|The wool-producing ‘factory’ is the 50 million or so follicles embedded in the skin of sheep. This unit covers in detail, how these follicles form, what cellular and molecular processes produce the fibre, how genetics and nutrition affect these processes, and how genetic engineering might be used to produce a better fibre. With an understanding of the biology of the skin and the fleece, the characteristics of the wool follicle and fibre can be related to production, technology and the processing of wool.
|Many aspects of follicle function reflect the derivation of follicles from skin, including biochemistry, molecular biology, kinetics and structure. The structure and function of skin is considered in these modules.
|The function of skin is described with emphasis on cell production, migration and terminal differentation.
|This module briefly describes the function of mammalian skin as a simple and an active boundary with particular reference to sheep skin and wool production. As with all structure/function issues it is useful to know the structure of the skin to understand the function of the skin. Many text books describe the structure and function of the skin in all species of animals. A lot of commonality exists between species in skin structure and function and it is possible to follow the patterns of skin evolution through the different species.
|Replacement of cells in the skin
|The cellular determinants of fibre production are the number of follicles, the number and size of cells in the bulb, the rate of cell division, the proportion of cells migrating to the fibre and the size of cells in the fibre. This module describes where cells divide in the epidermis and follicle and from where they are replaced.
|The Structure of Skin
|The structure of skin is described in detail with dermal, epidermal, and accessory structures covered. Follicle characteristics which influence fibre growth are also covered.
|This module briefly describes the structure of mammalian skin with particular reference to sheep skin and wool production. As with all structure/function issues it is useful to know the function of the skin to understand the structure of the skin. Many text books describe the structure and function of the skin in all species of animals. A lot of commonality exists between species in skin structure and function and it is possible to follow the patterns of skin evolution through the different species. This module contains a diagram of sheep skin and also a labelled photomicrograph of sheep skin.
|This module contains a basic description of the structure and function of the dermis and lists the components of the dermis. There is also a photomicrograph of the sheep dermis. For more information on the cells within the dermis see module “”Dermal Cells”” and for more information on the matrix see the module “Extracellular Matrix”.
|This module provides a brief description of the types of cells and their function in the dermis. For more information on the structure, function and components of the dermis see module “The Dermis”.
|Dermal accessory structures
|This module describes the accessory structures that are present within the dermis. Particular attention is given to the blood vessels and the nerves.
|This module describes the basic structure of the epidermis and the replacement and fate of cells within the epidermis. There is a photomicrograph of the epidermis of sheep skin.
|The extracellular matrix (ECM) consists of a ground substance and proteins such as collagen, elastin and reticulin. These are briefly described in this module. For more information on the structure, function and components of the dermis see module “The Dermis”.
|Communication between the extracellular matrix and cells
|A vital part of wool biology (and multicellularity of all organisms) is the ability of individual cells to work together as a whole organism. Communication between cells is required to regulate their development and organisation into tissues, to control growth and division and to coordinate diverse activities. Cells in higher animals communicate by signalling molecules, including proteins, small peptides (growth factors), amino acids, nucleotides, steroids, fatty acid derivatives and even dissolved gases such as nitric oxide and carbon monoxide. This module describes how the extracellular matrix (ECM) is involved in cell communication.
|Differences in blood flow through the skin of finewool and strongwool sheep
|Variations in wool production and quality are evident between breeds, strains and individuals in the same flock due to differences in the rate of wool growth and the characteristics of the fibre. Studies of sheep with different genetic potential for wool production and fibre diameter have found that differences in whole body functioning only play a minor role in genetic differences. Rather the differences lie in the functioning of the skin and its population of follicles. Morphological differences exist at the level of the skin, but the question remains – how are they maintained since the basic structure is the same? The answer maybe blood flow through the skin or the rate of nutrient uptake. This module describes the relationship between blood flow, nutrient uptake and wool growth.
|Estimating follicle and fibre density and S:P ratio
|This module describes methods that are used to calculate the number or density of follicles or fibres in the skin of sheep. The estimation of S:P ratio is also described. Photomicrographs of a new technique to estimate branched follicles are provided.
|This module describes follicle curvature, how the curvature of follicles in the skin is associated with particular fleece characteristics and how curvature can be measured.
|This module describes one of the characteristics related to the size of the productive unit – follicle density of the skin – and discusses how the density of follicles in the skin is associated with particular fleece characteristics.
|Follicle depth and evenness
|This module describes one of the characteristics related to the size of the productive unit – follicle depth – and discusses how how follicle depth, skin thickness and follicle evenness are associated with particular fleece characteristics.
|Skin Traits and Wool Growth
|Relationships between skin and follicle traits, and wool growth are described.
|Improvements in wool production using skin traits
|This module summarises the effect of skin traits on wool production and quality, describes how knowledge about skin traits and genetics can be used to improve wool production and gives the example of how DNA testing can be used to identify superior genotypes.