Chapter 20: The Circulatory System: Blood Vessels and Circulation

Merged flashcards from Chapter 20, McGraw Hill Anatomy and Physiology Tenth Edition, by Kenneth S. Saladin.

Blood vessel categories

• Arteries

• Veins

• Capillaries

Arteries

Blood vessel that carries blood away from the heart

Capillaries

Blood vessel that connects small arteries to veins, forming a circuit

Tunics

Vessel wall layers; there are three in total:

• Tunica interna

• Tunica media

• Tunica externa

Tunica interna

The innermost tunic that lines the blood vessel with a selectively permeable barrier and chemical secretions for constriction and dilation

Tunica media

The middle tunic consisting of smooth muscle, collagen, and elastic tissue for strength

Tunica externa

The outermost tunic made of loose connective tissue to connect with other organs as an anchor

Artery classes

Three classes:

• Conducting (elastic or large)

• Distributing (muscular or medium)

• Resistance (small)

Conducting (elastic or large) arteries

The biggest arteries (such as the aorta or common carotid) that expand and recoil with the systole and diastole to regulate pressure

Distributing (muscular or medium) arteries

The arteries that distribute blood to specific organs (such as the brachial, femoral, renal, or spenic)

Resistance (small) arteries

Smaller arteries to smaller areas

Arterioles

The smallest of the resistance arteries with a 200mm diameter

Aneurysm

A weak point in an artery or heart wall that forms a thin-walled, bulging sac that pulses and can rupture or cause pressure

Carotid sinuses

Baroreceptors (blood pressure sensors) in the walls of the internal carotid artery

Carotid bodies

Oval bodies near the branch of common carotids that function as chemoreceptors (chemistry montors) for O₂ and CO₂ respiration rates

Aortic bodies

The one to three chemoreceptors in the aortic arch

Capillaries

The smaller exchange vessels to allow gasses, nutrients, wastes, and hormones pass between blood and tissue fluid

Capillary types

Three types:

• Continuous capillaries

• Fenestrated capillaries

• Sinusoids

Continuous capillaries

The most common capillaries that allow smaller solutes (like glucose) to pass while blocking large molecules (proteins, blood cells, platelets)

Fenestrated capillaries

Capillaries found in organs needing rapid absorption or filtration (kidneys, small intestine) with filtration pores (fenestrations)

Fenestrations

Filtration pores in fenestrated capillaries that only allow very small molecules to pass

Sinusoids

A type of capillary found in the liver, bone marrow, and spleen for irregularly shaped spaces filled with blood, allowing particles to enter circulation

Capilalary beds

Networks of 10 to 100 capillaries - not all are used; 75% of all capillaries are shut down by precapillary sphincters

Precapillary sphincters

Controls flow in capillary beds supplied with blood; relaxation allows flow and contraction constricts entry

Veins

The thin-walled, flaccid vessels that collapse when empty and expand easily for steady, low pressure flow back to the heart

Postcapillary venules

The smallest veins with just a tunica interna, some fibroblasts, and pores for fluid exchange

Muscular venules

Veins that recieve blood from the post-capillary venules up to 1mm in diameter with one to 2 layers of smooth muscle

Medium veins

Veins up to 10mm in diameter with thick tunica media, externa, and interna as a result of venous valves while pumped by skeleta muscles

Varicose veins

The failure of venous valves in the merium veins as a result of blood pooling and distended veins; can happen as a result of hereditary weakness, obesity, and pregnancy

Skeletal muscle pump

Pump that propels venous blood back to the heart using skeletal muscles; found in the gastrocnemius (calves)

Large veins

Veins with a diameter greater than 10 mm with smooth muscle in all three tunics; thick tunica externa - includes the IVC/SVC, pulmonary veins, and internal jugular veins

Hemorrhoids

Varicrose veins of the anal canal

Flow

The amount of blood flowing thorugh an organ, tissue, or blood vessel in a given time (measured in mL/min)

Perfusion

Flow given per volume or mass of tissue in a given time (measured in mL/100g/min)

Hemodynamics

The physical principles of blood flow based on pressure and resistance

Blood pressure (BP)

The force blood exerts against a vessel wall

Sphygmomanometer (blood pressure cuff)

Tool to measure the blood pressure of an indiviudal at the brachial artery, near the left ventricle

Systolic pressure

The peak arterial BP taken during ventricular contraction

Diastolic pressure

Minimum arterial BP taken during ventricular relaxation

Normal blood pressure

120/75 mmHg

Pulse pressure

The difference between the systolic and diastolic pressure to measure force and stress of heart

Blood pressure speed

40 to 120 cm/s

Arteriosclerosis

The stiffening of arteires due to the deterioration of elastic tissues

Artherosclerosis

The build up of liquid deposits that become plaques

Hypertension

A chronic resting blood pressure higher than 130/80 that can weaken arteries, cause aneurysms, and promote artherosclerosis

Hypotension

A chronic low resting blood pressure caused by blood loss, dehydration, and anemia

Blood pressure factors

Three factors:

• Cardiac output

• Blood volume

• Resistance to flow

Peripheral resistance

Opposition to flow in vessels away from the heart

Peripheral resistance factors

Three resistance factors:

• Blood viscosity

• Vessel length

• Vessel radius

Blood viscosity

The ‘stickiness’ of blood, mainly from plasma proteins and RBCs to increase/decrease flow

Vessel length

More of this can cause more cumulative friction, thus decreasing flow

Vessel radius

The radius of a blood vessel; more of this decreases blood-vessel wall contact to speed up flow

Vasomotion

The movement of blood vessel walls, can be controlled:

• Locally

• Neurally

• Hormonally

Local vasomotor control

Done through:

• Autoregulation

• Vasoactive chemicals

• Reactive hyperemia

• Angiogenesis

Autoregulation

The ability of tissues to regulate their own blood supply; reacts to wastes with dilation and then reconstricts for homeostasis

Vasoactive chemicals

Substances secreted by platelets, endothelial cells, and perivascular tissues to stimulate vasomotor responses (constriction or dilation)

Reactive hypermia

Reaction to a cut off and restored blood supply with higher flow

Angiogenesis

The growth of new blood vessel; aids hypoxic tissues and can be controlled by growth factors or inhibitors

Neural vasomotor control

Done through:

• Baroreflexes

• Chemoreflexes

• Medullar ischemic reflexes

Baroreflex

A neural vasomotor response to changes in blood pressure; aims to stay around set point but cannot correct chronic hypertension due to new set point

Chemoreflex

A neural vasomotor response to changes in blood chemistry, especailly pH and oxygen concentrations, to adjust respiration and vasomotion

Medullary ischemic reflex

Automatic response to a drop in flow to the brain

Ischemia

Insufficient perfusion (flow)

Hormonal vasomotor control

Done through:

• Angiotensin II

• Aldosterone

• Natriuretic peptides

• Antidiuretic hormone

• Epinephrine and norepinephrine

Angiotensin II

Potent vasoconstictor that raises blood pressure

Antidiuretic hormone (ADH)

Promotes water retention and raises BP; can also act as a vasoconstrictor (hence its alternate name arginine vasopressin)

Vasomotion purposes

Two purposes:

• Raising or lowering of BP via centralized control throughout the whole body

• Modification of perfusion of an organ for central or local control (exercise or local circulation)

Capillary exchange

The two-way movement of fluid across capillary walls between the blood and tissues; done through either:

• diffusion

• transcytosis

• filtration

• reabsorption

Diffusion

The most important form of capillary exchange

• Glucose and oxygen diffuse out and carbon dioxide and wastes diffuse in the blood

Capillary diffusion requirements

The membrane must be permeable to the solute or passages must be available to pass through

• lipid-soluble substances can diffuse through membranes

• water-soluble membranes must go through pores

• larger particles are held back

Transcytosis

Vesicle-mediated transport via endo- and exo-cytosis across the capillary wall; very small fraction of solute exchange but crucial for fatty acids, albumin, and hormones like insulin

Filtration and reabsorption

Fluid filters out of arterial end of capillary and osmotically enters venous end in reabsorption, delivering cell materials while removing wastes; can vary like in kidneys (more filtration) vs lungs (more absorption to avoid fluids)

Edema

The accumulation of excess fluid in a tissue; fluid filters in faster than it is reabsorbed and can causae tissue death, suffocation, headaches, or circulatory shock

Venous return

The flow of blood back to the heart, done by:

• Pressure gradients

• Gravity

• Skeletal muscle pumps

• Thoracic pumps

• Cardiac suction

Pressure gradients

Venous return mechanism where blood pressure draws blood toward the heart

Gravity

Venous return mechanism where blood is drained from the head and neck

Skeletal muscle pump

Venous return mechanism where limb muscles squeeze blood out of veins

Thoracic pump

Venous return mechanism involving respiration:

• Inhalation expands the thoracic cavity

• Thoracic pressure on IVC decreases

• Abdominal pressure on IVC increases

• Blood is forced upward toward heart

Cardiac suction

Venous return mechanism where ventricle contraction pulls valves downwards to expand atrial space, drawing blood in from venae cavae

Venous pooling

The accumulation of blood in the limbs due to inactivity with decreased venous pressure; can be prevented by tensing leg muscles

Circulatory shock

Any state in which cardiac output is insufficient to meet body’s metabolic needs

Septic shock

Type of circulatory shock where bacterial toxins trigger vasodilation and increased capillary permeability

Anaphylactic shock

Type of circulatory shock where a severe immune reaction to a particle increases permeability

Compensated shock

A response to circulatory shock for spontaneous recovery; fainting is an example where blood flow is restored in a horizontal position

Decompensated shock

A response to circulatory shock when compensation fails; life-threatening positive feedback loops can occur and can cause cardiac and brain damage

Brain flow

Done through autoregulation, vasomotion. and spatial allocation at constant 700 mL/min

Brain flow damage

Seconds of deprivation causes unconsciousness, four to five minutes causes irreversible damage

Hypercapnia

The accumulation of CO₂ in the brain; triggers vasodilation for more flow due to lowered pH

Hypocapnia

Too low CO₂ in the brain; triggers vasoconstriction for less flow due to higher pH

Caused by hyperventilation; can lead to ischemia, dizziness, syncope

Transcient ischemic attack (TIA)

Brief episodes of cerebral ischemia caused by diseased cerebral arterial spasms

• Can cause dizziness, vision loss, wekaness, paralysis, headaches, and aphasia

• Must be treated as a warning for stroke

Cerebral vascular accident (CVA)

The common name for a stroke, it is the sudden death of brain tissue due to ischemia

• Can be caused by artherosclerosis, thrombosis, and ruptured aneurysm

• Effects include bindness, loss of sensation, loss of speech, paralaysis, or death

Resting blood flow

Constricted arterioles and less capillary activity at 1 L/min

Working blood flow

Dilated arteries with more muscle metabolistes at 20 L/min; away from digestive and urinary organs

Pulmonary blood pressure

25/10 mmHg; slower for more gas exchange for absorption in capillaries (nearly no filtration)

Alveoli

The part of the lung that delivers oxygen to its surrounding capillary beds

Ascending aorta

Where the left and right coronary arteries branch off to supply the heart

Aortic arch arteries

1. Brachiocephalic trunk (splits into the right common carotid and right subclavian)

2. Left common carotid

3. Left subclavian

Right common carotid

Supplies the right side of the head

Right subclavian

Supplies the right shoulder and upper limb

Left common carotid

Supplies the left side of the head