Biochemistry Flashcards
Which cells in the Islets of Langerhans secrete insulin?
Beta-cells
Which cells in the Islets of Langerhans secrete glucagon?
Alpha-cells
Which cells in the Islets of Langerhans secrete somatostatin?
Delta-cells
What is the initial structure that is cleaved to form insulin?
Preproinsulin
There is great variation in the amino acid sequence of insulin between species. True/False?
False
Very little variation
What is the effect of insulin upon amino acids, glucose and lipids?
Increases uptake into respective tissues
amino acid in muscle, glucose in muscle, lipid in adipose
Insulin inhibits lipolysis. True/False?
True
Through which transporter does glucose enter beta-cells in the pancreas?
GLUT2
What happens to glucose once in the beta-cell in the pancreas?
Phosphorylated to glucose-6-phosphate
Which enzymes carry out glucose phosphorylation?
Glucokinase
Hexokinase (RBCs)
Which two proteins make up a functional Katp channel?
Kir6.1 Sulphonylurea receptor (SUR1)
What inhibits the Katp channel? What happens as a result?
Intracellular ATP, causing depolarisation (less K efflux), causing opening of Ca channels to allow insulin exocytosis
What is MODY?
Maturity-onset diabetes of the young
Genetic defect in beta-cell function, causing early-onset type II diabetes
Which enzyme is impaired in MODY?
Glucokinase
causing defective glucose sensing
How are ketone bodies formed?
Derived from acetyl-CoA in B-oxidation
Give examples of ketone bodies
Acetone
Acetoacetic acid
B-hydroxybutric acid
Ketoacidosis is most associated with which diabetes - type 1 or 2?
Type 1
Sodium follows water everywhere. True/False?
False
Water follows sodium!
(WafS)
Concentration of Na inside the cell is more than concentration of Na outside the cell. True/False?
False
Concn of Na outside cell is greater than inside
What does mineralocorticoid activity refer to?
Sodium retention in exchange for potassium and/or hydrogen ions
What is the main steroid in the body with mineralocorticoid activity?
Aldosterone
Excess mineralocorticoid activity causes what?
Sodium retention
What effect does sodium loss have upon water?
Sodium loss means water loss (water follows sodium!)
Outline what happens in terms of sodium and water when blood pressure drops
Decreased blood pressure causes sodium + water retention in order to compensate and bring blood pressure up
Which hormone controls water reabsorption?
ADH
What effect does ADH have on water reabsorption and thus urine output?
Causes increased water reabsorption (anti-diuresis), producing low-volume concentrated urine
Concentrated/small volume urine has a high omolality. True/False?
True
What are the main causes of decreased sodium levels?
Too much water
Too little sodium
What are the main causes of increased sodium levels?
Too little water
Too much sodium
Decreased sodium levels can be due to too much water. How can this arise?
SIAD (inappropriate ADH secretion)
Compulsive water drinking
Decreased sodium levels can be due to too little sodium. How can this arise?
Sodium loss (renal insufficiency, gut fistulae) Decreased sodium intake (rare)
Increased sodium levels can be due to too little water. How can this arise?
Water loss (diabetes insipidus) Decreased water intake
Increased sodium levels can be due to too much sodium. How can this arise?
IV medication
Drowning in sea
High-salt feeds
Outline pathogenesis of Addison’s disease
Adrenal insufficiency; can't make enough aldosterone; can't retain enough sodium; lose sodium + water; low ECF volume, so patient is dehydrated + dizzy
What is the main osmotic stimulus for ADH release?
High sodium (high osmolality) causes increased ADH
Does hypovolaemia cause increased or decreased ADH release?
Increased ADH release (to compensate for loss of fluid)
Outline pathogenesis of diabetes insipidus
Disrupted pituitary; can't secrete ADH; less water reabsorption; lots of water lost in urine; sodium is high to reflect water deficit
