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Questions and Answers
What characterizes merocrine glands in their secretion process?
What characterizes merocrine glands in their secretion process?
- Use a ductless system for secretion
- Secrete through fragmentation of the cell
- Release by exocytosis of filled vesicles (correct)
- Release cytoplasmic contents along with the secretion
Which of the following is true about endocrine glands?
Which of the following is true about endocrine glands?
- They are typically found in the skin's superficial layers.
- They secrete substances onto a body surface directly.
- They always function in secretion alone without absorption.
- They lack ducts and release hormones into circulation. (correct)
What is a key feature of stratified squamous epithelium?
What is a key feature of stratified squamous epithelium?
- It consists of a single layer of cube-like cells.
- All cells extend to the apical surface.
- It only exists in the urinary system.
- The apical layer contains keratin in its keratinized form. (correct)
Where is ciliated simple columnar epithelium primarily found and what is its main function?
Where is ciliated simple columnar epithelium primarily found and what is its main function?
Nonciliated simple columnar epithelium is characterized by lacking which of the following?
Nonciliated simple columnar epithelium is characterized by lacking which of the following?
What distinguishes stratified cuboidal epithelium from other types of epithelium?
What distinguishes stratified cuboidal epithelium from other types of epithelium?
Which mechanism of exocrine gland secretion involves the cell losing part of its cytoplasm?
Which mechanism of exocrine gland secretion involves the cell losing part of its cytoplasm?
Transitional epithelium is uniquely suited for which of the following functions?
Transitional epithelium is uniquely suited for which of the following functions?
What is the primary function of ciliated simple columnar epithelium in the respiratory tract?
What is the primary function of ciliated simple columnar epithelium in the respiratory tract?
Which characteristic of simple cuboidal epithelium is crucial for its function in secretion and absorption?
Which characteristic of simple cuboidal epithelium is crucial for its function in secretion and absorption?
Which of the following is NOT a feature of stratified squamous epithelium?
Which of the following is NOT a feature of stratified squamous epithelium?
What distinguishes nonciliated simple columnar epithelium from its ciliated counterpart?
What distinguishes nonciliated simple columnar epithelium from its ciliated counterpart?
Where is stratified squamous epithelium predominantly found?
Where is stratified squamous epithelium predominantly found?
What characterizes holocrine secretion?
What characterizes holocrine secretion?
Which type of epithelium is primarily involved in the secretion of mucus to protect the stomach lining?
Which type of epithelium is primarily involved in the secretion of mucus to protect the stomach lining?
Which type of gland is classified as unicellular?
Which type of gland is classified as unicellular?
What is a common characteristic shared by both endocrine glands and exocrine glands?
What is a common characteristic shared by both endocrine glands and exocrine glands?
How are multicellular glands structurally classified?
How are multicellular glands structurally classified?
Which statement is true regarding serous secretions?
Which statement is true regarding serous secretions?
Which type of epithelium allows for rapid passage of substances due to its thin structure?
Which type of epithelium allows for rapid passage of substances due to its thin structure?
What type of secretory portion is typical of an acinar gland?
What type of secretory portion is typical of an acinar gland?
What feature is characteristic of pseudostratified epithelium?
What feature is characteristic of pseudostratified epithelium?
Which type of covering epithelium is specialized to accommodate stretching in the urinary bladder?
Which type of covering epithelium is specialized to accommodate stretching in the urinary bladder?
Which of the following features distinguishes a compound gland from a simple gland?
Which of the following features distinguishes a compound gland from a simple gland?
Which type of secretion is primarily produced by cells in the sublingual salivary glands?
Which type of secretion is primarily produced by cells in the sublingual salivary glands?
What describes the arrangement of tubular glands?
What describes the arrangement of tubular glands?
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Study Notes
Covering and Lining Epithelium
- Classified based on arrangement of cells in layers (simple, stratified, pseudostratified) and shape of cells (squamous, cuboidal, columnar, transitional)
- Simple epithelium has a single layer of cells functioning in diffusion, osmosis, filtration, secretion, or absorption
- Pseudostratified epithelium appears to have multiple layers, but all cells are attached to the basement membrane
- Stratified epithelium has two or more layers of cells that protect underlying tissues
Different Types of Covering and Lining Epithelium
- Squamous cells are thin and flat, allowing for rapid passage of substances
- Cuboidal cells are as tall as they are wide, functioning in secretion or absorption
- Columnar cells are much taller than they are wide, functioning in secretion and absorption
- Transitional cells change shape, becoming flat to cuboidal, found in organs that stretch
Simple Epithelium
- Simple squamous epithelium: single layer of flat cells for filtration or diffusion
- Simple cuboidal epithelium: cuboidal shaped cells with round, centrally located nuclei, found in thyroid gland and kidneys
- Simple columnar epithelium: column shaped cells with oval nuclei near the base, nonciliated and ciliated types
- Pseudostratified columnar epithelium: appears multilayered but all cells connect to the basement membrane, ciliated or nonciliated
Simple Squamous Epithelium
- Single layer of flattened cells, resembling a tiled floor
- Nucleus is centrally located and appears flattened oval or sphere
- Found at sites for filtration or diffusion
Covering and Lining Epithelium
- Endothelium: simple squamous epithelium lining heart, blood vessels, lymphatic vessels, derived from mesoderm
- Mesothelium: simple squamous epithelial layer of serous membranes such as pericardium, pleura, or peritoneum, derived from mesoderm
Simple Cuboidal Epithelium
- Cuboidal shaped cells, round, centrally located nuclei
- Functions in secretion and absorption, found in thyroid gland and kidneys
Simple Columnar Epithelium
- Column shaped cells with oval nuclei near the base
- Nonciliated and ciliated variations
Nonciliated Simple Columnar Epithelium
- Contains columnar cells with microvilli at apical surface and goblet cells
- Secreted mucus acts as a lubricant for linings of digestive, respiratory, reproductive, and urinary tracts
- Mucus prevents destruction of stomach lining by acidic gastric juices
Ciliated Simple Columnar Epithelium
- Columnar epithelial cells with cilia at the apical surface
- Goblet cells interspersed among ciliated columnar epithelia in respiratory tract
- Secreted mucus traps inhaled foreign particles, beating cilia move particles to the throat for removal
- Cilia also moves oocytes to the uterine tubes
Covering and Lining Epithelium
- Pseudostratified columnar epithelium appears to have several layers due to nuclei at various depths
- All cells attach to the basement membrane in a single layer but some do not extend to the apical surface
- Ciliated cells secrete mucus and bear cilia
- Nonciliated cells lack cilia and goblet cells
Stratified Epithelium
- Composed of two or more layers of cells
- Specific kind of stratified epithelium depends on the shape of cells in the apical layer
- Stratified squamous epithelium, Stratified cuboidal epithelium, Stratified columunar epithelium, Transitional epithelium
Stratified Squamous Epithelium
- Apical layer is composed of flat cells
- Cells are pushed up toward the apical layer, as they move further from blood supply, they dehydrate, harden, and die
- Keratinized form contains the fibrous protein keratin, found in superficial layers of skin
- Nonkeratinized form does not contain keratin, found in mouth and esophagus
Stratified Cuboidal Epithelium
- Fairly rare type of epithelium with cuboidal cells in the apical layer
- Functions in protection
Stratified Columnar Epithelium
- Also very uncommon, only the apical layer is made of columnar cells
- Basal layers have shorten, irregular shaped cells
- Functions in protection and secretion
Transitional Epithelium
- Found only in the urinary system
- Variable appearance, cells are cuboidal in relaxed state
- In stretched state, cells become flattened and appear squamous
- Ideal for hollow structures subjected to extension
Histology of Glands
- Classified by how their products are released: exocrine (ducts empty onto body surface) and endocrine (lack a duct, secrete into circulation)
Glands
- Paracrine secretion acts locally on cells within the same tissue, without entering circulation
- Exocrine glands have three release mechanisms: merocrine, apocrine, holocrine
Release Mechanisms
- Merocrine: release by exocytosis (fusion of filled vesicles to the apical cell membrane), most common mechanism
- Apocrine: release from the apical cell surface of content surrounded by cytoplasm and membrane, found in lactating mammary glands and other glands
- Holocrine: secretory products accumulate within a mature cell, cell undergoes apoptosis releasing both products and debris into gland lumen, found in sebaceous glands
Glands
- Glands can also be classified as Unicellular or Multicellular
- Unicellular: single secretory cells distributed amongst nonsecretory cells, example: goblet cells in columnar epithelium
Multicellular Glands
- Exhibit varying degrees of complexity
- Classified based on arrangement of secretory cells and presence or absence of branching duct elements
- Form tubular invaginations creating a secretory portion and a duct
Multicellular Glands
- Ducts can be simple (unbranched) or compound (branched)
- Secretory portion can be tubular (tube-shaped), alveolar/acinar (flask-shaped), or tubuloalveolar (duct terminates in a sac-like dilatation)
- Tubular portions can be straight, branched, or coiled
- Alveolar portions can be single or branched
Structural Classification of Exocrine Glands
- Multicellular glands categorized by:
- Whether ducts are branched or unbranched
- Shape of the secretory portion of the gland
- Simple gland: unbranched duct
- Compound gland: branched duct
- Tubular glands: tubular secretory parts
- Acinar glands: rounded secretory parts
- Tubuloacinar glands: both tubular and rounded secretory parts
Gland Secretions
- Exocrine glands emptying into internal body surfaces (GIT, respiratory, urogenital tracts) have mucous and/or serous secretions
- Mucous secretions are viscous, secreted by goblet cells, sublingual salivary glands, stomach goblet cells
- Mucous secretions are protein with extensively glycosylated anionic oligosaccharides, stains positive with PAS, granules lost in tissue preparation
- In H&E sections, mucous cells have empty cytoplasm with a basal nucleus
Gland Secretions
- Serous secretions are watery, containing non-glycosylated protein secretions
- Cytoplasm stains intensely with eosin
- Examples: pancreatic acinar cells, parotid gland, serous portion of mixed glands
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