Ch. 19: Blood Vessels

Lumen

The inside space or channel of a vessel

Arteries

carry blood away from heart. designed to withstand surges of pressure

Veins

carry blood towards heart, act as blood reservoir

Tunica Intima

Innermost layer; selectively permeable simple squamous endothelium; secretion of chemicals, repels blood cells/platelets, inflammation; only one with capillaries

Tunica Media

Middle layer; smooth, elastic muscle for vasomotion (constriction/dilation) and strengthen vessels

Tunica Externa

Outermost layer; loose connective tissue; anchors and protects the vessel, passage for nerves and lymphatic vessels; vaso vasorum

Vaso Vasorum

Small vessels that supply blood to the walls of larger vessels

Elastic Arteries

largest diamater(aorta, pulmonary trunk); expand during systole and recoil during diastole to reduce the effects of blood pressure surges

Muscular Arteries

contain the thickest layer of smooth muscle to adjust blood flow to specific organs based on demand(brachial and femoral artery)

Arterioles

Resistance vessels that lead into capillary bed; primary control of blood flow and peripheral resistance, affects BP

Capillaries

Microscopic vessels where nutrient and gas exchange occurs b/w blood and interstital fluid; types: continuous, fenestrated, sinusoids

Continuous Capillaries

• Location: most tissues

• Structure: tightly joined cells (few gaps)

• Function: lets small molecules pass, blocks large ones→ intracellular clefts

Fenestrated Capillaries

have holes (fenestrations) in the walls that allow larger materials to pass. Found in intestines, kidneys, endocrine glands

Sinusoids

Leaky, irregular capillaries in the liver, spleen, and bone marrow that allow cells to pass

Capacitance Vessels

Veins; act as blood reservoirs holding ~60% of blood at rest

Post capillary venules

• Tunica intima

• Extremely porous

Muscular venules

• Thin tunica media

• Thin tunica externa

Medium veins

• Have all 3 tunics

• Thick tunica media

• Large lumen

• Contain valves

Venous sinuses

• Thin walls, no smooth muscle

• Very large lumens

• No vasoconstriction

• Example: Coronary sinus

Large veins

• Have all layers

• Thick tunica externa (outer layer)

• No valves

Anastomoses

Vessel connections providing collateral pathways for blood flow

Physiology of Circulation

• blood flow(ml/min): volume of blood through tissue in a given time

• blood pressure(mmHg): force of bloood exerted on a vessel wall

• blood perfusion(ml/min/g): flow through the capillaries

Cerebral Arterial Circle(Circle of Willis)

ring shaped arteries at the base of the brain that connects the internal carotid and vertebral artery pathways to provide collateral blood flow

Peripheral Resistance (PR)

Friction that opposes blood flow through vessels- blood vessel diameter

Vessel Diameter

The most influential factor affecting peripheral resistance, controlled by ANS ; vasomotion, Smaller radius/diameter creates more resistance

Vessel Length

• Directly proportional to resistance

• Inversely proportional to flow

• ex: weight gain w angiogenesis

Blood Viscosity

• Directly proportional to resistance

• Inversely proportional to flow

• ex: increased hematocrit increases thickness of blood

Skeletal Muscle Pump

Muscle contractions that propel venous blood toward the heart

Respiratory Pump

• Inhalation ↓ intrathoracic pressure

• ↑ intraabdominal pressure (diaphragm contracts)

• Compresses abdominal veins

• Blood flows from high → low pressure (toward heart)

Short-term Neural BP Regulation

Controlled by the medulla oblongata via autonomic reflexest (baroreflex and chemoreflex) to rapidly adjust heart rate and vessel diameter

Baroreflex

Negative feedback mechanism for short-term blood pressure regulation; reduce HR, CO, and BP and dilates vessel

Chemoreflex

Response to pH(decrease), O2(decrease), or CO2(increase) changes; primarily adjusts breathing, secondarily increases perfusion

Transcytosis

Movement of specific macromolecules across endothelial cells via vesicles

Pinocytosis

non specific form of transcytosis

Blood flow through tissues

• intrinsic controls: autoregulation

• extrinsic controls: nervous and endocrine system

Capillary exchange of nutrients- Delivery

blood→ capillary→ interstitial space→ tissue

• o2, glucose, AA, lipids, minerals, hormones

• velocity slows blood to allow exchange

Mesenteric Artery

supplies blood to the intestines

Capillary exchange of nutrients- Removal

tissue→ interstitial space→ capillary→ blood

• Co2, ammonia, other wastes