Cardiovascular system I: Blood Vessels & Circulation

Circulatory System

heart, bus & blood

Cardiovascular system

heart & bvs

Cardiology

heart function/dysfunction & treatment

What do both systems do?

Function for transport, protection & regulation of various substances

Blood

Key tissue for functions. (Adults have 4-6L of blood)

Hemopoiesis

blood production

• produce 400 billion platelets, 100-200 billions RBCs & 10 billion WBCs daily

Leukopoiesis (Hemopoiesis)

WBC production

• lymphopoiesis

• myelopoiesis

Erythropoiesis (Hemopoiesis)

RBC production

Thrombopoiesis (Hemopoiesis)

Platelet production

Yolk Sac (Hemopoiesis)

Early site of hemopoiesis

• Later occurs in liver, spleen & eventually in the red bone marrow

Mesenchymal cells (Hemopoiesis)

Differentiate into hematopoietic stem cells (hemocytoblasts)

• Then divide into hemocytoblasts, lymphoid stem cells or myeloid stem cells

Lymphoid Stem Cells (Hemopoeisis)

Leave the bone marrow and move into parts of the lymphatic system

• Give rise to lymphoblasts, which differentiate into lymphocytes

Lymphocytes (Hemopoesis)

Inclue B-cells, T-cells and natural killer cells (NK)

Myeloid stem Cells (Hemopoesis)

These cells differentiate into

• Megakaryoblasts

• Proerythroblasts

• Myeloblasts

• Monoblasts

Megakaryoblasts (Hemopoiesis)

Fragment into platelets

Proerythroblasts(Hemopoesis)

Lose nuclei to form reticulocytes - erythrocytes

Myeloblasts (Hemopoesis)

Form granulocytes (basophils, neutrophils & eosinophils)

Monoblasts (Hemopoesis)

Become monocytes

Megakaryoblasts (Thrombopoiesis)

Form multinucleate megakaryocytes

Megakaryocytes (Thrombopoiesis)

Produce pseudopodia that become proplatelets

Proplatelets (Thrombopoiesis)

Extend into the bloodstream & break into platelets

How many platelets does one megakaryocytic produce? (Thrombopoiesis)

1,000-3,000 platelets

Hemostasis

Stops bleeding of injured vessels

• Platelets involved in forming clots

What are the steps of hemostasis

Vascular spasm, primary hemostasis, secondary hemostasis

Vascular spasm (Hemostasis)

Vessel constricts to minimize blood loss

Primary hemostasis (Hemostasis)

Platelets rush to injury site & forms temporary plug

Secondary hemostasis (Hemostasis)

Coagulation cascade is activated, bringing fibrin (protein) to create a stable clot

Blood Vessel Anatomy

Walls with three layers (tunics)

Tunica interna= intima (Blood Vessel anatomy)

Endothelium + connective tissue layers

• simple squamous epithelium over BM

• selectively permeable

• secrets dilators/constrictors

• normally repels blood cells/platelets

• produce cell-adhesion molecules if inflamed- causes WBC congregation

Tunica Media (Blood Vessel anatomy)

Smooth muscle, collagen & elastics

• Strengthens vessels

• prevents rupture from increases bp

• regulates bv diameter

  • vasoconstriction + vasodilation

Tunica externa = adventitia (Blood Vessel anatomy)

• loose connective tissues

• anchors blood vessels, often by merging w surrounding tissues

• provides passage for small nerves & lymphatics

  • -entry sites for vasa vasorum

  • small vessels supplying larger vessels

  • -entry site for Nervi vasorum

  • small nerves supplying muscle tissues

Arteries

• Thick tunic media; thin tunica externa

• classified by size

Conduction (Arteries)

• Elastic tissue layers

• Expand in systole/recoil in diastole

  • relieves/maintains downstream pressure

• E.g aorta, carotids, etc.

Distributing (Arteries)

• A.K.A = muscular arteries

• Distributes to specific organs

• ¾ of wall thickness = smooth muscle layers

Resistance (Arteries)

• aka small arteries

• typically don’t have individual names

• little elastic tissue (tunica media almost completely smooth muscle)

Arterioles (Arteries)

• smallest (1-3 laters of smooth muscle & thin tunica externa)

• Control amounts of blood to tissues/organs

• metarterioles link arterioles to capillaries

  • pre capillary muscular sphincters around entrances to capillaries

Veins

• Greater capacity for blood containment

  • thinner, flaccid walls

  • less muscular & elastic tissues

  • easily expand; collapse when empty

• have steady blood flow

  • low bp (10mm Hg)

• Merge to form larger veins

  • tributary systems

Venules (Veins)

• post capillary vules

  • more porous than capillaries

  • exchange fluid w surrounding tissues

  • lack muscle fibers

  • most wbcs enter circulation via these types of venules

• muscular venules

  • 1-2 layers of smooth muscle

  • thin externa

Medium veins (Veins)

• thin media & thick externa

• tunica interna forms venous valves

  • prevents backflow

  • -skeletal muscle propels blood back to heart

Large veins (Veins)

• some smooth muscle in all three tunics

• externa thickest layer- longitudinal bundles of smooth muscle

• E.g ivc, sec, pulmonary veins, jugulars etc.

Venous return depends on what

Pressure gradients, gravity, skeletal muscle pump, thoracic pump, cardiac suction

Pressure gradients (Venous Return)

• bp lower towards the heart

• 12-18mmHg in venules

• 5mmHg in ivc, ivc near entry to the heart

Gravity (Venous Return)

trains from head to neck

Skeletal muscle pump (Venous Return)

• against gravity in the limbs

• muscle contraction squeezes blood out between valves

Thoracic Pump (Venous Return)

• changes in thoracic & abdominal pressure force blood upwards

• faster flow during inhalation than exhalation

Cardiac suction (Venous Return)

• expanding atrial space

Venous return increases w exercise

• increased cardiac output, bp, vessel diameter, respiratory rate (activity of thoracic pump) & activity of the skeletal muscle pump

Inactivity can lead to (Venous Return)

venous pooling

• venous pressure can’t push blood against gravity

• prolonged standing - low cardiac output-dizziness & possible fainting/loss of consciousness

• problematic for bed-ridden patients

• important for jet pilots & astronauts to have pressurized suits

Capillaries

• exchange vessels for gases, nutrients, wastes & hormones

Endothelium + basal lamina (Capillaries)

• absent/scare in tendons, ligaments, epithelia, cornea & lens

Capillary beds (Capillaries)

• networks of 10-100 cpaillaries

• typically supplied by single arteriole

• use of pre capillary sphincters to control flow

• transition into venules

• body typically has ¾ of capillaries shut down

Three types of capillaries that are based on permeability (Capillaries)

• continuous

• fenstrated

• sinusoids

Continuous (Capillaries)

• allow passage of solutes as cells have tight junctions forming tube

• can contract

fenestrated (Capillaries)

• holes for filtration in organs that require rapid absorption/filtration (in kidneys & si)

sinusoids (Capillaries)

• irregular blood-filled spaces with large holes for passing proteins, clotting factors & new blood cells into circulation (in liver, bone marrow & spleen)

Simplest pathway (Circulatory routes)

• 1 capillary bed

Portal system (Circulatory routes)

• 2 capillary beds

• e.g liver & intestines

arteriovenous anastomosis= shunts (Circulatory routes)

• bypasses capillary beds

• anatomical insurance for blood circulation

• venous anastomoses

  • most common

• arterial anastomoses

  • common around joints

Blood supply

Blood supply to tissues

Blood flow (Blood supply)

• volume of blood flowing through ha tissue I na given time (mL/min)

  • impacted by pressure & resistance

  • - resistance - opposes flow

  • - pressure - causes flow using pressure gradients

  • liquid moves from high-pressure to low-pressure

perfusion (Blood supply)

• flow relative to tissue mass in a given time (mL/min./g)

Peripheral resistance is opposition to blow flow impacted by

• blood viscosity

• vessel length

• vessel radius

blood viscosity (Peripheral Resistance)

• Increased by rbcs & albumin

• decreased by anemia & low protein

vessel length (Peripheral Resistance)

• liquid encounters more cumulative friction over distance

• pressure & flow decline

Vessel radius (Peripheral Resistance)

• greatest influence on flow

• blood flow is proportional to vessel radius

  • small change to radius can have big impacts on flow

  • laminar flow- layers of flow (faster in center)

  • can be changed by vasoreflexes- affect velocity

blood pressure - bp

• force exerted on vessel walls

  • determined by cardiac output, resistance to flow & blood volume (regulated by kidneys)

• bp in veins fairly steady

  • lower than arteries

• bp in arteries pulsates

  • higher than veins

sphygmomanometer (Blood pressure)

brachial artery gives a close approximation of pressure exiting heart

• reads systolic pressure

• - peak BP in contraction

• reads diastolic pressure

• -minimum bp in relation

• Normal- 120/80 mmHg

Hypertension (Blood pressure)

bp too high

hypotension (Blood pressure)

bp too low