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UNIT-2 Integumentary system The integumentary system consists of the skin and its accessory structures like hair, skin glands, and nails (develop from the embryonic epidermis) and subcutaneous tissue. The skin, also known as the cutaneous membrane, covers the external surface of the body and is the largest organ of the body in both surface area and weight. In adults, the skin covers an area of about 2 square meters and weighs 4.5–5 kg. The skin consists of two main parts. The superficial epithelial tissue, is the epidermis. The deeper, connective tissue portion is the dermis. While the epidermis is avascular, the dermis is vascular. Deep to the dermis, but not part of the skin, is the subcutaneous layer. Also called the hypodermis. Epidermis The epidermis is composed of keratinized stratified squamous epithelium. It contains four principal types of cells: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. About 90% of epidermal cells are keratinocytes, which are arranged in four or five layers and produce the protein keratin. Keratinocytes also produce lamellar granules, which release a water-repellent sealant that decreases water entry and loss and inhibits the entry of foreign materials. About 8% of the epidermal cells are melanocytes produce the pigment melanin contributes to skin color. Langerhans cells arise from red bone marrow and migrate to the epidermis. They participate in immune responses against microbes that invade the skin, and are easily damaged by UV light. Merkel cells are the least numerous of the epidermal cells. They are located in the deepest layer of the epidermis, where they contact the flattened process of a sensory neuron (nerve cell), a structure called a Merkel (tactile) disc. Merkel cells and their associated Merkel discs detect touch sensations. In most regions of the body the epidermis has four strata or layers —stratum basale, stratum spinosum, stratum granulosum, and a thin stratum corneum. This is called thin skin. Where exposure to friction is greatest, such as in the fingertips, palms, and soles, the epidermis has five layers— stratum basale, stratum spinosum,
stratum granulosum, stratum lucidum, and a thick stratum corneum. Sratum basale -Deepest layer, composed of single row of cuboidal or columnar keratinocytes that contain scattered keratin intermediate filaments (tonofilaments). Stem cells undergo cell division to produce new keratinocytes and is also known as stratum germinativum. Melanocytes and Merkel cells associated with Merkel discs are scattered among keratinocytes. Sratum Spinosum -Eight to ten rows of many-sided keratinocytes with bundles of keratin intermediate filaments; contains arm like processes of melanocytes and Langerhans cells. Sratum Granulosum -Three to five rows of flattened keratinocytes, in which organelles are beginning to degenerate (apoptosis); cells contain the protein keratohyalin (converts keratin intermediate filaments into keratin) and lamellar granules (release lipid-rich, water-repellent secretion). Sratum Lucidum- Present only in skin of fingertips, palms, and soles; consists of four to six rows of clear, flat, dead keratinocytes with large amounts of keratin. Sratum Corneum- Twenty-five to thirty rows of dead, flat keratinocytes that contain mostly keratin. Its multiple layers of dead cells help the stratum corneum to protect deeper layers from injury and microbial invasion. Constant exposure of skin to friction causes an abnormal thickening of the stratum corneum called callus. Dermis / true skin / a strong, flexible, connective tissue mesh work of collagen, reticular and elastic fibers. Most part of the skin is composed of dermis. Dermis contains papillary and reticular layers. Papillary layer is next to stratum basale of the epidermis. It contains loose connective tissue with in the bundles of collagenous fibers. It also contains loose capillaries that nourish the epidermis. In some areas papillary layer have special nerve endings that serve as touch receptors (meissner’s corpuscles). Indentations of papillary layer in the palms and soles reflected over the epidermis to create ridges. Reticular layer: next to papillary layer. It is made of dense connective tissue with course of collagenous fiber bundles that
communicate with each other through a fine channels called ca naliculi. In spongy bone, osteocytes, matrix, and blood vessels are present but are not arranged in haversian systems. Types of bone- a)- Long bone, are called long as its length is greater than its width. The most obvious long bones are in the arm and leg. b)- Short bones are about equal in length, width and thickness, which are shaped with regular orientation. They occur in the wrist and ankle. c)- Flat bones are thin or curved more often they are flat. This includes ribs, scapulae, sternum and bone of cranium. d)- Irregular bones , they do not fit neatly into any other category. Examples are the vertebral, facial, and hipbone. e)- Sesamoid bones are small bones embedded within certain tendons, that connects muscle to bones. Typical sesamoid bones are patella. Fig. 12 Function of the skeletal system-
Support- skeleton provide the framework of the body and give attachment to muscles and tendons. Movement- it permits movement of the body by forming joints. Protection- skull, vertebral column, rib cage and pelvic girdle enclose and protect vital organs. Haemopoiesis – The cavities in spongy bone often contain red bone marrow, which produces red blood cells, platelets, and white blood cell. Mineral storage- it provides a reservoir of minerals, especially calcium phosphate. Q- Describe the structure of skull with diagram. Skull- The skull consists of 8 cranial bones and 14 facial bones. Cranial bone- The cranial bones enclose and protect the brain, eyes, and ears. These are the frontal bone, parietal bones (two), temporal bones (two), occipital bone, sphenoid bone and ethmoid bone. Frontal bone-The frontal bone forms the forehead and the anterior top of the skull. The coronal suture joins the frontal and parietal bones. Parietal bone- Two large parietal bones form the posterior top and the side walls of the skull. They articulate with each other at saggital suture, with occipital bone at the lambdoidal suture and with the temporal bone at squamous suture. Temporal bone- Each temporal bone on the side of the skull contains an external auditory meatus (ear canal), a middle ear cavity. The styloid process projects from lower part of temporal bone and support hyoid bone. Occipital bone - The occipital bone forms the lower, posterior part of the skull. Its foramen magnum is a large opening for the spinal cord, and the two condyles (rounded projections) on either side articulate with the atlas, the first cervical vertebra. Sphenoid bone - The sphenoid bone lies at the base of skull. It contains two pairs of wing like structure called lesser and greater wings and sella turcica for the pituitary gland. Ethmoid bone- The ethmoid bone forms the roof of nose and in between orbits, and the upper part of the nasal septum.
Inferior chonchae- On either side of the vomer are the inferior conchae which increase the surface area in nasal cavity. b) Write structure and function of pectoral girdle or pelvic girdle or vertebral coloumn. Pectoral girdle –it contain two scapulae and two clavicles that attach to axial skeleton at sternum. Clavicle-it is also called as collar bone. It is S- shaped which provides the link between the upper limb and the axial skeleton. It contains a shaft, two ends and four borders. It articulates with sternum at sternoclavicular joints and with acromian process of scapula at a cromioclavicular joint. Scapula- it is flat triangular-shaped, lying on the posterior chest wall. It has two surfaces, three angles and three borders. At the lateral angle a glenoid cavity which forms the shoulder joint with the head of the humerus. There are three processes ie. spinous process, acromion process and coracoid process for attachment to muscle and articulation. Fig. 14
Pelvic girdle- The pelvic girdle is formed by the two hip bones. Each hip bone consists of three fused bones, the ilium, ischium and pubis. Ilium part is attached posteriorly to sacrum of vertebral coloumn at sacroiliac joint. Pubis articulates with pubis of other hip bone at pubic symphysis (fibrocartilage). On its outer surface there is an acetabulum, which forms the hip joint with head of femur. Obturator foramen is a triangular opening which is bounded by pubic bone in front and ishchium behind. In comparison with the male pelvis, the female pelvis has lighter bones, wider and rounded. The shape of the female pelvis allows for the passage of the baby during childbirth. (fig. ) Fig. 15 Vertebral coloumn- is made of Individual bones, called vertebrae, which are classified as: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral fused into one sacrum and one coccyx. The vertebrae are
pubis and the joints between the vertebral bodies (intervertebral disc). Synovial joints (diarthroses)- they are also called as freely movable joint. Articular ends of bones are covered by hyaline cartilage which provides a smooth surface. The fibrous capsule encloses the joint. Lining of fibrous capsule is the synovial membrane, which secretes synovial fluid into the joint cavity. Synovial fluid is thick and slippery which prevents friction as the bones move. Synovial joint is further classified as: Ball and socket joint: The head or ball of one bone articulates with a socket of another bone which allows for a wide range of movement. Examples are the shoulder and hip joint. Hinge joints. Here, the movements is possible in one plane only. Examples are the elbow, knee joint. Gliding joints. Here, the articular surfaces of bone glide over each other, e.g. joints between the carpal bones and the tarsal bones. Pivot joints. In this joint, the rotation is the only possible movement_._ , e.g. proximal and distal radioulnar joints and the joint between the atlas and axis. Condyloid joint : the movement in one plane with some lateral movement, e.g. Temporal bone and mandible. Saddle joint- Movement in several planes, e.g. Carpometacarpal of thumb. Q- Discuss various types of movements. Types of movements- the following types of movement occurs at various joints. i) Flexion- A movement where similar surfaces come nearer to each other and reduces the angle between two bones eg. bending the forearm at the elbow. ii) Extension- A movement where similar surfaces go apart. This increases the angle between two bones eg. extending of the bent forearm at the elbow. iii) Adduction- A movement which brings the limb towards mid line. iv) Abduction- A movement where the limb goes away from the mid line. v) Rotation- A movement around a central axis involving 360^0.
vi) Circumduction- A movement involving flexion, extension, adduction, abduction which occur in a sequence. eg. Movements occur in shoulder and hip joint etc. Q- Give the microscopic anatomy of skeletal muscle fiber. Describe the physiology of skeletal muscle contraction with the help of suitable diagram. A muscle consists of a large number of muscle fibres. In addition to the sarcolemma mentioned previously, each fibre is enclosed in and attached to fine fibrous connective tissue called endomysium. Small bundles of fibres are enclosed in perimysium, and the whole muscle in epimysium. The fibrous tissue enclosing the fibres, the bundles and the whole muscle extends beyond the muscle fibres to become the tendon, which attaches the muscle to bone or skin. Microscopic anatomy- i)- Skeletal muscle is composed of thousands of muscle fibers. ii)- Each muscle fibers is surrounded by sarcolemma, below which many nuclei are present. iii)- Numerous mitochondria (produces ATP from glucoge and oxygen by aerobic respiration), myoglobins (similar to hemoglobin, stores oxygen) and bundles of myofibrils are present in sarcoplasm. iv) -Each myofibrils has repeating series of dark and light bands which consist of many units called sarcomere (smallest functional unit of skeletal muscle). Each sarcomere is separated by Z- line. v)- Dark area of sarcomere or ‘A- band’ contain thick filament & lighter area or ‘I- band’ contain thin filament. vi) Thick filament consists of contractile protein myosin and thin filament is of actin, Troponin, & tropomyosin. vii) Surrounding the sarcomeres of myofibril is the sarcoplasmic reticulum, which stores and release ca++ ions. NMJ- Region between axon terminal of motor neuron and motor end plate of skeletal muscle is called NMJ. Neurotransmitter (Ach) is stored in some vesicles in nerve terminals and release into NMJ. Skeletal muscle contraction- When a nerve impulse arrives at axon terminal, Ach is released by exocytosis process and release into NMJ (synapse). Acetylcholine bind with receptor on sarcolemma which open Na+ channel. Then
Muscle tone- most of our muscles are in a state of slight contraction; this state is known as muscle tone. Muscle tone is essential to maintain an upright posture. Alternate fibers contract to prevent muscle fatigue; regulated by the cerebellum. Muscles with poor tone are usually soft, but exercise will improve muscle tone. Muscle fatigue- when a skeletal muscle is contracted repeatedly, its strength of contraction progressively decreases and finally stops to contract. This state is known as muscle fatigue. This may be due to insufficient oxygen, energy (ATP), depletion of glycogen and increase lactic acid level. Types of muscle contraction Muscle contractions are classified as either isotonic or isometric. In isotonic contractions, the amount of tension in the muscle is constant but the length of the muscle change during contraction, example, if one end of the muscle is attached to a movable part, its contraction moves that part and tension will be same.. In isometric contractions, the length of the muscle will be same, but the amount of tension increases during the contraction. For example, if you put your palm on the table and push against table, you can feel your muscles contracting, tension is increased but there will be no movement. Energy Sources for Muscle Contraction
- The direct source of energy for muscle contraction is ATP, which releases energy when it breaks down to adenosine diphosphate (ADP). ATP → ADP + Phosphate + Energy + Heat.
- The secondary energy sources are creatine phosphate and glycogen. Creatine phosphate is broken down to creatine + phosphate + energy. The energy is used to synthesize more ATP. Some creatine is converted to creatinine which is excreted by the kidneys. Most creatine is used for the resynthesis of creatine phosphate.
- Glycogen is the most abundant energy source and is first broken down to glucose. Glucose is further broken down in cell respiration to produce ATP:
Glucose + O2 → CO2 + H2O + ATP + heat. ATP is used for contraction; heat contributes to body temperature; H2O becomes a part of intracellular fluid; CO2 is eventually exhaled.
- Oxygen is essential for the completion of cell respiration. Hemoglobin in red blood cells carries oxygen to muscles; myoglobin stores oxygen in muscles.
- Oxygen debt (recovery oxygen uptake): the extra requirement of oxygen is called oxygen debt. The oxygen consumption is much higher during severe exercise and If oxygen is not present in sufficient amounts, glucose is converted to lactic acid (anaerobic process), which causes muscle fatigue and contraction may become painful. Breathing rate remains high after exercise to deliver more oxygen to the liver, which converts lactic acid to pyruvic acid, a simple carbohydrate (ATP required).
