FUNCTION OF CARDIOVASCULAR SYSTEM
a transport system |
- O2 and CO2 between lungs and tissues |
- metabolites from Gastrointestinal tract (GIT) → store in tissues |
- hormones and intracellular messengers between organs and between cells in a tissue |
- waste products from tissue to sites of metabolism and excretion |
- components of immune system → protect from disease |
Components of cardiovascular system
heart |
arteries |
capillaries |
venules and veins |
Heart
a muscular pump forcing blood through blood vessels by its rhythmic contractions |
4 chambers: right atrium, left atrium, right ventricle, left ventricle |
atrium and ventricle on the same side communicate |
right and left sides are completely separated by the atrial and ventricular septae |
Arteries
convey blood to tissues, classified as: |
- conducting arteries |
- distributing arteries |
- arterioles |
Capillaries
exchange between artery and vein |
place for exchanging O2 and CO2 |
Venules and veins
convey blood from tissues back to heart |
Surface anatomy of the heart
lungs → left atrium (oxygenated blood) → left ventricle → tissues (via the systemic arterial system) → right atrium (deoxygenated venous blood) → right ventricle → lungs (via the pulmonary trunk)
Surface anatomy of the heart
pulmonary: 3-4
aortic: 4-5
left AV valve: 5-6
base
- formed by atria
- lies at the junction of dorsal and middle third of the thorax
- cranial and caudal vena cava and pulmonary veins enter the atria at the base
apex
- lies close to the sternum at about the level of the 6th costal cartilage
Left side of the heart
1. left ventricle
2. paraconal interventricular groove
3. right ventricle
4. coronary groove (fat fill)
5. pulmonary trunk
6. ligamentum arteriosum
7. aorta
8. brachiocephalic trunk
9. subclavian artery
10. right auricle
11. left auricle
12. coronary groove (contains fat and circumflex coronary vessels)
13. caudal vena cava
Surface of the Horses heart
PERICARDIUM
a close-fitting serous membrane covered the heart and origins of the major blood vessels
2 layers
- inner visceral pericardium
- outer parietal (fibrous) pericardium
Visceral pericardium (epicardium)
attached closely to heart wall |
have a layer of mesothelial cells - secrete pericardial fluid; overlying connective tissue rich in elastic fibers - merges with myocardium |
Parietal (fibrous) pericardium
3 layers |
- inner squamous mesothelium |
- collagen and elastic fibrous layer |
- outer mediastinal pleura |
→ give rise to a ligamentous fold which anchors the apex of the heart in its position in the thorax |
- In horses, cattle and pigs this attaches to the sternum (sternopericardial ligament) |
- In carnivores it attaches to the sternum by 2 ligaments (by phrenicopericardial and sternopericardial ligaments) |
pericardial cavity
- separated visceral and parietal pericardium
- contain a small volume of lubricant pericardial fluid
GENERAL ANATOMY OF THE HEART
RIGHT ATRIUM
forms the craniodorsal aspect of the base |
consists of main chamber (sinus venarum), and an auricle (blind ended sac) surrounds craniodorsal aspect of heart |
receives blood from body via venae canae |
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CAUDAL VENA CAVA enters RA caudodorsally |
coronary sinus |
- ventral to the entrance of caudal vena cava |
- carries most of venous blood from heart muscle |
- has a small semilunar valve |
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CRANIAL VENA CAVA enters RA craniodorsally |
terminal crest (an embryonic remnant of tissue) |
- ventral to the entrance of cranial vena cava |
- no functional significance |
| |
both conduct blood into RA from opposing directions → potentially causing considerable turbulence |
⇒ intervenous tubercle projects ventrally from dorsal wall of RA - direct blood from both venae cavae towards right AV opening |
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RIGHT AZYGOUS VEIN |
- drains blood from thoracic wall |
- joins cranial vena cava (in horse, dog and some ruminants) |
- enters heart directly between the vena cavae (in others) |
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LEFT AZYGOUS VEIN |
- may present in ruminant and pig |
- enters RA via coronary sinus |
inner surface of sinus venarum is mainly smooth |
auricle has pectinate muscle |
a series of muscular ridges |
additional structural support |
|
rest of embryonic foramen ovale |
- a conducted blood opening from R to LA in foetus, bypassing pulmonary circulation |
- in interatrial septum, caudal to intervenous tubercle |
- at birth, the foramen are closed, leaving depressed membranous fossa ovalis seen in mature heart |
RIGHT VENTRICLE
right cranial portion of heart (forms most of cranial border) |
receives blood from RA via right atrioventricular (AV) valve |
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inner surface has trabeculae carnae (muscular ridges) → reduce turbulence |
trabeculae septomarginalis or moderator band (muscular and fine fibrous strands) run between septum and ventricular wall |
⇒ provide structural support, conduct impulses rapidly to entire ventricle, ensure coordinated ventricular contraction |
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Blood flow from RV into lungs |
- RV is not fully separated by supraventricular crest (thin muscular ridge) → blood passes round the supraventricular crest, into conus arteriosus → pulmonary valve → pulmonary trunk → lungs |
pulmonary valve |
- 3 semilunar cusps |
- fit tightly together when ventricle is relaxed |
→ prevent blood backflow from pulmonary trunk into ventricle |
HEART VALVES
right AV valve has:
3 cusps (tricuspid) in most species
2 cusps (bicuspid) in dogs
THE CUSPS
are anchored to fibrous skeleton of heart where it encircles AV opening
free edges are attached by chordae tendineae (multiple fibrous strands) to papillary muscles (which project from ventricular wall)
- normally 3 papillary muscles
- each cusp attaches to 2 papillary muscles
- each papillary muscle anchors 2 cusps
RIGHT VENTRICLE - AV VALVE
separate atria from ventricles |
ventricle contracts → papillary muscles contract → AV valve closes |
→ prevents blood backflow into RA |
blood passes from RV into pulmonary arteries |
thin-walled RV (pulmonary circulation has relatively low resistance to blood flow) |
LEFT ATRIUM
dorso-caudal part of heart |
oxygenated blood from lungs enters LA via 7-8 pulmonary veins |
similar in general structure to RA |
present pectinate muscles |
valve of foramen ovale may be visible cranially in interatrial septum |
LEFT VENTRICLE
left caudal portion of heart (forms caudal border) |
conical - forms apex of heart |
thick-walled → generate greater pressure to pump blood to body |
blood from LA passes into LV via bicuspid (mitral) left AV valve |
trabeculae carnae are more prominent, papillary muscles (usually 2) are larger, trabeculae septomarginalis also present |
blood passes into aorta via aortic valve |
- like pulmonary valve has 3 main semilunar cusps |
- aorta distributes blood to body via its many branches |
SKELETON OF THE HEART
annuli fibrosi |
fibrous skeleton |
rings of collagen and elastic fibers encircle right and left AV valves, aorta and pulmonary trunk |
⇒ separate atria and ventricles; structural support |
anchor heart muscle ⇒ prevent distortion of openings during contraction |
⇒ prevent direct conduction of impulses from atria to ventricles |
supporting bundles of collagen also pass down interventricular septum |
fibrous trigone - a plate formed by dense fibrous skeleton between AV valves and base of aorta; composed of: |
- dense connective tissue (cat, pig) |
- cartilaginous (dog, horse) |
- partially ossifies → os cordis (ruminants, older individuals of other species) |
FUNCTION ANATOMY OF HEART
deoxygenated blood enters relaxed RA via cranial and caudal venae cavae |
coronary sinus (tiny RA opening) collects blood from coronary vessels → RA → right AV valve |
RA contracts ⇒ complete RV filling |
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RV contracts ⇒ ↑ RV pressure → close right AV valve, open pulmonary valve → pulmonary valve → pulmonary trunk → lungs |
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RV relaxes ⇒ ↓ RV pressure → close pulmonary valve (prevent backflow from lungs into RV) ) |
opens right AV valve, right ventricular filling begins again |
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oxygenated blood from lungs enters LA via pulmonary veins |
blood flows into LV via open left AV valve |
LA contracts ⇒ complete ventricular filling |
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LV contracts ⇒ ↑ LV pressure → closes left AV valve, opens aortic valve → aorta → rest of body |
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LV relaxes ⇒ ↓ LV pressure → closes aortic valve (prevent backflow from aorta into LV) |
CARDIAC CYCLE
systole is period of contraction, heart pumps the blood
diastole is period of relaxation, heart fills with blood
--------
use a stethoscope to locate a valvular insufficiency or stenosis (heard as a "murmur" on auscultation)
PHASES OF CARDIAC WORK
atrial systole |
▪ begin when atria, ventricles in diastole |
▪ AV valves open → passive ventricular filling |
▪ atrial depolarization → atria contract → completes ventricular filling |
▪ ECG ▫ P wave, PR interval |
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isovolumetric contraction |
▪ ventricular contraction begins (ventricular systole) → ventricular pressure > atrial pressure → AV valves close (S1); semilunar valves closed |
▪ ECG ▫ QRS complex |
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rapid ejection |
▪ ventricular systole continues → left ventricular pressure > aortic pressure → aortic valve open → blood ejected (SV) (blood also ejected into pulmonary vasculature via pulmonic valve) |
▪ ↑ aortic pressure |
▪ atrial filling begins |
▪ ECG ▫ ST segment |
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reduced ejection |
▪ ↓ ventricular ejection velocity |
▪ ↑ atrial pressure |
▪ ventricular repolarization begins |
▪ ECG ▫ T wave |
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isovolumetric relaxation |
▪ ventricles relaxed (ventricular diastole); ventricular pressure < aortic pressure → aortic valve closes (S2) |
▪ all valves closed |
▪ ventricular volume: constant |
▪ complete ventricular repolarization |
▪ ECG ▫ T wave ends |
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rapid ventricular filling |
▪ ventricular diastole continues → ventricular pressure < atrial pressure → AV valves open |
▪ passive ventricular filling |
relationship between cardiac cycle and ECG
P wave - atrial depolarization
QRS complex - ventricular depolarization
T wave - ventricular repolarization
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Pathway of electrical conduction
electrical impulse travels from SA node, goes through atrial internodal fibers to AV node |
impulses continue down conduction pathway via bundle of His into Purkinje fibers → ventricular myocytes |
trabeculae septomarginalis also carry Purkinje fibers to aid spread of electrical impulses to ventricles |
POSITION OF THE VALVES
valve |
side |
position |
pulmonary |
left |
3rd intercostal space at costochondral junction (above sternum) |
aortic |
left |
4th intercostal space below shoulder joint (above costochondral junction) |
left AV |
left |
4th - 5th intercostal space just below costochondral junction |
right AV |
right |
3rd – 4th intercostal space at costochondral junction |
SA node (sinoatrial node)
highest rate |
pacemaker - generate heart beat |
location: right atrial myocardium near junction with cranial vena cava |
regulated by: |
- sympathetic cardiac nerve fibers - ↑ discharge rate |
- right vagal (parasympathetic) nerve fibers - ↓ discharge rate |
AV node (atrioventricular node)
second highest discharge rate |
location: near coronary sinus on interatrial septum |
mainly controlled by left vagus nerve |
COMPARATIVE HEARTS
CANINE |
45o to sternum |
apex lies on sternum at junction of sternum and diaphragm, attached to latter by phrenicopericardial ligament |
right and left AV valves are bicuspid |
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EQUINE |
further cranial and ventral (2nd to 6th intercostal space) |
apex anchors to sternum by sternopericardial ligament |
horses in training have a larger heart (hypertrophy vs hyperplasia) |
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RUMINANT |
60% to left of midline (2nd to 5th intercostal space) - almost vertical |
apex anchors to sternum by sternopericardial ligament |
beware traumatic pericarditis |
| |
PORCINE |
relatively small - (between 2nd to 5th ribs) |
45o to sternum |
HISTOLOGY OF HEART
ENDOCARDIUM |
polygonal endothelial cells on basement membrane, supported by a subendothelial coat of fine collagenous and elastic fibers |
| |
MYOCARDIUM |
cardiac muscle → striated myocardial cells, electrically coupled at intercalated discs (essential for rhythmic contraction) |
form branching and anastomosing fibers |
perinuclear halo - pale staining cytoplasm surrounds cardiac muscle nuclei (central nucleus) |
endomysium - connective tissue sheath surrounds each muscle fiber, thickened at valve attachment points and fibrous skeleton |
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EPICARDIUM |
serous membrane - forms the visceral pericardium |
carries vasculature |
HISTORY OF BLOOD VESSELS
3 layers: tunica adventitia, tunica media, tunica intima
- external connective tissue
- tunica adventitia (most important)
+ external elastic lamina
- tunica media
- tunica intima
+ internal elastic lamina
+ subendothelial connective tissue
+ endothelium
- lumen
HISTORY OF BLOOD VESSELS - ARTERY
CONDUCTING (ELASTIC) ARTERIES |
large arteries, wide lumen → conduct large volumes of blood around body |
- tunica intima - all elements present |
- tunica media - mostly elastic fibers, but fine collagen fibers, fibroblasts, smooth muscle in between |
- tunica adventitia - no distinct external elastic lamina, blend with surrounding tissue |
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DISTRIBUTING (MUSCULAR) ARTERIES |
small and medium sized arteries, carry blood to specific tissues |
very thick wall → smaller lumen |
3 layers are present |
- elastic laminae well-defined |
- tunica media mainly has a thick layer of smooth muscle |
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ARTERIOLES |
lumen diameter < 200µm |
- tunica intima - lacks subendothelial coat |
- tunica media - has only 1-3 layers of smooth muscle cells |
- tunica adventitia - no external elastic lamina, connective tissue blends with surrounding tissue |
HISTORY OF BLOOD VESSELS - CAPPILARIES
- exchange site of metabolites and waste products |
- diameter < 10µm → allow to pass single blood cells |
- endothelial cells line basement membrane - surrounded by loose connective tissue |
- 5 types |
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CONTINUOUS CAPILLARIES |
- no pores or interruptions between endothelial cells |
- muscle, lungs, nervous tissue |
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FENESTRATED CAPILLARIES |
- have pores throughout endothelial walls |
- endocrine glands, intestines, where fluid transport is important |
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SINUSOIDAL CAPILLARIES |
- larger, more irregular shaped, no distinct basement membrane |
- endocrine organs, aortic and carotid bodies |
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SINUSOID |
- larger, basement membrane mostly absent, gaps in walls → exchange large molecules (proteins) |
- bone marrow, liver |
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SINUSES |
- larger than sinusoids with a discontinuous basement membrane |
- spleen |
HISTORY OF BLOOD VESSELS - VEIN
VENULES |
- lined by endothelial cells combined with loose connective tissue |
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SMALL AND MEDIUM VEINS |
- more smooth muscle, less muscular than similarly-sized arteries |
- thin tunica intima and tunica media, surrounded by well-developed tunica adventitia |
- may have valves formed by invaginations of the tunica intima → ensure blood flows in one direction |
| |
LARGE VEINS |
- tunica intima - thicker, may be internal elastic lamina |
- tunica media - mainly collagen and elastic fibers (may have smooth muscle) |
- tunica adventitia - thickest, has fibroelastic tissue. No valves in largest veins |
FUNCTIONAL ANATOMY OF BLOOD VESSELS
- store kinetic energy by elastic artery during systole |
- maintain blood pressure and blood flow by elastic fibers recoil in diastole |
- regulate blood supply by autonomic control of smooth muscle |
- provide resistance to pulse pressure for capillaries by arterioles |
- exchange site (capillaries) |
VENOUS RETURN
is aided by: |
muscular pump - limb muscles contract → external pressure on large veins |
respiratory pump - (-) pressure (during inspiration) in thorax helps return blood to heart |
cardiac pump - low (+) blood pressure (~ 15mmHg) in great veins returns to heart |
HAEMATOPOIESIS AND ANGIOGENESIS
haematopoiesis - sự tạo huyết
angiogenesis - sự tạo mạch
splanchnic mesoderm: trung bì tạng
peripheral cells: tế bào ngoại vi
vascular endothelium: nội mô mạch
embryo: phôi
vitelline: noãn hoàng
allantoic: nang
vascularize: tạo mạch máu
placenta: nhau thai
mesenchyme: trung mô
cord: sợi
arch: vòm
COMPARATIVE ANATOMY OF AORTIC ARCHES
aortic arches |
6 pairs, enclose pharynx |
ventral aorta to dorsal aorta |
fish |
- all 6 pairs may be functional |
birds and mammals |
- aortic arches I,II,V degenerate |
- aortic arches III, IV and VI remain |
SPECIALIZED CARDIOVASCULAR ELEMENTS
collateral circulation |
- most distributing arteries branches before ending in tissues |
- lung, intestine |
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anatomical end artery |
- no anastomosis exists |
- single artery supplies blood to a specific tissue piece with no collateral circulation |
- brain, cornea |
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functional end artery |
- anastomosis exists but not give enough blood |
- artery supplies blood to a specific tissue piece has insufficient collateral circulation |
- coronary, cerebral and retina arteries |
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retia mirabilia |
- major arteries which split suddenly into multiple parallel vessels |
renal glomerulus |
| |
arteriovenous anastomosis |
- blood shunts directly from an arteriole to a venule, bypassing capillary bed |
- skin, horse hoof |
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vasa vasorum |
- a fine network of vessels, supply walls of major blood vessels |
- in tunica adventitia / external tunica media |
| |
portal systems |
- a vein connects 2 capillary beds |
- hepatic portal system |
- hypothalamo-hypophyseal portal system |
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alternative venous drainage |
- some tissues are drained by two venous routes |
- bronchial, caudal vertebral column |
| |
veins without valves |
- some specially large veins lack valves |
- vertebral venous sinus, portal veins |
BRONCHIAL CIRCULATION
lungs have dual circulation between broncho-esophageal and pulmonary |
in pigs, carnivore, some ruminants, some blood from bronchi drains via brochial veins → azygous vein → enters RA |
remaining bronchial blood, all of it in horse, returns to heart via oxygenated pulmonary vein → LA |
CORONARY CIRCULATION
coronary arteries - first branches of aorta |
left and right coronary arteries |
- not form collateral circulations |
- functional end arteries supply myocardial capillary bed |
| |
LCA supplies left heart chambers |
RCA supplies right heart chambers |
considerable species variation |
venous drainage from myocardial capillary bed |
- great coronary vein → RA (at coronary sinus) |
small coronary vein (Thebesian veins) → into all 4 chambers |
| |
Carnivore and ruminant |
- LCA supplies paraconal and subsinuosal interventricular branches and left circumflex branch |
- RCA supplies right circumflex branch |
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horse and pig |
- LCA supplies paraconal interventricular branch |
- RCA forms right circumflex branch, and subsinuosal interventricular branch |
THE CONDUCTION SYSTEM
cardiac muscle fibers contracts on its own without external stimulus |
origin of heart beat from muscular (myogenic), not neural (neurogenic) |
| |
innervation of myocardium |
- response to change |
- from both sympathetic and parasympathetic stimuli |
- concentrated around nodes |
CONGENITAL CARDIOVASCULAR PROBLEMS
các vấn đề tim mạch bẩm sinh |
| |
SEPTAL DEFECTS (dị tật vách ngăn) |
Atrial |
foramen ovale can not close → ↑ load on right side (higher left atrial pressure) |
→ pulmonary congestion and relative pulmonic stenosis |
Ventricular |
↑ pulmonary blood flow, and left ventricular dilatation and failure |
| |
PATENT DUCTUS ARTERIOSUS (còn ống động mạch) |
blood flow from right to left cause pulmonary vascular resistance and right heart pressures decrease, left heart pressures increase |
→ pulmonary congestion and machinery murmur |
| |
VALVULAR DEFORMITIES (dị dạng van tim) |
stenosis (hẹp van tim) |
pulmonic stenosis → right ventricular hypertrophy and failure → "seagull" murmur |
aortic stenosis → poor coronary blood supply → sudden death, myocardial damage |
incompetencies (leakage or insufficiency) (hở van tim) |
common in AV valve → blood backflow |
| |
TETRALOGY OF FALLOT (tứ chứng Fallot) |
4 problems: |
- ventricular septal defect |
- pulmonic stenosis |
- aortic override |
right ventricular hypertrophy |
→ stunting and cyanosis |
| |
VASCULAR RING ANOMALY (Persistent Right Aortic Arch) |
abormal development of aortic arch → form constricting band around esophagus → megaesophagus |
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PORTOSYSTEMIC SHUNTS |
anastomosis forms between portal system and any of main veins |
toxic metabolic products from gut to bypass liver, go directly to heart → |
→ animal can't grow → hepatic encephalopathy (damage to brain tissues) |
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