09 September 2015

#115 Urine analysis, dipsticks and biosensors

The presence of glucose and ketones in urine indicates that a person may have diabetes. If the concentration for these rises above the renal threshold, then not all glucose has been absorbed from the filtrate in the proximal convoluted tubule --> so will be present in the urine.

A large quantity or long-term presence of protein in the urine indicates

  • disease affecting glomeruli
  • kidney infection
  • high blood pressure (can lead to heart disease)

1. Dip sticks: test for glucose, pH, ketones, proteins
- urine analysis
- involves 2 immobilized enzymes: glucose oxidase and peroxidase
- shows the sugar level in urine from bladder NOT the current blood sugar level

2. Biosensor: allows people with diabetes to check their blood to see how well they are controlling their glucose concentration
- blood analysis: quantitative data
- a pad impregnated with glucose oxidase catalyses reaction to form gluconolactone
--> generates tiny electric current that is detected by electrode and is read by a meter

Exam question: question 9, specimen paper 2016


  Syllabus 2016-2018

14.1  Homeostasis in mammals

Homeostasis in mammals requires complex systems to maintain  internal conditions near  constant.

The kidneys  remove wastes from the blood and are the effectors for controlling the water potential of the blood.

a)   discuss the importance of homeostasis in mammals and explain the principles  of homeostasis in terms of internal and external stimuli, receptors, central  control,  co-ordination systems, effectors (muscles and glands)

b)   define  the term  negative feedback and explain how it is involved in homeostatic mechanisms

c)   outline  the roles of the nervous system and endocrine system in co-ordinating homeostatic mechanisms, including thermoregulation, osmoregulation and the control of blood glucose concentration

d)   describe the deamination of amino  acids  and outline  the formation of urea  in the urea  cycle (biochemical detail of the urea  cycle is not required)

e)   describe the gross structure of the kidney and the detailed structure of the nephron with its associated blood vessels using photomicrographs and electron micrographs

f) describe how the processes of ultrafiltration and selective reabsorption are involved with the formation of urine in the nephron

g)   describe the roles of the hypothalamus, posterior pituitary, ADH and collecting  ducts in osmoregulation

h)   explain how the blood glucose concentration is regulated by negative feedback control mechanisms, with reference to insulin and glucagon

i) outline  the role of cyclic AMP as a second messenger with reference to the stimulation of liver cells by adrenaline and glucagon

j) describe the three main stages of cell signalling in the control of blood glucose by adrenaline as follows:

•   hormone-receptor interaction at the cell surface
•   formation of cyclic AMP which binds to kinase  proteins
an enzyme cascade involving activation  of enzymes by phosphorylation to amplify the signal

k)   explain the principles  of operation of dip sticks  containing glucose oxidase and peroxidase enzymes, and biosensors that can be used for quantitative measurements of glucose in blood and urine

l) explain how urine analysis  is used in diagnosis with reference to glucose, protein  and ketones

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