Histology Flashcards
(121 cards)
1
Q
Describe the stratum spinosum
A
- polyhedral-shaped cells- not in contact with the basement membrane
- Keratins 1 and 10 (HMW keratins). relace keratins 5 and 14 when basal keratinocytes migrate to the stratum spinosum
- keratohyalin granules develop
- tonofilaments will form intercellular bridges. the layers are held together by these, which are adheren-type junctions
2
Q
Describe stratum granulosum
A
- multilayered
- keratins 2e and 9
- flattened nucleated keratinocytes
- keratohylain aggregates: fillagrin induces cross-linkage of keratin filaments by disulfide bonds, no limiting membrane
- membrane coating granules (lamellar bodies)
- tonofilaments
3
Q
Describe stratum lucidum
A
- flat keratinocytes lacking nuclei and organelles
- only found in thick skin
- contain eleiden
4
Q
Describe stratum corneum
A
- multilayered
- thicker in thick skin (palms of your hands and soles of your feet)
- enucleated, flattened, dead keratinocytes
- cytoplasm replaced by keratin cross-linked with filaggrin –> produces cornified cell envelope
5
Q
Describe the stratum basale (germinativum)
A
- Deepest layer
- Columnar to high cubodial epithelium
- Keratins 5 and 14 (LMW keratins—single layer of cells held together by desmosomes
- This is the only layer of the epidermis in contact with the basal lamina –> only layer that has hemidesmosomes
- high mitotic activity
6
Q
Characterize the respiratory epithelium
A
Pseudostratified ciliated columnar epithelium
7
Q
Describe the epithelium that lines the nares
A
-Stratified squamous epithelium
8
Q
What are the 3 layers of the heart wall?
A
- Endocardium
- Myocardium
- Epicardium
9
Q
Describe characteristics of the endocardium
A
- Innermost layer, lining the atria and the ventricles
- Include endothelium and subendothelial CT
- continuous with the tunica intima of blood vessels entering and leaving the heart
- subendocardium is a layer located between the endocardium and the myocardium- contains nerves and Purkinje fibers
10
Q
Describe the myocardium
A
Consists of cardiac muscle cells (particularly the contractile muscle cells such as atrial and ventricular muscle)
11
Q
Describe the epicardium
A
- The visceral layer of the pericardium
- External surface is covered by simple squamous epithelium (mesothelium)
- Mesothelium overlies fibroelastic CT containing adipose cells, nerves, and coronary vessels
12
Q
Describe the tunica intima
A
- The innermost layer of blood vessels
- Contains endothelium, which is continuous with the endocardium, and basal lamina. Endothelial cells produce von willebrand’s factor VII
- contains subendothelial CT (found in all elastic and muscular arteries and some arterioles)
- contains internal elastic membrane (incomplete in elastic arteries but thick and complete in muscular arteries)
13
Q
Describe the tunica media
A
- The middle layer. What primarily gives arteries their major characteristics
- Made up of smooth muscle tissue and fibroblasts
- contains collagen (provides framework and limits distensibility) and elastic fibers
14
Q
Describe the tunica adventitia (externa)
A
- Outmost layer; lacking in arterioles
- consists of loose areolar CT tissue
- contains irregular fibroelastic tissue with adipocytes
- has small vessels (vaso vasorum) which penetrate the outer portion of the tunica media to supply oxygen and nutrients; and nerves (nervi vasorum)
15
Q
Describe characteristics of elastic arteries
A
- conducting arteries
- stretch during systole and recoil during diastole
- tunica media consists of layers of elastic fibers organized into elastic laminae
- has large lumen diameter
- includes: aorta, pulmonary trunk, large branches of the aorta
16
Q
Describe characteristics of muscular arteries
A
- distributing arteries
- tunica media consists of smooth muscle that responds to autonomic stimulation and hormones; the thickness of smooth muscle layer decreases as diameter becomes smaller; gradual transition from elastic artery to muscular artery
- includes all named arteries of body except elastic arteries
17
Q
Describe characteristics of arterioles
A
- thick tunica media in relation to size of the lumen
- small arteries
- tunica media consists of 1-3 layers of smooth muscle
- mean arterial pressure depends on proper tone of smooth muscles in arterioles; thickness of smooth muscle layer decreases as diameter becomes smaller
- gives rise to metarterioles which have a discontinuous layer of smooth muscle
- capability of vasoconstriction and vasodilation
18
Q
Describe continuous capillaries and give examples of where they can be found
A
- Endothelial cells have a complete (continuous) cytoplasm as well as a complete basal lamina.
- caveolae and vesicles transport substances through the cytoplasm in a bidirectional pathway.
- found in muscle, thymus, brain, bone, lungs
- in the lung, the thin endothelial cell cytoplasm allows diffusion of gases from the alveolus into the blood (CO2) and from the blood into the alveolus (O2)
19
Q
Describe fenestrated capillaries and give examples of where they can be found
A
- the endothelial cell has many fenestrae with or without a thin diaphragm. The basal lamina is continuous
- This type is present in tissue with substantial fluid transport (intestinal villi, choroid plexus, ciliary processes of the eyes)
- present in glomerular capillaries of the kidneys
20
Q
Describe discontinuous capillaries and give examples of where they could be found
A
- cytoplasm and basal lamina are discontinuous
- in the spleen, the endothelial cells are elongated and protrude into the lumen. Blood cells can readily pass through the walls of the splenic sinuses
21
Q
Describe veins in comparison to arteries
A
- compared to arteries, veins have a larger lumen, thinner wall, and valves present often (project into lumen of tunica intima)
- large veins have a layer of longitudinal smooth muscle in the inner aspect of the tunica adventitia
- have a high capacitance (contain about 70% of total blood volume)
22
Q
Describe the formation of an atherosclerotic plaque
A
- Damage to the endothelium of an artery is followed by a homing of blood monocytes in teh tunica intima after adhesion to VCAM-1. In the intima, monocytes change into macrophages expressing SR-A that internalizes modified cholesterol-rich low-density lipoprotein. LDL-containing multilocular depostis give macrophages a foamy appearance
- The atherosclerotic plaque developed in the intima consists of an athermoa core with abundant macrophages foamy cells and a fibrous cap. The fibrous cap contains collagen fibers produced by migrating smooth muscle cells from the tunica media.
- VCAM-1 mediated homing of T-cells contributes additional inflammatory components to the atherosclerotic plaque. T-cell macrophages interaction results in the product of metalloproteinases by macrophages and proinflammatory cytokines by T-cells.
- MMPs and inflammatory cytokines weaken and fracture the firbous cap. The thrombogenic potential of the plaque, resulting from the production of procoagulant tissue factor by macrophages, causes thrombosis leading to the obstruction or occlusion of the arterial lumen
23
Q
What are the different classifications of epidermal ridges?
A
- Primary dermal ridge- related to finger prints; found everywhere except forehead, external ear, perineum, and scrotum; formed during 3-4 month of fetal life; subdivided into two secondary dermal ridges by interpapillary peg
- Interpapillary peg- downward growth of epidermis along crest
- Secondary epidermal ridge- occur in double rows, branched; thin collagenous, reticular and elastic fibers
- Dermal papillae- upward projections from each secondary dermal ridge
24
Q
What are the functions of the integument system?
A
-Protection from mechanical injury, prevents desiccation, protects against foreign substances and microorganisms, protects against UV radiation, thermoregulation, regulation of BP (via dermal capillary network), excretion of metabolic waste products, synthesis of provitamin D
25
Differentiate between thick and thin skin
- Refers to the epidermis only
- Thick skin: occurs only on palms and soles and is hairless, displays all 5 epidermal layers
- Thin skin: occurs over rest of the body, thinnest thin skin is on the eyelids, thickest thin skin is on the back, thicker on extensor surfaces than flexor surfaces, epidermal layers less distinct and lacking stratum lucidum
26
List the layers of the epidermis in order from superficial to deep
Stratum corneum --> stratum lucidum --> stratum granulosum --> stratum spinosum --> stratum basale (germinativum)
27
What 2 layers of the epidermis make up the stratum malpighi?
Stratum basale (germinativum) an stratum spinosum
28
Describe the cornified cell envelope
- Extracellular: multi-lamellar lipid layer covalently linked to involucrine
- Intracellular: involucrine, small proline-rich proteins, loricrin, fillagrin and keratin complexes
29
Describe the process of keratinization
1. Lipids are covalently linked to involucrin, thus contributing to the formation of the epidermal permeability barrier. Lipids originate from lamellar bodies that first appear in the spinosum and granulosum layers and release their content into the extracellular space during the transition to the stratum lucidium and stratum corneum
2. The cornified cell envelope is a specialized structure that reinforces that PM of keratinocytes when they reach their final stage of differentiation. It consists of aggregates of keratins and fillagrin and a complex of 3 primers: involucrin, small proline-rich proteins, and loricrin, cross linked-by the enzyme TGK
3. Keratin filaments, aggregated by filaggrin, interact with the inner side of the PM to form the cell envelope
4. TIght juntions in the stratum granulosum containing claudin-1 and claudin-4, are components of the permeability barrier
30
Discriminate between the 2 layers of the dermis and list characteristics of each
1. Papillary layer (closest to epidermis)- loose CT, separated from epidermis by basal lamina, network of fine elastic fibers and abundant capillaries
2. Reticular layer- dense irregular CT; includes fibrocytes, macrophages, and adipocytes
31
List the characteristics and functions of Merkel cells
- are dendritic cells that interact with keratinocytes through E-cadherins
- are derived from monocyte precursors from the bone marrow; are antigen presenting cells
- primarily found in stratum spinosum (4 out of 5 epidermal layer)
- migrate from epidermis to lymph nodes. in the lymph nodes, they interact with T-cells in the deep cortex
- Birbeck granules: contains the proteins langerin and CD1a, involved in the uptake and delivery of antigens
32
List the characteristics and functions of Merkel cells
- mechanoreceptors. may also act as diffuse neuroendocrine cells (contain catecholamine-like granules)
- usually in stratum germinativum (deepest layer)
- present in fingertips and lips
33
List the characteristics and functions of melanocytes
- derived from melanoblasts
- do not form desmosome attachments in epidermis
- inject melanin granules into keratinocytes
- pathway for melanin formation: tyrosine --> 3,4-dihydroxyphenylalanine --> dopaquinone --> melanin. this pathway requieres tyrosinase
- color of skin depends on how many melanosomes are taken up by keratinocytes
34
Explain the embryonic origins of the epidermis and dermis
- Epidermis: starts off as a single layer of ectodermal cells. divide during 6th week to form periderm (sloughs off to form vernix caseosa) and inner cubodial germinal layer
- dermis is derived from mesoderm
35
List the characteristics of sebaceous glands
- are holocrine glands: when they release the sebum, the entire cell has to be decomposed and becomes part of the excretory material
- are branched acinar glands with short ducts
- found everywhere except palms and soles
- continuously produce sebum (an oily material that keeps the hair flexible. hair needs to be kept flexible because they are sensory structures)
- growth is stimulated at puberty by hormones
36
Describe characteristics of merocrine sweat (sudoriferous) glands
- coiled, simple tubular secretory portions that are lined by simple epithelium. apical dark secretory cells secrete glycoproteins. basal clear cells secrete water and electrolyes. myoepithelial cells contain these
- duct system consists of stratified cuboidal epithelium except in epidermis
- cholinergic endings (stimulated by acetylcholine)
37
Describe characteristics of apocrine sweat glands
- found in labia majora, areola, and axillary and anal regions
- secretions and thicker and more viscous than merocrine types
- excretory ducts open into hair follicle
- adrenergic innervation
- inactive until puberty
- special types: ceruminous glands and glands of moll (found in eye lids. produces tears that help prevent the eyes from sticking to itself)
- the secretory cells are cuboid
38
Describe the structure of a hair follicle, including the hair bulb and external/internal root sheath
- sebaceous glands and arrector pili muscles are associated with hair follicles
- hair bulb: expanded lower part of the hair follice, matrix (refers to an aggregation of cells that have mitotic activity --> growing part of the hair), vascularized dermal papilla
- external root sheath: down growth of epidermis
- internal root sheath: generated by bulb matrix, contains Henle's layer, Huxley's layer, and cuticle (which interlocks with cuticle of hair shaft)
39
What are primary lymphoid organs and where can you find them?
- Precursor cells mature into immunocompetent cells. Each cell is programmed to recognize a specific antigen
- In thymus and bone marrow
- lymphocytes originate in these organs
40
What are secondary lymphoid organs and where can you find them?
- Trapped antigens stimulate clonal expansions of mature T and B cells
- In lymph nodes, spleen, and tonsils
- lymphocytes take residency in these organs
41
Describe the function of the MHC
-Main function is the presentation of antigenic peptides to T cells. This is how a T-cell recognizes the signal they are getting and it's highly specific. What they are using for typing to see if someone is an organ/blood transplant donor
42
Describe MHC class I
- Expressed on surface of all cells except trophoblasts and RBCs
- CD8+ cells recognize peptide fragments of foreign proteins bound to MHC class I on the surface of cells
- CD8 is a member of the Ig superfamily
43
Describe MHC class II
- Expressed on the surface of B cells and antigen-presenting cells
- CD4+ T cells recognize peptide fragments presented here
44
Describe characteristics of CD4+ T cells
- Recognize antigens bound to MHC class II molecules
| - Helper cells: assist C8+ cell differentiation; assist B cell differntiation
45
Describe characteristics of CD8+ T cells
- Cytolytic T cells
- bind to an antigen presenting cell
- undergo mitosis
- release perforins (punch holes in the membranes of other cells) and fas ligand (cells have a Fas receptor. when it is bound to the receptor, it signals the cell to undergo apoptosis)
- recognizes antigens bound to MHC class I molecules
- mediators of cellular immunity
46
Describe characteristics of CD16+ T cells
- Natural killer T cells
- Activated (by tumor cell antigens) T helper cells release cytokines:
* interleukin 2: stimulates proliferation of NK cells
* interferon-gamma: activated NK cells
* macrophage activating factor: activates macrophages
* chemotactic factor
* tumor necrosis factor: kills tumor cells directly
47
Characterize the respiratory epithelium
-pseudostratified ciliated columnar epithelium: respiratory mucosa that line the respiratory pathway. also contains lamina propria and submucosa
48
Describe the epithelium that lines the nares
- Stratified squamous epithelium continuous with epidermis
| - contains sebaceous glands, sudoriferous glands, and hair follices
49
What are the cell types that make up the olfactory epithelium and what are the characteristics of this epithelium?
- Pseudostratified columnar epithelium without goblet cells
- no distinct membrane
- cell types: sustentacular cells, basal cells, olfactory cells, and glands of Bowman
50
List the characteristics and functions of sustentacular cells
-and support cells with pigment granules
51
List the characteristics and functions of basal cells
- contain pigment granules
| - stem cells: give rise to immature olfactory cells
52
Describe the characteristics and functions of olfactory cells
- bipolar neurons
- apical ends projects into nasal cavity as a knoblike ending with nonmotile cilia
- cilia posses G-protein-linked odor-specific receptors
- basal ends of the cell extends as an unmyelinated axon, bundled with other similar axons, through the ethmoid plate to mitral cells located in the olfactory bulb
- olfactory cells senesce and are replaced from basal cells
53
Describe the characteristics and functions of olfactory glands of Bowman
- located in the lamina propria
- secrete odorant-binding protein
- odorant-bind protein binds to odorant molecule in nasal cavity
54
Describe the kinds of tissues found in the epiglottis
- Lingual surface: covered with stratified squamous epithelium (one of the 2 places in the respiratory tract that does not contain pseudostratified ciliated)
- Pharyngeal surface: pseudostratified ciliated epithelium
55
Describe the kinds of tissue found in the false vocal cords
- pseudostratified ciliated epithelium
| - lamina with seromucous glands
56
Describe the kinds of tissue found in the true vocal cords
- stratified squamos epithelium
| - lacks seromucous glands in the lamina propria
57
Where are the 2 places in the respiratory tract that don't contain psuedostratified ciliated epithelium? What type of tissue do they have instead
- Lingual surface of the epiglottis and true vocal cords
| - contain stratified squamous epithelium
58
Describe the histology of the 3 layers of the trachea
1. Mucosa: pseudostratified ciliated columnar epithelim with thick basement membrane; lamina propria with delicate FECT
2. Submucosa: many sero-mucous glands
3. Adventitia: 16-20 horseshoe-shaped cartilages interconnected by FECT; opening between arms of horseshoe-shaped cartilages are closed by FECT, mucous membranes, and smooth muscle; contains mixed glands and capillaries
59
Describe the generalizations of the epithelium of the GI tract
- Stratified squamous at either end for protection and resisting friction
- simple columnar along most of length
60
Describe the mucous membrane lining the lip
- this mucosa consists of stratified squamous epithelium, basement membrane, and lamina propria
- dermis has a rich plexus of capillaries
61
Describe the mucous membrane lining the cheek
- stratified squamous epithelium
| - abundant elastic fibers present in the submucous
62
Describe the histological features of the teeth
- Ectoderm forms the enamel
| - Neural crest and mesoderm give rise to dental papillla --> forms dentin, cementum, and pulp
63
What is the dental lamina
- Dental primordium is formed from basal cells of the oral ectoderm
- The labiodental lamina is an epithelial shelf that grows from the thickened primordium into the mesenchyme as a bifid structure
- the external limb splits later to form a groove that deepens to separate the lip and the remainder of the mouth
- the internal limb is the dental lamina
64
List the three structures derived from the epithelial bud
1. Enamel organ: forms enamal and caps the:
2. Dental papilla: condensation of mesenchyme that gives rise to dentin and pulp
3. Dental sac (follicle): CT sac surrounds the enamel organ and dental papilla and forms cementum and the peridontal membrane
65
Describe the histology and specific functions of odontoblasts
- form the dentin matrix throughout the life of the tooth
- form single layer of cells lining pulp cavity
- Tomes' dental fibers are cytoplasmic extensions of the odontoblasts continuing through the predentin and dentinal layers to the dentin-enamel junction
- Increment lines represent growth spurts of the tooth during development
66
Describe the histology and specific functions of ameloblasts
- form enamel which covers only the tooth (is the hardest substance in the body)
- enamel is laid down in prisms. each prism is formed by one ameloblast
- secreting apical domains= tomes' processes
- increment lines of Retzius are periods of rhythmic growth
67
Describe the histology and functions of the periodontal membrane
- CT formed from dental sac with fibroblast, osteoblasts, cementoblasts, collagen fibers, blood vessels, and nerve fibers
- highly metabolically active tissue
- binds cementum to bony socket
- sharpey's fibers extend from cementum to alveolar wall via the membrane
- allows limited movement
- absorbs pressures of mastication and prevents this pressuring from damaging alveolar bone
- affected by diseases such as diabetes and scurvy
68
What is the sulcus terminalis?
The anterior two-thirds of the upper oral portion is separated from posterior one-third by the sulcus terminalis
69
Describe the filliform papillae
- most numerous of all the papillae with a conical appearance
- evenly distributed over the entire oral upper portion
- lack taste buds
70
Describe fungiform papillae
- relatively few in number
- interspersed singly amoun the parallel rows of filliform papillae
- have mushroom appearance
- taste buds are present only on the oral surface of the epithelium in contradistinction to the position of the taste buds on the circumvallate papillae whose taste buds are primarily located in the lateral walls
71
Describe the foliate papillae
- rudimentary in humans, but well developed in lower animals
| - the pharyngeal portion is free of papillae but contains lingual tonsils
72
Describe the circumvallate papillae
- located along the sulcus terminalis as projections surrounded by a moat
- taste buds are present on the lateral walls
- ducts on von ebner's glands (serous) open into the moat
73
Describe the structure of taste cells
- each cell is long and slender with an elongated central nucleus and terminates as short taste hair which projects into the external opening called the outer taste pore
- posses apical microvilli with taste receptors
- basal part of cell releases NTs
- taste cells are distributed between the supporting cells
74
Describe the mucosal layer of the gut tube
- innermost layer
- epithelium: stratified squamous transitioning to simple columnar
- lamina propria: loose areolar CT associated with epithelium
- muscularis mucosa
75
Describe the characteristics of the submucosa of the digestive tube
- dense, irregular CT
- vascularized
- contains a nerve plexus: Meissner's plexus
76
Describe the characteristics of the muscularis externa of the digestive tube
- inner circular layer of smooth muscle
- outer longitudinal layer of smooth muscle
- myenteric (auberbach's) nerve plexus lies between the two layers of muscle tissue
- regulates the size of the lumen
- regulates rhythmic movement of the GI tract
77
Describe the characteristics of the serosa of the digestive tube
- outermost layer
- serosa: composed of dense irregular CT; consists of a mesothelial lining and a layer of submesothelial CT; forms visceral peritoneum; covers intraperitoneal portions of abdominal organs
- adventitia: dense irregular CT with adipose tissue; covers retroperitoneal portions of digestive system
78
Describe the specializations of the esophagus
- Functions: digestion (in the mouth), addition of mucous to food bolus
- mucosa: stratified squamous non-keratinzed epithelium; mucous glands are found in the lamina propria and submucosa
- muscularis externa: undergoes transition from skeletal muscle in the upper third to mixture of skeletal and smooth muscle in the middle third to smooth muscle only in the lower third
79
Describe the transition zone between the esophagus and the stomach epithelium
-the esophagus has stratified squamous epithelium and the stomach has simple columnar epithelium
80
List the 4 regions of the stomach and compare the histology of each
1. Cardia- contains mostly mucous glands
2. Fundus- contains gastric glands; long tubular glands extending down to the muscularis mucosae
3. Body- contains gastric glands
4. Pylorus- contains mucous glands and hormone-secreting enteroendocrine cells
81
Describe the overall structure and regions of the gastric gland
- simple branched tubular glands
- narrow isthmus opens into bottom of a gastric pit
- fundus (base) of the gland extends into the lamina propria; where secretory glands are found
82
Describe the histology and function of parietal cells
- unique cell of the gastric gland**
- large pyramidal shaped, eosinophilic cell
- produces HCl and gastric intrinsic factor (necessary for absorption of vitamin B12)
- generates hydrogen ion from carbonic acid
- prominent intracellular canaliculi lined by microvilli
- tubulovesicle pools are part of exocytosis-endocytosis function
83
Describe the histology and function of chief cells
-secretes pepsinogen: inactive form of pepsin. becomes activated in an acidic environment. once it is secreted into the lumen where HCl has also been secreted --> will be activated. functions to degrade proteins
84
Describe histology and function of enteroendocrine cells
- small cells with secretory vesicles polarizes towards basal surface in proximity to blood vessels
- produce peptide hormones and serotonin
85
List the major structural features that increase surface area for absorption in the GI tract
- length of small intestine and large intestine
- plicae circulates (valves of kerckring) -folds in the mucosa
- villi
- microvilli
86
Describe the histology of the crypt-villus system
- each villus contains a core of lamina propria
- the crypts extend down between the villi below the bases of the villi
- crypts and villi constitute glands of the small intestine (villi extend into the lumen)
- wall of villus is composed of a simple columnar epithelium with goblet cells
- each villus contains a capillary plexus
- each villus contains a blind-ending lymphatic referred to as a lacteal
87
Describe the fine structure of a microvillus
- covered with glycoprotein and glycocalyx (contains an array of brush-border enzymes)
- bundles of actin filaments within microvillus is covered by a formin cap
- supported by a core of actin filaments
88
Describe the histological characteristics of the duodenum
- villii with wide spatulate of "leaflike" distal shapes --> tend to be expanded distally
- deep crypts of lieberkuhn: where secretion is drained into from the excretory ducts
- brunner's glands with excretory ducts in submucosa: secrete mucous
89
Describe the histological characteristics of the jejnum
- villi longer and narrow
- crypts of lieberkuhn present
- no glands in submucosa
90
Describe the histological characteristics of the ileum
- villi longer and narrow
- crypts of lieberkuhm present
- no glands in submucosa
91
Describe the histology of crypts of lieberkuhn
- simple tubular glands (simple columnar epithelium) within the intestinal mucosa
- open between adjacent villi and extend to muscularis mucosa
92
What are the cells that make up the crypts of liberkuhn
- goblet cells
- enterocytes
- paneth cells
- enteroendocrine cells
93
Describe the characteristics of enterocytes
- columnar epithelial cells that contain:
* basal nuclea, perinuclear golgi, apical brush border
* produces disaccharisadases
* involved in absorption of proteins, CHOs, lipids
- enzymes present on apical brush border are important in CHO digestion
- produce enteropeptidase which is necessary for the activation of pancreatic zymogens and proenzymes
94
Describe the paneth cells of the crypts of lieberkuhm
- basal crypt cells
- prominent eosinophilic granules
- produce lysozyme to control intestinal flora
95
Describe the enteroendocrine cells of the crypts of lieberkuhn
- stain with chromium
- agyrophilic
- produce peptide hormones and serotonin
- may produce paracrine or autorcrin secretions
- analogous to unicellular goblet cells
- formed from endodermal stem cells in all regions of the GI tract
96
Define Brunner's glands and explain where they are found
- found in submucosa of duodenum
- responsible for formation of bicarbonate and mucus; supplements bicarbonate from the pancreas; necessary to neutralize gastric acid
97
Describe the epithelium of the large intestine
- simple columnar epithelium
| - crypts but no villi
98
Describe the functions of the large intestine
- secretion of mucus for lubrication
- goblet cell is the prominent cell of the large intestine
- absorption of fluid
- formation of fecal mass
- continuation of digestion initiated in small intestine
99
Describe the structures of taeniae coli and appendix epipotoica in the large intestine
- Taeniae coli: the muscularis externa has an inner layer of smooth muscle and an outer layer of longitudinal muscles, which forms 3 bands. These bands cause the large intestine to be slightly bunched up
- Appendix epoptoica: an aggregate of adipocytes surrounded by the serosa
100
List the major features that provide a defensive mechanism for segments of the GI tract
- intestinal tight junction barrier
- the epithelial cells of the GI tract are held together by occluding junctions containing the transmembrane proteins claudins and occludins, which function to prevent paracellular transport
101
List the functions of Paneth cells
- found in bases of mucosal glands
- basophilic basal cytoplasm; supranuclear golgi complex; large, intensely acidophilic apical secretory granules
- secrete: lysozyme, defensins, tumor necrosis factor
102
What are Toll-like receptors?
- found on the surface of enterocytes
- recognize structurally conserved molecules broadly shared by pathogens but distinguishable rom host molecules (PAMPs). do not recognize specific patterns
103
What is the role of IgA in the immune defense of the GI tract?
- produced by GALT
- synthesized and secreted by plasma cells in the lamina propria of the gut; picked up at the basal surface of enterocytes and transported across the cell
- sIgA linked to a protein called secretory component that inhibits degradation of the sIgA by proteolytic enzymes in the GI lumen
- does not stimulate the complement system, but functions by coating microorganisms, thus inhibiting microorganism binding to the epithelium
104
What is GALT?
- the bulk of the body's immune defense is centered in the GALT
- includes transitory aggregations of lymphocytes, neutrophils, eosinophils
- permanent structures include the appendix, peyer's patches, mesenteric lymph nodes
105
What are Peyer's patches?
- dome shaped lymphoid structures under the mucosal surface
- contain B and T cell dependent areas
- posses HEVs, which facilitate entrance of lymphocytes into lymphoid organs from the bloodstream
- the mucosal covering of the dome of peyer's patches includes specialized M cells
- lymphocytes enter here through a postcapillary HEV by a homing mechanism
- stimulated lymphocytes exit the peyer's patch through efferent lymphatic vessels. peyer's patches lack afferent lymphatic vessels
106
Where does CHO digestion begin? What is the role of amylase?
- CHO digestion begins in the mouth
| - amylase hydrolyzes starch to form sugars
107
Where are disaccharides broken down to monosaccharides?
- in the brush border of the small intestine: there are lot of enzymes located in the brush border
- monosaccharides are absorbed by enterocytes, which involved SGLT-1
108
What is the sequential breakdown of proteins to amino acids? Where each step occur?
- begins in the stomach. proteins --> peptides through action of pepsin. requires acidic environment
- breakdown to peptides also occurs in the SI by enzymes secreted from the pancreas (trypsin, chymotrypsin, elastase, carboxypeptidase)
- further breakdown of oligopeptides to aa occurs in the intestinal brush border
109
Where does lipid digestion begin? What enzymes are involved?
- begins in the small intestine. lipids enter the SI as triglyceride droplets
- pancreatic lipase emulsifies these large droplets into smaller droplets and release FA and glycerol
110
What is the site of secretion, target and effects of cholecystokinin?
- Site of secretion: upper intestinal mucosa (duodenum), secreted in response to gastric contents
- Targets and effects: acts on pyloric sphincter to slow down emptying of stomach; stimulates bile release from gallbladder; stimulates secretion of pancreatic enzymes; competitive inhibitor of gastrins
111
What is the site of secretion, target, and effects of gastrin?
- site of secretion: pyloric-antral portion of the stomach
- target and effects: stimulates HCl production by gastric parietal cells; promotes growth of gastric mucosa; stimulates gastric motility; stimulates release of insulin by pancreatic beta-cells
112
What is the site of secretion, target, and effects for secretin?
- site of secretion: epithelial cells of duodenum. stimulated by acid contents of stomach
- target and effects: enhances release of insulin by pancreatic beta cells; stimulates bicarbonate secretion by pancreas
113
Compare the epithelium and musculature of the anal canal to other regions of the digestive tract
- Returns to stratified squamous epithelium
| - skeletal muscle returns as external anal sphincter
114
Describe intercalated ducts and their secretion
- lined with low cubodial cells
- cells with receptors or secretin
- secrete water and bicarbonate ions
115
Describe the ducts of the pancreas
- Duct of wirsung: main excrectory duct. will divide into interlobular (lined with simple columnar epithelium and goblet cells) and intercalated ducts
- duct of santorini is the smaller accessory duct
116
Describe the histology of the pancreatic acin
- is the excretory portion of the pancreas; secretes zymogens
- only serous acini are present in the exocrine pancreas
- no striated ducts. goes straight from intercalated ducts into excretory ducts
- no myoepithelial cells
117
Describe acinar cells of the pancreatic acinus
- pyramidal serious cells
- basal zone is basophilic and contains nucleus and RER
- apical zone contains zymogen granules
118
Describe the centroacinar cells
- unique to the pancreas
- forms a truncated cubodial epithelium within the lumen of acini
- continuous with the epithelium of the intercalated duct
119
Describe the histology of the pancreatic acin
- is the excretory portion of the pancreas; secretes zymogens
- only serous acini are present in the exocrine pancreas
- no striated ducts. goes straight from intercalated ducts into excretory ducts
- no myoepithelial cells
120
Describe acinar cells of the pancreatic acinus
- pyramidal serious cells
- basal zone is basophilic and contains nucleus and RER
- apical zone contains zymogen granules
121
Describe the centroacinar cells
- unique to the pancreas
- forms a truncated cubodial epithelium within the lumen of acini
- continuous with the epithelium of the intercalated duct
