Lecture 5 Structure and Function of Blood Vessels PDF

BIOL10811 Body Systems Lecture 5 Structure and function of blood vessels Prof Niggy Gouldsborough  Blood vessels All tissues have an arterial supply and a venous drainage Different types of blood vessels  Blood vessels...

BIOL10811 Body Systems Lecture 5 Structure and function of blood vessels Prof Niggy Gouldsborough  Blood vessels All tissues have an arterial supply and a venous drainage Different types of blood vessels  Blood vessels The different types of blood vessel each have different functions I N F E Blood vessels must: R I O R - be VEresilient N - be Aflexible C - always A V remain open A Blood vessel structure Lumen Tunica intima Tunica media Tunica adventitia  Blood Vessel Structure Tunica intima Endothelium – simple squamous epithelium Basal lamina of the epithelial cells Subendothelial connective tissue Tunica media Smooth muscle fibres in loose connective tissue May contain elastic fibres Tunica externa/adventia Connective tissue Merges with surrounding connective tissue May contain vaso vasorum  Arteries versus veins Arteries Veins Blood under high Blood under low pressure pressure Therefore thick walls Therefore thin walls Resemble garden hoses Resemble fire hoses May have valves to prevent backflow  Arteries versus veins When corresponding arteries and veins are compared the artery has a thicker wall Vein appears to have a smaller lumen maintains its shape Artery is more resilient the artery does not contain valves, the veins (Ashton, 2015) contain many valves  Types of arteries 1. Elastic (conducting) 2. Muscular (distributing) 3. Arterioles (resistance vessels)  Elastic (conducting) arteries e.g. aorta, brachiocephalic & common carotid x 33 I M E Diameter: up to 2.5 cm Withstand changes in pressure during the cardiac cycle and ensure continuous blood flow Structural adaptations (Young & Heath, 2000) thick tunica media with many elastic fibres and few smooth muscle cells  Muscular (distributing) Arteries Most named arteries e.g. brachial & femoral x 100 Diameter: 0.5 mm – 0.4 cm, Distribute blood to muscles and organs Capable of vasodilation and vasoconstriction in order to control the rate of blood flow to suit the needs of the organ Structural adaptations smooth muscle cells +++ in tunica media distinct internal (IEL) & external (EEL) E elastic laminae thick tunica externa 10 (Young & Heath, 2000)  Arterioles (resistance vessels) x 100 Capable of vasoconstriction & vasodilation Control blood flow to organs Involved in blood pressure control Diameter:  30 m Structural adaptations one to two layers of smooth muscle cells in tunica media poorly defined tunica externa (Young & Heath, 2000)  Capillaries Connect arterioles and venules (microcirculation) Site of gaseous exchange Thin walls facilitate diffusion Blood flow through capillaries is slow Structure permits 2-way exchange 8-μm (micrometres) in diameter Found near almost every cell Different types of capillaries Continuous Majority are continuous Skeletal and smooth muscle, CT and the lungs (Ashton, 2015)  Different types of capillaries Fenestrated Pores penetrate the endothelial lining Rapid exchange of water or large solutes (e.g. small peptides) Absorption (kidney, choroid plexus and endocrine glands) intercellular clefts (gaps between adjacent cells) (Ashton, 2015) Different types of capillaries Sinusoidal Spaces between endothelial cells Incomplete or absent BM Exchange of large solutes i.e. plasma proteins Specialised lining cells (e.g. in the liver, phagocytic cells engulf damaged RBCs) Blood moves slowly through sinusoids  Capillary Beds Capillaries organised into groups called capillary beds metarteriole precapillary sphincter arteriovenous anastomosis (Ashton, 2015)  Metarterioles A metarteriole supplies a single capillary bed Each metarteriole continues as a thoroughfare channel metarteriole thoroughfare channel which leads directly to a vein and has numerous capillaries leading off it Constriction of the metarteriole can reduce flow to a whole capillary bed (Ashton, 2015)  Precapillary sphincter Guard the entrance to each capillary. Contraction narrows entrance ∴↓flow Relaxation dilates entrance ∴ ↑ flow precapillary sphincter 18 (Ashton, 2015)  Arteriovenous anastomoses Form direct communication between the arteriole and venule When dilated blood bypasses the capillary bed and flows directly to venous circulation arteriovenous anastomosis (Ashton, 2015)  Venules Collect blood from capillary beds x 128 and deliver it to small veins Diameter: varies, average 20 m vein venules Structural adaptations Small – endothelium on a basement (Young & Heath, 2000) membrane Larger – increasing numbers of smooth muscle cells located outside endothelium  Veins (capacitance vessels) Classified according to size Small < 2mm in diameter Medium 2-9 mm in diameter Large > 9mm in diameter e.g. superior and inferior vena cavae Low pressure system Easily distensible (capacitance) x 128 Structural adaptations Thin walled Tunica externa is predominant Valves to aid blood flow (Young & Heath, 2000) Valves & the musculovenous pump Pressure changes  Distribution of blood 30-35% 65-70% (Adapted from Ashton, 2015)  Anatomical Terminology Define the terms Anatomical position Anterior (ventral) Posterior (dorsal) Superior Inferior Medial Lateral Proximal Distal Coronal/frontal plane Horizontal/transverse plane Sagittal plane  The anatomical position RIGHT LEFT  Anatomical directions Superior Medial Lateral Proximal Distal Inferior  Anatomical directions anterior/ventral posterior/dorsal Copyright © motifolio.com  Anatomical planes Coronal plane Transverse plane Midsagittal plane  Anatomical Planes Sagittal Coronal/frontal Transverse/horizontal passes from front to passes from side splits the body into back splitting body to side splitting upper and lower parts into right and left body into front sides and back sagittal section of Coronal section of Transverse section thorax head of head