the circulatory system Flashcards
Why do we need a circulatory system?
- link exchange surfaces with cells throughout the body
- small molecules move between cells and their surroundings by diffusion
- diffusion is only efficient over small distances because the time it takes to diffuse is proportional to the square of the distance
what do you need in the circulatory system?
a) circulatory fluid
b) set of interconnecting vessels
c) muscular pump, the heart
Heart activity
Arteries branch into arterioles and carry blood away from the heart to capillaries. Capillaries converge into venules and return blood capillaries to the veins, which return blood to the heart
capillary beds
- networks of capillaries
- site of chemical exchange between the blood and interstitial fluid
double circulation
- oxygen-poor and oxygen-rich blood are pumped separately from the right and left sides of the heart
- allows oxygenated blood to be separated from deoxygenated blood, which increases the efficiency of oxygen transport and energy production in the body
blood vessel
- vessels cavity is called the central lumen
- the epithelial layer that lines blood vessels is called the endothelium
why is the endothelium smooth?
- smooth blood flow
arteries
- carry blood away from the heart
- thick walls with three layers - endothelium, thick smooth muscle and connective tissue
- narrow lumen
- no valves
veins
- carry blood towards the heart
- thinner walls than arteries, with less smooth muscle and connective tissue
- wide lumen
- have valves
- irregular in shape
capillaries
- slightly wider than a red blood cell
- have thin walls to facilitate the exchange of materials
- major organs are usually filled to capacity
At the capillary beds where is exchange happening and how is it driven?
- exchange between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries
- the difference between blood pressure and osmotic pressure drives fluids out of capillaries at the arteriole end and into capillaries at the venule end
- most blood proteins and all the blood cells are too large to pass through the endothelium
heart circulation
- blood begins its flow with the right ventricle pumping blood to the lungs via the pulmonary
- in the lungs the blood loads O₂ and unloads CO₂
- oxygen rich blood from the lungs enters the heart at the left atrium via the pulmonary veins
- it is pumped through through the aorta to the body tissues by the left ventricle
- the aorta provides blood to the heart through the coronary arteries
- blood return to the heart through the superior vena cava and inferior vena cava
- the superior vena cava and inferior vena cava flow into the right atrium
cardiac cycle
the heart contracts and relaxes in a rhythmic cycle
systole
the contraction, or pumping phase
diastole
the relaxation, or filling
heart rate
- pulse, number of beats per minute
stroke volume
amount of blood pumped in a single contraction
cardiac output
volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume
atrioventricular valves
separate each atrium and ventricles
semilunar valves
control blood flow to the aorta and the pulmonary artery
1 - atrial and ventricular diastole
both relaxed blood flows into the atria and ventricles
2 - atrial systole and ventricular diastole
atria contracts blood flows into the relaxed ventricles
3 - ventricular systole and atrial diastole
ventricle contracts, blood exists, atria relaxed, blood enters
autorhythmic
some cardiac muscle cells are autorhythmic - they contract without any signal from the nervous system
sinoatrial node
pacemaker
- sets the rate and timing at which cardiac muscle cells contract
electrocardiogram (ECG/EKG)
impulses that travel during the cardiac cycle can be recorded on the ECG
ECG output
1 - signals from the SA node spread through the atria
2 - signals are delayed at the AV node
3 - bindle branches pass signals to the heart apex
4 - signals spread throughout the ventricles
pacemaker
regulated by two portions of the nervous system - the sympathetic and parasympathetic
- regulates by hormones and temperature
sympathetic division
speeds up the pacemaker
parasympathetic division
slows down the pacemaker
Blood
connective tissue consisting of several kinds of cells suspended in a liquid matrix called plasma
cellular elements occupy about 45% of the volume of blood
plasma
- contains inorganic salts as dissolved ions, sometimes called electrolytes
- plasma proteins influence blood pH and help maintain osmotic balance between blood and interstitial fluid
- particular plasma proteins function in lipid transport, immunity and blood clotting
- plasma is similar in composition to interstitial fluid, but plasma has a much higher protein concentration
Red blood cells
- erythrocytes - transport O₂
- most numerous blood cells
- contain haemoglobin - iron - containing protein that transport oxygen
- lack nuclei and mitochondria
white blood cells
leukocytes - function in defence
platelets
fragments of cells that are involved in clotting
stem cells
- Erythrocytes, leukocytes, and platelets all develop from a common source of stem cells in the red marrow of bones, especially ribs, vertebrae, sternum, and pelvis
- The hormone erythropoietin (EPO) stimulates erythrocyte production when O2 delivery is low
- Physicians can use recombinant EPO to treat people with conditions such as anemia
lungs
haemoglobin picks up oxygen because of the increased oxygen pressure in the capillaries of the lungs
tissues
- release oxygen to body cells as the oxygen pressure in the tissues is lower
Carbon dioxide
- CO2 from respiring cells diffuses into the blood and is transported in blood plasma, bound to haemoglobin
- CO2 produced during cellular respiration lowers blood pH and decreases the affinity of haemoglobin for O2 allowing it to pick up CO2
Bohr effect curves
explains why RBCs pick up and release oxygen
