CVS S1 - Introduction and histology of cardiovascular system Flashcards
What 3 factors affect diffusion?
- Area available for exchange
- Diffusion resistance
- Concentration gradient
How is the area available for exchange determined?
Capillary density - how many capillaries per unit volume
How is diffusion resistance determined?
Nature of the barrier and nature of the molecule diffusing
Path length
Why is adequate blood flow so important for maintenance of capillary exchange?
Unless blood is supplied at an appropriate rate, the gradients between capillary content and nearby cells will dissipate and nutrients will not be supplied at the the right rate for the prevailing metabolic activity
What are the main components of the CVS?
Pump - Heart
Distribution vessels - Arteries
Flow control - Arterioles and pre-capillary sphincters
Capacitance - ability to cope with changes in cardiac output via storage of blood in veins
How is blood volume distributed throughout the body in percentages?
Veins - 67%
Heart + lungs - 17%
Arteries and arterioles - 11%
Capillaries - 5%
What are the three main purposes of the cvs ?
- Deliver between 5 and 25 litres per min of blood to the body
- Maintain a blood flow of 0.75 litres per min to the brain
- Maintain blood flow to heart and kidneys at all times
What is the mediastinum?
Intervening region in the thoracic cavity between the right and left pleural cavities which are occupied by the lungs
What makes up the middle mediastinum?
Pericardial sac containing the heart, its coronary vessels and the roots of the aorta, superior and inferior vena cava and the pulmonary vessels
Describe the structure of the pericardium?
Two layers
Fibrous outer layer of connective tissue
Inner serous layer for lubrication that is split into two layers: the visceral (touching heart) and the parietal (attache to inside of the fibrous layer)
Where are the visceral and parietal layers of the serosa found?
Visceral - Outer lining of the heart
Parietal - Attached to inside of fibrous layer of pericardium
Describe the structure of elastic arteries
Tunica Intima - endothelium cells with long axes parallel to the long axes of the artery, narrow sub endothelium of connective tissue, discontinuous elastic lamina
Tunica Media - 40-70 fenestrated elastic membranes, smooth muscle and collagen between lamellae
Tunica Adventitia - Fibroelastic connective tissue containing vasa vasorum, nerve and lymph vessels
Describe the structure of muscular arteries
Tunica Intima - Endothelium and internal elastic lamina
Tunica media - 40 layers of smooth muscle connected via gap junctions, external elastic lamina
Tunica Adventitia - Fibroelastic connective tissue containing vasa vasorum, nerve lymph vessels and nerves
What is the function of the unmylinated nerve endings in the tunica adventitia of muscular arteries?
Noradrenaline is released from unmyelinated nerve endings and travels through fenestrations in the external elastic lamina to depolarise smooth muscle cells in the tunica media causing vasoconstriction
Describe the structure of arterioles
- No internal or external elastic lamina
- Diameter of less than 0.1mm
- 1-3 layers of smooth muscle cells
- Tunica adventitia is scant
What is the function of meta-arterioles?
Supply blood to the capillary bed
How is the structure of meta-arterioles related to their function?
Discontinuous smooth muscle which form pre-capillary sphincters around endothelial cells enabling control of blood flow into the capillary bed
Describe the structure of a capillary
- Single layer of endothelium with adjacent basement membrane
- Diameter of 7-10 micrometers and 1mm in length
How is the structure of capillaries adapted to their function?
- Slowest velocity of blood flow through capillaries as velocity is inversely proportional to cross sectional area means that there is maximum time for gas and nutrient exchange.
- Narrow diameter means that a red blood cell occupies the entire lumen so diffusion path length is short
What are the three types of capillaries?
- Continous
- Fenestrated
- Sinusoid
Describe the structure of continuous capillaries
Pericytes form branching network on outer surface of endothelium
What are pericytes?
Cells capable of forming smooth muscle cells or fibroblasts in angiogenesis, tumour growth and wound healing
Describe the structure of fenestrated capillaries
Pericytes still present yet there are pores in the endothelium
Describe the structure of sinusoids
Discontinuous basal lamina creates large openings in the endothelium enabling WBC and RBC to move in and out
What are discontinuous sinusoids?
Sinusoids with no tight junctions found in the liver and spleen
Describe the structure of post-capillary venuoles
- Diameter of 10-30 micrometers
- More permeable than capillaries and decreasing pressure
How does the structure of post-capillary venues relate to their function?
Site of most fluid and leukocyte emigration in inflammation due to increased permeability
Describe the structure of veins
- Wide diameter and thin wall
- More connective tissue in tunica media and less elastic lamina and smooth muscle cells
How does the structure of small to medium veins differ to large veins?
Small/medium - well developed tunica adventitia
Large - longitudinal smooth muscle in tunica adventitia and circular smooth muscle in tunica media
What is different about superficial veins of the leg?
Well defined muscle layer to aid transport of blood back to the heart overcoming gravity
