Special histology- specific points

The identification features of the particular slide with little explanation is given. The points in bold are specific features for a particular system and for a particular tissue

TRACHEA

Trachea:

1. Mucosa- pseudostratified ciliated columnar epithelium surrounded by lamina propria
2. Submucosa- connective tissue with seromucous tracheal glands, blood vessels, lymphatics, nerves
3. Fibromusculocartilaginous layer- anteriorly C-shaped hyaline cartilage, posteriorly two ends attached by fibrous tissue and smooth muscle (trachealis)
4. Hyaline cartilage- covered with perichondrium, homogeneous matrix due to same refractive index of ground substance and collagen fibers, cell nest surrounded by territorial matrix, interterritorial matrix between cell nests
5. Adventitia- loose connective tissue with blood vessels, lymphatics, nerves

LUNG

Lung:

1. Made up of intrapulmonary bronchi, bronchioles, alveoli
2. Intrapulmonary bronchi (secondary and tertiary bronchi)- pseudostratified ciliated columnar epithelium, surrounded by smooth muscle, islands of cartilage plates, adventitia
3. Bronchioles- columnar to low cuboidal epithelium from proximal (bronchiole) to distal end (respiratory bronchiole) surrounded by thin layer of smooth muscle
4. Alveoli- type I pneumocytes (simple squamous cells, for diffusion), type II pneumocytes (great alveolar cells, secrete surfactant), macrophages (phagocytosis) surrounded by connective tissue fibers with fibroblasts and capillaries

FILIFORM AND FUNGIFORM PAPILLAE

CIRCUMVALLATE PAPILLAE

Tongue:

1. Layers from superficial to deep- epithelium, lamina propria, skeletal muscle core
2. Mucosa- partially keratinized stratified squamous epithelium deep to which is lamina propria
3. Dorsal surface- surface projections forming papillae- filiform, fungiform and circumvallate papillae with taste buds
4. Filiform papillae- present throughout the dorsal surface, conical in shape with core of lamina propria covered by stratified squamous keratinized epithelium.
5. Fungiform papaillae- present mainly at the tip and sides of dorsal surface, mushroom shape with core of lamina propria covered by stratified squamous nonkeratinized epithelium. Taste buds are present at the surface
6. Circumvallate papillae- 8-12 in number arranged anteriorly along the V-shaped sulcus, core of lamina propria surrounded by stratified squamous non keratinized epithelium, base is narrow, surface is broader. Each papilla is surrounded all over by deep furrow,  side walls present taste buds extending completely through the epithelium, serous glands (von Ebner's glands) open into the base of furrow
7. Taste buds- oval in shape, small opening present at the surface called taste pore, has 3 types of cells (taste or gustatory cells, supporting or sustentacular cells, basal cells)
8. Core of the tongue- skeletal muscles intermingling with connective tissue, blood vessels, nerves, lymphatics

ESOPHAGUS

Esophagus:

1. 4 layers from deep (lumen) to superficial- mucosa, submucosa, muscularis externa, adventitia or serosa
2. Mucosa- stratified squamous nonkeratinized epithelium surrounded by lamina propria and muscularis mucosa
3. Submucosa- dense irregular connective tissue, mucosal (esophageal)glands , blood vessels, nerves and lymphatics
4. Muscularis externa- upper 1/3rd skeletal muscle, middle 1/3rd both skeletal and smooth muscle, lower 1/3rd smooth muscle
5. Adventitia- loose connective tissue, blood vessels, nerves, adipose tissue

STOMACH FUNDUS

Stomach fundus:

1. 4 layers from deep (lumen) to superficial- mucosa, submucosa, muscularis externa, serosa
2. Mucosa- simple columnar epithelium surrounded by lamina propria (filled with long tubular gastric glands) and muscularis mucosae
• Gastric glands open into gastric pits which are short (1/4th of thickness of mucosa)
• cells in glands- mucous neck cells, chief cells, parietal cells, enteroendocrine cells
3. Submucosa- dense irregular connective tissue, blood vessels, nerves and lymphatics
4. Muscularis externa- inner oblique, middle circular, outer longitudinal smooth muscle
5. Serosa- simple squamous mesothelium surrounding the connective tissue, blood vessels, nerves, adipose tissue

STOMACH PYLORUS

Stomach pylorus:

1. 4 layers from deep (lumen) to superficial- mucosa, submucosa, muscularis externa, serosa
2. Mucosa- simple columnar epithelium surrounded by lamina propria (filled with coiled tubular pyloric glands) and muscularis mucosae
• Pyloric glands open into gastric pits which are long (3/4th of thickness of mucosa)
• cells in glands- mainly mucous  cells, enteroendocrine cells
3. Submucosa- dense irregular connective tissue, blood vessels, nerves and lymphatics
4. Muscularis externa- inner oblique, middle circular, outer longitudinal smooth muscle
5. Serosa- simple squamous mesothelium surrounding loose connective tissue, blood vessels, nerves, adipose tissue

DUODENUM

Duodenum:

1. 4 layers from deep (lumen) to superficial- mucosa, submucosa, muscularis externa, adventitia or serosa
2. Mucosa- simple columnar epithelium with few goblet cells surrounded by lamina propria (filled with intestinal glands/ crypts of Lieberkuhn) and muscularis mucosae
• Plicae circularis (mucosal elevations with core of submucosa) numerous, 
• Villi (permanent mucosal folds with lymphatic capillary lacteal) long/tall, broad, numerous
3. Submucosa- dense irregular connective tissue, duodenal glands (Brunner's glands), blood vessels, nerves and lymphatics
4. Muscularis externa- inner circular, outer longitudinal smooth muscle
5. Serosa- simple squamous mesothelium surrounding connective tissue, blood vessels, nerves, adipose tissue

JEJUNUM

Jejunum:

1. 4 layers from deep (lumen) to superficial- mucosa, submucosa, muscularis externa, serosa
2. Mucosa- simple columnar epithelium with more goblet cells than duodenum surrounded by lamina propria (filled with intestinal glands/ crypts of Lieberkuhn) and muscularis mucosae
• Plicae circularis less than duodenum 
• Villi shorter, narrow, and fewer than duodenal villi  
3. Submucosa- dense irregular connective tissue, blood vessels, nerves and lymphatics
4. Muscularis externa- inner circular, outer longitudinal smooth muscle
5. Serosa- simple squamous mesothelium surrounding connective tissue, blood vessels, nerves, adipose tissue

Ileum:

1. 4 layers from deep (lumen) to superficial- mucosa, submucosa, muscularis externa, adventitia or serosa
2. Mucosa- simple columnar epithelium with more goblet cells surrounded by lamina propria (filled with intestinal glands/ crypts of Lieberkuhn) and muscularis mucosae
•  Plicae circularis very few, 
• Villi very few, shorter and narrower than duodenal and jejunal  villi,  
3. Submucosa- dense irregular connective tissue, blood vessels, nerves and lymphatics. 
• Payer's patches (Aggregations of lymphatic nodules) in lamina propria and submucosa
4. Muscularis externa- inner circular, outer longitudinal smooth muscle
5. Serosa- simple squamous mesothelium surrounding connective tissue, blood vessels, nerves, adipose tissue

LARGE INTESTINE

Large intestine:

1. 4 layers from deep (lumen) to superficial- mucosa, submucosa, muscularis externa, adventitia or serosa
2. Mucosa- simple columnar epithelium with numerous goblet cells surrounded by lamina propria (filled with intestinal glands/ crypts of Lieberkuhn) and muscularis mucosae
•  Plicae circularis and Villi absent. Temporary folds in undistended colon
3. Submucosa- dense irregular connective tissue, blood vessels, nerves and lymphatics
•  Lamina propria and submucosa filled with abundant diffuse lymphatic tissue 
4. Muscularis externa- inner circular, outer longitudinal smooth muscle condensed into three muscular bands called taeniae coli
5. Serosa- simple squamous mesothelium surrounding connective tissue, blood vessels, nerves, adipose tissue

APPENDIX

Appendix:

1. 4 layers from deep (lumen) to superficial- mucosa, submucosa, muscularis externa, adventitia or serosa
2. Mucosa- simple columnar epithelium with numerous goblet cells surrounded by lamina propria (few intestinal glands/ crypts of Lieberkuhn) and interrupted muscularis mucosae 
3. Submucosa- dense irregular connective tissue, blood vessels, nerves and lymphatics
• Lamina propria and submucosa filled with abundant diffuse lymphatic tissue and solitary lymphatic nodules disrupting muscularis mucosae
4. Muscularis externa- inner circular, outer longitudinal smooth muscle 
5. Serosa- simple squamous mesothelium surrounding connective tissue, blood vessels, nerves, adipose tissue

LIVER

Liver:

1. Covered by connective tissue capsule (Glisson's capsule)
2. Hepatic lobule- central vein surrounded by plates of liver cells (hepatocytes) and sinusoids radiating towards periphery
3. Portal triad- 3 to 6 per lobule present at periphery containing branches of hepatic artery, hepatic portal vein and bile duct
4. Sinusoids lined by fenestrated endothelial cells and Kuppfer cells / liver phagocytes (detoxify blood).
5. Perisinusoidal space of Disse- space between hepatocytes and sinusoids
6. Hepatic cells- 6 surfaces, 4 sides related to bile  canaliculi, 2 surfaces to sinusoids
7. Space of Mall- space between portal canal and hepatocytes

GALLBLADDER

Gallbladder:

1. 3 layers from deep (lumen) to superficial- mucosa,  muscularis, adventitia or serosa
2. Mucosa- tall columnar epithelium with lamina propria. Muscularis mucosae and submucosa absent
•  Temporary mucosal folds in nondistended state which may invaginate deep into lamina propria forming diverticula or crypts (Rokitansky-Aschoff sinus)
3. Muscularis- randomly oriented smooth muscle fibers and interlacing elastic fibers
4. Serosa covers free surface (simple squamous mesothelium surrounding connective tissue, blood vessels, nerves, adipose tissue) and adventitia covers attached surface (connective tissue, blood vessels, nerves, adipose tissue)

PANCREAS

Pancreas:

1. Exocrine part- closely packed serous acini with centroacinar cells which are parts of intercalated ducts
2. Endocrine part- islets of Langerhans/ pancreatic islets with alpha cells, beta cells, delta cells and pancreatic polypeptide cells
3. Centroacinar cells- cells of intercalated duct projecting into the serous acini 
4. Serous acini- small lumen with surrounding pyramidal cells having round nucleus at the lower 1/2 of the cell and protein secreting zymogenic granules at upper half
5. Islets of Langerhans- thin connective tissue capsule separates the islets from exocrine part, cells arranged in cords or clumps with connective tissue fibers and capillary network. alpha cells secrete glucagon, beta cells secrete insulin

KIDNEY

Kidney:

1. It is divided into outer cortex and inner medulla
2. Cortex- proximal convoluted tubule (PCT), distal convoluted tubule (DCT), renal corpuscle, medullary rays, interlobular arteries and veins
3. Medullary rays- straight portions of PCT and DCT, blood vessels and collecting tubules
4. Medulla (renal pyramids)- base directed towards cortex and apex (renal papilla) towards minor calyx. It has straight portions of PCT and DCT, loop of Henle
5. Structural and functional unit of kidney is nephron. It has renal corpuscle (tuft of capillary plexus called glomerulus surrounded by double layer of epithelial cells called Bowman's capsule), PCT, loop of Henle (thick descending portion of PCT, thin descending and ascending segment, thick ascending portion of DCT), DCT which opens into collecting tubule.
6. Lining epithelium- parietal layer of Bowman's capsule (simple squamous epithelium), visceral layer of Bowman's capsule (modified epithelial cells called podocytes), PCT (simple cuboidal cells surrounding small uneven lumen), DCT (low cuboidal cells surrounding larger lumen), loop of Henle (simple squamous cells), collecting tubule (cuboidal cells)
7. Juxtaglomerular apparatus- present at vascular pole, juxtaglomerular cells (modified smooth muscle cells of afferent glomerular arteriole), macula densa (narrow numerous columnar cells in DCT), messangial cells

URETER

Ureter:

1. 3 layers from deep (lumen) to superficial- mucosa, muscularis, serosa
2. Mucosa- transitional epithelium surrounded by lamina propria (fibroelastic connective tissue). Muscularis mucosae and submucosa absent
3. Muscularis- inner longitudinal and outer circular smooth muscle layers. In lower 1/3rd it has one more layer outer longitudinal smooth muscle layer
4. Serosa- thin connective tissue layer with mesothelium

URINARY BLADDER

Urinary bladder:

1. 3 layers from deep (lumen) to superficial- mucosa, muscularis, serosa
2. Mucosa- thrown into temporary mucosal folds lined by transitional epithelium surrounded by lamina propria (fibroelastic connective tissue). Muscularis mucosae and submucosa absent
• transitional epithelium- basal layer of low columnar or cuboidal cells, intermediate layers of  polyhedral cells, superficial layer of large cuboidal cells. the superficial cells are covered by plasma membrane. 
• In distended state the superficial layers become flattened and the number of layers reduces to 2 or 3. The mucosal folds disappear. 
3. Muscularis- very thick, inner longitudinal, middle circular and outer longitudinal smooth muscle layers which cannot be distinguished. 
4. Serosa (thin connective tissue layer with mesothelium) covering the superior surface and adventitia (thin connective tissue layer) covering the inferior surface

PITUITARY GLAND

Pituitary gland:

1. Adenohypophysis- pars distalis, pars tuberalis, pars inermedia
• Pars distalis- Cells depending on staining 
• chromophobes (50%), 
• chromophils 
1. acidophils- somatotrophs (somatotropin), mammotrophs (prolactin)
2. basophils- thyrotrophs (thyroid stimulating hormone), gonadotrophs     (follicle stimulating hormone, leutinizing hormone, testosterone), corticotrophs (adrenocorticotrophic hormone)
• Pars intermedia- colloid filled vesicles surrounded by cells secreting melanocyte stimulating  hormone
2. Neurohypophysis- median eminence, infundibulum, pars nervosa
• Pars nervosa- unmyelinated axons arising in hypothalamus, dilated terminal end for storing hormones oxytocin and vasopressin (Herring bodies), pituicytes

THYROID GLAND

Thyroid gland:

1. Structural and functional units are thyroid folllicles lined by follicular cells and colloid in the lumen
2. Follicular cells vary in shape- Hyperactive state- columnar cells, normal state- cuboidal cells, inactive state- squamous cells
3. Parafollicular cells either present in between the follicles or in the follicles (between follicular cells and basement membrane)

SUPRARENAL GLAND

Adrenal/ suprarenal gland:

1. Cortex- 3 layers, zona glomerulosa, zona fasciculata, zona reticularis
• zona glomerulosa- cells arranged in ovoid groups or clumps, secrete mineralocorticoids
• zona fasciculata- cells arranged vertically in columns, secrete glucocorticoids
• zona reticularis- cells arranged in network of cords or clumps, secrete sex hormone
2. Medulla- cells are modified postganglionic sympathetic neurons, secrete catecholamines (epinephrine, norepinephrine)

TESTES

Testes:

1. Numerous cross-sections of seminiferous tubules surrounded by interstitial connective tissue with fibroblast, muscle like cells, bloodvessels, nerves and lymphatics
2. Seminiferous tubule- stratified germinal epithelium with spermatogenic cells and sustentacular cells (supporting/ Sertoli cells) 
3. Interstitial cells of Leydig present between seminiferous tubules produce testosterone

Epididymis:

1. Numerous cross-sections of duct lined by pseudostratified columnar epithelium with tall columnar (principal) cells having stereocilia and basal cells
2. Duct surrounded by thin smooth muscle layers and connective tissue

VAS DEFERENS

Vas deferens/ ductus deferens:

1. Mucosa- pseudostratified columnar epithelium with stereocilia surrounded by lamina propria
2. Muscularis- inner longitudinal, middle circular, outer longitudinal smooth muscle layers
3. Adventitia- connective tissue with numerous blood vessels, nerves and lymphatics

PROSTATE

Prostate:

1. It has glandular and fibromuscular part
2. Glandular part- branched tubuloacinar glands lined by simple columnar or pseudostratified columnar epithelium. Prostatic concretions seen in acini
3. Fibromuscular stroma- smooth muscle bundle and connective tissue fibers surround the glandular part
4. Prostatic concretions or corpora amylacea- prostatic secretions calcified

UTERUS

Uterus:

1. 3 layers from inside out- endometrium, myometrium, perimetrium
2. Endometrium-
• stratum functionalis with uterine glands and blood vessels which will be sloughed off during menstruation
• stratum basalis with remnants of uterine glands and blood vessels
3. Myometrium- very thick smooth muscle layer
4. Perimetrium- serosa or adventitia

UTERINE TUBE

Uterine tube/ fallopian tube:

1. 3 layers- mucosa, muscularis, serosa
2. Mucosa- extensive mucosal folds, lined by simple columnar ciliated and non ciliated (peg cells) epithelium. It is surrounded by lamina propria
3. Muscularis- inner circular and outer longitudinal smooth muscle layers
4. Serosa- connective tissue with mesothelium

OVARY

Ovary:

1. Cortex- different stages of follicles (primordial, primary, secondary and tertiary/ mature follicles), corpus luteum, corpus albicans, attretic follicles
2. Medulla- connective tissue with numerous blood vessels, nerves and lymphatics

CORNEA

Cornea:

1. Corneal epithelium- stratified squamous non keratinized epithelium
2. Bowman's membrane/ anterior limiting membrane- thick homogeneous layer supports basement membrane
3. Substantia propria/ corneal stroma- parallel bundles of collagen fibers and flat fibroblasts
4. Descemet's membrane/ posterior limiting membrane- thick basement membrane of posterior epithelium
5. Posterior epithelium/ corneal endothelium- simple squamous  or low cuboidal epithelium

RETINA

Retina:

1. Pigment epithelium
2. Layer of rods and cones
3. outer limiting membrane- processes of Muller's cells
4. Outer nuclear layer- nuclei of rods and cones
5. Outer plexiform layer- synapse between axons of rods and cones, dendrites of bipolar and horizontal cells
6. Inner nuclear layer- nuclei of bipolar, horizontal, amacrine and Muller's cells
7. Inner plexiform layer- synapse between axons of bipolar cells, dendrites of amacrine and ganglionic cells
8. Ganglionic cell layer- nuclei of ganglionic cells and neuroglia
9. Nerve fiber layer- axons of ganglionic cells, inner fibers of Muller's cells
10. Inner limiting membrane- termination of inner fibers of Muller's cells

Cerebrum:

1. Molecular layer- neuroglial and horizontal cells of Cajal
2. External granular layer- neuroglial and small pyramidal cells
3. External pyramidal layer- medium sized pyramidal cells, neuroglial cells
4. Internal granular layer- small granular cells, medium sized pyramidal cells, neuroglia
5. Internal pyramidal layer- large sized pyramidal cells, neuroglia
6. Multiform layer- fusiform cells, stellate cells, cells of Martinotti

CEREBELLUM

Cerebellum:

1. Molecular layer- stellate cells, basket cells, dendrites of Purkinje cells, axons of granule cells, basket cells
2. Purkinje cell layer- single layer of Purkinje cells
3. Granular layer- granule cells, Golgi type II cells, glomeruli
4. Glomeruli- synapse between rosette (dilated terminal of mossy fiber), dendrite of granule cell, axon of Golgi type II cell, neuroglia
5. Inner core of white matter- climbing fibers, mossy fibers, axons of Purkinje cells

General histology - specific points

The identification features of the particular slide with little bit of explanation is given. The points in bold are specific features for a particular system and for a particular tissue.

Hyaline cartilage:

1. Covered by outer fibrous and inner chondrogenic perichondrium
2. Homogeneous, glossy, transparent, basophilic matrix due to same refractive index for collagen type II fibers and ground substance
3. Territorial matrix surrounding cell nest and interterritorial matrix between cell nests
4. Chondrocytes arranged in the form of cell nest prevalent in the center
5. Cell nest/ isogenous group- 2 to 4 cells present in groups surrounded by territorial matrix

Elastic cartilage:

1. Covered by outer fibrous and inner chondrogenic perichondrium
2. Matrix with more elastic fibers along with collagen type II fibers embedded in ground substance
3. Larger chondrocytes in lacunae more prevalent in the center

White fibro cartilage:

1. Devoid (absence) of perichondrium
2. Collagen fibers running parallel to each other in bundles and less of ground substance in the matrix 
3. Chondrocytes arranged in rows

Bone:

In the same diagram both transverse section and longitudinal section are drawn.

Bone Transverse Section:

1. Covered by periosteum with outer fibrous and inner osteogenic layers
2. Matrix with Haversian systems (Haversian canal surrounded by concentric lamellae)
3. Outer circumferential lamellae present deep to periosteum, interstitial lamellae present between Haversian systems, inner circumferential lamellae covers endosteum
4. Lamellae are thin plates of fibers and calcified matrix
5. Lacunae are spaces with osteocytes present between two lamellae
6. Canaliculi are thin spaces extending from lacunae with cytoplasmic processes 

Bone Longitudinal Section:

1. Haversian canals run longitudinally connected by transverse channels called Volkmann's canal
2. Lamellae arranged parallel to the Haversian canals
3. Between adjacent lamellae are lacunae with osteocytes
4. Haversian canals are surrounded by concentric lamellae, Volkmann's canals pass through lamellae connecting two Haversian canals. They contain blood vessels and nerves providing nutrition to bone

Skeletal muscle Transverse Section:

1. Whole muscle surrounded by epimysium, bundle of muscle fibers (fascicle) by perimysium and single fiber by endomysium
2. Nuclei are situated peripherally beneath sarcolemma
3. Epimysium- dense irregular connective tissue, perimysium- less dense irregular connective tissue, endomysium- thin connective tissue

 Skeletal muscle Longitudinal Section:

1. Unbranched, long, voluntary cylindrical fibers with sarcolemma, sarcoplasm
2. Multinuclei placed beneath sarcolemma in each muscle fiber
3. Cross-striations- light I band and dark A band formed by contractile proteins actin and myosin
4. Sarcolemma- cell membrane, plasma membrane
5. Sarcoplasm- cytoplasm
6. Sarcomere- functional contractile unit of muscle fiber having contractile proteins actin and myosin, extends between two Z lines
7. I band is formed by only actin filaments attached to Z line. A band is formed by myosin filaments in the center and overlapped by actin filaments at the side

Cardiac muscle:

1. Branched, short, involuntary cylindrical fibers
2. Each muscle fiber has one or two  nuclei in the center
3. Cross-striations- light I band and dark A band formed by contractile proteins actin and myosin
4. Intercalated disc- Cell junctional complex present between adjacent muscle fibers

Smooth muscle:

1. Spindle shaped, non striated, involuntary muscle fibers
2. Each muscle fiber has oval nucleus in the center
3. It is found in the walls of digestive system, respiratory system, urinary system, genital system, blood vessels
4. It appears smooth since the protein filaments are not arranged regularly in order

Peripheral nerve TS:

1. Whole nerve is surrounded by connective tissue epineurium, fascicle by perineurium and each nerve fiber by endoneurium
2. Between individual axons are seen numerous nuclei of Schwann cells
3. Each axon is surrounded by myelin sheath
4. Along with the connective tissue, there are blood vessels, nerves, lymphatics, adipose tissue

Sympathetic / autonomic ganglion:

1. Multipolar, irregular shaped, smaller, scattered neurons
2. Eccentric nucleus in each neuron
3. Few satellite cells present around neurons
4. Irregular shape of the cell is due to attachment of dendritic processes
6. The satellite cells provide the structural and 
7. metabolic support to the neurons and insulate the neurons.
8. Randomly arranged bundles of nerve fibers

Spinal ganglion/ Dorsal root ganglion:

1. Pseudounipolar, larger neurons present in groups
2. Fascicles of nerve fibers pass between unipolar neurons
3. Nucleus with prominent nucleolus present in the center of neuron
4. Satellite cells surrounding the neurons are more
5. Fascicles of nerve fibers are the peripheral processes of bifurcating single axon of unipolar neuron
6. The satellite cells provide the structural and metabolic support to the neurons and insulate the neurons.

Large sized artery/ Elastic artery:

1. Three layers from inside out- tunica intima, tunica media, tunica adventitia
2. Tunica intima-  lined by squamous cells (endothelium) surrounded by subendothelial connective tissue
3. Tunica media is very thick with more number of elastic fibers, few smooth muscle fibers
4. Tunica adventitia- connective tissue, vasa vasorum, nerves
5. Subendothelial layer- loose connective tissue, few smooth muscle fibers, elastic fibers
6. More number of elastic fibers give the artery the resilience where the artery can expand when more blood flows through the vessel and come back to its original position, so that there is steady flow of blood
7. Example- aorta, brachiocephalic trunk, common carotid artery, subclavian artery

Medium sized artery/ distributing artery:

1. Three layers from inside out- tunica intima, tunica media, tunica adventitia
2. Tunica intima-  lined by squamous cells (endothelium) surrounded by subendothelial connective tissue. Internal elastic lamina is more prominent
3. Tunica media is as thick as tunica adventitia with more number of smooth muscle fibers. 
4. Tunica adventitia- very thin with connective tissue, vasa vasorum, nerves
5. More number of smooth muscle fibers allows the artery to distribute blood to most parts of the body by its contraction

Medium sized vein:

1. Three layers from inside out- tunica intima, tunica media, tunica adventitia
2. Tunica intima-  lined by squamous cells (endothelium) surrounded by subendothelial connective tissue. 
3. Tunica media - very thin. 
4. Tunica adventitia- very thick with connective tissue, vasa vasorum, nerves

Large sized vein:

1. The thickness of the wall is half the size of the corresponding artery. Three layers from inside out- tunica intima, tunica media, tunica adventitia
2. Tunica intima-  lined by squamous cells (endothelium)
3. Tunica media is thin with connective tissue and smooth muscle fibers
4. Tunica adventitia is very thick compared to other two layers with connective tissue, vasa vasorum, nerves, longitudinally running smooth muscle fibers 

Lymph node:

1. Covered by connective tissue capsule sending incomplete trabeculae into lymphnode along with blood vessels and nerves
2. Cortex: lymphatic nodules with germinal centers (B lymphocytes) , paracortex in deeper zone (T lymphocytes)
3. Subcapsular sinus deep to capsule, trabecular sinus around trabeculae
4. Medulla: medullary sinus, medullary cords
5. Lymph flow: afferent lymphatic vessels-- subcapsular sinus--trabecular sinus--medullary sinus--efferent lymphatic vessel
6. Sinuses- spaces with lymph supported by network of fine reticular fibers
7. Lymph nodes filter the lymph by phagocytosis and acts as the principal site in which T and B lymphocytes undergo antigen-dependent proliferation and differentiation into effector lymphocytes (plasma cells and T cells) and memory B cells.
8. Germinal center is the active site of lymphocyte proliferation

Thymus:

1. Covered by connective tissue capsule sending incomplete trabeculae into thymus along with blood vessels and nerves.
2. Each lobule is divided into cortex and medulla
3. Cortex has dense aggregations of thymic lymphocytes
4. Medulla has few lymphocytes,  more epithelial reticular cells and Hassall's corpuscles
5. Thymus shows age changes. Just after birth it is at its greatest development and by puberty it starts to regress and is replaced by adipose tissue
6. Hassall's corpuscles- oval hyalinized structures with round aggregations of flattened epithelial cells and central calcified or degenerated epithelial cells
7. Blood-thymus barrier- endothelial cells, epithelial reticular cells, macrophages which does not allow the substances transported in blood vessel to interact with developing T cells in the cortex

Spleen:

1. Covered by connective tissue capsule sending incomplete trabeculae into spleen along with blood vessels and nerves.
2. Divided into red pulp and white pulp
3. Red pulp: Splenic cords of Billroth (small lymphocytes, red blood cells, neutrophils, eosinophils, ), pulp arteries and venous sinuses
4. White pulp: lymphatic nodules with  germinal centers and central artery

Tonsil:

1. Free surface is covered by stratified squamous nonkeratinized epithelium which invaginates into tonsil to form tonsillar crypts
2. The crypts are surrounded by numerous lymphatic nodules
3. Attached surface is covered by connective tissue capsule which sends septa towards surface of tonsil. It acts as barrier from spreading tonsillar infections.
4. Function of stratified squamous nonkeratinized epithelium is protection

Thick skin:

1. Epidermis: 5 layers- stratum basale, stratum spinosum , stratum granulosum , stratum lucidum , stratum corneum 
2. Dermis: papillary layer and reticular layer with sweat glands
3. Stratum basale- divides to increase number of cells, differentiate into other cells
4. Stratum spinosum- polygonal cells, intermediate keratin filaments increase in number
5. Stratum granulosum- intermediate keratin filaments and  keratohyalin granules join to form keratin
6. Stratum lucidum- lacks nucleus, densely packed keratin, contain eleidin
7. Stratum corneum- lacks nucleus and organelles, full of keratin

Thin skin:

1. Epidermis: 4 layers, stratum lucidum absent. Stratum basale, stratum spinosum, stratum granulosum, stratum corneum
2. Dermis: papillary layer and reticular layer with hair follicle, sebaceous glands, arrector pili muscle and sweat glands
3. Hair follicle- from inside out- inner root sheath, outer root sheath, connective tissue sheath
4. Sweat glands- simple coiled tubular glands, lower coiled part forms secretory portion, upper tube forms duct, secrete non-viscous fluid
5. Sebaceous gland- simple or branched acinar glands, open into hair follicle, secrete sebum
6. Arrector pili muscle- smooth muscle attached to dermal papillae and hair shaft below the sebaceous gland, when it contract hair becomes straight

Serous salivary gland:

1. Covered by connective tissue capsule which send septa along with blood vessels and nerves into gland dividing into lobes and lobules
2. Lobe has numerous serous acini, numerous intercalated ducts with less connective tissue
3. Salivary glands are compound tubuloacinar glands
4. Acini or alveoli- small, sac-like dilations located at the end of the first part of the excretory duct system called the intercalated ducts
5. Serous acini- serous cells surround small lumen. Each serous cell is pyramidal in shape with round nucleus in the lower half and zymogen granules in the upper half due to which cytoplasm stains dark with eosin
6. Intercalated duct- simple cuboidal epithelium, striated duct- simple cuboidal to columnar epithelium with infoldings of the cell membrane at the base, interlobular/ interlobar duct- pseudostratified columnar to stratified cuboidal epithelium
7. Myoepithelial cells contractile in nature, present in both type of alveoli, intercalated ducts. Flat, highly branching cells surround the acini between acinar cells and basement membrane. Helps in expelling secretory products from the acini.

Mucous salivary gland:

1. Covered by connective tissue capsule which send septa along with blood vessels and nerves into gland dividing into lobes and lobules
2. Lobe has predominantly mucous acini, few serous acini, few intercalated ducts, more of striated ducts
3. Mucous acini- mucous cells surround large lumen. Each mucous cell is columnar in shape with flat nucleus pushed towards the basement membrane and the cytoplasm appears pale, frothy due to washing off of mucinogen granules during the slide preparation

Mixed salivary gland:

1. Covered by connective tissue capsule which send septa along with blood vessels and nerves into gland dividing into lobes and lobules
2. Lobe has mucous acini, serous acini, serous demilune (crescents of Gianuzzi), very few or absent intralobular ducts, more number of interlobular ducts, more amount of connective tissue
3. Serous demilune / crescents of Gianuzzi- mucous acini capped with serous cells in the form of half moon or crescent shape

Placenta:

1. It has fetal part and maternal part
2. Fetal part: covered by amniotic membrane, mesoderm with blood vessels, chorion.
3. Chorionic villi- Primary chorionic villi (core of cytotrophoblast cells covered by syncitiotrophoblast), secondary villi (core of mesoderm covered by cytotrophoblast and syncitiotrophoblast), tertiary villi (core of mesoderm with fetal blood vessels covered by cytotrophoblast and syncitiotrophoblast)
4. Intervillous spaces: filled with maternal blood
5. Maternal surface formed by decidua basalis, with endometrial blood vessels

Umbilical cord:

1. Covered by amniotic membrane
2. It has two umbilical arteries and one umbilical vein surrounded by Wharton's jelly (embryonic mesoderm)
3. Wharton’s jelly is a mass of loose connective tissue with fibroblasts separated by fine collagen fibers and ground substance containing hydrated glycosaminoglycans rich in hyaluronic acid
4. The two umbilical arteries carry deoxygenated blood from the fetus to the placenta and one umbilical vein that returns oxygenated blood from the placenta to the fetus.