Anatomy and Histology- bone and skin PDF

Preview

Summary

CAL 1- BONE AND SKIN
examining histology slides...

Description

Slide 1 - Developing bone The epiphyseal plate is responsible for the future lengthening of a long bone. It is a layer of hyaline cartilage where ossification occurs in immature bones. On the epiphyseal side of the epiphyseal plate, cartilage is formed. On the diaphyseal side, cartilage is ossified, and the diaphysis grows in length. It is divided into five zones: (1) zone of reserve cartilage, a region of small scattered chondrocytes. These chondrocytes do not participate in bone growth but secure the epiphyseal plate to the osseous tissue of the epiphysis. (2) zone of cell proliferation, where slightly larger chondrocytes are arranged in rows whose longitudinal axis is parallel to the growing bone. They make new chondrocytes (via mitosis) to replace those that die at the diaphyseal end of the plate.; (3) zone of cell maturation and hypertrophy, where chondrocytes mature and enlarge, and the matrix between adjoining cells becomes very thin; (4) zone of calcifying cartilage, where lacunae become confluent and the matrix between adjacent rows of chondrocytes becomes calcified, causing subsequent chondrocytic death; and (5) zone of provisional ossification, where osteoblasts deposit bone on the calcified cartilage remnants between the adjacent rows. Osteoclasts absorb the calcified complex.

1. What type of cartilage can be identified in this slide? How do other types of cartilage differ? By what mechanisms does growth of cartilage generally occur? For hyaline cartilage the matrix is smooth and basophilic in appearance. It has two regions, the territorial matrix, which is darker and surrounds lacunae, and the interterritorial matrix, which is lighter in color. The collagen fibrils are masked by the ground substance. For elastic cartilage the matrix contains numerous dark elastic fibers in addition to the collagen fibrils. While in fibrocartilage the ground substance of the matrix is very scanty. Many thick collagen bundles are located between parallel rows of chondrocytes. The cells that are present in hyaline and elastic cartilage are chondrocytes, chondroblasts, and chondrogenic cells. While the chondrocytes in fibrocartilage are smaller than those in hyaline or elastic cartilage, and they are arranged in parallel longitudinal rows between bundles of thick collagen fibers. The perichondrium is usually absent in fibrocartilage. Cartilage growth occurs through two different processes: interstitial growth and appositional growth 2. Where is the epiphyseal plate located? What type of tissue lies on either side of the epiphyseal plate? The epiphyseal plate is located in between the middle and end of long bone such as the bones of the arms and legs Connective tissue (hyaline cartilage) lies on either side of the epiphyseal plate 3. Discuss the process of endochondral ossification using a suitable drawing of the epiphyseal plate. Indicate in your diagram the direction of cartilage proliferation and the direction of bone growth. In endochondral ossification, bone develops by replacing hyaline cartilage. Cartilage does not become bone. Instead, cartilage serves as a template to be completely replaced by new bone. Endochondral ossification takes much longer than intramembranous ossification. As more matrix is produced, the chondrocytes in the center of the cartilaginous model grow in size. As the matrix calcifies, nutrients can no longer reach the chondrocytes. This results in their death and the disintegration of the surrounding cartilage. Blood vessels invade the resulting spaces, not only enlarging the cavities but also carrying osteogenic cells with them, many of which will become osteoblasts. These enlarging spaces eventually combine to become the medullary cavity. As the cartilage grows, capillaries penetrate it. This penetration initiates the transformation of the perichondrium (membrane that covers the cartilage) into the bone-producing periosteum. Here, the osteoblasts form a periosteal collar of compact bone around the cartilage of the diaphysis.

4. Can you identify any obvious artifacts? If so, which ones and where? bone marrow and blood vessel See figure 1 5. Can you identify a secondary ossification centre? If so, where? The secondary ossification center is usually found in the epiphysis which is in the zone of reserve cartilage

Slide 2 - Compact Bone

1.How does compact bone differ from spongy (trabecular) bone? Compact bone is the denser, stronger of the two types of bone tissue. It can be found under the periosteum and in the diaphyses of long bones, where it provides support and protection. The microscopic structural unit of compact bone is called an osteon, or Haversian system. Each osteon is composed of concentric rings of calcified matrix called lamellae. Running down the center of each osteon is the central canal, or Haversian canal, which contains blood vessels, nerves, and lymphatic vessels. These vessels and nerves branch off at right angles through a perforating canal, also known as Volkmann’s canals, to extend to the periosteum and endosteum. The osteocytes are located inside spaces called lacunae, found at the borders of adjacent lamellae. Canaliculi connect with the canaliculi of other lacunae and eventually with the central canal. This system allows nutrients to be transported to the osteocytes and wastes to be removed from them. Spongy bone contains osteocytes housed in lacunae, but they are not arranged in concentric circles as seen in compact bone. Instead, the lacunae and osteocytes are found in a lattice-like network of matrix spikes called trabeculae.

2.How does the arrangement of the bone architecture relate to its function? Compact bone is the denser, stronger of the two types of bone tissue. It can be found under the periosteum and in the diaphyses of long bones, where it provides support and protection. In spongy bone the trabeculae may appear to be a random network, but each trabecula forms along lines of stress to provide strength to the bone. The spaces of the trabeculated network provide balance to the dense and heavy compact bone by making bones lighter so that muscles can move them more easily. In addition, the spaces in some spongy bones contain red marrow, protected by the trabeculae, where hematopoiesis occurs. 3.Comment on communication and exchange of substances between cells, and between osteons in compact bone. Canaliculi connect with the canaliculi of other lacunae and eventually with the central canal. This system allows nutrients to be transported to the osteocytes and wastes to be removed from them. 4. What is normally present in the central (white) region of the transverse section of compact bone? Haversian canal is located in the center of compact bone 5. Briefly discuss a disease process affecting the structure of bone Osteoporosis is a decrease in bone mass arising from lack of bone formation or from increased bone resorption. It usually occurs in old age due to a decline in growth hormone and in post menapopausal women because of decreased estrogen secretion. Estrogen binds to receptors on osteoblasts and stimulates the secretion of bone matrix. Without estrogen osteoclastic activity reduces bone mass making the bones more liable to fracture.

Slide 3 - Thick Skin

1.Was this section taken from thin skin or thick skin? It was taken from thick skin because it has a thick stratum corneum and it’s hairless. 2. Why are there distinguishable layers of keratinocytes in the epidermal layer? Keratinocytes contain keratohyalin granules.The granules contain precursors of the protein filaggrin that will eventually empty into the cytoplasm and aggregate the keratin filaments that are starting to fill the cells.

3. What other cell types might be found in the epidermis? Melanocytes, langerhans’ cells and markel’s cells 4.What type of connective tissue makes up the dermis? Dense irregular collagenous connective tissue

5. What structures can be found in the dermis on this slide, and what is their function in skin? Discuss their structure as evidenced on this slide. Blood Vessels- The blood vessels of the dermis provide nutrients to the skin and help regulate body temperature. Heat makes the blood vessels enlarge (dilate), allowing large amounts of blood to circulate near the skin surface, where the heat can be released. Cold makes the blood vessels narrow (constrict), retaining the body's heat Ducts - The ducts open out onto epidermal ridges at a sweat pore. They secrete a watery fluid which is hypotonic to plasma; its evaporation is important for thermoregulation. Eccrine sweat glands - Eccrine sweat glands help to maintain homoeostasis by stabilizing body temperature 6. Are there any sebaceous glands in this preparation? No sebaceous glands are not found in thick skin because it has no hair.

Slide 4- SCALP

1. The sectioned hair follicles appear to differ as one navigates from the left edge of this section up towards the right edge. How can this be explained? On the left hand side they are larger and more spaced apart because the section of tissue was sliced diagonally. On the right hand side the slice is deeper within the skin because fat tissues can be seen. On the left hand side we can see the epidermis so the slice was taken at a higher section on the skin

2. Describe the structure of the hair follicle and how this relates to hair growth? The wall of the hair follicle is made of three concentric layers of cells. The cells of the internal root sheath surround the root of the growing hair and extend just up to the hair shaft. They are derived from the basal cells of the hair matrix. The external root sheath, which is an extension of the epidermis, encloses the hair root. It is made of basal cells at the base of the hair root and tends to be more keratinous in the upper regions. The glassy membrane is a thick, clear connective tissue sheath covering the hair root, connecting it to the tissue of the dermis. 3. What is the function of the sebaceous glands? A sebaceous gland is a type of oil gland that is found all over the body and helps to lubricate and waterproof the skin and hair. Most sebaceous glands are associated with hair follicles. They generate and excrete sebum, a mixture of lipids, onto the skin surface, thereby naturally lubricating the dry and dead layer of keratinized cells of the stratum corneum, keeping it pliable. The fatty acids of sebum also have antibacterial properties, and prevent water loss from the skin in low-humidity environments....