Anatomy of the Circulatory System Flashcards
What must all blood vessels be?
- Resilient
- Flexible
- Remain open
What is the common three layered structure of blood vessels?
- Lumen
- tunica intima
- Tunica media
- Tunica adventitia/externa
What is tunica intima made up of?
- Endothelium: simple squamous epithelium
- Basal lamina of the epithelial cells
- Subendothelial connective tissue
What is the tunica media made up of?
- Smooth muscle fibres in loose connective tissues
- May contain elastic fibres
What is the tunica externa made up of?
- connective tissue
- Merges with surrounding connective tissue
- May contain vaso vasorum (vessels that suply that vein)
What are the differences between arteries and veins?
- Arteries are under high pressure and veins are under low pressure
- Arteries have a thicker wall
- Arteries appear to have a smaller lumen
- Arteries maintain their shape
- Arteries are more resilient
- The artery doesn’t contain valves but the vein may
What are the three types of arteries?
- Elastic (conducting)
- Muscular (distributing)
- Arterioles (resistance vessels)
Give features of Elastic Arteries
- large arteries such as the aorta and carotid
- Diameter: 2.5cm
- withstand changes in pressure during the cardiac cycle and ensure continuous flow
- Thick tunica media with many elastic fibres and few smooth muscle cells
Give features of Muscular arteries
- Most named arteries are muscular arteries
- Diameter: 0.5mm-0.4cm
- distribute blood to muscle and organs
- capable of vasodilation and vasoconstriction in order to control the rate of blood flow to suit the needs of the organisms
- Smooth muscle cells in tunica media
- Distinct internal (IEL) and external (EEL) elastic laminae
- thick tunica externa
Give features of arterioles
- capable of vasoconstriction and vasodilation
- Control Blood flow to organs
- Involved in blood pressure control
- Diameter: < 30 um
- One to two layers of smooth muscle in tunica media
- poorly defined tunica externa
Give features of Capillaries
- Connect arterioles and venules (microcirculation)
- Site of gaseous exchange
- Thin walls facilitate diffusion
- Structure permits 2-way exchange
- 8 um in diameter
- Slow blood flow through them
What are the three types of capillary?
- Continuous
- Fenestrated
- Sinusoids
Give features of Continuous capillaries
- majority of them
- no gaps between cells
- found in skeletal and smooth muscle, CT and the lungs
Give features of Fenestrated Capillaries
- Pores penetrate the endothelium
- Allows rapid exchange of water or larger solutes (e.g. small peptides)
- Found in kidney, choriod plexus and endocrine glands
Give features of Sinusoids
- spaces between endothelial cells
- Incomplete or absent basement membrane
- exchange of large solutes i.e. plasma proteins
- slow flow
- found in liver
- very leaky
What are capillaries organised into?
Capillary beds
What is flow through capillary beds controlled by?
- Metarterioles
- Precapillary sphincters
- Arteriovenous anastomoses
Give features of metarterioles
- supplies whole capillary bed
- each metarteriole continues as a thoroughfare channel which leads directly to a vein and had numerous capillaries leading off it
- Constriction of the metarteriole can reduce flow to a whole capillary bed
Give features of Precapillary sphincter
- guard the entrance to each capillary
- contraction narrows the entrance and reduces flow
- relaxation dilates the entrance and increases flow
give features of arteriovenous anastomoses
- forms direct communication between the arteriole and venule
- When dilated blood bypasses the capillary bed and flows directly to the venous circulation
Give features of venules
- collect blood from capillary beds and deliver it to small veins
- diameter of around 20 um
- small venules just have endothelium on a basement membrane
- larger venules have an increasing number of smooth muscle cells located outside the endothelium
How are veins classified?
According to size:
- small <2mm in diameter
- medium: 2-9mm in diameter
- larger > 9mm in diameter e.g. superior and inferior vena cavae
What are some features of veins?
- under a low pressure system
- easily distensible (can hold blood)
- think walled
- predominant tunica externa
- valves to aid blood flow
What are the 3 blood circulatory systems?
- systemic
- pulmonary
- specialised circulatory systems
What 3 types of specialised circulatory systems are there?
- portal
- coronary
- foetal
What do circulatory systems transport?
- O2
- Nutrients
- CO
- metabolic waste
- cells of immune system
- hormones
What are some key features of the blood circulatory system?
- closed circuit
- arteries carry blood away from the heart
- veins give blood back to the heart
- capillaries are found between the arteries and veins and are the site of gas exchange
Give features of the systemic circulatory system
- high pressure system (arterial side)
- takes O2 rich blood from the left side of the heart to the body tissues
- Returns O2 poor blood from the tissues to the right side of the heart
Give features of the Pulmonary Circulatory system
- low pressure system
- take blood low in oxygen from the right side of the heart to the lungs
- takes blood rich in oxygen from the lungs to the left side of the heart
- pulmonary arteries carry blood away from the heart therefore oxygen poor
- Pulmonary veins carry blood towards the heart and are oxygen rich
What does the lymphatic system consist of?
- network of lymph vessels
- lymph
- lymphatic tissues and organs
Lymphoid cells including lymphocytes and smaller number of phagocytes and other cells
What are the functions of the lymphatic system?
- Involved in the body’s defence mechanism
- Provides a mechanism for the drainage of interstitial fluid
What are the different names for interstitial fluid?
- In the capillaries it is called plasma
- in the interstitial space it is called interstitial fluid
How does capillary exchange work?
- Capillary blood pressure (CPB) pushes fluid out into the capillary into the interstitial fluid *taking nutrients, gases ect.) - filtration
- Blood colloic osmotic pressure (BCOP) pulls fluid back into the capillary (bringing waste, gases ect.) - reabsorption. BCOP is mainly due to plasma proteins
- CBP decreases with progression along capillary
- BCOP (oncotic pressure) remains constant
How much of fluid is reabsorbed in capillary exchange and what happens to the rest of the fluid?
- approximately 85% is reabsorbed
- The remainder must be removed from the interstitial space otherwise oedema will result (swelling)
- The lymphatic system is responsible for bringing back the excess interstitial fluid. It is picked up by the lymph capillaries
How is excess interstitial fluid removed?
- lymph capillaries are blind ended tubes that are located adjacent to capillary beds
- the excess interstitial fluid enters the lymphatic capillary and is called lymph
- lymph passes through the lymphatic circulation and returns to the blood system
How does lymphatic drainage work?
- Lymph capillaries -> lymph vessels -> lymph trunks -> thoracic duct/ right lymphatic duct -? subclavian vein
- lymph re-enters the blood vascular circulation
- along the lymph vessels we have lymph nodes which filter the lymph. Foreign particles get trapped between the lymph nodes
- Lymph nodes get enlarged if you are ill sometimes
What does the right lymphatic duct do?
- drains lymph from the right side of the head, the thorax and upper limb
- lymph leaves lymphatic duct and goes to the right subclavian vein
What does the Thoracic duct do?
- drains lymph from the remainder of the body
- Lymph then goes into the left subclavian vein
How are the tunica media, tunica intima and tunica externa bound together
with collagen fibres
How is the tunica media separated from the tunica externa?
By a thin band of elastic fibres called the external elastic membrane
What is the difference between the tunica externa in arteries and veins?
- In arteries the tunica externa contains collagen fibres with scattered bands of elastic fibres
- In veins it is generally thicker than the tunica media and contains networks of elastic fibres and bundles of smooth muscle cells
why does the lumen of arteries sometimes have a pleated appearance?
Because when an artery constricts it’s endothelium folds
Why are arterioles also called resistance vessels?
As the force opposing blood flow is called resistance
when do aneurysms occur?
When local blood pressure exceeds the capacity of the elastic components of the arterial walls the result is an aneurysm or bulge in the weakened wall of the artery
What is arterial anastomosis?
When more than one artery supplies blood to a capillary bed and the multiple arteries fuse before giving rise to arterioles
What are collaterals?
Multiple arteries that supply blood to a capillary bed
What does it mean when exchange occurs between blood and interstitial fluid in continuous capillaries by bulk transport?
the movement of materials by endocytosis or exocytosis at the inner endothelial surface
What is angiogenesis?
The formation of new blood vessels from pre-existing vessels and occurs under the direction of the vascular endothelial growth factor
How do Lymphatic Capillaries vary from blood capillaries?
- they are closed at one end
- they have larger luminal diameters
- have thinner walls
- have flattened or irregular outline in sectional view
- they are lined by endothelial cells but the basement membrane is incomplete or absent
- they are not tightly bound together but do overlap. The region of overlap acts as a one way valve
What helps lymph flow?
- contractions of the skeletal muscles surrounding the vessels
- valves
What are the two sets of lymphatic vessels that collect lymph from the lymphatic capillaries and what is the difference between them?
- Superficial lymphatics: located closer to the skin
- Deep lymphatics: accompany deep arteries and veins supplying skeletal muscles and other organs of the neck limbs, trunk and walls of visceral organs
What do lymphocytes do?
Respond to specific invading pathogens as well as to abnormal body cells and foreign proteins. They eliminate these threats or render them harmless through a combination of physical and chemical attacks
What are lymphoid tissues?
Connective tissues dominated by lymphocytes
Where do lymphoid nodules occur?
In the connective tissue deep to the epithelia lining the respiratory tract where they are known as tonsils
What are the tonsils?
Large lymphoid nodules in the wall of the pharynx. Most people have 5
What is tonsillitis?
An inflammation of the tonsils (especially the palatine tonsils)
What is the mucosa-associated lymphoid tissue (MALT)
The collection of lymphoid tissues that protect the epithelia of the digestive, respiratory, urinary and reproductive systems
What are aggregated lymphoid nodules?
Clusters of lymphoid nodules deep to the epithelial lining of the intestine
What are a few examples of lymphoid organs?
lymph nodes, thymus and spleen
Where do blood vessels and nerves reach the lymph nodes?
At a shallow indentation called the hilum
what is the typical lymph node shaped like?
Kidney bean
What is capitance?
Word explaining the relationship between the volume of blood in a blood vessel and pressure
