Chapter 26: The human Chapter 26: The human circulatory systemcirculatory system
Leaving Certificate BiologyLeaving Certificate Biology
Higher LevelHigher Level
The Circulatory SystemThe Circulatory System• The circulatory system of the human is a closed
system whereby blood continually flows around the body inside a network of blood vessels and oxygen, carbon dioxide, nutrients, and wastes diffuses into and out of these vessels.
– The closed system involves blood flowing through structures in the following order: strong muscular heart, arteries, arterioles, capillaries, venules, veins and finally back to the heart
The Circulatory SystemThe Circulatory System
• Advantages of the closed circulatory system are:– Blood can be pumped around the body fast
for fast and efficient delivery of oxygen and nutrients and fast and efficient removal of wastes
– Blood can be directed to different areas of the body through constriction and dilation of the blood vessels where needed
Blood VesselsBlood Vessels
• Arteries: carry blood away from heart• Arterioles (small arteries): carry blood from the
arteries to the capillaries• Capillaries: carry a single-file of red blood cells
through their lumens delivering oxygen and nutrients and removing wastes from local cells and tissues
• Venules (small veins): carry blood from the capillaries to the veins
• Veins: carry blood towards the heart
Arteries and VeinsArteries and Veins
VALVE
ARTERY VEIN
Collagen
SmoothMuscle
(involuntary)
Elastictissue
Endothelialcells
Smalllumen,
Novalves
Largelumen,
withvalves
Thick wall Thin wall
Differences between arteries and Differences between arteries and veinsveins
Artery Vein
Carries blood away from heart
Carries blood toward heart
Blood under high pressure Blood under low pressure
Thick walls Thin walls
Pulse flow Smooth flow
Narrow lumen Large lumen
No valves Valves present
Blood rich in oxygen (except pulmonary artery)
Blood poor in oxygen (except pulmonary veins)
Smooth Muscle, Skeletal Muscle Smooth Muscle, Skeletal Muscle and Valvesand Valves
• Smooth muscle is involuntary (not under conscious control): surrounds arteries and veins and help to push blood along
• Skeletal muscles in the legs and arms help to push blood along veins back to the heart
• Valves present in veins help to prevent blood flowing backwards thus preventing pooling of blood in the extremities
The HeartThe Heart
• Located slightly to the left of the sternum between the lungs above the diaphragm
• Composed of cardiac muscle (doesn’t fatigue as easily as skeletal or smooth muscle)
• Size of clenched fist
INTERNAL INTERNAL STRUCTURE STRUCTURE OF THE OF THE HUMAN HUMAN HEARTHEART(Fig. 27.9(Fig. 27.9p 261)p 261)
Double CirculationDouble Circulation
• In the heart there is two separate pumps – one on the right and one on the left – separated by the septum
• Double circulation in the human is necessary in order to keep deoxygenated (right-side) blood separate from oxygenated blood (left-side)
• The two circuits are called:– Pulmonary circuit– Systemic circuit
Blood Flow Through the Blood Flow Through the Pulmonary CircuitPulmonary Circuit
• Deoxygenated blood enters right atrium from the superior and inferior vena cavae which have carried blood from the upper and lower bodies, respectively
• Right atrium contracts and blood flows through the tricuspid valve
• Blood then enters right ventricle which in turn contracts• Right ventricular contraction causes the tricuspid valve to
close and the semi-lunar valve to open and blood flows in the pulmonary artery
• The pulmonary artery carries blood to the lungs to become re-oxygenated as the blood flows through the capillaries that surround the alveoli
Blood Flow Through the Blood Flow Through the Systemic CircuitSystemic Circuit
• Oxygenated blood is carried from the lungs via the pulmonary veins to the left atrium
• Blood enters the left atrium and the left atrium contracts forcing blood through the bicuspid valve
• Blood then enters left ventricle which in turn contracts more strongly than the right ventricle but at the same time
• Left ventricular contraction causes the bicuspid valve to close and the semi-lunar valve to open and blood flows into the aorta
• The aorta carries the blood to the head, upper body, and lower body to deliver oxygen and nutrients
Coronary ArteriesCoronary Arteries
The Hepatic Portal SystemThe Hepatic Portal System
The hepatic portal system begins in the capillaries of the digestive system and ends in the portal vein – it does not connect directly to the heart
The portal blood contains substances absorbed by the stomach and intestines
Detailed Study of the Heart BeatDetailed Study of the Heart Beat
Detailed Study of the Heart Beat Detailed Study of the Heart Beat (cont.)(cont.)
• The rate at which the SA node fires can be controlled by various factors:– Exercise– Temperature– Emotion– Shock
Heart SoundsHeart Sounds
• Sound of the heart beat is caused by the opening and closing of the valves of the heart
• The “lub” sound is caused by the closing of the tricuspid and bicuspid valves closing and the semi-lunar valves opening as the ventricles contract
• The “dub” sound is caused by the semi-lunar valves closing as the ventricles relax
PulsePulse
• A pulse is the pressure the flowing blood exerts on the walls of an artery causing the walls of the artery to expand
• Pulse can be felt most easily on the wrist or on the neck
• Pulse rate (pulses/min) is an indicator of heart rate (heart beats/min)
• Average heart rate is 72 bpm in an adult
Blood PressureBlood Pressure
Blood Pressure (continued)Blood Pressure (continued)• Drugs that reduce blood pressure and hence
heart rate are:– Anti-hypertensives: stimulate vasodilation where the
smooth muscle surrounding all the blood vessels relax and the blood vessels widen thereby reducing blood pressure
– Diuretics: stimulate loss of water from the blood by closing the pores present in the collecting duct of nephrons – therefore water is NOT reabsorbed into the blood – if there is reduced blood volume this reduces blood pressure and also heart rate
– Beta-blockers: act on the pacemaker of the heart directly reducing its rate
Effects of Smoking, Diet, and Exercise on the Effects of Smoking, Diet, and Exercise on the Circulatory SystemCirculatory System
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