Anatomical structure and cellular composition
The adenohypophysis is formed from epithelial tissue and structurally divided into three components:
- Anterior lobe — the largest part of the gland.
- Intermediate lobe (pars intermedia) — a narrow strip of tissue containing follicles. It is separated from the anterior lobe by the hypophyseal cleft.
- Tuberal part — a small extension directly adjacent to the pituitary stalk.
The glandular cells of the anterior lobe are classified by their affinity for specific stains:
- Eosinophilic (acidophilic) cells ($\alpha$-cells).
- Basophilic cells ($\beta$- and $\delta$-cells).
- Chromophobe cells ($\gamma$-cells) — according to mainstream data, do not secrete hormones, although some researchers suggest they play a role in corticotropin synthesis.
What hormones does the adenohypophysis synthesize?
Adenohypophyseal cells produce hormones. Glandotropic hormones enter the blood, bind to specific receptors on endocrine glands, activate second messenger systems, and trigger the synthesis of effector hormones in the periphery.
Hormones of the adenohypophysis:
- Growth hormone (GH, somatotropin) — involved in the regulation of growth and metabolism.
- Prolactin (PRL, luteotropic hormone) — associated with lactation.
- Thyroid-stimulating hormone (TSH) — regulates thyroid function.
- Adrenocorticotropic hormone (ACTH, corticotropin) — regulates adrenal function.
- Gonadotropic hormones — follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which regulate gonadal function.
- Melanocyte-stimulating hormone (MSH) — associated with pigmentation.
- Lipotropin (LPH) — associated with lipolysis.
Mechanism of hypothalamic regulation
Unlike the neurohypophysis, the adenohypophysis has no direct neuronal connections with the hypothalamus. Control is exerted humorally via the hypophyseal portal system.
- Small-celled nuclei of the medial hypothalamus, including periventricular areas, synthesize hypophysiotropic neurohormones: releasing hormones (stimulate the synthesis and secretion of adenohypophyseal hormones) and inhibiting hormones (inhibit the synthesis and secretion of glandotropic hormones).
- Through axons, these substances are transported to the median eminence.
- Neurosecretion is released into the primary capillary network.
- Through the vessels of the portal system, blood carries the hormones to the secondary capillary network (sinusoids) located in the adenohypophysis.
The system operates on the negative feedback principle: the level of peripheral hormones regulates the secretion of hypothalamic and pituitary hormones. During puberty, girls also develop a positive feedback mechanism: peak estradiol levels trigger an LH and FSH surge associated with ovulation.
Clinical significance and pathologies
Disorders of the adenohypophysis may be associated with tumor processes. Hormonally active tumors, such as adenomas, lead to excessive hormone synthesis, while hormonally inactive tumors cause the destruction of functional pituitary tissue.
- Panhypopituitarism (Simmonds' disease, pituitary cachexia): a severe syndrome based on the impairment of all pituitary functions. It manifests as weight loss, bradycardia, decreased libido, reduced skin pigmentation, and hair loss. Sudden loss of pituitary function can cause a life-threatening Addisonian (hypoadrenal) crisis.
- Infectious lesions: in hemorrhagic fever with renal syndrome (HFRS), the anterior pituitary acts as one of the secondary sites of viral replication.
- Pharmacological regulation: gonadotropin-releasing hormone analogs, such as goserelin, are used in oncology. With prolonged use, they cause receptor desensitization, suppressing the secretion of FSH and LH, which reduces gonadal stimulation.
Class and exam questions
How does the hypothalamus transmit signals to the adenohypophysis?
Signals are transmitted humorally. Neurosecretory cells of the hypothalamus release liberins and statins into the primary capillary network, from which they enter the secondary network (sinusoids) via the hypophyseal portal system and act on adenohypophyseal cells.
Which cells of the adenohypophysis produce growth hormone?
Growth hormone (somatotropin, GH) is produced by specific cells of the adenohypophysis.
What are liberins and statins?
These are hypophysiotropic hormones of the hypothalamus. Liberins (releasing hormones) stimulate the synthesis and secretion of adenohypophyseal hormones, while statins, such as somatostatin or dopamine, inhibit the synthesis and secretion of glandotropic hormones.
What else to study on this topic
- Hypophyseal portal system
- Hypothalamic liberins and statins
- Glandotropic hormones
- Panhypopituitarism (Simmonds' disease)
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