Cardiovascular #2 Flashcards
3 Layers of a blood vessel
1) Tunica Interna aka Tunica Intima - adjacent to lumen
2) Tunica Media - middle layer (includes smooth muscle and elastic fibers)
3) Tunica Externa - adjacent to surround tissue
Elasticity of Arteries
- The walls of the arteries are elastic
- Allows them to absorb the pressure created by ventricles of the heart
- Creates a pressure resevoir
Which anatomy of the artery regulates its diameter?
Smooth muscles of the Tunica media
Effects of elastic expansion and recoil or the aorta and its branches
- Maintains steady flow of blood during diastole
- Smooths out pressure fluctuations
- ↓ stress on small arteries
2 Types of Arteries
1) Elastic or Conducting Arteries
2) Muscular or Distributing Arteries
Characteristics of Elastic Arteries
- Large diameter
- More elastic fibers
- Less smooth muscle
- Function as pressure reservoirs
Characteristics of Muscular Arteries
- Medium diameter
- Fewer elastic fibers
- More smooth muscle
- Distribute blood to various parts of the body
Anastamosies
- Union of the branches of 2 or more arteries supplying the same region of the body
- Provides an alternate route for blood flow
End Arteries
Arteries that do not form an anastomosis
What happens if an End Artery gets blocked
Blood cannot get to that part of the body and necrosis can occur
3 Arterial Sense Organs
1) Carotid Sinuses
2) Carotid Bodies
3) Aortic Bodies
Carotid Sinuses
- Baroreceptor (sensitive to pressure ∆ )
- Located in internal carotid artery
- Monitors BP and signals brainstem ↓ HR and dilate vessels
Carotid Bodies
- Oval bodies near carotids (cluster of chemoreceptors)
monitor blood chemistry - Adjust respiratory rate to stabilize pH, CO2, and O2
Aortic Bodies
- In walls of aorta (cluster of chemoreceptors)
monitor blood chemistry - Adjust respiratory rate to stabilize pH, CO2, and O2
Capillaries
- Microscopic vessels that connect arterioles & venules
- Walls made of single layer of cells and a basement membrane
- Thin walls permit the exchange of nutrients & wastes
Capillary Bed Routes
1) Most Common Route - heart»_space;> arteries»_space;> arterioles»_space;> capillaries»_space;> venules»_space;> veins
2) Portal System - Blood flows through two consecutive capillary networks before returning to heart:
- Hypothalamus/pituitary
- Kidneys
- Hepatic Portal System between intestines - liver
3 Types of blood vessel anastomoses
1) Arteriovenous Shunt - artery flows directly into vein
2) Venous Anastamoses- most common, blockage less serious
3) Arterial Anastomoses- colateral circulation (coronary)
Continous Capillaries found in ___?
Most tissues
Fenestrated Capillaries found in ____?
Kidneys, small intestine, choroid plexus, ciliary bodies (eyes)
Sinusoid Capillaries found in _____?
Liver, bone marrow and spleen
3 method by which substances cross capillary walls
- Diffusion
- Transcytosis
- Bulk flow
Examples of substances that cross capillary walls by diffusion?
1) Oxygen
2) Carbon dioxide
3) Glucose
4) Amino acids
5) Some hormones
Examples of substances that cross capillary walls by transcytosis
- Large lipid-insoluble molecules (like insulin) cross capillary walls in vesicles via transcytosis
- Examples of substances that cross capillary walls by Bulk Flow
- Characteristics of Bulk Flow
- Large numbers of ions, molecules, or particles in a fluid move together in the same direction
- Passive process
- Occurs from an area of high pressure to low pressure
- Continues as long as a pressure difference exists
- Regulates volumes of blood and interstitial fluid
Filtration
- Pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid
- i.e. Blood hydrostatic pressure (BHP) and interstitial fluid osmotic pressure (IFOP)
Reabsorption
- Pressure-driven movement of fluid and solutes from interstitial fluid into blood capillaries
- i.e. Interstitial fluid hydrostatic pressure (IFHP) and blood colloid osmotic pressure (BCOP)
Causes of Edema
1) ↑ Capillary Filtration
2) ↓ Capillary Reabsorption
3 causes of ↑ Capillary Filtration
1) Poor venous return (i.e. CHF and pulmonary edema, insufficient muscular activity)
2) Kidney failure (water retention, hypertension)
3) Histamine makes capillaries more permeable
Causes of ↓ Capillary Reabsorption
Hypoproteinemia, cirrhosis, famine, burns, kidney disease
Obstructed lymphatic drainage
Consequences of Edema
1) Tissue necrosis - oxygen delivery and waste removal impaired
2) Pulmonary edema - suffocation
3) Cerebral edema - headaches, nausea, seizures and coma
4) Circulatory shock - excess fluid in tissue spaces causes low blood volume and low BP
Veins
1) Have lower BP: 10mmHg with little fluctuation
2) Thinner walls, less muscular and elastic tissue
3) Expand easily and have high capacitance
4) Have valves - aid skeletal muscles in upward blood flow
Venules
- More porous than capillaries
- Muscular venules have tunica media
Venous Sinuses
- Veins with thin walls, large lumens, no smooth muscle
Veins compared to Arteries
- Veins have a thinner tunica interna and media
- Veins have thicker tunica externa
- Veins have less elastic tissue and less smooth muscle than arteries
Venous Return is assisted by
- One-Way Valves
- Respiratory pump
- Skeletal muscle pump
- Gravity (for head and neck)
- Cardiac suction of expanding atrial space
Effects of Inhalation on Respiratory Pump
- ↑ Blood flow to thoracic veins
- ↓ Thoracic pressure
- Blood moves superiorly
- ↑ intra-abdominal pressure
Effects of Exhalation on Respiratory Pump
- ↑ Blood flow into heart and abdominal veins
- ↑ Thoracic pressure
- Diaphragm relaxes
- ↓ intra-abdominal pressure
At rest, where is the largest portion of the blood located?
In the systemic veins and venules (the blood reservoir)
Blood Flow vs Perfusion
Blood Flow - Volume of blood flowing through a tissue in a given time (ml/min)
Perfusion - Rate of blood flow per given mass of tissue (ml/min/100g)
Poiseuille’s Law
F = (πr^4ΔP)/8ηl; where F = flow in L/s η = viscosity in Pa/s r = radius of tube in meters l = length of tube in meters
Calculate Cardiac Output
- CO = HR × SV
- CO = MAP ÷ resistance (R)
Mean Arterial Pressure (MAP)
- Measurements taken at intervals of cardiac cycle
- Best estimate: diastolic pressure + (1/3 of pulse pressure)
- Varies with gravity: ex: standing: 62 – head; 180 - ankle
What determines BP
- CO
- Blood Volume
- Vascular resistance
BP changes with distances
BP highest near left ventricle and lowers as it moves away i.e. highest near aorta and lowest vena cava
Vascular Resistance
The opposition to blood flow due to friction between blood and the walls of blood vessels
Vascular Resistance depends on which 3 things?
- Size of the blood vessel lumen
- Blood viscosity
- Total blood vessel length
Regulation of BP and flow
1) Local control - Autoregulation
2) Neural control - Vasomotor Center in Medulla Oblongata
3) Hormonal control - RAAS, ANP, ADH, Epi
Metabolic theory of Autoregulation
Tissue inadequately perfused results in wastes accumulating, which = vasodilation
Vasoactive chemicals’ role in auto regulation of BP
Substances that stimulate vasomotion. i.e. histamine and bradykinin
What is Reactive Hyperemia
Transient increase in organ blood flow that occurs following a brief period of ischemia (e.g., arterial occlusion)
What is Angiogenesis
Growth of new blood vessels. i.e. regrowth of uterine lining, around obstructions, exercise, malignant tumors
3 Autonomic Reflexes involved in the neural control of BP
- Baroreflexes
- Chemoreflexes
- Medullary ischemic reflex
Baroreflex
- Changes in BP detected by stretch receptors baroreceptors
- ↓ in BP = ↑in HR, contractility and vasoconstriction
- Acute HTN = opposite response
- Inhibited by inhalation anesthetics
Baroreceptor Locations
Located in large arteries above heart:
1) Aortic arch
2) Aortic sinuses (behind aortic valve cusps)
3) Carotid sinus (base of each internal carotid artery)
Chemoreceptors
- Sensors that detect changes in CO2, O2, and pH
- Located in aortic arch, external carotids and subclavian arteries
- Primary role - adjust respiration
- Secondary role - vasomotor
- Inibited by inhalation anesthesia
Physiological factors that stimulate chemoreceptors?
Hypoxemia, hypercapnia and acidosis stimulate chemoreceptors, which stimulate vasomotor center to cause vasoconstriction, ↑ BP, ↑ lung perfusion and gas exchange
Medullary Ischemic Reflex
Inadequate perfusion of brainstem
Effects of Medullary Ischemic Reflex
- Cardiac/vasomotor centers send sympathetic signals to heart & blood vessels
- ↑ C.O. and causes widespread vasoconstriction
- ↑ BP
Hormonal Control of BP
1) Atrial Natriuretic Peptide (ANP) - ↑ Na excretion which ↓ BP
2) Antidiuretic Hormone (ADH) - ↑ water retention and vasoconstriction which leads to ↑ BP
3) EPI and NE - catecholamines released from adrenal medulla ↑ cardiac output & BP
Where would you feel for the following pulses:
1) Superior Temporal Artery
2) Facial Artery
3) Common Carotid Artery
4) Brachial Artery
5) Femoral Artery
6) Popliteal Artery
7) Radial Artery
8) Dorsal Artery of Foot
1) Superior Temporal Artery - Medial to ear
2) Facial Artery - Mandible, on line with corners of mouth
3) Common Carotid Artery - Lateral to larynx (voice box)
4) Brachial Artery - Medial side of biceps brachia muscle
5) Femoral Artery - Inferior to inguinal ligament
6) Popliteal Artery - Posterior to knee
7) Radial Artery - Lateral aspect of wrist
8) Dorsal Artery of Foot - Superior to instep of foot
Valsalva Maneuver
- Forced expiration against closed glottis
- Mediated by baroreceptors -> CN. IX and X
- Vasomotor Center (Medulla)
- ↓SNS, ↑ PSNS
- ↑ intrathoracic pressure = ↓ venous return = ↓ CO
Ocularcardiac Reflex
- Aka Aschner phenomenon
- Traction on extraocular muscle (esp. medial rectus), conjunctiva or orbital structures = ↓ BP and HR
Besides traction of extra ocular muscle, 3 things that could cause stimulation of ocular cardiac reflex
- Retrobulbar block
- Ocular trauma
- Pressure on remaining tissue post enucleation
How do you reverse the Oculocardiac Reflex?
Vagal response antagonized by anticholinergics like atropine and glycopyrrolate
Celiac Reflex
- Caused by traction on mesentery, gallbladder, or other structures in thorax or abd. cavity during surgery and pneumoperitoneum
- Causes Bradycardia, Apnea, Hypotension
- Resolved by removing initiating stimulus
- Vagal response antagonized by anticholinergics like atropine and glycopyrrolate
Bainbridge Reflex
- Atrial stretch reflex
- ↑ in HR due to an ↑ in CVP
- Stretch receptors in RA, Vena caval jct. & Pulmonary veins
- Sense ↑ venous return to heart
- ↓ ADH, ↑ SNS, ANP
Cushing Reflex
- Response to CNS ischemia secondary to ↑ ICP
- Causes ↑ Vasoconstriction
- If MAP < 50%, vasomotor area becomes ischemic
Maximal stim. of Vasomotor ctr. Occurs - Results in Cushing’s Triad: HTN, bradycardia, Irreg. Resp.
- Triad indicates sustained ↑ ICP prior to herniation/death
Define Shock
Shock is an inadequate CO that results in failure of the CV system to meet the metabolic demands of body cells
5 Types of Shock
1) Hypovolemic
2) Neurogenic (from ↓ vasomotor tone)
3) Cardiogenic (Acute MI)
4) Vascular (normal vol. w/ ↑ vasodilation i.e. anaphylactic or septic shock
5) Obstructive (PE , Cardiac Tamponade)
Homeostatic Responses to Shock
- Activation of the RAAS
- Secretion of ADH
- Activation of the SNS
- Release of local vasodilators
SxS of Shock
1) Same as dramatic decrease in BP
2) Clammy, cool, pale skin
3) Tachycardia, weak but rapid pulse
4) Sweating
5) Hypotension (SBP <90 mmHg)
6) Altered mental status
7) ↓ urinary output
8) Thirst
9) Acidosis
Responses to Hypovolemic Shock
- ↑ Renin
- ↑ ADH
- ↑ Epi
Compensated Shock
Homeostatic mechanisms bring about recovery
BP triggers baroreflex and production of angiotensin II, both stimulate vasoconstriction
What are the 3 life-threatening positive feedback loops of Decompensated Shock
1) ↓ CO = myocardial ischemia and infarction = ↓ CO
2) slow circulation = disseminated intravascular coagulation = slow circulation
3) ischemia and acidosis of brainstem = ↓ vasomotor tone, vasodilation = ↓ CO = ischemia and acidosis of brainstem
