transport in humans Flashcards
double circulation
blood passing through the heart twice before it completes one circuit
consists of: pulmonary circulation and systemic circulation
advantages:
-> allows blood to enter the lungs at a lower pressure than that of systemic circulation.
• blood flows more slowly through lungs
• provides more time for blood to be well-oxygenated before returning to the heart
-> allows blood to enter systemic circulation a a higher pressure than blood entering the lungs
• oxygenated blood is distributed more quickly to body tissues
pulmonary circulation
transports blood between the heart and the lungs
- pulmonary arteries transport deoxygenated blood from heart to lungs
- oxygenated blood goes back to the heart via pulmonary veins
systemic circulation
transport blood between the heart and other part of the body
- oxygenated blood leaves the heart via the aorta and is transported by the arteries to all parts of the body except the lungs
- deoxygenated blood returns to the heart via the veins
blood
- acts as a transport medium that carries various substances from one part of the body to another
- protect the body against pathogens (disease-causing micro-organism)
- blood clotting at wounds to prevent excessive loss of blood
plasma
consists of mainly (90%) water and (10%) dissolved substances
these dissolved substances include:
- soluble proteins such as antibodies (defense against pathogens), fibrinogen and prothrombin (for clotting of blood)
- dissolved mineral salts
- dissolved food substances (e.g. glucose and amino acids)
- excretory products (urea, uric acid and creatinine)
- hormones such as insulin and glucagon
blood platelets/ thrombocytes
membrane-bound fragments of cytoplasm from certain bone marrow cells
function:
• blood clotting to
=> prevent excessive loss of blood
=> prevent foreign particles from entering the blood stream
- – blood clotting —
1. when blood vessels are damaged, damaged tissues and blood platelets will release an enzyme known as thrombikinase
2. thrombikinase converts prothrombin into thrombin, in the presence of calcium ions
3. thrombin catalyses the conversion of the soluble protein fibrinogen into insoluble threads of fibrin
4. fibrin threads entangle blood cells and the whole mass forms a clot.
white blood cells
colourless since they ack haemoglobin irregular in shape contains nucleus larger than red blood cells ability to move some can change their shapes to engulf foreign particles, or to squeeze through capillary walls into spaces among tissue cells
function:
• phagocytosis
=> the process of engulfing and ingesting foreign particles such as the bacteria by the white blood cells
• production of antibodies
=> presence of disease-causing micro-organisms would stimulate the white blood cells to produce antibodies
=> function of antibodies is to neutralise the toxins produced by the bacteria.
red blood cells
function:
• oxygen is transported from the lungs to all parts of the body by red blood cells. oxygen binds reversibly to haemoglobin to form oxyhaemoglobin
• as blood passes through tissues that are deficient in oxygen, oxyhaemoglobin readily releases its oxygen to the tissue cells.
contains haemoglobin
• haemoglobin combines reversibly with oxygen
=> enables RBC to transport oxygen from lungs to all cells in the body
elastic
• turn bell shaped to squeeze through blood capillaries
=> enables RBC to transport oxygen from lungs to all cells in body
circular, biconcave
• increases cell’s surface area to volume ratio
=> increases the rate of diffusion of oxygen in and out of the red blood cell
no nucleus
• increase its capacity for haemoglobin
=> transport more oxygen
blood groups
blood group A - antigen A - antibody b
blood group B - antigen B - antibody a
blood group AB - antigen AB - no antibody
blood group O - no antigen - antibody a & b
donor's blood type - recipient's blood type (A, B, O, AB) A - ✔ ✘ ✘ ✔ B - ✘ ✔ ✘ ✔ O - ✔ ✔ ✔ ✔ AB - ✘ ✘ ✘ ✔
agglutination
transfusing a different blood type can cause the recipient’s blood to agglutinate and this can lead tp death
acclimatization
- concentration of oxygen in the atmosphere is low at high altitudes
- hence the body cannot take in sufficient oxygen to maintain its metabolic rate
- in response to this, the body will produce more red blood cells to compensate the lower concentration of oxygen, increasing the haemoglobin content per unit volume of blood
artery
=> blood vessels that carry blood away from the heart
- arteries branch to form small arteries which branch further to form arterioles.
- blood is forced out of the heart at high pressure, hence arteries need to have thick muscular and elastic walls to withstand the pressure
- elasticity of the artery walls allows arteries to stretch each time the heart pumps out a spurt of blood
- this throbbing of the artery is called pulse
- arterial wall regulate the lumen diameter by contraction and relaxation
- when the muscles contract, the artery constricts (lumen becomes narrower) and less blood flows through per unit time
- when the muscles relax, the artery dilates (lumen becomes more wider and more blood flows in per unit time
veins
=> the blood vessels that carry blood towards the heart
- the blood pressure in the vein is lower than that in the arteries. Hence blood flows more slowly and smoothly in the veins
- veins have thinner walls with less muscular and elastic tissues
- veins have semi-lunar valves to prevent backflow of blood
- many veins are situated between large skeletal muscles. Contraction of these muscles (e.g. during exercise) exerts pressure on the veins, pushing the blood to move more quickly
capillaries
=> the blood vessels found in between the cells of almost all tissues. they are the smallest and thinnest of all the blood vessels
• capillaries have pores in their membranes. this allows certain substances to diffuse quickly through the capillary walls
• when an arteriole branches into capillaries, the total cross-sectional area increases
–> this provides larger surface area to volume ratio for the efficient exchange of substances between the blood and the tissue cells
–> it also lowers the blood pressure in the capillaries, allowing the flow of blood to slow down, giving more time for the exchange of substances.
exchange of substances
- tissue cells are bathed in tissue fluid, which is a colourless liquid that allows diffusion of dissolved substances between tissue cells and the blood capillaries
- tissue fluid is similar to blood plasma but without plasma proteins. it also contains some white blood cells that have squeezed through the capillary walls (but no red blood cells)
- blood at the arterial end of the capillary is under high pressure. this forces blood plasma, together with its dissolved oxygen and food substances, out of the capillary walls into the spaces between the tissue cells and into the cells
- at venous end, the blood pressure is lower, so some tissue fluid re-enters the capillary
• waste products like carbon dioxide diffuse from the cells into the tissue fluid and then into the blood in the capillaries, to be transported to excretory organs for removal
