Hormonal Communication (OCR A Level Biology): Flashcards

The adrenal glands are situated above each kidney.

The cortex produces steroid hormones:

• Aldosterone – regulates levels of salts (sodium and potassium) and water balance in the blood, affecting blood volume and pressure

• Cortisol – the primary stress hormone; regulates metabolism of glucose, proteins and fats to release usable energy

The medulla produces adrenaline, a hormone released at times of stress or excitement.

It affects many body organs, preparing the body to respond to emergency situations, and initiates the "fight or flight" response.

The endocrine system is used to control functions that do not need instant responses.

• Thermoregulation – the control of body temperature

• Osmoregulation – the control of the water potential of body fluids

• The control of blood glucose concentration

Each adrenal gland consists of two main areas:

• A central medulla

• An outer cortex

True

False — the adrenal cortex produces the steroid hormones; the medulla produces adrenaline.

A gland that secretes substances via a duct (rather than directly into the blood).

A gland that secretes hormones directly into the blood (not via a duct).

The pancreas functions as both:

• an endocrine gland

• an exocrine gland

To produce pancreatic juice (containing digestive enzymes), which is delivered to the small intestine where it helps in the digestion of food.

To produce the hormones glucagon and insulin.

They are performed by different tissues, which can be clearly seen and distinguished from each other when observed under a microscope.

Most cells secrete digestive enzymes (exocrine function), while small sections of cells produce hormones (endocrine function).

Small sections of cells found throughout the pancreas that carry out its endocrine function by producing hormones.

• Alpha cells secrete glucagon

• Beta cells secrete insulin

Within the islets of Langerhans, alpha cells secrete glucagon and beta cells secrete insulin.

The branch of biology that studies the microscopic anatomy of biological tissues (also known as microanatomy).

By staining sections of pancreatic tissue and viewing them under a microscope.

The stained samples can then be examined for drawing and labelling to identify the exocrine and endocrine tissues.

To show the exocrine tissue and the endocrine tissue (the islets of Langerhans) in different colours, so the two tissue types can be distinguished.

True

False — the islets of Langerhans carry out the endocrine function, producing the hormones glucagon and insulin.

• Absorption in the gut following carbohydrate digestion

• Hydrolysis of glycogen stores

• Conversion of non-carbohydrates (such as lipids, lactate and amino acids) to glucose

Insulin and glucagon.

• α cells secrete glucagon

• β cells secrete insulin

These cells also act as the receptors that detect changes in blood glucose concentration and initiate the response.

The breakdown of glycogen to produce glucose molecules. It is triggered by glucagon and releases glucose into the bloodstream, increasing blood glucose concentration to within the normal range.

The synthesis of glycogen from glucose molecules. It is triggered by insulin and removes glucose from the bloodstream, decreasing blood glucose concentration to within the normal range.

The synthesis of glucose from non-carbohydrate molecules (such as fatty acids and amino acids). It is triggered by glucagon and releases glucose into the bloodstream, increasing blood glucose concentration to within the normal range.

• The α cells respond by secreting glucagon

• The β cells respond by stopping the secretion of insulin

The fall in insulin concentration reduces the use of glucose by liver and muscle cells.

• Glucagon binds to receptors on the cell surface membrane, causing a conformational change that activates a G protein

• The G protein activates the enzyme adenylyl cyclase

• Adenylyl cyclase catalyses the conversion of ATP to the second messenger cyclic AMP (cAMP)

• cAMP activates protein kinase A enzymes

• Protein kinase A activates phosphorylase kinase enzymes by adding phosphate groups

• Phosphorylase kinase activates glycogen phosphorylase enzymes

• Glycogen phosphorylase catalyses the breakdown of glycogen to glucose (glycogenolysis)

It amplifies the original signal from glucagon, so that a small amount of hormone results in the release of a large amount of glucose by the liver, raising blood glucose concentration back to a normal level.

Adrenaline binds to different receptors on the surface of liver cells that activate the same enzyme cascade as glucagon, leading to the breakdown of glycogen by glycogen phosphorylase.

It also stimulates the breakdown of glycogen stores in muscle during exercise; here the glucose produced remains in the muscle cells for respiration.

• Glucose enters the β cells by facilitated diffusion and is respired to produce ATP

• High ATP concentration causes potassium channels to close, changing the membrane potential

• This opens voltage-gated calcium channels

• The influx of calcium ions causes insulin-containing vesicles to fuse with the cell surface membrane and secrete insulin into the capillaries

Insulin binds to specific receptors on the membranes of target cells (muscle, fat and liver cells).

This stimulates the cells to add more glucose transporter proteins to their cell surface membrane, increasing permeability to glucose.

As a result, the rate of facilitated diffusion of glucose into the cells increases.

Insulin stimulates glycogenesis in the liver:

• Once glucose enters a liver cell, an enzyme rapidly converts it to glucose phosphate

• Other enzymes convert glucose phosphate into glycogen

This removes glucose from the blood, lowering blood glucose concentration.

Blood glucose concentration is regulated by negative feedback control mechanisms, in which receptors detect a change and effectors act to counteract it.

Converting glucose into glycogen lowers the glucose concentration inside the liver cell.

This maintains a steep diffusion gradient between the blood in the capillaries and the liver cells, so glucose continues to diffuse in.

False — insulin is secreted by the β cells; the α cells secrete glucagon.

True

A condition in which the homeostatic control of blood glucose has failed or deteriorated, due to disrupted insulin function, allowing the glucose concentration in the blood to rise.

Their blood glucose concentration rises so high that the kidneys are unable to filter out all of the excess glucose, so some passes into the urine.

The increased blood glucose concentration causes the kidneys to produce large quantities of urine.

This leads to dehydration, which makes the individual feel thirsty.

The pancreas fails to produce sufficient insulin to control blood glucose levels.

It usually begins in childhood due to an autoimmune response, in which the immune system (T cells) attacks the β cells of the islets of Langerhans in the pancreas.

In Type 1 diabetes, the body's immune system (T cells) attacks the β cells of the islets of Langerhans in the pancreas.

• Regular blood tests to monitor blood glucose

• Insulin injections (fast-acting or slow-acting, allowing different levels of control)

• A diabetes-appropriate diet

In Type 2 diabetes the pancreas still produces insulin, but the receptors have reduced in number or no longer respond to it.

This reduced sensitivity to insulin (in the liver and fat storage tissues) causes reduced glucose uptake and an uncontrolled high blood glucose concentration.

• Obesity

• Physical inactivity

• High blood pressure

• High blood cholesterol

Genetics is also an influencing factor (having a relative with Type 2 diabetes, or belonging to certain ethnic groups, increases risk).

A sugar- and fat-controlled diet and an exercise regime are usually sufficient treatments.

The high blood glucose concentration lowers the water potential of the blood.

This causes more water to move from the tissues into the blood vessels by osmosis.

The resulting larger volume of blood in the circulatory system causes blood pressure to increase.

DNA that has been altered by introducing nucleotides from another source.

• The human insulin gene is isolated; restriction endonucleases cut open bacterial plasmids and the human DNA, and DNA ligase splices them together

• The recombinant plasmids are inserted into Escherichia coli by transformation (calcium ion bath then heat or electric shock)

• Transgenic bacteria are identified using markers, then isolated, purified and placed into fermenters with optimal conditions

• The bacteria multiply by binary fission and express insulin, which is extracted and purified

• Identical to human insulin (unless modified to act faster or slower)

• Reliable supply to meet demand

• Fewer ethical, moral or religious concerns (not extracted from cows or pigs)

• Fewer rejection problems, side effects or allergic reactions

• Cheaper to produce in large volumes

• Useful for people with animal insulin tolerance

Stem cells can be treated so that they differentiate into pancreatic β cells.

These new β cells can then be transplanted into the pancreas of a diabetic individual, replacing the damaged cells and allowing insulin to be produced.

Early-stage research has had some success in mice but has not yet advanced to human trials.

Insulin is a protein.

If taken orally it would be digested by the enzyme protease in the gut before it could enter the bloodstream.

True

False — the pancreas still produces insulin, but the receptors have reduced in number or no longer respond to it.