The heart pumps blood through contraction (systole) and relaxation (diastole), with valves (AV and semilunar) preventing backflow.
Intercalated discs in cardiac muscle cells have desmosomes for mechanical tension and gap junctions for rapid electrical impulse transmission.
Hypertrophic cardiomyopathy in cats involves thickened ventricular walls, while dilated cardiomyopathy in dogs leads to weakened, enlarged ventricles, both affecting circulation.
The AV valves open during atrial systole to allow blood into the ventricles, while the semilunar valves open during ventricular systole to allow blood into the arteries.
Calcium binds to troponin, allowing actin-myosin interaction for contraction, and is regulated by the sarcoplasmic reticulum during the contraction-relaxation cycle.
The thicker myocardium in the left ventricle allows it to pump blood through the systemic circulation, which requires more force due to higher resistance.
Blood flows from the right atrium through the tricuspid valve to the right ventricle, then to the lungs via the pulmonary valve. Oxygenated blood returns to the left atrium, passes through the bicuspid valve to the left ventricle, and is pumped through the aortic valve into the aorta.
The blood-brain barrier (BBB) protects the brain by regulating the passage of substances, allowing essential nutrients and preventing toxins from entering.
Arteries have thick walls to handle high pressure, veins have valves to prevent backflow, and capillaries have thin walls to facilitate gas and nutrient exchange.
Coronary circulation supplies oxygenated blood directly to the heart muscle. Impairment can lead to ischemia and heart attacks due to reduced oxygen supply to the heart.
Lecture 11 answers:
Capillary exchange occurs via diffusion (oxygen, carbon dioxide), transcytosis (insulin), and bulk flow (ions and water). Diffusion allows small molecules to cross concentration gradients, while transcytosis is for large, lipid-insoluble molecules. Bulk flow regulates fluid volumes based on pressure gradients.
Hydrostatic pressure pushes fluids out of capillaries, while osmotic pressure pulls fluids into capillaries. Hydrostatic pressure is higher at the arterial end, driving filtration, and lower at the venous end, where reabsorption predominates due to the higher osmotic pressure.
Continuous capillaries (in skin, muscles) are the least permeable, allowing small molecules to pass. Fenestrated capillaries (in kidneys, intestines) allow larger molecules through pores. Sinusoidal capillaries (in liver, bone marrow) have large gaps for cells to pass. Each type is suited to the needs of the respective organ.
Edema results from increased capillary permeability (e.g., inflammation), reduced plasma proteins (e.g., malnutrition), increased hydrostatic pressure (e.g., heart failure), or lymphatic blockage (e.g., tumors). These factors lead to an imbalance of fluid retention and filtration in tissues.
The lymphatic system returns excess interstitial fluid to the bloodstream. Failure, as in lymphatic obstruction, leads to fluid accumulation (edema), such as swelling in limbs due to blocked lymph vessels or lymph nodes.
Hydrostatic pressure pushes fluid out of capillaries, while osmotic pressure pulls it back in. If hydrostatic pressure increases (e.g., in hypertension), more fluid is forced out, potentially leading to edema. In contrast, if osmotic pressure decreases (e.g., due to low albumin), fluid reabsorption decreases, also leading to edema.
The myogenic response is a localized mechanism where blood vessels contract or dilate in response to changes in pressure, maintaining stable perfusion. In systemic circulation, vessels dilate when oxygen is low, while in pulmonary circulation, they constrict to direct blood to better-oxygenated areas of the lung.
Baroreceptors detect changes in blood pressure and adjust heart rate and vessel dilation via the cardiovascular center. Chemoreceptors sense changes in CO2, O2, and pH, adjusting both cardiovascular and respiratory functions to maintain homeostasis.
During exercise, blood flow is redirected to muscles and lungs, while the heart works harder (higher heart rate and stroke volume). Regular training increases the heart’s efficiency, leading to a lower resting heart rate and higher stroke volume.
The renin-angiotensin-aldosterone system regulates blood pressure by promoting vasoconstriction and water retention. If overactive, it can lead to chronic hypertension due to excessive blood volume and pressure.