Human Physiology Lesson 12c- Blood Vessels

Circulation Question

Transport of Blood How is blood transported around the body?

Blood Vessels

Blood Vessels NEED TO KNOW THE DIFFERENT TYPES AND HOW THEY ARE ADAPTED TO THEIR FUNCTION

Blood vessels Where does blood have to move most quickly? Why? Where does blood have to slow down, and why?

Blood Vessels Draw, describe and explain the structure and function of an artery, a capillary and a vein (use page 238) Describe the job of the coronary arteries and the problems that arise if they are blocked

Blood Vessels

Artery

ARTERY STRUCTURE Lumen-Relatively small. Blood travels at a high resistance Smooth Muscle- Contracts to move blood along the artery. This contraction of smooth muscle is known as peristalsis. Smooth muscle makes up the majority of an artery Elastic tissue-fairly large proportion of elastic tissue because the blood in an artery is under very high pressure. The elastic tissue maintains the shape of the artery.

Artery Function Transportation of OXYGENATED BLOOD to organs (exception is the pulmonary artery which transports deoxygenated blood to the lungs) Carries blood at a very high pressure Always leaves the heart

Arteries and arterioles

Veins

Veins and venules STRUCTURE Lumen relatively large. A lot larger than the lumen of an artery. This allows blood to flow with little resistance. Less elastic tissue and smooth muscle than an artery Contains valves. This prevents the back flow of blood. Positioned between large muscles. When the muscles contract they force blood along

Veins Blood is at lower pressure Walls thinner Walls less muscular As muscles contract they pinch the veins Valves ensure blood flows back to the heart 23

Vein Function Transportation of DEOXYGENATED BLOOD to organs (exception is the pulmonary vein which transports oxygenated blood from the lungs) Always to the heart apart from the pulmonary vein

Veins and valves

Capillaries How are they adapted? Adaptation Importance Very small Thin-walled Numerous 29

Capillaries How are they adapted? Adaptation Importance Very small 5-20µm in diameter High surface area to volume ratio When RBCs squeeze out, surface area increases & increase of diffusion Thin-walled Thin layer of endothelium and its basement membrane, no connective tissue Smooth, thin and flexible Numerous Form capillary bed Provides large surface area 30

Use the diagram to compare arteries, capillaries and veins 31

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Arteries and Arterioles Veins and Venules Capillaries Arteries and Arterioles                                                                                                                                                                                  

Blood Vessels ARTERY VEIN CAPILLARY

Blood Vessels ARTERY VEIN CAPILLARY Thick muscular wall Thin muscular wall No elastic tissue Elastic tissue Contains valves No muscular wall Small lumen Large lumen Constricts Impermeable Permeable Little elastic tissue

How blood is transported Arteries: Structures that carry blood away from the heart Rigid to take pressure of blood right out of heart Veins: Looser to expand more Store great quantities of blood Capillaries: Very narrow tubes between arteries and veins where diffusion occurs 36

Arteries Capillaries Veins 37

Arteries Capillaries Veins Thick muscular wall Large amount of elastic tissue Small lumen Blood under high pressure Valves when aorta and pulmonary artery begin in the heart No muscle No elastic tissue Relatively large lumen Blood under low pressure No valves Thin muscle wall Little elastic tissue Semi-lunar valves maintain one-way flow of blood 38

What does this diagram show? 39

VASOCONSTRICTION: reduction of blood flow -Arterioles connect arteries with capillaries -They become smaller as approach target tissues -Can be constricted = reduce blood flow -Can be dilated = increase blood flow VASOCONSTRICTION: reduction of blood flow VASODILATION: increase of blood flow 40

Key Questions Suggest why arteries close to the heart have more elastic fibres in their walls than arteries further away from the heart In the disease atherosclerosis, or ‘hardening of the arteries’, layers of cholesterol build up inside artery walls, reducing their elasticity. Why is this dangerous? How does the size of capillaries enable them to carry out their function of metabolic exchange Suggest a reason for the following: a) Normal venous pressure in the feet is about 25mmHg. When a soldier stands at attention the blood pressure in his feet rises very quickly to about 90mmHg b) When you breathe in, that is when the volume of the thorax increases, blood moves through the veins towards the heart 41

Elastic fibres allow the artery to stretch and recoil as blood pulses through. Nearer the heart, the pressure is higher so more elastic fibres are needed to cope with these large pressures and pressure changes If arteries cannot expand as a surge of blood at high pressure enters them, they are more likely to burst. Moreover, the build-up cholesterol narrows the lumen, so forcing blood through a narrower space, which can increase its pressure, further increasing the risk of the vessel bursting. There is also a risk of the vessel becoming permanently blocked. Capillaries are small, thin walled, and very numerous – maximising the rate of exchange of metabolic substances by diffusion Gravity pulls blood downwards. Normally, contraction and relaxation of leg muscles squeezes in on leg veins; valves in them ensure blood moves upwards and not downwards. When standing to attention, these muscles are still, so blood accumulates in the feet. 4b.As thoracic volume increases, pressure inside the thorax decreases. This decreases the pressure in the blood vessels in the thorax. The effect is very small in the arteries, but more significant in the veins. The relatively low pressure of the blood in the veins in the thorax, compared with the pressure in the veins elsewhere, produces a pressure difference causing blood movement towards the thorax. 42