Condet

Anthony RB Smith MD FRCOG

• Consultant Gynaecologist, The Warrell Unit, St Mary?
• Hospital, Manchester

The relative fluidity of the membrane is particularly important in a cold environment medicine 657 purchase frumil 5mg with visa. A cold environment tends to compress membranes composed largely of saturated fatty acids treatment modality definition buy generic frumil 5mg on-line, making them less fluid and more susceptible to rupturing symptoms xanax overdose safe frumil 5mg. Many organisms (fish are one example) are capable of adapting to cold environments by changing the proportion of unsaturated fatty acids in their membranes in response to the lowering of the temperature medications not to be crushed discount frumil 5mg fast delivery. Animals have an additional membrane constituent that assists in maintaining fluidity. Cholesterol, which lies alongside the phospholipids in the membrane, tends to dampen the effects of temperature on the membrane. Thus, this lipid functions as a buffer, preventing lower temperatures from inhibiting fluidity and preventing increased temperatures from increasing fluidity too much. Thus, cholesterol extends, in both directions, the range of temperature in which the membrane is appropriately fluid and consequently functional. Cholesterol also serves other functions, such as organizing clusters of transmembrane proteins into lipid rafts. The Components and Functions of the Plasma Membrane Component Phospholipid Cholesterol Integral proteins (for example, integrins) Peripheral proteins Carbohydrates (components of glycoproteins and glycolipids) Table 5. May or may not penetrate through both layers On the inner or outer surface of the phospholipid bilayer; not embedded within the phospholipids Generally attached to proteins on the outside membrane layer this OpenStax book is available for free at cnx. Many infectious diseases, such as smallpox, polio, diphtheria, and tetanus, were conquered by the use of vaccines. Immunologists are the physicians and scientists who research and develop vaccines, as well as treat and study allergies or other immune problems. Immunologists are called in to help treat organ transplantation patients, who must have their immune systems suppressed so that their bodies will not reject a transplanted organ. Others work on questions about how the immune system affects diseases such as cancer. In the past, the importance of having a healthy immune system in preventing cancer was not at all understood. Immunologists must possess knowledge of the functions of the human body as they relate to issues beyond immunization, and knowledge of pharmacology and medical technology, such as medications, therapies, test materials, and surgical procedures. In other words, plasma membranes are selectively permeable-they allow some substances to pass through, but not others. Some cells require larger amounts of specific substances than do other cells; they must have a way of obtaining these materials from extracellular fluids. This may happen passively, as certain materials move back and forth, or the cell may have special mechanisms that facilitate transport. All cells spend the majority of their energy to maintain an imbalance of sodium and potassium ions between the interior and exterior of the cell. Passive transport is a naturally occurring phenomenon and does not require the cell to exert any of its energy to accomplish the movement. In passive transport, substances move from an area of higher concentration to an area of lower concentration. A physical space in which there is a range of concentrations of a single substance is said to have a concentration gradient. Selective Permeability Plasma membranes are asymmetric: the interior of the membrane is not identical to the exterior of the membrane. In fact, there is a considerable difference between the array of phospholipids and proteins between the two leaflets that form a membrane. On the interior of the membrane, some proteins serve to anchor the membrane to fibers of the cytoskeleton. There are peripheral proteins on the exterior of the membrane that bind elements of the extracellular matrix. Carbohydrates, 144 Chapter 5 Structure and Function of Plasma Membranes attached to lipids or proteins, are also found on the exterior surface of the plasma membrane. These carbohydrate complexes help the cell bind substances that the cell needs in the extracellular fluid. Recall that plasma membranes are amphiphilic: They have hydrophilic and hydrophobic regions. This characteristic helps the movement of some materials through the membrane and hinders the movement of others.

This helps to control the volume of blood flowing into a tissue at different times medicine 513 cheap frumil 5mg without a prescription. For example medications resembling percocet 512 buy frumil 5mg otc, during exercise symptoms zollinger ellison syndrome purchase 5mg frumil overnight delivery, arterioles that supply blood to muscles in your legs would be wide (dilated) as their walls relax treatment associates generic frumil 5 mg line, while those carrying blood to the gut wall would be narrow (constricted). The cells of the endothelium are very thin, except where there is a nucleus (red). The function of capillaries is to take blood as close as possible to all cells, allowing rapid transfer of substances between cells and blood. Capillaries form a network throughout every tissue in the body except the cornea and cartilage. The small size of capillaries is obviously of great importance in allowing them to bring blood as close as possible to each group of cells in the body. A human capillary is approximately 7 m in diameter, about the same size as a red blood cell (Figure 8. Moreover, the walls of capillaries are extremely thin, made up of a single layer of endothelial cells. As red blood cells carrying oxygen squeeze through a capillary, they are brought to within as little as 1 m of the cells outside the capillary which need the oxygen. In most capillaries, there are tiny gaps between the individual cells that form the endothelium. As we shall see later in this chapter, these gaps are important in allowing some components of the blood to seep through into the spaces between the cells in all the tissues of the body. By the time blood reaches the capillaries, it has already lost a great deal of the pressure originally supplied to it by the contraction of the ventricles. Veins As blood leaves a capillary bed, the capillaries gradually join with one another, forming larger vessels called venules. They have the same three layers as arteries, but the tunica media is much thinner and has far fewer elastic fibres and muscle fibres. The low blood pressure in veins creates a problem: how can this blood be returned to the heart The problem is perhaps most obvious if you consider how blood can return from your legs. Whenever you tense these muscles, they squeeze inwards on the veins in your legs, temporarily raising the pressure within them. Chapter 8: Transport in mammals this squeezing, in itself, would not help to push the blood back towards the heart; blood would just squidge up and down as you walked. To keep the blood flowing in the right direction, veins contain half-moon valves, or semilunar valves, formed from their endothelium (Figure 8. Thus, when you contract your leg muscles, the blood in the veins is squeezed up through these valves, but cannot pass down through them. Note that blood samples are normally taken from veins, rather than from arteries, because of the lower pressure in them (Figure 8. When a soldier stands motionless at attention, the blood pressure in his feet rises very quickly to about 90 mm Hg. They are therefore used when a blood sample is being taken, or to donate blood for transfusions. Blood pressure / mmHg 80 60 40 20 0 venae cavae pulmonary arterioles arteries pulmonary veins aorta arteries arterioles capillaries venules veins capillaries venules Systemic circulation Pulmonary circulation Figure 8. These solutes include nutrients such as glucose and waste products such as urea that are being transported from one place to another in the body. Solutes also include protein molecules, called plasma proteins, that remain in the blood all the time. As blood flows through capillaries within tissues, some of the plasma leaks out through the gaps between the cells in the walls of the capillary, and seeps into the spaces between the cells of the tissues. However, it contains far fewer protein molecules than blood plasma, as these are too large to escape easily through the tiny holes in the capillary endothelium. Red blood cells are much too large to pass through, so tissue fluid does not contain these, but some white blood cells can squeeze through and move freely around in tissue fluid. The volume of fluid which leaves the capillary to form tissue fluid is the result of two opposing pressures.

They include the familiar bread mold symptoms 9 days after ovulation cheap 5 mg frumil, Rhizopus stolonifer treatment alternatives for safe communities buy frumil 5 mg line, which rapidly propagates on the surfaces of breads medicine 0031 purchase frumil 5mg, fruits treatment authorization request discount 5 mg frumil free shipping, and vegetables. Most species are saprobes, living off decaying organic material; a few are parasites, particularly of insects. The metabolic products of other species of Rhizopus are intermediates in the synthesis of semi-synthetic steroid hormones. Zygomycetes have a thallus of coenocytic hyphae in which the nuclei are haploid when the organism is in the vegetative stage. The black tips of bread mold are the swollen sporangia packed with black spores (Figure 24. When spores land on a suitable substrate, they germinate and produce a new mycelium. The developing diploid zygospores have thick coats that protect them from desiccation and other hazards. When the zygospore germinates, it undergoes meiosis and produces haploid spores, which will, in turn, grow into a new organism. This form of sexual reproduction in fungi is called conjugation (although it differs markedly from conjugation in bacteria and protists), giving rise to the name "conjugated fungi". In the sexual life cycle, plus and minus mating types conjugate to form a zygosporangium. Some play a beneficial role, such as the yeasts used in baking, brewing, and wine fermentation, plus truffles and morels, which are held as gourmet delicacies. Ascomycetes not only infest and destroy crops directly; they also produce poisonous secondary metabolites that make crops unfit for consumption. Filamentous ascomycetes produce this OpenStax book is available for free at cnx. Conidia and asci, which are used respectively for asexual and sexual reproductions, are usually separated from the vegetative hyphae by blocked (non-perforated) septa. Asexual reproduction is frequent and involves the production of conidiophores that release haploid conidiospores (Figure 24. Sexual reproduction starts with the development of special hyphae from either one of two types of mating strains (Figure 24. The "male" strain produces an antheridium and the "female" strain develops an ascogonium. At fertilization, the antheridium and the ascogonium combine in plasmogamy without nuclear fusion. Special ascogenous hyphae arise, in which pairs of nuclei migrate: one from the "male" strain and one from the "female" strain. During sexual reproduction, thousands of asci fill a fruiting body called the ascocarp. The ascospores are then released, germinate, and form hyphae that are disseminated in the environment and start new mycelia (Figure 24. A haploid zygote that forms in the ascocarp undergoes karyogamy, meiosis, and mitosis to form eight ascospores. A dikaryotic ascus that forms in the ascocarp undergoes plasmogamy, meiosis, and mitosis to form eight ascospores. The basidia, which are the reproductive organs of these fungi, are often contained within the familiar mushroom, commonly seen in fields after rain, on the supermarket shelves, and growing on your lawn (Figure 24. These mushroom-producing basidiomyces are sometimes referred to as "gill fungi" because of the presence of gill-like structures on the underside of the cap. This group also includes shelf fungus, which cling to the bark of trees like small shelves. In addition, the basidiomycota includes smuts and rusts, which are important plant pathogens; toadstools, and shelf fungi stacked on tree trunks. Most edible fungi belong to the Phylum Basidiomycota; however, some basidiomycetes produce deadly toxins. The body of this fungus, its mycelium, is underground and grows outward in a circle. As it grows, the mycelium depletes the soil of nitrogen, causing the mycelia to grow away from the center and leading to the "fairy ring" of fruiting bodies where there is adequate soil nitrogen. Spores are generally produced through sexual reproduction, rather than asexual reproduction.

Rabbits digest their food twice: the first time food passes through the digestive system treatment whooping cough buy discount frumil 5 mg on line, it collects in the cecum treatment 4 sore throat purchase 5mg frumil with amex, and then it passes as soft feces called cecotrophes medications and grapefruit juice discount 5 mg frumil visa. Avian Birds face special challenges when it comes to obtaining nutrition from food symptoms 38 weeks pregnant purchase frumil 5mg with visa. Birds have evolved a variety of beak types that reflect the vast variety in their diet, ranging from seeds and insects to fruits and nuts. Because most birds fly, their metabolic rates are high in order to efficiently process food and keep their body weight low. The stomach of birds has two chambers: the proventriculus, where gastric juices are produced to digest the food before it enters the stomach, and the gizzard, where the food is stored, soaked, and mechanically ground. Most of the chemical digestion and absorption happens in the intestine and the waste is excreted through the cloaca. Food passes from the crop to the first of two stomachs, called the proventriculus, which contains digestive juices that break down food. From the proventriculus, the food enters the second stomach, called the gizzard, which grinds food. Some birds swallow stones or grit, which are stored in the gizzard, to aid the grinding process. Instead, uric acid from the kidneys is secreted into the large intestine and combined with waste from the digestive process. Recent fossil evidence has shown that the evolutionary divergence of birds from other land animals was characterized by streamlining and simplifying the digestive system. The horny beak, lack of jaws, and the smaller tongue of the birds can be traced back to their dinosaur ancestors. The emergence of these changes seems to coincide with the inclusion of seeds in the bird diet. Seed-eating birds have beaks that are shaped for grabbing seeds and the two-compartment stomach allows for delegation of tasks. Since birds need to remain light in order to fly, their metabolic rates are very high, which means they digest their food very quickly and need to eat often. Contrast this with the ruminants, where the digestion of plant matter takes a very long time. Ruminants Ruminants are mainly herbivores like cows, sheep, and goats, whose entire diet consists of eating large amounts of roughage or fiber. They have evolved digestive systems that help them digest vast amounts of cellulose. The four compartments of the stomach are called the rumen, reticulum, omasum, and abomasum. These chambers contain many microbes that break down cellulose and ferment ingested food. The abomasum is the "true" stomach and is the equivalent of the monogastric stomach chamber where gastric juices are secreted. The four-compartment gastric chamber provides larger space and the microbial support necessary to digest plant material in ruminants. The fermentation process produces large amounts of gas in the stomach chamber, which must be eliminated. As in other animals, the small intestine plays an important role in nutrient absorption, and the large intestine helps in the elimination of waste. The first two stomachs, the rumen and the reticulum, contain prokaryotes and protists that are able to digest cellulose fiber. The ruminant regurgitates cud from the reticulum, chews it, and swallows it into a third stomach, the omasum, which removes water. The cud then passes onto the fourth stomach, the abomasum, where it is digested by enzymes produced by the ruminant. Digesting plant material is not easy because plant cell walls contain the polymeric sugar molecule cellulose. The digestive enzymes of these animals cannot break down cellulose, but microorganisms present in the digestive system can.

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