Lung • It is the main organ of respiration where the gas exchange takes place between blood and atmospheric air. • It occupies the greater part of thoracic cavity. • Color: pink in well bled animals

Anatomical features

• The consistency of lung is soft, spongy and elastic. It has low specific gravity. • It floats in water (due to air contents). The lung of still born animals sink in water as it contain no air. • Each lung has apex, base, 3 surfaces and 3 borders • Apex: present cranially in cupula pleurae • Base: it is oblique, faces caudoventrally, lies on diaphragm • Dorsal border: between medial and costal surface

Pulmonary lobules

• It is a small unit of lung tissue with irregular borders. It surrounded by inter lobular CT. it may be ventilated by small bronchus or bronchioles. • The degree of lobulation depends on amount of inter lobular CT

In dog lobulation not seen by naked eye (smooth appearance

In pig: lobulation is visible

In ox: lobulation is very clear

In Sheep: lobulation is absent

In goat: lobulation in cranial and middle lobe

In horse: lobulation not clear Lobation of lung Species Left lung Right lung Cranial Divided cranial Middle Carnivores Caudal Caudal Accessory Cranial (Tracheal bronchus) Divided cranial Middle Pig Caudal Caudal Accessory Divided cranial (Tracheal bronchus) Divided cranial Ruminants Middle Caudal Caudal Accessory Cranial cranial Horse Caudal Caudal Accessory

The thoracic Cavity

• The thoracic cavity is the part of the body cavity that lies cranial to the diaphragm.

• The part of the skeleton which consists of thoracic vertebrae, ribs with their cartilages and the sternum is known as, rib cage or Bony thorax (laterally flattened cone which is opened at both cranial and caudal ends, the apex of the cone lies cranially and its base lies caudally) Boundaries of the thoracic cavity

Dorsal wall (Roof) Ventral wall (floor) Lateral wall 1- The muscles above the 1-The transverse thoracic 1- The ribs and the thoracic vertebrae. muscle dorsal to the intercostal muscles. sternum. 2- The thoracic vertebrae 2- The sternum and the 2- Some muscles of the and the intervertebral cartilages of the sternal shoulder girdle. discs ribs.

3- The medial aspect of 3- The ventral 3- The pectoral muscles the arm and shoulder longitudinal ligament and ventral to the sternum. the thoracic part of region of the thoracic longus colli m. limb are applied on the lateral wall of the thorax. Openings of the thoracic cavity

Cranial thoracic aperture (thoracic inlet) Caudal thoracic aperture (thoracic outlet)

Shape Small, narrow and oval in shape Large and wide

Boundaries Dorsally by the first thoracic vertebra Dorsally by the last thoracic v. Laterally by the first pair of ribs Laterally by the last pair of ribs and the costal arch and the xiphoid process of Ventrally by the Manubrium of the sternum the sternum Ventrally by it is closed by diaphragm .

Structures 1- Longus coli muscle, Structures passed through the three pass 2- Esophagus and Trachea openings of the diaphragm and the through it lumbocostal arches. 3-The blood vessels supplying the head, neck, thoracic limb and lateral thoracic wall 4-Lymphatics. 5-Thymus in young animals 6-The two vagus nerves, the recurrent nerves (from vagus), The two phrenic nerves and sympathetic chains. The pleura

• The pleura is the serous membrane which lines the thoracic cavity and the lungs. It is arranged in the form of two pleural sacs (right and left), which surround both lungs. • The two pleural sacs are separated by the mediastinum. • As any serous membrane, the pleura is formed of two layers; the parietal pleura and the visceral pleura (pulmonary pleura). • The two layers are continuous at the root of the lung to form the pulmonary ligament. • The two layers are separated by a narrow space The pleural cavity, which contains a small film of serous fluid. Costal pleura (The parietal pleura) It is loosely attached to the endothoracic fascia which lines the ribs and costal cartilages. caudally it reflects onto the diaphragm to form the diaphragmatic pleura. The line of this reflection is the diaphragmatic line of pleural reflection. Diaphragmatic pleura Is the part of the parietal pleura which covers the diaphragm. form with the costal pleura costodiaphragmatic recess, which lies caudoventral to the basal border of the lung. Mediastinal pleura It is formed by the reflection of the costal pleura (dorsally and ventrally) and diaphragmatic pleura caudally. • two lines of reflections :Vertebral & sternal line of pleural reflection. • two recesses: Dorsal & ventral costomediastinal recesses . The mediastinum • The mediastinum is the interval between the two pleural sacs. • It is median in position but may displaced by the pressure of the two lungs. • It extends longitudinally from the thoracic inlet cranially to the diaphragm caudally and from the thoracic vertebrae dorsally to the sternum ventrally. • All the structures in the thoracic cavity are located in the space of the mediasinum except: 1- The two lungs, 2- The caudal vena cava and 3- The right phrenic nerve caudally. parts of the mediastinum Middle mediastinum Caudal mediastinum (post- Cranial mediastinum (precardiac) (Cardiac). cardiac) 1-Thoracic part of longus coli muscle. 1-The and the large 1-The thoracic part of the 2-Thoracic part of the esophagus and blood vessels at the base of esophagus. trachea the heart. 2-The thoracic and the 3-The thymus in young animals. 2-The thoracic part of the caudal mediastinal lymph 4-The cranial mediastinal Ln. and the esophagus and the principle node. end of the thoracic duct. bronchi. 3-Neves; the dorsal and 5-Branches of the brachiocephalic trunk. 3-The two vagi, the two ventral vagal trunks 6-Some nerves as, the sympathetic phrenic Nn. and the (terminal branches of the chains, the right & left vagus nerves sympathetic chains. two vagi), the right and left recurrent nerves and the right & left sympathetic chains and the phrenic nerves. left phrenic nerve only.

structures related to the pleura

1- The mediastinal recess: It is the part of the right pleural cavity which lies between the caudal mediastinum and the plica . It contains the accessory lobe of right lung. 2- The plica venae cavae: It is a fold of parietal pleura of the right pleural sac which enclose the caudal vena cava and the caudal part of right phrenic nerve. It lies between the accessory and diaphragmatic lobes of the right lung. 3- The pulmonary ligament: It is formed by the continuity of mediastinal pleura (parietal) and pulmonary pleura (visceral) caudal to the root of the lung. in Animals Organs of the cardiovascular system -Circulatory system made up of: 1- organ: -heart 2- tissues & cells: a-blood vessels -arteries -veins -capillaries b- blood: -red blood cells -plasma The blood vessels are arranged as two circuits of blood flow, following a figure of 8 pattern with the heart in the centre. The larger, systemic circulation conveys oxygenated blood from the heart to all the organs of the body and transports deoxygenated blood back to the heart. The smaller, conveys deoxygenated blood from the heart to the exchange tissue of the lungs, where it is oxygenated before it is returned to the heart. Circulatory systems open closed

hemolymph blood • In fishes the blood only passes through the heart once on its way to the gills and then r o u n d t h e r e s t of t h e b o d y . • However, in mammals and birds that have lungs, the blood passes through the heart twice: once on its way to the lungs where it picks up oxygen and then through the heart again to be pumped all over the body. The heart is therefore two separate pumps, side by side

Vertebrate Heart • 4-Chambered heart – atria () • thin wall • collection chamber left • receive blood atrium

– ventricles right • thick wall pump atrium • pump blood out

right left ventricle Lub-dub, lub-dub • 4 valves in the heart – flaps of connective tissue – prevent backflow • Heart sounds – closing of valves SL – “Lub” • force blood against AV closed AV valves AV – “Dub” • force of blood against semilunar valves • Heart murmur – leaking valve causes hissing sound – blood squirts backward through valve • The pericardium, or heart sac, is the fibroserous covering of the heart. It is essentially a deeply invaginated sac, contains a small amount of serous fluid (liquor pericardii) which facilitates movement of the heart against the pericardium.

• The pericardium can be divided 1- Serous pericardium -Visceral layer - Parietal layer 2 - Fibrous pericardium

• The visceral layer of the pericardium is firmly attached to the heart wall, forming the epicardium. It covers the myocardium, the coronary vessels and fat on the surface of the heart.

• The parietal layer of the serous pericardium is firmly fused to the fibrous pericardium.

• The base of the fibrous pericardium is continuous with the great arteries and veins that leave and enter the heart, uniting with the adventitia of these vessels. Ventrally it continues into the following ligaments:

Sternopericardiac Phrenopericardiac ligament ligament (only present in the dog ) Position and size of the heart • The heart is located within the mediastinum with the larger part (60%) lying to the left of the median plane. It extends between the third and sixth (seventh in the cat and dog) rib. The heart base is roughly located on a horizontal plane drawn through the middle of the thorax. Most of the surface of the heart is covered by the lung, • Variations in position and size occur among species, breeds and individuals, according to age, condition and the presence of disease. As a rough guide, the heart provides about 0.75% of the body weight.

Compartments of the heart

• The heart is divided internally by a longitudinal interatrial & into left and right sides. These in turn are incompletely divided by a transverse septum into the blood receiving atria (atrium cordis) and the blood-pumping ventricles

The right atrium • forms the right, dorsocranial part of the base of the heart. • It receives the blood from the cranial and caudal vena cava and the coronary sinus (sinus coronarius), which collects the venous blood from most of the heart itself. • It is divided into a main part, the sinus of the venae cavae (sinus venarum cavarum) and a blind-ended part, the right auricle. It is separated from the left atrium by the • The intervenous tubercle is a transverse ridge of tissue between the openings of the two vena cavae, protrudes into the interior of the right atrium.

• It directs the inflow of blood through the Right atrioventricular opening.

• Just caudal to this tubercle, on the interatrial septum is a depressed area, the oval fossa, which is the remnant of the foramen ovale of foetal development.

• The internal surface of the wall of the right auricle is strengthened by interlacing muscular bands (pectinat ms). Left atrium

The left atrium forms the left, dorsocaudal part of the base of the heart. It receives the oxygenated blood from the pulmonary veins. It is similar to the right atrium in shape and structure It opens into the left ventricle by the left atrioventricular opening. Several openings mark the entrance of the pulmonary veins into the left atrium.

Ventricles of the heart

• The ventricles constitute the majority of the mass of the heart. They are separated from the atria by a transverse, incomplete septum, which is indicated on the surface by the coronary groove . Right ventricle

The right ventricle is crescent shaped in cross section. It does not extend as far the apex of the heart, which is usually formed by the left ventricle alone.

The conus arteriosus is the funnel-shaped part of the right ventricle, which is separated from the main chamber by the supraventricular crest and considered as the entrance to the • The supraventricular crest is a blunt, obliquely positioned ridge of muscle that projects ventrally between the origin of the conus arteriosus and atrioventricular opening. • The right atrioventricular opening is the right atrioventricular or : It is composed of three cusps that attach peripherally to the fibrous rings of the "" encircling the atrioventricular opening. • Each cusp is enforced by fibrous strands, the .

• The chordae tendineae arise from conical shaped muscular projections, the papillary muscles. There are generally three of these muscles

• The chordae tendineae are so arranged that they connect each muscle to two cusps and each cusp to two muscles.

• The is located at the root of the pulmonary trunk and consists of three semilunar cusps.

• The lumen of the right ventricle is crossed by a branched or single muscular band (trabecula septomarginalis), that passes from the interventricular septum to the outer wall.

• The ventral part of the right ventricle is marked by numerous myocardial ridges (), that project mainly from the outer wall. Left ventricle • The left ventricle is conical in shape with its apex forming the apex of the heart. • The walls of the left ventricle are thicker than the ones of the right, however the volume of both ventricles is the same. In the cat, there are two muscular bands crossing the interior of the ventricle from the outer wall to the interventricular septum (trabeculae septomarginalis). • The left atrioventricular opening is occupied by the left atrioventricular valve), also known as . Its structure is similar to the right atrioventricular valve in form but consists of two cusps. • There are only two in the left ventricle. • The is the opening from the left ventricle into the ascending aorta. It is closed by the • Peripheral to each of the semilunar cusps of the aortic valve, the wall of the aorta is dilated to form the three aortic sinuses. • The widening of the base of the ascending aorta, formed by the aortic sinuses, is the aortic bulb. • The right and left leave the right and left aortic sinuses.

Structure of the cardiac wall • The wall of the heart consists of three layers • , • Myocardium, • Epicardium. Cardiac skeleton

The fibrous skeleton of the heart is made up of dense connective tissue rings that encircle the four heart orifices (anuli fibrosi).

Function:-

1- the area for myocardial tissue origination and attachment, 2- give an attachment and support to the valves. 3- that separates the atria from the ventricles.

Blood vessels of the heart • Blood supply to the heart is provided the coronary arteries and their branches. They originate from two of the three sinuses above the semilunar valves at the root of the aorta. 1 - The left coronary artery arises from the left sinus of the aortic bulb. It passes between the left auricle and the pulmonary trunk to the coronary groove, where it divides into the interventricular paraconal branch and the circumflex branch 2- The right coronary artery arises from the right sinus of the aortic bulb and passes between the right auricle and the pulmonary trunk to the coronary groove.

Innervations of the heart

• Innervation of the heart is provided by the autonomic nervous system. • Sympathetic fibers are supplied by the satellite ganglion and the middle cervical ganglion. (Accelerator nerve) • Parasympathetic fibers arise as branches of the vagus nerve either directly or from the recurrent laryngeal nerve. (depressor nerve).

Conducting system of the heart The conducting system consists of the following parts • • • Atrioventricular bundle or 1- Right bundle 2- Left bundle 1. The Sinoatrial node is located below the endocardium of the right atrial wall ventral to the opening of the cranial vena cava.. It is richly innervated by both the sympathetic and parasympathetic nervous systems. 2. The atrioventricular node, is located in the interatrial septum close to the opening of the coronary sinus 3. The atrioventricular bundle penetrates the cardiac skeleton before dividing into right and left bundles under the endocardium of the interventricular septum. 4. The right branch crosses the cavity of the right ventricle in the septomarginal trabecula of this chamber. It ends in the outer ventricular wall of the right ventricle. 5. The left branch is more diffuse and ramifies in the outer wall of the left ventricle. 6. The final branches of these bundles are known as subendocardial branches or Purkinje fibres. Electrical signals

stimulates ventricles to allows atria to empty contract from bottom to completely before top, driving ventricles contract blood into arteries

• heart pumping controlled by electrical impulses

Function of the heart

• Alternating between contraction and relaxation results in a pumping action, that makes the blood circulate through the body. The phase of contraction is called systole, relaxation is called diastole. During systole the atria of the heart contract first, followed by a contraction of the ventricles, which takes about double the time of the latter

Blood vessels The ascending aorta on the right side of the pulmonary trunk The ascending aorta passes caudally (aortic arch) and reaches the vertebral column at the level of the sixth thoracic vertebra slightly to the left of the median plane and continues from there as the descending aorta The aortic arch • is joined to the pulmonary trunk by the ligamentum arteriosum, the remnant of the fetal ductus arteriosus. Immediately after birth, when the new-born starts to breathe, the tunica media of the ductus arteriosus contracts and the inner tunic starts to transform. Normally the lumen of the vessel is obliterated within the first week postpartum.

Cranial branches of the aortic arch

Brachiocephalic trunk • The brachiocephalic trunk arises from the aortic arch and branches cranially. • It provides the blood supply for the thoracic limbs, the neck, the head and the ventral portion of the thorax. • The brachiocephalic trunk gives: 1) Left subclavian artery (a. subclavia sinistra), 2) Right subclavian artery (a. subclavia dextra), 3) Bicarotid trunk (truncus bicaroticus). In the pig, cat and dog, the left subclavian artery takes a separate origin from the aortic arch.

Left Subclavian artery

• The left subclavian arteries supplies blood to the forelimbs, the neck and cranial and ventral parts of the thorax. • Branches of the subclavian artery 1 Costocervical trunk (truncus costocervicalis), » Supreme intercostal artery. » dorsal scapular. 2 Deep cervical artery 3 Vertebral artery (a. vertebralis) 4 Superficial cervical artery 5 Internal thoracic artery Musculophrenic artery. Cranial epigastric artery, 6- Axillary artery, the direct continuation of the subclavian artery.

Blood supply of head and neck • The bicarotid trunk is a short common trunk, which arises from the brachiocephalic trunk. • extends cranially and branches into the left and right common carotid arteries. • In the dog and cat the common carotid arteries arise separately from the brachiocephalic trunk. • The origin of the right being distal to the left, therefore these animals do not have a bicarotid trunk.

The common carotid arteries

• ascend the neck to each side of the trachea accompanied by the vagosympathetic trunk and the caudal (recurrent) laryngeal nerve.

• Except for some small branches to the esophagus, the trachea and the adjacent muscles, the only significant branches are detached close to its termination

1- Caudal thyroid artery thyroid gland, 2- Cranial thyroid artery thyroid gland, 1- Cranial laryngeal artery : larynx, 2- Ascending pharyngeal artery:pharynx, 3- Occipital artery): nuchal musculature, Caudal meningeal artery: Meninges, 4- Internal carotid artery : brain, 5- External carotid artery

• Close to this division lies the carotid body (glomus caroticum), a chemoreceptor, which responds to changes in blood pressure.. The occipital artery

• provides blood supply to the muscles of the nuchal region, the caudal meninges, the middle and internal ear before it anastomoses with the vertebral artery, thus taking part in the supply to the brain The internal carotid artery • enters the cranial cavity after forming a characteristic s- shaped flexure at the base of the skull in the horse and dog.

• In the horse the internal carotid artery passes through the guttural pouch, a diverticulum of the auditory tube, peculiar to the horse. Erosion of the vessel wall in horses with guttural pouch mycosis causes bleeding, which can be fatal.

• In the horse and the dog, the internal carotid artery is responsible for vascularisation of the brain. In the other domestic mammals this is achieved by branches of the maxillary artery. The external carotid artery

• is the largest of the terminal branches of the common carotid artery and appears as the direct continuation of the parent trunk. It continues as the maxillary artery and detaches several branches to provide the blood supply to the muscles, bones and organs of the head, other than the brain. External carotid artery

1) Linguofacial artery, 1- Ascending palatine artery: pharynx, 2- Lingual artery: tongue, 3- Facial artery: 1. Sublingual artery: tongue 2. Inferior labial artery; face, lower lip, 3. Superior labial artery; face, upper lip, 4. Lateral nasal artery: face, nose, 5. Dorsal nasal artery: face, nose, 6. Angular artery of the orbit: face, eye lids, 2) Masseteric artery: masseter muscle, 3) Caudal auricular artery: external ear 4) Superficial temporal a: a- Transverse facial artery: masseter muscle, b- Rostral auricular artery: external ear,

The maxillary artery The 1st part

1- Inferior alveolar artery:

a- Alveolar branches : lower teeth,

b- Mental artery : mental angle,

2- Pterygoid branches

3- Rostral tympanic artery

4- Middle meningeal artery : meninges,

5- Caudal deep temporal artery : temporal muscle, The 2nd part (within the canal)

1- Rostral deep temporal artery: temporal muscle,

2- External ophthalmic artery:

a- Supraorbital artery : frontal region,

b- Ethmoid artery: ethmoid, orbit,

c- Lacrimal artery : lacrimal gland,

d- Rostral meningeal artery: meninges,

e- Internal ophthalmic artery: retina.

rd The 3 part

1- Buccal artery

2- Infraorbital artery: teeth, maxilla, nose,

3- Descending palatine artery:

a- Sphenoplatine artery : nasal cavity,

b- Greater palatine artery : hard palate,

c- Lesser palatine artery : soft palate,

Clinically important landmarks: • Pulse palpation in the horse : Facial artery at the facial notch on the ventral border of the mandible. • Arterial blood sampling: 1- Linguofacial artery at the facial notch on the Ventral border of the mandible 2- common carotid artery at the base of the neck,

3- Transverse facial artery ventral to the temporomandibular joint. The descending aorta

aortic hiatus thoracic portion abdominal portion

Thoracic cavity Abdominal cavity

At the level of the caudal lumbar vertebrae it divides into its terminal branches: A- 2 External iliac a. B- 2 Internal iliac a. C- Median sacral a

Thoracic aorta and abdominal aorta

• Branches of the thoracic aorta:- 1) Dorsal intercostal arteries: thoracic and abdominal wall, spinal cord. 2) Bronchoesophageal artery: a- Bronchial branches bronchial tree, b- Ephageal branches esophagus, 3) Costoabdominal artery abdominal wall 4) Cranial phrenic artery diaphragm present in the horse only abdominal aorta

Parietal branches Visceral branches

segmental arteries, 1.Phrenico-abdominal which are called artery lumbar arteries 2.Celiac artery, 3.Cranial mesenteric artery 4.Renal arteries), 5.Testicular / ovarian arteries 6.Caudal mesenteric artery

Viceral branches of abdominal aorta

1) Caudal phrenic artery present in all the domestic mammals, other than the horse:diaphragm. 2) Celiac artery, • Splenic artery , 1- Splenic branches (a. lienalis), 2- Left gastroepiploic artery 3- Short gastric branches

• Left gastric artery 1- Visceral branch 2- Esophygeal branch

• Hepatic artery , 1- Hepatic branches 2- Right gastric artery (pyloric region) 3- Right gastroepiploic artery 4- Cranial Pancreaticodudenal artery

3- Cranial mesenteric artery • It gives the following branches: 1- Caudal pancreaticoduodenal artery 2- Jejunal arteries , 3- Ileocolic artery, A- Cecal arteries ((medial and lateral cecal branch) B- Heal arteries (ilial a), C- Colic branch (to the ventral u-shape of the ascending colon). 4- Right colic artery (to the dorsal u-shape of the ascending colon), 5- Middle colic artery (to the transverse colon),

3- Caudal mesenteric artery

1- Left colic artery.

2- Cranial rectal artery.

Termination of the abdominal aorta

1- Right and left external iliac artery 2- Right and left internal iliac artery 3- Median sacral artery. External iliac artery

1. Uterine artery ( only mare), 2. Deep circumflex iliac artery 3. Deep femoral artery : A- Pudendoepigastric arterial trunk - External pudendal artery. (Scrotum, mammary gland) - Caudal epigastric artery. (abdominal muscles). B- medial circumflex femoral artery 4- Femoral artery, which passes through the femoral canal and gives: 1) Lateral circumflex femoral artery, 2) Caudal femoral artery, 3) Saphenous artery, 4) Descending genicular artery, 5- Popliteal artery: 1) Caudal tibial artery, 2) Cranial tibial artery: A- Dorsal pedal artery B- Dorsal metatarsal artery: 1- Lateral plantar digital artery 2-Medial plantar digital artery

Internal iliac artery • The internal iliac artery provides blood supply to the pelvic viscera and the walls of the pelvic cavity, including the lumbar muscles and the overlying muscles of the gluteal region. • It is one of the terminal branches of the aorta and in the horse the median sacral artery can arise either from the left or the right internal iliac artery. The median sacral artery gives origin to segmental branches.

A- Lumbar arteries: to the vertebral column and associated structures (Opposite the 6th lumbar vertebra) divides into: B- Caudal gluteal artery: 1. Cranial gluteal artery: (it exits through the greater sciatic foramen) supply the dorsolateral wall of the pelvis and the croup. 2. Obturator artery: (arising either from the caudal or cranial gluteal artery), it leaves the pelvic cavity together with its satellite vein and nerve by the obturator foramen and gives the middle artery of the penis in male and middle artery of the clitoris in female. 3. Iliolumbar artery: to deep lumbar muscles C- Internal pudendal artery: to the pelvic viscera. 1 - Uterine artery: not found in mare 2 - Umbilical artery: In the stallion, it releases the small artery of the deferent duct In both sexes, it gives the cranial vesical artery and ends as the round ligament of the urinary blaader. 3 - Vaginal artery (prostatic artery in the male): 1- Branch to deferent duct or uterine branch 2- Caudal vesical artery 3- Ureteric branch 4- Urethral branch 5- Middle rectal artery 4- Ventral perineal artery

5 - Caudal rectal artery

6- Vestibular artery or artery of the penis

7- Dorsal artery of the penis left lateral views of the male and female arterial supply to the canine pelvis. 1 - aorta 2 - external iliac 3 - Internal iliac 4 - median sacral 5 - cranial gluteal 6 - caudal gluteal 7 - Internal pudendal 8 - ventral perineal 9 – penile 10 - caudal superficial epigastric 11 - caudal deep epigastric 12 - artery of the ductus deferens 13 - urogenital 14 - testicular 15 - ovarian 16 - uterine 17 - pudendoepigastric trunk which gives 18 - cranial rectal 19 - caudal rectal 20 - obturator 21 - umbilical 22 - vesical