What are the beta 1 effects associated with cardiac function?

The effects of beta 1 adrenergic receptors on cardiac function are primarily related to their role in increasing myocardial contractility and heart rate. Beta 1 receptors are predominantly found in the heart, and their activation leads to enhanced contractility, known as positive inotropic effects, which means that the force of contraction of the heart muscle increases. This is crucial for conditions where increased cardiac output is necessary, such as during physical activity or in response to stress.

Additionally, stimulation of beta 1 receptors increases the heart rate through positive chronotropic effects, resulting from accelerated conduction through the sinoatrial (SA) node. This ensures that more blood is pumped per minute, which is vital for meeting the body's increased oxygen and nutrient demands during heightened physiological activity.

In contrast, the other options present effects that do not align with the known actions of beta 1 stimulation. Increased urethral resistance is unrelated to cardiac function and more associated with alpha adrenergic effects. Decreased contractility and conduction velocity contradict the stimulatory effects of beta 1 receptors, which enhance both. Increased diversity in respiratory rate is also unrelated to cardiac function and does not involve beta 1 receptor activity, as these receptors specifically influence cardiovascular parameters rather than respiratory rhythms.