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Circulatory System – Part 2. A&P1 Tutor: Eleshia Howell. Innervation to heart. The heart is influenced by autonomic nerves originating in the cardiovascular centre in medulla oblongata. The VAGUS nerve supplies parasympathetic stimulation, producing slow, regular heart beat.

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circulatory system part 2

Circulatory System – Part 2


Tutor: Eleshia Howell

(c) Eleshia Howell, 2012

innervation to heart
Innervation to heart
  • The heart is influenced by autonomic nerves originating in the cardiovascular centre in medulla oblongata.
  • The VAGUS nerve supplies parasympathetic stimulation, producing slow, regular heart beat.
  • The cardiac accelerator nerves supply the sympathetic stimulation to increase the rate and force of contraction.

(c) Eleshia Howell, 2012

factors affecting heart rate
Factors affecting heart rate
  • Gender
  • Autonomic (sympathetic and parasympathetic) nerve activity
  • Age
  • Circulating hormones, e.g. adrenaline (epinephrine), thyroxine
  • Activity and exercise
  • Temperature
  • The baroreceptor reflex
  • Emotional states

(c) Eleshia Howell, 2012

the cardiac cycle
The cardiac cycle
  • Heart beat = contraction & relaxation
  • Contraction = systole; Relaxation = diastole
  • Healthy adult heart beats 60-80 times /min
  • A full cardiac cycle consists of:
    • Atrial systole
    • Ventricular systole
    • Complete cardiac diastole
  • If we use 74 bpm as an example, then each cycle lasts 0.8 seconds
  • READ p84 Textbook...

(c) Eleshia Howell, 2012


Electrical impulses can be detected through the use of and electrocardiograph (ECG). Electrodes are attached to a person’s chest and limbs to detect the pattern of impulses, the time interval between cycles and parts of the cycle.

  • The impulses are named P, Q, R, S, T.
  • Examining the ECG provides information about the state of the myocardium and the cardiac conduction system.
  • Tachycardia = fast heart rate
  • Bradycardia = slow heart rate

(c) Eleshia Howell, 2012


Cardiac output = amount of blood ejected from each ventricle per minute.

The amount expelled by each contraction = stroke volume.

Stroke volume x Heart rate = cardiac output

(c) Eleshia Howell, 2012


Cardiac output can be greatly increased to meet the demands of exercise ~ this is known as cardiac reserve.

  • When increased blood supply is needed to meet tissue requirements of oxygen and nutrients, heart rate and/or stroke volume can be increased.
  • Factors affecting cardiac output include:
    • Arterial blood pressure
    • Blood volume
    • Venous return
    • Heart rate

(c) Eleshia Howell, 2012

blood pressure bp
Blood pressure (bp)
  • The force or pressure that the blood exerts on the walls of the blood vessels.
  • Systemic arterial BP maintains the essential flow of blood into and out of the organs; it comes from the left ventricle pumping blood into the aorta.
  • Keeping BP within normal limits is very important – vessels can be damaged, causing clots or bleeding from ruptured site. Too low will provide inadequate supply to vital organs such as kidneys, brain, heart.

(c) Eleshia Howell, 2012


Blood pressure varies according to:

    • Time of day – falls at rest, during sleep
    • Posture
    • Age – increases with age
    • Gender – usually higher in women than men.

Systolic & Diastolic pressure:

  • When left ventricle contracts and pushes blood into aorta, this is the systolic blood pressure. In adults = 120mmHg
  • When complete cardiac diastole occurs, the heart is resting, creating diastolic blood pressure. = 80mmHg

(c) Eleshia Howell, 2012


Arterial BP is measured with a sphygmomanometer and is usually expressed with systolic pressure written above diastolic. Eg 120/80

  • It is the distension and recoil of the elastic arterial walls of the systemic circulation which maintains diastolic pressure.
  • Cardiac output and peripheral resistance determine blood pressure.
  • Peripheral resistance is offered by the tunica medica in the arterioles – when the elastic tissue is replaced with more fibrous tissue with age, blood pressure rises.

(c) Eleshia Howell, 2012


The internal organs are also capable of monitoring and adjusting blood flow and pressure in their own supply vessels. This autoregulation helps to protect the tissues against damaging changes in systemic pressure.

  • This is especially important in the kidneys, where increased pressure will damage the delicate glomerular capillary beds; and in the brain, which is highly sensitive to changes in levels of cellular waste.

(c) Eleshia Howell, 2012

control of blood pressure
Control of blood pressure

Controlled in 2 ways –

  • Short term – from moment to moment, involving baroreceptor reflex, chemoreceptors and circulating hormones. All controlled by cardiovascular centre ~ interconnected neurones in medulla and pons of brain stem that receive, integrate and co-ordinate inputs from baro/chemo receptors and higher brain centres.
  • Long term – regulation by kidneys and the renin-angiotensin-aldosterone system.

(c) Eleshia Howell, 2012


Baroreceptors detect pressure changes (stretch) within the arch of the aorta and the carotid sinuses. A rise in BP detected by these sites increases parasympathetic nerve activity (via the CVC) to slow the heart rate. Likewise if pressure drops, sympathetic stimulation is increased, speeding up heart rate. This is the baroreceptor reflex.

  • Chemoreceptors are also situated in the aortic and carotid bodies but are primarily involved in control of respiration. They are sensitive to changes in CO2, O2 and blood pH. If failing tissue perfusion is detected, heart rate is increased to improve blood supply.

(c) Eleshia Howell, 2012


Higher brain centre input to CVC is influenced by emotional states, eg fear, anxiety, pain, which may affect blood pressure. Hypothalamus controls body temperature and may also influence the CVC to respond by adjusting the diameter of blood vessels.

  • Kidney role in blood pressure will be discussed further during study of the urinary system.

(c) Eleshia Howell, 2012

  • The pulse is a wave of distension and elongation felt in the artery wall each time the left ventricle ejects blood into the systemic circulation.
  • Approx 60-80ml of blood is expelled into the full aorta; the pressure wave is transmitted throughout the arterial system and can be felt at any point where a superficial artery can be palpated
  • Pulse palpation provides information regarding the heart rate, regularity and volume / strength of pressure.

(c) Eleshia Howell, 2012



(c) Eleshia Howell, 2012

pulmonary circulation
Pulmonary circulation
  • Is the circulation of blood from the right ventricle to the lungs, and back to the left atrium.
  • In the lungs, CO2 is excreted, O2 is absorbed
  • Pulmonary artery carries deoxygenated blood from right ventricle, branching left and right to travel to lungs. Within the lung, these vessels divide further into smaller branches to serve the upper, middle and lower lobes of the lungs, before subdividing into tiny capillary networks.

(c) Eleshia Howell, 2012


Two pulmonary veins leave each lung, returning oxygenated blood to the left atrium, which then travels down into left ventricle before being pumped into the aorta for general circulation.

(c) Eleshia Howell, 2012

systemic circulation
Systemic circulation
  • The system of blood vessels which supply blood to all the areas of the body excluding the lungs.
  • Comprises of arterial and venous networks.
  • The aorta is the major artery within the body from which all systemic blood is transported. Various arteries branch off from the aorta to supply limbs, body areas and organs.
  • Blood is returned to the heart by the superior and inferior vena cavae, which gather deoxygenated blood from the upper and lower body respectively.

(c) Eleshia Howell, 2012



Main arteries

(c) Eleshia Howell, 2012


P93, Main Veins

(c) Eleshia Howell, 2012


Carotid Arteries – bilateral neck.

  • Branch into internal and external arteries to supply the brain and head & neck respectively. Internal branch contributes to circulusarteriosus which supplies brain.

(c) Eleshia Howell, 2012

venous return from head neck
Venous return from head & neck
  • Veins from face, head and neck feed into Jugular veins, which then enter the subclavian and brachiocephalic veins before emptying into superior vena cava

(c) Eleshia Howell, 2012


Subclavian artery –

Branches off from aortic arch to supply the arms


(c) Eleshia Howell, 2012


A series of deep and superficial veins return blood from arm to the heart.


(c) Eleshia Howell, 2012

thoracic abdomen
Thoracic & abdomen

Descending aorta – numerous paired branches to serve the organs of the thoracic cavity.

Abdominal aorta – supplies organs of abdomen and branches into left and right iliac arteries to supply legs.

Larger veins from the thorax drain into azygos and hemiazygos veins which run perpendicular with the spinal column.

Main veins from abdomen drain into Inferior Vena cava, as does right & left iliac veins from legs.

(c) Eleshia Howell, 2012



(c) Eleshia Howell, 2012


Abdominal aorta branches, p101

(c) Eleshia Howell, 2012