The deserts have a very varied location and are characterized by very sparse vegetation. The soil is very arid and the rainfall is low and irregular, below 250 mm of annual water. During the day the temperature is high, but at night there is rapid heat loss that radiates into the atmosphere and the temperature becomes excessively low.
The divisions that occur during segmentation are called cleavages, and the cells that form are called blastomers. In the Animal Kingdom, the difference in the quantity and distribution of calf in the egg determines differences in segmentation, the lower the rate of division. Because of this, we can consider two basic types of segmentation: holoblastic or total that occurs in the whole zygote; meroblastic or partial, which occurs only in part of the egg.
Sustainable Planet The Sustainable Planet movement is part of a project that aims to soften our impact on the environment. This project suggests some changes in our habits that aim to reduce the consumption of three essential and limited resources: Water, Electricity and Fuels. Water - It falls from the sky, but is a rare and exhaustible resource in many parts of the world.
In humans, as in all mammals, circulation is through a closed system of blood vessels whose functional core is the heart. The circulation is responsible for the dissemination of food and oxygen and removal of the remains formed by cellular activities, this work is performed by the blood.
Salivary amylase digests starch and other polysaccharides (such as glycogen), reducing them to maltose (disaccharide) molecules. Salts, in saliva, neutralize acidic substances and maintain a slightly acidic pH in the mouth (6, 7), ideal for the action of ptialin. The food, which turns into a food bolus, is pushed by the tongue to the bottom of the pharynx, being sent to the esophagus, driven by peristaltic waves (as shown in the figure below), taking between 5 and 10 seconds to travel through the esophagus.
Living cells are subject to osmosis, a physicochemical process that causes them to lose or gain water with varying volume. Throughout the evolutionary process, animals have developed various mechanisms to regulate the osmotic process to which they are subjected. These mechanisms constitute what is called osmoregulation.
Many of the observations that led Charles Darwin to elaborate his evolutionary theory occurred during his voyage around the world as a naturalist on the English ship H. S. Beagle. During the five-year voyage that began in 1831, Darwin visited various places in South America (including Brazil) and Australia, as well as several tropical archipelagos.
Freshwater animals have the reverse osmotic problem of saltwater animals. The cells and internal fluids of freshwater animals are hypertonic to the environment, so they are always absorbing water by osmosis. Freshwater fish have to eliminate large amounts of water in the urine and thus lose important salts.
The human species has four parathyroid glands, which adhere to the back of the thyroid. Parathyroids produce parathyroid hormone, which is responsible for increasing the level of calcium in the blood. Parathyroid hormone deficiency Parathyroid hormone deficiency causes a decrease in the amount of calcium in the blood, which causes skeletal muscle cells to contract convulsively.
In the late nineteenth century, in Germany, medical student Paul Langerhans was studying slides containing sections of pancreatic tissue under the microscope and found a profusion of groups of pancreatic cells surrounded by blood vessels. These groupings, which were later called Langerhans islets (or pancreatic islets), are the production sites of two hormones, insulin (from Latin, insula = island) and glucagon.
The whole living cell and in particular the nerve cells show electrical potential difference (DDP) between the inner and outer faces of their cell membrane. This DDP is generated by the difference in ion concentration inside and outside the cell. As the cytoplasm contains proportionally fewer positive ions than the external liquid, the inner surface of the membrane is negative relative to the outer one.
Emphysema is very rare in people who have never smoked. It is the complete obstruction of the bronchioles, with increased resistance to air passage, especially during expirations. Thus, rupture of the walls of the alveoli may occur, with formation of large cavities. This decreases the lung's efficiency in absorbing oxygen and there is an overload of the heart to compensate for lung deficiency.
It is an inflammation of the mucous membranes lining the nasal cavities due to allergic processes. As a consequence of the inflammation, the cells start producing excess mucus, which runs down the nostrils. Repeated outbreaks of allergic rhinitis in children may cause definitive nasal obstruction, which leads to bone changes at the base of the skull.
Among the various adaptations that favor the conquest of the terrestrial environment by vertebrates are an efficient waterproofed body lining, an adequate skeletal support system of the organism and its organs and a skillful mechanism that allows the movement of the organism through the environment.
Many insects have body hair that is able to vibrate in response to sound waves of certain frequencies, allowing to detect various types of sound. Others have more elaborate sound pickup organs - the tympanic organs - usually located in the paws. Tympanic organs consist of a membrane (tympanic membrane) that vibrates in response to certain sound frequencies.
The set of bones and cartilage that protect the organs and allow movement forms the skeletal system, whose basic functions are support, protection, movement, mineral reserves (mainly calcium and phosphorus) and blood cell production (hematopoiesis). Bone Types Almost all bones in the body can be classified into 4 types according to their shape: Long - Longer than Broad.
The amount of bone mass present in the skeleton is the result of formation and resorption. This turnover is directly related to the bodily need to maintain a physiological concentration of ionized calcium in organic fluids and especially to the need to maintain the structural integrity of the skeleton.
The organism's relationship with the environment and the coordination of the work of the various internal organs are in charge of two important systems: the nervous and the hormonal. Nerve coordination involves the participation of nerve cells, called neurons. Hormonal coordination includes the participation of hormones, chemicals that spread through the blood and connect various organs, controlling their actions.
These changes do not modify the amount of chromosomes in a cell, but determine the appearance of abnormal chromosomes. The aberrations we describe below almost always lead to serious problems, including gamete formation. This is because during meiosis, the chromosome with the deficiency anomalously matches its unchanged counterpart, affecting the progress of the meiotic process.