Stored triacylglycerols are mobilized by lipase, which hydrolyzes stored triglycerides. Mobilization of triacylglycerols is controlled by both neural and hormonal factors: Norepinephrine: Activates lipase Denervated fat will continue to deposit even in a state of starvation. Androgens are anti-adipogenic and estrogens are pro-adipogenic. The released FFAs may be re-esterified or released to the circulation and bound to albumin for transfer to other cells.
Endocrine function Adipose tissue produces a number of hormones and cytokines. Leptin: Protein product of the ob gene Acts on the hypothalamus to increase energy expenditure and decrease appetite Adiponectin: Decreases gluconeogenesis and stimulates glucose uptake Modulates lipid catabolism Obesity is associated with reduced levels of adiponectin.
Obesity is associated with elevated levels. Heat production Major function of brown adipose tissue: nonshivering thermogenesis; important for newborns Brown adipose tissue is very vascular and regulated by sympathetic stimulation.
Thermogenin uncouples the oxidation of fatty acids from the generation of ATP. The resultant energy is dissipated as heat. Other functions of adipose tissue Insulation from heat and cold by the subcutaneous layer Protective padding and structural support of visceral organs, mammary tissue, periorbital tissue, bone marrow, and in areas of mechanical stress palms and soles of feet Related videos.
Obesity is usually due to a sedentary lifestyle and an increased caloric intake, but there are also uncommon secondary causes. Cellulitis is less common in men because they have a smoother, strand-free dermal interface in the thigh and buttock areas. Lipodystrophies: rare congenital or acquired syndromes associated with a loss of healthy adipose tissue: Generalized lipodystrophy can be associated with diabetes, hepatic steatosis, pancreatitis, and metabolic syndrome.
Fat necrosis: condition associated with mechanical trauma e. Fat embolism: an embolus composed of a cluster of adipocytes that enters the bloodstream and results in the blockage of blood flow: Fat emboli can present as pulmonary emboli after fractures of the long bones owing to the release of bone marrow fat. Calciphylaxis: skin and subcutaneous fat necrosis, with small blood vessel necrosis, calcium precipitation, and thrombosis: Calciphylaxis is a complication of dialysis and renal failure and is also seen in primary hyperparathyroidism This condition is often lethal.
Inflammation may involve eosinophils, neutrophils, granulomas, and histiocytes with lymphophagocytosis, among others. Panniculitis may sometimes resolve without treatment, but it is often managed with antibiotics and anti-inflammatory drugs.
Mesenteritis inflammation mesenteric panniculitis : usually benign condition presenting as space-occupying lesion consisting of chronic inflammation with fat necrosis and proliferation of myofibroblasts involving single or multiple areas of the mesentery: Mesenteritis inflammation often presents with fever, but it can also be asymptomatic.
This condition mostly affects middle-aged males. Prognosis is excellent, with most lesions regressing within 2 years. Tumors: Hibernoma: a benign neoplasm of brown adipose tissue: Hibernoma is the only pathologic lesion of brown adipose tissue. Tumors mostly occur in sites corresponding to the distribution of brown adipose tissue—the interscapular area, neck, mediastinum, and axilla. Hibernoma presents as a painless slow-growing subcutaneous mass, and it may achieve a size of up to 23 cm.
Treatment is surgical excision. Lipoma: a benign neoplasm of adipocytes white adipose tissue : Lipoma is the most common soft tissue tumor in adults. Many variants of lipoma exist, including angiolipoma, atypical lipoma, myxolipoma, and spindle cell lipoma.
Lipoma usually presents as a painless soft tissue nodule. Diagnosis is usually established clinically and supported by tissue biopsy. The usual treatment is surgical excision, but smaller asymptomatic lesions may not require any treatment. Liposarcoma: a rare malignant tumor originating from adipocytes.
This tumor is a kind of soft tissue sarcoma. Symptoms depend on the site of origin. Clinically, liposarcoma may be difficult to distinguish from a lipoma. Diagnosis is established with biopsy, and the mainstay of treatment is complete surgical excision. License: CC BY 2. Like skeletal muscle, it has cross striations in its cells, but cardiac muscle has a single, centrally located nucleus. Cardiac muscle is not under voluntary control but can be influenced by the autonomic nervous system to speed up or slow down.
An added feature to cardiac muscle cells is a line than extends along the end of the cell as it abuts the next cardiac cell in the row. This line is called an intercalated disc: it assists in passing electrical impulse efficiently from one cell to the next and maintains the strong connection between neighboring cardiac cells. Figure 1. Smooth muscle cells do not have striations, while skeletal muscle cells do.
Cardiac muscle cells have striations, but, unlike the multinucleate skeletal cells, they have only one nucleus. Cardiac muscle tissue also has intercalated discs, specialized regions running along the plasma membrane that join adjacent cardiac muscle cells and assist in passing an electrical impulse from cell to cell. Nervous tissues are made of cells specialized to receive and transmit electrical impulses from specific areas of the body and to send them to specific locations in the body.
The main cell of the nervous system is the neuron, illustrated in Figure 2. The large structure with a central nucleus is the cell body of the neuron. Projections from the cell body are either dendrites specialized in receiving input or a single axon specialized in transmitting impulses. Some glial cells are also shown. The function of muscle tissue smooth, skeletal, and cardiac is to contract, while nervous tissue is responsible for communication. There are three types of muscle in animal bodies: smooth, skeletal, and cardiac.
They differ by the presence or absence of striations or bands, the number and location of nuclei, whether they are voluntarily or involuntarily controlled, and their location within the body.
Smooth muscle cells have a single, centrally-located nucleus and are spindle shaped. Constriction of smooth muscle occurs under involuntary, autonomic nervous control in response to local conditions in the tissues. Smooth muscle tissue is also called non-striated as it lacks the banded appearance of skeletal and cardiac muscle. The walls of blood vessels, the tubes of the digestive system, and the tubes of the reproductive systems are composed primarily of smooth muscle.
Contractions of smooth muscle move food through the digestive tracts and push blood through the blood vessels. Skeletal muscle has striations across its cells caused by the arrangement of the contractile proteins, actin and myosin, that run throughout the muscle fiber. Skeletal muscle cells can contract by the attachment of myosin to actin filaments in the muscle, which then ratchets the actin filaments toward the center of the cells.
These muscle cells are relatively long and have multiple nuclei along the edge of the cell. Skeletal muscle is under voluntary, somatic nervous system control and is found in the muscles that move bones. Stimulation of these cells by somatic motor neurons signals the cells to contract. Cardiac muscle is found only in the heart. Similar to skeletal muscle, it has cross striations in its cells, but cardiac muscle has a single, centrally-located nucleus; the muscle branches in many directions.
Cardiac muscle is not under voluntary control, but is influenced by the autonomic nervous system to speed up or slow down the heart beat.
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