Topic 6.2 The Blood System Flashcards
Circulation
The blood system continuously transports substances to cells and simultaneously collects waste products.
Circulatory system
The human heart has 4 chambers, 2 atria (blood-returning “reservoirs”) and 2 ventricles (blood-expelling “pumps”).
Blood vessels
Three types:
- Arteries (3 layers)
- Veins (3 layers)
- Capillaries (single layer)
Arteries
Conveys blood from heart ventricles to the body and lungs with high pressure.
Structure of arteries
- Narrow lumen (relative to wall thickness) to maintain blood pressure at approx. 80-120 mmHg
- Thick wall and outer layer of collagen to prevent rupturing
- Inner layer of muscle and elastic fibers to maintain pulse flow, allowing for contractions and flexibility
Flow of blood in arteries
Expulsion of blood from heart upon ventricular contraction in pulses, which are maintained by muscle and elastic fibers.
- Pulse flow moves forward as elastic recoil in inner layer causes the narrow lumen to contract and “push” blood
Veins
Collect blood from tissues to the atria of the heart at a low pressure.
Structure of veins
- Wide lumen to maximize blood flow
- Thin wall with less muscle and elastic fibers because of low pressure at approx. 5-10 mmHg
- Possesses valves to prevent backflow and blood pooling
Flow of blood in veins
- Low pressure makes it difficult for the blood to move against gravity, so valves are utilized to prevent backflow
- Skeletal muscles and arterial muscles can help venous blood flow in the right direction
Capillaries
Exchange materials between cells in tissues and blood at a low pressure.
Structure of capillaries
- Small diameter with the width of one red blood cell
- Single-layer endothelium to minimize diffusion distance for permeable materials
- Surrounded by a basement membrane
- Can contain spores
Process of circulation
- Atria collect blood from veins (right atrium from superior/inferior vena cava, left atrium from the pulmonary veins)
- Atria contract and AV valves open, causing ventricles to fill with blood
- Ventricles contract, AV valves close, and semilunar valves open
- Blood is pumped into arteries as semilunar valves close
- Cycle repeats
Myogenic heart contraction
The signal for cardiac compression arises within the heart tissue itself (initiated by cardiomyocytes rather than brain cells).
Sinoatrial (SA) node
A cluster of cardiomyocytes (heart muscle cells) that direct the contraction of heart muscle tissue.
- Acts as the primary pacemaker, controlling heart rate
- If the SA node fails, a secondary pacemaker (atrioventricular AV node) maintains cardiac contractions at a slower rate
- If both the SA and AV nodes fail, a final tertiary pacemaker (Bundle of His) coordinates contractions at the slowest rate
Electrical conduction of a heartbeat
The sequence of electrical conduction ensures a delay between atrial and ventricular contractions, resulting in two heart sounds (lub dub) and a maximized blood flow.
- SA node sends out electrical impulse to stimulate the contraction of the myocardium
- The impulse causes the atria to contract and stimulate the AV node at the junction between the atrium and ventricle
- The AV node sends signals down from the septum via the Bundle of His
- The Bundle of His innervates Purkinje fibers in the ventricular wall, causing ventricular contraction
Chambers of the heart
- 2 atria: small chambers near the top of the heart that collect blood from the body and lungs
- 2 ventricles: larger chambers near the bottom of the heart that pump blood to the body and lungs
- Right side: pulmonary deoxygenated set of atrium/ventricle that provides circulation for the lungs
- Left side: systemic oxygenated set of atrium/ventricle that provides circulation for the rest of the body
- The left side of the heart is stronger because it is pumped farther
Valves in the heart
- Atrioventricular (AV) valves: bicuspid (left) and tricuspid (right), located between the atria and ventricles
- Semilunar valves: aortic (left) and pulmonary (right) between the ventricles and arteries
Blood vessels connected to the heart
- Vena cava (superior and inferior): feeds into right atrium, returning deoxygenated blood from the body
- Pulmonary artery: connects to the right ventricle and sends deoxygenated blood to the lungs
- Pulmonary vein: connects to the left atrium and returns oxygenated blood from the lungs
- Aorta: extends from the left ventricle and sends oxygenated blood around the body
Signaling for heart rates
Basal heart rate is determined within the heart by the pacemaker, but can be regulated by external signals.
- Nerve signals from the brain can trigger rapid change, endocrine signals can trigger more sustained change
- Changes to blood pressure or blood pH will trigger changes in heart rate
Nerve signalling
The pacemaker is under involuntary control from the brain by the brain stem.
Hormonal signalling
Heart rates can undergo sustained increases in response to hormonal signaling to prepare for vigorous physical activity.
- Example: adrenaline released by adrenal glands can increase heart rate by activating chemical pathways
