Chapter 20 Flashcards
Most common circulatory route?
Heart -> arteries -> arterioles -> capillaries -> venules -> veins
What are portal systems?
When blood flows through 2 consecutive capillary networks, interconnected by a vein, before returning to the heart
Notable portal systems?
Between the hypothalamus and anterior pituitary, in the kidneys, and between the intestines to the liver
What is anastomosis?
A point of convergence between 2 blood vessels other than capillaries. Provides alternate routes of travel for blood so clots don’t cause issues
What are arteries?
Thick, pressure-withstanding blood vessels that carry blood away from the heart
What are veins?
Blood vessels with a large circumference which carry blood to the heart
What are capillaries?
The site of gas exchange, connecting small arteries or arterioles to small veins or venules
Why do artery walls have elastic membranes?
To allow recoil for continuous blood flow
Why do veins have valves?
They are under very low pressure which may make it hard for blood to flow in the proper direction, so valves help with this and push it in one direction
How do veins act as a blood reservoir?
At any given time, the majority of the body’s blood is sitting in veins, waiting to constrict and send blood to the heart in the case of low BP
Types of arteries?
Conducting arteries, distributing arteries, and arteriole arteries
What are conducting arteries?
AKA elastic or large arteries, they are the largest arteries and have a thick media and layer of elastic tissue for recoil
What are distributing arteries?
AKA muscular or medium arteries, they distribute blood to specific organs or tissues
What are arteriole arteries?
AKA small arteries, they control the amount of blood distributed to various organs
What factors affect systemic vascular resistance (SVR)?
Blood viscosity, vessel length, flow characteristics, and vessel radius
Blood pressure formula?
BP = cardiac output x systemic vascular resistance
What layers make up the artery walls?
Tunica interna, tunica media, and tunica externa
What is the tunica interna?
Innermost of the arteries’ walls, it has an endothelium that acts as a selectively permeable barrier, and also usually repels blood cells and platelets to prevent unnecessary clotting
What is the tunica media?
Middle layer of the arteries’ walls, it consists of smooth muscle, collagen, and elastic tissue, and serves vasomotion - vasoconstriction and vasodilation - to increase or decrease SVR
What is the tunica externa?
The outermost layers of the arteries’ walls, it contains vasa vasorum - small vessels that supply blood to outer half of larger vessels. While blood from lumen nourishes inner half via diffusion
What is a pulse?
A wave of pressure caused by the expansion and recoil of arteries
What arteries are used for palpating pulses?
Superficial temporal, facial, common carotid, radial, brachial, femoral, popliteal, dorsal, posterior tibial, and dorsal pedal
What are carotid and aortic sinuses?
Baroreceptors that adjust blood pressure via baroreflex
What are carotid and aortic bodies?
Chemoreceptors that adjust the body’s O2 and CO2 levels and repair blood pH
How do the carotid and aortic bodies influence blood pH?
When oxygen levels drop / CO2 levels increase, vagus and glossopharyngeal nerves activate, sending signal to brainstem, activating phrenic nerve, activating diaphragm, increasing respiration
How do the carotid and aortic sinuses influence blood pressure?
When blood pressure increases, arteries stretch, activate baroreceptors, stimulate cardioinhibitory neurons, parasympathetic nerve releases acetylcholine, reducing pacemaker cells’ action potentials, decreasing heart rate, lowering blood pressure. And vice versa when BP is low
How does blood viscosity impact SVR?
RBC count and albumin concentration affect the thickness of the blood. High viscosity from polycythemia increases SVR, low viscosity from anemia decreases SVR
How does vessel length impact SVR?
Pressure and flow decline with distance traveled due to friction
How does vessel radius impact SVR?
It is in fact the most significant and powerful influence over SVR - vasoconstriction and vasodilation increase and decrease blood pressure
How do flow characteristics influence SVR?
Fast flow - more resistance - turbulent flow
Slow flow - less resistance - laminar flow
What is flow?
The amount of blood flowing through an organ, tissue, or blood vessel in a given time
What is flow in a resting individual?
Usually 5.25 L/min
What is perfusion?
The flow per given volume or mass of tissue
What is hemodynamics?
Physical properties of blood flow
How do resistance and pressure affect flow?
High pressure = greater flow
High resistance = lower flow
What is blood pressure?
The force that blood exerts against a vessel wall
What is systolic pressure?
Peak arterial pressure during ventricular contraction
What is diastolic pressure?
Minimum arterial pressure during ventricular contraction
What is pulse pressure?
The difference between systolic and diastolic pressure
What is mean arterial pressure (MAP)?
The mean pressure you would obtain from taking measurements at several intervals throughout the cardiac cycle
What does MAP influence the risk of getting?
Syncope (fainting), atherosclerosis, kidney failure, edema, and aneurysm
How does blood flow differ from arteries, capillaries, and veins?
In arteries it is pulsatile, in capillaries and veins it is steady
What is arteriosclerosis?
Hardening of arteries due to cumulative damage by free radicals
What is atherosclerosis?
Growth of lipid deposits in arterial walls - they can become calcified and make arteries hard and crunchy
What is hypertension?
Chronic high blood pressure
What blood pressure indicated hypertension?
A resting blood pressure higher than 140/90
What is hypotension?
Chronic low blood pressure. Happens near end of life a lot
What is peripheral resistance?
Opposition to flow that the blood encounters in vessels away from the heart
What is peripheral resistance dependent on?
Blood viscosity, vessel length, and vessel radius
What is laminar flow?
When blood flows in layers - faster in the middle of the vessels, slower near the walls
Most significant point of control over peripheral resistance?
Arterioles, because they are positioned well, outnumber other arteries, and are very muscular in proportion to their diameters
What is autoregulation?
The ability of tissues to regulate their own blood supply
What are vasoactive chemicals?
Chemicals released under trauma, inflammation, exercise, etc. which stimulate vasodilation
What is angiogenesis?
Growth of new blood vessels
When does angiogenesis occur?
Regrowth of uterine lining after menstrual period, development of higher density of blood capillaries in muscles of athletes, and growth of arterial bypasses around obstructions in coronary circulation
What is the vasomotor center an integrating center for?
Baroreflexes, chemoreflexes, and medullary ischemic reflexes
What are medullary ischemic reflexes?
Raise blood pressure to restore normal cerebral perfusion
What hormones can influence blood pressure?
Angiotensin II, aldosterone, natriuretic peptides, antidiuretic hormone, epinephrine and norepinephrine
What does vasomotion do?
Generalized raising and lowering of blood pressure, and selectively modifying perfusion of a particular organ and rerouting blood from one region of the body to another
What does the aortic arch split off into?
Brachiocephalic artery, left common carotid artery, and left subclavian artery
What does the brachiocephalic artery split into?
Right subclavian, which transitions into brachial artery, which divides into radial and ulnar arteries
What does the brachiocephalic artery supply?
Head, neck, upper extremities
What does the left common carotid artery supply?
Head and neck
What does the left subclavian artery supply?
Head, neck, arms
What does the brachial artery supply?
Arm
What do the radial and ulnar arteries supply?
Forearm
What does the axillary artery supply?
Pecs and deltoid
What does the celiac trunk split off into?
Splenic arteries, hepatic artery, and gastric artery
What does the superior mesenteric artery supply?
Large intestine
What do the renal arteries supply?
Kidneys
What do the gonadal arteries supply?
Testes and ovary
What does the inferior mesenteric artery supply?
Small intestine
What does the popliteal artery supply?
Back of knee
What does the posterior tibial artery supply?
Back of leg
What does the anterior tibial artery supply?
Front of leg
What does the dorsal artery supply?
The top of the foot
What artery can you palpate to judge the body’s circulation?
The dorsal artery on the foot
What are precapillary sphincters?
Little muscles that regulate blood flow to certain organs, and allows you to regulate blood pressure by redirecting blood back to the veins
What is the only site of nutrient, waste, and hormone exchange?
Capillaries
3 capillary types?
Continuous capillaries, fenestrated capillaries, sinusoids
What are continuous capillaries?
The least permeable, they allow diffusion of glucose and regulate blood flow (using pericytes)
What are fenestrated capillaries?
Medium permeable, they’re in organs that require rapid absorption or filtration and allow passage of glucose
How do lipid-soluble substances diffuse?
Directly through the plasma membrane. Can be done by steroid hormones, O2, and CO2, for example
How do substances that are not lipid-soluble diffuse?
They go through filtration pores or intercellular clefts. Can be done by glucose and electrolytes, while larger molecules like protein are held back
What is transcytosis?
The name for when endothelial cells pick up material on one side by pinocytosis, transport the vesicles across the cell, and discharge material on the other side by exocytosis. For fatty acids, albumin (protein) and some hormones like insulin
How do water-soluble substances diffuse?
They pass through filtration pores and intercellular clefts. Stuff like glucose and electrolytes
What is blood hydrostatic pressure?
Drives water-soluble fluid out of the capillary
What is colloid osmotic pressure?
Draws water-soluble fluid into the capillary. Results from plasma proteins like albumin
What is interstitial hydrostatic pressure?
Negative pressure from the lymphatic system that moves fluids into the tissue
What is tissue osmotic pressure?
Proteins present in tissue pulls fluid into the capillaries
What is edema?
Accumulation of excess fluid in a tissue
Risks of pulmonary edema?
Suffocation
Risks of cerebral edema?
Headaches, nausea, seizures, and coma
What causes edema?
An increase in hydrostatic pressure due to heart failure or inflammation
3 primary causes of edema?
Increased capillary filtration, reduces capillary reabsorption, and obstructed lymphatic drainage
What is the purpose of valves?
Ensuring one-way flow of blood toward the heart
What is venous return?
The flow of blood back to the heart
How is venous return achieved?
Pressure gradient, gravity, skeletal muscle pump, thoracic pump, and cardiac suction
What is central venous pressure?
Pressure at the point where venae cavae enter the heart
What is venous pooling?
Blood accumulating in the limbs when a person is still for a while since venous pressure isn’t high enough to override gravity
What is circulatory shock?
Any state in which cardiac output is insufficient to meet the body’s metabolic needs
Forms of circulatory shock?
Cardiogenic shock and low venous return
What is cardiogenic shock?
Inadequate pumping by the heart
What is low venous return?
Cardiac output is low because too little blood is returning to the heart
Forms of low venous return shock?
Hypovolemic shock, obstructed venous return shock, and venous pooling shock
What is hypovolemic shock?
Low of blood volume due to hemorrhage, trauma, bleeding ulcers, burns, or dehydration
What is obstructed venous return shock?
When any object, like a tumor or an aneurysm, compresses a vein and impedes its’ blood flow
What is venous pooling shock?
When the body has a normal blood volume, but too much of it accumulates in the lower body
What is neurogenic shock?
A form of venous pooling shock that results from a sudden loss of vasomotor tone, allowing blood vessels to dilate
What is septic shock?
Bacterial toxins trigger vasodilation and increased capillary permeability
What is anaphylactic shock?
Exposure to an antigen to which a person is allergic, causing release of histamine which causes generalized vasodilation and increased capillary permeability
Smallest veins?
Postcapillary venules
What are medium veins?
Up to 10mm in diameter, they have a thin tunica media and a thick tunica externa
What forms venous valves?
Tunica interna
What are large veins?
Over 10mm in diameter, they include venae cavae, pulmonary veins, internal jugular veins, and renal veins
What are capacitance vessels?
Veins are considered this, since they contain like 50% of the systemic blood volume at any given time
What happens in veins when blood pressure drops?
Vasoconstriction occurs, moving blood toward the heart, working to fix blood pressure
How does the muscular pump work?
Contracting your muscles pushes against the walls of the veins, displacing blood toward the heart
How does the respiratory pump work?
When you inhale, thoracic volume increases, causing drop in intrapleural pressure, negative pressure acts like a vacuum, suctioning blood into the heart
How does exercise increase venous return?
Heart beats faster and harder, vessels of skeletal muscles and lungs and heart dilate, respiratory rate increases, skeletal muscle pump increases
Control over vasomotion?
Local control, neural control, and hormonal control
What is local control over vasomotion?
Tissue releases vasodilators
What is neural control over vasomotion?
Sympathetic nervous system causes vasoconstriction
What is hormonal control over vasomotion?
Epinephrine and angiotensin II cause vasoconstriction
What type of blood vessel holds the greatest volume of blood?
Veins
Blood normally flows into a capillary bed from?
A metarteriole
Substance that is likely to cause a rapid drop in blood pressure?
Histamine
Why is blood flow faster in venules than capillaries?
Larger diameter
How is pulse pressure calculated?
Subtracting diastolic pressure from systolic pressure
Longest blood vessel in the body?
Saphenous vein
What are varicose veins?
A permanently distend vein, common in lower legs, due to weakened valves
What are hemorrhoids?
Distend veins found in the anus due to weakened valves
What is orthostatic hypertension?
Temporary low BP and dizziness when suddenly standing
What is the organ where blood flow fluctuates the least?
To the brain
What happens if the brain loses oxygen?
For a couple seconds, loss of consciousness. For 4-5 minutes, irreversible damage
How does blood flow change in response to different functions?
It is redirected to different parts of the brain
How does the brain regulate its blood flow?
In response to changes in blood pressure and chemistry
Main chemical stimulus for cerebral autoregulation?
pH
What happens when there is too much CO2 or O2 in the brain?
Low CO2 - local vasodilation
Low O2 - local vasoconstriction
What is hyperventilation?
Exhaling CO2 faster than the body can produce it, leading to hypocapnia
Effects of hyperventilation?
Cerebral vasoconstriction, ischemia, dizziness, and sometimes syncope
What are transient ischemic attacks?
Dizziness, loss of vision, weakness, paralysis, headache, or aphasia resulting from brief episodes of cerebral ischemia
What is a stroke?
AKA cerebrovascular accident, sudden death of brain tissue caused by ischemia
Effects of a stroke?
Blindness, paralysis, loss of sensation, and loss of speech
What happens to blood flow during strenuous exercise?
Blood is diverted from the digestive tract and kidneys to meet the needs of working muscles
How does muscular contraction affect blood flow?
It compresses blood vessels, impeding flow. Sustained isometric contraction fatigues more quickly than intermittent isotonic contraction
Blood vessels carry what blood in the systemic and pulmonary circuits?
Pulmonary: arteries are oxygen-poor, veins are oxygen-rich
Systemic: arteries are oxygen-rich, veins are oxygen-poor
Why do capillaries in the pulmonary circuit have a lower pressure than those in the systemic circuit?
To help blood flow more slowly, allowing more time for gas exchange, and preventing fluid accumulation for the same reason
What do systemic arteries do in response to hypoxia?
Dilate and improve tissue perfusion
What do pulmonary arteries do in response to hypoxia?
Contract, redirecting blood flow to another, better ventilated region
What does the pulmonary trunk branch into?
Right and left pulmonary arteries
What does the right pulmonary artery branch into?
Upper branch and lower branch
Where do arteries in the lungs lead?
To capillary beds surrounding pulmonary alveoli
Where does pulmonary blood go after leaving alveolar capillaries?
It flows into venules and veins, ultimately leading to the main pulmonary veins
Primary purpose of pulmonary circuit?
Exchanging CO2 for O2
How do lungs get systemic blood supply?
From bronchial arteries
