Histology Pre-Final Reviewer PDF

HISTOLOGY PRE FINAL REVIEWER blood to the arteries of both the systemic and pulmonary Flow of Blood through the Heart CIRCULATORY SYSTEM - It is the organ system that delivers circulations....

HISTOLOGY PRE FINAL REVIEWER blood to the arteries of both the systemic and pulmonary Flow of Blood through the Heart CIRCULATORY SYSTEM - It is the organ system that delivers circulations. Superior vena cava, Inferior vena cava, and Coronary sinus ( nutrients, oxygen hormones and other needed substances to the Four chambers of the heart: Right and left ventricle the vein into which the cardiac veins drain) bring cells of the body from various points of origin. It also moves the and Right and left atria unoxygenated blood from the different parts of the body to the carbon dioxide and waste and secretory products generated by the Atria comprise the superior while the Ventricles occupy right atrium. Blood goes into the right ventricle through the cells to their disposal areas and or target organs. additionally it the inferior part of the heart tricuspid orifice. Right ventricle contracts, bringing blood into aids in fighting of pathogenic microorganisms by transporting the Left ventricle - is the pump of the systemic circulation the pulmonary trunk which carries the blood to the lungs for cells and substances needed for this purpose. Right ventricle - is the pump of the pulmonary oxygenation. From the lungs, oxygenated blood is brought back circulation to the heart’s left atrium by the pulmonary veins. Blood goes to Two closely related systems make up the circulatory system: Interatrial Septum - The chambers on the right side of the left ventricle through the mitral orifice. Left ventricle cardiovascular system (blood) and lymph vascular system the heart are separated from those on the left superiorly contracts, bringing blood into the aorta which distributes the (lymph). Interventricular Septum - The chambers on the right oxygenated blood to all parts of the body. side of the heart are separated from those on the left Cardiovascular system inferiorly Pericardium - This connective tissue envelops the heart. Consist of the heart and the blood vascular system, The right atrium communicates with the right 1. Fibrous pericardium - External pouch, lines the central which refers to the blood vessels that form a closed ventricle via the right atrioventricular orifice mediastinum and has dense connective tissue. circuit to and from the heart. (tricuspid orifice) which is guarded by the right 2. Serous pericardium - Has two layers (parietal and Three types of blood vessels: Capillary, Artery, Vein atrioventricular valve (tricuspid valve) visceral) because during development, the heart and the Capillaries - connect the terminal branches of the The left atrium communicates with the left ventricle great vessels which lie on the internal surface of the arteries to the initial tributaries of veins. through the left atrioventricular orifice (bicuspid fibrous pericardium invaginate it from behind. Arteries - bring blood from the heart to the capillaries orifice; mitral orifice) which is guarded by the left Parietal pericardium - The more external of Veins - bring blood from the capillaries back to the atrioventricular valve (bicuspid valve; mitral valve). the layers of the serous pericardium adheres to heart. Superior and inferior vena cavae - Are continuous the fibrous pericardium. Made up of loose Heart and the blood vessels comprise to continuous with the right atrium connective tissue that is covered on its free systems of tubes: Pulmonary circulation and Systemic Pulmonary trunk - Are continuous with the right surface by mesothelium. circulation ventricle Visceral pericardium - the more internal layer Pulmonary circulation - brings blood from the heart to Pulmonary veins left and right - are continuous with adheres to the heart. Also covered on its free the lungs and then back to the heart the left atrium surface by mesothelium, it is synonymous with Systemic circulation - brings blood from the heart to all Aorta - Are continuous with the left ventricle the epicardium. the other tissues and organs of the body and then back to Semilunar orifices - in the ventricles, refers to the Pericardial cavity - The space between the the heart orifices of the pulmonary trunk and the aorta parietal and the visceral pericardia which Semilunar valves - pulmonic and aortic valves are one contains a small amount of fluid (pericardial Heart - Is a hollow muscular organ about the size of a clenched way valves that guard fluid). fist which is located in the central mediastinum of the thoracic Pericardial fluid - Amounts to 15 to 50 ml in cavity by contracting it acts as a pump (systole) that propels adults, it reduces friction within the  pericardium by lubricating the luminal surface cardiac muscle fibers (cells). They are arranged in sheets fibers. They are seen to be larger, paler, and containing more of the visceral and parietal pericardia which that wind around the atria and the ventricles in a glycogen in their cytoplasm than the typical cardiac muscle cells. allows the membranes to easily glide over each complex spiraling course they originate and insert into They interconnect with each other through a variety of cell to cell other when the heart contracts. the cardiac skeleton. They secrete two polypeptide attachments including desmosomes, gap junctions, and fascia Mesothelial cells - Are serous secreting cells hormones: adherence to comprise the impulse conducting system of the that are responsible for elaborating pericardial Atrial Natriuretic Peptide (ANP) & Brain heart. The impulse conducting system of the heart has several fluid. Natriuretic Peptide (BNP) - Participate in components: Sino atrial node, 3 internodal tracts, cardiorenal homeostasis and whose target atrioventricular node, AV bundle of his, 2 bundle branches Histologic layers of the heart organs are the kidneys, adrenals, pituitary gland and purkinje fibers. 1. Endocardium - The thinnest histologic layer of the and brain. heart it lines all the internal surfaces of the heart and is 3. Epicardium - Synonymous with the visceral SA node - Consist of a dense network of interwoven purkinje continuous with the innermost histologic layer of the pericardium, forms the outermost histologic layer of the fibers that are slightly smaller than those found elsewhere in the great vessels that enter and exit the heart. Four heart. consists of loose connective tissue that is lined on heart it is about 10 mm in length and 3 mm in width it is located histologic layers of endocardium: its external surface by mesothelium. embedded in the sub epicardially at the boundary of the right atrium and the Endothelium - The layer that adjoins the epicardium are networks of elastic fibers, blood vessels superior vena cava. It is also called the cardiac pacemaker cardiac lumen is a simple squamous epithelium and nerves. Contains a lot of adipose cells. because its purkinje fibers generate the electrical impulse Subendothelium - Deep to the endothelium is (cardiac impulse) that initiates cardiac contraction. The impulse a very thin layer of loose connective tissue Cardiac skeleton - Dense connective tissue that forms the central from the sa node is propagated to the atrial musculature and Denser connective tissue - External to the sub support of the heart into which the cardiac muscles and valves are reaches the av node via 3 small bundles of perkinje fibers to wit: endothelium that comprises the thickest portion attached. It has three components: anterior internobal tract (of Bachman); middle internoudal of the endocardium. this layer contains Septum membranaceum - Refers to the part of the tract (Wenckebach); posterior internobal tract (of Thorel). abundant collagen fibers fibroblast and a great cardiac skeleton that is in the interventricular septum number of elastic elements as well as smooth Annuli Fibrosi - Surrounds the AV and semilunar AV node - Is another collection of purkinje fibers it is about 6 muscle cells which are numerous over the orifices mm long and 2 to 3 mm wide and is located in the myocardium interventricular septum. Trigona Fibrosa - Between the semilunar and the AV of the posterior lower part of the interatrial septum. From the AV Subendocardium - External to the dense orifices node, the cardiac impulse is propagated into the AV bundle (of connective tissue, this layer is another loose his), which is the direct continuation of the AV node. The AV connective tissue. It is a misnomer because the Cardiac valves - The AV and semilunar valves are similar in bundle (of his) is located in the dense connective tissue of the layer is part of the endocardium. It contains structure microscopically. They consist of reduplicated trigonum fibrosum. It is formed by purkinje fibers that course many blood vessels and nerves and many of the endocardia and a core of dense connective tissue that is downward towards the ventricles. At the area of the septum purkinje fibers that comprise the impulse continuous with the annuli fibrosi. membranaceum, the av bundle bifurcates to form the right and conducting system of the heart. left bundle branches. The right bundle branch runs downward 2. Myocardium - Lies external to the endocardium, The Purkinje fibers - The contraction of the cardiac muscle fibers is along the periphery of the septum membranous in the thickest layer of the heart. it is the thickest in the left triggered by electrical impulse that is generated and propagated subendocardium of the right ventricle. In the interventricular ventricle and thinnest in the atria. consist of mainly by a population of non-contractile modified cardiac muscle septum, it splits into many fine branches that are simply called purkinje fibers, which spread through the musculature of the layer of endothelial cells that rest on a basal lamina they Histologic layers of arteries and veins entire right ventricle. The left bundle branch is also in the lie on a bed of connective tissue. They are 7 to 9 1. Tunica intima - Consists of an endothelium and subendocardium but of the left ventricle. It ramifies and its micrometer. Red blood cells have to pass through most subendothelial layer. In most arteries a third histologic numerous branches supply the myocardium of the left ventricle. capillaries in single file and with difficulty. This heavy layer is present in the tunica intima this layer consists of traffic condition allows time for exchange of gases to the nonfibrillar form of elastin, lies external to the Blood and lymph vessels and nerves of the heart take place between the red blood cells and the subendothelial layer and is known as the internal elastic The heart wall is supplied by the right and left coronary surrounding tissue. Capillary endothelial cells have an lamina. The endothelial cells of arteries are often seen arteries that arise from the ascending aorta. Cardiac veins drain ovoid or elongated nucleus that bulges into the lumen of in electron micrographs to contain rod shaped it. Anastomoses among the branches of the coronary arteries exist the vessel while their attenuated cytoplasm is clear to cytoplasmic inclusions called Weibel-Palade bodies or but they are insufficient in providing alternate routes for blood finely granular. granules Because they are storage sites for the von circulation in case of obstruction to the major vessels. Willebrand factor, Which is a large protein that is Consequently, the coronary arteries are functionally end arteries. Pericytes - Associated with capillaries that are slender elongated necessary for normal coagulation of blood. Most of the cardiac veins empty into the coronary sinus, which cells that look like fibroblasts. They envelop but are not part of 2. Tunica media - Mainly made up of concentrically in turn opens into the right atrium. The heart receives efferent the wall of capillaries. They influence the luminal size of arranged smooth muscle fibers. The external elastic nerve fibers from the vagus nerve (CN X) and sympathetic capillaries because they contain actin, myosin, tropomyosin and lamina is external to the smooth muscle layer. It is made division of the autonomic nervous system. desmin which makes them contractile. Some are phagocytic and up of nonfibrillar form of elastin. some serve as stem cells that when needed as in case of injury 3. Tunica adventitia - made up of loose connective tissue Blood vascular system can differentiate into endothelial or smooth muscle cells. where the cells and fibers are arranged longitudinally. The collective term for all the blood vessels in the body of which there are three types: arteries, veins, and Types of capillaries Arteries capillaries. as in the heart the luminal surface of all the 1. Continuous capillaries (Type I capillaries) - Are found 1. Small arteries (Arterioles) - their diameter ranges from blood vessels is lined by endothelium. in muscles, lungs, central nervous system and skin. 40 to 400 micrometer. They have thick walls and Endothelium - Lining material that facilitates the flow 2. Fenestrated capillaries (Type II capillaries) - Are narrow lumens that offer considerable resistance to of blood through the blood vessels and regulates the found in the mucous membranes of the gastrointestinal blood flow. The branch of the smallest arterioles that passage of substances and cells to and from the blood. tract, many endocrine glands, pancreas, and renal connects with a capillary is referred to as metarteriole They excrete substances including von Willebrand glomerulus. The cytoplasm of the endothelial cells is or precapillary, which control the flow of blood into factor, endothelins, prostacyclins, nitric oxide. They very thin and is pierced at intervals by “pores” that the capillary and do not form a continuous layer. The excrete substances (interleukins) that enhance the range in size from 60 to 80 nm. The pores are bridged by tunica intima of the smallest arterials consist only of activity of WBCs and induce the migration of these cells a diaphragm. endothelium and in larger vessels the tunica intima may from blood to the site of injury or infection. They 3. Sinusoidal capillaries - Are found in the parenchyma of have an internal elastic membrane. The tunica media produce growth factors that help maintain the some organs including the liver spleen bone marrow and of arterioles consist of a single layer of smooth muscle vasculature and enhance repair and regeneration of certain endocrine glands. They have irregular and large cells. The tunica advantage of arterioles is thinner than blood vessels. They also exhibit phagocytosis. cross-sectional outlines and they have true the tunica media and composed of loose connective Capillaries - Are the simplest of the blood vessels. They discontinuities in their endothelium that allow free tissue that merges with surrounding connective tissue. have a very thin wall that consists simply of a single passage of blood. 2. Medium arteries (Muscular Arteries; Distributing amount of connective tissue and smooth muscle cells. 3. Veins - Typically merge and remerge to form vessels Arteries) - They have a well developed tunica media The tunica adventitia is thin and contains vasa that have progressively bigger caliber and thicker walls. that contains numerous muscle fibers. They distribute vasorum. They have larger diameter more irregular lumen and blood to the different parts of the body hence they are Diastole - When the heart is resting after a thinner wall they have more connective tissue elements also known as distributing arteries. The tunica intima contraction and are classified into three types according to their of muscular arteries shows three distinct layers: Systole - Contraction of the heart caliber: endothelium, subendothelium and internal elastic Small veins (Venules) - Diameter is 1.0 mm or membrane. The tunica media of muscular arteries is Sensory organs associated with arteries less. The tunica media can only be appreciated composed mainly of layers of circularly arranged 1. Carotid and Aortic Bodies - Sensitive to changes in that have aluminal diameter of at least 50 smooth muscle cells that are embedded in a small the O2 and CO2 tension in the blood. Carotid bodies are micrometer. The tunica adventitia of venues is amount of connective tissue. The tunica adventitia is two small structures that are embedded in the tunica thick in relation to the overall thickness of their well developed, sometimes thick and contains lymph adventitia at the bifurcation of each common carotid wall. vessels, nerves, and vasa vasorum. artery. Aortic bodies are located at the aortic arch Medium veins - Include almost all the named Vasa Vasorum - Are small blood vessels that adjacent to the right subclavian artery. veins. their diameter ranges from 1 to 9 mm. are present within the wall of large blood Type I (Glomus cells) - Chemoreceptors. They The tunica intima consists of an endothelium vessels. They supply the tissues of the blood are pale staining round or oval cells that have and a thin sub-endothelial layer that is made up vessel wall that are unable to get oxygen and few cytoplasmic processes. They have a large of a minimal amount of connective tissue. The nutrients by diffusion from the blood that nucleus and possess the usual complement of tunica media is composed of small bundles of circulates in the vessel lumen. In arteries they cytoplasmic organelles and they resemble the circularly arranged smooth muscle cells. The are confined in adventitia, however in veins chromaffin cells of the adrenal medulla. that tunica adventitia is made up of connective they are also found in media. have dance court cytoplasmic granules that tissue forms the thickest histologic layer and 3. Large arteries (Elastic Arteries; Conducting contain catecholamines. may have some vasa vasorum. Arteries) - They are called conducting arteries because Type II (Sheath cells) - Glial like and they Large veins - Inferior and superior vena cava, they serve as major conduits in the transport of blood function merely as supportive cells. their pulmonary and portal veins are examples. The away from the heart. Has a wall that is relatively thin nucleus is more irregular in shape and they do tunica intima is thicker but identical to smaller compared to the caliber of the vessel. The wall is not contain cytoplasmic granules in their veins. The tunica media is poorly developed yellowish due to the presence of an abundant amount of cytoplasm. They envelope 4-6 glomus cells. and very few smooth muscle fibers are present elastin. The tunica intima of the large artery consists of 2. Carotid sinuses - They are baroreceptors that are but vasa vasorum exists. The tunica adventitia an endothelium, a subendothelium that is made up of sensitive to stretch and are able to detect changes in is very thick and consist of three zones: loose connective tissue that has a sprinkling of smooth blood pressure within the arteries. Slightly dilated area internal zone of dense fibroelastic connective muscle cells and an internal elastic membrane. The in the left and right internal carotid arteries. The tissue, a middle zone of smooth muscle fibers tunica media is the thickest of the three histologic layer tunica media is attenuated. The tunica adventitia is that are arranged longitudinally, and an outer of a large artery, has the presence of concentrically thick and contains numerous sensory nerve fibers that zone consisting of course of not collagen and arranged sheets of elastin called elastic lamellae. 40 to form networks. They come from the glossopharyngeal elastic fibers and it is well supplied with vasa 70 in adults. In between the elastic lamellae is a variable nerve (CN IX). vasorum.  Venous valves - Semilunar folds that usually system. The wall of lymph capillaries consists simply of materials and waste products. It is also a huge sense organ that is come in pairs. They are inward projections of endothelium. receptive to touch, pain, pressure and temperature. Their cells the tunica intima and consist of a core of dense Lymph vessels has tunica intima that consist of assist in the immune response of the body and it is also a site for connective tissue that is richly supplied with endothelium and an underlying thin connective tissue production of vitamin D which occurs when 7-dehydrocholesterol many elastic elements and covered on its free layer; tunica media that is made up of one or two layers that is present in its epithelial cover reacts with ultraviolet light surfaces by endothelium. of smooth muscle cells; and tunica adventitia that is from the sun. The appendages of the skin consists of hair, nail, composed of bundles of elastic and collagen fibers. and cutaneous glands that include sweat and sebaceous glands. Modification in the organization of blood vessels Lymph vessels are interrupted along their course by The skin and its appendages are often collectively referred to as Atriovenous Anastomoses (AV Shunts) - Connect lymph nodes. the integumentary system. small arteries directly to small veins. They form a large Lymph vessels all over the body ultimately drain into the number of small histologically recognizable bodies two lymphatic ducts: Layers of the skin called glomera that are richly supplied with nerve fibers ❖ Right lymphatic duct - Smaller and shorter. Epidermis - The more superficial layer is an epithelial that regulates the body temperature. All the lymph that lymph vessels collect from coat derived from ectoderm. Portal systems - An artery or vein is interposed between structures on the right side of the body above Dermis (Corium)- Is made up of connective tissue two sets of capillary beds. the diaphragm. It drains its lymph into the right derived from mesoderm. brachiocephalic vein at the junction of the Lymph Vascular System - Substantial amount of water and internal jugular and subclavian veins. Dermal papillae - Tissue elements of the dermis form irregular some plasma proteins leak out from the cardiovascular system ❖ Thoracic duct - Collects the lymph from the conical projections that invade the epidermis to interdigitate with into the interstitial space through the walls of the capillaries and parts of the body that are not served by invaginations of the epidermis called epidermal ridges. this system collects the escapees from plasma and return them to tributaries of the right lymphatic duct. It drains the venous side of the circulation. its lymph into the venous system at the junction Hypodermis or Subcutaneous Tissue - The dermis is anchored Lymph capillaries - Smallest tubes that comprise the of the left jugular and subclavian veins. to the underlying tissues by loose connective tissue that contains system fluid from the interstitial space and turns the numerous adipose cells. lymph vascular system via SKIN AND ITS APPENDAGES Lymph - When interstitial fluid enters the lymph SKIN - Also called the integument, is the tough protective Epidermis - Is a keratinized stratified squamous epithelium. capillaries. It is a milky substance which aside from external covering of the body that is continuous with the mucosa It’s most superficial layer is continuously shed such that the water and proteins contains lymphocytes and fat droplets that lines the mouth, nose, anal canal, genital openings and eyes. epidermis is completely renewed every 20 to 30 days. This (chylomicra). It is the largest organ of the body in terms of weight accounting renewal process is the responsibility of the keratinocytes, the Lymph capillaries unite to form small lymph vessels for about 15% of a person's body weight. Its surface area in principal cells of the layer. which in turn unite to form successively larger vessels adults exceeds 1.5 m2. Its thickness ranges from 0.5 to 5.0 mm that ultimately converge into two large lymph ducts that depending on its location. The thinnest is on the eyelids and the Keratinocytes - Comprise 85% to 95% of the cell population of drain into veins at the base of the neck. thickest is on the soles of the feet. It prevents harmful substances the epidermis. They are cells that are specialized to produce Lymph capillaries are present in all tissues, organs, and from entering the body, loss of body fluids and prevents the sun's keratin, an intermediate filament that is also present but in much organ systems of the body except in cartilage, bone and ultraviolet rays from damaging underlying tissue. It also forms lesser amounts in other epithelial cells. bone marrow, teeth, placenta and the central nervous sweat that helps regulate body temperature and excrete waste Types of skin (Thick and Thin) Stratum Granulosum - Consist of three to five layers of Other cell types in the epidermis THICK - The epidermis is 0.4-1.4 mm thick. Dermal papillae is keratinocytes that are more flattened. The keratinocytes have a Melanocytes - Cells that are specialized to produce longer. Contains numerous sweat glands but lacks hair follicles pyknotic nucleus and degenerated cytoplasmic organelles. There melanin pigment. They are present in certain parts of the and sebaceous glands. is a presence of numerous dark basophilic granules in their body notably the skin and uvea in the eye. in the skin ❖ Covers the palms and soles. Its epidermis consist of cytoplasm called keratohayaline granules That contain a they comprise seven to 10% of the cell population of the five layers from the deepest to the most superficial: histidine rich protein called profillagrin which when the cells epidermis some melanocytes are also present in the 1. Stratum basale (stratum germinativum) reach the stratum corneum becomes fillagrin that provides the superficial region of the dermis. They appear as “clear 2. Stratum spinosum (prickle cell layer) interfilamentous matrix for the aggregation of keratin filaments. cells” that are difficult to tell apart from the other clear 3. Stratum granulosum There is also a presence of membrane bound lipid containing cells in the skin but can be distinguished with the aid of 4. Stratum lucidum (clear layer) secretory granules called lamellar granules in the cytoplasm special methods such as the DOPA technique, The 5. Stratum corneum (horny cell layer) because they consist of closely packed parallel lamellae, they highly branched processes of the melanocytes are ❖ Cornified layer - Stratum cornium and stratum lucidum form an important barrier against the entry or exit of substances selectively blackened and the cells become ❖ Stratum Malpighii - The three other layers to and from the body. The keratinocytes in the stratum recognizable.They are small cells with rounded bodies granulosum can no longer divide because they are dead cells. and long but thin processes that are in contact with Stratume Basale (Stratum Germinativum) - Consist mainly of neighboring keratinocytes their cytoplasm contains a fair a single layer of tall cuboidal keratinocytes that rest on a Stratum Lucidum (Clear layer) - Consist mainly of 4 to 6 share of organelles and many electron dense membrane basement membrane that have large nucleus and basophilic layers of flat dead anucleate keratinocytes that form a light bound granules called melanosomes, Where melanin is cytoplasm and contains numerous ribosomes, golgi complex, staining translucent and discontinuous layer superficial to the formed from the amino acid tyrosine through a series of endoplasmic reticulum, a limited number of mitochondria, and a stratum granulosum. The keratinocytes in this layer are already enzyme catalyzed chemical reactions. Each melanocyte few keratin filaments. They are bound on their lateral and upper devoid of organelles but their keratin filaments form thick supplies up to 30 keratinocytes with melanin. a surfaces to neighboring cells by desmosomes and to the basal bundles that are parallel to the skin surface. melanocyte and the keratinocytes that it supplies with lamina by hemidesmosomes. melanin are collectively referred to as an epidermal Stratum Corneum (Horny cell layer) - Consists of 15 to 20 melanin unit. Stratum Spinosum (Prickle Cell Layer) - Consist mainly of rows of latent keratinocytes whose cytoplasm consist entirely of ❖ Skin color is an admixture of three pigments: polyhedral keratinocytes that are arranged into several layers. keratin filaments that are embedded in an amorphous matrix. carotene, a substance that is present in the These cells are shorter and less intensely basophilic in routine Squames comprising the stratum disjunctum are free of each intercellular substance of the epidermis that histologic preparations. Their cytoplasm contains the same other and get continuously shed off or desquamated. gives the skin a yellowish hue; hemoglobin, organelles but their keratin filaments are more numerous and they the red oxygen carrying pigment present in the form bundles called tonofibrils that also converge and insert into THIN - The epidermis is 0.075-0.75 mm thick. Dermal papillae rbcs that circulate in the capillaries of the the numerous desmosomes. The keratinocytes are still tightly is shorter. Contains sweat glands, hair follicles, sebaceous dermis; and melanin that gives skin its brown bound to their neighbors by desmosomes because they are the glands.Covers the whole body except the palms and soles: to black shade. only cell to cell junctions that exist among the cells of the stratum spinosum is much thinner, stratum granulosum is poorly epidermis. They appear as spines or hairs that protrude out of the developed or absent, does not have stratum lucidum, stratum Langerhan cells - Are myeloid related dendritic cells, cells that is the reason why it is referred to as “intercellular corneum is much thinner. The epidermis has only three layers: antigen presenting cells (APCs) that are present not only bridges”. They are merely preparation artifacts. stratum basale, stratum spinosum, stratum corneum. in the skin but also in other stratified squamous epithelia  such as those in the oral cavity esophagus and vagina. In Dermis (Corneum) - It is much thicker than the epidermis and Hypodermis (Subcutaneous tissue) - Refers to the loose the skin they are mostly in the epidermis where they ranges from 0.6 mm on the eyelid to 4.0 mm on the back. It is connective tissue that binds the dermis of the skin to the comprise 3 to 8% of the cells but a limited number are composed of connective tissue that forms two histologic layers: underlying structures. in many areas of the body it allows the skin scattered in the dermis. In the epidermis, langerhan cells papillary and reticular. to slide over the underlying structures but it is not a part of the are most numerous in the stratum spinosum. They are Papillary layer - Is the more superficial of the two skin. It contains numerous adipose cells except over the eyelids, clear cells that look similar to melanocytes with their layers of the dermis. Made up of loose connective tissue penis, scrotum, nipples, and areola, where the subcutaneous dark nucleus and pale staining cytoplasm but with the and is well demarcated from the epidermis by the latter's tissue is notably devoid of these cells. in individuals who are use of special techniques such as staining with gold basement membrane. The connective tissue contains overnourished the adipose cells in the hypodermis over certain chloride the dendritic nature of their process become type VII collagen fibers that insert into and help areas of the body are particularly numerous and they form layers apparent and they become distinguishable. Langerhan anchor the papillary layer into the basement membrane of adipose tissue called panniculus adiposus. cells in the epidermis are easy to identify because they of the epidermis. The bulk of the connective tissue that lock desmosomes and keratin filaments; they also comprises the papillary layer form conical projections Nerve endings in skin contain rod shaped membrane bound granules called into the epidermis called dermal papillae, Which are Simple nerve endings (free nerve endings) Birbeck granules or vermiform granules, whose more numerous in areas that are subjected to great Expanded tip nerve endings (merkel discs) function is undetermined yet. In the embryo, langerhan pressure such as the soles of the feet their core contains Encapsulated nerve endings (Ruffini’s corpuscles, cells are derived from the bone marrow they colonize capillary bed that supplies the overlying epidermis with end bulbs of Krause, Vater-Pacinian Corpuscles, and the skin as early as the 5th or 6th week of embryonic blood and nerve endings. Meissner’s Corpuscles. life. Reticular layer - Is thicker than the papillary layer. It is Efferent nerve fibers - Regulate the activity of its Merkel cells - Are the list in number among the cell responsible for the toughness and strength of skin. It glands and smooth muscle cells including those in blood types in the epidermis they usually occur singly and consists of dense irregular connective tissue that is vessels occasionally in clusters in the basal region of the richly supplied with blood vessels and whose collagen epidermis in all parts of the body but they are the most fibers form coarse bundles that are mostly oriented Appendages of the skin - Are structures that are derived from numerous in the palms and soles. merkel cells also parallel to the skin. They provide elasticity to the skin. the epidermis. They have specific functions and are mostly appear as clear cells they are distinguishable under the Sweat glands, sebaceous glands, and hair follicles, are confined to the dermis and consist of hair, nail, and cutaneous light microscope only if specific immunohistochemical embedded in the connective tissue of the reticular layer. glands namely the sebaceous glands and sweat glands. techniques are applied. Merkel cells are disc shaped smooth muscle cells are also present in this layer of the cells with short cytoplasmic processes they are bound to dermis. Those that are associated with hair follicles form Hair - Is a filamentous keratinized structure that covers neighboring keratinocytes by desmosomes their bundles called arrector pili muscles. In areas such as practically the whole body except the lips, palms, soles, distal cytoplasm is shown to be devoid of keratin filaments but the scrotum in males and areola of the breast in females dorsal parts of the fingers and toes, prepuce, and glands of the has small granules with electron dense course that the smooth muscle fibers form interlacing bundles in the penis, labia minora and inner surface of the labia majora, clitoris contain a hormone similar to the catecholamine secreted deep part of the reticular layer. In the head and neck and nipple. The part of a hair that projects from the surface of the by the adrenal medulla. It is supplied with an axon connective tissue bands in the reticular layer serve as skin is called shaft, while the part that is embedded in the skin is termination of a sensory neuron that penetrates the basal insertions of skeletal muscle that comprises the muscles called root. the hair roots are implanted obliquely. lamina and they form a merkel disc, a sensory of facial expression. mechanical receptor that responds to pressure and touch. Hair follicle - Each hair root is enclosed by two epithelial Medulla - Absent in thin hair, occupies the core of hair. It is Internal root sheath - Surrounds the initial segment of the hair sheaths, external and internal root sheaths. A hair root and its formed by the cells of the hair matrix that immediately surrounds and is formed by the multiplication and differentiation of the sheaths comprise hair follicle. Associated with each hair follicle the apex of the dermal papilla. When these cells differentiate they most peripheral cells in the hair matrix. It consists of three are one or more sebaceous glands whose ducts open into the transform into large vacuolated cells that contain little keratin concentric layers but as the cells of the internal root sheath move upper third of the follicle and also associated with a hair follicle filaments. They degenerate and die thus the medulla of mature upward they degenerate and die such that above the level of the is the arrector pili muscles, a thin smooth muscle whose one end hair consist of dead and disintegrating vacuolated cells. sebaceous glands, the inner root sheath is no longer present. is attached to the connective tissue surrounding the hair follicle at end is attached to the connective tissues surrounding the hair Cortex - Surrounds the medulla and is the thickest of the External root sheath - Envelopes the internal root sheath. It follicle at about its mid length. This muscle courses close to the concentric layers of hair. It is formed by the cells in the hair consists essentially of the epidermis of the skin that was pulled sebaceous gland that is associated with the hair follicle before it matrix that externally surround the medulla producing cells. downwards by that invaginating hair follicle. Near the skin attaches its other end to the dermis. Contraction of the arrector When cells differentiate they transform into fusiform cells that surface, it exhibits all the layers of the epidermis of thin skin. But pili muscle straightens the hair and forces out the secretions from synthesize a large amount of keratin filaments. they also produce the deepest portion of the hair follicle is reduced to a single layer the acini of the sebaceous gland. Simultaneous contraction of numerous trichoyaline granules that contain an insoluble that corresponds to the stratum basale of the epidermis. The numerous arrector pili muscles result in “goose pimple” or protein, trichoyalin, which is produced by the cells of the external root sheath is separated from the dermis by a thick “goose flesh”. In actively growing hair, the hair follicle has an stratum granulosum in the epidermis, is an immediate filament basement membrane referred to as glassy membrane. expanded bulbous proximal portion called hair bulb. The base of associated protein that serves to aggregate keratin filament the hair bulb has a deep concavity which is occupied by a hair bundles. Lanceolate endings - Nerve endings that are in contact with hair papilla which consists of connective tissue where capillaries that bulbs and which resemble Meissner’s corpuscles structurally. supply the hair follicle with nutrients and oxygen are embedded. Cuticle - Is the thinnest of the three concentric layers of hair. It is The epithelial cells in the bulb that are associated with the hair formed by the cells in the hermatrix that externally surround the Nails (nail plates) - Cyst of heavily keratinized epithelial cells papilla form the hair matrix that envelopes the papilla. cortex producing cells. When these cells differentiate, They that form protective covers on the dorsal surfaces of the terminal transform into flattened cells that synthesize a lot of keratin. In ends of the digits. They grow continuously but those in the In hair, the counterparts of the cell in the stratum basale of the mature hair the cuticle consists of several layers of dead flattened fingers grow faster than those in the toes. In the same limb, the epidermis are the cells of the hair matrix; they are the cells that but heavily keratinized cells. nail of the middle digit grows faster than the others. proliferate and get pushed upward as they differentiate, degenerate and die. They also produce hard keratin hence when A hair follicle has an active growth period (anagen) that Nail plate - Is essentially synonymous with the stratum corneum the cells die they are not shed but rather they stick to each other alternates with arrest period (telogen). There is a brief third of the epidermis. It rests on a nail bed which consists of the and string out to form hair. Scattered among the cells of the hair period (catagen) between anagen and catagen characterized. In stratum spinosum and stratum basale of the underlying epidermis. matrix are melanocytes, the cells responsible for the color of the the scalp the growth period lasts for 2 to 4 years and the rest Growth occurs at the nail matrix, which is part of the nail root. hair. period lasts for about 3 months. The eyebrow is only from 1 to 2 The distal edge of the nail plate hangs free but its proximal part, months while the rest period is 3 to 4 months. the nail root, is mostly hidden in the nail groove. The nail root Mature hair has three distinct concentric histologic layers: extends from the lunula, the white crescent shaped area at the medulla, cortex, and cuticle. Sheaths of hair proximal exposed region of the nail plate to the nail matrix, the Internal root sheath and External root sheath form the outer most proximal region of the nail plate. In the nail groove, the nail layers of the hair follicle. plate is covered on both its dorsal and ventral surfaces by layers of the epidermis that covers the dorsal surface of the nail plate is Sweat Glands - Has two types of sweat glands: Eccrine and The dock of the sweat gland is lined by stratified cuboidal referred to as the nail fold. At the lunula, the distal end of the nail Apocrine. epithelium that consists of two layers of cuboidal cells. It drains fold is highly keratinized and referred to as eponychium (nail into the skin surface through an orifice called sweat pore. The cuticle). It consists of the stratum corneum of the overlying skin. Eccrine sweat glands - Are much more numerous than apocrine cells of the duct that help prevent excessive loss of electrolytes Under the free end of the distal part of a nail is a thickened sweat glands, which is why the term sweat gland, unless from the body by absorbing some of the sodium ions in sweat. accumulation of stratum corneum called hyponychium. qualified, refers to eccrine sweat glands.Widely distributed in the skin all over the body, but are most numerous on the palms and Sweat glands are merocrine glands whose primary function is to Nail growth is the function of the cells of the nail matrix, which soles. estimates put the number of echin sweat glands in the body help regulate body temperature. They do this by producing a clear corresponds to the cells of the stratum basale of epidermis. These at 3 million, about 250,000 of which are in the soles. the only fluid, called sweat, evaporates on, and cools, the skin surface. cells differentiate into a single type of highly keratinized cells. skin areas where they are absent or those in the margins of the They also excrete some waste materials and products from the lips, concha of the external ear, nipple, labia minora, glans and body. Sebaceous glands - Are essentially appendages of hair; hence prepuce of the penis. they are found in all areas where hair is present. on the average Modified sweat glands - Are likewise present in there are about 100 sebaceous glands per square centimeter of The sweat gland is a simple coiled tubular gland- both its certain parts of the body (glands of Moll in the eyelids, skin. But on the face, forehead, and scalp, they are numerous secretory portion and duct are coiled. Its secretory portion, which whose secretions are released into the follicles of the (400 to 900/cm2) during puberty stimulated by testosterone in has a slightly bigger diameter than its duct, is embedded deep in eyelashes; glands of Zeis, Are the usual sites for styes; men and the ovarian and adrenal androgens in women, they the dermis and the hypodermis. It consists of a pseudostratified Ceruminous glands of the external auditory canal, become very active and give rise to acne and pimples. They are low columnar epithelium that is seen to contain three types of which produces cerumen; and the mammary glands, simple branched alveolar glands that are embedded in the cells: light, dark, and myoepithelial cells. which secrete milk. dermis and occasionally also in the hypodermis. They are Light cells - Rest on a basal lamina, are broad on their holocrine glands, which means their secretory products consist basal portion but tapering towards the lumen. They Apocrine Sweat Glands - found only in the axilla, around the not only of the secretion of cells but also of the cells that produce secrete water entrolite and are responsible for most of anus, areola of the breast, and labia majora. They are also coiled these secretions. Acinus of a sebaceous gland is seen as the watery component of sweat. tubular glands but are much larger (secretory portion = 3 to 5 consisting of a single layer of flattened or cuboidal peripherally Dark cells - Are broad at their luminal surface and mm in diameter) than the eccrine sweat glands (secretory portion located cells (basal cells) that surround a mass of larger paler narrow at their base. They are smaller and fewer than the = 0.4 mm in diameter). Their ducks are lined by a stratified staining fat droplets containing cells that are at various stages of clear cells. They contain dance glycoprotein containing cuboidal epithelium. Myoepithelial cells are associated with the differentiation. The basal cells have a spherical nucleus, the usual secretory granules in their cytoplasm that are responsible acini. Apocrine sweat glands only become functional at puberty complement of organelles, and some fat droplets. The typical for the dark appearance of the cells. The granules because their secretory cells lose their apical cytoplasm into their sebaceous gland has a short duct that is lined by stratified contain glycoproteins with bactericidal activity. secretion. They are also merocrine glands. squamous epithelium that is continuous with the external root Myoepithelial cells - Are morphologically similar to sheath of the hair follicle. Secretory product of sebaceous glands those present in other exocrine glands, are located is called sebum. It is produced in the alveoli of the gland as between the secretory cells and the basal lamina. Their follows. Sebum lubricates hair and possibly helps maintain the contraction helps propel secretion of the secretory cells soft texture of skin. into the ducts.