Histology Study Guide PDF

1 STUDY GUIDE GENERAL HISTOLOGY Module: 2 Class: 1st year Duration: 8 Weeks Facilitator: Maj Abdullah Qamar Reference Books: Junqueira's Basic HISTOLOGY Text and Atlas Difiores-atlas-of-histology...

1 STUDY GUIDE GENERAL HISTOLOGY Module: 2 Class: 1st year Duration: 8 Weeks Facilitator: Maj Abdullah Qamar Reference Books: Junqueira's Basic HISTOLOGY Text and Atlas Difiores-atlas-of-histology Maj Abdullah Qamar  2 LEARNING OBJECTIVES Serial Topic Lecture / Knowledge Practical / Skill 1 Bone Describe microscopic features of Identify different types of bone bones and types of ossification microscopically Enlist the location of different Draw a labelled diagram showing the types of bones histological structure of different types of bone with hematoxylin and eosin 2 Muscle Describe the microscopic Identify the different types of muscle features of skeletal, smooth and microscopically. cardiac muscle Draw a labeled histological diagram of different types of muscles with hematoxylin and eosin 3 Circulatory System Discuss the general histological Identify elastic artery, muscular artery plan of blood vessels. and large vein under light microscope Describe and compare the and enlist at least two identification histological structure of: points for each. Elastic artery Draw labelled diagram of elastic artery, Muscular artery muscular artery and large vein with the Arteriole help of eosin and hematoxylin pencils Different types of Capillaries on the histology notebook Venule Medium sized vein Large vein 5 Immune System Enumerate the cells of immune Identify slides of lymph node, thymus, system. spleen and palatine tonsils under light Describe the structure of primary microscope and enlist at least two and secondary lymph nodule. identification points for each Describe the histological features of: Lymph node Thymus Spleen Tonsils Compare the histological structure of thymus, lymph node, spleen and tonsils Maj Abdullah Qamar  3 Topic Lecture / Knowledge Practical / Skill Bone Describe microscopic features of Identify different types of bone bones and types of ossification microscopically Enlist the location of different Draw a labelled diagram showing the types of bones histological structure of different types of bone with hematoxylin and eosin FEATURES OF BONE CELLS Parameters Osteoblasts Osteocytes Osteoclasis (blast=bud,sprout) (clast=break) 1. Origin Derived from Derived from osteoblast Derived from blood osteoprogenitor cells monocytes 2. Location Found on the surface of Found embedded in the Found on the bone bony matrix between the surface of the bone lamellae, surrounded by in Howship’s lacunae and canaliculi lacunae 3. Shape Cuboidal, young cells Oval in shape with many Large irregular giant cytoplasmic processes, cells mature cells 4. Cytoplasm Basophilic Less basophilic Acidophilic 5. Nucleus Single, large, round, Single, small, elongated, Multinucleated (5- euchromatic heterochromatic 50 in number) 6. histochemical Alkaline phosphatase - Alkaline reaction activity - positive phosphatase activity - positive 7. Electron microscopic More rough Less rough endoplasmic Abundant structure endoplasmic reticulum reticulum mitochondria and lysosomes 8. Function Bone formation Bone maintenance Bone destroying (resorption) Maj Abdullah Qamar  4 BONE MICROARCHITECTURE All adult bones exhibit similar histology consisting of cells, bony matrix, and the neurovascular bundle (blood vessels, nerves, and lymphatics). Examination of bone in cross section shows two types: compact bone and cancellous (spongy) bone. In long bones, the outer cylindrical part is the dense compact bone. The inner surface of the bone adjacent to the marrow cavity is the cancellous (spongy, not dense) bone with numerous interconnecting areas; however, both types of bone have a similar microscopic appearance. In newborns, the marrow cavities of long bones are red and produce blood cells. In adults, the marrow cavities of long bones are yellow and filled with adipose (fat) cells BONE TYPES Distribution and orientation of the collagen fibers in the bone matrix indicate the bone type. The compact and cancellous adult bones exhibit a consistent structural pattern after maturation and mineralization. In contrast, woven (immature or primary) bone shows a random arrangement of collagen fibers; this type of arrangement is nonlamellar. The woven bone is encountered in the fetus during skeletal development and in repair of bone fractures. Also, the woven bone is temporary and is replaced by lamellar or mature bone as the individual ages. The lamellar (secondary or mature) bone exhibits organized lamellae that are either multiple parallel or concentric layers of calcified matrix arranged around the central canals with the neurovascular bundle, or the osteons. Each lamella exhibits a parallel arrangement of collagen fibers that follow a helical course. Also, the bone cells, now called osteocytes, are in lacunae at regular intervals between the concentric layers of lamellae and are arranged circumferentially around the central canal. The matrix is more calcified in the lamellar bone than in the woven bone, and, as a result, the lamellar bone is stronger than the woven or immature bone. Maj Abdullah Qamar 5 Maj Abdullah Qamar 6 Maj Abdullah Qamar  7 POINTS OF IDENTIFICATION Compact (dense) bone Haversian systems with Haversian canals and (C.S Ground Section) concentric lamellae of bone matrix Interstitial lamellae Typical bone cells, i.e. osteocytes within lacunae and radiating canaliculi Perforating canals (Volkmann’s canals) Spongy (cancellous bone) Trabeculae of bone matrix separated by marrow spaces Haemopoietic tissue in marrow spaces Osteocytes are seen embedded in the bone matrix of the trabeculae Maj Abdullah Qamar  8 PROCESS OF BONE FORMATION (OSSIFICATION) Endochondral Ossification Most bones develop by this process, with a hyaline cartilage model preceding bone Hyaline cartilage model grows in length and width, then calcifies, and chondrocytes die Mesenchymal cells in the periosteum differentiate into osteoprogenitor cells and form osteoblasts Osteoblasts synthesize the osteoid matrix, which calcifies and traps osteoblasts in lacunae as osteocytes Osteocytes establish cell-to-cell communication via canaliculi that open into blood channels Primary ossification center forms in the diaphysis and secondary center of ossification in the epiphysis Epiphyseal plate between the diaphysis and epiphysis allows for growth in bone length Eventually, all cartilage is replaced by bone except the articular cartilage Intramembranous Ossification Mesenchymal cells differentiate directly into osteoblasts Osteoblasts produce the osteoid matrix that quickly calcifies Osteoblasts initially form spongy bone that consists of trabeculae and trap osteocytes Mandible, maxilla, clavicle, and flat skull bones are formed by this process Fontanelles in newborn skulls represent intramembranous ossification in progress Maj Abdullah Qamar  9 Topic Lecture / Knowledge Practical / Skill Muscle Describe the microscopic Identify the different types of muscle features of skeletal, smooth and microscopically. cardiac muscle Draw a labeled histological diagram of different types of muscles with hematoxylin and eosin SKELETAL MUSCLE Fibers are multinucleated with peripheral nuclei Multiple nuclei are because of the fusion of mesenchyme myoblasts during embryonic development Each muscle fiber is composed of myofibrils and myofilaments Actin and myosin filaments form distinct cross-striation patterns Light I bands contain thin actin, and dark A bands contain thick myosin filaments Dense Z line bisects I bands; between Z lines is the contractile unit, the sarcomere Accessory proteins align and stabilize actin and myosin filaments Titin protein anchors myosin filaments, and α-actinin binds actin filaments to Z lines Titin centers, positions, and acts like a spring between myosin and Z lines The protein nebulin anchors thin filaments to Z lines and regulates actin filament length The protein desmin links myofibrils at Z lines and attaches them to the sarcolemma Muscle is surrounded by connective tissue epimysium Muscle fascicles are surrounded by connective tissue perimysium Each muscle fiber is surrounded by connective tissue endomysium Voluntary muscles are under conscious control Neuromuscular spindles are specialized stretch receptors in almost all skeletal muscles Intrafusal fibers and nerve endings are found in spindle capsules Stretching of muscle produces a stretch reflex and movement to shorten muscle Maj Abdullah Qamar  10 CARDIAC MUSCLE Located in the heart and large vessels attached to the heart Cross-striations of actin and myosin form similar I bands, A bands, and Z lines as in skeletal muscle Characterized by dense junctional complexes called intercalated discs that contain gap junctions Contain one or two central nuclei; fibers are shorter and show branching T tubules are located at Z lines and are larger in skeletal muscle The sarcoplasmic reticulum is less well developed than in skeletal muscles Mitochondria are larger and more abundant in cardiac fibers Gap junctions couple all fibers for rhythmic contraction and form the functional syncytium For contraction, calcium is imported from outside the cell and from the sarcoplasmic reticulum Exhibit autorhythmicity and spontaneously generate stimuli The autonomic nervous system innervates the heart and influences heart rate and blood pressure Maj Abdullah Qamar  11 SMOOTH MUSCLE Found in hollow organs and blood vessels Zonula adherens binds muscle cells, whereas gap junctions provide functional coupling Contain actin and myosin filaments without cross-striation patterns Fibers are fusiform in shape and contain single central nuclei In intestines, muscles are arranged in concentric layers and in blood vessels in a circular pattern Actin and myosin filaments are present, but they do not show regular arrangement or striations Actin and myosin form lattice network, and they insert into dense bodies in sarcoplasm and cytoplasm Dense bodies contain α-actinin and other Z-disc proteins The sarcoplasmic reticulum is not well developed for calcium storage Sarcolemma contains invaginations called caveolae Caveolae may control influx of calcium into the cell after stimulation Following stimulation, calcium enters sarcoplasm from the caveolae and sarcoplasmic reticulum Calmodulin, a calcium-binding protein, stimulates actin and myosin interaction Actin and myosin contract muscle by a sliding mechanism similar to skeletal muscle Maj Abdullah Qamar  12 Connection of dense bodies with adjacent cells transmits force of contraction to all cells Exhibit spontaneous activity and maintain tonus in hollow organs Peristaltic contractions propel contents in the organs Gap junctions couple muscles and allow ionic communication between all fibers Innervated by postganglionic neurons of sympathetic and parasympathetic divisions Involuntary muscles regulated by autonomic nervous system, hormones, and stretching POINTS OF IDENTIFICATION Skeletal muscle (L.S.) Cross striations are prominent (dark A bands and light I bands) Multiple peripheral nuclei Long, Cylindrical fibers without branching Smooth muscle (L.S.) Spindle shaped cells Single centrally placed nucleus Non-striated cells Non-branching fibers Cardiac muscle (L.S.) Cross striations (less prominent) with dark A bands and light I bands Short branching fibers Single, oval, centrally placed nucleus Intercalated discs Maj Abdullah Qamar  13 COMPARISON OF MUSCLE FIBERS Structural Features Skeletal Muscle Fiber Cardiac Muscle Smooth Muscle Fiber Fiber 1. Shape, Size, Large & elongate, Short & narrow, Short & Fusiform, Diameter length= upto 100 cm, Length = 80-100 µm, Length = 20-200 µm, Diameter = 10-100 µm Diameter=10-15 µm Diameter = 02-10 µm 2. Location Skeleton muscles, Heart, Superior & Vessels & Visceral Visceral striated Inferior venae cavae, organs (digestive & Pulmonary veins respiratory tracts, Muscles (tongue, uterus, urinary esophagus, diaphragm) bladder & others) 3. Connective tissue Epimysium, Perimysium, Endomysium Endomysium & less component Endomysium (Subendocardial & organized C.T subpericardial C.T) sheaths 4. Muscle fiber Single Branched Single, small, closely (single or branched ) arrangement packed 5. Striations Present Present Absent 6. Nucleus Many, Peripheral Single, Central Single, central at widest part of cell 7. T- Tubules Triad (with two terminal Diad,(with small No T-tubules, cisternae) present at A-I terminal cisternae) junction, Two T-Tubules present at Z line, One Well-developed SER, per sarcomere T-tubule per Many invaginations & sarcomere vesicles 8. Cell to cell None Intercalated discs Gap junctions (Nexus) junction containing: i. Fasciae adherents ii. Desmosomes iii. Gap junctions 9. Special features Well-developed SER & Intercalated discs Dense bodies & T-tubles Cytoplasmic vesicles 10. Growth & None None (in normal Present Regeneration condition) Maj Abdullah Qamar  14 Topic Lecture / Knowledge Practical / Skill Circulatory System Discuss the general histological Identify elastic artery, muscular artery and plan of blood vessels. large vein under light microscope and enlist Describe and compare the at least two identification points for each. histological structure of: Elastic artery Draw labelled diagram of elastic artery, Muscular artery muscular artery and large vein with the help of eosin and hematoxylin pencils on the Arteriole histology notebook Different types of Capillaries Venule Medium sized vein Large vein STRUCTURAL PLAN OF ARTERIES Wall consists of three layers: inner tunica intima, middle tunica media, and outer tunica adventitia Tunica intima consists of endothelium and subendothelial connective tissue Tunica media is composed mainly of smooth muscle fibers with some elasticfibers In elastic and muscular arteries, smooth muscles produce elastic fibers and some collagen Tunica adventitia contains primarily collagen type I and elastic fibers Internal elastic lamina (IEL) separates tunica intima from tunica media Fenestrations in IEL allow diffusion of nutrients to deeper cells External elastic lamina (EEL) separates tunica media from tunica adventitia STRUCTURAL PLAN OF VEINS Capillaries unite to form larger vessels called venules and postcapillary venules Thinner walls, larger diameters, and more structural variation than arteries Blood under low pressure; valves are present to prevent backflow of blood in extremities Blood flow toward heart is due to muscular contractions around veins and valves Valves absent in veins of the viscera, the CNS, and the inferior and superior venae cavae Maj Abdullah Qamar  15 Wall consists of three layers: tunica intima, tunica media, and tunica adventitia Tunica intima consists of endothelium and subendothelial connective tissue Tunica media is thin, and smooth muscle intermixes with connective tissue fibers Tunica adventitia is the thickest layer, with longitudinal smooth muscle fibers TYPES OF CAPILLARIES Consist of thin endothelium, basal lamina, and pericytes Continuous capillaries are most common; endothelium forms solid lining Continuous capillaries found in most organs Fenestrated capillaries contain pores or fenestrations in endothelium Fenestrated capillaries found in endocrine glands, small intestine, and kidney glomeruli Sinusoidal capillaries exhibit wide diameters with wide gaps between endothelial cells Basement membrane incomplete or absent in sinusoidal capillaries Sinusoidal capillaries found in the liver, spleen, and bone marrow Maj Abdullah Qamar 16 Maj Abdullah Qamar  17 MAJOR BLOOD VESSEL TYPES & THEIR IMPORTANT FEATURES Types Outer Tunica Intima Tunica Media Tunica Adventitia diameter Elastic > 10 mm Endothelium; Many elastic lamellae Connective tissue, arteries connective tissue with (50-60) alternating with thinner than media, smooth muscle smooth muscle with vasa vasorum Muscular 10-1 mm Endothelium; Many smooth muscle Connective tissue, arteries connective tissue with layers, with much less thinner than media, smooth muscle, elastic material with vasa vasorum internal elastic lamina may be present prominent Small arteries 1-0.1 Endothelium; 3-10 layers of smooth Connective tissue, mm connective tissue less muscle thinner than media; smooth muscle no vasa vasorum Arterioles 100-10 Endothelium; no 1-3 layers of smooth Very thin connective µm connective tissue or muscle tissue layer smooth muscle Capillaries 10-4 µm Endothelium only Pericytes only None Venules 10-100 Endothelium; no Scattered smooth None (post µm valves muscle cells capillary, collecting and muscular) Small veins 0.1-1 Endothelium; Thin, 2-3 loose layers of Connective tissue, mm connective tissue with smooth muscle cells thinner than media, scattered smooth muscle fibers Medium 1-10 mm Endothelium; 3-5 more distinct layers Thicker than media; veins connective tissue, of smooth muscle longitudinal smooth with valves muscle may be present Large veins > 10 mm Endothelium; > 5 layers of smooth Thickest layer, with connective tissue, muslce, with much bundled longitudinal smooth muscle cells; collagen smooth muscle prominent valves Maj Abdullah Qamar  18 POINTS OF IDENTIFICATION Large (elastic) arteries Well-developed subendothelial layer in tunical intima Tunica media has many elastic lamellae Vasa vasorum in tunica adventitia Medium (muscular) Well-developed internal elastic lamina (thrown into arteries wavy folds) Thick tunica media with many smooth muscle fibers External elastic lamina Elastic fibers in tunica adventitia Arterioles and small Tunica intima has endothelial cells arteries Tunica media has 1 or 2 layers of smooth muscle fibers A small artery may have up to eight layers of smooth muscle fibers Tunica adventitia is thin Large veins Poorly developed tunica media Thick tunica adventitia with longitudinally oriented bundles of smooth muscle fibers Medium veins Thin tunica media with few smooth muscle fibers and less elastic fibers Large collapsed lumen Maj Abdullah Qamar  19 Topic Lecture / Knowledge Practical / Skill Immune System Enumerate the cells of immune Identify slides of lymph node, thymus, system. spleen and palatine tonsils under light Describe the structure of primary microscope and enlist at least two and secondary lymph nodule. identification points for each Describe the histological features of: Lymph node Thymus Spleen Tonsils Compare the histological structure of thymus, lymph node, spleen and tonsils IMMUNE SYSTEM Protects organism against invading pathogens and has wide distribution Contains aggregates of immune cells (lymphocytes) in nodules or lymphoid organs Major organs are subdivided into primary and secondary lymphoid organs Primary lymph organs are bone marrow and thymus Secondary lymph organs are the lymph nodes, tonsils, spleen, and mucosa associated lymphoid tissue (MALT) MALT is in the digestive tract (GALT), respiratory tract (BALT), bone, and Peyer patches TYPES OF IMMUNE RESPONSES Innate Immune Response First line of defense that limits the spread of infection Response composed of the rapid response of phagocytic cells and their functions Response is nonspecific and does not produce memory cells Adaptive Immune Response Targets specific invading organisms and provides specific or adaptive response Response is slower than innate response but produces memory cells that can respond to secondary encounters Production of long-lived memory cells is main function of adaptive immunity Maj Abdullah Qamar  20 Two types of specific responses are humoral and mediated immune responses In humoral-mediated response, antigens induce B cells to transform into plasma cells. Plasma cells, in turn, secrete specific antibodies to destroy antigens In cell-mediated response, T cells are activated, release cytokines, stimulate other T and B cells, bind to target cells, and destroy them PERCENTAGE OF T AND B CELLS IN LYMPHOID ORGANS Lymphoid Organ T Lymphocytes (%) B Lymphocytes (%) Thymus 100 0 Bone marrow 10 90 Spleen 45 55 Lymph nodes 60 40 Blood 70 30 LYMPH NODES Distributed along the paths of lymphatic vessels Most prominent in inguinal and axillary regions Major function is lymph filtration and phagocytosis of foreign material from lymph Surrounded by connective tissue capsule that sends trabeculae into the interior of the organ Exhibit an outer dark-staining cortex and an inner light-staining medulla Lymphatic nodules, some with germinal centers, are aggregated in the cortex Lymphatic nodules without germinal centers are primary lymphatic nodules Lymphatic nodules with antigen stimulation and lighter germinal centers are secondary nodules Afferent lymph vessels with valves penetrate the capsule and enter subcapsular sinus Major blood vessels present in connective tissue trabeculae Medullary cords in the medulla contain plasma cells, macrophages, and lymphocytes Medullary sinuses are capillary channels that drain lymph from cortical regions Efferent lymphatic vessels drain lymph from the medullary sinuses to exit at the hilus Maj Abdullah Qamar  21 Produce and store B and T cells B cells accumulate in lymphatic nodules and when activated form germinal centers Deeper region of the cortex is the paracortex, occupied by T cells T cells concentrate in deep cortical or paracortex regions Activate B cells to give rise to plasma cells and memory B cells B and T cells enter lymph nodes through postcapillary high endothelial venules High endothelium in postcapillary venules contains adhesive molecules as homing receptors for lymphocytes Both B and T cells leave bloodstream through high endothelial venules High endothelial venules present in numerous other lymphoid organs except the spleen Maj Abdullah Qamar  22 SPLEEN Largest lymphoid organ with extensive blood supply; filters blood and serves as a blood reservoir Surrounded by a connective tissue capsule that divides it into red and white pulp White pulp consists of lymphatic nodules with a germinal center around a central artery T predominant in periarteriolar lymphatic sheets (PALS) around central arteries Red pulp consists of splenic cords and splenic (blood) sinusoids Splenic cords contain macrophages, lymphocytes, plasma cells, and different blood cells Does not exhibit cortex and medulla but contains lymphatic nodules White pulp is the site of immune response to blood-borne antigens T cells surround the central arteries, whereas B cells are mainly in the lymphatic nodules APCs and macrophages are found in white pulp Breaks down hemoglobin from worn-out erythrocytes and recycles iron to bone marrow Degrades heme from hemoglobin, which is then excreted in the bile During fetal life is an important hematopoietic organ and in adults serves as blood reservoir Maj Abdullah Qamar  23 THYMUS GLAND Lobulated lymphoepithelial organ with dark-staining cortex and light staining medulla Most active in childhood and has an important role early in life in immune system development Site where immature lymphocytes from the bone marrow mature into T cells, helper T cells, and cytotoxic T cells Thymic nurse cells promote lymphocyte differentiation, proliferation, and maturation Blood–thymus barrier prevents developing lymphocytes contacting blood borne antigens Sends mature T cells to populate the lymph nodes, the spleen, and the lymphatic tissues Epithelial reticular cells secrete numerous hormones needed for lymphocyte maturation Epithelial reticular cells form thymic (Hassall) corpuscles in the medulla Maturation of T cells involves positive and negative selection Involutes and becomes filled with adipose tissues as the individual ages Removal early in life results in loss of immunologic competence Maj Abdullah Qamar  24 Tonsils Diffuse lymphoid tissue and nodules in the oral pharynx Palatine and lingual tonsils covered by stratified squamous epithelium and show crypts Pharyngeal tonsil is single and covered by pseudostratified ciliated epithelium Some lymphatic nodules contain germinal centers COMPARISON OF THREE TYPES OF TONSILS Parameters Palatine Lingual Pharyngeal Location Posterolateral wall of oral Posterior third of tongue Roof & posterior wall of cavity nasopharynx Number Two (right, left) Numerous One Epithelium Stratified squamous non- Stratified squamous non- Ciliated pseudo stratified keratinized, (Epithelium is keratinized, intraepithelial columnar epithelium, with difficult to recognize lymphocytes & dendritic patches of stratified because it is densly cells present squamous non-keratinzied infiltrated with dendritic cells & lymphocytes) Capsule Band of dense C.T but No capsule Thinner than palatine incomplete because it only tonsil. Present on deep covers deep aspect of tonsil aspect Crypts Present (10-20 in number) Each nodule has single Absent, rather longitudinal crypt folds (called pleats )are present Lymphoid Numerous lymphatic Lymphatic tissue is present Lymphatic tissue is more Tissue nodules in parenchyma with as typical modules diffuse germinal centers Maj Abdullah Qamar  25 POINTS OF IDENTIFICATION Lingual tonsils Epithelium is stratified squamous non-keratinized Lymphatic tissue is present as typical nodules Each nodule has single crypt Lymph node Many afferent lymphatic vessels on convex surface Cortex has lymphatic nodules without central arteriole Subcapsular sinus along with other sinuses Medullary cords and sinuses in the medulla Thymus Characteristic lobules each one consisting of cortex and medulla Thymic (Hassall’s) corpuscles in medulla No sinuses No afferent lymphatics Spleen Red pulp (splenic cords and venous sinusoids) White pulp containing lymphatic nodules with definite central artery placed eccentrically No differentiation of cortex and medulla Maj Abdullah Qamar