Test 2: Blood Vessels & Lymphatic System FINAL Flashcards
Lymphatic System Functions
- Fluid Recovery
- Immunity
- Lipid Reabsorbtion
3 Vessel Layers
- Tunica Interna
- Tunica Media
- Tunica Externa
Vaso Vasorum
Smaller blood vessels supplying larger one
Supply blood to at least the outer half of the vessel wall (within the tunic externa)
*Tissues within the inner half of the vessel are likely supplied by diffusion from the lumen
Tunica Interna: Structure & Function
Structure:
Lines inside of the vessel
Consists of simple squamous epithelium (endothilium)
Function
Lining is selectively permeable barrier
Secretes chemicals to influence vasodialation and vasoconstriction
Endothelium: Smooth lining prevents blood cells and platelets from congregating/ sticking to walls. Also, when tissue around vessel is inflammed, endothelium cells produce cell-adhesion molecules that induce leukocytes to adhere to surface. Congreare where their defense mechanisms are needed.
Tunica Media: Structure & Function
Structure:
Middle layer of blood vessel
Consists of smooth muscles, collagen, and elastic tissue
Smooth muscle & elastic tissue vary between vessels
Function:
Tunica Media strengthens vessels and prevents blood pressume from rupturing the vessel
Also regulates the diameter of the vessel
Tunica Externa: Structure & Function
Structure:
Outermost layer
Consists of loose connective tissue that merges with other blood vessels, nerves, or other ogans
Function:
Anchors vessels to adjacent tissues and provides passage for small nerves, lymphatic vessels, and smaller blood vessels
Why are arteries called resistance vessels ?
Have strong, resilient tissue structure that can withstand heavy loads of blood and pressure
They are more muscular than veins and can retain their shape when empty
3 Types of Arteries
- Conducting (elastic or large) arteries:
- Distributing (muscular or medium) arteries
- Resistance (small) arteries
- Metaraterioles
Conducting (elastic or large) Arteries: Structure & Function
Arteries are sometimes called resistance vessels because of their strong, resilient tissue structure
Structure:
The largest
Has tons of elastic tissue, internal elastic lamina, at the border between interna and media
Function:
They expand when they recieve blood during ventricular systole and recoil during diastole. Expansion takes pressure of smaller downstream vessels. Recoil maintains pressure during relaxation and keeps blood moving.
Examples: aorta, common caratid, subclavian, pulmonary trunk, common iliac
Arteriosclerosis
Stiffening of arteries (usually with age)- Hypertension?
Protective effect of arteries weaken and downstream vessels are subjected with greaer stress and risks of aneurysm and hemorrhage rise
Distributing (muscular or medium) Arteries: Structure & Function
Smaller branches of arteries that supply blood to specific organs
Structure:
Compared to exit ramps where as conducting arteries are interstate highways
These arteries have a ton of muscle (more than elastic tissue- about 3/4 of wall thickness)
Function:
Supply blood to specific organs
Example: femoral, brachial, renal, and splenic
Resistance (Small) Arteries: Structure & Function
–Resistance (small) arteries
Structure:
- Arterioles: smallest arteries
- Thicker tunica media in proportion to their lumen than large arteries and very little tunica externa
Function:
–Control amount of blood to various organs
Metaarteriales
Link arterioles directly to venules
Provide shortcuts through which blood could bypass capillaries
•Muscle cells form a precapillary sphincter around entrance to capillary
–Constriction of these sphincters reduces blood flow through their capillaries
–Diverts blood to other tissues
Types of Blood Vessels
- Arteries carry blood away from heart
- Veins carry blood back to heart
- Capillaries connect smallest arteries to smallest veins
Aneurysm
•Aneurysm—weak point in artery or heart wall
Mechanism
–Forms a thin-walled, bulging sac that pulsates with each heartbeat and may rupture at any time
–Dissecting aneurysm: blood accumulates between tunics of artery and separates them, usually because of degeneration of the tunica media
–Most common sites: abdominal aorta, renal arteries, and arterial circle at base of brain
Causes
–Result from congenital weakness of blood vessels, trauma, or bacterial infections
Most common cause is atherosclerosis and hypertension
Symptoms
–Can cause pain by putting pressure on other structures
–Can rupture causing hemorrhage
Arterial Sense Organs
•Sensory structures in walls of major vessels that monitor blood pressure and chemistry
–Transmit information to brainstem to regulate heart rate, blood vessel diameter, and respiration
Arterial Sense Organs: Types
- Carotide Bodies: Baroreceptors
- Carotid Bodies: Chemoreceptors
- Aortic Bodies: Chemoreceptors
Carotid sinuses: baroreceptors
- In walls of internal carotid artery
- Monitor blood pressure
–Transmit signals through glossopharyngeal nerve
–Allow for baroreflex
Carotid Bodies: Chemoreceptors
- Oval bodies near branch of common carotids
- Monitor blood chemistry
- Transmit signals through glossopharyngeal nerve to brainstem respiratory centers
Adjust respiratory rate to stabilize pH, CO_2, and O_2
Aaortic Bodies: Chemoreceptors
- One to three bodies in walls of aortic arch
- Same structure and function as carotid bodies, but innervation is by vagus nerve
Capillaries
•exchange vessels: site where gasses, nutrients, wastes, and hormones pass between the blood and tissue fluid
–The “business end” of the cardiovascular system
–Composed of endothelium and basal lamina
–Absent or scarce in tendons, ligaments, epithelia, cornea, and lens of the eye
Capillary Types
–Three capillary types distinguished by ease with which substances pass through their walls (permeability):
- continuous capillaries
- fenestrated capillaries
- sinusoids
Continuous Capillaries
–Continuous capillaries:
Location: occur in most tissues
Structure:
- Endothelial cells have tight junctions forming a continuous tube with intercellular clefts
- Allow passage of solutes such as glucose
- Pericytes wrap around the capillaries and contain the same contractile protein as muscle
Function:
–Contract and regulate blood flow
Fenestrated Capillaries
Location: kidneys, small intestine
Structure:
- Organs that require rapid absorption or filtration
- Endothelial cells riddled with holes called filtration pores (fenestrations)
–Spanned by very thin glycoprotein layer
Allow passage of only small molecules
Function:
- Allow for rapid absorbtion/ filtation
- Allow passage of only small molecules
Sinusoid Capillaries
–Sinusoids (discontinuous capillaries):
Location: liver, bone marrow, spleen
Structure:
•Irregular blood-filled spaces with large fenestrations
Function:
•Allow proteins (albumin), clotting factors, and new blood cells to enter the circulation
Capillary Beds: Structure
•Capillary beds are networks of 10-100 capillaries
–Usually supplied by a single arteriole or metarteriole
–At distal end, capillaries transition to venules or drain into a throroughfare channel (continuation of metarteriole)
Capillary Beds: Arteriole constriction AND pre-capillary sphincters (relax/ contraction)
–At any given time, three-fourths of body’s capillaries are shut down
- Most control of flow involves constriction of arterioles that are upstream from the capillaries
- Within the capillary bed, precapillary shincters control flow
–When sphincters are relaxed, capillaries are well perfused with blood
–When sphincters contract, they constrict the entry to the capillary and blood bypasses the capillary
Veins: Struture & Function
Structure:
- Greater capacity for blood containment than arteries
- Thinner walls, flaccid, less muscular and elastic tissue
Function:
- Collapse when empty, expand easily
- Have steady blood flow
- Merge to form larger veins
- Subjected to relatively low blood pressure
–Averages 10 mm Hg with little fluctuation
Vein Types
- Post Capillary Venules- smallest veins
- Muscular Venules- up to 1 mm in diameter
- Medium Veins- up to 10 mm in diameter
- Venuous Sinuses
- Large Veins- > 10 mm in diameter
Post Capillary Veins; Structure/ Function
–Smallest Veins
Structure/ Function:
–Even more porous than capillaries so also exchange fluid with surrounding tissues
–Tunica interna with a few fibroblasts and no muscle fibers
–Most leukocytes emigrate from the bloodstream through venule walls
Muscular Veins: Structure/ Function
Structure/ Function:
-Up to 1 mm in diameter
–One or 2 layers of smooth muscle in tunica media
–Have a thin tunica externa
Medium Veins: Structure/ Function
Structure/ Function:
•up to 10 mm in diameter
–Thin tunica media and thick tunica externa
–Tunica interna forms venous valves
–Varicose veins result in part from the failure of these valves
–Skeletal muscle pump propels venous blood back toward the heart
Venous Sinuses: Structure/ Function
–Veins with especially thin walls, large lumens, and no smooth muscle
–Dural venous sinus and coronary sinus of the heart
–Not capable of vasomotor responses
Large Veins: Structure/ Function
–Some smooth muscle in all three tunics
–Thin tunica media with moderate amount of smooth muscle
–Tunica externa is thickest layer
•Contains longitudinal bundles of smooth muscle
–Venae cavae, pulmonary veins, internal jugular veins, and renal veins
Varicose Veins
•Blood pools in the lower legs of people who stand for long periods stretching the veins
–Cusps of the valves pull apart in enlarged superficial veins, further weakening vessels
–Blood backflows and further distends the vessels, their walls grow weak and develop into varicose veins
- Hereditary weakness, obesity, and pregnancy also promote problems
- Hemorrhoids are varicose veins of the anal canal
Circulatory Routes: Simplest
•Simplest and most common route for blood
– Heart > arteries > arterioles > capillaries > venules > veins
–Passes through only one network of capillaries from the time it leaves the heart until the time it returns
Capillary Exhange
- The most important blood in the body is in the capillaries
- Only through capillary walls are exchanges made between the blood and surrounding tissues
- Capillary exchange—two-way movement of fluid across capillary walls
–Water, oxygen, glucose, amino acids, lipids, minerals, antibodies, hormones, wastes, carbon dioxide, ammonia
Circulatory Routes: Portal System
–Blood flows through two consecutive capillary networks before returning to heart
- Between hypothalamus and anterior pituitary
- In kidneys
- Between intestines to liver
Capillary Exchange: Three Routes/ Openings
•Chemicals pass through the capillary wall by three routes
- Through endothelial cell cytoplasm
- Intercellular clefts between endothelial cells
- Filtration pores (fenestrations) of the fenestrated capillaries
Circulatory Routes: Anastomosis
convergence point between two vessels other than capillaries
Capillary Exchange: Mechanisms Involved
–Diffusion, transcytosis, filtration, and reabsorption
Circulatory Route: Arteriovenous Anastomosis
(shunt)
Artery flows directly into vein, bypassing capillaries
Capillary Exchange Mechanism: Diffusion
•Diffusion is the most important form of capillary exchange
–Glucose and oxygen, being more concentrated in blood, diffuse out of the blood
–Carbon dioxide and other waste, being more concentrated in tissue fluid, diffuse into the blood
•Capillary diffusion can only occur if:
–The solute can permeate the plasma membranes of the endothelial cell, or
–Find passages large enough to pass through
•Filtration pores and intracellular clefts
Circulatory Route: Venous Anastomosis
–Most common
–One vein empties directly into another
–Reason vein blockage is less serious than arterial blockage
Difussion: molecules & passivity
1.Lipid-soluble substances
–Steroid hormones, O_2, and CO_2 diffuse easily through plasma membranes
2.Water-soluble substances
–Glucose and electrolytes must pass through filtration pores and intercellular clefts
3.Large particles such as proteins held back
Circulatory Route: Arterial Anastomosis
–Two arteries merge
–Provides collateral (alternative) routes of blood supply to a tissue
–Coronary circulation and common around joints
Capillary Exchange Mechanism: Transcytosis
- endothelial cells pick up material on one side of their membrane by pinocytosis or receptor-mediated endocytosis, transport vesicles across cell, and discharge material on other side by exocytosis
- Important for fatty acids, albumin, and some hormones (insulin)
Capillary Exchange Mechanism: Filtration & Reabsorbtion
- Fluid filters out of the arterial end of the capillary and osmotically reenters at the venous end
- Delivers materials to the cell and removes metabolic wastes
- Opposing forces:
–Blood hydrostatic pressure drives fluid out of capillary
•High on arterial end of capillary, low on venous end
–Colloid osmotic pressure (COP) draws fluid into capillary
- Results from plasma proteins (albumin)—more in blood
- Oncotic pressure = net COP (blood COP − tissue COP)
- Hydrostatic pressure
–Physical force exerted against a surface by a liquid
- Blood pressure in vessels is hydrostatic pressure
- Capillaries reabsorb about 85% of the fluid they filter
- Other 15% is absorbed by the lymphatic system and returned to the blood
The Forces of Capillary Filtation and Reabsorbtion
- Capillary filtration at arterial end
- Capillary reabsorption at venous end
- Variations
–Location
- Glomeruli—devoted to filtration
- Alveolar capillary—devoted to absorption
–Activity or trauma
Increases filtration
Variations in Capillary Filtration and Reabsorbtion
- Capillaries usually reabsorb most of the fluid they filter with certain exceptions
–Kidney capillaries in glomeruli do not reabsorb
–Alveolar capillaries in lung absorb completely to keep fluid out of air spaces
- Capillary activity varies from moment to moment
–Collapsed in resting tissue, reabsorption predominates since BP is low
–Metabolically active tissue has increase in capillary flow and BP
•Increase in muscular bulk by 25% due to accumulation of fluid
Edema
•accumulation of excess fluid in a tissue
–Occurs when fluid filters into a tissue faster than it is absorbed
Edema Causes: 3 Types
1.Increased capillary filtration
•Kidney failure, histamine release, old age, poor venous return
2.Reduced capillary absorption
•Hypoproteinemia, liver disease, dietary protein deficiency
3.Obstructed lymphatic drainage
•Surgical removal of lymph nodes
Venous Return
•the flow of blood back to the heart; relies on: pressure gradient, gravity, skeletal muscle pump, thoracic pump, and cardiac suction
Edema Types
1.Tissue necrosis
–Oxygen delivery and waste removal impaired
2.Pulmonary edema
–Suffocation threat
3.Cerebral edema
–Headaches, nausea, seizures, and coma
4.Severe edema or circulatory shock
–Excess fluid in tissue spaces causes low blood volume and low blood pressure
Venous Return: Mechanisms
1.Pressure gradient
- Blood pressure is the most important force in venous return
- 7 to 13 mm Hg venous pressure toward heart
- Venules (12 to 18 mm Hg) to central venous pressure: point where the venae cavae enter the heart (~5 mm Hg)
2.Gravity drains blood from head and neck
3.Skeletal muscle pump in the limbs
•Contracting muscle squeezes blood out of the compressed part of the vein
4.Thoracic (respiratory) pump
•Inhalation—thoracic cavity expands and thoracic pressure decreases, abdominal pressure increases, forcing blood upward
–Central venous pressure fluctuates
- 2 mm Hg—inhalation, 6 mm Hg—exhalation
- Blood flows faster with inhalation
5.Cardiac suction of expanding atrial space
Skeletal Muscle Blood Flow
- Variable blood flow depending on state of exertion
- At rest
–Arterioles constrict, most capillary beds shut down
–Total flow about 1 L/min.
•During exercise
–Arterioles dilate in response to muscle metabolites such as lactate, CO_2, and H^+
–Blood flow can increase 20-fold
- Blood is diverted from digestive and urinary organs
- Muscular contraction impedes flow
–Isometric contraction causes fatigue faster than intermittent isotonic contractions
Lung Blood Flow
- Low pulmonary blood pressure
- Flow slower, more time for gas exchange
–Oncotic pressure overrides blood (hydrostatic) pressure
- Pulmonary capillaries absorb fluid (almost no filtration)
- Prevents fluid accumulation in alveolar walls and lumens
- Unique response to hypoxia
–Pulmonary arteries constrict in diseased area
–Redirects flow to better ventilated region
Circulatory Shock
•any state in which cardiac output is insufficient to meet the body’s metabolic needs
Hypertenson: The Silent Killer
- Hypertension—most common cardiovascular disease affecting about 30% of Americans over 50
- “The silent killer”
–Major cause of heart failure, stroke, and kidney failure
•Damages heart by increasing afterload
–Myocardium enlarges until overstretched and inefficient
•Renal arterioles thicken in response to stress
–Drop in renal BP leads to salt retention (aldosterone) and worsens the overall hypertension
Circulatory Shock Types
- Cardiogenic Shock
- Low Venous Return Shock- 3 types:
- Hypovolemic shock (most cemmon)
- Obstructed venous return shock
- Venous Pooling (vascular) shock) - Neurogenic Shock
- Septic Shock
- Anaphalatic Shock
- Compensated Shock
- Decompensated Shock
Lymphatic System Function: Fluid Recovery
–Fluid continually filters from the blood capillaries into the tissue spaces
- Blood capillaries reabsorb 85%
- 15% (2 to 4 L/day) of the water and about half of the plasma proteins enter the lymphatic system and then are returned to the blood
Circulatory Shock: Cardiogenic Shock
–inadequate pumping of heart (MI)
Lymphatic System Function: Immunity
–Excess filtered fluid picks up foreign cells and chemicals from the tissues
- Passes through lymph nodes where immune cells stand guard against foreign matter
- Activates a protective immune response
Circulatory Shock: Low Venous Return (LVR)
cardiac output is low because too little blood is returning to the heart
Lympathic System Function: Lipid Absorbtion
–Lacteals in small intestine absorb dietary lipids that are not absorbed by the blood capillaries
LVR Shock: Hypovolemic Shock
•most common
–Loss of blood volume: trauma, burns, dehydration
Lymphatic System: Parts
- Lymph: the recovered fluid
- Lymphatic vessels: Transport the lymph
- Lymphatic tissues: composed of aggregates of lymphocytes and macrophages that popoulate many organs in the body
- Lymphatic organs: defense cells are especaially concentrated in these organs. They are seperated from surrounding organs by connective tissue capsules
LVR Shock: Obstructed Venous Return Shock
–Tumor or aneurysm compresses a vein
Lymph: Structure/ Function
–Clear, colorless fluid, similar to plasma, but much less protein
–Originates as extracellular fluid drawn into lymphatic capillaries
–Chemical composition varies in different places (in intestines, after lymph nodes)
LVR Shock: Venous Pooling (Vascular) Shock
–Long periods of standing, sitting, or widespread vasodilation
Lymphatic Vessels- Capillaries: Structure/ Function
-Also called terminal lymphatics
–Penetrate nearly every tissue of the body
•Absent from cartilage, cornea, bone, and bone marrow
–Capillary wall is endothelial cells overlapping each other like roof shingles
–Closed at one end
–Cells tethered to surrounding tissue by protein filaments
•Gaps between cells are large enough to allow bacteria and cells to enter lymphatic capillary
–Endothelium creates valve-like flaps that open when interstitial fluid pressure is high, and close when it is low
Neurogenic Shock
•loss of vasomotor tone, vasodilation
–Causes from emotional shock to brainstem injury
Lymphatic Vessels- Larger Ones: Structure/ Function
•Larger ones composed of three layers
–Tunica interna: endothelium and valves
–Tunica media: elastic fibers, smooth muscle
–Tunica externa: thin outer layer
- Converge into larger and larger vessels
- Collecting vessels course through many lymph nodes
Septic Shock
–Bacterial toxins trigger vasodilation and increased capillary permeability
Lymphatic Vessels: Six Lymphatic Trunks
- Jugular
- Subclavian
- Bronchomediastinal
- Intercostal
- Intestinal (unpaired)
- Lumbar
Anaphaletic Shock
–Severe immune reaction to antigen, histamine release, generalized vasodilation, increased capillary permeability
Lymphatic Vessels: Two Collecting Ducts
- Right Lymphatic Duct: receives lymph from right arm, right side of head and thorax; empties into right subclavian vein
- Thoracic Duct: –larger and longer, begins as a prominent sac in abdomen called the cisterna chyli; receives lymph from below diaphragm, left arm, left side of head, neck, and thorax; empties into left subclavian vein
Circulatory Shock: Responses
1.Compensated shock
–Several homeostatic mechanisms bring about spontaneous recovery
•Example: If a person faints and falls to a horizontal position, gravity restores blood flow to the brain
2.Decompensated shock
–When compensation fails
–Life-threatening positive feedback loops occur
–Condition gets worse causing damage to cardiac and brain tissue
Flow of lymph
- Lymph flows under forces similar to those that govern venous return, except no pump (heart)
- Lymph flows at low pressure and slower speed than venous blood
- Moved along by rhythmic contractions of lymphatic vessels
–Stretching of vessels stimulates contraction
Brain Blood Flow
•Total blood flow to the brain fluctuates less than that of any other organ (700 mL/min.)
–Seconds of deprivation causes loss of consciousness
–Four to 5 minutes causes irreversible brain damage
–Though total flow is constant, blood is shifted to active brain areas from moment to moment
Lymphatic Vessels: Subclavian Veins
collect from thoracic duct
Brain Blood Flow 2
•Brain regulates its own blood flow to match changes in BP and chemistry
–Cerebral arteries dilate as systemic BP drops, constrict as BP rises
–Main chemical stimulus: pH
- CO_2+ H_2 O →H_2 CO_3® H^++〖(HCO_3)〗^-
- Hypercapnia—CO_2 levels increase in brain, pH decreases, triggers vasodilation
- Hypocapnia—raises pH, stimulates vasoconstriction
–Occurs with hyperventilation, may lead to ischemia, dizziness, and sometimes syncope
Flow of Lymph: Mechanisms
- Flow aided by skeletal muscle pump
- Arterial pulsation rhythmically squeezes lymphatic vessels
- Thoracic pump aids flow from abdominal to thoracic cavity
- Valves prevent backward flow
- Rapidly flowing blood in subclavian veins, draws lymph into it
- Exercise significantly increases lymphatic return
Hypercapnia vs Hypocapnia
- Hypercapnia—CO_2 levels increase in brain, pH decreases, triggers vasodilation
- Hypocapnia—raises pH, stimulates vasoconstriction
–Occurs with hyperventilation, may lead to ischemia, dizziness, and sometimes syncope
Lymphatic Cell Types
- Natural killer (NK) cells
- T lymphocytes (T cells)
- B lymphocytes (B cells)
- Macrophages
- Dendritic Cells
- Reticular Cells
Transient Ischemic Attacks (TIAs)
•brief episodes of cerebral ischemia
–Caused by spasms of diseased cerebral arteries
–Dizziness, loss of vision, weakness, paralysis, headache, or aphasia
–Lasts from a moment to a few hours
Often early warning of impending stroke
Lymphatic Cell: Natural Killer Cells
–Large lymphocytes that attack and destroy bacteria, transplanted tissue, host cells infected with viruses or that have turned cancerous
Stroke (or Cerebral Vascular Accident)
–Sudden death of brain tissue caused by ischemia
•Atherosclerosis, thrombosis, ruptured aneurysm
–Effects range from unnoticeable to fatal
•Blindness, paralysis, loss of sensation, loss of speech common
–Recovery depends on surrounding neurons, collateral circulation
Lymphatic Cell: T Cells
Mature in thymus
Lymphatic Cells: B Cells
-Mature/ Develop in the bone marrow
–Activation causes proliferation and differentiation into plasma cells that produce antibodies
Lymphatic Cells: Macrophages
–Large, avidly phagocytic cells of connective tissue
–Develop from monocytes
–Phagocytize tissue debris, dead neutrophils, bacteria, and other foreign matter
–Process foreign matter and display antigenic fragments to certain T cells alerting immune system to the presence of the enemy
–Antigen-presenting cells (APCs)
Lymphatic Cells: Dendritic Cells
–Branched, mobile APCs found in epidermis, mucous membranes, and lymphatic organs
–Alert immune system to pathogens that have breached the body surface
Hypertension Types
1.Primary:
–Obesity, sedentary behavior, diet, nicotine
–90% of cases
2.Secondary:
–Kidney disease, atherosclerosis, hyperthyroidism, Cushing syndrome
–10% of cases
Lymphatic Cells: Reticular Cells
–Branched stationary cells that contribute to the stroma of a lymphatic organ