Pituitary and Pineal Gland Lecture Notes

Flashcards covering the pituitary and pineal glands, including their structure, function, hormone regulation, and clinical relevance.

Pituitary Gland

Also known as hypophysis; another main gland in the endocrine system.

Introduction to Endocrine Secretion

Secretory cells release hormones into vascular compartments, hormones distributed via capillaries, no ducts involved, endocrine cells in heart, thymus, gut, kidneys, testis, ovaries.

Endocrine Hormone Distribution

Via blood to distant targets.

Paracrine Hormone Distribution

To nearby cells.

Juxtacrine Hormone Distribution

Via direct contact.

Autocrine Hormone Distribution

Affects the producing cell.

Hydrophilic Hormones

Proteins, peptides, amino acid derivatives.

Hydrophobic Hormones

Steroids, thyroid hormones (with transport proteins).

The Pituitary Gland (Hypophysis)

Weighs ~0.5 g; in sella turcica. 'Master gland' linking brain and endocrine system, dual origin: Brain and oral ectoderm.

Pituitary Gland Anatomy

Composed of an anterior part and a posterior part that is directly attached to the hypothalamus region of the brain by an infundibular stalk. The gland occupies a fossa of the sphenoid bone called the sella turcica.

Neurohypophyseal bud

From diencephalon.

Hypophyseal (Rathke) pouch

From oral cavity.

Neurohypophysis

Posterior part of the pituitary gland formed during development.

Adenohypophysis

Anterior part of the pituitary gland formed during development.

Neurohypophysis Structure

Pars nervosa, infundibulum.

Adenohypophysis Structure

Pars distalis (75%), pars tuberalis, pars intermedia.

Hypothalamic-Hypophyseal Tract & Blood Supply

Neural connection via tract, blood from superior & inferior hypophyseal arteries, portal system carries regulatory peptides.

Adenohypophysis (Anterior Pituitary)

75%, hormone production, cell types: Chromophils (Basophils, Acidophils), Chromophobes, regulates metabolism, growth, reproduction.

Pars tuberalis

Gonadotrophs.

Pars intermedia

Corticotrophs, chromophobes, colloid cysts, produces MSH, β-endorphin, γ-LPH.

Anterior Pituitary Hormone Regulation

Controlled by hypothalamic hormones, feedback loops maintain hormone levels, CNS stimuli influence pituitary function.

Neurohypophysis (Posterior Pituitary)

Neural tissue; unmyelinated axons, pituicytes (glial-like cells), hormones: ADH (Kidney water reabsorption), Oxytocin (Uterine contraction, milk ejection).

Hormone Release Mechanism

Hormones stored in Herring bodies, released into fenestrated capillaries, stimuli: Blood osmolality ↑ → ADH, Nursing → Oxytocin reflex.

Clinical Relevance of Pituitary Function

Feedback maintains balance, disruption affects growth, metabolism, reproduction, key to managing endocrine disorders.

Posterior Pituitary Dysfunction

Posterior pituitary function can be adversely affected by heritable mutations in the gene for vasopressin (ADH)-neurophysin, by compression from a tumor in adjacent tissues, and by head trauma. By lowering levels of vasopressin, such conditions can produce diabetes insipidus, a disorder characterized by inability to concentrate urine, which leads to frequent urination (polyuria) and increased thirst (polydipsia).

The Pineal Gland

Also known as epiphysis cerebri, regulates daily bodily rhythms, small, pine cone-shaped organ, size: 5–8 mm by 3–5 mm, develops from neuroectoderm, located in posterior wall of third ventricle.

Structure of the Pineal Gland

Covered by pia mater connective tissue, divided into lobules by septa containing blood vessels, attached to brain by a short stalk.

Pinealocytes

Prominent, abundant secretory cells. Features: Slightly basophilic cytoplasm, irregular, euchromatic nuclei, contain secretory vesicles, mitochondria, and long processes, extend to vascularized septa, ending near capillaries, produce melatonin (a tryptophan derivative).

Interstitial Glial Cells in the Pineal Gland

Modified astrocytes, staining positively for glial fibrillary acidic protein, which represent about 5% of the cells. These have elongated nuclei more heavily stained than those of pinealocytes and are usually found in perivascular areas and between the groups of pinealocytes.

Melatonin Secretion

Controlled by light and darkness, promoted by darkness, inhibited by daylight, causes diurnal blood melatonin fluctuations, affects hypothalamus, pituitary, and other endocrine tissues, governs the circadian (24-hour) rhythm.

Pineal Gland Function as a Neuroendocrine Transducer

Acts as a neuroendocrine transducer, converting sensory input regarding light and darkness into variations in many hormonal functions.

Neural Pathways of the Pineal Gland

Unmyelinated sympathetic nerve fibers end among pinealocytes. Light/dark signals transmitted via: Retinas, Retinohypothalamic tract, Suprachiasmatic nucleus, Sympathetic fibers.

Interstitial Glial Cells

Modified astrocytes, stain positive for glial fibrillary acidic protein (GFAP), About 5% of pineal gland cells, located in perivascular areas and between pinealocyte groups.

Corpora Arenacea (Brain Sand)

Calcium and magnesium salt concretions, formed by mineralized extracellular protein deposits, appear in childhood, increase with age, no effect on gland function, useful as radiological landmarks.

Pineal Tumors

Tumors from pinealocytes are very rare, can be benign or highly malignant.