By: Sachi Estreller |Section B
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Histology
Third Shifting Reviewer
RESPIRATORY SYSTEM
Conducting System
Nasal cavity paranasal sinuses
nasopharynx trachea primary bronchi secondary bronchi terminal bronchioles
Contains mucus-secreting cells and cilia
For cleansing, warming, and conducting of air Gaseous Interchange System
Transitional airways (respiratory bronchiole) alveolar duct/ sac alveoli and pulmonary capillaries
From the terminal bronchioles, there is a series of “transitional airways”: respiratory bronchioles and alveolar ducts
For gas exchange
Nasal Cavity
Consists of external vestibule and internal nasal fossa
Two nasal cavities divided by a cartilaginous nasal septum
Function enhanced through enlarged surface area by turbinate system
o Temperature regulation o Humidity
o Trapping of particulate matter
Olfactory mucosa at the roof of the nasal cavity which function as receptors for smell
Conchae
o Superior: olfactory epithelium Mucous secreted by
Bowman’s gland; no goblet cells
Has olfactory hair/ cilia which are receptor structures
o Middle and Inferior: respiratory epithelium
With goblet cells
Nasal Mucosa
Composed of “respiratory epithelium”: pseudostratified columnar ciliated epithelium with goblet cells
Lamina propria is rich in vessels and serous and mucous glands
o Temperature of inspired air: adjusted by rich plexus of blood vessels and serous gland secretions
o Trapping of particulate matter: mucus-secreting glands and cilia
Nasopharynx
Composed of respiratory epithelium o Patches of squamous epithelium
increase with age
Lamina propria rich in serous and mucous glands and large masses of lymphoid tissue called the adenoids or nasopharyngeal tonsil (part of Waldeyer’s Ring)
Larynx
False Vocal Cord
Upper fold composed of respiratory epithelium True Vocal Cord
Lower fold composed of stratified squamous epithelium
Contains the vocalis muscle and vocalis ligament Ventricle
Narrow cleft between the true and false vocal cords composed of respiratory epithelium with seromucous glands
Terminates as a blind-ending saccule
Epiglottis
Stratified squamous non-keratinizing epithelium
Elastic cartilage that presents with degenerative fatty changes with aging
Trachea
Flexible tube of fibro-elastic tissue and cartilage which permits expansion, extension, and recoil
Composed of respiratory epithelium with the following components:
o Tall pseudostratified ciliated columnar cells (more plentiful in lower trachea) o Goblet cells
o Serous cells
o Basal cells (neuroendocrine system) o Basal stem cells
o Thick basement membrane
Lamina Propria consists of loose and highly vascular connective tissue
Submucosa contains seromucinous glands that decrease in number at the lower parts; merges with perichondrium of underlying hyaline cartilage rings
C-Shaped Hyaline Cartilage Rings
o Support tracheal mucosa and prevent its collapse
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Trachealis Muscle
o Join free ends of the rings posteriorly o Contraction reduces tracheal diameter
and assists in raising intrathoracic pressure during coughing
Primary Bronchus
Respiratory epithelium is less tall and contains fewer goblet cells
Lamina Propria is separated from submucosa by a layer of smooth muscle (smooth muscle more prominent)
Submucosa contains fewer seromucinous glands
Cartilage exist as flattened plates rather than distinct rings
Has Bronchus Associated Lymphoid Tissue (BALT), component of diffuse MALT
Tertiary (Segmental) Bronchus
Respiratory epithelium has little
pseudostratification with greatly diminished goblet cell number
Lamina Propria is thin, elastic, and completely encircled by smooth muscle disposed in a spiral manner
Submucosa has sparce seromucinous glands
Cartilage disposed to few irregular plates and does not extend beyond the tertiary bronchi
MALT are present in the adventitia
Bronchiole
Ciliated columnar epithelium with goblet cells o In the terminal and respiratory
bronchioles, goblet cells are replaced by clara cells (tall columnar cells with apical secretory granules)
< 1mm in diameter with no cartilage or submucosal gland components
Smooth muscle and neuroendocrine cells are present
Terminal Part of the Respiratory Tree
Terminal Bronchioles
Smallest diameter passages of purely conducting portion of respiratory tree
Further divide to form respiratory bronchioles Respiratory Bronchioles
Ciliated cuboidal epithelium with clara cells (no goblet cells)
o Clara cells are non-ciliated cells that function to produce one component of surfactant, act as stem cells, and detoxify noxious substances
Contain few alveoli that start to function for gas exchange; alveoli increase in number
Divide to form alveolar ducts Alveolar Ducts
With numerous alveoli along their length
End in alveolar sacs which open into several alveoli
Smooth muscle component appear knob-like
Alveoli
Surface Epithelium
Type I Pneumocytes (Small Alveolar Cells) o About 40% of epithelium o Large, squamous cells
o Alveolar lining cells that is part of the thin gaseous diffusion barrier
Type II Pneumocytes (Great Alveolar Cells) o About 60% of epithelium o Rounded cells with large nuclei
(dispersed chromatin and dispersed nucleoli)
o Lamellar Bodies
Fine vacuoles in cytoplasm that contain phopholipid palmityl
phosphatidylcholine) Storage and release site of
surfactant o Functions:
Secrete surfactant (tubular myelin) which serves to reduce surface tension, preventing alveolar collapse during expiration
Surfactant has aqueous hypophase and lipid monolayer Retain capacity for cell
division and can differentiate to Type I Pneumocytes as needed
Supporting Tissue
Fine reticular, collagenous and elastic fibers with occasional fibroblasts
Elastin and septal collagen of the alveolar wall are continuous with those of adjacent alveoli
Alveolar septum
o Composed of 3 laminar structures constituted by a central basement membrane and 2 very thin cytoplasmic layers
o Septa contains small openings called alveolar pores of Kohn, which allow
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movement of air between alveoli and also movement of pathogenic organisms
Blood Vessels
Air-Blood Barrier
o Type 1 pneumocyte + fused basement membrane + capillary endothelium o Basement membrane of the capillary
endothelium is directly applied to basement membrane of surface epithelium, without interfering supporting tissue
Alveolar Wall
Composed mainly of capillaries that form a basket-like arrangement around each alveolus
Type I pneumocytes are located on the convex side of the basement membrane
Surface endothelial cells located on the concave side of the basement membrane
Type II pneumocytes are located at the branching point of the alveolar septum
Alveolar Macrophage
Found within alveolar spaces and septa
Function in the phagocytosis and removal of unwanted material that gains access to the air spaces
After phagocytosing particles:
o Most become trapped in mucus and coughed up as sputum
o Others stay in septa
o Others gain access to lymphatic system
Pulmonary Vasculature
Large Elastic Pulmonary Artery
Pulmonary trunk, main right and left pulmonary arteries, major lobar branches
Similar to the aorta with prominent elastic lamellae as part of the tunica media
Layers are thinner and less substantial than the aortic counterpart since intravascular pressures are much lower
Muscular Pulmonary Artery
Transition is at the point where bronchi lose cartilage plates and become bronchioles
Elastic fibers are disposed into internal and external elastic laminae
Tunica media is largely composed of smooth muscle and collagen
Small Pulmonary Arterioles
Tunica media becomes thinner and eventually becomes discontinous
Small Pulmonary Vein
Amount of smooth muscle in tunica media increases progressively along venous network
With ill-formed elastic laminae
The Visceral Pleura
Outer surface lined by a layer of flattened cuboidal mesothelium supported by thin basement membrane
Mesothelial cells have plentiful long surface microvilli which trap hyaluronic acid that enhances the lubrication of the two surfaces
Fibrous supporting tissue consists of collagen and elastin fibers
By: Sachi Estreller |Section B
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ORAL TISSUES
Functions
o Mastication
Ingestion, fragmentation, and moistening of food for swallowing
o Speech and facial expression o Sensory reception
o Breathing
Oral Mucosa
Protective mucous membrane that contains many sensory receptors
Lined by stratified squamous epithelium (keratinized in areas subject to considerable friction)
Lamina Propria
o In highly mobile areas: connected to underlying muscle by loose
submucosal supporting tissue (eg. soft palate)
o In fixed areas: connected to periosteum of bone by dense fibrous submucosa (eg. hard palate)
Submucosa exhibit small salivary glands of both serous and mucous types
Lip
External surface covered by hairy skin which passes through a transition zone to merge with the inner oral mucosa
Vermillion Border
o Transition zone which has a thin, lightly keratinized epidermis and richly vascularised dermis
o Devoid of sweat and sebaceous glands
Inner surface composed of thick stratified squamous epithelium with numerous accessory salivary glands in the submucosa
Bundles of circumoral skeletal muscle is sandwiched between the internal and external surfaces
Palatal Mucosa
Thick stratified squamous epithelium supported by tough, densely collagenous lamina propria
Thrown into transverse folds called rugae to assist in mastication
Tooth Structure
Crown
o Projects into oral cavity protected by enamel covering
o Enamel
Hard, transluscent substance composed of parallel enamel rods of highly calcified material cemented together by interprismatic calcified material
Root
o Embedded in the bony alveolar ridge o Invested by a thin layer of cementum o Cementum
Amorphous calcified tissue connected to the bone of the alveolar socket by
periodontal ligament Generally acellular and
becomes thicker at the root apex
Dentine
o Composed of calcified organic matrix similar to bone, but is more highly mineralized due to inorganic hydroxyapatite crystals o Dental Pulp
Contained in the central pulp cavity formed by dentine Resembles primitive
mesenchyme and contains stellate fibroblasts, reticulin fibers, fine collagen fibers, and ground substance Richly vascularised and
innervated o Dental Tubules
Radiate to periphery of dentine
o Odontoblasts
Tall columnar cells on the surface of the dental papilla Responsible for dentine
formation
Initiate tooth formation by deposition of organic dentine between odontoblastic and ameloblastic layers Dentine formed is pervaded
by odontoblastic processes dentine tubules o Ameloblasts
Induces enamel formation by calcification of dentine matrix
Periodontal Membrane
o Thin fibrous attachment between tooth root and alveolar bone that functions as the sling of the tooth within socket
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o Permit slight movements of teeth and cushioning during chewing
o Sharpey’s Fibers
Run obliquely downwards from alveolar bone to cementum
o Epithelial Rests of Malassez Small clumps of epithelial
cells scattered throughout periodontal membrane
Gingiva
Oral mucosa covering the upper part of the alveolar ridge that forms a tight protective cuff around the tooth
Composed of thick stratified squamous
epithelium that undergoes abrupt transition to a thin layer of epithelial cells at the tip of the free gingiva
Attached Gingiva
o Protective covering to upper alveolar bone
Free Gingiva
o Cuff around the enamel at the neck of the tooth
Gingival Crevice
o Potential space between the gingival cuff (free gingiva) and enamel of the crown of the tooth (cemento-enamel junction)
o Crevicular epithelium easily breached by pathogenic organisms
Tongue
Muscular organ covered by oral mucosa o Body of the tongue consists of
interlacing bundles of skeletal muscle fibers
o Mucous membrane bound to muscle layer by dense collagenous lamina propria
o Small serous and mucous accessory salivary glands are scattered throughout the muscle and lamina propria
Sulcus Terminalis
o V-shaped groove that demarcated the anterior 2/3 from posterior 1/3
Anterior 2/3
o Filiform Papillae
Most numerous and appear as short bristles
Dense supporting tissue core with a heavily keratinized surface projection
o Fungiform Papillae
Small red and globular Thin, non-keratinized
epithelium which is richly vascularized
o Circumvallate Papillae
Largest and least common Located immediately
anterior to the sulcus terminalis
Contain most of the taste buds
o Follicular Papillae
Rudimentary in humans o Von Ebner’s Glands
Aggregates of serous glands that open into the base of the circumvallate clefts Secrete watery fluid that
dissolves food and facilitates taste reception
Posterior 1/3
o Smooth stratified squamous epithelium overlying lymphoid tissue termed as the lingual tonsils (part of Waldeyer’s Ring)
Salivary Glands
Produce 600-1500 ml of saliva daily, which is a hypotonic watery secretion containing variable amounts of mucus, amylase and lysozyme, antibodies, and inorganic ions
Salivary Secretory Unit
o Consists of a terminal branched tubulo-acinar structure composed exclusively of either serous or mucous secretory cells
o Terminal secretory units merge to form small intercalated ducts (cuboidal secretory cells) which drain into larger striated ducts (tall columnar cells) o Striated ducts
Function to reabsorb and secrete ions which produce hypotonic saliva with less Na and Cl and more K and HCO3 than plasma
Basal cytoplasm appears striated because of the presence of basal interdigitations of cytoplasmic processes of adjacent cells
Larger in serous glands than in mucous glands
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o Myoepithelial Cells
Force secretion from acinar lumen into duct system on contraction
Located between basal plasma membranes of secretory cells and basement membrane
Minor Salivary Glands
o Secrete continuously under local control
o Scattered throughout oral mucosa
Major Salivary Glands
o Secrete in response to parasympathetic activity o Parotid Gland
Composed mainly of serous secretory units
Divided into numerous lobules with supporting tissue septa that convey blood vessels, nerves, and large excretory ducts Main duct: Stensen’s o Sublingual Gland
Composed mainly of mucous secretory units
Large excretory duct lined by stratified cuboidal epithelium is present in tissue septum As ducts merge to form
major excretory duct, lining transforms into stratified squamous epithelium Contains occasional
adipocytes
Main ducts: Bartholin and Rivinus
o Submandibular Gland
Composed of a mix of serous and mucous secretory units Mixed secretory units are
composed of mucous acini with serous demilunes Mucous cell nuclei are
condensed and flattened Serous cell nuclei are
rounded and centrally-positioned
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GASTROINTESTINAL TRACT
Functions to break down food for absorption into the body:
o Ingestion o Fragmentation o Digestion o Absorption o Elimination
Structure of the GI Tract
Functional Layers
Mucosa
o Epithelium o Lamina Propria
Loose supporting tissue with diffuse lymphocytes and plasma cells (except for stomach)
o Muscularis Mucosa
Keeps the mucosal surface and glands in constant gentle agitation which expels secretions from glandular crypts and enhances contact of epithelium and food for absorption
Submucosa
o Loose collagenous and adipose supporting tissue
o Contains the larger blood vessels, lymphatics, and nerves
o No glands present except in esophagus and duodenum
o Meissner’s Plexus
Supply mucosal glands and muscularis mucosae
Muscularis Propria
o Smooth muscle usually arranged as ICOL. In the stomach, there is an inner oblique layer.
o Auerbach’s Plexus
Between the two muscle layers
Supply surrounding smooth muscle
Adventitia
o Outer layer of supporting tissue that conducts the major vessels, nerves, and variable adipose tissue
Mucosal Forms in the GI Tract
Protective
o Stratified squamous type
o Found in oral cavity, esophagus, and anal canal
Secretory
o Long, closely packed tubular glands that are simple or branched o Found only in the stomach
Absorptive
o Arranged into finger-like projections called cilli which increase the surface area with intervening short glands called crypts
o Found in the small intestine
Absorptive/ Protective
o Arranged into closely packed, straight tubular glands and goblet cells specialized for water absorption and lubrication
o Found in large intestine
Motility
Peristalsis initiated by Interstitial Cells of Cajal (pacemaker cells)
Modulated by ANS
Parasympathetic increases motility while sympathetic does the opposite
Esophagus
Strong muscular tube that conveys food from the oropharynx to the stomach
Thick stratified squamous epithelium
Lamina propria is narrow and contains scattered lymphoid aggregates
Submucosa is loose with many elastic fibers and small seromucous glands
Muscularis propria is thick: ICOL o Bundles of skeletal muscle
predominate in the upper 1/3 of esophagus
o Smooth muscle predominate in lower 2/3
Gastro-esophageal sphincter
Physiologic sphincter
Factors: diaphragmatic contraction, greater intra-abdominal pressure, unidirectional peristalsis, maintenance of correct anatomical arrangements of the structures
Abrupt transition from stratified squamous epithelium to tightly packed glandular secretory mucosa
Muscularis mucosa, submucosa, and muscularis propria continue uninterrupted
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Stomach
Distensible organ responsible for mechanical and chemical breakdown of food into chime
Tall columnar epithelium Rugae
Longitudinal folds in the mucosa during non-distended state
Cardia
Small area of mucus-secreting glands
Cardiac glands are compound tubular in nature Fundus and Body
Consist of glands that secrete acid-pepsin gastric juices; branched tubular in nature
Gastric glands
o Simple tubular glands that extend from level of the muscularis mucosae to open into the stomach lumen via gastric pits of foveoli
o 1-7 gastric glands may open into 1 gastric pit
o Surface Mucous Cells
Short surface microvilli Secrete bicarbonate o Neck Mucous Cells
At the neck and base of gastric glands
Have larger secretory granules and more polyribosomes than surface mucous cells
o Parietal (Oxyntic) Cells
At isthmus of gastric glands Secrete gastric acid and
intrinsic factor
Eosinophilic cytoplasm with centrally-located nucleus; feature numerous mitochondria
Luminal plasma membrane form canaliculi with projecting short microvilli Canaliculi are related to
tubulovesicular system responsible for secretion of gastric acid
o Chief Peptic (Zymogenic) Cells Most common
At base of gastric glands Secrete pepsin
Basophilic and granular cytomplasm with basally-located nuclei; feature numerous RER
o Neuroendocrine Cells
At base of gastric glands Secrete serotonin, etc. o Stem Cells
At neck of gastric glands Replace all other cell types as
needed
Muscularis Propria
o Inner oblique, middle circular, and outer longitudinal layers
Mucosa
o Devoid of lymphoid cells
o With tall columnar mucus-secreting cells that protect epithelium from auto-digestion
Pylorus
Secrete two types of mucus and gastrin
Gastric Glands
o Coiled/ Convoluted branched tubular o Lined almost exclusively by
mucus-secreting cells
o G cells that secrete gastrin are mainly found in the neck of the glands
Gastro-duodenal Junction
Anatomical sphincter
Sharp transition from glandular mucosa to villous mucosa
Pyloric sphincter is marked by a thickening of the circular layer of the muscularis
ICOL is continuous from pylorus to duodenum
Duodenum
Main function is to neutralize gastric acid and pepsin
Simple tall columnar epithelium with striated cuticular border and goblet cells
Mucosa
o Villi: longest and foliate
o Characteristic villous form interspersed with short glands known as Crypts of Lieberkuhn that extend down to muscularis mucosae
o Goblet cells least numerous among the three
o Plicae circulares not prominent
Brunner’s Glands
o Unique feature of the duodenum o Extensive mass of coiled branched
tubular glands in the submucosa o Tall columnar cells with mucigen-filled
cytoplasm and basally located nuclei o Pass through the muscularis mucosae
to open into the crypts between the villi
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o Secrete thin alkaline mucus, lysozyme, and epidermal growth factor
Neuroendocrine Cells
o Secrete secretin and cholecystokinin which promote pancreatic and bile secretion
Jejunum
Mucosa
o Villi: intermediate length, clevate/rounded o Goblet cells fairly present
o Plicae Circulares most prominent here
Ileum
Mucosa
o Villi: shortest, conical o Peyer’s Patches predominate
o Goblet cells most numerous among the three
o Plicae Circulares fairly prominent in proximal ileum but absent in distal parts
Ileocecal Junction
o Abrupt transition from villiform lining to glandular lining
o Ileocecal valve consists of a thickened extension of muscularis propria
Intestinal Villi and Crypts
Simple columnar epithelium continuous with the crypts; Cores of villi are the extensions of lamina propria
Small lymphatic vessels drain into a single lacteal at the center of the villus. These lacteals transport absorbed lipid into the circulatory system via the thoracic duct
Cell Types
Enterocytes
o Most numerous and main absorptive cells; Tall columnar cells with surface microvilli
o Main feature of cytoplasm is numerous free ribosomes, scattered
mitochondria, and membranous vesicles containing lipoprotein droplets o Glycocalyx of microvilli prominent and
acts as site for adsorption of pancreatic digestive enzymes o Transcytosis is an important
mechanism for uptake of
macromolecules from gut lumen into the blood
Involves endocytosis with transfer to the ECF at base of enterocyte
Goblet Cels
o Produce mucin for lubrication and protection of epithelium
Paneth Cells
o At the base of crypts
o Have prominent, eosinophilic apical granules
o Defensive function: part of innate immune system; contain defensins, lysozyme, and phospholipase A
Neuroendocrine Cell
o Regulate GI motility and secretion
Stem Cells
o At the base of crypts; Replenish cell types
Intraepithelial Lymphocytes o Mostly T cells for defense
Colon
Muscular layer still follows ICOL pattern but the longitudinal layer forms bands of teniae coli except in the rectum
Indistinct cuticular border
Glands
o Consist of absorptive cells and mucus-secreting goblet cells
o Goblet cells predominate in the base while columnar absorptive cells predominate in the luminal surface
Appendix
o Presence of masses of lymphoid tissue in the mucosa and submucosa, especially present in the young o Mucosal glands less closely packed
than in the large intestine
Recto-anal Junction
o Rectal mucosa is same as the rest of the large bowel except that it has even more numerous goblet cells
o At the junction, abrupt transition to stratified squamous epithelium is observed
o A transition from skin containing sebaceous glands to large apocrine sweat glands (peri-anal glands of Gay) is also seen.
o Columns of Morgagni
Longitudinal folds found immediately above the anal valves
o Circumanal Glands
Branched tubular glands that open at the recto-anal junction into small pits at the distal ends of the Columns of Morgagni
By: Sachi Estreller |Section B
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ACCESSORY GLANDS OF THE GI SYSTEM
Liver
Functions
Fat metabolism: oxidation of TAGs, synthesis of plasma lipoproteins, cholesterol, and
phospholipids
Carbohydrate metabolism: regulation of blood glucose concentrations
Protein metabolism: synthesis of plasma proteins, non-essential amino acids, detoxification of waste products
Storage: glycogen, vitamins, iron
Secretion: bile Structure
Structural integrity maintained by meshwork of extracellular matrix in the form of reticulin fibers (collagen type III), which becomes continuous with the liver capsule at the periphery
Glisson’s Capsule
o Capsule composed of collagenous tissue
o Portal Canal: thickened part of the Glisson’s capsule at the angles of the hepatic lobule that contains the portal triad
Hepatocytes
o Main functional cell
o Large polyhedral cells with round nuclei (peripherally dispersed chromatin and prominent nucleoli) o >50% of hepatocytes contain twice the
normal complement of chromosomes within a single nucleus
o Store significant amounts of glycogen and lipid
o With numerous mitochondria and RER o Arranged as thin plates separated by
fine vascular sinusoids
Hepatic Sinusoids
o Low-resistance system of vascular channels that allows blood to come into contact with hepatocytes o Lined by flat endothelial lining cells
with flattened nuclei
o Endothelium is discontinuous and fenestrated, has no basement membrane, and is separated from the hepatocytes by the space of Disse o Cell Types:
Endothelial cells: flat nuclei and thin fenestrated cytoplasm
Kupffer cells: plump phagocytic cells with plump nuclei
Stellate cells of Ito: contains lipid droplets containing vitamin A; also produces ECM and collagen; causes fibrosis during cirrhosis
Hepatic Lobule
o Anatomical unit of the liver
o Hexagonal in shape and centered on a terminal cenrilobular venule
o Portal tracts are positioned at the angles of the hexagon
Hepatic Acinus
o Structural unit of the liver o Berry-shaped and centered on the
portal tract
o Lies between two or more centrilobular venules o Divided into three zones:
Zone 1: highest perfusion, near the portal triad Zone 2: intermediate Zone 3: least perfusion, near
the central vein; contain high levels of esterases and low levels of oxidative enzymes
Portal Tracts
Branched collagenous network through which the hepatic artery, portal vein, and bile ducts pass
Portal Vein
o Largest of the three components of the portal tract
o Lined by thin endothelial cells
Hepatic Artery
o Thick-walled structures but smaller than portal vein
Bile Duct
o Bile canaliculi contain ATPase and alkaline phosphatase; better demonstrated by silver impregnation o Bile canaliculi are located within each plate of hepatocytes drain into canals of Hering which is lined by simple cuboidal or columnar epithelium o Canals of Hering then drain to bile
ductules which merge to form trabecular ducts intrahepatic duct right/left hepatic duct common hepatic duct common bile duct
Limiting Plate
o Layer of hepatocytes immediately bordering the portal tract
Centrilobular Venules
o Site where hepatic artery and portal vein drains
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Gallbladder
Muscular sac lined by simple columnar epithelium (basal nuclei) with microvilli
Submucosa is loose and contains many elastin fibers, blood vessels, and lymphatics, which drain water reabsorbed from bile during the concentration process
Muscular layer has oblique, longitudinal, and transverse orientations but no distinct layers
Rokitansky-Aschoff Bodies
o Normal feature that may be mistaken for malignant proliferating gland in the gallbladder
Pancreas
Lobulated gland covered by a thin collagenous capsule which extends as delicate septa between the lobules
Exocrine pancreas
Consists of closely packed secretory acini
Acinar Cells
o Each acinus is made up of an irregular cluster of pyramid-shaped secretory cells
o Apices of the cells project towards the central lumen of a minute duct o With basal nuclei and basophilic
cytoplasm
Centroacinar Cells
o Terminal lining cells of intercalated ducts
o Located at the centers of the acini
Intercalated Ducts
o Simple low cuboidal epithelium o Smallest of the tributaries that drain
into intralobular ducts interlobular ducts
Endocrine pancreas
Forms islets of langerhans most numerous in the tail of the pancreas
Main secretory products are insulin and glucagon
Islets of Langerhans
o Composed of up to 3000 secretory cells supported by fine collagenous network with fenestrated capillaries each enclosed by a capsule o Each islet is supplied by three
arterioles and drained by six venules o Secretory cells
Alpha cells (25%): glucagon Beta cells (60%): insulin Delta cells: somatostatin
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ENDOCRINE SYSTEM
Responsible for synthesis and secretion of hormones:
o Protein and glycoprotein molecules o Small peptide molecules
o Amino acid derivatives o Steroids
General histological characteristics
o Composed of islands of secretory cells of epithelial origin with intervening supporting tissue rich in vasculature o Cells have prominent nuclei and
abundant mitochondria, ER, golgi bodies, and secretory vesicles
Pituitary Gland
Bean-shaped gland at the base of the brain beneath the third ventricle, seated at the sella turcica
Secretion of hormones under the influence of hypothalamus
Hormones Secreted
Hormones that act on non-endocrine tissue o Growth hormone
o Prolactin o ADH o Oxytocin
o Melanocyte-stimulating Hormone
Trophic Hormones (modulate other endocrine glands)
o Thyroid Stimulating Hormone o Adenocorticotrophic Hormone o Gonadotrophic Hormone o Follicle Stimulating Hormone o Luteinising Hormone
Anterior Pituitary
Also called adenohypophysis
Embryological origin: Rathke’s pouch
Pars tuberalis
o Extension of the adenohypophysis that surrounds the neural stalk
Secretion of hormones controlled by hypothalamus by way of releasing hormones conducted from median hypothalamic eminence to the pituitary portal system (except prolactin secretion which is controlled by dopamine)
Cell Types
o Somatotrophs
Most numerous
Secretes growth hormone With secretory granules of
moderate size
o Mammotrophs
20% of cells; increase in number during pregnancy Secretes prolactin o Corticotrophs
20% of cells
Secretes ACTH split from a larger peptide known as pro-opiomelanocortin (also gives rise to lipotropins and endorphins)
Sparse secretory granules at the extreme periphery o Thyrotrophs
5% of cells Secretes TSH
Smaller and peripherally-located granules o Gonadotrophs 5% of cells Secrete FSH and LH Variably-sized granules Pars Intermedia
Thin zone of tissue lying against posterior pituitary
Derived from Rathke’s Pouch
Composed of basophilic cells lying between the anterior and posterior hypothalamus
Contain secretory granules similar to corticotrophs, and produces pro-opiomelanocortin
Posterior Pituitary
Also called neurophysis or pars nervosa
Composed of non-myelinated axons whose cell bodies are located in the hypothalamus
o Axons are supported by glial cells called pituicytes
Secretes stored ADH (supraoptic nucleus) and oxytocin (paraventricular nucleus) from hypothalamus
Neurosecretion
o Posterior pituitary secretes hormones in response to impulses from the hypothalamus
o Neurosecretory granules are passed down from hypothalamus and accumulate in the Herring bodies, which are disended terminations of the axons
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Thyroid Gland
Butter-fly shaped gland that lies in the neck Hormones Secreted
Tri-iodothyronine (T3) and Thyroxine (T4) o Iodine-containing hormones o T3 is the metabolically active form o Regulates the BMR and influence
growth and maturation
o Secretion dependent on TSH from anterior pituitary
Calcitonin
o Regulates blood calcium levels in conjunction with PTH (lowers blood calcium levels)
o Secretion dependent only on calcium levels
Thyroid Follicle
Functional unit of the gland
Spheroidal structures composed of a single layer of cuboidal epithelial cells bounded by basement membrane
Store thyroglobulin, which is the storage form of T3 and T4
Lining epithelial cells
o Synthesize glycoprotein component of thyroglobulin
o Convert iodide to iodine o Inactive: simple flat or cuboidal o Active: tall and columnar
Thyroid C Cell
Also called parafollicular cell
Found in thyroid as individual scattered cells in the follicle lining or as small clumps in the interstices between follicles
Secrete calcitonin
Parathyroid Gland
Small oval endocrine glands closely associated with the thyroid gland; most important regulator of calcium
Regulate serum calcium and phosphate levels by:
o Increase osteoclastic resorption o Increase renal tubular reabsorption of
calcium and inhibiting reabsorption of phosphate ions from filtrate
o Promote absorption of calcium from the intestines
Secretion is stimulated by decreased blood calcium levels
Structure
Thin fibrous capsule gives rise to septa that divide parenchyma into nodules and that carry vessels and nerves
Glandular Cells
o Arranged as clusters, ribbons, or glands o Chief/ Principal Cells
Small with round central nuclei and eosinophilic cytoplasm
Synthesize and secrete PTH o Oxyphil Cells
Occur in nodules
With eosinophilic cytoplasm packed with mitochondria Do not secrete PTH and
increase in number with age
Adrenal Gland
Small flattened endocrine glands closely applied to the upper pole of each kidney
Has a dense fibrous capsule that provides support for the delicate collagenous framework supporting the secretory cells
A prominent vein is characteristically at the center of the gland
Supplied by the superior, middle, and inferior suprarenal arteries
o Cortex is supplied by short cortical arteries
o Medulla is supplied by long cortical arteries
o All drain into the central vein
Adrenal Cortex
Secretes steroid hormones: mineralocorticoids, glucocorticoids, and sex hormones
Secretion controlled by ACTH (glucocorticoids) and the RAAS (mineralocorticoids)
Characteristics of Steroid Secreting Cells o Associated with fenestrated capillaries o Rounded cell nucleus with one or more
nucleoli
o Cytoplasm contains many large lipid droplets containing cholesterol esters o Numerous mitochondria and SER
Zona Glomerulosa o Outermost zone
o Secretory cells arranged in irregular ovoid clusters separated by fibrous trabeculae
o Cells have round nuclei and less cytoplasm (plenty SER and mitochondria, scanty lipid droplets) than cells in the next zone
By: Sachi Estreller |Section B
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o Secretes mineralocorticoids (mainly aldosterone)
Zona Fasciculata
o Broadest of the three zones o Secretory cells arranged in parallel
cords disposed at right angles separated by strands of collagen o Secretes glucocorticoids (mainly cortisol) and small amounts of androgens
Zona Reticularis
o Thin and innermost layer
o Secretory cells are closely packed and irregularly arranged in cords separated by wide-diameter capillaries
o Cells are smaller with less cytoplasm than cells in the previous zone o Secretes small amounts of androgens
and glucocortocoids
Adrenal Medulla
Secretes catecholamines: adrenaline and noradrenaline
Secretion directly controlled by sympathetic NS
Chormaffin Cells
o Secretory cells of the adrenal medulla o Composed of cells occurring in clusters
with granular basophilic cytoplasm o Those secreting noradrenaline exhibit
a more positive chromaffin reaction and a wider clear halo around the dense core granules in the cytoplasm than those secreting adrenaline
Pineal Gland
Small spherical gland that lies in the midline of the brain
Synthesizes melatonin that induces rhythmical changes in the endocrine activity of the hypothalamus, pituitary, ovaries, and testes in response to light changes received by the retina
Secretory Cells
o Pinealocytes (Pineal Chief Cells) Highly modified neurons Round nuclei with granular
cytoplasm
Granules contain melatonin and serotonin
o Neuroglial Cells
Similar to astrocytes
Pineal Sand
o Basophilic extracellular bodies consisting of concentric layers of calcium and magnesium phosphate in an organic matrix
o Characteristic of aging pineal gland
Diffuse Endocrine System
Scattered system of neuroendocrine cells particularly important in the respiratory and GI tracts
Gastrointestinal Neuroendocrine Cells
Scattered in the mucosa of GI tract and in pancreatic and biliary ducts
Secrete hormones that regulate and coordinate GI activity in concert with the ANS (eg. CCK, VIP, NO)
May be endocrine, paracrine, or neurocrine Respiratory Neuroendocrine Cells
Involved in local and autonomically mediated regulation of respiratory function
Scattered individually in the epithelium or in clumps protruding into the airway
Secrete hormones such as serotonin, bombesin, and leu-enkephalin
