6.2 - Blood System

Question 1

Arteries

Answer 1

Blood vessels carrying blood away from the heart to body tissues

• tunica externa: tough outer layer
• tunica media: muscle tissue that withstands high presseure without bursting and elastin fibres that store energy when stretched to recoil and maintain high blood pressure
• tunica intima: endothelium lining

Question 2

Arterial pressure

Answer 2

arterial systole: peak blood pressure when blood enters the artery from heart
Arterial diastole: blood pressure dieback

vasoconstriction: contraction of circular muscle narrowing of artery lumen restricting blood flow to parts of the body in arterioles or increasing blood pressure in arteries
vasodilation: relaxation of circular muscles widening of artery lumen increasing blood flow to part of the body

Question 3

Heart diagram and flow

Answer 3

• Heart chambers: separated by septum
• Right chamber of the heart: deoxygenated blood
• Superior and inferior vena cava: where deoxygenated blood
  from the systemic circuit enters the right atrium
• Right atrium: contracts pushing blood through the
  atrioventricular valve into the right ventricle
• Right ventricle: pushes blood through the semi-lunar valve into
  the pulmonary arteries
• Pulmonary arteries: sends deoxygenated blood to the lungs for
  gas exchange
• Left chamber of the heart: oxygenated blood
• Pulmonary veins: oxygenated blood enters the left atrium
• Left atrium: contraction pushes blood through atrio-ventricular
  valve into the left ventricle
• Left ventricle: pushes blood through the semilunar valve and
  out through the aorta
• Aorta: sends oxygenated blood to other tissues through arteries

Question 4

Atherosclerosis (development + causes + consequences)

Answer 4

Atherosclerosis: development of atheroma in artery walls
Development:
- Accumulation of lipoproteins in the arteries
- Endothelium cells and smooth muscle signal phagocytes
- Phagocytes engulf lipoproteins by endocytosis and enlarge forming an atheroma
- Smooth muscle cells form a tough cap over the atheroma protruding into the lumen
- Lumen narrows limiting blood flow

Occlusion of coronary arteries: when lumen of coronary artery is narrowed reducing blood flow and oxygen and nutrient supply to the heart muscle

• Lack of oxygen causes pain and heart rate to increase to maintain blood circulation
• Rupturing of atheroma can cause blood clots blocking blood flow

Causes of atherosclerosis:

• High blood concentration of LDL (low density lipoproteins)
• High blood glucose concentration from obesity, overeating, diabetes
• High blood pressure from smoking, stress
• Consumption of trans fats -> damage endothelium of artery

Question 5

Capillaries

Answer 5

narrowest blood vessels (10um) that branch out to form capillary networks to transport blood to all tissues (exception, lens and cornea in eyes).

• Capillary wall: very permeable to allow exchange between tissue cells and blood
• Thin layer of endothelium cells with pores between cells
• Cannot withstand high pressures
• Permeability differs between tissues and overtime, changing in response to the specific needs of the tissue

Tissue fluid flows between tissue cells to exchange useful substances and waste products before returning to capillaries containing oxygen, glucose and smaller substances formed from plasma leaking out of capillaries through the pores.

Question 6

Veins

Answer 6

Blood vessels that transport blood from capillaties to heart
Exception: hepatic portal vein carries blood from stomac and intestines to liver

• Vein wall: thinner and less muscle and elastic fibres due to lower blood pressure than in arteries
• Dilate more with larger lumen, holding more blood than arteries
• Blood flow: assisted by pressure from contraction of surrounding muscles squeezing adjacent veins (skeletal muscles) and Valves that maintain unidirectional circulation in veins by preventing backflow if blood pressure is too low
  (Backflowing blood get caught in flaps and blocks the lumen
  Foreflowing blood opens the valve by pushing flaps to the side)

Question 7

Double circulation

Answer 7

heart has 2 separate pumps forming the pulmonary and systemic circuits to prevent mixing of deoxygenated and oxygenated blood

pulmonary circuit: deoxygenated blood from the systemic circuit is reoxygenated after passing to and from the lungs

systemic circuit: oxygenated blood from the pulmonary circuit becomes deoxygenated after going to and from the body tissues

Question 8

Myogenic contractions of the heart

Answer 8

myocyte muscle cells contract from electrical impulses initiated by the sinoatrial node in the right atrium setting the pace of each heartbeat

• atrial systole: electrical signal propagates through the atrial wall causing the contraction of right and left atrium
• ventricular systole: after time delay allowing ventricles to fill, the electrical signal reaches atrioventricular node causing contraction of right and left ventricle

Question 9

Heart rate control

Answer 9

cardiovascular centre in the medulla signals sinoatrial node through 2 branches
branch 1 to increase heart rate:
- low oxygen concentration, blood pressure or pH (high CO2)
branch 2 to decrease heart rate:
- high oxygen concentration, blood pressure or pH

Question 10

Epinephrine

Answer 10

hormone in blood secreted by brain to signal sinoatrial node to increase heart rate before physical activity (in preparation)