Organs & Tissues

Internal organs characteristic of vertebrates includes a liver, kidneys, and endocrine glands. All vertegrates have a heart and a closed circulatory system.

Endocrine glands: secrte hormones that help regulate many of the body’s functios.

Epithelium: is a basic tissue type that lines all body surfaces, cavities and tubes. All epithelia are supported by an avascular connective tissue layer called the which contains and Epithelium is classified according to shape as follows:

simple squamous epithelium: is 1 layer and flat.
simple cuboidal epithelium: is 1 layer and square; The ovary is simple squamous to cuboidal
simple columnar epithelium: is 1 layer and columnar; lines most of digestive track, oviduct/fallopian tube (where occurs), uterus.
stratified squamous epithelium: is more than 1 cell layer and flat. Examples include the skin, vagina

Organs & Tissues derived from

Integument/skin: Skin consists of two main parts: the epidermis on the outside and a lower layer of connective tissue which includes the two layered dermis. Skin is sometimes categorized as either thick such as that found on the foot or palm of the hand or thin. Thick skin has 5 layers in the epidermis whereas thin skin contains 4 layers. The various cells of the skin are attached to each other through type junctions and to the basement membrane through

epidermis is made up of a stratified (multilayed) squamous (flattened) epithelium composed largely of The epidermis is renewed by lying in its basal layer. Other cells associated with the epiermis are merkel cells which function as mechanoreceptors and langerhan cells which are phagocytic and present processed antigens to .
dermis consists of the 1) papillary layerwhich is a loose connective tissue with fine fibers and 2) reticular layer.

Hair and sweat glands which penetrate into the dermis are actually down growths from the epidermal layer. Glands can have ducts (exocrine) or no ducts (endocrine). Sweat glands are made up of a cuboidal (shaped like a cube) epithelium surrounded by myoepithelial cells. One modified type of sweat glands are the mammary glands whose growth and development of the epithelium of the glands is regulated by steroid hormones.

Sensory Epithelium:The sensory epithelium of the eye and ear do not regenerate while the olfactory epithelium will regenerate.

(1) Neural retina: consists of several cell layers. lie closest to the external world so that light must pass through them to reach the photoreceptor cells which are classified as rods or cones which contain different rhodopsins. Rods are especially sensitive at low light levels while cones deter color and fine detail. Photoreceptors, like auditory hair cells, are permanent cells that do not divide and thus are not replaced if destroyed but the rhodopsin molecules are continually replaced.

(2) Ears: are the sensory epithelium responsible for hearing. Ears have auditory hair cells with protruding microvilli which held in an elaborate epithelial structure of supporting cells and overlaid by a mass of extracellular matrix. The hair cells convert mechanical stimuli into electrical signals. Sounds vibrations tilt the microvilli and open or close gated ion channels . The flow of electric charge carried into the cell by the ions alters the membrane potential and controls the release of neurotransmitter at the cell’s basal end, where the cell synapses with a nerve ending. Auditory hair cells, unlike olfactory neurons have to last a lifetime.

(2) Olfactory epithelium of the nose: contain . Basal stem cells in the epithelium generate replacements for the olfactory neurons that are lost.

Organs & Tissues derived from

Simple Columnar Epithelium of the Digestive Track: is made up of secretory mucous cells, absorptive cells as well as stem cells.

Colon: is a simple columnar epithelium whose function is water absorption. The colons has goblet cellswhich sythesize and secrete mucus which is a fecal lubrication.

Liver: is composed of two major types of differentiated epithelial cells: hepatocytes, cloated in the hepatic parenchymal plates, and biliary epithelial cells located in the bile ducts. Both of these differentiated lineages are dervied embryonically from a common founder cell, the hepatoblast, a derivative of the endoderm of the ventral foregut (Coleman, J. Pathology, 142(5), 1993).

Lungs: are formed from an outpocketing of the gut lining in the embryo. Repeated branching of a system of tubes terminate in several hundred million air filled sacs called alveoli which which contain . which engulf foreign matter and bacteria are associated with the lungs.

Lungs: is the site where nutrients that have been absorbed from the gut and then transferred to the blood are processed by hepatocytes. Liver cell loss stimulates liver cell replacement.

Organs & Tissues derived from

Blood vessels: are lined with endothelial cells. New vessels originate as capillaries which sprout from existing small vessels in response to specific signals in a process called angiogenesis. Angiogenesis is stimulated by hypoxia which results in the release of growth factors. Stimulation of cells around endothelial cells called pericytes may play an important role in the process.

kidney: The kidney filters plasma and excretes soluble waste products of metabolism. To prevent the los of serum proteins in the urine, the kidneys have a size selective barrier at the level of the glomeruli, the proximal protion of nephrons. The epitehlial cells (podocytes) of the glomerulus have processes (pedicles) that interdigitate to form a comb-linke structure through which serum is filtered and which excludes macromolcules of 70 kDa and alrger. Thus, two of the most abudnatn serum proteins, albumin and IgG are excluded form the priamry urine. After glomerular filtration the primary urine flows downstream to the tubular portiosn of the nephron. The proximal convoluted tubule (PCT), located immediately distal to the glomerulus, is reponsible for the reabsorption of mlus: is a key structural and functional element of the kidney.

–Glomerus is a key structural and functional element of the kidney. Each glomerulus is found as part of a larger structure that serves as the main functional unit of the kidney and is called a nehpon. About a million nephrones are found in each kidney. Each glomerulus is a network of up to fifty parallel capillaries encased in a structure known as Bowman’s capsule. The area inside Bowman’s capsule that is not taken up by the glomerular capillaries is known as Bowman’s space. The glomerulus functions as a filter, separating water and certain solutes from teh proteins and cells of the blood into Bowman’s space for futher processing in the conoluted tubules, loop of Henle, and collecting duct of the nephron. (US63555245)

—-Glomerului are specialized renal capillary tufts which carry out the fitration of the plasma. Under normal conditions, the glomerular ultrafiltrate and ruine contain little if any protein. Glomerular disease (glomerulonephritis) is characterized by an increase in the permeability of the glomerular basement membrane (GBM), the primary ultrafiltration barrier restricting the passage of plasma proteins into the urine.