Question

1-The importance of adipose tissue as an adipokine secreting-tissue ?

2- Kidney stones: types and causes?

please i need a Complete, not brief, answer (detailed)

Answer 1

1. The importance of adipose tissue as an adipokine secreting-tissue :-

Due to its large quantity, adipose tissue represents an important, but often neglected endocrine organ.

Its cells (adipocytes) form an extensive amount of peptide hormones known as adipokines (or adipocytokines). In general, they mainly regulate the energy metabolism and their effect on appetite and feeding behaviour influences a long-term regulation of the body weight. Apart from affecting the metabolism they also modulate immune functions and the course of the inflammatory processes. Among the most important and well-known hormones are leptin, adiponectin and resistin.

In addition to the direct production of its own hormones the adipose tissue influences hormones secreted by other endocrine organs. For example, an excessive amount of adipose tissue can significantly contribute to the formation of insulin resistance, type 2 diabetes or atherosclerosis.

Leptin :-
There are several hypotheses explaining the mechanism by which the adipokines work. The so-called lipostatic hypothesis claims that the adipose tissue produces, proportionally to its amount in the body, signaling molecules affecting hypothalamus and leading to an increase in energy expenditure and decrease in food intake. The first uncovered mediator of this kind was leptin.

Structure and synthesis -
Leptin is a 167 amino acid hormone, a product of the ob gene (“ob” derived from the word obesity). Its receptor is coded by a db gene, which exists in several alternative splicing forms. Different forms of this receptor can be found in different parts of the body – e.g. in brain (hypothalamus mainly) or in peripheral tissues.

Leptin is synthesized mainly by adipocytes of the white adipose tissue and the synthesized amount correlates with the quantity of the adipose tissue in the body. Obese people therefore produce more leptin than people with normal body weight. Apart from white adipose tissue, leptin is synthesized at lesser extent by other tissues as well (e.g. brown adipose tissue, skeletal muscles, stomach, liver or placenta).

Function and pathology-
Leptin extensively regulates the energy intake and expenditure by its influence over feeding behaviour, appetite, hunger and energy metabolism. Because its amount in bloodstream corresponds to the amount of adipose tissue, it provides the brain with feedback information about the status of energy reserves.

Leptin passes through the hematoencephalic barrier and has an anorexigenic effect on hypothalamus, suppressing appetite and increasing the energy expenditure. In periphery it influences the sensitivity towards insulin. It thus acts against the orexigenic effect of neuropeptide Y, which, on the contrary, increases appetite and stimulates the secretion of insulin. Leptin activates an enzyme AMP-kinase (AMPK) located in myocytes, which causes an increase in TAG oxidation in muscles.

There exist rare cases of mutations damaging the leptin receptor or the leptin itself. They present themselves as often morbidly extensive obesity occurring at low age and dyslipidemia, which results from an uncontrolled hunger and gluttony. An increased production of insulin in this patients leads to the development of the insulin resistance.

In contrast, most of the obese patients do not have a leptin deficiency. On the contrary, because the leptin is formed proportionally to the amount of adipose tissue in the body, obese people usually have rather hyperleptinemia and leptin resistance. Therapeutic administration of leptin, which was at first considered a universal cure for obesity, thus helps only a fraction of patients (those with a mutation affecting the leptin or its receptor).

Adiponectin :-
Structure and synthesis-
Adiponectin is a protein hormone produced mainly by adipocytes of the adipose tissue. Its concentration in blood is quite high (several orders higher compared to leptin).

Another difference from leptin is the correlation between the amount of body fat and the synthesis of the hormones. In the case of adiponectin it is negative and that is why obese patients have plasma concentrations lower than patients with normal BMI.

There exist several polymeric isoforms of adiponectin in blood plasma (trimers, hexamers or higher polymer structures), each having different effect on body.

Function-
Adiponectin is a hormone mainly influencing the metabolism of saccharides and lipids, increasing the sensitivity of tissues to insulin. Its effect leads to an increased transport and utilization of glucose and free fatty acids in muscles, liver and adipose cells and inhibits gluconeogenesis in liver.

Adiponectin, at the same time prevents the development of atherosclerosis, especially at early stages of its formation. It inhibits the transformation of macrophages to foam cells and decreases the expression of the surface adhesive receptors.

Resistin:-
Similar to other adipokines, resistin belongs to the group of proteins synthesized by adipocytes. It can also be formed by cells of the immune system and its expression is regulated mainly by a presence of proinflammatory cytokines IL-6 and TNFα.

Animal experiments have shown that the administration of resistin reduces the glucose tolerance and insulin sensitivity. It is therefore probable that the increased concentration is involved in the development of insulin resistance. The association of resistin with obesity and diabetes is still unclear, the results of experimental studies on humans were contradictory. It is thought that its importance in humans lies rather in the regulation of inflammatory processes.

2. Kidney stones: types and causes :-

There are mainly 5 types of kidney stones. They are :-

• Calcium Oxalate Stones

The most common type of kidney stone is a calcium oxalate stone. These result when the urine contains low levels of citrate and high levels of calcium and either oxalate or uric acid. Calcium oxalate stones are linked with foods high in oxalate, which is a naturally occurring substance in plants and animals. These include beets, black tea, chocolate, nuts, potatoes, and spinach.

If you continually develop calcium oxalate stones, your doctor may recommend further evaluation of your urinary function and metabolism. This requires blood tests and the collection of urine at home for at least one 24-hour period. Your doctor may also recommend dietary modifications to reduce the likelihood of kidney stones returning.

• Calcium Phosphate Stones

Calcium phosphate kidney stones are caused by abnormalities in the way the urinary system functions. Your doctor may order a series of blood and urine tests to determine whether any urinary or kidney problems could be causing this type of stone, which often occurs simultaneously with calcium oxalate stones.

• Struvite Stones

More common in women, struvite stones form as a result of certain types of urinary tract infections. These stones tend to grow quickly and become large, sometimes occupying the entire kidney. Left untreated, they can cause frequent and sometimes severe urinary tract infections and loss of kidney function.

• Uric Acid Stones

More common in men, uric acid stones tend to occur in people who don’t drink enough water or have a diet high in animal protein. They are also more likely to occur in people who have gout, a family history of this type of kidney stone, or in those who’ve had chemotherapy.

• Cystine Stones

Cystine stones are caused by a hereditary genetic disorder called cystinuria that can lead to excessive amounts of the amino acid cystine collecting in the urine. This can result in the formation of stones in the kidneys, bladder, and ureters, which transport urine from the kidneys to the bladder.

Why kidney stone occurs :-

  Kidney stones form when your urine contains more crystal-forming substances such as calcium, oxalate and uric acid than fluid in your urine can dilute. At the same time, your urine may lack substances that prevent crystals from sticking together, creating an ideal environment for kidney stones to form.

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