Unit F214: Communication, Homeostasis & Energy Hormones By Ms Cullen

Hormones From Greek ‘To Set In Motion’. Chemical messenger from one cell/group of cells to another. Mainly secreted from endocrine glands into bloodstream to act on distant organs. Most hormones are polypeptides or proteins, some such as testosterone are steroids. Rate of production often linked to a negative feedback system. Neurones may stimulate production. Most hormones have a short life and are broken down by enzymes in the blood or cells, often in the liver, or are lost in urine.

Endocrine Gland A gland that excretes hormones directly into the blood stream. They are ductless glands. Exocrine Gland A gland that carries a secretion into a duct. eg salivary glands secrete saliva into the salivary ducts, which transport saliva to the mouth.

Major endocrine glands 1.Pineal gland 2.Pituitary gland 3. Thyroid gland 4. Thymus 5. Adrenal gland 6. Pancreas 7. Ovary 8. Testis Male Female Biology for OCR diagram P.27

Hormones Although hormones are carried in the blood all over the body, they only affect their particular target cells. This is because these target cells have the correct receptors. Target cells are usually grouped together to form target tissues. Protein hormones, eg insulin, will bind with a receptor on the outer surface of the plasma membrane & bring about a response without actually entering the cell. Steroid hormones are lipid-soluble, so they diffuse through the plasma membrane to receptors in the cytoplasm.

First and Second Messengers Hormones affect their target cells by attaching to receptors, this is an example of cell signalling. This in turn sets about a series of events within the cell. We will use adrenaline and how it affects the liver cells as an example Biology for OCR diagram P.28

Adrenaline Adrenaline is produced by the adrenal glands and affects a number of target organs and tissues (including heart, gut and iris). It is released as a response to excitement, danger or stress. Adrenaline prepares the body for vigorous activity, sometimes known as ‘the flight or fight hormone’.

Adrenaline Adrenaline is a catecholamine, made from amino acids. It is not soluble in lipids and therefore its target cells have their receptors on their plasma membranes. When the adrenaline binds with its receptor the receptor shape changes, this causes it to interact with another protein in the membrane known as a G-protein.

Adrenaline The G-protein then splits. One part combines with an inactive enzyme adenyl cyclase. This activates the enzyme, which converts ATP into cyclic AMP (cAMP). Biology for OCR diagram P.29

Week 4 The action of adrenaline

The Functions of the Adrenal Glands 1.Using ‘OCR Biology A2’ textbook P. 23 write notes on the function of the adrenal medulla and the adrenal cortex. 2.Complete Qs on P.23 in as much detail as possible.

Comparison of Nervous and Chemical Coordination NervousChemical(endocrine) Message is: Electrochemical(impulses)Chemical(hormones) Transmission route Specialised nerve cells Blood system Effects Rapid & short term (blinking) Slower, but usually long lasting (growth)

Control of Heart Rate in Humans Heart rate is measured in beats per minute (bpm) The heart muscle is myogenic – this means it can initiate its own contractions. The heart can change its rate in 3 different ways: 1. increases the number of bpm 2. increases the strength of its contractions 3. increases the volume of blood pumped per beat (the stroke volume)

Pacemaker The heart has its own pacemaker known as the sinoatrial node (SAN). The SAN can activate an action potential which travels as a wave over the atria walls, through the atrioventricular node (AVN) and down the purkyne fibres to the ventricles, where it causes a contraction. The SAN can receive action potentials along 2 different nerves; the vagus nerve which reduces the heart rate and the accelerator which increases heart rate. These nerves are affected by the cardiovascular centre in the medulla oblongata of the brain. The heart muscle responds to the presence of the hormone adrenaline in the blood.

Week 4 The control of heart rate

Artificial Pacemakers These deliver an electrical impulse to the heart. First developed in 1928, but had to be attached to a light fitting!! Modern pacemakers are only about 4cm long and are placed under the skin & fat on the chest. They are able to respond to the activity of the patient.