practice

Explanation

         Fibroblast is the principal cell of connective tissue. Fibroblasts are responsible for the synthesis of collagen, elastic and reticular fibers, and the complex carbohydrates of the ground substance. Ground substance occupies the space between the cells and fibers (intercellular space). Research suggests that a single fibroblast is capable of producing all of the extracellular matrix components.

Explanation

Capillaries are the smallest diameter blood vessels, often smaller than the diameter of an erythrocyte. Based on their morphology, 3 types of capillaries are distinguished: continuous, fenestrated and discontinuous (sinusoidal) capillaries. Sinusoidal capillaries are typically found in the liver, spleen and bone marrow. They are bigger in diameter and more irregularly shaped than other capillaries, the basal lamina underlying the endothelium may be partially or even completely absent.

Fenestrated capillaries are found in endocrine glands and sites of fluid and metabolite absorption such as gallbladder and intestinal tract. Continuous capillaries are typically found in muscle, lung and the CNS.

Explanation

Explanation

Satellite cells are interposed between the plasma membrane of the muscle fiber and its external lamina. They are small cells with scant cytoplasm. Satellite cells function as stem cells that, after injury, proliferate to give rise to new myoblasts. As long as the external lamina remains intact, the myoblasts fuse within the external lamina to form myotubes, which then mature into a new fiber.

Explanation

Trachea → main (primary or large) bronchi → lobar (secondary or median) bronchi → segmental (tertiary or small) bronchi → bronchioles (terminal bronchiole → respiratory bronchiole) → alveoli.

As the bronchi decrease in size because of branching, the cartilage plates become smaller and less numerous. The second change observed in the wall of the intrapulmonary bronchus is the addition of smooth muscle to form a complete circumferential layer. The smooth muscles become an increasingly conspicuous layer as the amount of cartilage diminishes. The muscularis layer is more attenuated and loosely organized in smaller bronchi where it may appear discontinuous because of its spiral course. 

Explanation

Alveolar epithelium is composed of type I and II alveolar cells and occasional brush cells. Type II alveolar cells or type II pneumocytes or septal cells are secretory cells. Their apical cytoplasm is filled with granules as stacks of parallel membrane lamellae, the lamellar bodies. They are rich in a mixture of phospholipids, neutral lipids and proteins that is secreted by exocytosis to form an alveolar lining, surface-active agent called surfactant.

Explanation

Explanation

Explanation

Explanation

Explanation

Metaphysis is a portion of the bone between epiphysis and diaphysis. During bone growth, the metaphyseal plate is responsible for the longitudinal growth of the bone. Actual lengthening of the bone occurs when new cartilage matrix is produced at this plate. Production of new cartilage matrix pushes the epiphysis away from the diaphysis, elongating the bone. The events that follow this incremental growth, namely: hypertrophy, calcification, resorption and ossification, simply involve the mechanism by which the newly formed cartilage is replaced by bone tissue during development.

Explanation

Juxtaglomerular apparatus is formed by 3 different structures:

·        Macula densa: is the end portion of thick ascending segment as it opens into the distal convoluted tubule. It is situated between the afferent and efferent arterioles of the same nephron. It is very close to afferent arteriole. Macula densa is formed by tightly packed cuboidal epithelial cells.

·        Mesangial cells: are situated in the triangular region bound by afferent arteriole, efferent arteriole and macula densa.

·        Juxtaglomerular cells: are specialized smooth muscle cells situated in the wall of afferent arteriole just before it enters the Bowman’s capsule.

Explanation

Seborrhea is a chronic relapsing but usually mild dermatitis. It is an inflammatory skin disorder affecting the scalp, face and torso. Typically, it presents with scaly, flaky, itchy and red skin. It particularly affects the sebaceous-gland-rich areas of skin. It is a malfunction of the sebaceous glands; And vitamin imbalance play a leading role in the pathogenesis of this disease.

Explanation

Monocytes are the precursors of the cells of the mononuclear phagocytic system. Monocytes are the largest of the white blood cells in a blood smear. They travel from the bone marrow to the body tissues, where they differentiate into the various phagocytes of the mononuclear phagocytic system i.e. connective tissue macrophages (histiocytes), osteoclasts, alveolar macrophages, perisinusoidal macrophages in the liver (kupffer cells) and macrophages of lymph nodes, spleen and bone marrow, among others. Monocytes remain in the blood for only about 3 days. Monocytes transform into macrophages, which function as antigen presenting cells in the immune system.

Explanation

The mucosa layer of the bronchi is composed of pseudostratified epithelium with the same cellular composition as the trachea. The basal cells serve as a reserve cell population (regenerative property) that maintains individual cell replacement in the epithelium. Basal cells tend to be prominent because their nuclei form a row in close proximity to the basal lamina. Although nuclei of other cells reside at this same general level within the epithelium, they are relatively sparse. Thus, most of the nuclei near the basement membrane belong to basal cells.

Explanation

The tunics of veins are not as distinct or well defined as the tunics of arteries. Veins are divided into 3 types:

* Small veins/venules: postcapillary and muscular venules

* Medium veins

* Large veins

Arteries:

·        Large or elastic arteries

·        Medium or muscular arteries

·        Small arteries and arterioles

Muscular venules are distinguished from postcapillary venules by the presence of a tunica media. Postcapillary venules possess an endothelial lining with its basal lamina and pericytes. Postcapillary venules have no true tunica media.

·        Tunica intima: consists of endothelium with its basal lamina

·        Tunica media: smooth muscle cells

·        Tunica adventitia: collagen fibers

A vessel without tunica media, also lack muscular tissue. Muscular artery, arteriole and artery of mixed type all have tunica media. Only capillaries and postcapillary venules lack tunica media.

Also a prominent internal elastic membrane helps to distinguish muscular arteries from elastic arteries and muscular venules.

Explanation

In an adult, erythrocyte, granulocytes, monocytes and platelets are formed in the red bone marrow (RBM); lymphocytes are also formed in the RBM and in the lymphatic tissues. Hemopoiesis (hematopoiesis) includes both erythropoiesis and leukopoiesis as well as thrombopioesis (development of platelets). Erythrocytes develop from the multipotential myeloid stem cell under the influence of erythropiotein. The erythropiotein-sensitive erythrocyte progenitor cells give rise to the first recognizable erythrocyte precursor, the proerythroblast.

    Proerythroblast → basophilic erythroblast → polychromatophilic erythroblast → orthochromatophilic erythroblast (normoblast) → polychromatophilic erythrocyte (reticulocyte) → Erythrocyte.

       In normal blood, reticulocytes (new erythrocytes) constitute 1-2% of total erythrocyte count. 

Explanation

Organ of corti is the receptor organ for hearing. Organ of corti is made up of sensory elements called hair cells and various supporting cells. Cells of organ of corti are: inner and outer hair cells (external and internal receptor cells); external and internal phalangeal cells; external limiting cells (cells of Hensen); cells of Claudius.

Explanation

Trachea → main (primary or large) bronchi → lobar (secondary or median) bronchi → segmental (tertiary or small) bronchi → bronchioles (terminal bronchiole → respiratory bronchiole) → alveoli.

Explanation

Early in male development, mesenchyme separating the seminiferous cords gives rise to leydig (interstitial) cells that produce testosterone to stimulate development of the indifferent primordium into a testis. Leydig cells are large, polygonal, eosinophilic cells that typically contain lipid droplets. Leydig cells differentiate and secrete testosterone during early fetal life. Secretion of testosterone is required during embryonic development, sexual maturation and reproductive function:

·        In the embryo, secretion of testosterone and other androgens is essential for the normal development of the gonads in the male fetus.

·        At puberty, secretion of testosterone is responsible for the initiation of sperm production, accessory sex gland secretion and development of secondary sex characteristics.

·        In the adult, secretion of testosterone is essential for the maintenance of spermatogenesis and of secondary sex characteristics, genital excurrent ducts and accessory sex glands.

Explanation

Myoepithelial cells are contractile cells that embrace the basal aspect of the acinar secretory cells in salivary glands. Myo – Muscle

Explanation

At puberty, a pool of growing follicles is established and continuously maintained from the supply of primordial follicles. A primary oocyte, together with its surrounding flat epithelial cells forms the primordial follicle. Each month 15 – 20 follicles selected from this pool begin to mature, passing through 3 stages namely: primary or preantral; secondary or antral and preovulatory (graafian follicle). As the primary oocyte begins to grow, surrounding follicular cells change from flat to cuboidal and proliferate to produce a stratified epithelium (which can be 1 - 2 layers but usually more) of granulose cells and the unit is called a primary follicle.

Explanation

Explanation

Bile capillaries/bile canaliculus is a  small canal formed by apposed grooves on the surface of adjacent hepatocytes. Bile canaliculi form a complete loop around four sides of the idealized six-sided hepatocytes. The hepatocytes separate blood and bile, so they do not mix. Bile flow is centrifugal i.e. from the region of the central vein toward the portal canal (a direction opposite to the blood flow).

Explanation

Specific names are given to epithelium in certain locations:

·        Endothelium is the epithelial lining of the vascular system (e.g. artery)

·        Mesothelium is the epithelium that lines the walls and covers the contents of the closed cavities of the body i.e. the abdominal, pericardial and pleural cavities.

Endothelium and mesothelium are the simple squamous (flat) epithelial lining the vascular system and body cavities respectively.

Explanation

True dermal ridges are present in thick skin in addition to dermal papillae. Dermal ridges tend to have a parallel arrangement, with the dermal papillae located between them. These ridges form a distinctive pattern that is genetically unique to each individual and is reflected in the appearance of epidermal grooves and ridges on the surface of the skin. These patterns are the basis of the science of dermatoglyphics, or fingerprint and footprint identification. The dermal ridges and papillae are most prominent in the thick skin of the palmar and plantar surfaces.

Explanation

Juxtaglomerular apparatus is formed by 3 different structures:

·        Macula densa: is the end portion of thick ascending segment as it opens into the distal convoluted tubule. It is situated between the afferent and efferent arterioles of the same nephron. It is very close to afferent arteriole. Macula densa is formed by tightly packed cuboidal epithelial cells.

·        Mesangial cells: are situated in the triangular region bound by afferent arteriole, efferent arteriole and macula densa.

·        Juxtaglomerular cells: are specialized smooth muscle cells situated in the wall of afferent arteriole just before it enters the Bowman’s capsule.

Explanation

The tunics of veins are not as distinct or well defined as the tunics of arteries. Veins are divided into 3 types:

* Small veins/venules: postcapillary and muscular venules

* Medium veins

* Large veins

Arteries:

·        Large or elastic arteries

·        Medium or muscular arteries

·        Small arteries and arterioles

Muscular venules are distinguished from postcapillary venules by the presence of a tunica media. Postcapillary venules possess an endothelial lining with its basal lamina and pericytes. Postcapillary venules have no true tunica media.

·        Tunica intima: consists of endothelium with its basal lamina

·        Tunica media: smooth muscle cells

·        Tunica adventitia: collagen fibers

A vessel without tunica media, also lack muscular tissue. Muscular artery, arteriole and artery of mixed type all have tunica media. Only capillaries and postcapillary venules lack tunica media.

Also a prominent internal elastic membrane helps to distinguish muscular arteries from elastic arteries and muscular venules.

Explanation

Lingual papillae cover the dorsal surface of the tongue anterior to the sulcus terminalis of the tongue. 4 types:

* Circumvallate papillae: large, dome-shaped structures that reside in the mucosa just anterior to the sulcus terminalis . It divides the tongue into anterior 2/3 and posterior 1/3.  Human tongue has 8-12 of it. It has taste buds.

* Filiform papillae: smallest and most numerous. No taste buds, serve only a mechanical role, distributed over the entire anterior dorsal surface. They are the ones that will be coated since they are numerous and serve mechanical role.

* Fungiform papillae: mushroom shaped, have taste buds

* Foliate papillae: occur on the lateral edge of the tongue.

Taste buds are present on fungiform, foliate and circumvallate papillae.

Explanation

         The embryonic period or period of organogenesis occurs from the 3^rd-8^th weeks of development. The kidney come from 3 slightly overlapping kidney systems – pronephros, mesonephros and metanephros. Metanephros is the definitive kidney, it appears in the 5^th week. Collecting ducts of the permanent kidney develop from the ureteric bud, the bud dilates forming the primitive renal pelvis. These buds continue to subdivide until 12 or more generations of tubules have formed. The tubules of the second order enlarge and absorb those of the 3^rd and 4^th generations, forming the minor calyces of the renal pelvis. During further development, collecting tubules of the 5^th and successive generations elongate considerably and converge on the minor calyx, forming the renal pyramid. The ureteric bud gives rise to the ureter, the renal pelvis, major and minor calyces.

Explanation

Neurons are classified on the basis of the number of processes extending from the cell body:

·        Pseudounipolar: neurons have one process (extension), which divides close to the cell body into two long processes (axon and dendrite). The vast majority are located in the dorsal root ganglia and cranial nerve ganglia.

·        Unipolar neurons have only one pole. From a single pole, both axon and dendrite arise. This type of nerve cells is present only in embryonic stage in human beings.

·        Bipolar neurons have two poles – one axon and one dendrite.

·        Multipolar neurons have many poles – one axon and two or more dendrites.

Explanation

         The spleen is about the size of a clenched fist and is the largest lymphatic organ. It is located in the upper left quadrant of the abdominal cavity and has a rich blood supply. Most of the spleen consists of splenic pulp. Splenic pulp is divided into two regions: white and red pulp. White pulp consists of a thick accumulation of lymphocytes surrounding a central artery. Lymphocytes that aggregate around the central artery constitute the periarterial lymphatic sheath (PALS). The red pulp contains large numbers of RBCs that it filters and degrades.

Explanation

     Granular or rough endoplasmic reticulum (i.e. rough surface) is a region of endoplasmic reticulum associated with ribosomes. It is the site of protein synthesis and modification of newly synthesized proteins.

Explanation

Proerythroblast → basophilic erythroblast → polychromatophilic erythroblast → orthochromatophilic erythroblast (normoblast) → polychromatophilic erythrocyte (reticulocyte) → Erythrocyte (red blood cell).

The orthochromatophilic erythroblast (normoblast) has a small, compact, densely stained nucleus. The cytoplasm is eosinophilic because of the large amount of hemoglobin. It is only slightly larger than a mature erythrocyte. It loses its nucleus  by extruding it from the cell, it is then ready to pass into a blood sinus of the red bone marrow.

Explanation

          Cardiac muscle has the same types and arrangement of contractile filaments as skeletal muscle. Cardiac muscle fibers exhibit densely staining cross bands called intercalated disks, that cross the fibers in a linear fashion or frequently in a way that resembles the risers of a stairway. The intercalated disks represent highly specialized attachment sites between adjacent cells. The cardiac muscle nucleus lies in the center of the cell which is one feature that helps distinguish them from multinucleated skeletal muscle fibers, whose nuclei lie immediately under the plasma membrane. Cardiac muscle cells exhibit a spontaneous rhythmic contraction.

Explanation

The nephron consists of the renal corpuscle and a tubule system. The renal corpuscle represents the beginning of the nephron. It consists of the glomerular capillary tuft which possesses numerous fenestrations and the surrounding visceral and parietal epithelial layers (bilayer) of Bowman’s capsule. Bowman’s capsule is the initial portion of the nephron where blood flowing through the glomerular capillaries undergoes filtration to produce the glomerular ultrafiltrate.

Explanation

The embryonic period or period of organogenesis occurs from the third – eighth weeks of development and is the time when each of the 3 germ layers: ectoderm, mesoderm and endoderm, give rise to a number of specific tissues and organs.

Explanation

Parietal (oxyntic) cells are found in the neck of the fundic glands, among the mucus neck cells and in the deeper part of the gland. They secrete HCl and intrinsic factor. When examined with the transmission electron microscope they are seen to have an extensive intracellular canalicular system that communicates with the lumen of the gland. Also an elaborate tubulo-vesicular membrane system is present in the cytoplasm adjacent to the canaliculi. Numerous mitochondria with complex cristae and many matrix granules supply the high levels of energy necessary for acid secretion.

Explanation

Alveolar epithelium is composed of type I and II alveolar cells and occasional brush cells. Type II alveolar cells or type II pneumocytes or septal cells are secretory cells. Their apical cytoplasm is filled with granules as stacks of parallel membrane lamellae, the lamellar bodies. They are rich in a mixture of phospholipids, neutral lipids and proteins that is secreted by exocytosis to form an alveolar lining, surface-active agent called surfactant.

Explanation

Mesenchyme refers to loosely organized embryonic connective tissue regardless of origin. Undifferentiated embryonic mesenchymal cells are round/cuboidal in shape. During development, visceral myogenesis is shortly preceded by mesenchymal cell elongation. Undifferentiated embryonic mesenchymal cells from intestine (abundant visceral muscle), lung (some visceral muscle) or kidney (no visceral muscle); these cells differentiate into smooth muscle upon elongation.

Explanation

Cerebral cortex consists of gray mater that surrounds the deeper white mater. The cerebral cortex is formed by 6 layers of structures:

·        Molecular or plexiform layer or horizontal layer ( contains horizontal cells of cajal).

·        External granular/stellate layer

·        Outer pyramidal layer

·        Internal granular/stellate layer

·        Internal pyramidal layer

·        Fusiform cell layer

Layers of grey mater in cerebellum:

·        Outer molecular or plexiform layer

·        Intermediate purkinje layer

·        Inner granular layer

Explanation

The embryonic period or period of organogenesis occurs from the third – eighth weeks of development and is the time when each of the 3 germ layers: ectoderm, mesoderm and endoderm, give rise to a number of specific tissues and organs.

Explanation

The tunics of veins are not as distinct or well defined as the tunics of arteries. Veins are divided into 3 types:

* Small veins/venules: postcapillary and muscular venules

* Medium veins

* Large veins

Arteries:

·        Large or elastic arteries

·        Medium or muscular arteries

·        Small arteries and arterioles

Muscular venules are distinguished from postcapillary venules by the presence of a tunica media. Postcapillary venules possess an endothelial lining with its basal lamina and pericytes. Postcapillary venules have no true tunica media.

·        Tunica intima: consists of endothelium with its basal lamina

·        Tunica media: smooth muscle cells

·        Tunica adventitia: collagen fibers

A vessel without tunica media, also lack muscular tissue. Muscular artery, arteriole and artery of mixed type all have tunica media. Only capillaries and postcapillary venules lack tunica media.

Also a prominent internal elastic membrane helps to distinguish muscular arteries from elastic arteries and muscular venules.

Explanation

* Lens: a transparent, crystalline, biconcave structure; suspended from the inner surface of the ciliary body by a ring of radially oriented fibers, the zonule of zinn. Diopter is a unit of measurement of the optical power of a lens or curved mirror.

* Vitreous body: composed of a transparent gel substance that fills the vitreous chamber. It contains hyaluronic acid, widely dispersed collagen fibrils and other proteins and glycoproteins. The fluid component of the vitreous body is called vitreous humor.

* Cornea: anterior window of the eye.

* The cornea is continuous with the sclera. The sclera is composed of dense fibrous connective tissue that provdes attachment for the extrinsic muscles of the eye. It constitutes the “white” of the eye.

* The ciliary body is a ring-like thickening that extends inward just posterior to the level of the corneoscleral junction. Within the ciliary body is the ciliary muscle, a smooth muscle that is responsible for lens accommodation. Contraction of the ciliary muscle changes the shape of the lens, which enables it to bring light rays from different distances to focus on the retina.

Explanation

Lymph nodes are small encapsulated organs located along the pathway of lymphatic vessels. The supporting elements of the lymph node are:

            Capsule: composed of dense connective tissue that surrounds the node.

            Trabeculae: composed of dense connective tissue, which extend from the

                                    capsule into the substance of the node, forming a gross

                                    framework.

            Reticular tissue: composed of reticular cells and reticular fibers that forms a

                                           fine supporting meshwork throughout the remainder of

                                           the organ.

The parenchyma of the lymph node is divided into a cortex and medulla. The cortex consists of lymphocytes which are organized into nodules. The medulla of the lymph node consists of the medullary cords and medullary sinuses.

            Tonsils: form a ring of lymphatic tissue at the entrance of the oropharynx; consisting of aggregations of lymphatic nodules.

            Thymus is a lymphoepithelial organ located in the superior mediastinum. It possess a thin connective tissue capsule from which trabeculae extend into the parenchyma of the organ. The trabeculae establish domains in the thymus called thymic lobules. Thymic or hassall’s corpuscles are a distinguishing feature of the thymic medulla.

            Spleen is the largest lymphatic organ. Most of the spleen consists of splenic pulp. Splenic pulp is divided into white pulp and red pulp. The spleen is enclosed by a dense connective tissue capsule from which trabeculae extend into the parenchyma of the organ.

            Red bone marrow lies entirely within the spaces of bone in the medullary cavity of young long bones and the spaces of spongy bone.

Explanation

Normally all of femoral ossification centres fuse between the ages 14-18years old. Therefore a radiolucent zone between the head and shaft of femur at age 13 years old is normal.

Explanation

Alveolar macrophages remove inhaled particulate matter from the air spaces and red blood cells (RBCs) from the septum of alveoli. They are unusual in that they function both in the connective tissue of the septum (alveolar wall) and in the air space of the alveolus (surface of alveolar cells). In air spaces they scavenge the surface to remove inhaled particulate matter (e.g. dust, pollen, pathogens), thus giving them one of their alternate names – Dust cells. They also phagocytose infectious organisms such as Mycobacterium tuberculosis. Other macrophages remain in the septal connective tissue, where, filled with accumulated phagocytized material, they may remain for much of an individual’s life. Thus, at autopsy, the lungs of urban dwellers as well as smokers will usually show many alveolar and septal macrophages filled with carbon particles, anthracotic pigment and birefringent needle-like particles of silica.

Type I alveolar cells (type I pneumocytes): the junctions formed between this cells form an effective barrier between the air space and the components of the septal wall. They are not capable of cell division. They make up 95% of the surface of the alveoli.

Type II alveolar cells: secretory cells; have lamellar bodies; progenitor cells for type I alveolar cells.

Clara cells: non-ciliated; low columnar/cuboidal cell with secretory granules. They secrete components of surfactant, degrade toxins and act as reserve cells.

Endothelial cells line blood vessels.

Explanation

Satellite cells are interposed between the plasma membrane of the muscle fiber and its external lamina. They are small cells with scant cytoplasm. Satellite cells function as stem cells that, after injury, proliferate to give rise to new myoblasts. As long as the external lamina remains intact, the myoblasts fuse within the external lamina to form myotubes, which then mature into a new fiber.

Explanation

There are 3 ways to describe the structure of the liver in terms of a functional unit: the classic lobule; portal lobule and the liver acinus. The classic lobule is the traditional way to describe the organization of the liver parenchyma. The classic hepatic lobule is a roughly hexagonal (6-sided) mass of tissue. At the center of the lobule is a relatively large venule, the terminal hepatic venule (central vein), into which the sinusoids drain. At the angles of the hexagon are the portal areas (portal canals), loose stromal connective tissue characterized by the presence of the portal triad. The portal triad is composed of the branches of the hepatic artery, portal vein and the bile duct.

Explanation

Schwann cells are the major glial cells in peripheral nervous system (PNS). They provide myelination (insulation); also promote axonal regeneration. Derived from neural crest. Increase conduction velocity via salutatory conduction at the nodes of ranvier, where there is a high concentration of Na⁺ channels. They may be injured in Guillain-Barrė syndrome. Fibrous cells and protoplasmic cells are types of astrocytes forming blood-brain barrier, supporting network, mainataining the chemical environment and involved in recycling of neurotrtansmitters. Microglial cells are derived from monocytes – they engulf and destroy microorganisms and cellular debris. Ependymal cells form the epithelial lining of the ventricles of the brain and spinal cord.

Explanation

Connective tissue proper are divided into 2 general subtypes: loose connective tissue (LCT) and dense connective tissue (DCT). DCT is further subcategorized into: Dense irregular connective tissue and dense regular connective tissue. Dense regular connective tissue is the main functional component of tendons, ligaments and aponeuroses. Dense irregular connective tissue is characterized by abundant fibers and few cells. It contains mostly collagen fibers. Because of its high proportion of collagen fibers, it provides significant strength. Typically, its fibers are arranged in bundles oriented in various directions (thus the term “irregular”) that can withstand stresses on organs or structures. Skin contains a relatively thick layer of dense irregular connective tissue in the dermis, called the reticular or deep layer of the dermis. It provides resistance to tearing as a consequence of stretching forces from different directions.

Explanation

Lingual papillae cover the dorsal surface of the tongue anterior to the sulcus terminalis of the tongue. 4 types:

* Filiform papillae: smallest and most numerous. No taste buds, serve only a mechanical role, distributed over the entire anterior dorsal surface. They are the ones that will be coated since they are numerous and serve mechanical role.

* Fungiform papillae: mushroom shaped, have taste buds

* Circumvallate papillae: large, dome-shaped structures that reside in the mucosa just anterior to the sulcus terminalis . It divides the tongue into anterior 2/3 and posterior 1/3.  Human tongue has 8-12 of it. It has taste buds.

* Foliate papillae: occur on the lateral edge of the tongue.

Taste buds are present on fungiform, foliate and circumvallate papillae.

Explanation

Olfactory receptors (1^st order neuron) → Mitral cells (2^nd order neuron) → Olfactory tract → Olfactory trigone, anterior perforated substance, septum pellucidum (3^rd order neuron) → Uncus of parahippocampal gyrus.

The Olfactroy analyzer is one of the oldest ones so it features several fibers that take the shortest route to the Olfactory cortex i.e. do not relay within the thalamus.

Gustatory: through its 2^nd order neuron from medial lemniscus → thalamus.

Visual: through its subcortical visual centers → pulvinar of thalamus

Tactile (skin analyzer); Auditory: through lateral lemniscus of inferior colliculi of tectal plate and medial geniculate bodies of metathalamus.

Explanation

Explanation

Explanation

Anchoring junctions provide lateral adhesions between epithelial cells. 2 types: Zonula adherens and Macula adherens or Desmosome. In epidermal cells, the desmosome is the only attachment device present. On the cytoplasmic side of the plasma membrane of each of the adjoining cells is a disk shaped structure consisting of very dense material called the desmosomal attachment plaque. This attachment plaques anchors intermediate filaments. The intercellular space is occupied by electron-dense material containing desmocollins and desmogleins. Tight junctions – occluding junction.

Explanation

Osteoprogenitor cell is a resting cell that can transform into an osteoblast (bone forming cells) and secrete bone matrix. They are found on the external and internal surfaces of bones. They comprise the periosteal cells that form the innermost layer of the periosteum and the endosteal cells that line the marrow cavities. Electron micrographs reveal profiles of rough endoplasmic reticulum (rER) and free ribosomes as well as a small golgi apparatus and other organelles (developed synthesis organelles- rER, ribosomes, golgi apparatus).

Explanation

The adrenal gland (suprarenal gland) has a secretory parenchymal tissue organized into cortical and medullary regions. Adrenal cortex (derived from mesoderm; steroid-secreting portion) and medulla (derived from neural crest; catecholamine-secreting portion). The adrenal cortex is divided into 3 zones on the basis of arrangement of its cells:

* Zona glomerulosa (15%): arranged in closely packed ovoid clusters; secretes aldosterone.

* Zona fasciculata (80%): large and polyhedral; arranged in long straight cords; secretes cortisol.

* Zona reticularis (5-7%): cells are arranged in anastomosing cords separated by fenestrated capillaries; secretes androgens.

Explanation

On the 8^th day of development embryoblast differentiate into two layers:

* a layer of small cuboidal cells adjacent to the blastocyst cavity – hypoblast layer

* a layer of high columnar cells adjacent to the amniotic cavity – epiblast layer.

Together the layers form a flat disc – the embryonic shield which separates the amniotic cavity from the yolk sac.

Explanation

Retina contains the visual receptors – rods and cones are composed of 4 structures: outer segment, inner segment, cell body and synaptic terminal. The outer segment of rod cell (which is the terminal portion as described in the question) is formed by the modified cilia and it contains a pile of freely floating flat membranous disks. There are about 1000 disks in each rod. Disks in rod cells are closed structures and contain the photosensitive pigment, the rhodopsin. The outer segment of cones is small and conical. It does not contain separate membranous disks as in rods. In cone, the infoldings of cell membrane form saccules, which are the counterparts of rod disks.

Explanation

The wall of the trachea consists of 4 layers:

*Mucosa: composed of a ciliated, pseudostratified epithelium and an elastic, fiber-rich lamina propria.

*Submucosa: composed of a slightly denser connective tissue than the lamina propria.

*Cartilaginous: composed of C-shaped (open circles) hyaline cartilages.

*Adventitia: composed of connective tissue that binds the trachea to adjacent structures.

Submucosal glands are composed of mucus-secreting acini. Bronchi (both segmental and lobar) have muscularis mucosa which is absent in trachea. No cartilage plates in bronchioles (terminal bronchiole). Cartilages in the larynx are arytenoids, epiglottis, cricoids, thyroid