5.1.5 Animal Responses – Adrenaline and Controlling Heart Rate By Ms Cullen

Adrenal glands

Adrenal glands Adrenal cortex – Adrenal medulla –

Adrenal cortex Production of hormones by the adrenal cortex is controlled by hormones released from pituitary glands in the brain

Glucocorticoids release of these hormones is controlled by the hypothalamus Cortisol- Corticosterone-

Mineralocorticoids release is mediated by signals triggered by kidney Aldosterone-

Androgens These hormones are converted elsewhere in the body to female hormones (oestrogens) and male hormones (androgens); however, these steroid hormones are produced in much larger amounts by the ovaries (oestrogen) in women and testes (androgens) in men.

Adrenal medulla Hormones are released when the sympathetic nervous system is stimulated. This occurs when the body is stressed.

Adrenaline Adrenaline- This increases the heart rate by sending blood quickly to the muscles and brain. It also rapidly raises blood glucose concentration levels by converting glycogen to glucose in the liver

Noradrenaline Noradrenaline- This hormone works with adrenaline in response to stress, producing effects such as increased heart rate, widening of pupils, widening of air passages in the lungs, and narrowing of blood vessels in non-essential organs

Adrenaline Adrenaline is produced by the medulla of 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’.

Flight or fight response An instinct that all mammals possess In a potentially dangerous situation the body automatically triggers a series of physical responses intended to help the animal survive by preparing the body to either run or fight for life.

Flight or fight response

Physiological responses

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..........

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).

The action of adrenaline

Questions Explain why target cells must have a receptor. (4 marks) 2. Explain how the effects of adrenaline prepare the body for activity. (15 marks)

Control of Heart Rate

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. 2. 3.

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.

You do also have nerves and Hormones to speed up or slow down heart rate which are controlled by cardiovasular centre in your brain. sympathetic nerves to heart accelerate heart rate - vagus nerve decelerates heart rate

The rhythmic sequence of contractions is coordinated by the sinoatrial (SA) {pacemaker} and atrioventricular (AV) nodes. Human heartbeats originate from SA node near the right atrium. SA gives electrical stimulation that initiates atrial contraction by creating an action potential. The signal spreads to the atrioventricular node (AV node). Small delay at the AV node Signals carried from the AV node, slightly delayed, (allows blood to fill ventricles) through bundle of His fibres and Purkyne fibres cause the ventricles to contract simultaneously Modified muscle cells contract, sending a signal to other muscle cells in the heart to contract.

Electrical impulses in the heart originate in the sinoatrial node and travel through the intrinsic conducting system to the heart muscle.

The impulses stimulate the myocardial muscle fibres to contract and thus induce systole. http://library.med.utah.edu/kw/pharm/hyper_heart1.html

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.