Blood Vessels

BLOOD VESSELS & HEMODYNAMICS

FUNCTION OF CIRCULATORY SYSTEM (START OF LECTURE VIDEO# 1)

  • General Purpose

    • Carries blood to and from the heart to the tissues of the body and back

    • Exchange of substances

    • Nutrients, waste products, and gases (Oxygen & Carbon Dioxide)

      • Oxygen and nutrients diffuse from blood to cells

      • Carbon dioxide diffuses from cells to blood vessels

  • Transport Functions

    • Carries hormones, enzymes, gases

    • Directs blood flow

    • Volume of blood transported is critical for maintaining homeostasis

TYPES OF BLOOD (CATEGORIES)

  • Arteries

    • Thick muscular walls

    • Located beneath the skin

    • Carry oxygenated blood from the heart to tissues

    • Arterioles: Small arteries connecting to capillaries

  • Capillaries

    • Small blood vessels with thin walls

    • Site for substance exchange between blood and body tissues

  • Veins

    • Characterized by thin walls

    • Contain valves to prevent backflow

    • Located closer to skin surfaces

    • Convey deoxygenated blood from tissues back to the heart

    • Venules: Connect capillaries to larger veins

  • Vaso Vasorum

    • Small blood vessels supplying blood to the cells of the walls (tunica externa) of arteries and veins

FEATURES OF BLOOD VESSELS (LAYERS/TUNICS) (END OF LECTURE VIDEO# 1)

  • Tunica Intima:

    • Internal layer composed of endothelial cells (simple squamous), basement membrane, and lamina propria

    • Lamina propria made up of elastic/collagen membrane separating the intima from the media

  • Tunica Media:

    • Middle layer made up of smooth muscles and elastic/collagen fibers

    • Controls diameter of blood vessels under sympathetic control

    • Vasoconstriction: Decreases blood vessel diameter

    • Vasodilation: Increases blood vessel diameter

  • Tunica Externa:

    • Outer layer made up of dense connective tissues and loose connective tissues

TYPES OF ARTERIES (START OF LECTURE VIDEO# 2)

  • Elastic Arteries

    • Large arteries with more elastic fibers and fewer smooth muscle layers (6-7)

    • Conduct blood from the heart to medium-sized muscular arteries

    • Example: Aorta

  • Muscular Arteries

    • Medium-sized arteries with more muscle than elastic fibers in the tunica media

    • Capable of greater vasoconstriction and vasodilation to adjust blood flow

    • Thicker walls

    • Known as distributing arteries

    • Examples: Brachial and axillary

  • Arterioles

    • Small arteries delivering blood to capillaries

    • Tunica media with 2-3 layers of smooth muscle

    • Metarterioles: branches into capillary beds, connecting arterioles to capillaries

VENULES

  • Small veins that collect blood from capillaries

  • Tunica media with only a few smooth muscle cells and scattered fibroblasts

VEINS

  • Composed of the same three tunics as arteries but have:

    • A thinner tunica interna and media

    • A thicker tunica externa

    • Less elastic tissue and smooth muscle

    • Thinner-walled compared to arteries

    • Valves to prevent backflow of blood

TYPES OF CAPILLARIES (END OF LECTURE VIDEO# 2)

  • Continuous Capillaries

    • Small intercellular clefts (gaps between neighboring cells)

    • Found in skeletal and smooth muscle and lungs

  • Fenestrated Capillaries

    • Mid-sized intercellular clefts

    • Contain large fenestra allowing molecules to leave

    • Found in kidneys, small intestines, choroid plexuses, endocrine glands

  • Sinusoids

    • Very large gaps (intercellular clefts) allowing for leakage of molecules

    • Found in the liver, bone marrow, spleen, anterior pituitary, parathyroid gland

CIRCULATORY ROUTES (START OF LECTURE VIDEO# 3)

  • Pulmonary Circulation

    • Blood flow from the right side of the heart to the lungs and back

  • Systemic Circulation

    • Blood flow from the left side of the heart to the body and back

  • Hepatic Portal Circulation

    • Capillaries of the GI tract to capillaries in the liver

    • More active after food absorption

  • Fetal Circulation

    • Blood flows from the fetal heart through the umbilical cord to the placenta and back

  • Coronary Circulation

    • Blood supply to and from the heart

PULMONARY CIRCULATION (END OF LECTURE VIDEO# 3)

  • Blood transported between the lungs and heart

  • Oxygenation Process

    • Blood releases carbon dioxide into the alveoli of the lungs and takes up oxygen

  • Alveoli: location in the lungs for gas exchange

  • Pathway of Blood Flow

    • Starts from right atrium (deoxygenated blood) → right ventricle → pulmonary trunk → left/right pulmonary arteries → lungs (alveoli) → out through pulmonary veins (oxygenated blood; exits each lung, right and left) → into left atrium → left ventricle → out through the aorta via the aortic semilunar valve

SYSTEMIC CIRCULATION (START OF LECTURE VIDEO# 4)

  • Blood is transported between the heart and other organs

  • Oxygenated blood is pumped into:

    • Left atrium → left ventricle → out through the aorta → into the body

  • Deoxygenated blood returns via the veins → inferior vena cava

SYSTEMIC CIRCULATION: ARTERIAL BRANCHES OF SYSTEMIC CIRCULATION

  • Branches from Aorta

    • Supply arms, head, lower limbs, and all viscera with oxygen (O2) from the lungs

  • Major Divisions of the Aorta

    • Ascending Aorta: branches up from the left ventricle towards the base of the heart

    • Arch of the Aorta: curve between the ascending and descending aorta

    • Descending Aorta: longest part extending into the abdomen/pelvis

    • Thoracic Aorta: located in the thorax/chest

    • Abdominal Aorta: extends into the diaphragm into two pelvic arteries

ARTERIAL BRANCHES OF SYSTEMIC CIRCULATION (UPPER LIMBS)

  • Branches from Aortic Arch

    1. Brachiocephalic Artery

    • Right Common Carotid Artery: supplies the side of the head and neck

      • Right Internal Carotid Arteries: involved in baroreceptor reflex

      • Right External Carotid Arteries: supplies neck and face (e.g., tongue, mouth, thyroid gland, larynx, middle and inner ear)

    1. Right Subclavian Artery: transports blood to the upper limbs

    • Right Vertebral Artery: supplies upper spinal cord, brain stem, cerebellum, posterior part of neck

    1. Left Subclavian Artery: transport blood to the upper limb

    • Left Vertebral Artery: supplies blood to upper spinal cord, brain stem, cerebellum

    • Branches into Basilar Artery: supplies the back of the brain

    • Branches into Left Internal Thoracic: supplies thoracic and abdominal walls

    1. Left Common Carotid Artery

    • Left Internal Carotid Arteries: involves in baroreceptor reflex

    • Left External Carotid Arteries: blood to brain, face, neck

ASCENDING AORTA

  • Coronary Arteries

    • Right and left coronary arteries branch to supply the heart muscle

    • Supply anterior and posterior heart regions

  • Atria: receiving chambers of the heart

  • Pericardium: tissue collection surrounding the heart

  • Pericardial Cavity: fluid-filled space around the heart

  • Coronary Vessels: supply blood to the heart wall

  • Ventricles: larger pumping chambers of the heart

  • Heart Wall Composition

    • Composed of three layers including a thick middle layer of cardiac muscle

LOWER LIMB ARTERIES (BRANCH FROM DESCENDING AORTA)

  • Pathway

    • Left ventricle → ascending aorta → aortic arch → descending aorta → thoracic aorta → abdominal aorta

  • Celiac Trunk

    • Splenic Artery: supplies spleen, pancreas, and stomach

    • Left Gastric Artery: supplies stomach

    • Common Hepatic Artery: supplies liver, gallbladder, small intestines

    • Superior Mesenteric Artery: supplies small intestines, cecum, ascending colon, transverse colon

    • Inferior Phrenic Artery: supplies diaphragm

LOWER LIMB ARTERIES (BRANCH FROM DESCENDING AORTA: END OF LECTURE VIDEO# 4)

  • L/R Suprarenal Arteries: supply adrenal glands

  • L/R Renal Arteries: supply kidneys

  • L/R Gonadal Arteries: supply ovaries/testes

  • Lumbar Arteries: supply back and abdominal wall

  • Inferior Mesenteric Artery: supplies descending colon, sigmoid colon, rectum

  • Common Iliac Artery (Left and Right)

    • Right/Left External Iliac Artery: supplies lower limb and anterior abdominal wall

    • Right/Left Internal Iliac Artery: supplies pelvic organs, genitalia, and hip

VEINS OF THE SYSTEMIC CIRCULATION (START OF LECTURE VIDEO# 5)

  • General Function

    • Drain blood from entire body and return it to the right side of the heart

  • Deep vs. Superficial Veins

    • Deep veins parallel arteries in the region

    • Superficial veins found just beneath the skin

  • Venous Drainage

    • All venous blood drains to either the superior (upper body) or inferior (lower body) vena cava or coronary sinus (heart)

MAJOR SYSTEMIC VEINS

  • Drainage into Right Atrium of the Heart

    • Superior Vena Cava: drains head and upper extremities

    • Inferior Vena Cava: drains abdomen, pelvis, and lower limbs

    • Coronary Sinus: large vein draining heart muscle back into the heart

MAJOR SYSTEMIC VEINS (CONTINUED)

  • Cardiac Veins

    • Transport blood from walls of the heart through the coronary sinus into the right atrium

  • Veins of Head and Neck

    • Brachiocephalic Vein: drains blood from the head, neck, arms back to the heart

    • External Jugular Veins: drain blood from the posterior head and neck

    • Subclavian Veins: right side of the limbs into the right/left brachiocephalic

    • Internal Jugular Veins: drain blood from anterior head, face, and neck

    • Branches directly into R/L brachiocephalic veins

MAJOR SYSTEMIC VEINS (CONTINUED)

  • Internal Thoracic Veins

    • Drain from thoracic and abdominal walls into R/L brachiocephalic veins

    • Ultimately, brachiocephalic veins drain into superior vena cava → right atrium of the heart

MAJOR SYSTEMIC VEINS (UPPER LIMBS)

  • Axillary Vein: drains blood from upper limb and armpit towards the heart

  • Brachial Veins: drain blood from the upper arm (between elbow and shoulder)

  • Radial Veins: drain blood from hand and forearm

  • Ulnar Veins: drain medial aspect of the forearm

  • Median Cubital Vein: returns blood from the forearm

  • Digital Veins: carry blood from the fingers

MAJOR SYSTEMIC VEINS (LOWER BODY)

  • All drain into the inferior vena cava

    • Hepatic Veins: drain liver

    • Gastric Veins: drain blood from the stomach

    • Hepatic Portal Veins: drain blood from liver, gallbladder

    • Superior Mesenteric Vein: drains small intestines, cecum, ascending colon, transverse colon

    • Splenic Vein: drains spleen and pancreas

    • Inferior Mesenteric Vein: drains descending colon, sigmoid colon, upper rectum

  • R/L Lumbar Veins: drain posterior abdominal wall

  • R/L Renal Veins: drain kidneys

  • R/L Suprarenal Veins: drain adrenal medulla

  • R/L Gonadal Veins: drain testis and ovaries

  • R/L Phrenic Veins: drain diaphragm

  • Common Iliac Veins (Left and Right)

    • External Iliac Veins: drain lower limb, anterior abdominal wall

    • Internal Iliac Veins: drain pelvic organs, genitalia, and hip

HEPATIC PORTAL CIRCULATION (START OF LECTURE VIDEO# 6)

  • Collects blood from veins of the pancreas, spleen, stomach, intestines, and gallbladder

  • Directs blood into the hepatic portal vein of the liver before returning to the heart

    • Purpose: Enables nutrient utilization and detoxification by the liver

BLOOD CIRCULATION

  • Distribution

    • 64% of blood volume at rest is in systemic veins and venules; function as blood reservoir

    • Found in veins of skin and abdominal organs (liver and spleen)

    • Blood is diverted in times of need

    • Increased muscular activity produces venoconstriction

    • Hemorrhage causes venoconstriction to help maintain blood pressure

    • 13% of blood volume in arteries and arterioles

LAMINAR AND TURBULENT FLOW IN VESSELS (END OF LECTURE VIDEO# 6)

  • Blood Flow in Vessels

  • Laminar Flow

    • Blood moving in a smooth, streamlined fashion

    • Steady rate in long, smooth vessels

    • Silent sound

  • Turbulent Flow

    • Blood flow is irregular and chaotic

    • Causes murmurs

    • Example: Constriction of blood vessels or an obstruction

  • Reynolds Number

    • Formula: (Re = rac{DV imes P}{N})

    • Where:

      • D = Diameter

      • V = Velocity

      • P = Density

      • N = Viscosity

    • Values:

      • Less than 2000 indicates laminar flow

      • More than 3000 indicates turbulent flow

CONTROL OF BLOOD PRESSURE & FLOW (START OF LECTURE VIDEO# 7)

  • Cardiovascular Center in Medulla Oblongata

    • Helps regulate heart function

    • Specific neurons regulate blood vessel diameter

HEMODYNAMICS: FACTORS AFFECTING BLOOD FLOW

  • Blood Pressure (BP)

    • Pressure exerted on walls of blood vessels; in clinical use, refers to arteries

    • Measurement: Brachial artery is commonly used; measured with a sphygmomanometer

    • Korotkoff Sounds: Sounds heard during pressure measurement

    • Systolic Blood Pressure: Recorded during ventricular contraction

    • Example: 120 mm Hg

    • Diastolic Blood Pressure: Recorded during ventricular relaxation

    • Example: 80 mm Hg

    • Provides information about systemic vascular resistance

BLOOD PRESSURE: RANGES (END OF LECTURE VIDEO# 7)

  • Normal Blood Pressure

    • The normal reading for a young adult male is 120/80 mm Hg

    • Average values can vary based on multiple factors

EVALUATING CIRCULATION

  • Pulse

    • A pressure wave reflecting heartbeats

    • Normal pulse rate: between 70-80 beats/min

    • Tachycardia: Pulse rate over 100 beats/min (SA node signaling faster)

    • Bradycardia: Pulse rate under 60 beats/min (SA node signaling slower)

  • Pulse Points

    • Major pulse points include:

    • Brachial

    • Temporal

    • Carotid

    • Radial

    • Femoral

    • Popliteal

    • Axillary