Brunner's glands are compound tubular submucosal glands found in that portion of the duodenum, above the hepatopancreatic sphincter. The main function of these glands is to produce a mucus-rich alkaline secretion i.e. Mucous in order to: protect the duodenum from the acidic content of chyme, they secrete epidermal growth factor, which inhibits parietal and chief cells of the stomach from secreting acid and their digestive enzymes. This is another form of protection for the duodenum, they are the distinguishing feature of the duodenum, are named for the Swiss physician who first described them, Johann Conrad Brunner. The duodenum is distinguished from other regions of the small intestine by the presence of submucosal Brunner's glands, which may pack the submucosa so that the typical submucosal connective tissue is obscured; the Brunner glands, which empty into the intestinal glands, secrete an alkaline fluid composed of mucin, which exerts a physiologic anti-acid function by coating the duodenal epithelium, therefore protecting it from the acid chyme of the stomach.
Furthermore, in response to the presence of acid in the duodenum, these glands secrete pepsinogen and urogastrone, which inhibit gastric acid secretion. The main function of these glands is to produce a mucus-rich alkaline secretion in order to: protect the duodenum from the acidic content of chyme provide an alkaline condition for the intestinal enzymes to be active, thus enabling absorption to take place lubricate the intestinal walls Hyperplasia of Brunner glands with a lesion greater than 1 cm was described as a Brunner gland adenoma. Several features of these lesions favor their designation as hamartomas, including the lack of encapsulation; these hamartomas are rare, with 150 cases described in the literature.6 It is estimated that they represent 5-10% of benign duodenal tumors. They are variable in size 1–3 cm, with only a few reported cases of lesions larger than 5 cm. Most patients with Brunner gland hamartomas are asymptomatic or have nonspecific complaints such as nausea, bloating, or vague abdominal pain.
Most reports in the literature describe local surgical resection of Brunner gland hamartoma via duodenotomy. Successful endoscopic resection has been reported and is used for pedunculated Brunner gland hamartomas; the endoscopic approach in selective cases appears to be safe, less invasive, less costly. Peutz-Jeghers syndrome Histology image: 11504loa – Histology Learning System at Boston University - "Digestive System: Alimentary Canal: pyloro/duodenal junction, duodenum" Histology image: 11513loa – Histology Learning System at Boston University - "Digestive System: Alimentary Canal: pyloro/duodenal junction" Histology image: 11609loa – Histology Learning System at Boston University - "Digestive System: Alimentary Canal: duodenum, plicae circularis"
In chemistry, pH is a scale used to specify how acidic or basic a water-based solution is. Acidic solutions have a lower pH, while basic solutions have a higher pH. At room temperature, pure water is neither acidic nor basic and has a pH of 7; the pH scale is logarithmic and approximates the negative of the base 10 logarithm of the molar concentration of hydrogen ions in a solution. More it is the negative of the base 10 logarithm of the activity of the hydrogen ion. At 25 °C, solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic; the neutral value of the pH depends on the temperature, being lower than 7 if the temperature increases. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for strong acids and bases respectively; the pH scale is traceable to a set of standard solutions whose pH is established by international agreement. Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode.
The pH of aqueous solutions can be measured with a glass electrode and a pH meter, or a color-changing indicator. Measurements of pH are important in chemistry, medicine, water treatment, many other applications; the concept of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909 and revised to the modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells. In the first papers, the notation had the "H" as a subscript to the lowercase "p", as so: pH; the exact meaning of the "p" in "pH" is disputed, but according to the Carlsberg Foundation, pH stands for "power of hydrogen". It has been suggested that the "p" stands for the German Potenz, others refer to French puissance. Another suggestion is that the "p" stands for the Latin terms pondus hydrogenii, potentia hydrogenii, or potential hydrogen, it is suggested that Sørensen used the letters "p" and "q" to label the test solution and the reference solution.
In chemistry, the p stands for "decimal cologarithm of", is used in the term pKa, used for acid dissociation constants. Bacteriologist Alice C. Evans, famed for her work's influence on dairying and food safety, credited William Mansfield Clark and colleagues with developing pH measuring methods in the 1910s, which had a wide influence on laboratory and industrial use thereafter. In her memoir, she does not mention how much, or how little and colleagues knew about Sørensen's work a few years prior, she said: In these studies Dr. Clark's attention was directed to the effect of acid on the growth of bacteria, he found that it is the intensity of the acid in terms of hydrogen-ion concentration that affects their growth. But existing methods of measuring acidity determined not the intensity, of the acid. Next, with his collaborators, Dr. Clark developed accurate methods for measuring hydrogen-ion concentration; these methods replaced the inaccurate titration method of determining acid content in use in biologic laboratories throughout the world.
They were found to be applicable in many industrial and other processes in which they came into wide usage. The first electronic method for measuring pH was invented by Arnold Orville Beckman, a professor at California Institute of Technology in 1934, it was in response to local citrus grower Sunkist that wanted a better method for testing the pH of lemons they were picking from their nearby orchards. PH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH+, in a solution. PH = − log 10 = log 10 For example, for a solution with a hydrogen ion activity of 5×10−6 we get 1/ = 2×105, thus such a solution has a pH of log10 = 5.3. For a commonplace example based on the facts that the masses of a mole of water, a mole of hydrogen ions, a mole of hydroxide ions are 18 g, 1 g, 17 g, a quantity of 107 moles of pure water, or 180 tonnes, contains close to 1 g of dissociated hydrogen ions and 17 g of hydroxide ions. Note that pH depends on temperature. For instance at 0 °C the pH of pure water is 7.47.
At 25 °C it's 7.00, at 100 °C it's 6.14. This definition was adopted because ion-selective electrodes, which are used to measure pH, respond to activity. Ideally, electrode potential, E, follows the Nernst equation, for the hydrogen ion can be written as E = E 0 + R T F ln = E 0 − 2.303 R T F pH where E is a measured potential, E0 is the standard electrode potential, R is the gas const
Smooth muscle is an involuntary non-striated muscle. It is divided into two subgroups. Within single-unit cells, the whole bundle or sheet contracts as a syncytium. Smooth muscle cells are found in the walls of hollow organs, including the stomach, urinary bladder and uterus, in the walls of passageways, such as the arteries and veins of the circulatory system, the tracts of the respiratory and reproductive systems; these cells are present in the eyes and are able to change the size of the iris and alter the shape of the lens. In the skin, smooth muscle cells cause hair to stand erect in response to cold fear. Most smooth muscle is of the single-unit variety, that is, either the whole muscle contracts or the whole muscle relaxes, but there is multiunit smooth muscle in the trachea, the large elastic arteries, the iris of the eye. Single unit smooth muscle, however, is most common and lines blood vessels, the urinary tract, the digestive tract. However, the terms single- and multi-unit smooth muscle represents an oversimplification.
This is due to the fact that smooth muscles for the most part are controlled and influenced by a combination of different neural elements. In addition, it has been observed that most of the time there will be some cell to cell communication and activators/ inhibitors produced locally; this leads to a somewhat coordinated response in multiunit smooth muscle. Smooth muscle is fundamentally different from skeletal muscle and cardiac muscle in terms of structure, regulation of contraction, excitation-contraction coupling. Smooth muscle cells known as myocytes, have a fusiform shape and, like striated muscle, can tense and relax. However, smooth muscle tissue tends to demonstrate greater elasticity and function within a larger length-tension curve than striated muscle; this ability to stretch and still maintain contractility is important in organs like the intestines and urinary bladder. In the relaxed state, each cell is 20 -- 500 micrometers in length. A substantial portion of the volume of the cytoplasm of smooth muscle cells are taken up by the molecules myosin and actin, which together have the capability to contract, through a chain of tensile structures, make the entire smooth muscle tissue contract with them.
Myosin is class II in smooth muscle. Myosin II contains two heavy chains which constitute the tail domains; each of these heavy chains contains the N-terminal head domain, while the C-terminal tails take on a coiled-coil morphology, holding the two heavy chains together. Thus, myosin II has two heads. In smooth muscle, there is a single gene that codes for the heavy chains myosin II, but there are splice variants of this gene that result in four distinct isoforms. Smooth muscle may contain MHC, not involved in contraction, that can arise from multiple genes. Myosin II contains 4 light chains, resulting in 2 per head, weighing 20 and 17 kDa; these bind the heavy chains in the "neck" region between the head and tail. The MLC20 is known as the regulatory light chain and participates in muscle contraction. Two MLC20 isoforms are found in smooth muscle, they are encoded by different genes, but only one isoform participates in contraction; the MLC17 is known as the essential light chain. Its exact function is unclear, but it's believed that it contributes to the structural stability of the myosin head along with MLC20.
Two variants of MLC17 exist as a result of alternative splicing at the MLC17 gene. Different combinations of heavy and light chains allow for up to hundreds of different types of myosin structures, but it is unlikely that more than a few such combinations are used or permitted within a specific smooth muscle bed. In the uterus, a shift in myosin expression has been hypothesized to avail for changes in the directions of uterine contractions that are seen during the menstrual cycle; the thin filaments that form part of the contractile machinery are predominantly composed of α- and γ-actin. Smooth muscle α-actin is the predominant isoform within smooth muscle. There are lots of actin that does not take part in contraction, but that polymerizes just below the plasma membrane in the presence of a contractile stimulant and may thereby assist in mechanical tension. Alpha actin is expressed as distinct genetic isoforms such as smooth muscle, cardiac muscle and skeletal muscle specific isoforms of alpha actin.
The ratio of actin to myosin is between 10:1 in smooth muscle. Conversely, from a mass ratio standpoint, myosin is the dominant protein in striated skeletal muscle with the actin to myosin ratio falling in the 1:2 to 1:3 range. A typical value for healthy young adults is 1:2.2.. Tropomyosin is present in smooth muscle, spanning seven actin monomers and is laid out end to end over the entire length of the thin filaments. In striated muscle, tropomyosin serves to block actin–myosin interactions until calcium is present, but in smooth muscle, its function is unknown. Calponin molecules may exist in equal number as actin, has been proposed to be a load-bearing protein. Caldesmon has been suggested to be involved in tethering actin and tropomyosin, thereby enhance the ability of smooth muscle to maintain tension. All three of these proteins may have a role in inhibiting the ATPase activity of the m
Peristalsis is a radially symmetrical contraction and relaxation of muscles that propagates in a wave down a tube, in an anterograde direction. In much of a digestive tract such as the human gastrointestinal tract, smooth muscle tissue contracts in sequence to produce a peristaltic wave, which propels a ball of food along the tract. Peristaltic movement comprises relaxation of circular smooth muscles their contraction behind the chewed material to keep it from moving backward longitudinal contraction to push it forward. Earthworms use a similar mechanism to drive their locomotion, some modern machinery imitates this design; the word comes from New Latin and is derived from the Greek peristellein, "to wrap around," from peri-, "around" + stellein, "draw in, bring together. After food is chewed into a bolus, it is moved through the esophagus. Smooth muscles contract behind the bolus to prevent it from being squeezed back into the mouth. Rhythmic, unidirectional waves of contractions work to force the food into the stomach.
The migrating motor complex helps trigger peristaltic waves. This process works in one direction only and its sole esophageal function is to move food from the mouth into the stomach. In the esophagus, two types of peristalsis occur: First, there is a primary peristaltic wave, which occurs when the bolus enters the esophagus during swallowing; the primary peristaltic wave forces the bolus down the esophagus and into the stomach in a wave lasting about 8–9 seconds. The wave travels down to the stomach if the bolus of food descends at a greater rate than the wave itself, continues if for some reason the bolus gets stuck further up the esophagus. In the event that the bolus gets stuck or moves slower than the primary peristaltic wave, stretch receptors in the esophageal lining are stimulated and a local reflex response causes a secondary peristaltic wave around the bolus, forcing it further down the esophagus, these secondary waves continue indefinitely until the bolus enters the stomach; the process of peristalsis is controlled by the medulla oblongata.
Esophageal peristalsis is assessed by performing an esophageal motility study. During vomiting, the propulsion of food up the esophagus and out the mouth comes from contraction of the abdominal muscles. Once processed and digested by the stomach, the milky chyme is squeezed through the pyloric sphincter into the small intestine. Once past the stomach, a typical peristaltic wave only lasts for a few seconds, travelling at only a few centimeters per second, its primary purpose is to mix the chyme in the intestine rather than to move it forward in the intestine. Through this process of mixing and continued digestion and absorption of nutrients, the chyme works its way through the small intestine to the large intestine. In contrast to peristalsis, segmentation contractions result in that churning and mixing without pushing materials further down the digestive tract. Although the large intestine has peristalsis of the type that the small intestine uses, it is not the primary propulsion. Instead, general contractions called mass movements occur one to three times per day in the large intestine, propelling the chyme toward the rectum.
Mass movements tend to be triggered by meals, as the presence of chyme in the stomach and duodenum prompts them. The human lymphatic system has no central pump. Instead, lymph circulates through peristalsis in the lymph capillaries, as well as valves in the capillaries, compression during contraction of adjacent skeletal muscle, arterial pulsation. During ejaculation, the smooth muscle in the walls of the vas deferens contracts reflexively in peristalsis, propelling sperm from the testicles to the urethra; the earthworm is a limbless annelid worm with a hydrostatic skeleton. Its hydrostatic skeleton consists of a fluid-filled body cavity surrounded by an extensible body wall; the worm moves by radially constricting the anterior portion of its body, resulting in an increase in length via hydrostatic pressure. This constricted region propagates posteriorly along the worm's body; as a result, each segment is extended forward relaxes and re-contacts the substrate, with hair-like setae preventing backwards slipping.
A peristaltic pump is a positive-displacement pump in which a motor pinches advancing portions of a flexible tube to propel a fluid within the tube. The pump isolates the fluid from the machinery, important if the fluid is abrasive or must remain sterile. Robots have been designed. Catastalsis is a related intestinal muscle process. Aperistalsis refers to a lack of propulsion, it can result from achalasia of the smooth muscle involved. Basal electrical rhythm is a slow wave of electrical activity. Ileus is a disruption of the normal propulsive ability of the gastrointestinal tract caused by the failure of peristalsis. Retroperistalsis, the reverse of peristalsis Interactive 3D display of swallow waves at menne-biomed.de Peristalsis at the US National Library of Medicine Medical Subject Headings Essentials of Human Physiology by Thomas M. Nosek. Section 6/6ch3/s6ch3_9. Overview at colostate.edu
A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge. However, in quantum physics, organic chemistry, biochemistry, the term molecule is used less also being applied to polyatomic ions. In the kinetic theory of gases, the term molecule is used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules as they are monatomic molecules. A molecule may be homonuclear, that is, it consists of atoms of one chemical element, as with oxygen. Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are not considered single molecules. Molecules as components of matter are common in organic substances, they make up most of the oceans and atmosphere. However, the majority of familiar solid substances on Earth, including most of the minerals that make up the crust and core of the Earth, contain many chemical bonds, but are not made of identifiable molecules.
No typical molecule can be defined for ionic crystals and covalent crystals, although these are composed of repeating unit cells that extend either in a plane or three-dimensionally. The theme of repeated unit-cellular-structure holds for most condensed phases with metallic bonding, which means that solid metals are not made of molecules. In glasses, atoms may be held together by chemical bonds with no presence of any definable molecule, nor any of the regularity of repeating units that characterizes crystals; the science of molecules is called molecular chemistry or molecular physics, depending on whether the focus is on chemistry or physics. Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of chemical bonds, while molecular physics deals with the laws governing their structure and properties. In practice, this distinction is vague. In molecular sciences, a molecule consists of a stable system composed of two or more atoms.
Polyatomic ions may sometimes be usefully thought of as electrically charged molecules. The term unstable molecule is used for reactive species, i.e. short-lived assemblies of electrons and nuclei, such as radicals, molecular ions, Rydberg molecules, transition states, van der Waals complexes, or systems of colliding atoms as in Bose–Einstein condensate. According to Merriam-Webster and the Online Etymology Dictionary, the word "molecule" derives from the Latin "moles" or small unit of mass. Molecule – "extremely minute particle", from French molécule, from New Latin molecula, diminutive of Latin moles "mass, barrier". A vague meaning at first; the definition of the molecule has evolved. Earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties; this definition breaks down since many substances in ordinary experience, such as rocks and metals, are composed of large crystalline networks of chemically bonded atoms or ions, but are not made of discrete molecules.
Molecules are held together by ionic bonding. Several types of non-metal elements exist only as molecules in the environment. For example, hydrogen only exists as hydrogen molecule. A molecule of a compound is made out of two or more elements. A covalent bond is a chemical bond; these electron pairs are termed shared pairs or bonding pairs, the stable balance of attractive and repulsive forces between atoms, when they share electrons, is termed covalent bonding. Ionic bonding is a type of chemical bond that involves the electrostatic attraction between oppositely charged ions, is the primary interaction occurring in ionic compounds; the ions are atoms that have lost one or more electrons and atoms that have gained one or more electrons. This transfer of electrons is termed electrovalence in contrast to covalence. In the simplest case, the cation is a metal atom and the anion is a nonmetal atom, but these ions can be of a more complicated nature, e.g. molecular ions like NH4+ or SO42−. An ionic bond is the transfer of electrons from a metal to a non-metal for both atoms to obtain a full valence shell.
Most molecules are far too small to be seen with the naked eye. DNA, a macromolecule, can reach macroscopic sizes, as can molecules of many polymers. Molecules used as building blocks for organic synthesis have a dimension of a few angstroms to several dozen Å, or around one billionth of a meter. Single molecules cannot be observed by light, but small molecules and the outlines of individual atoms may be traced in some circumstances by use of an atomic force microscope; some of the largest molecules are supermolecules. The smallest molecule is the diatomic hydrogen, with a bond length of 0.74 Å. Effective molecular radius is the size; the table of permselectivity for different substances contains examples. The chemical formula for a molecule uses one line of chemical element symbols and sometimes al
The jejunal arteries are branches of the superior mesenteric artery which supply the jejunum
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m