Circulation and Heart

Question 1

What are the species differences of aortic branching?

Answer 1

Dog and pig: have a brachiocephalic trunk and left subclavian artery.

Horse and cow: have a brachiocephalic trunk to supply everything, giving both right and left subclavian arteries.

Question 2

Describe branches of the aorta.

Answer 2

brachiocephalic trunk and left subclavian artery* > right subclavian artery* > left and right common carotid arteries

Question 3

What are the branches of the subclavian arteries and what do they supply?

Answer 3

Vertebral arteries - one of the main arteries supplying the brain and vertebral column.

Internal thoracic - gives rise to ventral intercostal arteries and terminates as cranial epigastric and musculophrenic arteries.

Costocervical trunk - dorsal neck and dorsal intercostal arteries to first few rib spaces.

Superficial cervical arteries - ventral neck

Axillary arteries - armpits that branch to forelimbs

Question 4

What do the common carotid arteries supply?

Answer 4

Ascend either side of neck and divide at the base of the skull. Supplies to internal carotid arteries to the brain and external carotid arteries to the head and neck.

Question 5

What do intercostal arteries supply?

Answer 5

Intercostal muscles. Dorsal intercostal arteries branch off aorta and are supplied by costocervical trunk. Ventral intercostal arteries branch off internal thoracic artery and anastamose with dorsal intercostal arteries.

Question 6

What is the bronchio-oesophageal artery?

Answer 6

Small ventral aortic branch near base of heart. Gives off bronchial arteries and branches to oesophagus.

Question 7

What is the pulmonary trunk?

Answer 7

Exits from right ventricle, carrying deoxygenated blood to lungs. Divides into left and right pulmonary arteries.

Question 8

What is the caudal vena cava?

Answer 8

Receives blood returning from abdominal and pelvic regions. Enters via thoracic cavity through diaphragm, then draining into the right atrium.

Question 9

What is the cranial vena cava?

Answer 9

Receives blood returning from the head, neck and forelimbs. Runs right and ventral to the trachea. Drains into the right atrium.

Question 10

What is the internal thoracic vein?

Answer 10

Mirrors path of the internal thoracic artery. Ventral intercostal veins drain into the internal thoracic vein.

Question 11

What are the species variations of the brachiocephalic veins?

Answer 11

Dogs and pigs: external jugular vein, supplying head and neck, and subclavian vein fuse to form the brachiocephalic vein. The right and left brachiocephalic veins fuse to form the cranial vena cava.

Horses and ruminants: external jugulars merge to form bijugular trunk. This fuses with the subclavian veins to form cranial vena cava.

Question 12

What are the species differences in azygous vein?

Answer 12

Originates in abdomen and enters thoracic cavity via diaphragm and runs along aorta.

Dogs and horses: single right azygous vein that either drains into cranial vena cava or right atrium.

Pigs: single left azygous vein.

Ruminants: both right and left azygous vein.

Question 13

What are intercostal veins?

Answer 13

Dorsal intercostal veins drain to azygous vein caudal to the heart or costocervical vein if cranial to heart. Ventral intercostal veins drain to internal thoracic vein. Dorsal and ventral intercostal veins anastamose.

Question 14

What is the costocervical vein?

Answer 14

Cranial dorsal intercostal veins and dorsal neck muscles drain to it.

Question 15

What are pulmonary veins?

Answer 15

Oxygenated blood from lungs drains into the left atrium.

Question 16

Name the 3 unpaired abdominal arteries and what they supply.

Answer 16

Coeliac artery - foregut

Cranial mesenteric artery - midgut

Caudal mesenteric artery - hindgut

Question 17

Name the 7 paired abdominal arteries and what they supply.

Answer 17

Phrenico-abdominal - cranial dorsolateral abdominal wall, dorsal diaphragm and adrenal glands.

Renal - kidneys

Gonadal - testes/ovaries

Deep circumflex iliac - caudal dorsolateral abdomonal wall

External iliac (the aortic bifurcation) - hindlimbs

Internal iliac - pelvis and genitalia

Median sacral - tail

Question 18

Describe the abdominal veins.

Answer 18

Generally mirror path of abdominal arteries, except no unpaired veins/no venous equivalent. This is because they are replaced by hepatic portal system:

Abdominal aorta >hepatic and cranial mesenteric arteries > hepatic portal vein > hepatic vein > caudal vena cava

Question 19

Name the 4 thoracic lymphocentres and their locations and drainages.

Answer 19

Dorsal thoracic - parietal pleura at dorsal 5th/6th intercostal space. Drains structures of the dorsal thoracic wall.

Ventral thoracic - embedded in fat around sternum at level of 2nd rib.

Bronchial centre - tracheal bifurcation. Drain lymph from lungs.

Mediastinal - in 2 groups in the dog: cranial mediastinal and middle near base of heart. Drain medistinal viscera and neck structures. Is the secondary filtration station for other 3 and drain to large lymphatic vessels.

Question 20

Describe the abdominal lymphatic vessels.

Answer 20

Thoracic duct is the largest, draining whole body except the right forelimb and right cranial thorax. Originates in abdomen where it is called the cisterna chyli and drains into the left brachiocephalic vein or cranial vena cava.

Right lymphatic duct drains right cranial thorax, right forelimb and right neck. Drains into cranial vena cava.

Tracheal ducts from head and neck drain to brachiocephalic vein.

Question 21

Describe the position of the heart in the mediastinum.

Answer 21

Middle ventral mediastinum, with base levelled at position of the tracheal bifurcation. The heart has a slight incline to the left hand side in a 5:4 ratio towards the left.

Question 22

Give the species variations for position of the heart in relation to specific ribs.

Answer 22

Dog and horse = 3rd to 7th ribs
Cat = 4th to 6th ribs
Ruminant = 3rd to 6th ribs
Pig = 2nd to 5th ribs

Question 23

What are the 3 layers of the heart?

Answer 23

Endocardium - smooth inner surface
Myocardium - middle layer of cardiac cells
Epicardium - visceral serous pericardium

Question 24

Describe the heart skeleton and its species variation.

Answer 24

• Plate of fibrous connective tissue between atria and ventricles for electrical insulation between them.
• Fibrous rings support valves and are a site for muscle attachment.
• Some species have strengthening fibrocartilage or bone. In cattle, ossa cordis are nodules of bone that support valves (splanchnic bones).

Question 25

What is the ligamentum arteriosum?

Answer 25

A ligamentous attachment between aorta and pulmonary trunk.
It is a remnant of a fetal structure called the ductus arteriosus. In the fetus, this is a patent vessel that connects the 2 vessels, channeling blood from the pulmonary circulation and immature lungs to the systemic circulation directly.
At birth, the ductus arteriosus becomes the ligamentum arteriosum.

Question 26

Describe the structure of the atrioventricular valves.

Answer 26

Cusps are fused at the base but separate at their free edges. Free edges attached to chordae tendinae, which are attached to papillary muscles.
Each muscle attached to 2 cusps and each cusp attached to 2 different muscles, preventing eversion during contraction. Papillary muscles contract when ventricles contract, pulling chordae tendinae taught.

Question 27

What is the cause of blood turbulence in the right atrium and how is this prevented?

Answer 27

Cranial and caudal vena cava openings are opposite to one another and so their blood flows are head on.

To prevent turbulence and clotting, projection of tissue called intravenous tubercle directs bloodstream ventrally down to the right interventricular valve.

Question 28

What is the fossa ovalis?

Answer 28

Remnant of the fetal structure, foramen ovale. Is a shallow oval depression in septal wall between atria.

Question 29

How does blood exit the right ventricle?

Answer 29

Via conus arteriosus, a cone shaped exit to the pulmonary trunk.

Question 30

What are trabeculae carnae?

Answer 30

Irregular ridges of muscular walls of both ventricles. They act to reduce turbulence.

Question 31

What is the trabeculae septomarginalis?

Answer 31

Thin band of muscle. Acts as a shortcut for purkinje fibres to ensure all ventricular walls contract simultaneously.

Question 32

Where do coronary arteries originate?

Answer 32

Aortic sinuses, located above each cusp of aortic valve. 3 cusps: cranial cusp, caudal sinistral (left) cusp, caudal dextral (right) cusp.
Right coronary artery arises from aortic sinus above cranial cusp. Left coronary artery arises from sinus above caudal sinistral cusp.

Question 33

Describe the branches of the left coronary artery.

Answer 33

Branches into 2 on the left face:

• Left interventricular/paraconal branch, which runs down groove to supply the left of the heart.
• Circumflex branch, which runs along the coronary groove to supply the right of the heart.

Question 34

What is the species variation of the circumflex branch?

Answer 34

Dog and ruminant: circumflex reaches the right side and runs down the interventricular groove, becoming the interventricular/subsinuosal branch (the LHS supplies the RHS).

Horse and pig: circumflex branch terminates before it reaches the right groove. The right coronary artery supplies the right side of the heart.

Question 35

Describe the right coronary artery in dogs and ruminants.

Answer 35

Emerges under right auricle and reaches coronary groove. Terminates before it reaches the subsinuosal groove.

Question 36

Describe the coronary veins.

Answer 36

Great cardiac vein originates near apex and ascends in the left interventricular groove to reach the right side.

Middle cardiac vein ascends the right interventricular/subsinuosal groove and joins great cardiac vein at coronary sinus.

Question 37

Where do coronary veins drain?

Answer 37

The right atrium via the coronary sinus.