(b)++Heart+processes

(5) What is double circulation? Describe how this works.

Double circulation describes the method in which blood flows through our bodies. It is characteristic for mammals. Double circulation consists of two separate circulation systems. The first one is the **systemic circuit**, which transports oxygenated blood away from the heart, through the body in arteries and deoxygenated blood back to the heart in veins. The second individual circuit is called the **pulmonary circuit.** It transports deoxygenated blood from the heart to the lungs to be re-oxygenated. Generally, the systemic circuit transports blood through the whole body, while the pulmonary circuit merely transports deoxygenated blood from the heart to the lung.



(6) We need to know the overall process of how the heart beats, but not the specific chemical messengers involved.

(a) Define myogenic & pacemaker then describe how our heart beats (i.e. describe the nerve impulses). Myogenic heart beats originate (begin) at the heart. These are caused by nerve impulses that start at the heart from the Sino-Atrial Node (SA node) in the right atrium. The Sino-Atrial Node is also known as the cardiac pacemaker. This pacemaker is made of specialised muscle cells that send impulses at regular intervals, which spread over the atria’s walls, causing contractions to occur simultaneously.

(b) What is the sequence of contractions? Atrial Systole - contraction of the heart muscles (myocardia) in the left and right atria Ventricular Systole - contraction of myocardia in the left and right ventricles

(c) How (& when) do the ventricles contract? The Atrio-Ventricular Node is connected to a bundle of specialised cardiac fibres. These fibres reticulate out into Purkinje tissue. Impulses travel from the Atrio-Ventricular Node through the cardiac fibres into the apex of the heart, from where they spread through Purkinje tissue. The movement of the impulse makes ventricular contractions start at the heart’s apex. As the contraction happens, blood is pushed out of the heart into the arteries.

(d) How can our brain modify our heart-rate (details please, including name of hormone)? The brain can change the frequency of our heartbeats. Cardiac frequency can be decreased or increased by impulses from the medulla oblongata 1, through the parasympathetic part of the autonomous nervous system 2.

1 Medulla oblongata is the lower part of the brain stem 2 Autonomous nervous system controls involuntary actions (mainly)

(7) What type of circulation system do humans have? A double circulation system – where the blood coming from the body goes into the heart, to the lungs, back to the heart, and then to the body again. This is why the heart is divided into two sides and 4 chambers.

(8) Copy & complete the following table, on your own paper.

Features of our blood vessels Only one epithelial cell thick, Thin cell walls composed of endothelium So small that red blood cells need to pass through it in a single line ||
 * || **Artery**  ||  **Vein**  ||  **capillary**  ||
 * Direction of blood flow || Away from the heart || Towards the heart || From the arteries to the veins (connects the two) ||
 * Cross-section / description || Consists of 3 layers: outer layer of tissue, muscular middle and inner layer of epithelial cells || Structure just as the arteries, but with thinner layers of tissue -> therefore smaller || Smallest of all blood vessels,
 * Blood speed || fast || slow || slow ||
 * Blood pressure || high || low || low ||
 * Presence of valves (Y/N) || No || Yes || No ||

(9) Explain the terms vasodilation & vasoconstriction.

Vasodilation: The blood vessels in the skin become wider which increases the flow of blood to the skin. As a result, the skin becomes warmer which increases heat loss to the environment. Convection and radiation are increased.



Vasoconstriction: The blood vessels in the skin contract which decreases the flow of blood to skin. As a result, the skin becomes colder, reducing the heat loss to the environment. Convection and radiation are decreased.