Blood Vessels Flashcards
What are the layers of the blood vessels?
1) Tunica intima (contain endothelium, intimate contact with the blood, in vessels larger than 1mm they contain subendothelial layer (basement membrane + loose connective tissue)
2) Tunica media (middle tunica, smooth muscle cells (controlled by our autonomic nervous system) & sheets of elastin, can vasodialate and constrict) bulkiest in arteries
3) Tunica externa/adventitia (collagen fibers, protects and reinforce the vessel anchoring it to surrounding structures, infiltrated with nerve fibers, lymphatic vessels, network of elastic fibers)
What is the vasa vasorum?
Vessels that nourishes the external tissue of the blood vessels
What are the different types of vessels?
1) Elastic arteries (pressure reservoirs)
2) Muscular arteries (distributing arteries)
3) Arterioles (resistance arteries)
4) Terminal arteriole
5) capillaries (exchange vessels)
6) post-capillary venule
7) small veins (capacitance vessels)
8) Large veins (capacitance vessels)
What are the different types of vessels?
1) Arteries
- Elastic arteries (highest in elastic tissue, smooth muscle, low in collagen outs tissue)
- Muscular arteries (low elastic, highest in smooth muscle & collagenous tissue)
- Arteriole (low elastic, smooth muscle & collagenous fibers)
2) Capillaries (only endothelium)
3) Veins
- Venule (no elastic, low in smooth muscles and collagenous tissue)
- Vein (vey little elastic, smooth muscle & collagenous tissue are present)
What are the functions of arteries?
1) Pressure reservoir
2) distributing vessels
3) resistance vessels
Where are the elastic arteries found?
Near the heart in the Aorta & its major branches, largest in diameter, they act as the pressure reservoirs
Where is the muscular artery found and what does it do?
They are found after the elastic arteries, where they function as distributing vessels, delivering blood to specific organs, thickest tunica media, more active in vasoconstriction due to low elastic tissue
Where are the arterioles found and what is its function?
Smallest artery, controls blood flow to the capillaries, they are controlled via neural, hormonal and chemical influences, they are the resistance vessels
What is the function of capillaries?
Exchange vessels, smallest blood vessel
What is a pericyte?
Spider-shaped contractile stem cells, which can generate new vessels or scar tissue, which can stabilize the capillary walls and control the permeability of the capillaries
What are the types of capillaries?
1) continuous capillaries (lest permeable & most common)
2) fenestrated capillaries (large fenestration to increase permeability)
3) sinusoid capillary (most permeable least common)
Where is continuous capillary found?
1) skin
2) muscle
3) lungs
4) CNS
They have associated pericytes,
What is the structure of continuous capillaries?
They have associated pericyte, most continuous capillaries have intercellular clefts between endothelial cells. However, brain capillary endothelial cells lack intercellular clefts and have tight junctions around their entire perimeter
Where is fenestrated capillary found?
In areas of active filtration & endocrine hormone secretion:
1) kidney
2) small intestine
What is the structure of fenestrated capillaries?
Fenestrations are Swiss cheese-like holes that tunnel through
endothelial cells, usually covered by a very thin layer of condensed extracellular glycoproteins. This layer has little effect on solute and fluid movement, the number of fenestrations in capillaries increases during active absorption of nutrients.
Where is sinusoidal capillary found?
1) liver
2) bone marrow
3) spleen
4) Adrenal medulla
What is the structure of sinusoidal capillaries?
Have large intercellular clefts as well as fenestrations;
few tight junctions, incomplete basement membranes, Are irregularly shaped and have larger lumens than other capillaries, Allow large molecules and even cells to pass across their walls, Blood flows slowly through their tortuous channels, Macrophages may extend processes through the clefts to catch “prey” or, in liver, form part of the sinusoid wall.
What is the differences between the different types of capillaries?
All of them have tight junctions, which joins their endothelium leaving gaps of intercellular cleft which differs in size between them
What is micro-circulation?
The flow of blood from an arteriole to a venule
How is blood flow through the capillaries controlled?
By the diameter of the terminal arteriole and the arterioles upstream from it
How is the amount of blood flow into a capillary bed controlled?
Via chemicals and vasomotor nerve
What is a vascular shunt, and how does blood flow through it?
1) its a shunt that connect the terminal arteriole to the postcapillary venule bypassing the true capillaries, it consists of metarteriole and a thoroughfare channel, controlled via sphincter muscles which restricts the blood flow into the true capillaries
What is the function of the veins?
Blood reservoirs (capacitance vessels)
How many types of veins are there?
1) venule (extremely porous, the adhesion of WBC in them indicates inflammatory)
2) veins (formed by the joining of the venules, they can hold 65% of the blood at a given moment)
What is the difference between veins and arteries?
1) veins carry deoxygenated blood towards the heart
2) veins have thinner walls and (larger lumens, which offers little resistance to blood flow)
3) veins have valves (formed by the folds of tunica intima, it is another adaption veins have to compensate for the low venous pressure, most abundant in the limbs)
What is varicose veins?
They are the veins which are dialated due to leaky valves, usually in the lower limbs, it is caused by heredity or anything that blocks the venous return like obesity/pregnancy etc, elevated venous pressure which can cause hemorrhoids.
How many percent of blood is held in the heart at any given moment?
8%
Which blood vessels have the highest amount of blood at any given time?
Systemic veins
What is venous sinuses?
1) coronary sinus
2) dural venous sinuses
They are highly specialized, flattened veins with extremely thin walls composed only of endothelium, supported by the tissues that surround them
What is collateral channels?
Vascular or arterial vessels joining providing alternative pathway for the supply of blood to the organs
Where does arterial anastomoses occur?
Around joints, abdominal organs, heart, brain
Give an example of arteriovenous anastomoses
metarteriole–thoroughfare channel shunts of capillary beds that connect arterioles and venules
What is the difference between arteriosclerosis & atherosclerosis?
Arteriosclerosis is when the arterial walls becomes thicker and stiffer resulting in hypertension, while atherosclerosis is when an atheroma intrudes into the lumen causing arterial spasm
What are the most viable arteries when it comes to atherosclerosis?
1) aorta
2) coronary artery
3) carotid artery
How does atherosclerosis develop?
1) endothelium is injured
2) lipids accumulate and oxidize in the tunica intima
3) smooth muscle cells proliferate and a fibrous cap forms
4) the plaque becomes unstable
What is meant by blood flow?
It is the volume of blood flowing through a vessel, organ, or the entire circulation in a given moment (ml/min) it is equivelant to the cardiac output
What is meant by blood pressure?
It is the force per unit area exerted on a vessel wall by the blood within (mm Hg)
What is meant by the term resistance?
It is the opposition to flow which measures the amount of friction blood encounters as it passes through the vessels
What is the source of resistance in our blood?
1) Blood viscosity (the higher the viscosity the higher the resistance)
2) total blood vessel length (the longer the vessel the higher the resistance)
3) blood vessel diameter (the larger the vessel diameter the lower the resistance)
What is the relationship between blood flow, pressure & resistance?
Blood flow (F) = Blood pressure / resistance
Where does the steepest drop in blood pressure occur?
In the arteriole
What is meant by systolic pressure?
Due to the contraction of the left ventricle, which supplies the blood with kinetic energy and expels it to the aorta
what is meant by the diastolic pressure?
it is the pressure drop that occurs in the aorta as the walls of the aorta recoil after blood ejection
What is the pulse pressure?
It is the difference between the systolic and diastolic pressure
What is the mean arterial pressure?
It is the pressure that propels blood to the tissue
MAP = DIASTOLIC PRESSURE + PULSE PRESSURE/3
WHAT ARE THE FUNCTIONAL ADAPTIONS VEINS HAVE THAT ARE IMPORTANT TO PROMOTE ADEQUATE VENOUS RETURN?
1) muscular pump (the skeletal muscle activity which milks the blood back to the heart)
2) respiratory pump (moves blood towards the heart as pressure changes in the ventral body cavity during breathing)
3) sympathetic vasoconstriction
What factors influence blood pressure?
1) cardiac output (SV*HR)
2) resistance
3) blood volume
How is the blood pressure regulated?
1) Short term regulation (nervous system (baroreceptors, chemoreceptors, higher brain centers) & blood-borne hormones)
2) Long term regulation (kidneys)
How does the neural controls alter blood pressure?
1) maintaining adequate MAP via blood vessel diameter
2) altering blood distribution
How is the cardiac output controlled?
1) Low BP, increases sympathetic activity, increases epinephrine in blood, increases contractility of the heart, decreases ESV, increases stroke volume
2) exercise, increases respiratory pump, muscular pump, sympathetic vasoconstriction, venous return, EDV, stroke volume
What is baroreceptors and how does it help maintain BP?
They are pressure sensitive mechanoreceptors that responds to changes in arterial pressure and stretch found in the carotid sinus
by activating cardioacceleratory or cardoinhibitory centers which either increase or decrease sympathetic impulses, heart rate, contractility, cardiac output, vasoconstriction, vasodialation depending on the stimulus
What is chemoreceptor reflexes and how does it help maintain BP?
Found in the carotid and aortic bodies, when CO2 level rises, O2 level lowers, pH decreases, they send impulses to the cardiacceleratory center which increases the cardiac output, & the vasomotor center causing vasoconstriction rising the BP increasing the return of blood to the heart and lungs
What is the higher brain centers and how does it help maintain BP?
They are reflexes which regulates BP in the medulla oblongate of the brain stem, cerebral cortex, and hypothalamus they control it in situations like (speaking, fight-flight responses) by mediating the redistribution of blood flow and other cardiovascular responses
What are the hormones that increases blood pressure?
1) epinephrine and norepinephrine (NE)
2) Angiotensin II
3) Antidiuretic hormone (DH)
4) Aldosterone
What is the hormone that decreases blood pressure?
Atrial natriuretic peptide (ANP)
How does epinephrine and norepinephrine affects the blood pressure?
During periods of stress
1) it increases the cardiac output (HR & contractility) acting on the heart B1 receptors
2) increases peripheral resistance acting in the arterioles a-receptors (causing vasoconstriction)
How does angiotensin II affect the BP?
When BP or Blood Volume are low the kidneys secrets renin which acts on the enzyme to generate angiotensin II, it increases peripheral resistance acting in the arterioles (causing vasoconstriction)
How does antidiuretic hormone (vasopressin) affect BP?
1) increases peripheral resistance acting in the arterioles (causing vasoconstriction)
2) increases blood volume via decreasing its water loss acting on the kidney tubule cells
How does aldosterone affects BP?
increases blood volume via decreasing its water & salt loss acting on the kidney tubule cells
How does atrial natriuretic peptide (ANP) affects BP?
It decreases the peripheral resistance acting on the arterioles causing vasodialation
What are the short term hormonal controls?
1) adrenal medulla hormones (epinephrine & norepinephrine)
2) angiotensin II
3) atrial natriuretic peptide (ANP)
4) Antidiuretic hormone (ADH)
How is the BP regulated for a long term?
Blood volume via, renal mechanism
What is the difference between direct and indirect renal mechanism?
The direct renal mechanism alters blood volume independently of hormones, while the indirect mechanism uses the renin-angitensin-aldosterone mechanism
How does angiotensin II stabilized arterial pressure?
1) stimulates adrenal cortex to secrete aldosterone, enhancing renal reabsorption of sodium
2) promotes water reabsobroption via secreting ADH from the posterior pituitary
3) triggers the sensation of thirst
4) it promotes vasoconstriction, increasing the peripheral resistance
What is hypertension?
Chronically elevated BP, sustained increase in systolic >140 & diastolic >90 mm Hg it is a silent killer straining and damaging the heart and arteries, leading to heart failure, vascular disease, renal failure & stroke
What causes primary hypertension?
1) heredity
2) diet
3) obesity
4) age
5) diabetes mellitus
6) stress
7) smoking
What is secondary hypertension and what causes it?
due to identifiable conditions:
1) obstructed renal arteries
2) kidney disease
3) endocrine disorders such as hyperthyroidism and Cushing’s syndrome
What is hypotension?
low blood pressure (below 90/60 mm Hg)
What causes hypotension?
1) Addison’s disease (inadequate adrenal cortex function)
2) hypothyroidism
3) severe malnutrition
Hypotension is usually a concern only if it leads to inadequate blood flow to tissues
What is a circulatory shock?
Is a one of the acute hypotension symptoms, where blood vessels are inadequately filled and blood cannot circulate normally causing cell death and eventually organ damage
What is hypovolemic shock?
The most common circulatory shock, “low blood volume” due to large fluid loss, like
1) acute hemorrhage
2) severe vomiting
3) diarrhea
4) extensive burns
What is a vascular shock?
Poor circulation of blood due to extreme vasodialation, dropping the peripheral resistance there are several types:
1) Anaphylactic (loss of vasomotor tone due to anaphylaxis, a systemic allergic reaction in which the massive release of the chemical messenger histamine triggers body wide vasodilation)
2) Neurogenic shock (failure of autonomic nervous system regulation)
3) septic shock (“septicemia” severe systemic bacterial infection)
What is cardiogenic shock?
Pump failure, due to myocardial damage
How is blood flow regulated through the tissues?
1) intrinsic controls (autoregulation), achieved by the smooth muscles of arteriole stat feed any given tissue (Control is entirely from within the tissue or organ, Uses paracrines or properties of muscle tissue)
2) extrinsic controls, prevent extreme situations (like all arteriole dilate) by acting on the smooth muscle maintaining BP via the sympathetic nervous system & hormones of the nervous and endocrine system (Control is from outside of the tissue or organ, Uses nerves or hormones)
What is meant by autoregulation?
The adage ent of our organs/tissue to get the needed blood flow during different activities in the day
How does organs regulate their own blood flow (intrinsic control)?
By varying the resistance of the arterioles via:
1) metabolic (chemical)
2) myogenic (physical)
What is reactive hyperemia?
Dramatic increase of blood flow into a tissue, after its blood supply have been blocked
What causes the metabolic control to be activated, and how does it control it?
It is caused by increased levels of H+, K+, adenosine, prostaglandins and low oxygen levels which is regulated via:
1) Nitric Oxide secretion (vasodilator), but counterattacked by endothelia’s (vasoconstriction) but when the tissue is in more need of blood flow the equilibrium favors the nitric oxide
What is the myogenic response?
The response of the vascular smooth muscles, where increases intravascular pressure causes the vessel to constricts
What is angiogenesis?
Where our body develops new vessels to supply more nutrients to a given organ over the period of weeks
What does the hormone ANP do?
Vasodialate a blood vessels
How does the intrinsic control initiate vasodialation?
1) metabolically:
- decrease oxygen levels
-increase CO2, H+, K+ - secretion of prostaglandins, adenosine, nitric oxide
2) myogenically
-reduced stretch (decrease intravascular pressure)
How does the intrinsic control initiate vasodialation?
1) myogenically
- Streching (due to increase intravascular pressure)
2) metabolically
- endothelins
How does the extrinsic controls initiate vasodialation?
1) neural control
- decrease in sympathetic tone
2) hormonal
Secretion of atrial natriuretic peptide
How does the extrinsic control initiate vasoconstriction?
1) neurally
- increase in sympathetic tone
2) hormonal
- secretion of:
1) angiotensin II
2) antidiuretic hormone
3) epinephrine
4) norepinephrine
What are the factors involved in capillary exchange?
1) velocity an corossectional area (the reader the cross sectional area the slower the blood flow)
2) vasomotion (intemitting the blood flow, due to the on & off of vasoconstriction & vasodialation)
3) routes across the capillary for diffusion:
- Lipid-soluble molecules through the lipid bilayer membrane (respiratory gasses)
- small water soluble solutes through fluid-filled clefts or fenestrations (amino acids & sugars “water-soluble”)
- Large molecules through pinocytosis (proteins)
What is meant by bulk flow?
It determines the fluid volume in the blood stream and interstitial space, the amount and direction of flow across a capillary reflects the balance between the hydrostatic and colloid osmotic pressures
What is the hydrostatic pressure (HP)?
The force exerted by a fluid pressing against a wall, in the capillary the hydrostatic pressure is equal to the capillary blood pressure, and it is opposed by the hydrostatic pressure of the interstitial fluid which usually considered to be zero as the lymphatic constantly drains its fluid
- In the capillary it pushes the fluid out of the capillary
- In the interstitial fluid it pushes the fluid into the capillary
What is colloid osmotic pressure (OP)?
The force opposing the hydrostatic pressure, created by large
non-diffusible molecules (plasma proteins) which develops the capillary colloid osmotic pressure (OPc)
- In the capillary it pulls fluid into the capillary
- In the interstitial fluid it pulls the fluid out of the capillary
What is the net filtration pressure?
- considers all forces acting on the capillary bed
It is the net of fluid going out of the capillary at the arteriolar end and fluid return back at the venous end, it is the sum of ((HPc + OPif) - (OPc + HPif))
What is edema and what causes it?
It is an abnormal increase in the amount of interstitial fluid, can be caused by increased out flow of fluids or decreased in-flow of fluids:
1) increase in capillary hydrostatic pressure
2) increased interstitial fluid osmotic pressure due to inflammation which increases capillary permeability
3) decreased capillary colloid osmotic pressure (due to hypoproteinemia, due to liver disease, protein malnutrition or glomerulonephritis)
4) decreased drainage of interstitial fluid through the lymphatic vessels
