Exam 1: Blood Vessels Flashcards
Major Types of Blood Vessels
- arteries
- — branch into smaller and smaller structures
- — carry blood away from the heart - veins
- — merge into larger and larger vessels
- — carry blood back to the heart - capillaries
- — smallest vessels
- — directly serve the needs of the tissues
Arterioles
- vessels smaller than the arteries
- carry blood directly into the capillary beds
Venules
- vessels smaller than the veins
- carry blood directly away from the capillary beds
Layers/Tunics of Blood Vessels
- from interior to exterior
1. Tunica Interna/Intima
2. Tunica Media
3. Tunica Externa
Lumen
- the blood containing space in the middle of a vessel
Tunica Interna/Intima
- simple squamous cell epithelium and associated connective tissue
- this epithelium is continuous with the endocardium of the heart
Tunica Media
- mostly circularly arranged
- smooth muscle cells and sheets of elastin
- smooth muscle is innervated by sympathetic nerve fibers
- — allows for vasoconstriction and vasodilation to maintain blood pressure
Tunica Externa
- aka tunica adventitia
- made up of collagen fibers to protect the vessel
- the very largest vessels have tiny blood vessels within the tunica externa
- — vasa vasorum
Arteries: the aorta and its major branches
- the large arteries near the heart
- — have the largest lumens
- — have the most elastin
- — allows these vessels to expand and withstand large differences in pressure
Arteries: as you get farther and farther from the heart….
- arteries divide into smaller and smaller branches
- greater amounts of smooth muscle
- less elastin
- larger arterioles: all three tunics
- smaller arterioles: a layer of smooth muscle around an epithelial lining
Capillaries: Tunics and diameter
- smallest blood vessels
- only a tunica interna
- — epithelium and basement membrane
- RBCs pass through capillaries in single file
- — diameter is only one cell thick
Capillaries: Molecule Exchange
- oxy, nutrients, and hormones are exchanged with the tissues
- some epithelial cells are continuous
- — tight junctions
- some are leaky
- — pores in the epithelium and an incomplete basement membrane
- — allows large molecules and WBCs to pass through the walls
Capillary Beds
- interweaving network of capillaries
- two types of vessels: metarteriole and true capillaries
- capillary sphincter
Metarteriole
- found in capillary beds
- thoroughfare channel which connects the arteriole and the venule at opposite ends of the bed
Capillary Sphincter
- found in capillary beds
- a cuff of smooth muscle fibers
- surrounds the root of each true capillary and acts as a valve to regulate blood flow
- when the sphincters are closed, the blood is shunted through the metarteriole
Small Venules
- closer to capillary bed
- collect blood from capillaries
- very porous, allowing fluid and WBC’s to pass through easily
- consist mostly of epithelium
Larger Venules
- farther from the capillary beds
- a few layers of smooth muscle and a thin tunica externa
Veins
- venules join to form veins
- the same three distinct tunics as the arteries
- — but have thinner walls with less smooth muscle and elastin
- larger lumens than arteries
- tunica externa is the largest of the layers
How much of the body’s blood supply is found in the veins at any one time?
- 2/3
Blood Pressure in the Veins
- is low
- because the effects of ventricular contraction are not present
- to prevent backflow, veins have valves formed from folds in the tunica interna
- — valves are most abundant in the extremities where the upward flow of blood is opposed by gravity
Venous Sinuses
- specialized, flattened veins with thin walls
- supported by surrounding tissue
Varicose Veins
- veins that are dilated due to stretched walls and incompetent valves
- often occurs if there is a restriction hindering the return flow of blood to the heart
- superficial veins receive little support from underlying tissues
- — often in the legs
Anastomoses
- formed when veins or arteries unite
- arterial anastomoses provide alternative routes for blood to reach an area
- venous anastomoses are more common
Blood Flow
- the volume of blood flowing through a vessel in a specific time
- measured in ml/min
- in order for blood to flow, there must be a difference in pressure
- Flow = change in pressure / resistance
Blood Pressure
- the force per unit area exerted by the blood on the vessel wall
- measured in mmHg
- systemic blood pressure is highest in the aorta and zero in the right atrium
Resistance
- the opposition to flow (friction)
- function of blood viscosity, vessel length, and vessel diameter
Arterial Blood Pressure
- a function of the elasticity of the arteries and the amount of blood being pumped through them at any one time
Pulse pressure
- the difference between the systolic and diastolic pressure
- systolic pressure occurs bc of ventricular contraction
- diastolic pressure occurs bc of ventricular relaxation
Control of Blood Pressure
- neural controls
- hormones
- kidneys
Neural Controls of Blood Pressure
- responds to the demands of various organs by altering blood distribution
- maintains adequate pressure by altering blood vessel diameter
- — regulated by sympathetic neurons in the medulla oblongata
- — baroreceptors
- — chemoreceptors
- higher brain centers also effect blood pressure
- — hypothalamus
Baroreceptors
- pressure sensor
- neural receptors located in the aortic arch and carotid sinuses
- — sinuses: dilations in the internal carotid arteries
- vessel is stretched (ex: by high blood pressure) –> baroreceptors initiate a reflex arc to the medulla –> vasodilation –> decrease in blood pressure
Chemoreceptors
detect sharp drops in O2 and increases in CO2 –> vasoconstriction –> increase in blood pressure –> speeds the return of blood to the heart and lungs (which can balance the O2/CO2 ratios)
Hormonal control of blood pressure
- adrenal hormones, ADH, NO
- inflammatory chemicals
- — histamine= vasodialator
- regulate blood volume
- vasoconstriction
Kidneys help control blood pressure
- Rises in blood pressure also induce the kidneys to remove fluid from circulation
- blood pressure declines, the kidneys release renin resulting in an increase in angiotensin II, a potent vasoconstrictor.
Hypertension
- high blood pressure
- major cause of heart failure, vascular disease, renal failure, and stroke
- the heart must work harder to counteract hypertension –> weakening of the heart
- primary or secondary hypertension
Primary Hypertension
- no known cause
- about 90% of cases
- diet, obesity, age, race, heredity, stress, and smoking may all play a part
Secondary Hypertension
- due to an identifiable disorder
- ex: kidney disease or a hormonal disorder
Tissue Perfusion
- blood flow through the body tissues
Circulatory Shock
- inadequate perfusion of the tissues
- hypovolemic shock
- – most common type
- – loss of blood volume
- vascular shock: a significant drop in blood pressure due to extreme vasodilation
- cardiogenic shock: pumping of the heart fail to provide enough circulation to the tissues
Aorta
- ascending: leaves the left ventricle and goes up
- aortic arch: bends sharply to the left
- — three branches - descending: runs inferiorly through the thoracic cavity
- abdominal aorta: the descending after it passes through the diaphragm
Branches of the Aortic Arch
- Brachiocephalic
- – branches into the right common carotid and the right subclavian arteries - Left Common Carotid
- Left Subclavian
- – from it, branches the right and left vertebral arteries which pass through the transverse foramina of the cervical vertebrae and supply part of the brain
Branches of the Right/Left Common Carotid
- each has two branches:
1. internal carotids: which supply the brain and orbits
2. external carotids: supply the head and neck
Right and Left Axillary Arteries
- pass through the axillae
- right/left subclavian –> right/light axillary –> right/left brachial artery
- -> right/left radial and ulnar arteries
Abdominal Aorta Splits into…
abdominal aorta –> right/left common iliac –> right/left external iliacs which pass through the pelvis –> right/left femoral arteries –> right/left popliteal arteries which pass through the intercondylar notch of the femur –> anterior and posterior tibial arteries
- posterior tibial passes posteriorly to the medial maleolus
- anterior tibial –> dorsalis pedis artery in the dorsal foot
Celiac Trunk
- large, ventral, unpaired branch of the aorta
- shortly after the aorta passes through the diaphragm
- celiac –> left gastric, common hepatic, splenic arteries
Superior and Inferior Mesenteric Arteries
- two unpaired arteries that branch off the abdominal aorta
- supply the small and large intestines
- between them are the paired renal arteries and the paired testicular/ovarian arteries
Deoxygenated blood leaves the right ventricle–>……..lungs
pulmonary trunk –> right and left pulmonary arteries –> right: three lobar arteries, left: two lobar arteries
Pulse
- when the left ventricle contracts, a pressure wave is sent along the elastic arteries through the arterial tree
- can be felt by compressing an artery near the surface against deeper firmer tissue
- heart rate = pulses per minute
- can be taken at: radial, carotid, brachial, temporal, ulnar, femoral, popliteal, posterior tibal, dorsalis pedis
Veins of the Forearm
radial + ulnar –> brachial
Veins of the Upper Arm
- brachial + basilic –> axillary
- cephalic (lower and upper arm) + axillary –> subclavian
- medial cubital vein: an anastomosis of the cubital region
- — joins the cephalic and the basilic
The subclavians are joined by….
- subclavians + external jugulars (join first) + internal jugulars (join 2nd) –> brachiocephalic veins
- right brachiocephalic + left brachiocephalic –> superior vena cava which enters the right atrium
Veins of the Leg
- anterior tibial vein + posterior tibial vein –> popliteal vein which crosses the back of the knee –> femoral vein
- great saphenous vein: drains the foot and medially runs the length of the leg
- — great saphenous + femoral –> external iliac
- external iliac + internal iliac –> common iliac
- right common iliac + left common iliac –> inferior vena cava
Superior Mesenteric Vein
- drains the entire small intestine
- — rich with nutrients
- superior menenteric + inferior mesenteric + splenic –> hepatic portal vein
Hepatic portal Vein
- enters the liver and branches again and again, eventually into small capillaries
- after filtering through the liver, vessels merge into larger vessels –> right and left hepatic veins –> inferior vena cava
Right and Left Renal Veins
- drain the kidneys
Right and Left Gonadal Vein
- testicular or ovarian
- right: enters the inferior vena cava directly
- left: enters the left renal vein
