The Epithelium Flashcards
A fertilized egg _____ many times to produce many small cells.
Divides
These cells arrange themselves into _____ _____ _____–ectoderm, mesoderm, and endoderm.
Three germ layers
These germ layers ______ into various kinds of tissues.
Differentiate
Ectoderm (8)
- Epidermis of skin and derivatives (sweat glands, hair follicles)
- Epithelial lining of mouth and anus
- Cornea and lens of eye
- Nervous system
- Sensory receptors in epidermis
- Adrenal medulla
- Tooth enamel
- Epithelium of pineal and pituitary glands
Mesoderm (10)
- Notochord
- Skeletal system
- Muscular system
- Muscular layer of stomach and intestine
- Excretory system
- Circulatory and lymphatic systems
- Reproductive system (except germ cells)
- Dermis of skin
- Lining of body cavity
- Adrenal cortex
Endoderm (7)
- Epithelial lining of digestive tract
- Epithelial lining of respiratory system
- Lining of urethra, urinary bladder, and reproductive system
- Liver
- Pancreas
- Thymus
- Thyroid and parathyroid glands
A tissue is _____ as a group of cells of ____ ___ that perform a common function.
Defined; common origin
Tissues are ____ ____ of organs.
Building blocks
A sound knowledge of _____ is essential in understanding organ physiology.
Tissues
Basic types of tissues (5)
- Epithelium
- Connective Tissue
- Blood
- Muscle Tissue
- Nervous Tissue
Most epithelia arise from _____ or _____.
Ectoderm; Endoderm
Skin and cornea are _____ in origin.
Ectodermal
Glands (sudoriferous or sweat, sebaceous or oil, and mammary) are formed by _______ or ______ of ectoderm.
Invagination; Evagination
_____ glands are ductless and _____ have ducts.
Endocrine; Exocrine
Alimentary canal is ______ in origin.
Endodermal
Functional Specialization of Epithelia (6)
- Absorption
- Secretion
- Transport
- Protection
- Excretion
- Sensory Reception
General Characteristics of Epithelium (6)
- Little or no intercellular space
- Avascular
- Supplied with nerves
- Held in position by connective tissue underneath
- Basement membrane present
- Subject to wear and tear and rapid proliferation
Epithelial cells have high ____ ____.
Mitotic index
Epithelial cells are exposed to the surface and hence access to _____ and _____.
Pathogens; Carcinogens
Most common types of cancerous or malignant tumors originate from _________ _____.
Epithelial cells
Tumors invade or metastasize to _____ _____.
Distant tissues
Carcinomas originate from ______ ______.
Surface epithelium
Adenocarcinomas originate from ______ ______.
Glandular epithelium
Some epithelial tumors are _____.
Benign
Papillomas originate from ____ _____.
Surface epithelium
Adenomas originate from _____ _____.
Glandular epithelium
Classification of epithelia according to cell shape.
- Squamous
- Cuboidal
- Columnar
Classification of epithelia according to number of layers.
- Simple
- Stratified
- Pseudostratified
Additional kinds of epithelia
- Transitional or uroepithelium
- Germinal epithelium
Classification of epithelia according to location and function.
- Covering or lining epithelium - lines surfaces
- Glandular epithelium - glands
Simple Squamous Epithelium: Description
Single layer of flattened cells
Simple Squamous Epithelium: Functions
- Filtration
- Absorption
- Protection
Simple Squamous Epithelium: Location
- Tympanic membrane
- Bowman’s capsule
- Lung epithelium
- Mesothelium
- Endothelium
- Endocardium
Mesothelium
Lines the contents of the closed body cavities such as abdominal, pericardial, and pleural
Endothelium
Lining of blood and lymphatic vessels
Endocardium
Lining of ventricles and atria of the heart
Simple Squamous Epithelium: Clinical Point
Mesothelioma
Mesothelioma
- Aggressive tumors of parietal and visceral serous membranes
- Caused by exposure to asbestos
- Shortness of breath, chest pain, accumulation of pleural
Simple Cuboidal Epithelium: Description
Single layer of cells with roughly equal height and width–box like
Simple Cuboidal Epithelium: Functions
- Absorption
- Secretion
Simple Cuboidal Epithelium: Location
- Thyroid gland
- Free surface of ovaries
- Ducts of glands
- Kidney tubules
Simple Columnar Epithelium: Description
- Single layer of cells that are taller than they are wider
- Often have microvilli
- Lateral surfaces with various kinds of junctions
Simple Columnar Epithelium: Functions
- Absorption
- Secretion
Simple Columnar Epithelium: Location
- Lining of hollow organs
- Digestive tract
- Uterus
- Oviduct
- Bronchi
- Gallbladder
Modified Simple Columnar Epithelium
- Goblet cells
- Simple columnar ciliated
Goblet cells
- Mucus secretion
- Digestive tract
Simple columnar ciliated
- Dust protection in respiratory tract
- Oviduct
Stratified Squamous: Functions and Locations
- Protection - epidermis, mouth, esophagus, conjunctiva, cornea, vagina, portions of female urethra
- Keratinized - protection - epidermis
- Nonkeratinized - protection - mouth, tongue, vagina
Stratified Cuboidal: Functions and Locations
Protection - ducts of glands, urethra
Stratified Columnar: Functions and Locations
Protection, secretion - male urethra, pharynx, epiglottis
Pseudostratified Columnar: Functions and Locations
Protection - male urethra, excretory ducts of parotid, and other glands
Ciliated Pseudostratified Columnar: Functions and Locations
Dust trapping, moving mucus - greater part of trachea and bronchi, Eustachian tube
Transitional (Uroepithelium): Functions and Locations
Prevent organ rupture - urinary bladder, ureter
Epithelial cells are ______; basal and distal surface differ in structure
Polarized
Golgi complex ______ or _______
Adluminal; supranuclear
Polarity less evident in ________ epithelium
Stratified
Apical Plasma Membrane
Rich in glycolipids, cholesterol, H+ ATPase, hydrolytic enzymes, transport proteins for release of secretory products
Lateral Plasma Membrane
Has Na+/K+ ATPase and receptors for hormones and neurotransmitters
Basal Plasma Membrane
Has binding sites for basal lamina
Cell cohesion depends on a family of glycoproteins called ________ or ________.
Cell adhesion molecules (CAM); Integrins
One such protein ______ is responsible for mutual cell to cell recognition.
Cadherin
Six or more surface glycoproteins are identified and one class depends on ______.
Ca++
Other molecules called _____ bind to CAM–examples–fibronectin, laminin, and collagen.
Ligands
Zonula Occludens or Tight Junctions
- A belt around PM of adjacent cells
- Function is to maintain osmotic pressure
- Found among columnar epithelial cells
Zonula Adherens
- Function is to maintain osmotic pressure
- Found among columnar epithelial cells
Desmosomes or Macula Adherens
- Function is to maintain osmotic pressure
- Found among columnar epithelial cells
- Consist of central lamina, attachment plaques, transmembrane linkers, and tonofilaments
Gap Junctions or Nexus
- Involved in electrical coupling and hormonal actions
- Found commonly in nerve and muscle cells
- Consist of six subunits of proteins
- Contain hydrophilic pores
- Allow ions, water, cAMP, etc.
Basal Lamina Functions
Physical supports by attachments; ultrafiltration (kidney endothelium)
Basal Lamina Layers
- Lamina rara or lucida
- Lamina densa
Lamina rara or lucida
-Adjacent to epithelium–consists of proteoglycans laminin and type IV collagen secreted by epithelium
Lamina densa
-Adjacent to connective tissue–consists of type VII collagen and fibronection
Brush border or Microvilli (Function, Location, Description)
- Functions: absorption, secretion
- Location: digestive system and kidney tubules
- Consist of actin, villin, and glycocalyx
Stereocilia (Function, Location, Description)
- Function: absorption
- Location: found in pseudostratified columnar epithelium of epididymis
- Are non-motile cilia
Cilia (Functions, Description)
- Functions: Rapid to and fro movement, transport of fluid over the surface of respiratory tract
- 50-100 per cell and are motile
- Have a core structure called axoneme
- Axoneme consists of long microtubules
- Microtubules arranged in 9 doublets + 2 singlets
- Tubules slide over each other for movement
Flagella (Functions, Location)
- Function - Rapid and propelling movement
- Found in spermatozoa
- Usually one/cell–longest in mammalian spermatozoa
Wear and tear of epithelium in skin, GI, and glands and respiratory passages
- Skin: keratinization and shedding of cells
- GI: very active loss and renewal
- Glands and respiratory passages: loss is rare, cells are long lived
- Loss of cells is balanced by active mitotic proliferation
Some organs require _____ _____ composed of cells specialized for uptake of ions and small molecules.
Absorptive epithelium
Absorptive epithelia contain ______ and _____ proteins.
Carrier; Channel
Absorptive epithelia have ____ ____ and _____ _____ of basal cell membrane to increase surface area.
Brush border; multiple infoldings
Secretion
Uptake of substances from blood and transformation into complex forms within cells for a later release (examples: hormones, gastric juices)
Excretion
Simple diffusion of excretory (waste) products across epithelial membranes (examples: CO2)
Cells or associations of cells specialized for secretion are called ______.
Glands
Exocrine glands
Release their products into a system of ducts opening onto an external surface (example: digestive glands)
Endocrine glands
Release their products into blood or lymph for transport to target cells
Paracrine or Paraneurones
Release their products into extracellular spaces–transport by simple diffusion to target cells in the vicinity
Glands can be _______ to synthesize and release proteins.
Stimulated
Glands contain ______ granules in their cytoplasm.
Zymogen
Central Dogma of Molecular Biology
DNA (Replication) –> (Transcription) RNA –> (Translation) ribosomes –> Protein
Merocrine glands
Release of products from cell membrane while cell being intact (example: goblet cells, sweat glands)
Apocrine glands
Involves loss of a part of apical cell cytoplasm; less common (example: mammary glands)
Holocrine glands
Involves complete loss of cells discharging product (example: oil glands, spermatozoa)
Unicellular Exocrine Gland
Goblet cells are the only example
Multicellular exocrine glands
- Sheet of epithelium or secretory sheet (ex. gastric mucosa)
- Intraepithelial gland (ex. nasal mucosa, male urethra)
Classes of Simple Exocrine Glands
- Simple tubular
- Simple coiled tubular
- Simple branched tubular
- Simple acinar
- Branched acinar
Simple Exocrine Glands Characteristic
Open by one duct
Example of Simple Tubular
Crypts of Liberkuhn
Example of Simple Coiled Tubular
Sweat glands
Example of Simple Branched Tubular
Uterine, esophageal, and Brunner’s glands
Example of Simple Acinar
No example in mammals
Example of Branched Acinar
Sebaceous or oil glands
How are Compound Exocrine Glands Classified?
- According to shape
- According to nature of secretion
Compound Exocrine Gland Shapes
- Tubular
- Acinar or alveolar
- Saccular
Compound Exocrine Gland Secretions
- Mucous (thick)
- Serous (watery)
- Mixed (both, ex. salivary glands)
Tubular Compound Exocrine Gland Example
Mucus glands of oral cavity
Acinar or Alveolar Compound Exocrine Gland Example
Salivary glands
Saccular Compound Exocrine Gland Example
Mammary and prostate glands
Exocrine glands are enclosed in ____ and divided into _____ and lobules.
Sacs; lobes
Exocrine glands have _______ tissue, _____ and lymphatic vessels, _____ supply, and ______ and ductules.
Connective; blood; nerve; ducts
Connective tissues work as ______, the _______ cells or tissues.
Stroma; supporting
Epithelium works as ______, the ______ cells or tissues.
Parenchyma; functional
Physiological (nervous) Control of Exocrine Secretion
Varies from gland to gland, mostly via Autonomic Nervous System (ANS)–acetylcholine also involved
(example: smell–entirely nervous through vagus nerve)
Hormonal Control of Exocrine Secretion
Involves gastrin, cholecystokinin, secretin
Dual Control of Exocrine Secretion
Involving both physiological and hormonal
example: food placed in stomach
Endocrine glands are ______–they release hormones into the blood which stimulate target cells somewhere else.
Ductless
Endocrine glands develop by ________ of epithelia and lose connection.
Evagination
Examples of endocrine glands
pituitary, thyroid, parathyroid, pancreas, adrenal, pineal, testes, ovaries, and placenta
Polypeptide (Protein) Secreting Endocrine Glands have cells rich in ______, _______, and ______. They _____ capable of storing hormones before release.
Ribosomes; Rough endoplasmic reticulum; Golgi complex; ARE
Steroid Secreting Endocrine Glands have little ______, few ______, rich in _____, abundant ______________, and numerous ________. They store __________ hormones & store the precursor cholesterol.
RER; ribosomes; SER; lipid droplets; mitochondria; very little
Polypeptide (Protein) Secreting Endocrine Gland Examples
Pancreas–Islets of Langerhans–insulin
Steroid Secreting Endocrine Gland Examples
Adrenal, Ovaries, Testes
In protein or water soluble hormones, the hormone, or _____ ______, binds to membrane ___ and ___ protein.
First messenger; Receptor and G
In protein or water soluble hormones, binding activates membrane _____ ______.
Adenylate cyclase (AC)
In protein or water soluble hormones, Adenylate Cyclase hydrolyzes _____ to _____, which is the _____ _____,
ATP to cAMP; second messenger
In protein or water soluble hormones, cAMP activate intracellular _____ _____ to initiate a chain of events for cellular response.
Enzyme kinase
Example of protein or water soluble hormones
Conversion of glycogen to glucose by liver cells by hormone epinephrine from adrenal glands
In steroid hormones, there is no _____ on the plasma membrane–the hormone enters the cytoplasm and binds to ______ ______.
Receptor; Intracellular receptor
In steroid hormones, the hormone-receptor complex binds to ____ and activates genes for cellular response.
DNA
Steroid hormone examples
Testosterone, estrogens, and progesterone
Endocrine cells are _____ ______ with extremely thin endothelium.
Richly vascular
Both blood and lymph are capable of ______ transport.
Hormone
Endocrine cells (EC) have essentially ___ _______–very thin basement membrane of EC and narrow intercellular spaces
No barrier
Most hormones are released into the ______, the only examples for _____ are _____ and _____.
Blood; Lymph; Thyroid and testes
Simplest form of hormonal control
Negative feedback system (output inhibits input)
Rise in blood sugar level stimulates pancreas to release _____. This causes an uptake of glucose into cells. Resulting low blood sugar ______ the release of insulin. This an example of ________ feedback.
Insulin; Inhibits ; Negative
_____ mobilizes Ca++ from bone and increased Ca++ ______ release of PTH.
PTH; Inhibits
In the complex form of hormone control, the _____ ____ are under the control of the nervous system.
Endocrine cells
In the complex form of hormone control, output _______ output.
Increases
An example of ________ feedback, is _____ ________.
Positive; Milk ejection
Two systems coordinate body activities– _________ and _______.
Nervous; Endocrine
Neuro-endocrinology involves _________.
Paraneurons
Some substances which act as neurotransmitters and hormones are _____________ and ______________.
Norepinephrine; Vassopressin (ADH)
Chemical messengers in diffuse system are called ___________.
Neuropeptides
There are ____ identified neuropeptides, including enteroendocrine or gastroenteropancreatic cells, gustatory cells, bronchial epithelium.
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