chapter 13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 13

Blood, Heart

and Circulation

13-1


Chapter 13 Outline Overview Blood Pulmonary and Systemic Circulations Heart Valves Cardiac Cycle Electrical Activity of the Heart Structure of Blood Vessels Heart Disease Lymphatic System

13-2

Overview

13-3


Functions of Circulatory System

Plays roles in transportation of respiratory gases, delivery of nutrients and hormones, and waste removal And in temperature regulation, clotting, and immune

function

13-4


Components of Circulatory System

Include cardiovascular and lymphatic systems Heart pumps blood thru cardiovascular system Blood vessels carry blood from heart to cells and

back Includes arteries, arterioles, capillaries, venules,

veins Lymphatic system picks up excess fluid filtered out in

capillary beds and returns it to veins Its lymph nodes are part of immune system

13-5

Blood

13-6


Composition of Blood

Consists of formed elements (cells) suspended and carried in plasma (fluid part)

When centrifuged, blood separates into heavier formed elements on bottom and plasma on top

13-7


Composition of Blood

Total blood volume is about 5L Plasma is straw-colored liquid consisting of H2O and

dissolved solutes Includes ions, metabolites, hormones, antibodies

Red blood cells (RBCs) comprise most of formed elements % of RBCs in centrifuged blood sample = hematocrit

Hematocrit is 36-46% in women; 41-53% in men

13-8


Plasma Proteins

Constitute 7-9% of plasma 3 types of plasma proteins: albumins, globulins, and

fibrinogen Albumin accounts for 60-80%

Creates colloid osmotic pressure that draws H2O from interstitial fluid into capillaries to maintain blood volume and pressure

Globulins carry lipids Gamma globulins are antibodies

Fibrinogen serves as clotting factor Converted to fibrin Serum is fluid left when blood clots

13-9


Formed Elements

Are erythrocytes (RBCs) and leukocytes (WBCs)

RBCs are flattened biconcave discs Shape provides increased

surface area for diffusion Lack nuclei and mitochondria Each RBC contains 280

million hemoglobins About 300 billion RBCs are

produced each day

13-10


Leukocytes

Have a nucleus, mitochondria, and amoeboid ability Can squeeze through capillary walls (diapedesis)

Granular leukocytes help detoxify foreign substances and release heparin Include eosinophils, basophils, and neutrophils

13-11


Leukocytes continued

Agranular leukocytes are phagocytic and produce antibodies

Include lymphocytes and monocytes

13-12


Platelets (thrombocytes)

Are smallest of formed elements, lack nucleus

Are amoeboid fragments of megakaryocytes from bone marrow

Constitute most of mass of blood clots

Release serotonin to vasoconstrict and reduce blood flow to clot area

Secrete growth factors to maintain integrity of blood vessel wall

Survive 5-9 days

13-13


Hematopoiesis

Is formation of blood cells from stem cells in bone marrow (myeloid tissue) and lymphoid tissue Marrow produces about 500 billion blood cells/day In fetus occurs in liver

13-14


Hematopoiesis continued

Erythropoiesis is formation of RBCs Stimulated by erythropoietin (EPO) from kidney

Leukopoiesis is formation of WBCs Stimulated by variety of cytokines

= autocrine regulators secreted by immune system

13-15


Erythropoiesis

2.5 million RBCs are produced/sec

Lifespan of 120 days

Old RBCs removed from blood by phagocytic cells in liver, spleen, and bone marrow Iron recycled

back into hemoglobin production

13-16


RBC Antigens and Blood Typing

Antigens present on RBC surface specify blood type Major antigen group is ABO system

Type A blood has only A antigens Type B has only B antigens Type AB has both A and B antigens Type O has neither A or B antigens

13-17


Transfusion Reactions

People with Type A blood make antibodies to Type B RBCs, but not to Type A

Type B blood has antibodies to Type A RBCs but not to Type B

Type AB blood doesn’t have antibodies to A or B

Type O has antibodies to both Type A and B

If different blood types are mixed, antibodies will cause mixture to agglutinate

13-18


Transfusion Reactions continued

If blood types don't match, recipient’s antibodies agglutinate donor’s RBCs

Type O is “universal donor” because lacks A and B antigens Recipient’s antibodies

won’t agglutinate donor’s Type O RBCs

Type AB is “universal recipient” because doesn’t make anti-A or anti-B antibodies Won’t agglutinate

donor’s RBCs

13-19


Rh Factor

Is another type of antigen found on RBCs Rh+ has Rho(D) antigens; Rh- does not Can cause problems when Rh- mother has Rh+ babies

At birth, mother may be exposed to Rh+ blood of fetus

In later pregnancies mom may produce Rh antibodies In Erythroblastosis fetalis, this happens and

antibodies cross placenta causing hemolysis of fetal RBCs

13-20


Hemostasis

Is cessation of bleeding Promoted by reactions initiated by vessel injury:

Vasoconstriction restricts blood flow to area Platelet plug forms

Plug and surroundings are infiltrated by web of fibrin, forming clot

13-21


Role of Platelets

Platelets don't stick to intact endothelium because of presence of prostacyclin (PGI2--a prostaglandin) and NO Keep clots from

forming and are vasodilators

13-22


Role of Platelets

Damage to endothelium allows platelets to bind to exposed collagen von Willebrand factor

increases bond by binding to both collagen and platelets

Platelets stick to collagen and release ADP, serotonin, and thromboxane A2

= platelet release reaction

13-23


Role of Platelets continued

Serotonin and thromboxane A2 stimulate vasoconstriction, reducing blood flow to wound

ADP and thromboxane A2 cause other platelets to become sticky and attach and undergo platelet release reaction This continues until

platelet plug is formed

13-24


Platelet plug becomes infiltrated by meshwork of fibrin Clot now contains platelets, fibrin and trapped RBCs

Platelet plug undergoes plug contraction to form more compact plug

Role of Fibrin

13-25


Can occur via 2 pathways: Intrinsic pathway clots damaged vessels and blood left in test

tube Initiated by exposure of blood to negatively charged

surface of glass or blood vessel collagen This activates factor XII (a protease) which initiates a

series of clotting factors Ca2+ and phospholipids convert prothrombin to

thrombin Thrombin converts fibrinogen to fibrin which

polymerizes to form a mesh Damage outside blood vessels releases tissue

thromboplastin that triggers a clotting shortcut (= extrinsic pathway)

Conversion of Fibrinogen to Fibrin

13-26


Dissolution of Clots

When damage is repaired, activated factor XII causes activation of kallikrein Kallikrein converts plasminogen to plasmin

Plasmin digests fibrin, dissolving clot

13-29


Anticoagulants

Clotting can be prevented by Ca+2 chelators (e.g. sodium citrate or EDTA) or heparin which activates antithrombin III (blocks

thrombin) Coumarin blocks clotting by inhibiting activation of Vit

K Vit K works indirectly by reducing Ca+2 availability

13-30

Pulmonary and Systemic Circulations

13-31


Structure of Heart

Heart has 4 chambers 2 atria receive blood from venous system 2 ventricles pump blood to arteries 2 sides of heart are 2 pumps separated by muscular septum

13-32


Structure of Heart continued

Between atria and ventricles is layer of dense connective tissue called fibrous skeleton Which structurally and functionally separates the

twoMyocardial cells of atria attach to top of fibrous

skeleton and form 1 unit (or myocardium)Cells from ventricles attach to bottom and form

another unit Fibrous skeleton also forms rings, the annuli fibrosi,

to hold heart valves

13-33


Pulmonary and Systemic Circulations

Blood coming from tissues enters superior and inferior vena cavae which empties into right atrium, then goes to right ventricle which pumps it through pulmonary arteries to lungs

13-34


Pulmonary and Systemic Circulations continued

Oxygenated blood from lungs passes thru pulmonary veins to left atrium, then to left ventricle which pumps it through aorta to body

13-35



Pulmonary circulation is path of blood from right ventricle through lungs and back to heart

Systemic circulation is path of blood from left ventricle to body and back to heart

Rate of flow through systemic circulation = flow rate thru pulmonary circuit

13-36



13-37

Resistance in systemic circuit > pulmonary Work done by left ventricle pumping to systemic is 5-7X

greaterMakes left ventricle more muscular (and 3-4X thicker)

Heart Valves

13-38


Atrioventricular Valves

Blood flows from atria into ventricles thru 1-way atrioventricular (AV) valves Between right

atrium and ventricle is tricuspid valve

Between left atrium and ventricle is bicuspid or mitral valve

13-39


Atrioventricular Valves continued

Opening and closing of valves results from pressure differences High pressure of ventricular contraction is prevented

from everting AV valves by contraction of papillary muscles which are connected to AVs by chorda tendinea

13-40


Semilunar Valves

During ventricular contraction blood is pumped through aortic and pulmonary semilunar valves Close during

relaxation

13-41

Cardiac Cycle

13-42


Cardiac Cycle

Is repeating pattern of contraction and relaxation of heart Systole refers to contraction phase Diastole refers to relaxation phase Both atria contract simultaneously; ventricles follow

0.1-0.2 sec later

13-43


Cardiac Cycle

End-diastolic volume is volume of blood in ventricles at end of diastole

Stroke volume is amount of blood ejected from ventricles during systole

End-systolic volume is amount of blood left in ventricles at end of systole

13-44


As ventricles contract, pressure rises, closing AV valves Called isovolumetric contraction because all valves are

closed When pressure in ventricles exceeds that in aorta,

semilunar valves open and ejection begins As pressure in ventricle falls below that in aorta, back

pressure closes semilunars All valves are closed and ventricles undergo isovolumetric

relaxation When pressure in ventricles falls below atria, AVs open

and ventricles fill Atrial systole sends its blood into ventricles

Cardiac Cycle continued

13-45


Heart Sounds

Closing of AV and semilunar valves produces sounds that can be heard thru stethoscope Lub (1st sound) produced by closing of AV valves Dub (2nd sound) produced by closing of semilunars

13-47


Heart Murmurs

Are abnormal sounds produced by abnormal patterns of blood flow in heart

Many caused by defective heart valves Can be of congenital origin In rheumatic fever, damage can be from antibodies

made in response to strep infection

13-48


Heart Murmurs continued

In mitral stenosis, mitral valve becomes thickened and calcified, impairing blood flow from left atrium to left ventricle Accumulation of blood in left ventricle can cause

pulmonary hypertension Valves are incompetent when don't close properly

Can be from damage to papillary muscles

13-49


Murmurs caused by septal defects are usually congenital Due to holes in septum between left and right sides of heart Pressure causes blood to pass from left to right

Heart Murmurs continued

13-50

Electrical Activity of Heart

13-51


Electrical Activity of Heart

Myocardial cells are short, branched, and interconnected by gap junctions

Entire muscle that forms a chamber is called a myocardium or functional syncytium Because APs originating in any cell are transmitted

to all others Chambers separated by nonconductive tissue

13-52


SA Node Pacemaker

In normal heart, SA node functions as pacemaker Depolarizes

spontaneously to threshold (= pacemaker potential)

13-53


Membrane voltage begins at -60mV and gradually depolarizes to -40 threshold

Spontaneous depolarization is caused by Na+ flowing through channel that opens when hyperpolarized (HCN channel)

At threshold V-gated Ca2+ channels open, creating upstroke and contraction

Repolarization is via opening of V-gated K+ channels

SA Node Pacemaker continued

13-54


Ectopic Pacemakers

Other tissues in heart are spontaneously active But are slower than SA node Are stimulated to produce APs by SA node before

spontaneously depolarize to threshold If APs from SA node are prevented from reaching

these, they will generate pacemaker potentials

13-55


Myocardial APs

Myocardial cells have RMP of –90 mV Depolarized to threshold by APs originating in SA node

13-56


Myocardial APs continued

Upstroke occurs as V-gated Na+ channels open

MP rapidly declines to 15mV and stays there for 200-300 msec (plateau phase) Plateau results from

balance between slow Ca2+ influx and K+ efflux

Repolarization due to opening of extra K+ channels

13-57


Conducting Tissues of Heart

APs from SA node spread through atrial myocardium via gap junctions

But need special pathway to ventricles because of non-conducting fibrous tissue AV node at base of

right atrium and bundle of His conduct APs to ventricles

Insert Fig 13.20

13-58


Conducting Tissues of Heart continued

In septum of ventricles, His divides into right and left bundle branches Which give rise to

Purkinje fibers in walls of ventricles These stimulate

contraction of ventricles

13-59


Conduction of APs

APs from SA node spread at rate of 0.8 -1 m/sec Time delay occurs as APs pass through AV node

Has slow conduction of 0.03– 0.05 m/sec AP speed increases in Purkinje fibers to 5 m/sec

Ventricular contraction begins 0.1–0.2 sec after contraction of atria

13-60


Excitation-Contraction Coupling

Depolarization of myocardial cells opens V-gated Ca2+ channels in sarcolemma This depolarization opens V-gated and Ca2+ release

channels in SR (calcium-induced-calcium-release) Ca2+ binds to troponin and stimulates contraction (as

in skeletal muscle) During repolarization Ca2+ pumped out of cell and

into SR

13-61


Refractory Periods

Heart contracts as syncytium and thus cannot sustain force

Its AP lasts about 250 msec

Has a refractory period almost as long as AP

Cannot be stimulated to contract again until has relaxed

13-62


Electrocardiogram (ECG/EKG)

Is a recording of electrical activity of heart conducted thru ions in body to surface

13-63


Types of ECG Recordings

Bipolar leads record voltage between electrodes placed on wrists and legs (right leg is ground)

Lead I records between right arm and left arm

Lead II: right arm and left leg

Lead III: left arm and left leg

13-64


Types of ECG Recordings continued

Unipolar leads record voltage between a single electrode placed on body and ground built into ECG machine Limb leads go on right

arm (AVR), left arm (AVL), and left leg (AVF)

The 6 chest leads, placed as shown, allow certain abnormalities to be detected

13-65


3 distinct waves are produced during cardiac cycle P wave caused by atrial depolarization

ECG

13-66


QRS complex is caused by ventricular depolarization T wave results from ventricular repolarization

ECG

13-67


Correlation of ECG with Heart Sounds

1st heart sound (lub) comes immediately after QRS wave as AV valves close

2nd heart sound (dub) comes as T wave begins and semilunar valves close

13-68

Structure of Blood Vessels

13-69


Structure of Blood Vessels

Innermost layer of all vessels is the endothelium Capillaries are made of only endothelial cells Arteries and veins have 3 layers called tunica externa,

media, and interna Externa is connective tissue Media is mostly smooth muscle Interna is made of endothelium, basement

membrane, and elastin Although have same basic elements, arteries and

veins are quite different13-70


Arteries

Large arteries are muscular and elastic Contain lots of elastin Expand during systole and recoil during diastole

Helps maintain smooth blood flow during diastole

13-72


Arteries Small arteries and arterioles are muscular

Provide most resistance in circulatory system Arterioles cause greatest pressure drop

Mostly connect to capillary beds Some connect directly to veins to form arteriovenous

anastomoses

13-73


Provide extensive surface area for exchange Blood flow through a capillary bed is determined by

state of precapillary sphincters of arteriole supplying it

Capillaries

13-74


In continuous capillaries, endothelial cells are tightly joined together Have narrow intercellular channels that permit exchange

of molecules smaller than proteins Present in muscle, lungs, adipose tissue

Fenestrated capillaries have wide intercellular pores Very permeable Present in kidneys, endocrine glands, intestines.

Discontinuous capillaries have large gaps in endothelium Are large and leaky Present in liver, spleen, bone marrow

Types of Capillaries

13-75


Contain majority of blood in circulatory system Very compliant (expand readily) Contain very low pressure (about 2mm Hg)

Insufficient to return blood to heart

Veins

13-76


Blood is moved toward heart by contraction of surrounding skeletal muscles (skeletal muscle pump) And pressure

drops in chest during breathing

1-way venous valves ensure blood moves only toward heart

Veins

13-77

Heart Disease

13-78


Atherosclerosis

Is most common form of arteriosclerosis (hardening of arteries) Accounts for 50% of

deaths in US Localized plaques

(atheromas) reduce flow in an artery And act as sites for

thrombus (blood clots)

13-79


Atherosclerosis

Plaques begin at sites of damage to endothelium E.g. from

hypertension, smoking, high cholesterol, or diabetes

13-80


Atherosclerosis

Plaques begin at sites of damage to endothelium E.g. from

hypertension, smoking, high cholesterol, or diabetes

13-81


Cholesterol and Plasma Lipoproteins

High blood cholesterol is associated with risk of atherosclerosis

Lipids, including cholesterol, are carried in blood attached to LDLs (low-density lipoproteins) and HDLs (high-density lipoproteins)

13-82


Cholesterol and Plasma Lipoproteins

LDLs and HDLs are produced in liver and taken into cells by receptor-mediated endocytosis In cells LDL is oxidized

Oxidized LDL can injure endothelial cells facilitating plaque formation

Arteries have receptors for LDL but not HDLWhich is why HDL isn't atherosclerotic

13-83


Ischemic Heart Disease

Is most commonly due to atherosclerosis in coronary arteries

Ischemia occurs when blood supply to tissue is deficient Causes increased lactic acid from anaerobic

metabolism Often accompanied by angina pectoris (chest pain)

13-84


Ischemic Heart Disease continued

Detectable by changes in S-T segment of ECG

13-85


Ischemic Heart Disease continued

13-86

Myocardial infarction (MI) is a heart attack Usually caused by occlusion of a coronary artery

Causing heart muscle to dieDiagnosed by high levels of creatine

phosphokinase (CPK) and lactate dehydrogenase (LDH) And presence of plasma troponin T and I from

damaged muscleDead cells are replaced by noncontractile scar

tissue


Arrhythmias Detected on ECG

Arrhythmias are abnormal heart rhythmsHeart rate <60/min is bradycardia; >100/min is

tachycardia

13-87


Arrhythmias Detected on ECG continued

In flutter, contraction rates can be 200-300/min In fibrillation, contraction of myocardial cells is uncoordinated

and pumping ineffective Ventricular fibrillation is life-threatening

Electrical defibrillation resynchronizes heart by depolarizing all cells at same time

13-88


AV node block occurs when node is damaged First–degree AV node block is when conduction

through AV node > 0.2 sec Causes long P-R interval

Second-degree AV node block is when only 1 out of 2-4 atrial APs can pass to ventricles Causes P waves with no QRS

In third-degree or complete AV node block no atrial activity passes to ventricles Ventricles are driven slowly by bundle of His or

Purkinjes


13-89


In third-degree or complete AV node block, no atrial activity passes to ventricles Ventricles are driven slowly by bundle of His or

Purkinjes


13-92

Lymphatic System

13-93


Lymphatic System

Has 3 basic functions: Transports interstitial fluid (lymph) back to blood Transports absorbed fat from small intestine to

blood Helps provide immunological defenses against

pathogens

13-94


Lymphatic System continued

Lymphatic capillaries are closed-end tubes that form vast networks in intercellular spaces Very porous,

absorb proteins, microorganisms, fat

13-95



13-96

Lymph is carried from lymph capillaries to lymph ducts to lymph nodes


Lymph nodes filter lymph before returning it to veins via thoracic duct or right lymphatic duct

Nodes make lymphocytes and contain phagocytic cells that remove pathogens

Lymphocytes also made in tonsils, spleen, thymus


13-97

chapter 13

Documents

mcgrawhill companies

blood separates

blood clots13

blood flow

centrifuged blood sample

antibodiesred blood

formed elements cells

heavier formed elements