Anaphy

**LESSON 1The Circulatory System**

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The Cardiovascular System

  • A closed system of the heart and blood vessels
      * the heart pumps blood
      * blood vessels allow blood to circulate to all the body parts
  • Functions:
      * transport oxygen, nutrients, cell wastes, hormones to and from cells
  • Size: Fist
  • Weight:
  • Location:
  • Orientation

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Coverings of the Heart

Pericardium - double-walled sac

  • fibrous pericardium
      * loose and superficial
  • serous membrane
      * deep to fibrous pericardium
      * has 2 layers:
        * parietal pericardium
        * visceral pericardium

 

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Coverings of the Heart
  1. Epicardium
  • outside layer; visceral pericardium
  1. Myocardium
  • middle layer
  • mostly cardiac muscle
  1. Endocardium
  • inner layer known as endothelium

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Chambers & Associated Vessels

Interatrial septum

  • separates the two atria longitudinally

Interventricular septum

  • separates the two ventricles longitudinally

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Heart functions as a double pump

  • Arteries carry blood away from the heart
  • Veins carry blood (V)back to the heart

Double Pump

  • Right side works as the pulmonary circuit pump
  • Left side works as the systemic circuit pump

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Pulmonary Circulation

  • blood flows from the right side of the heart to the lungs and back to the left side of the heart
      * blood is pumped out of the right side through the pulmonary trunk, which splits into pulmonary arteries and takes oxygen-blood to lungs
      * oxygen-rich blood returns to the heart from the lungs via pulmonary veins
  • End point is the lungs

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Circulation PathwayLegend: Blue: deoxygenated; Red: oxygenated \n Superior Vena Cava (above diaphragm), Inferior Vena Cava (below diaphragm), Coronary Sinus (heart wall)Right AtriumTricuspid ValveRIght Ventricleincreased pressure would close the tricuspid valve and open the semilunar valvePulmonary Semilunar Valvefound at the base of the pulmonary trunkPulmonary TrunkLeft and Right Pulmonary ArteriesLungsfor oxygenationPulmonary Vein Left Atrium (Start of Systemic Circulation)Bicuspid/Mitral ValveLeft Ventricleincreased pressure would open the aortic valve and close the bicuspid valveAortic Semilunar ValveAortaBody Organs (then back to one)

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Systemic circulation

  • Oxygen-rich blood returned to the left side of the heart is pumped out into the aorta
      * blood circulates to systemic arteries and to all body tissues
      * left ventricle has thicker walls because it pumps blood to the body through the systemic circuit
  • Oxygen-poor blood returns to the right atrium via systemic veins, which empty blood into the superior or inferior vena cava

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Heart Valves

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Heart Valves

  • allow blood to flow in only one direction
  • prevent backflow

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Atrioventricular (AV) valves

  • between atria and ventricles
      * left AV valve : bicuspid (mitral) valve
      * right AV valve : tricuspid valve
  • anchored the cusps in place by chordae tendineae (heart strings) to the walls of the ventricles
  • open during heart relaxation, when blood fills the chamber
      * if atrium has high pressure, AV valves open
  • closed during ventricular contraction
      * if there is high pressure in the ventricles, AV valves close then lilipat yung pressure sa semilunar valves, making them open

 

Semilunar valves

  • between ventricle and artery
      * pulmonary semilunar valve
      * aortic semilunar valve
  • closed during heart relaxation (ventricular filling, passive transportation)
  • open during ventricular contraction (increasing pressure and tension in the ventricle)

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Cardiac Circulation

Cardiac Circulation

  • blood in the heart chambers does not nourish the myocardium
  • the heart has its own nourishing circulatory system:
      * coronary arteries—branch from the aorta to supply the heart muscle with oxygenated blood
      * cardiac veins—drain the myocardium of blood
      * coronary sinus—a large vein on the posterior of the heart; receives blood from cardiac veins
  • Blood empties into the right atrium via the coronary sinus
  • endothelium: prevents the heart from directly absorbing the blood that passes through it

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Physiology of the Heart

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Intrinsic conduction system of the heart

  • cardiac muscle contracts spontaneously and independently of nerve impulses
  • spontaneous contractions occur in a regular and continuous way
  • Atrial cells beat 60 times per minute
      * Smaller and thinner so faster transmission of signals compared to ventricular
  • Ventricular cells beat 20-40 times per minute
  • need a unifying control system—the intrinsic conduction system (nodal system)
      * Creation of local action potential from the atrium to the ventricle

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Normal heart activity: stimulation of atrial cells before ventricular cells

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Two systems regulate heart activity:

  • Autonomic nervous system
  • Intrinsic conduction system (nodal system)
      * sets the heart rhythm
      * composed of special nervous tissue (capable of making and transmitting action potentials)
      * ensures heart muscle depolarization in one direction only (atria to ventricles)
        * Depolarization - change of charge (ex. Sodium potassium pump)
        * Action Potential - charge changes, creating nerve impulses
      * enforces a heart rate of 75 beats per minute
  1. the sinoatrial node (SA node/pacemaker) starts each heartbeat
  • Detecting if there is already blood entering the atria
  1. impulse spreads through the atria to the AV node
  • All the atrial cells have already been depolarized
  1. Atria contract
  • Blood flow from atria to ventricle
  1. At the AV node, the impulse is delayed briefly
  • You need to drain all the blood first
  1. Impulse travels through the AV bundle, bundle branches, and Purkinje fibers (smallest branch)
  • Purkinje makes sure that nerve impulse will reach all cardiac muscle
  1. Ventricles contract; blood is ejected from the heart

 

Tachycardia—rapid heart rate, over 100 beats per minute

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Bradycardia—slow heart rate, less than 60 beats per minutes

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Cardiac cycle and heart sounds

  • the cardiac cycle refers to one complete heartbeat, in which both atria and ventricles contract and then relax
      * systole = contraction
      * diastole = relaxation
  • average heart rate - 75 beats per minute
  • cardiac cycle length is normally 0.8 second

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Cardiac cycle

  • Atrial diastole (ventricular filling)
      * heart is relaxed
      * pressure in heart is low
      * atrioventricular valves are open
      * blood flows passively (higher to lower concentration) from the atria and intro ventricles
      * semilunar valves are closed thus atrioventricular valves are open

 

  • Atrial systole
      * ventricles remain in diastole
      * atria contract
      * AV Node has received the impulse
      * blood is forced into the ventricles to complete ventricular filling

 

  • Isovolumetric contraction
      * atrial systole ends; ventricular systole begins
      * intraventricular pressure rises
      * AV valves close
      * for a moment, the ventricles are completely closed chambers

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  • Ventricular systole (ejection phase)
      * ventricles continue to contract
      * intraventricular pressure now surpasses the pressure in the major arteries leaving the heart
      * semilunar valves open
      * blood is ejected from the ventricles
      * atria are relaxed and filling with blood (simultaneously)

 

  • Isovolumetric relaxation
      * ventricular diastole begins
      * pressure falls below that in the major arteries
      * semilunar valves close
      * for another moment, the ventricles are completely closed chambers
      * when atrial pressure increases above intraventricular pressure, the AV valves open

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Heart sounds

  • Lub
      * longer, louder heart sound caused by the closing of the AV valves
  • Dub
      * short, sharp heart sound caused by the closing of the semilunar valves at the end of ventricular systole

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Cardiac output (CO)

  • amount of blood pumped by each side (ventricle) of the heart in 1 minute
  • Pulse rate x 70 = Cardiac output
      * Normal CO = 5,250 mL

Stroke volume (SV)

  • volume of blood pumped by each ventricle in one contraction (each heartbeat)
  • about 70 ml (60%) of blood is pumped out of is pumped out of the left ventricle with each heartbeat

Heart rate (HR)

  • typically 75 beats per minute
      * 60-70 female, 70-80 male

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Regulation of stroke volume

  • 60% of blood in ventricles (about 70 ml) is pumped with each heartbeat
      * There will be blood left, determining the stretch output to continue the pumping mechanism
  • starling’s law of the heart
      * the critical factor controlling SV is how much cardiac muscle is stretched
      * the more the cardiac muscle is stretched, the stronger the contraction
  • Venous return is the important factor influencing the stretch of heart muscle
      * Actual blood left inside the ventricle

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Factors modifying basic heart rate:

  1. Neural (ANS) controls
  • sympathetic nervous system speeds heart rate (fight or flight)
      * Ex. stress
  • parasympathetic nervous system, primarily vagus nerve fibers, slow and steady the heart rate
      * Complimenting the SNS; normalize
  1. Hormones and ions
  • epinephrine and thyroxine speed heart rate
  • excess or lack of calcium, sodium, and potassium ions also modify heart activity
  1. Physical factors
  • age, gender, exercise, body temperature, influence heart rate

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Blood Vessels

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  • form a closed vascular system that transports blood to the tissues back to the heart
  • vessels that carry blood away from the heart
      * arteries and arterioles
  • Vessels that play a role in exchanges/connections between tissues and blood
      * capillary beds
  • Vessels that return blood
      * venules and veins

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Microscopic Anatomy

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Three layers (tunics) in blood vessels (except the capillaries)

  1. Tunica Intima - friction reducing lining
  • endothelium
  • Capillaries only have tunica intima
  1. Tunica Media
  • smooth muscle and elastic tissue - contract minimally
  • controlled by sympathetic nervous system
  1. Tunica externa - forms protective outermost covering
  • Mostly fibrous connective tissue - anchorage of blood vessels to an organ/tissue
      * Ex. collagen fibers or firmness, resisting the stretching mechanism
  • Supports and protects the vessel

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Vasodilation - increase in the diameter of the lumen of the vessel

Vasoconstriction - decrease in the diameter

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*insert microscopic anatomy

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Structural differences in arteries, veins, and capillaries:

  • Arteries have a heavier, stronger, stretchier tunica media than veins to withstand changes in pressure
  • Veins have a thinner tunica media than arteries and operate under low pressure
      * veins also have valves to prevent backflow of blood
      * Lumen of veins is larger than that of arteries, because arteries have thicker tunica media
      * Skeletal muscle “milks” blood in veins toward the heart
        * Pushes the vessel and increases the pressure in blood that opens the vessels
        * Contractile muscle in smooth muscle is not enough, that's why we rely on the contractions of skeletal muscle
  • Capillaries
      * only one cell layer thick (tunica intima)
      * Allow for exchanges between blood and tissue
      * Forms networks called capillary beds that consist of:
        * A vascular shunt
        * True capillaries - type of branch that is connecting terminal arteriole to post capillary venule
      * blood flow through a capillary bed is known as microcirculation

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Major Veins of Systemic Circulation

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*insert pic

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  • Median cubital vein - kuhanan ng dugo

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Arterial Supply of the brain

  • Internal carotid arteries divide into:
      * Anterior and middle cerebral arteries
        * These arteries supply most of the cerebrum
  • Vertebral arteries join once within the skull to form the basilar artery
      * Basilar artery serves the brainstem and cerebellum
      * Distinct separation to ensure that they will be getting enough minerals  and nutrients
  • Anterior and posterior blood supplies are united by small communicating arterial branches
  • Result - complete circle of connecting blood vessels called cerebral arterial circle or circle of Wilis

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Hepatic Portal Circulation

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  • Hepatic portal circulation is formed by veins draining the digestive organs which empty into the hepatic portal vein:
      * Digestive organs
      * Spleen
      * Pancreas
  • Hepatic portal vein carries his blood to the liver, where it is processed before returning to systemic circulation
      * Toxin must be removed before going back to the heart
      * Accumulation of toxins will be abnormal reactions of tissue cells
      * As stomach and intestine absorbed the nutrients > blood will absorbed the toxins > enter hepatic vein> Blood will be filtered by the liver > Liver cells will be absorbing the toxins leaving the Carbon dioxide > enter inferior vena cava

 

 

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Developmental aspects of the Cardiovascular system

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  • In an embryo
      * The heart develops as a simple tube and pumps blood by week 4 of pregnancy
      * The heart becomes a four-chambered organ capable of acting as a double pump over the next 3 weeks
        * Week 7 - complete circulation of blood
  • Umbilical cord
      * Carries nutrients and oxygen from maternal blood to fetal blood
      * Fetal wastes move from blood to maternal blood
      * Point of reference is the fetus
      * Houses:
  1. One umbilical vein, which carries nutrient and oxygen rich blood to the fetus
  2. Two umbilical arteries which carry wastes and carbon dioxide-rich blood from the fetus to placenta

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FETAL CIRCULATION

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  • From the Placenta > umbilical Vein > Ductus Venosus > Inferior Vena Cava >  Right Atrium > Foramen Ovale > Left Atrium > Left Ventricle > Aorta > umbilical arteries
  • Right Atrium > RV > Ductus Arteriosus > Aorta
      * The mother is responsible for filtering the materials
      * Ductus Venosus - bypasses the entry to the liver; no need for hepatic portal circulation
      * RV - directs to foramen ovale
      * Ductus Arteriosus - bypass lungs

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  • Shunts bypassing the lungs and liver are present in a fetus
      * Blood flow bypasses the liver through the ductus venosus and enters the inferior vena cava -> right atrium of heart

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  • Age related problems associated with the cardiovascular system include:
      * Weakening of venous valves
        * Hard to regulate body temperature
      * Varicose veins - inflamed blood vessels
      * Progressive arteriosclerosis - because of fat
      * Hypertension resulting from loss of elasticity of vessels
      * Coronary artery disease resulting from fatty, calcified deposits in the vessels

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