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a transport system
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- O2 and CO2 between lungs and tissues
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- metabolites from Gastrointestinal tract (GIT) → store in tissues
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- hormones and intracellular messengers between organs and between cells in a tissue
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- waste products from tissue to sites of metabolism and excretion
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- components of immune system → protect from disease
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heart
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arteries
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capillaries
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venules and veins
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a muscular pump forcing blood through blood vessels by its rhythmic contractions
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4 chambers: right atrium, left atrium, right ventricle, left ventricle
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atrium and ventricle on the same side communicate
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right and left sides are completely separated by the atrial and ventricular septae
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convey blood to tissues, classified as:
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- conducting arteries
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- distributing arteries
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- arterioles
|
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exchange between artery and vein
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place for exchanging O2 and CO2
|
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convey blood from tissues back to heart
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attached closely to heart wall
|
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have a layer of mesothelial cells - secrete pericardial fluid; overlying connective tissue rich in elastic fibers - merges with myocardium
|
|
3 layers
|
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- inner squamous mesothelium
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- collagen and elastic fibrous layer
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- outer mediastinal pleura
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→ give rise to a ligamentous fold which anchors the apex of the heart in its position in the thorax
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- In horses, cattle and pigs this attaches to the sternum (sternopericardial ligament)
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- In carnivores it attaches to the sternum by 2 ligaments (by phrenicopericardial and sternopericardial ligaments)
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forms the craniodorsal aspect of the base
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consists of main chamber (sinus venarum), and an auricle (blind ended sac) surrounds craniodorsal aspect of heart
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receives blood from body via venae canae
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CAUDAL VENA CAVA enters RA caudodorsally
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coronary sinus
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- ventral to the entrance of caudal vena cava
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- carries most of venous blood from heart muscle
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- has a small semilunar valve
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|
CRANIAL VENA CAVA enters RA craniodorsally
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terminal crest (an embryonic remnant of tissue)
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|
- ventral to the entrance of cranial vena cava
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- no functional significance
|
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both conduct blood into RA from opposing directions → potentially causing considerable turbulence
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|
⇒ intervenous tubercle projects ventrally from dorsal wall of RA - direct blood from both venae cavae towards right AV opening
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|
|
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RIGHT AZYGOUS VEIN
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- drains blood from thoracic wall
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|
- joins cranial vena cava (in horse, dog and some ruminants)
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- enters heart directly between the vena cavae (in others)
|
|
LEFT AZYGOUS VEIN
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- may present in ruminant and pig
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- enters RA via coronary sinus
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inner surface of sinus venarum is mainly smooth
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auricle has pectinate muscle
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a series of muscular ridges
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additional structural support
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|
|
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rest of embryonic foramen ovale
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|
- a conducted blood opening from R to LA in foetus, bypassing pulmonary circulation
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- in interatrial septum, caudal to intervenous tubercle
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- at birth, the foramen are closed, leaving depressed membranous fossa ovalis seen in mature heart
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|
right cranial portion of heart (forms most of cranial border)
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|
receives blood from RA via right atrioventricular (AV) valve
|
|
inner surface has trabeculae carnae (muscular ridges) → reduce turbulence
|
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trabeculae septomarginalis or moderator band (muscular and fine fibrous strands) run between septum and ventricular wall
|
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⇒ provide structural support, conduct impulses rapidly to entire ventricle, ensure coordinated ventricular contraction
|
|
Blood flow from RV into lungs
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|
- 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
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|
pulmonary valve
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|
- 3 semilunar cusps
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- fit tightly together when ventricle is relaxed
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→ prevent blood backflow from pulmonary trunk into ventricle
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separate atria from ventricles
|
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ventricle contracts → papillary muscles contract → AV valve closes
|
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→ prevents blood backflow into RA
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blood passes from RV into pulmonary arteries
|
|
thin-walled RV (pulmonary circulation has relatively low resistance to blood flow)
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dorso-caudal part of heart
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|
oxygenated blood from lungs enters LA via 7-8 pulmonary veins
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similar in general structure to RA
|
|
present pectinate muscles
|
|
valve of foramen ovale may be visible cranially in interatrial septum
|
|
left caudal portion of heart (forms caudal border)
|
|
conical - forms apex of heart
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thick-walled → generate greater pressure to pump blood to body
|
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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
|
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blood passes into aorta via aortic valve
|
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- like pulmonary valve has 3 main semilunar cusps
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- aorta distributes blood to body via its many branches
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|
annuli fibrosi
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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
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⇒ prevent direct conduction of impulses from atria to ventricles
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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)
|
|
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
|
|
RV relaxes ⇒ ↓ RV pressure → close pulmonary valve (prevent backflow from lungs into RV) )
|
|
opens right AV valve, right ventricular filling begins again
|
|
oxygenated blood from lungs enters LA via pulmonary veins
|
|
blood flows into LV via open left AV valve
|
|
LA contracts ⇒ complete ventricular filling
|
|
LV contracts ⇒ ↑ LV pressure → closes left AV valve, opens aortic valve → aorta → rest of body
|
|
LV relaxes ⇒ ↓ LV pressure → closes aortic valve (prevent backflow from aorta into LV)
|
|
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
|
|
isovolumetric contraction
|
|
▪ ventricular contraction begins (ventricular systole) → ventricular pressure > atrial pressure → AV valves close (S1); semilunar valves closed
|
|
▪ ECG ▫ QRS complex
|
|
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
|
|
reduced ejection
|
|
▪ ↓ ventricular ejection velocity
|
|
▪ ↑ atrial pressure
|
|
▪ ventricular repolarization begins
|
|
▪ ECG ▫ T wave
|
|
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
|
|
rapid ventricular filling
|
|
▪ ventricular diastole continues → ventricular pressure < atrial pressure → AV valves open
|
|
▪ passive ventricular filling
|
|
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
|
|
valve
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side
|
position
|
|
pulmonary
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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
|
|
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
|
|
second highest discharge rate
|
|
location: near coronary sinus on interatrial septum
|
|
mainly controlled by left vagus nerve
|
|
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
|
|
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)
|
|
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
|
|
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
|
|
EPICARDIUM
|
|
serous membrane - forms the visceral pericardium
|
|
carries vasculature
|
|
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
|
|
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
|
|
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
|
|
- 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
|
|
CONTINUOUS CAPILLARIES
|
|
- no pores or interruptions between endothelial cells
|
|
- muscle, lungs, nervous tissue
|
|
FENESTRATED CAPILLARIES
|
|
- have pores throughout endothelial walls
|
|
- endocrine glands, intestines, where fluid transport is important
|
|
SINUSOIDAL CAPILLARIES
|
|
- larger, more irregular shaped, no distinct basement membrane
|
|
- endocrine organs, aortic and carotid bodies
|
|
SINUSOID
|
|
- larger, basement membrane mostly absent, gaps in walls → exchange large molecules (proteins)
|
|
- bone marrow, liver
|
|
SINUSES
|
|
- larger than sinusoids with a discontinuous basement membrane
|
|
- spleen
|
|
VENULES
|
|
- lined by endothelial cells combined with loose connective tissue
|
|
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
|
|
- 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)
|
|
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
|
|
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
|
|
collateral circulation
|
|
- most distributing arteries branches before ending in tissues
|
|
- lung, intestine
|
|
anatomical end artery
|
|
- no anastomosis exists
|
|
- single artery supplies blood to a specific tissue piece with no collateral circulation
|
|
- brain, cornea
|
|
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
|
|
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
|
|
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
|
|
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
|
|
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 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
|
|
horse and pig
|
|
- LCA supplies paraconal interventricular branch
|
|
- RCA forms right circumflex branch, and subsinuosal interventricular branch
|
|
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
|
|
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
|
|
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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