A
from PPT: 4-10 mmol/L
Guidelines fasting glucose : 3.5-5.5 mmol/L
6
Q
What do renal tubular cells do regarding the glucose?
A
- Renal tubular cells reabsorb almost all of the filtered glucose and little glucose is lost unchanged from the body
7
Q
Functions of glucagon (3)
A
- Stimulates production of glucose by glycogenolysis and gluconeogenesis
- It increases ketogenesis in the liver
- It increases lipolysis in adipose tissue
8
Q
Epinephrine functions (2)
A
- It stimulates glycogenolysis/glycogen breakdown and decreases use of glucose, increasing its blood concentration
- It stimulates glucagon secretion and inhibits insulin secretion
9
Q
Growth hormone functions (3)
A
- It stimulates gluconeogenesis
- It stimulates lipolysis
- It inhibits insulin-stimulated glucose uptake
10
Q
Cortisol functions (2)
A
- It stimulates gluconeogenesis
- It stimulates breakdown of protein and fat
11
Q
Thyroxine functions (not direct) (3)
A
- It stimulates glycogenolysis
- It stimulates rate of gastric emptying
- It increases glucose intestinal absorption
12
Q
Somatostatin function
A
- Somatostatin inhibits secretion of glucagon and insulin by the pancreas
13
Q
What are ketone bodies?
A
Water-soluble molecules produced from fatty acids in the liver
14
Q
What are 3 things that happen when insulin is low in regards to ketone bodies?
A
- increased lipolysis
- decreased re-esterification of fatty acids to triglycerides
- increased plasma free fatty acids
15
Q
Increased amount of __________ increases fatty acid oxidation in the liver
A
glucagon
16
Q
_______ and ________ lead to acetoacetate accumulation in the blood
A
increased hepatic ketone production
decreased peripheral tissue metabolism
17
Q
In severe ___________ ratio of beta-hydroxybutyrate to acetoacetate may increase _________ due to large amount of NADH which favors beta-hydroxybutyrate
A
diabetes
6:1
18
Q
What are 2 enzymatic methods of glucose determination?
A
Hexokinase and
glucose oxidase method
19
Q
What is Hexokinase method and what are interfering substances?
A
- 2 reactions, measures increase in absorbance of NADP (it is directly proportional to glucose)
- Interfering substances: RBC esters, bilirubin, triglycerides (500 and up), drugs, fructose
20
Q
What is glucose oxidase method and what are interfering substances?
A
- specific for beta-D-glucose, may be coupled with peroxidase indicator reaction or by measuring oxygen consumption using oxygen electrode
- Interfering substances: ascorbic acid, uric acid, bilirubin, haemoglobin, tetracycline, glutathione, galactose, d-xylose
21
Q
In serum and plasma values are 10-15% _______ than in whole blood
A
higher
22
Q
Serum or plasma must be separated within 1h to prevent degradation by _________, glucose is stable for 24h in whole blood when preserved with ______________
A
glycolysis
sodium fluoride
23
Q
Serum/plasma fasting glucose values?
A
Serum/plasma fasting 74-100 mg/dL; CSF 60% of that value
24
Q
Other methods for detection of glucose are (2)
A
- Reduction method, which is based on the ability of glucose to reduce Cu++ to Cu+, less sensitive, substances that could reduce Cu++: fructose, galactose, vitamin C, uric acid, etc.
- Enzymatic method (more specific and precise result): Glucose is oxidized by glucose oxidase gluconic acid + H2O2 red dye
25
Glucose procedure (6)
- Centrifuge 3ml EDTA blood, 2000 rpm for 10min to separate plasma and use plasma sample
- Pipette into each of the 3 reaction tubes: standard glucose, sample plasma, DW
- Mix content well, incubate at 37C for 10min
- Using cuvette tube, read the sample and standard absorbance against the blank at 500 nm.
- Calculate from the fasting sample using this formula Glucose (mg/dl) = (Abs. sample/abs. standard) * standard conc. (100 mg/dl); normal range 70-100 mg/dl
26
Urine glucose measures can be _____ and ______
quantitative and qualitative
27
Benedict’s copper reduction reaction
qualitative measure of glucose
- Cupric ions to cuprous ions to produce a yellow or red cuprous compound
- All reducing sugars produce positive result, and some other reducing substances do as well
28
Urine strip test
qualitative measure
- Urine strip tests use glucose oxidase reaction
- Test has glucose oxidase, peroxidase and chromogen
- Reaction is specific for glucose
- ascorbic acid and urates may give false-negative; hydrogen peroxide or oxidizing agents may give false-positive
29
Quantitative measures are (2)
- Hexokinase or glucose oxidase method
30
_________ may cause falsely lower results in glucose oxidase
Uric acid
31
Glycosuria causes (4)
- DM
- Glucose infusion
- Renal glycosuria (Fanconi’s syndrome)
- Pregnancy
32
False-negative causes of glycosuria
- Large amount of ascorbic acid
- Therapeutic dose of ascorbic acid
- After tetracycline
33
Lactosuria may occur in (2)
- Late pregnancy and during lactation
- Lactase deficiency
34
Glycosuria is seen in (14)
Diabetes mellitus-not diag.
Renal glycosuria.
Hereditary defects in the metabolism of other reducing substances like galactose, pentose, and fructose.
Pregnancy.
Liver diseases.
Pancreatic diseases.
Thyrotoxicosis.
Cushing’s syndrome.
Acromegaly.
Brain injuries.
Shock.
Fanconi’s syndrome (Tubular defect).
Advanced renal tubular diseases.
Nephrotoxic chemicals like carbon monoxide, lead, and mercury.
35
What is Glycated hemoglobin (HbA1)
- An indicator of long-term glycemic control
- In adults it is combination of HbA1, A2 and F
- The average lifespan of the erythrocyte is 120 days, and glycated hemoglobin describes the average glucose levels in the blood over that life span
- Glycemic control 90-120 days, unaffected by daily variations; affected by conditions that affect lifespan of hemoglobin molecule
- Glycated hemoglobin (HbA1c) is formed by non-enzymatic glycation of hemoglobin and is dependent on the mean plasma glucose concentrations and on the lifespan of the red cell
36
The ________ the value of HbA1, the _______ the glycemic control
The higher the value of HbA1, the poorer the glycemic control
37
Values of HbA1 in non-diabetic, diabetic and pre-diabetic (3)
- In non-diabetic: < 5.7%
- In diabetic: > 6.5%
- In pre-diabetic: 5.7-6.4%
38
What is glucose tolerance test?
- How body metabolizes sugar and how quickly it is cleared from the blood
- Used to diagnose: pre-diabetes, DM, insulin resistance and reactive hypoglycemia
39
What are 2 glucose tolerance tests?
- Oral glucose tolerance test (OGTT)
- Ingestion of glucose in 5min
- Fasting blood sugar is measured before ingestion
- Intravenous glucose tolerance test (IGTT)
- Glucose is injected in the vein for 3min
- Blood insulin levels are measured before
40
Most common indications to check for diabetes (4)
* obese patients
* pregnant patients (as a screening test during the
24th – 28th weeks of pregnancy)
* patients with non-healing skin infections or
recurrent attacks of skin infections
* patients with family history of diabetes
41
Preparation for glucose test (3)?
1. Do not restrict carbohydrate intake at least 3 days prior to the test (balanced diet containing at least 150 – 200 g CHO/ day for three days)
2. No eating and drinking or exercise strenuously for at least 8 hours before the first blood sugar is taken
3. All medications taken by the subject must be noted and stopped, if possible, at least three days prior to the test
42
Procedure for OGTT (4)
1. The subject fasts for 10-14 hours or overnight.
2. Blood and urine samples are taken for analysis at zero time (baseline).
3. The subject is then given a glucose solution to drink. He / She ingests 1 g/kg BW in 300 ml. It should be drunk within 5 minutes.
4. Blood and urine samples are taken every 30 min (after taking glucose solution) for 3 hours.
43
Values for OGTT
- Normal: 70-99 mg/dl (3.9-5.5 mmol/L)
- Pre-diabetes: 100-125 mg/dl (5.6-6.9 mmol/L)
- Diabetes: 126 mg/dl (7 mmol/L)
44
ADA criteria for diabetes diagnosis (3/4)
1. Symptoms (polyuria, polydipsia, polyphagia, unexplained weight loss) of DM plus random casual plasma glucose concentration > 200 mg/dl (11.1 mmol/L)
2. FPG ≥126 mg/dL (7 mmol/L). Fasting is defined as no caloric intake for at least 8 hours.
3. 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an OGTT. The test should be performed using a glucose load containing the equivalent of 75 g anhydrous glucose dissolved in water.
(Not in our presentation)
4. In a patient with classic symptoms of hyperglycemia or hyperglycemic crisis, a random plasma glucose ≥200 mg/dL (11.1 mmol/L).
45
What is hypoglycemia?
- Symptoms occur when glucose is below 50 mg/dl
- 2 types: reactive (after meals) and fasting (post-absorptive)
- Reactive is not related to a disease, fasting is
46
Causes of reactive hypoglycemia (3)
- Excessive insulin
- Ethanol ingestion
- Overregulation of diabetes
47
Whipple's triad in hypoglycemia (3)
- Fasting hypoglycemia (<50 mg/dl, <2.7 mmol/L)
- Symptoms of hypoglycemia
- Relief after IV glucose
(a collection of three signs that suggests that a patient's symptoms result from hypoglycaemia that may indicate insulinoma.)
