Lecture 6 Flashcards
Where is the location of the heart?
- Ventral position in chest
- Anterior to diaphragm
List the structures of the heart
- 4 chambers
- Right ventricle –> blood flow to the lungs (venous side)
- Left ventricle –> blood flow to systemic system (Aortic side)
How does the human heart compare to that of marine mammals?
- Although different body shape, orientation of the heart remains the same
- Structures have the same name across mammals
How does an adult beluga heart compare to the newborn
Adult: more rounded and flatted dorso-ventral shape
Newborn: ventricular walls not as thick due to placental assistance on circulation
What happens to the heart with age after birth of beluga?
Left ventricle wall becomes thicker because heart fully takes over blood circulation
- No longer relying on placental assistance
How does heart size differ between marine mammals in terms of mass percentage.
- In small cetaceans and pinnipeds, the heart weighs about 0.5-1% of the body mass
- In great whales, it is SMALLER (0.3-0.5%)
What role does cardiac fat play?
- All animals have this around their heart
- More noticable in marine mammals
- When stressed this fat rapidly used
- Fat used as an energy source incase of lack of food
How are cardiac measurements (i.e. SV, HR, CO…) determined?
- Chamber size, SV, resting CO, and HR of marine mammals are within land mammal measurements
- Relative to body mass
- Heart bigger in larger mammals
What is SV, HR, and resting CO?
- SV = Stroke Volume = volume of blood ejected from LV per heart beat
- HR = Heart Rate = number of heart beats per minute
- Resting CO = resting cardiac output = stroke volume x heart rate
What is one difference in marine mammalian hearts
- Greater stores of glycogen in hearts of some seals
- Suggest higher anaerobic capability
What is the pericardium?
- Tough fluid fild sac surrounds heart
Fluid serves to: - Lubricate heart
- Amount similar in all spaces
- Manatee has more fluid
How does the pericardium differ between species?
- Human paricardium is relatively thin
Pinnipeds vary: - Sea Lion very thin
- Grey seal thicker
What are the valves within the heart?
- RA & RV (Tricuspid valve)
- RV & Pulmonary Artery (Pulmonary semilunar valve)
- LA & LV (Mitral valve / Bicuspid valve)
- LV & Aorta (Aortic semilunar valve)
Describe the atrioventricular valves
- Leaflets (tricuspid 3; mitral 2)
Help keep valve closed during systole
- Chordae tendinae (hold leaflets down)
- Papillary Muscles (attached to chordae tendinae to reinforce valve closure)
What are the semilunar valves?
- Between ventricle and outflow tract
- Aortic valve
- Pulmonary valve
What is the Myocardium and what are the layers?
Myocardium = muscle of the heart (3 layers)
Epicardium - outside (well vascularized)
Subendocardium - middle layer
Endocardium - inner layer (well vascularized)
What is the Trabenculae Carnae?
- Muscle bundles inside of heart
- Reinforce and help heart to pump efficiently
What is the Coronary System?
- Arteries: supply heart muscle with blood (Provide oxygen and energy)
- Opening just after semilunar valve
- When Aortic semilunar valve opens, coronary artery is closed
- Veins: removes waste products
What phase does the heart get oxygenated blood?
Diastole
What do the left and right coronary veins do?
- Drain the left and right myocardium
- Join to empty into coronary sinus which then empties into the right atrium
What is the structure of the Aorta?
- Largest artery
- Originates from the left ventricle
- Extends down through chest/abdomen
When reaches pelvic area branches into: - In species with hind limbs eg pinnipeds –> the common iliac arteries
- In cetaceans; sirenians - continues as sacral (or caudal) artery to tail
- sends branches the hypogastric arteries
What is the Windkessel Effect
- When arteries recoril and push blood further
- Aorta needs to be elastic, able to stretch to adjust to differing voluems
Describe the structure of the aorta in pinnipeds
- The aortic bulb just after the heart increase in size by 30-40%
- After the aortic arch, it decreases in diameter by 50% as a slender tube in the abdomen
What is unique about the aortic bulb size?
- Bulb size determines diving behaviors in pinnipeds
- Shallow diving leopard seals = smaller bulb
- Deeper diving Weddell seal = larger bulb
What type of adaptation does the increased aortic bulb allow for?
- increased lung perfusion while on surface
- maintains blood pressure throughout dives
How does the aortic bulb in pinnipeds differ from cetaceans?
- thickness of bulb’s wall
- organization of elastic tissue
What is unique about Sirenian hearts?
- Deep inter-ventricle cleft along the full length of the ventricles and dorsally located left atrium
How do manatee hearts differ from dugongs?
- Manatees have an enlarged aortic bulb (bulbous swelling) that dugongs don’t have
What are the three notable changes from normal mammalian cardio systems?
- Diving responses
- thermoregulation
- larger body mass
How does the cardiovascular system regulate heat?
- Uses a countercurrent heat exchange system
- arterial blood heats the venous return
List the adaptations of the cardiovascular system (6 things)
- large blood volumes
- Large blood holding structures (spleen/venous sinus)
- venous sphincter muscles
- aortic windkessel effect
- Vascular retia mirabilia (complext vascular system)
- Vascular changes to help with thermoregulation
What do the arteries of pinnipeds have that humans do not?
- dense nerve networks at the proximal and distal ends of arteries
- allows for blood flow to be diverted during dives
What is venous capacitance and what parts of the cardiovascular system are involved? (How much blood does it hold?)
areas to “store” blood
- large hepatic sinus (sack between liver and diaphragm)
- large inferior vena cava
- about 1/5th of blood volume stored
What does venous capacitance allow for?
- blood to be quickly squeezed into the circulatory system to maintain blood pressures depending on external pressures
Describe the venous system of marine mammals
- few to no valves in veins
- Veins contain more elastin in walls
- thought to do the same thing as valves (prevent back flow)
Describe the spleen’s purpose and size in pinnipeds
- LARGE in seals/sea lions
- about 4.5% of its body weight
- storage for oxygenated RBCs
- about 30% blood volume of weddell seal can be stored in spleen
How does the spleen compare between phocids and otariids?
- In phocid seals, diving capacity strongly correlates with spleen size
- NOT THE SAME IN OTARIIDS
What pinniped animal has the largest spleen?
- Elephant seal
- spleen’s relative weight is 3 times that of terrestrial mammals
How do cetacean spleens compare to pinniped spleens?
- very small (0.02% body weight) compared to terrestrial animals
- NO CORRELATION to their diving capacity
What do seals and whales have which sends blood back from the body and the brain to the heart?
- Extradural venous system
- In pinnipeds (on dorsal aspect of spinal cord but outside the dura mater)
- In cetaceans (on ventral side)
What is the extradural venous system thought to control?
- thermoregulation of the brain
How does the blood volume storage of marine mammals compare to humans?
- 2 to 3 TIMES GREATER than humans
- Blood volume is generally larger in very active and longer diving species
What is the Retia Mirabilia and where is it found?
- Unique system of blood vessels found in marine mammals
- Found usually in dorsal wall of thoracic cavity and extremities
- Mainly arteries but also very thin walled veins
What is unique about the Retia Mirabilia?
- Contorted spirals serve as blood reservoirs to increase O2 during diving
What marine mammal has the most developed thoracic retia of all cetaceans?
- Sperm whales
What adaptation does the venous system take on in pinnipeds?
- Venous System ENLARGED and INCREASED
- results in ENHANCED capacity
What are three important aspects of the posterior vena cava?
- Frequently developed as a pair of vessels
- thin elastic walls capable of considerable distension
- receive blood draining from plexi within their flippers, pelvis, kidneys and abdominal wall
What does the vena cava have that is anterior to the diaphram?
- Muscular Caval Sphincter (innervated by phrenic nerve)
- controls blood entering from the posterior vena cava from the hepatic sinus
Where do veins enter the anterior vena cava?
- Pericardial plexis
What is the pericardial plexis?
- forms a ring around base of pericardium
- sends leaf like projections into pleural cavities containing lungs
What type of tissue does the pericardial plexis contain?
- coiled collagenous elastic and smooth muscle fibers
- suggest expanssion capabilities
What does the walrus have and lack in the cardiovascular system
HAS
- large hepatic sinus
- developed caval sphincter
- SINGLE vena cava (thoracic region)
LACKS
- Pericardial plexis
- Stellate plexus
How do the veins of cetaceans compare to pinnipeds?
- Veins NOT as enlarged as pinnipeds
- vena cava enlarged in hepatic area in SOME species
- NO caval sphincter OR hepatic sinus
- INSTEAD they have a pair of large veins running ventrally to spinal cord (Extradural veins - EDV)
Describe the EDV in Phoca Vitulina (harbor seals)
- Large vein lying DORSAL to the cord
- communicates posteriorly with stellate renal plexus and the pelvic plexuses, and anteriorly with intracranial venous sinuses
Describe the EDV in Phocaena (Harbor porpoise)
- Large vein VENTRAL to the cord
- main communication is with the anterior vena cava
Describe the EDV in Balenoptera foetus (Baleen whale)
- TWO SMALL veins lying VENTRAL to the cord
- communicate with the anterior vena cava via the dorsal thoracic veins
How does a shark heart compare to a marine mammal heart?
- Shark heart chambers are in series not parallel
What is the largest oxygen storage sites
- hemoglobin in RBC
- myoglobin in muscles
What is responsible for muscle color?
MYOGLOBIN
- Lots in marine mammals
Why are RBCs good for oxygen storage?
- Hemoglobin can bind 4 oxygen molecules
- Increase O2 storage by 100% w/o increasing plasma osmotic pressure
How does RBCs compare between diving and non-diving mammals
- RBCs are the same size
- Some diving mammals have relatively higher blood volume (species dependent)
What is unique about diving mammals in terms of blood composition?
- More RBCs per unit of blood
- Increases hematocrit
- increase total Hb volume
During diving where is much of total O2 stored?
- myoglobin
How do skeletal muscles do in low O2 conditions
- VERY tolerant to hypoxia
- Deprive other organs of O2 from hemoglobin
