Atrial systole begins

A. Hormone at E - Growth Hormone (GH): The diagram indicates that hormone E is released from the anterior pituitary and targets the liver and skeletal muscles. In the liver, it stimulates the production of insulin-like growth factors (IGFs) to promote systemic growth. Its action on skeletal muscle facilitates protein synthesis and tissue hypertrophy.

B. Hormone A - Prolactin (PRL): The diagram depicts hormone A traveling from the adenohypophysis to the mammary glands. This protein hormone is essential for initiating and maintaining milk production following parturition. Its secretion is regulated by hypothalamic dopamine, which serves as a primary prolactin-inhibiting factor.

C. Hormone B - Thyroid-stimulating Hormone (TSH): The pathway labeled B shows a tropic hormone targeting the thyroid gland. TSH stimulates the follicular cells of the thyroid to synthesize and release thyroxine and triiodothyronine. This hormone is a critical regulator of systemic basal metabolic rate and cellular heat production.

D. Hormone C - Gonadotropins (FSH and LH): Label C represents the gonadotropins, specifically follicle-stimulating hormone and luteinizing hormone, which target the testes and ovaries. These hormones regulate gametogenesis and the secretion of sex steroids like testosterone and estrogen. They are essential for the maintenance of reproductive cycles and secondary sexual characteristics.

E. Hormone at D - Adrenocorticotropic Hormone (ACTH): The diagram shows hormone D being secreted from the anterior pituitary and traveling specifically to the adrenal gland. More specifically, it targets the adrenal cortex to regulate the production of steroid hormones. It is a critical component of the hypothalamic-pituitary-adrenal (HPA) axis.

A. visceral layers of the serous pericardium; parietal layers of the serous pericardium: These terms describe the thin, double-layered membrane that surrounds and protects the heart, forming the pericardial cavity. They are not chambers of the heart but rather protective coverings that facilitate frictionless movement. This choice incorrectly identifies serous membranes as anatomical internal heart cavities.

B. ventricles; atria: This selection inverts the correct anatomical arrangement of the human heart. The ventricles are the thick-walled, inferior pumping chambers that propel blood out into the pulmonary and systemic circuits. The atria are located superiorly to the ventricles and serve as the receiving chambers for returning blood.

C. atria; ventricles: The heart is divided into four chambers, with the two atria serving as the superior receiving chambers and the two ventricles as the inferior pumping chambers. The atria are separated from the ventricles by atrioventricular valves to ensure unidirectional blood flow. This accurately describes the vertical spatial relationship of the heart's internal anatomy.

D. left ventricles; right ventricles: These are the two inferior pumping chambers of the heart, located side-by-side rather than in a superior-inferior arrangement. While they differ in wall thickness and pressure output, both are situated below the level of the atria. They are separated by the thick interventricular septum.

E. left atria; right atria: These represent the two superior receiving chambers of the heart, divided by the interatrial septum. Like the ventricles, they are positioned horizontally relative to one another rather than vertically. They are both located superior to their respective ventricles within the thoracic cavity.