Glandular Epithelium: Histology

Overview

Epithelial tissue

• 1 of the 4 main kinds of tissues in the body (along with muscular, nervous, and connective tissues)
• Lines the surfaces of most of the external and internal structures of the body
• General structure: one or more layers of epithelial cells organized over a basement membrane Basement membrane A darkly stained mat-like extracellular matrix (ecm) that separates cell layers, such as epithelium from endothelium or a layer of connective tissue. The ecm layer that supports an overlying epithelium or endothelium is called basal lamina. Basement membrane (bm) can be formed by the fusion of either two adjacent basal laminae or a basal lamina with an adjacent reticular lamina of connective tissue. Bm, composed mainly of type IV collagen; glycoprotein laminin; and proteoglycan, provides barriers as well as channels between interacting cell layers. Thin Basement Membrane Nephropathy (TBMN) (composed primarily of collagen Collagen A polypeptide substance comprising about one third of the total protein in mammalian organisms. It is the main constituent of skin; connective tissue; and the organic substance of bones (bone and bones) and teeth (tooth). Connective Tissue: Histology) that separates it from the underlying connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology
• Can be subdivided into:
  • Secretory (e.g., glands)
  • Nonsecretory (e.g., skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions)

Types of glands

• Exocrine glands:
  • Synthesize and secrete their products onto a surface:
    • Directly: unicellular Unicellular Cell Types: Eukaryotic versus Prokaryotic glands
    • Via a tube (duct): multicellular Multicellular Cell Types: Eukaryotic versus Prokaryotic glands
  • Examples:
    • Sweat glands Sweat glands Sweat-producing structures that are embedded in the dermis. Each gland consists of a single tube, a coiled body, and a superficial duct. Soft Tissue Abscess
    • Sebaceous glands
    • Salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy
    • Mucous glands in the intestinal and respiratory tracts
    • Pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy (digestive enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes)
  • Unicellular Unicellular Cell Types: Eukaryotic versus Prokaryotic (e.g., goblet cells):
    • Secrete by exocytosis Exocytosis Cellular release of material within membrane-limited vesicles by fusion of the vesicles with the cell membrane. The Cell: Cell Membrane
    • Present in the intestinal and respiratory tracts
  • Multicellular Multicellular Cell Types: Eukaryotic versus Prokaryotic:
    • Secreted by ducts
    • Composed of 2 basic parts:
      • Epithelium-derived duct
      • Secretory unit (acinus)
    • Connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology surrounds the acinus and supplies it with blood and nerve fibers Nerve Fibers Slender processes of neurons, including the axons and their glial envelopes (myelin sheath). Nerve fibers conduct nerve impulses to and from the central nervous system. Nervous System: Histology.
• Endocrine glands:
  • Ductless
  • Synthesize and secrete their products into the extracellular space
  • Secretory products reach target cells via the blood.
  • Examples:
    • Pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy ( insulin Insulin Insulin is a peptide hormone that is produced by the beta cells of the pancreas. Insulin plays a role in metabolic functions such as glucose uptake, glycolysis, glycogenesis, lipogenesis, and protein synthesis. Exogenous insulin may be needed for individuals with diabetes mellitus, in whom there is a deficiency in endogenous insulin or increased insulin resistance. Insulin, glucagon Glucagon A 29-amino acid pancreatic peptide derived from proglucagon which is also the precursor of intestinal glucagon-like peptides. Glucagon is secreted by pancreatic alpha cells and plays an important role in regulation of blood glucose concentration, ketone metabolism, and several other biochemical and physiological processes. Gastrointestinal Secretions)
    • Thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy
    • Adrenal glands Adrenal Glands The adrenal glands are a pair of retroperitoneal endocrine glands located above the kidneys. The outer parenchyma is called the adrenal cortex and has 3 distinct zones, each with its own secretory products. Beneath the cortex lies the adrenal medulla, which secretes catecholamines involved in the fight-or-flight response. Adrenal Glands: Anatomy
    • Ovaries Ovaries Ovaries are the paired gonads of the female reproductive system that contain haploid gametes known as oocytes. The ovaries are located intraperitoneally in the pelvis, just posterior to the broad ligament, and are connected to the pelvic sidewall and to the uterus by ligaments. These organs function to secrete hormones (estrogen and progesterone) and to produce the female germ cells (oocytes). Ovaries: Anatomy
    • Testes Testes Gonadal Hormones
    • Pituitary Pituitary A small, unpaired gland situated in the sella turcica. It is connected to the hypothalamus by a short stalk which is called the infundibulum. Hormones: Overview and Types gland
  • Hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types produced in epithelial cells are released into the interstitial fluid Interstitial fluid Body Fluid Compartments.
• Paracrine glands: Secretions affect adjacent epithelial cells.

Exocrine Glands

Structural classification

• Simple glands: unbranched ducts
• Compound glands: branched ducts
• Based on the secretory unit shape:
  • Alveolar (secretory cells forming small sacs)
  • Tubular (secretory cells forming tubes)
  • Tubuloalveolar (a mix of alveolar and tubular)

Ways of secretion Secretion Coagulation Studies

• Merocrine secretion Secretion Coagulation Studies:
  • Most glands are merocrine.
  • Secretory cells are not altered by the process of secretion Secretion Coagulation Studies.
  • Cells produce and store the products at the apex of the cell → stimulation → granules move to the apical surface and release products by exocytosis Exocytosis Cellular release of material within membrane-limited vesicles by fusion of the vesicles with the cell membrane. The Cell: Cell Membrane
  • Examples: pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas: Anatomy, salivary and sweat glands Sweat glands Sweat-producing structures that are embedded in the dermis. Each gland consists of a single tube, a coiled body, and a superficial duct. Soft Tissue Abscess
• Apocrine secretion Secretion Coagulation Studies: Secretion Secretion Coagulation Studies product is stored at the apical surface → component of apical surface breaks off → secretion Secretion Coagulation Studies product + part of the cytoplasm released
  • The release of lipid droplets Droplets Varicella-Zoster Virus/Chickenpox by mammary glands is an example of apocrine secretion Secretion Coagulation Studies.
  • Secretions of the mammary glands are merocrine when proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis are released in milk.
• Holocrine secretion Secretion Coagulation Studies:
  • Cells synthesize the product and accumulate it in the cytoplasm → undergoes apoptosis Apoptosis A regulated cell death mechanism characterized by distinctive morphologic changes in the nucleus and cytoplasm, including the endonucleolytic cleavage of genomic DNA, at regularly spaced, internucleosomal sites, I.e., DNA fragmentation. It is genetically-programmed and serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth. Ischemic Cell Damage → cell is lost in the luminal space
  • Example: sebaceous glands of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions

Clinical Relevance

• Diseases of the salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy: Sialadenosis Sialadenosis Sialadenosis is a chronic, bilateral, noninflammatory hypertrophy of the salivary glands. Diseases of the Salivary Glands, sialadenitis Sialadenitis Inflammation of salivary tissue (salivary glands), usually due to infection or injuries. Diseases of the Salivary Glands, sialolithiasis Sialolithiasis Calculi occurring in a salivary gland. Most salivary gland calculi occur in the submandibular gland, but can also occur in the parotid gland and in the sublingual and minor salivary glands. Diseases of the Salivary Glands, and neoplasms Neoplasms New abnormal growth of tissue. Malignant neoplasms show a greater degree of anaplasia and have the properties of invasion and metastasis, compared to benign neoplasms. Benign Bone Tumors are among the disease processes that affect salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy. The common symptom among these conditions is swelling Swelling Inflammation. Salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy can swell repeatedly either bilaterally ( sialadenosis Sialadenosis Sialadenosis is a chronic, bilateral, noninflammatory hypertrophy of the salivary glands. Diseases of the Salivary Glands) or unilaterally ( sialadenitis Sialadenitis Inflammation of salivary tissue (salivary glands), usually due to infection or injuries. Diseases of the Salivary Glands). The parotid gland Parotid gland The largest of the three pairs of salivary glands. They lie on the sides of the face immediately below and in front of the ear. Salivary Glands: Anatomy is commonly affected by infection ( mumps Mumps Mumps is caused by a single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae. Mumps is typically a disease of childhood, which manifests initially with fever, muscle pain, headache, poor appetite, and a general feeling of malaise, and is classically followed by parotitis. Mumps Virus/Mumps). Some glands may even develop stones in the salivary ducts ( sialolithiasis Sialolithiasis Calculi occurring in a salivary gland. Most salivary gland calculi occur in the submandibular gland, but can also occur in the parotid gland and in the sublingual and minor salivary glands. Diseases of the Salivary Glands).
• Goiter Goiter A goiter is a chronic enlargement of the thyroid gland due to nonneoplastic growth occurring in the setting of hypothyroidism, hyperthyroidism, or euthyroidism. Morphologically, thyroid enlargement can be diffuse (smooth consistency) or nodular (uninodular or multinodular). Goiter and thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy nodule Nodule Chalazion: a swollen thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy gland due to hyposecretion or hypersecretion of the thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy hormone or due to inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation. A goiter Goiter A goiter is a chronic enlargement of the thyroid gland due to nonneoplastic growth occurring in the setting of hypothyroidism, hyperthyroidism, or euthyroidism. Morphologically, thyroid enlargement can be diffuse (smooth consistency) or nodular (uninodular or multinodular). Goiter can be composed of a single nodule Nodule Chalazion (solitary nodular goiter Goiter A goiter is a chronic enlargement of the thyroid gland due to nonneoplastic growth occurring in the setting of hypothyroidism, hyperthyroidism, or euthyroidism. Morphologically, thyroid enlargement can be diffuse (smooth consistency) or nodular (uninodular or multinodular). Goiter) or > 1 nodule Nodule Chalazion/ swelling Swelling Inflammation/lump in different parts of the gland ( multinodular goiter Multinodular goiter An enlarged thyroid gland containing multiple nodules (thyroid nodule), usually resulting from recurrent thyroid hyperplasia and involution over many years to produce the irregular enlargement. Multinodular goiters may be nontoxic or may induce thyrotoxicosis. Goiter).
• Hyperparathyroidism Hyperparathyroidism Hyperparathyroidism is a condition associated with elevated blood levels of parathyroid hormone (PTH). Depending on the pathogenesis of this condition, hyperparathyroidism can be defined as primary, secondary or tertiary. Hyperparathyroidism: pathologically elevated parathyroid Parathyroid The parathyroid glands are 2 pairs of small endocrine glands found in close proximity to the thyroid gland. The superior parathyroid glands are lodged within the parenchyma of the upper poles of the right and left thyroid lobes; the inferior parathyroid glands are close to the inferior tips or poles of the lobes. Parathyroid Glands: Anatomy hormone (PTH) levels. Depending on the pathogenesis, hyperparathyroidism Hyperparathyroidism Hyperparathyroidism is a condition associated with elevated blood levels of parathyroid hormone (PTH). Depending on the pathogenesis of this condition, hyperparathyroidism can be defined as primary, secondary or tertiary. Hyperparathyroidism can present as 3 forms: primary, secondary, and tertiary hyperparathyroidism Tertiary Hyperparathyroidism Hyperparathyroidism. The most frequent cause includes adenomas of the parathyroid Parathyroid The parathyroid glands are 2 pairs of small endocrine glands found in close proximity to the thyroid gland. The superior parathyroid glands are lodged within the parenchyma of the upper poles of the right and left thyroid lobes; the inferior parathyroid glands are close to the inferior tips or poles of the lobes. Parathyroid Glands: Anatomy gland.
• Sjogren syndrome: a systemic chronic inflammatory disease characterized by infiltrative lymphocytic inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the exocrine organs.