Year 11 Human Biology - Circulatory System

what is blood composed of

55% plasma and 45% formed elements

describe blood plasma

liquid matrix of blood

91% water

contains proteins (albumins, fibrinogen, antibodies), nutrients (glucose, a.a. etc), waste (c02, urea etc), hormones and minerals (mg2+, NH4+ etc)

what are the 3 formed elements

red blood cells (erythrocytes)

white blood cells (leucocytes)

platelets (thrombocytes)

describe red blood cells

carry oxygen and carbon dioxide

biconcave for increased s.a

no nucleus for more haemoglobin space

haemoglobin (red pigment protein which binds to o2 in high regions of it and breaks that bond in low regions)

has 02 carrying enzymes

flexibe membrane to fit through vessels

7\.5 micrometre size

around 5 million per ml of blood

describe white blood cells

defence cells

larger than red blood cells but fewer numbers (roughly 6-9 thousand per ml of blood)

what are the 2 types of white blood cells

granulocytes and lymphocytes

describe granulocytes

granular cytoplasm + segmented nucleus


1. neutrophils → conduct phagocytosis
2. basophils → release histomines
3. eosinophils → inflame when reacting to bacteria or parasite

describe lymphocytes

smooth cytoplasm


1. monocytes → become macrophages during infection
2. lymphocytes → specific immune responders

a) b cells = anitbodies

b) t cells = killers

describe platelets

fragments of cytoplasm with a membrane which help blood clot

describe the heart

organ which pumps blood through vessels to supply body with o2 and hormones and remove waste

where is the heart located

in mediastenum in chest cavity

what size and shape is the heart

human fist size

roughly 12 x 9 x 6 cm

a conical shape with narrow apex

what is the pericardium

a double membrane which allows frictionless movement of the heart and holds it in place

also prevents overstretching

what do atria do

receive blood

describe right atria

receives blood from the body through both vena cava

describe left atria

receives blood from lungs throguh pulmonary vein

what do ventricles do

send blood

describe right ventricle

pumps blood to lungs via pulmonary artery

describe left ventricle

pumps blood to body via aorta

what do valves do

prevent blood backflow

what are the atrioventricular valves and their locations

tricuspid → between right atria and ventricle

bicuspid (mitral) → between left atria and ventricle

what are the semilunar valves and their locations

pulmonary → entry to pulmonary artery

aortic → entry to aorta

how many cusps does each valve have

all have 3 except for bicuspid which has 2

which vessels carry blood into the heart

superior vena cava

inferior vena cava

pulmonary vein

which vessels take blood out of the heart

pulmonary artery and aorta

which vessels exchange blood for the heart

coronary artery and vein

what is the cardiac cycle

the sequence of events in one heartbeat

describe systole

muscles contract, sending blood out of the chambers

describe atrial systole

atria contract, sending blood into ventricles

describe ventricular systole

ventricles contract, sending blood out of heart

describe diastole

muscle relaxes, so lumen fill with blood

can be atrial, ventricular or atrioventricular

how long does 1 heart beat take

about 0.8 seconds

describe the steps of a heartbeat

1. atrial systole (ventricular diastole) → atria contract, increasing bp in atria and sending blood into ventricles.

atrioventricular valves open and semilunar valves closed

ventricle walls stretch as they fill with blood
2. ventricular systole (atrial diastole) → ventricles contract, increasing bp in ventricles and sending blood to lungs or body

atrioventricular valves closed and semilunar valves open
3. Atrioventricular diastole → atria and ventricles receive blood from veins

blood flows via a.v. into ventricles

semilunar valves closed

what happens if diastole is too quick

heart efficieny decreases because the heart is not pumping it’s full capacity

what makes the lub dub sounds

the closing of valves

lub = a.v.

dub = s.lunar

what is the pace maker

a group of neurons in right atria whcih generate impulse to begin heart contractions

which heart side pumps what blood

right → deoxygenated

left → oxygenated

describe arteries role

carry blood away from heart under high pressure

describe arteries structure

thick elastic and muscular walls

simple epithelial innermost layer

elastic fibres on outermost layer which expand and recoil to keep blood flowing

no valves

describe vein role

carry blood too heart under low pressure and against gravity

describe vein structure

thin walls with little muscle and not many elastic fibres

large lumen

valves

easily collapsible

describe capillary role

bring blood close to cells to exchange materials

describe capillary structure

1 layer of sqaumois epithelial cells

thin walls

what is the double circulation of the heart

the blood is pumped to the lungs and then returns before being pumped to the body

what are the 2 parts of double circulation called

pulmonary circulation → to the lungs

systemic circulation → to the body

what is a portal system/circulation, with an example

when blood flows from 1 capillary network to another

e.g. hepatic network brings nutrient rich blood from small interstine to the liver

what is blood flow

the volume of blood which flows in and out of an organ/tissue in a given time

how can blood flow be regulated

change cardiac output or change vessel diameter

describe cardiac output

volume of blood pumped by 1 ventricle in 1 minute

formula → cardiac output = stroke volume (volume of blood per beat) x bpm

unit is ml/min

describe vasodilation

vessels lumen increases in size as smooth muscle relaxes, increasing blood flow

describe vasoconstriction

vessels lumen decreases in size as smooth muscle constricts, decreasing blood flow

what is blood coagulation

process of converting blood into semi solid clot

list the steps to make a blood clot

1. injured cells release thromboplastin
2. in presence of Ca 2+, thromboplastin converts inactive enzyme prothrombin into active thrombin
3. thrombin converts soluble fibrinogen into insoluble fibrin
4. fibrin fibres form mesh which traps rbc, wbc, platelets and plasma

what do blood clots prevent

blood loss and pathogen entry

how does a scab form

when fibrin fibres contract, they close wound gap and force serum (plasma minus fibrinogen) out of wound

describe platelet plugging action

for minor wounds, when platelets touch rough vessel surfaces they become sticky and clumo together to plug wound

what is the first response for vessel injury

constrict to reduce blood flow