Higher Human Biology Unit 2 Physiology & Health KEY AREA 5: Structure and Function of Arteries, Capillaries and Veins

Higher Human Biology We are going to build on the knowledge and skills that you developed during N5 and will learn about the following Physiology & Health key areas : - Key Area 1 – Reproductive Organs Key Area 2 –Hormonal Control of Reproduction Key Area 3 – Biology of Controlling Fertility Key Area 4 – Ante- and Postnatal Screening Key Area 5 – Structure and Function of Arteries, Capillaries and Veins Key Area 6 – Structure and Function of the heart Key Area 7 – Pathology of Cardiovascular Disease (CVD) Key Area 8 – Blood Glucose Levels and Obesity

Physiology & Health KEY AREA 5 – Structure and Function of Arteries, Capillaries and Veins a)Structure and function of arteries, capillaries and veins b)Exchange of materials between tissue fluid and cells

N5 Revision - Role of Blood Vessels The three types of blood vessel are Arteries, Capillaries & Veins Arteries divide up into capillaries, then capillaries join up to make Veins

N5 Revision - Arteries, Capillaries & Veins Arteries thick muscular walls a narrow channel carry blood under high pressure AWAY from the heart a pulse indicates that blood is flowing through an artery Arteries carry Oxygen and nutrients Capillaries thin walled to allow exchange of gas, food and wastes Capillaries form networks through organs and tissues and have a large surface area Oxygen leaves capillaries and enters tissues/cells Carbon Dioxide leaves tissues/cells and enters capillaries Veins Veins thin muscular walls and a wide channel and carry blood under low pressure TO the heart Veins contain valves to prevent blood flowing backwards Veins carry Carbon Dioxide and Wastes Thick muscular wall Thin walled (only 1 cell thick) Valves to stop blood flowing backwards

Physiology & Health Learning Intentions KEY AREA 5 – Structure and Function of Arteries, Capillaries and Veins a)Structure and function of arteries, capillaries and veins b)Exchange of materials between tissue fluid and cells

5a) Arteries, Capillaries & Veins

ArteriesCapillariesVeins Function Carry blood away from heart at high pressure Allow the exchange of substances Carry blood to the heart at low pressure Wall Structure Thick & Strong Outer Layer (elastic fibres) Middle Layer (muscle) Inner Layer (elastic fibres) Lining of endothelium Very thin Only one cell thick Thin walled Outer Layer (elastic fibres) Middle Layer (muscle) Inner Layer (elastic fibres) Lining of endothelium Lumen Narrow LumenVery narrowWider Lumen Valves NO YES to stop back flow Divide up into ArteriolesBlood is transported from arterioles (small arteries) to venules (small veins) by passing through the dense network of tiny microscopic vessels called capillaries Venules How structure is related to function Strength & elasticity needed to:- -withstand pulsing of blood -prevent bursting -help to maintain blood pressure -for vasconstriction/vasodilation Thin walls, and narrow lumen:- - materials can easily be exchanged Wide lumen: - Less resistance to blood flow

5c) Arteries, Capillaries & Veins Capillary

5d) Vasoconstriction and Vasodilation The smooth muscular middle layer of arterioles can contract (vasoconstriction) or relax (vasodilation) to control blood flow e.g. during a football match, arterioles undergo vasodilation at muscles to increase the flow of blood to working muscles, and arterioles in the small intestine undergo vasoconstriction to reduce blood flow to these regions

5e) Exchange of materials – Blood Plasma Blood consists of red blood cells, white blood cells, platelets and plasma Plasma is a watery yellow fluid that contains all the blood cells and glucose, amino acids, carbon dioxide, plasma proteins and ions

5f) Exchange of materials – Tissue Fluid Blood arriving at the arteriole side of a capillary bed is at a higher pressure than the blood in the capillaries, so blood is forced into these narrow capillaries As blood is forced into the narrow capillaries, it undergoes pressure filtration and much of the plasma is squeezed out through the thin walls. Tissue fluid differs from blood plasma as it contains little or no protein because the protein molecules are too big to pass through Tissue Fluid

5g) Exchange of materials – Tissue Fluid continued Tissue fluid diffuses into cells, supplying cells with glucose, oxygen and other substances Carbon Dioxide and other metabolic wastes diffuse out of the cells and into the tissue fluid to be excreted Most of the tissue fluid returns to the blood in the capillaries at the venule side of the capillary bed Excess tissue fluid is absorbed by thin-walled lymphatic vessels, and the fluid is now called lymph. The lymphatic system returns lymph fluid to the circulatory system (bloodstream)

Physiology & Health Questions KEY AREA 5 – Structure & Function of arteries, capillaries and veins 1.Testing Your Knowledge 1Page 163 Q’s Quick Quiz