20 topics with brief reviews: definitions, key facts, and class questions.
The endocrine system is the master chemical conductor of our body. In this section, we break down the microscopic structure of the endocrine glands, their general organization, as well as the classification and subtle mechanisms of hormone action.
We will study both the central components (the hypothalamo-hypophysial system, all lobes of the pituitary gland, and the pineal gland) and the peripheral organs: the thyroid and parathyroid glands, the adrenal glands (with a detailed analysis of their embryogenesis and medulla). A separate block is dedicated to organs with mixed function—the endocrine parts of the pancreas, kidneys, thymus, gonads, placenta, as well as the extensive diffuse endocrine system.
What is most frequently asked in class? Instructors love the hypophysial portal blood system, the follicular structure of the thyroid gland, and the zonal architecture of the adrenal cortex. Be sure to pay attention to the difference in the origin of the adrenal cortex and medulla—this is a classic examination question.
How do endocrine glands differ histologically from exocrine glands?
Endocrine glands are completely devoid of excretory ducts and terminal sections. In addition, they are characterized by a very dense network of blood capillaries into which the secretion is directly released.
What is the difference between the effects of FSH and LH in women?
FSH primarily stimulates primary follicular growth in the ovaries. LH ensures their final maturation and is responsible for the formation of the corpus luteum at the site of the ruptured follicle. They jointly implement estrogen secretion.
Through what pathway does the hypothalamus transmit regulatory signals to the adenohypophysis?
Signals (releasing and inhibiting hormones) are delivered via the portal circulatory system through sinusoidal capillaries with fenestrated endothelium, ensuring a high metabolic exchange rate.
Is melanocyte-stimulating hormone (MSH) capable of increasing the number of pigment cells?
No, this hormone exclusively stimulates the intracellular synthesis of the pigment melanin, but does not induce proliferation (multiplication) of the melanocytes themselves.
Are hormones synthesized in the posterior pituitary gland?
No, endogenous hormone synthesis is completely absent in the neurohypophysis. There are no endocrine cells (adenocytes) here; the lobe functions solely as a depot.
Why is the pineal gland called the "third eye"?
Its activity directly depends on illumination. In lower vertebrates (fish, amphibians), the cells of the pineal gland are themselves photoreceptors, whereas in mammals, the signal from the retina reaches the gland via a complex pathway through the sympathetic system.
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