Blood

• arteries are blood vessels that carry blood away

  from the heart to the rest of the body.

  Arteries need to be strong and flexible because the blood

  they carry from the heart is under great pressure.

  The elastic nature of arteries allows the arterial walls to

  expand and contract to move blood through the arteries.
• Veins are blood vessels that carry blood from the

  rest of the body back to the heart.

  Blood is under much less pressure when returning to the

  heart. In fact, veins do not expand and contract to keep

  blood moving – instead, they rely on the activity of

  skeletal muscles to help maintain circulation.
• as you walk, your leg muscles push against

  the veins – which moves the blood towards the heart.

  If you sit for too long, the lack of exercise makes it harder

  for the blood to move upwards.
• Capillary walls are very, very thin so that materials can

  diffuse in and out of the blood quickly and easily.
• Blood pressure is the force with which blood pushes

  against the wall of an artery.

  The healthy resting blood pressure for a young adult is

  around 120/70 mm Hg.
• 120/70 mm Hg, The top number of the fraction is known as the systolic

  pressure. This is the amount of pressure on the walls of an

  artery when the left ventricle contracts to pump blood

  through the body.

  The bottom number is known as the diastolic pressure.

  This is the pressure in the artery when the left ventricle

  relaxes.
• Blood pressure depends on how elastic and unblocked the

  arteries are, and on the strength of the heart contraction.

  The more blockages, the harder the heart must pump.

  Blood pressure rises

  Blood pressure also rises naturally with activity, stress,

  and strong emotions, but it should drop again with rest.
• People with permanently high blood pressure have

  hypertension, which can lead to a heart attack or stroke.

  A heart attack occurs when the arteries to the heart muscle

  are damaged or blocked.

  A stroke can occur when blood flow to the brain is

  interrupted.

  People can keep their blood pressure low through weight

  loss, proper diet, and exercise.
• Lifestyle choices strongly influence the health of your

  circulatory system.

  Smoking, lack of exercise, excessive weight, long-term

  stress, few fruits and vegetables, lots of saturated fats – all

  of these are linked to high risk of developing heart disease.

  For example, in artherosclerosis, blood flow is partially or

  fully blocked by a sticky material called plaque.
• Bypass surgery may be necessary

  A healthy blood vessel from another part of the body

  (usually the leg) is attached to the artery on either side of the

  blockage. Blood can then “bypass” the obstruction.
• Blood


  A sticky mixture of cells, cell fragments, and fluid particles of fat, nutrients, and dissolved gases
• Separating blood in a test tube

  1. Separates into two main parts

  2. Reddish-brown band at the bottom contains red blood cells, white blood cells, and platelets

  3. Clear pale-yellow fluid at the top is plasma
• Platelets


  Cell fragments (produced in bone marrow) that help in blood clotting
• Plasma


  A clear pale-yellow fluid that makes up 55% of the blood, roughly 90% water
• Plasma


  • Many types of molecules dissolve in it and can then be distributed throughout the body, including sugar, hormones, vitamins, salts, and waste products
  • The movement of all these substances plays a critical role in maintaining homeostasis
• Blood components

  • Red blood cells
  • Several types of white blood cells
  • Platelets
• Red blood cells

  Make up 45% of all cells in blood
• Red blood cells

  • Transport O₂ to the cells
  • Carry CO₂ away from them
• Red blood cells circulate through the body for about 120 days before they begin to degrade
• Degraded red blood cells

  1. Carried to the liver

  2. Liver breaks up the cells

  3. Liver recycles them
• White blood cells


  • Defend the body against infection
  • Remove foreign material and dead cells
• Ways white blood cells defend


  • Surround and ingest microorganisms
  • Produce chemicals that destroy pathogens
• Unlike red blood cells, white blood cells can move beyond the circulatory system and attack pathogens in the body's tissues
• White blood cells are considered part of the immune system