6.2 blood system Flashcards
1
Q
what is the purpose of the circulatory system?
A
- helps to facilitate the movement of molecules, bringing them from the external surfaces to the inner tissues and vice versa
2
Q
what does human blood consist of?
A
- plasma and cellular components
- plasma:
• 90% water
• plasma proteins, blood electrolytes (ions), other dissolved products - cellular components:
• 2 main types of cells: red blood cells (erythrocytes), white blood cells (leukocytes for defence and immunity)
• platelets: not true cells; more like fragments of cells w no organelles (involved in blood clotting)
3
Q
what is the purpose of arteries?
A
- convey blood at high pressure from the ventricles to the tissues of the body
- in general, transport blood away from the heart towards the rest of the body
- contractions of the ventricles generate the necessary pressure to move the blood in the blood vessels
- as arteries are the blood vessels nearest to the heart, are of high pressures
• how?? -> heart ventricles have thick muscular walls
• why?? -> against gravity? - helps body to carry out the function of transporting substances around the body
4
Q
what is the structure of arteries?
A
FROM IN TO OUT:
BASEMENT MEMBRANE
- not made of cells; connective tissues protein
TUNICA INTIMA (intimate) - mainly made of endothelial cells and connective tissues
TUNICA MEDIA (medium) - smooth muscles and elastic tissues
TUNICA EXTERNA
- mainly made of collagen fibres
5
Q
how is blood pressure maintained in between pump cycles?
A
- muscle and elastic fibres assist
- heart beats in cycles
- periods between each contraction where the pressure with the blood vessels will drop
- smooth muscles (tunica media) in arterial walls contract
- cross sectional area of arteries decreases
- increases pressure
- maintains the pressure between pump cycles
- elastic fibres (tunica media) stretch when pressure in arteries increases during ventricular contraction
- in between pump cycles fibres recoil and push inwards,
- collagen fibres (tunica externa) prevent artery from bursting during ventricular contraction
6
Q
what are capillaries? (structure etc)
A
- blood vessels that have thin walls consisting of a single layer of endothelial cells
- very narrow in diameter; about the width of a red blood cell
- as red blood cells pass through capillaries, cells may flex a little; increases the surface available for gaseous exchange with red blood cells
- when arteries branch into arterioles and then into capillaries, increases total surface area of blood vessels, increased efficiency for diffusion
- 1 celled thickness & presence of pores within capillary wall allows for increased permeability to certain substances
- capillaries covered with basement membrane, basement membrane is permeable to many substances and allows them to pass through freely
7
Q
how do veins carry blood?
A
- collect blood at low pressure from the tissues of the body and return it to the atria of the heart
- as blood in arteries are distributed to numerous capillaries before flowing into the veins, pressure of blood that enters veins much lower than arteries
- lumen of veins are also much larger than that of arteries, to maximise the flow of blood that is already at low pressure, back to the heart
- walls of veins are also thinner with a lesser amount of elastic fibres and muscles present within
- due to low pressures in veins, movement of blood is also helped along with the contraction of skeletal muscles around them, as well as the valves present within
- veins often run parallel to arteries, and the expansion and contraction in arteries can help push the blood along in veins
8
Q
what is the structure of veins?
A
IN TO OUT
- large central lumen through which blood flows
- endothelium
- thin inner layer of muscle and elastic fibres
- thin outer wall
9
Q
how is backflow of blood prevented?
A
- valves in veins and heart
- due to low pressures within veins, difficult for blood to flow against the forces of gravity
- to avoid backflow of blood due to gravity, numerous 1 way valves present in veins
- semi lunar valves made of connective tissues that fold flat against walls when blood flows in 1 direction, but open up when blood flows in opposite direction, closing vein and preventing backflow of blood
10
Q
compare structure of arteries, veins, and capillaries such that you can identify them from the structure of their walls
A
CAPILLARIES
- 1 cell thick
- generally small
ARTERIES
- thicker walls
- more elastic tissues and muscles
- small lumen
VEINS
- comparatively larger lumen
- thinner walls
11
Q
elaborate on william harvey’s discovery of the circulation of blood with heart acting as pump
A
- before harvey’s discoveries, people thought the supplies of arteries and veins were separate
- thought that arteries pump heat via heart to lungs for cooling, and veins pump natural blood from liver
- based on simple experiments, including those that dealt with the valves in veins, harvey discovered that:
• arteries and veins part of same network of blood vessels
• arteries brought blood from heart to rest of the body
• veins brought blood from rest of body back towards the heart
12
Q
explain the need and existence of separate blood circulation for lungs
A
- most land vertebrates have double circulation system, with separate circulation for lungs
- humans: 4 chambered heart split into left and right; left 2 handle taking in oxygenated blood from heart to pump to rest of body; right 2 take in deoxygenated blood to pump to lungs
- ensures that though blood flow is continuous (a red blood cell will alternate between pulmonary and systemic circuit), oxygenated and non- oxygenated blood do not mix
- circuits run at 2 pressures so ur lungs dont blow up lmao
- high pressure in systemic circuit so ur blood can run everywhere
- low pressure in pulmonary circuit so sensitive tissues in lungs are fine and so capillaries dont blow up;
- rbc move slower in lungs for more time for gaseous exchange
13
Q
why is double circulation needed for maintenance of different pressures?
A
- besides ensuring oxygenated and deoxygenated blood don’t mix, double circulation also allows for 2 different sets of pressures to be maintained
- blood pressure in pulmonary circuit much lower than systemic circuit, as blood has to travel shorter distance to lungs and back
- with lower pressure, blood also moves slower and have longer time in lungs for oxygen to diffuse into red blood cells
- systemic circuit needs much higher pressure to pump blood throughout body, especially in larger animals
- lower pressure needed means that muscle walls in right ventricles are much thinner
14
Q
briefly talk about the heart chambers
A
- atria (singular: atrium) receives blood from veins into heart, with left atrium receiving oxygenated blood from pulmonary vein and right atrium receiving deoxygenated blood from vena cavae
- atrioventricular (AV) valves prevent backflow of blood from ventricles to atria during ventricular contraction, with bicuspid valves in left and tricuspid valves in right
- semilunar valves present between arteries and ventricles to prevent backflow of blood into ventricles between cardiac contractions
15
Q
how is heart beat initiated?
A
- by group of specialized muscle cells in right atrium called sinoatrial node
- cardiac muscles contract under nervous stimulation (like most muscle cells), but unlike other muscles origin of the nerve impulses are NOT from brain
- all muscles are capable of transmitting impulses; muscle impulses trigger the muscle to contract
- sinoatrial node are a group of highly specialised muscle cells found in right atrium of heart
- can spontaneously produce electrical impulse that travels in a wave down throughout heart
- leads to contraction of cardiac muscles as expected during cardiac cycle
