3.4.7 Hormones and control of blood glucose

What happens when the concentration of glucose decreases ?

not enough glucose for respiration. Increases- disrupt normal function of cells.

What is more branched amylopectin or glycogen?

Glycogen is more branched than amylopectin.

What is glycogen made up of?

Made from alpha glucose with 1-4 and 1-6 glycosidic bonds.

What is the cells in the endocrine tisssue in the pancrease that secreted the two hormones that control blood glucose called?

Islets of Langerhans

What are the two type of cells that make up the islets of langerhans called?

Alpha and beta cells

What do alpha and beta cells secrete?

alpha cells secrete glucagon, beta cells secrete insulin.

What are the receptors and what are the effectors?

Alpha and beta cells act as receptors and initiate the response for controlling blood glucose concentration. Liver, muscle and fat cells are effectors in response to insulin.

When is insulin secreted?

Secretion of insulin- when blood glucose concentration increases, it is detected by beta cells. Beta cells secrete insulin. Glucose is absorbed in the beta cells via carrier proteins, which causes insulin containing vesicles to move towards the cell-surface membrane, where they release insulin.

Insulin circulates around the body, it stimulates the uptake of glucose by muscle, fat and liver cells.

How is glucose uptaken?

Muscle, fat, adipose and liver cells have glucose transporter proteins in their surface membranes. These membrane proteins allow for the uptake of glucose by facilitated diffusion. The glucose transporter proteins on target cells are insulin-sensitive. Insulin binds to specific receptors on the membranes, which stimulates them to activate/add more glucose transporter protiens to their cell membrane, so rate of facilitated diffusion increases. Insulin stimulates glycogenesis (conversion of glucose to glycogen), which helps maintain a steep diffusion gradient. Insulin also triggers an increase in respiration rate.

What does an increase in blood glucose mean in terms of the two hormones?

Increase in blood glucose- less glucagon and more insulin

What is glycogenolysis?

Glycogenolysis- splitting glycogen to glucose

What is gluconeogenesis?

Gluconeogenesis- amino acids and lipids made into glucose.

When is glucagon secreted?

When there is a decrease in blood glucose concentration.

Describe what happens when there is a decrease in blood glucose concentration?

Glucagon stimulates the breakdown of glycogen to glucose.

Beta cells stop the secretion of insulin.

A decrease in blood insulin concentration reduces the use of glucose by liver and muscle cells.

Glucagon binds to receptors on liver cells, which causes a conformational change which activates a G protein. The activated G protein activates the enzyme adenylyl cyclase, which catalyses the conversion of ATP to the second messenger cyclic AMP (cAMP). cAMP binds to protien kinase A enzymes, activating them, which activates glycogen phosphorylase enzymes. These enzymes catalyse the breakdown of glycogen to glucose (glycogenolysis).

Describe the levels of the two hormones when there is a decrease in blood glucose

Decrease in blood glucose- more glucagon and less insulin.

What is glycogenesis?

Glycogenesis- making glucose (condensation reaction).

What hormone can also affect the blood glucose concentration?

Adrenaline can affect blood glucose concentration

What happens when adrenaline is secreted?

when secreted it increases the concentration of blood glucose. It does this by binding to different receptors to activate the same response that occurs when glucagon binds to specific receptors.

Adrenaline binds to receptors, causes adenylyl cyclase to change shape and become activated. Activated adenyl cyclase catalyses the conversion of ATP to the second messenger cyclic AMP (cAMP). cAMP binds to protein kinase A enzymes, which activates phosphorylase kinase enzymes by adding a phosphate group. Active phosphorlyase kinase enzymes activate glucogen phosphorylase enzymes, which cataylyses the breakdown of glycogen to glucose. Adrenaline also stimulates the breakdown of glycogen stores in muscle during exercise. Glucose produced remains in the muscle cells where it is needed for respiration.

Summarise all the type of conversions and their names

Glycgogenesis is the synthesis of glycogen from glucose molecules

Triggered by insulin.

Glycogenolysis is the breakdown of glycogen to produce glucose molecule.

Triggered by glucagon.

Gluconeogenesis is the synthesis of glucose molecules from non-carbohydrate molecules.

Triggered by glucagon.

How can glucose enter the bloodstream?

Glucose can enter bloodstream from- absorption in the gut, hydrolysis of glycogen, non-carbohydrates converted into glucose.

What is the cause of diabetes?

Causes of diabetes- insulin function is distrupted. Kidney can't filter out excess glucose so it appears in urine, increases glucose concentration causes kidneys to produce large quantities of urine.

Describe type 1 diabetes

Pancreas fails to produce sufficent insulin to control blood glucose levels. Happens due to an autoimmune response where the immune system attacks the beta cells of the islets of langerhans. Lack of insulin also affects glycogen stores, which results in an individual feeling fatigued.

Type 1 diabetes is normally treated with regular blood tests, insulin injections and a diabetes-appropriate diet.

Describe type 2 diabetes

In type II diabetes the pancreas still produces insulin but the receptors have reduced in number or no longer respond to it.

The lack of response to insulin means there is a reduced glucose uptake which leads to an uncontrolled high blood glucose concentration.

For early-stage type II diabetes, a sugar and fat controlled diet and an exercise regime are usually sufficient treatments.

Individuals with poorly controlled diabetes often suffer from high blood pressure. The high blood glucose concentration lowers the water potential of the blood which causes more water to move from the tissues into the blood vessels by osmosis. As a result, there is a larger volume of blood within the circulatory system which causes blood pressure to increase.

does obesity cause diabetes?

Correlation of obesity and diabetes does not mean causation.

How can you test a sample to determine its concentration of sugar?

Benedicts test can be used to carry out a quantitative test on an unknown urine sample to determine the concentration of sugar. The intensity of any colour change seen relates to the concentration of reducing sugar present in the sample. A quantitative test can be carried out by setting up standard solutions with known concentrations of reducing sugar. The same procedure is carried out on a urine sample with an unknown concentration of reducing sugar which is then compared to the stock solution colours to estimate the concentration of reducing sugar present. To avoid issues with human interpretation of colour, a colorimeter could be used.