Anatomy of the Heart

Question 1

What are the four chambers of the heart?

Answer 1

• right atrium
• left atrium
• right ventricle
• left ventricle

Question 2

What does each side for the heart receive?

How are the two sides separated?

Answer 2

The right side receives deoxygenated blood returning from tissues.
The left side receives oxygenated blood from lungs to send to tissues.

The left and right side are separated by atrial and ventricular septae

Question 3

What are the parts of the surface anatomy of the heart?

Answer 3

There is a base, apex, right and left surfaces and cranial and caudal borders

Question 4

Where is the base of the heart?

What enters the base of the heart?

Answer 4

It lies at the junction of dorsal and middle thirds of the thorax and is formed by atria

Cranial and caudal vena cava + pulmonary veins enter the atria via the base

Question 5

Where is the apex of the heart?

Where is the long axis of the heart?

Answer 5

It lies close to the sternum at the level of the sixth costal cartilage

It is drawn between the base and apex which lies at an angle which varies with species. In larger animals, the apex is more vertical

Question 6

Where is the cranial border of the heart?

What is the cranial border formed by?

Answer 6

It runs parallel with the sternum and is curved

It is formed by the right atrium and ventricle which lie cranial and to the right

Question 7

Where is the caudal border of the heart?

What is the cranial border formed by?

Answer 7

It is shorter and nearly completely vertical

It is formed by the left atrium and ventricle which lie caudally and to the left

Question 8

Where is the left surface of the heart?

Answer 8

It does not correspond exactly to the surface facing left but is so called because both auricles are visible from the left side.

Question 9

Where is the right surface of the heart?

Answer 9

It does not correspond exactly to the surface facing right but is so called because the atria are visible from the right side

Question 10

How are the atria and ventricles divided externally?

Answer 10

They are indicated externally by the coronary groove which contains main vessels that supply the heart. These are called the coronary arteries and veins. Further grooves extend from the coronary groove to the apex, marking divisions between left and right ventricles

Question 11

What are the grooves on the external heart called?

What do the grooves contain?

Answer 11

Coronary groove = main groove separating atria and ventricles
Paracondal groove = groove on the left surface
Subsinuosal groove = groove on the right surface

The groove contain interventricular coronary blood vessels, lymphatics, nerves and fat

Question 12

What is the pericardium?

What are the layers of the pericardium?

Answer 12

The pericardium is a close fitting serous membrane which covers the heart and the origin of major blood vessels.

The two layers of the pericardium are the inner visceral and outer parietal.

Question 13

What is the function of the visceral pericardium?

What does the visceral pericardium consist of?

Answer 13

It is adhered closely to the heart wall and is regarded as the outer layer of the heart or also known as the epicardium

It consists of a layer of mesothelial cells, which secrete pericardial fluid, and overlying connective tissue rich in elastic fibres which merges with the myocardium

Question 14

What is the function of the parietal pericardium?

What does the parietal pericardium consist of?

Answer 14

This layer gives rise to the ligamentous fold which anchors the apex of the heart. In the horse, cattle and pigs, this anchors the apex to the sternum = known as the sternopericardial ligament. In carnivores, this anchors the apex to the diaphragm = known as the phrenicopericardial ligament

This layer consists of three layers; inner squamous mesothelium, collagen and elastic fibrous layer, and the outer mediastinal pleura

Question 15

How are the visceral and parietal pericardium separated?

Answer 15

They are separated by a pericardial cavity which normally contains a small volume of lubricant also known as pericardial fluid

Question 16

Where is the right atrium in the heart?

What does the right atrium consist of?

Answer 16

It forms the right cranial aspect of the heart and lies dorsal to the right venticle

It consist of the main chamber, known as the sinus venarum, and the auricle, which is a blind ending sac which wraps around the craniodorsal aspect of the heart

Question 17

How does the right atrium receive blood?

Answer 17

It receives blood from the vena cava.
The caudal vena cava drains the body caudal to the heart and enters the right atrium caudodorsally. Ventral to this entrance, the coronary sinus lies, which carries most venous blood from the heart muscles it self and has small semilunar valves.
The cranial vena cava drains the head and forelimbs, entering craniodorsally into the right atrium. Ventral to the entrance, there is embryonic remnant tissue which has no functional significance

Question 18

How does the heart counter the turbulence caused by the cranial and caudal vena cava entering the right atrium?

Answer 18

Since the cranial and caudal vena cava both conduct blood into the right atrium from opposing directions, this causes turbulence. To counter this, an intravenous tubercle projects from the dorsal wall of the right atrium ventrally. This acts to direct blood from both vena cava towards the atrioventricular opening

Question 19

Where does the right azygous vein drain from and to?

Answer 19

It drains blood from the thoracic wall and joins the cranial vena cava or enters the heart directly between the vena cava

Question 20

What species if the left azygous vein found in and where does it drain to?

Answer 20

This vein may be present in pigs and ruminants.

It enters the right atrium via the coronary sinus

Question 21

What is the interatrial septum?

Where is the intertribal septum?

Answer 21

It is an opening which conducts blood from right to left atrium in the foetus, bypassing pulmonary circulation. It lies remnant of embryonic foreman ovals

It is caudal to the intravenous tubercle and at birth the foramen sells. leaving a depressed membranous fossa ovalis

Question 22

Where is the right ventricle in the heart?

Answer 22

It occupies the right cranial portion of the heart and forms most of the cranial border

Question 23

How does the right ventricle receive blood?

Answer 23

It receives blood from the right atrium via the right atrioventricular (AV) valve.

Question 24

What does the right atrioventricular (AV) valve consist of?

Answer 24

In most species the AV valve is composed of three cusps also known as tricuspid. The dog only has two cusps also known as bicuspid. The cusps are anchored to the fibrous skeleton of the heart where it encircles the AV opening. The free end go the cusps are attached to multiple fibrous strands, also known as chordate tendinae. These strands attach to papillary muscles which project from the ventricular wall.
There are generally three papilla muscles with each cusps attaching to two papillary muscles and each papillary muscles anchor two cusps.

Question 25

What are the steps for blood pumping through the right ventricle?

Answer 25

1. ventricle contracts
2. AV valve closes
3. chordate tendineae prevents eversion of cusps into the atria
4. blood passes from right ventricle into pulmonary arteries
5. back flow into right atrium is prevented

Question 26

What is the inner surface of the right ventricle made of?

Answer 26

It consists of muscular ridges called trabecular carnage which reduce turbulence.
It also has muscular and fine fibrous strands called trabecular spetomarginalis or moderator band which runs between the septum and ventricular wall. These strands provide structural support and conduct impulses rapidly to the entire ventricle

Question 27

How is the right ventricle divided?

Answer 27

It is incompletely divided by a muscular projection called supraventicular crest. Blood passes round this crest into conus arterioles through the pulmonary valve and into the pulmonary trunk to reach the lungs

Question 28

What does the pulmonary valve consist of?

Answer 28

It has three semilunar cusps which fit tightly together when the ventricle is relaxed, preventing blood flowing back into the ventricle from the pulmonary trunk.

Question 29

How does the left atrium receive blood?

Answer 29

It receives oxygenated blood returning from the lungs via 7/8 pulmonary veins.

Question 30

How is the left atrium structured?

Answer 30

It is structured similarly to the right atrium but occupies the dorsocaudal part of the heart. It also has pectinate muscles and sometimes the valve of foreman oval may be visible cranially in the intertribal septum.

Question 31

Where is the left ventricle in the heart?

Answer 31

It occupies the left caudal portion of the heart and forms the caudal border. It is conical shaped and forms the apex of the heart.

Question 32

How is the left ventricle structured?

Answer 32

The left ventricular wall is much thicker than the right as it has to generate greater pressure to pump blood to the body. Trabecular carnage is more prominent and papillary muscles are larger than the right ventricle. Trabecular septomarginalis is also present.

Question 33

How does the left ventricle receive and distribute blood?

Answer 33

It receives blood from the let atrium via bicuspid (mitral) left AV valve.
The aorta distributes blood to the body via many branches.

Question 34

How is structural support provided to the heart?

Answer 34

It is provided by a fibrous skeleton called annuli fibrosi. This consists of rings of collagen and elastic fibres encircling the left and right AV valves, aorta and pulmonary trunk. This separates the heart into atrial and ventricular components.

Question 35

What is the function of the annuli fibrosi?

Answer 35

It anchors the heart muscle, prevents distortion of opening during contraction and prevent direct conduction of electrical impulses from the atria tenth ventricles. ensuring this occurs only along specialised conduction pathways.