Cardio

• • right ventricular flow of blood to lungs
  • left ventricular flow to systemic side
• Heart Size

  • in small cetaceans and pinnipeds, it weighs approx. 0.5-1% of the body mass
  • in great whales its smaller → 0.3-0.5%
• Cardiac fat

  • fat layer around heart, more noticeable in marine mammals and when stressed this fat is rapidly used
• Stroke volume ⇒ volume of blood ejected from LV per heart beat
• Heart rate ⇒ number of heart beats per minute
• Resting cardiac output ⇒ stroke volume x heart rate (volume per minute)
• Heart

  • greater stores of glycogen in hearts of some seals
  • glycogen →(glycolysis)→ pyruvate→ oxidative phosphorylation
  • suggests higher anaerobic capacity (ability to maintain cellular life without O2 compared to land mammals)
• Pericardium

  • tough fluid filled sac surrounds heart
  • fluid serves to:
  • lubricate heart (prevents rubbing)
  • amount similar in all species (relative to size)
  • except manatee → has more
  • thickness of pericardium varies
  • humans are relatively thin
  • pinnipeds vary→ sea lion very thin, grey seal thicker
• Valves

  • prevents blood from flowing in wrong direction
  • found between:
  • RA and RV (tricuspid valve)
  • RV and PA (pulmonary valve)
  • LA and LV (mitral valve)
  • LV and aorta (aortic valve)
• Atrioventricular valves have:

  • leaflets (tricuspid 3 (thinner, not easily identified), mitral 2)
  • chordae tendinae → give extra strength to prevent back flow at high pressure
  • papillary muscles
  • chordae tendinae and papillary muscles help keep valve closed during ventricular systole

  semilunar valves (3 half moon leaflets)

  between ventricle and outflow tract

  • aortic valve
  • pulmonary valve
• Myocardium

  • muscle of heart → 3 layers
  • epicardium - outer
  • subendocardium - middle (not as vascularized)
  • endocardium - inner
• Trabeculae Carnae

  • muscle bundles inside of heart
  • reinforce and help heart to pump efficiently
• arteries- supplies heart muscle with blood (oxygen and energy)

  veins- removes waste products
• Left and right coronary arteries

  • supply LV and RV
• Left and right coronary veins

  • drain LV and RV myocardium
  • join to empty into coronary sinus which then empties into right atrium
• Aorta

  • largest artery
  • originates from LV
  • extends down through chest and abdomen
• Aorta

  • when reaches pelvic area branches into:
  • in species with hind limbs (ex. pinnipeds) → the common iliac arteries
  • in cetaceans; sirenians→ continues as sacral or caudal artery to tail
  • send branches the hypogastric arteries
• Aorta- needs to be very elastic, able to stretch to adjust to differing volumes (Windkessel effect)
• in pinnipeds, ascending aorta just outside of heart increases by 30-40% and forms an elastic bulb → aortic bulb
• after aortic arch it decreases in diameter by 50% and continues as a slender tube in abdomen
• There may be correlation between size of bulb and diving habits within pinnipeds

  • shallow diving leopard seal = smaller bulb
  • deep diving Weddell seal = larger bulbadaptation allows for:
  • increased lung perfusion while on surface
  • maintains blood pressure throughout dives
• Aortic Bulb → Cetaceans

  • can be found in cetaceans but have key differences from pinnipeds
  • thickness of bulb’s walls
  • organization of its elastic tissues
• Heart of Sirenians

  • have deep inter-ventricle cleft along the full length of the ventricles and a dorsally located left atrium
  • manatees have a bulbous swelling of aorta which is not found in dugongs, since mostly in rivers
• • vascular changes to help with thermoregulation
  • counter current heat exchange system
  • larger blood volumes
  • large blood holding structures such as spleen and venous sinuses
  • venous sphincter muscles
  • aortic Windkessel effect (ability to stretch)
  • vascular retia mirabilia and vascular changes to help with thermoregulation
• In arteries of pinnipeds

  • dense amount of nerves at both proximal and distal ends (close and away from body)
  • during dives allows for blood vessels to stay closed when would normally want to open to flow through to extremities or organs
  • so blood would be sent to important organs such as brain and heart
• Venous capacitance or areas to store blood is highly developed especially in some seals

  • includes a large hepatic sinus and inferior vena cava where 1/5 of seal’s blood volume stored
  • allows for blood to be quickly squeezed into circulatory system to maintain blood pressure due to external pressure in dives
• • many marine mammals also have few or no valves in their veins compared to land mammals
  • instead have more elastin content in walls of veins → do same as valves (prevent backwards movement)
• Spleen

  • in sea lions and seals is LARGE
  • comprises approx. 4.5% of body weight
  • serves as storage site for oxygenated rbc
• • in certain seals, spleen is a significant storage of blood that up to 30% of volume is storedin phocid seals (not otariids) diving capacity is correlated with spleen size
  • increase of blood cells might be necessary due to fluctuation of rbc between resting and diving states or during stressful situations
  • elephant seal has largest spleen
• in cetacean spleens

  • very small (0.02% of body weight)
  • no correlation to diving capacity
• Seal and whales

  • have an extradural venous system which receives blood from brain, back and pelvic area
  • in pinnipeds lies on dorsal aspect of spinal cord but outside the dura mater, between it and periosteum lining of spinal canal
  • in cetaceans it is on ventral aspect
  • may help with thermoregulation of brain
  • larger blood volumes contribute to increased O2 stores
  • 2-3X greater than avg. human value
  • generally larger in very active and longer diving species
• Retia Mirabilia

  • contorted spirals that serve as blood reservoirs to increase O2 stores during diving
  • unique system of blood vessels found in marine mammals
  • other animals use it for heat exchange and not as blood/oxygen reserves
  • found in specific tissue → usually in dorsal wall of thoracic cavity and extremities
  • tissue contains blood vessels, mostly arteries but some thin walled veins
  • forms extensive network of contorted spirals
  • sperm whales have most developed thoracic retia of all cetaceans
• • Posterior Vena Cava
  • often a pair of vessels rather than just one
  • have thin elastic walls capable of considerable distension
  • receive blood draining from plexi (network of veins) within their flippers, pelvis, kidneys and abdominal wall
• pinnipeds- along posterior vena cava, posterior to diaphragm is a hepatic sinus = enlarged area which collects blood to send to the heart
• pinnipeds

  • anterior to diaphragm, vena cava has a muscular caval sphincter which surrounds it
  • anterior to the vena cava, there is a pericardial plexis where veins enter into vena cava
• pinnipeds

  • pericardial plexis forms a ring around base of pericardium where it send out leaf like projections into pleural cavity which contain lungs, helps expand to contain more blood
  • veins in this region are thick and are composed of coiled collagenous elastic and smooth muscle fibres which suggest considerable capacity for expansion
• Walrus

  • large hepatic sinus and developed caval sphincter but have a single vena cava and NO well developed pericardial plexis nor stellate plexus
• Cetaceans

  • veins are not as enlarged as in pinnipeds although their vena cava is enlarged in hepatic area in SOME species
  • have no caval sphincter or hepatic sinus
  • do have a pair of large veins that run ventrally to spinal cord that may assist in their diving abilities (EDV)
• extradural intravertebral venous system is well developed in all specimens of Pinnipedia and is present in all adult and fetal Cetacea
• in harbour seals → large vein lying dorsal to the cord, which communicates posteriorly with the stellate renal plexus and the pelvic plexuses, and anteriorly with the intracranial venous sinuses