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Here is a thorough overview of the endocrine glands, drawn from Junqueira's Basic Histology (17e) and Guyton & Hall Medical Physiology:

Endocrine Glands - Overview

Locations of the major endocrine glands and the hormones they release
Junqueira's Basic Histology, Fig. 20-1 - Major endocrine glands (left) and organs with endocrine cells (right)
Endocrine glands are ductless glands that secrete hormones directly into the bloodstream, lymphatics, or intercellular spaces. Unlike exocrine glands, they have no secretory ducts. Hormones travel through the circulation to reach target cells bearing specific receptors.

Types of Hormonal Signaling

TypeDescriptionExample
EndocrineHormone travels via blood to distant targetCortisol from adrenal → liver
ParacrineActs on nearby cells through interstitial fluidGastrin from pyloric G cells
AutocrineActs on the secreting cell itselfIGF-1
JuxtacrineSignaling molecule stays on cell surfaceEmbryonic tissue interactions

The Major Endocrine Glands

1. Hypothalamus

Although primarily neural tissue, the hypothalamus functions as the master regulator of the endocrine system through releasing and inhibiting hormones that control the pituitary.
HormoneAction
TRH (Thyrotropin-releasing hormone)Stimulates TSH and prolactin release
CRH (Corticotropin-releasing hormone)Stimulates ACTH release
GHRH / SomatostatinStimulates / inhibits growth hormone
GnRHStimulates LH and FSH release
DopamineInhibits prolactin release
ADH (vasopressin) & OxytocinStored and released by posterior pituitary

2. Pituitary Gland (Hypophysis)

The "master gland" - weighs ~0.5 g, sits in the sella turcica of the sphenoid bone, and has two distinct parts:
Anterior Pituitary (Adenohypophysis) - arises from oral ectoderm (Rathke's pouch):
  • GH - promotes growth and protein synthesis
  • TSH - stimulates thyroid hormone synthesis
  • ACTH - stimulates adrenocortical hormone synthesis
  • FSH - ovarian follicle growth / sperm maturation
  • LH - ovulation, corpus luteum, testosterone synthesis
  • Prolactin - breast development and milk secretion
  • MSH - melanocyte stimulation
Posterior Pituitary (Neurohypophysis) - neural outgrowth from the brain:
  • ADH (Vasopressin) - water reabsorption in kidneys, vasoconstriction
  • Oxytocin - uterine contractions, milk ejection

3. Thyroid Gland

Located anterior to the larynx in the neck.
  • T3 (Triiodothyronine) & T4 (Thyroxine) - raise basal metabolic rate of nearly all cells; amine hormones transported bound to proteins
  • Calcitonin (from parafollicular C cells) - lowers blood calcium by promoting bone deposition

4. Parathyroid Glands

Four small glands on the posterior surface of the thyroid.
  • PTH (Parathyroid hormone) - raises blood calcium (opposes calcitonin); increases bone resorption, renal calcium reabsorption, and vitamin D activation

5. Adrenal Glands

Paired glands sitting atop each kidney, with two functionally distinct zones:
Adrenal Cortex (steroid hormones, 3 zones):
  • Zona glomerulosa - Aldosterone (mineralocorticoid): increases Na⁺ reabsorption and K⁺ excretion
  • Zona fasciculata - Cortisol (glucocorticoid): regulates glucose/fat metabolism, anti-inflammatory
  • Zona reticularis - Androgens (DHEA): weak sex steroids
Adrenal Medulla (chromaffin cells, neural crest origin):
  • Epinephrine & Norepinephrine - catecholamines that mediate the "fight or flight" sympathetic response

6. Pancreatic Islets (Islets of Langerhans)

Scattered clusters within the exocrine pancreas:
  • Alpha cells - Glucagon: raises blood glucose
  • Beta cells - Insulin: lowers blood glucose (most abundant islet cell)
  • Delta cells - Somatostatin: inhibits insulin and glucagon secretion
  • PP cells - Pancreatic polypeptide: inhibits pancreatic exocrine secretion

7. Gonads

Testes:
  • Testosterone & Androgens (Leydig cells) - male secondary sex characteristics, spermatogenesis
  • Inhibin (Sertoli cells) - inhibits FSH
Ovaries:
  • Estrogen - female secondary sex characteristics, endometrial proliferation
  • Progesterone - prepares uterus for implantation, maintains pregnancy
  • Inhibin - inhibits FSH

8. Pineal Gland

Small gland deep in the brain, between the cerebral hemispheres.
  • Melatonin - regulates circadian rhythm and sleep-wake cycles; secretion peaks at night

Organs With Secondary Endocrine Functions

OrganHormoneFunction
HypothalamusADH, OxytocinReleased via posterior pituitary
ThymusThymopoietin, ThymosinsT-cell maturation
HeartAtriopeptin (ANP)Reduces blood pressure and Na⁺
KidneyCalcitriol (active vit D), EPOCalcium balance, erythropoiesis
GI TractGastrin, Secretin, CCK, GIP, VIPDigestive regulation
Adipose tissueLeptin, AdiponectinEnergy balance, metabolism

Hormone Chemistry

Hormones fall into three chemical classes, which determines how they act:
ClassExamplesReceptor LocationAction Mechanism
Peptides/ProteinsInsulin, GH, ACTH, PTHCell surface2nd messenger (cAMP, IP3)
SteroidsCortisol, Aldosterone, EstrogenIntracellularDirect gene transcription
AminesEpinephrine, T3/T4Surface (catecholamines) / Intracellular (thyroid)Mixed

Feedback Control

Most endocrine axes operate by negative feedback:
  • The hypothalamus releases a hormone → stimulates pituitary → pituitary stimulates target gland → target gland hormone rises → feeds back to inhibit hypothalamus and pituitary
  • Example: Hypothalamus (CRH) → Pituitary (ACTH) → Adrenal (Cortisol) → Cortisol inhibits CRH/ACTH
  • Positive feedback is rare; classic example is the LH surge at ovulation triggered by rising estrogen
Sources: Junqueira's Basic Histology, 17e, Chapter 20; Guyton and Hall Textbook of Medical Physiology, Table 75.1; THIEME General Anatomy and Musculoskeletal System

Search for clinical images of endocrine gland histology and pathology

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Here is a curated gallery of clinical histology and pathology images of the endocrine glands, drawn from Junqueira's Basic Histology (17e) and Robbins & Kumar Basic Pathology:

Endocrine Gland Histology & Pathology - Image Gallery

1. PITUITARY GLAND - Anatomy & Structure

Pituitary gland anatomy showing anterior pituitary (pars tuberalis, pars intermedia, pars distalis) and posterior pituitary (infundibular stalk, pars nervosa) in the sella turcica
Fig. 20-2 - Pituitary gland anatomy. The anterior lobe (adenohypophysis) sits in the sella turcica of the sphenoid bone. The posterior lobe (neurohypophysis) connects directly to the hypothalamus via the infundibular stalk. The pars intermedia lies between the two lobes. (Junqueira's Basic Histology, 17e)

2. HYPOTHALAMUS-PITUITARY AXIS - Hormone Control Diagram

Hypothalamic-pituitary axis showing releasing and inhibiting hormones (TRH, CRH, GHRH, GnRH, PIH, GHIH) and the six anterior pituitary hormones (TSH, ACTH, GH, PRL, FSH, LH) with their target organs
Fig. 20-5 - Hypothalamic-pituitary hormonal axis. Hypothalamic releasing hormones travel via the portal blood supply to stimulate the six major anterior pituitary hormones, each targeting a specific peripheral organ. (Junqueira's Basic Histology, 17e)

3. HYPOTHALAMUS-PITUITARY AXIS - Pathology Summary (Robbins)

Robbins pathology diagram of hypothalamic-pituitary axis showing stimulatory (+) and inhibitory (-) connections: TRH→TSH→Thyroid, CRH→ACTH→Adrenal cortex, GHRH/GHIH→GH, GnRH→FSH/LH→Ovary/testis, PIF (Dopamine)→Prolactin→Mammary glands
Fig. 18.2 - Hypothalamic-pituitary axis (Robbins). Stimulatory (+) and inhibitory (-) connections are clearly annotated. Dopamine (prolactin-inhibiting factor) uniquely inhibits prolactin release - loss of this inhibition causes hyperprolactinemia. (Robbins & Kumar Basic Pathology)

4. PARS INTERMEDIA - Histology (H&E)

H&E histology of pituitary pars intermedia showing pars distalis (PD, left), pars intermedia (PI, center) with colloid-filled cysts (C) of variable size, basophilic cells (B) invading the pars nervosa (PN, right), x56
Fig. 20-9 - Pars intermedia histology. The narrow pars intermedia (PI) lies between the pars distalis (PD) and pars nervosa (PN). Key features are the colloid-filled cysts (C) - remnants of the embryonic Rathke's pouch - and basophilic corticotroph cells (B). (x56, H&E) (Junqueira's Basic Histology, 17e)

5. PITUITARY ADENOMA - Gross & Histology (Pathology)

Pituitary adenoma: (A) gross coronal brain section showing a large tan-colored adenoma growing beyond the sella turcica and distorting overlying brain; (B) H&E histology showing monomorphic cells with scant interspersed reticulin, typical of adenoma
Fig. 18.3 - Pituitary adenoma. (A) Gross specimen: large non-functioning adenoma that has grown beyond the sella turcica and distorts the overlying brain. Non-functioning adenomas tend to be larger at diagnosis than hormone-secreting ones. (B) Histology: monomorphic cells with scant reticulin - contrast with the mixed chromophil population of normal pituitary. (Robbins & Kumar Basic Pathology)

6. THYROID GLAND - Low-Power Histology (H&E)

Low-power H&E of thyroid gland showing fibrous capsule (C) with septa (S) dividing the parenchyma into lobules, and densely packed colloid-filled follicles of variable size throughout the gland
Fig. 20-19a - Thyroid gland (low power). The capsule (C) sends septa (S) with blood vessels into the parenchyma. The entire gland consists of colloid-filled follicles packed closely together - the only endocrine gland that stores hormones extracellularly in the follicular colloid (thyroglobulin). (Junqueira's Basic Histology, 17e)

7. THYROID FOLLICLES - High-Power Histology

High-power H&E of thyroid follicles showing follicular lumens (L) filled with pink homogeneous thyroglobulin colloid, surrounded by a single layer of follicular epithelial cells (thyrocytes), with a parafollicular C cell (C) visible between follicles
Fig. 20-19b - Thyroid follicles (high power). Follicular lumens (L) are filled with homogeneous eosinophilic colloid (thyroglobulin). A parafollicular C cell (C) - the calcitonin-secreting cell - is identified between follicles. Thyrocyte height reflects activity: tall columnar = active (high TSH), flat squamous = inactive. (Junqueira's Basic Histology, 17e)

8. THYROID HORMONE SYNTHESIS - Cellular Diagram

Detailed cellular diagram of thyrocyte showing the 6-step thyroid hormone synthesis: (1) thyroglobulin synthesis in rER, (2) iodide uptake via NIS symporter, (3) I- transported to colloid via pendrin, (4) iodination of tyrosines by thyroid peroxidase in colloid to form MIT/DIT, (5) endocytosis and lysosomal degradation, (6) T3/T4 secreted into capillaries. Right panel shows chemical structures of T3 and T4
Fig. 20-21 - Thyroid hormone synthesis. The 6-step process: thyroglobulin synthesis → iodide uptake via Na⁺/I⁻ symporter (NIS) → iodide transport to colloid via pendrin → thyroid peroxidase-mediated iodination → endocytosis of iodinated thyroglobulin → lysosomal cleavage releasing T3 and T4. Both phases are driven by TSH. (Junqueira's Basic Histology, 17e)

9. ADRENAL GLAND - Zones (Diagram + Histology)

Adrenal gland: left shows gross cross-section with adrenal cortex (yellow/tan) surrounding the medulla (purple); center diagram labels zones: Capsule, Zona glomerulosa, Zona fasciculata (thickest), Zona reticularis, Adrenal medulla; right is actual H&E histology at 35x showing the same layered zonation
Fig. 20-14 - Adrenal gland zones. The cortex has 3 concentric zones, each producing different steroid hormones:
  • Zona glomerulosa (outermost, ~15%) → Aldosterone (mineralocorticoid)
  • Zona fasciculata (middle, ~65-80%) → Cortisol (glucocorticoid) - cells appear vacuolated due to lipid droplets
  • Zona reticularis (inner) → Androgens (DHEA)
  • Adrenal medulla (center, neural crest origin) → Epinephrine & Norepinephrine (Junqueira's Basic Histology, 17e)

10. ADRENAL CORTEX CELL - Electron Microscopy

Transmission electron micrograph (TEM) at x25,700 of zona fasciculata steroid-secreting cells showing: lipid droplets (L) with cholesterol esters, mitochondria (M) with tubular vesicular cristae (characteristic of steroid cells), abundant smooth ER (SER), autophagosomes (A), Golgi apparatus (G), euchromatic nuclei (N)
Fig. 20-13 - Adrenocortical cell ultrastructure (TEM, x25,700). Classic features of steroid-secreting cells: lipid droplets (L) containing cholesterol substrate, mitochondria (M) with tubular (not shelf-like) cristae containing steroidogenic enzymes, and abundant smooth ER (SER) for steroid synthesis. Steroids are not stored - they diffuse directly through the plasma membrane. (Junqueira's Basic Histology, 17e)

Key Histological Findings - Quick Reference

GlandKey Histological FeatureClinical Significance
Pituitary anteriorMixed basophils, eosinophils, chromophobesChromophobe = degranulated / stem cells
Pituitary intermediateColloid cysts (Rathke remnants)Craniopharyngioma arises from remnants
Pituitary adenomaMonomorphic cells, loss of reticulinBitemporal hemianopsia if large
ThyroidColloid-filled follicles, variable epithelial heightLow columnar = active; flat = hypoactive
Adrenal zona fasciculataVacuolated "spongy" cells (lipid-laden)Lipid washed out in H&E = pale, foamy look
Adrenal medullaChromaffin cells (neural crest)Pheochromocytoma from these cells
Pancreatic isletsPale islets within exocrine parenchymaBeta cell loss → Type 1 DM
Sources: Junqueira's Basic Histology - Text and Atlas, 17e; Robbins & Kumar Basic Pathology
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