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Circulatory System: Introduction

Circulatory System: Circulatory System: IntroductionIntroduction

Dr. Carmen E. RexachDr. Carmen E. RexachAnatomy 35Anatomy 35

Mt. San Antonio CollegeMt. San Antonio College

Components

• Cardiovascular system

• Lymphatic system

Cardiovascular system

• Heart, blood vessels, blood

• Functions:– transport of

nutrients, hormones, oxygen, waste, carbon dioxide

Lymphatic system

• Lymph nodes, lymphatic vessels, lymph

• Functions– Immune Response– Absorption of fat

from gi tract (lacteal)– Controlling volume of

interstitial fluid and blood

Cardiovascular system and Lymphatic system work in tandem

Hematology• Study of blood and components• Two parts

– Formed elements• Erythrocytes• Leukocytes• Thrombocytes (Platelets)

– Plasma

Hematocrit

Plasma (Blood Matrix)• Predominately water • Major solutes

– Salts– minerals– bicarbonate buffer– sugars, amino acids, vitamins

Plasma Proteins

• Predominately made in liver• Major plasma proteins

– Albumins– Lipoproteins– Clotting Factors– Globulins

• Including antibodies – Gamma globulins– made by lymphocytes

FormedElements

Formed elements

• Erythrocytes– Red blood cells– anucleate– lack mitochondria– millions of

hemoglobin molecules

– Life span = 3-4 months

Leukocytes• Nonspecific

– Neutrophils– Eosinophils– Basophils– NK cells– Monocytes,

macrophage• Specific

– T-lymphocytes– B-lymphocytes

granulocytes

Neutrophils (PMN’s)• the first WBC at an

infection site• 50-60% of circulating

leukocytes• voracious phagocytes• use lysozyme and

oxygen radicals to destroy microbes

Polymorphonuclear cells….can you tell why?

Eosinophils• slightly phagocytic• Effective against

helminths• Allergic and

hypersensitivity reactions

• Contribute to chronic inflammation

Note the large red stained granules

Basophils• mature into mast cells of

loose connective tissue• Smallest immune

effector cells• Produce:

– heparin • an anticoagulant

– histamine • Vasodilator• increases capillary

permeability• important to

inflammation, especially related to allergies

Note large blue granules

Monocytes

• Become macrophage when activated

• eat microbes cellular debris

• Antigen Presenting Cells– link nonspecific body

defenses to the immune responseLarge C-shaped

nucleus….and no granules!

Diapedesis

macropha

Lymphocytes• Involved in specific

immune response• Present in small

numbers until activated

• T cells primarily circulate, B cells primarily in lymph nodes Large nucleus almost

completely fills cell

Formed elements

• Thrombocytes– Formed by

disintegration of megakaryocytes

– Released into plasma

– Last 3-5 days– Important in blood

clotting

Platelet plug formation

• Activation of platelets makes them sticky

• Results in the formation of a platelet plug when blood vessel is damaged

The Heart• a dual pump (R and L)• Functions:

– 1) unidirectional flow of blood through heart and vessels

– 2) dual pump to lungs and systemic circulation to pick up oxygen, distribute it to tissues, carry CO2 back to lungs to be eliminated

– 3) develops blood pressure by alternate cycles of relaxation and contraction

Layers of heart wall• Endocardium

– Tunica intima of the heart– Composed of simple squamous epithelium + loose CT

• Myocardium– Tunica media – cardiac muscle

• branched• interdigitated• 1 centrally located nucleus• striated• intercalated discs

• Epicardium– Tunica externa or visceral pericardium – simple squamous epithelium and loose CT

• Parietal pericardium– a fibrous CT loose fitting sac – Lined with simple squamous epi.

Four chambers

• Dual pump– Functional

• Pulmonary circuit• Systemic circuit

– Two regions• Atria• Ventricles

Atria• thin walled receiving

chambers• derived from veins• auricles

– folded extensions of the atria

– increase volume• pectinate muscle

– atrial muscle, “honeycomb”appearance

Atria

• R atrium receives blood from the systemic circuit

• Openings– superior vena cava– inferior vena cava– coronary sinus (thebesian

valve)• L atrium receives blood

from the lungs• openings

– from pulmonary veins

Ventricles

• thick walled• pumping chambers derived

from arteries• trabeculae = “crossbars of

flesh”• R ventricle

– thinner wall– pumps to lungs– moderator bands control

the volume of the RV if present

• L ventricle– 2-3 X’s thicker than the RV– pumps to systemic circuit

Septa• cross walls or dividers of the hearts

– interatrial - between atria– interventricular - between ventricles– atrioventricular - between atria and

ventricles

Atrioventricular septum• Two parts

– 1. cardiac skeleton• a fibrous CT skeleton supporting the heart valves and

chambers– 2. heart valves (in the atrioventricular septum)

• atrioventricular (cuspid valves) between atria and ventricles

• semilunar valves between ventricles and major arteries

Atrioventricular valves• Function

– Permit atrioventricular flow– Prevent ventriculoatrial reflux

• Attached to accessory structures– chordae tendineae

• fibrous cords• “heart strings”

– papillary muscles • fingerlike muscles attached to

chordae tendineae• keep valves closed during

ventricular contraction

Semilunar (SLV) valves

• Between ventricles and major arteries– pulmonary trunk– aorta

• Permit– ventriculoarterial flow

• Prevent– arterioventricular reflux

Intrinsic conduction System

• sends rhythmic impulses through the heart to synchronize heart rate and stimulate contraction

• sinoatrial (SA) node– Pacemaker– located in R atrium near the superior

vena cava

Cardiac conduction system• Atrioventricular (AV) node

– first structure used to stimulate contraction of the ventricles, located near the center of the AV septum

• atrioventricular (AV) bundle – Bundle of HIS

• bundle branches – lead to the L and R ventricle respectively

• Purkinje fibers – terminal branches of the conduction system– continuous with cardiac muscle fibers.

Embryonic Development of the Heart

• day 18-20:– the entire embryo is disc shaped– all blood vessels begin as blood islands in splanchnic mesoderm

surrounding the head and neck

For more detailed information, http://pie.med.utoronto.ca/HTBG/HTBG_content/HTBG_heartEmbryologyApp.html

Dorsal view

Development of heart• day 20-21:

– embryo curls– the heart folds into the thorax & becomes a pair of

tubes

Heart Development

• day 22– pair of tubes fuse– heart begins

pumping – 4 bulges develop

(beginning at bottom: venous to arterial)

• sinus venosus• atrium• ventricle• bulbus cordis

Before 2 months

• the heart forms an S shape-

• ventricle moves caudally (to bottom)

• atrium moves cranially (to top)

By 2 months

• 4 distinct chambers develop

• interatrial septum grows caudally (from top to bottom)

• interventricularseptum grows cranially (from bottom to top)

• foramen ovale and a hole in the superior interventricularseptum retained until birth

• bulbus cordis splits into the pulmonary trunk and ascending aorta

Major CVS Circuits• 1. systemic

– high variable resistance circuit– Includes coronary circulation

• the vasa vasorum of the heart

• 2. pulmonary– low, constant resistance circuit