stomach anatomy Alternate titles: ventriculus By The Editors of Encyclopaedia Britannica Last Updated: Sep 29, 2022 Edit History human stomach human stomach See all media Key People: William Beaumont Related Topics: chyme gastric gland pylorus gizzard parietal cell Summary Read a brief summary of this topic stomach, saclike expansion of the digestive system, between the esophagus and the small intestine; it is located in the anterior portion of the abdominal cavity in most vertebrates. The stomach serves as a temporary receptacle for storage and mechanical distribution of food before it is passed into the intestine. In animals whose stomachs contain digestive glands, some of the chemical processes of digestion also occur in the stomach. Humans structures of the human stomach structures of the human stomach Discover why the human stomach rumbles Discover why the human stomach rumblesSee all videos for this article The human stomach is subdivided into four regions: the fundus, an expanded area curving up above the cardiac opening (the opening from the stomach into the esophagus); the body, or intermediate region, the central and largest portion; the antrum, the lowermost, somewhat funnel-shaped portion of the stomach; and the pylorus, a narrowing where the stomach joins the small intestine. Each of the openings, the cardiac and the pyloric, has a sphincter muscle that keeps the neighbouring region closed, except when food is passing through. In this manner, food is enclosed by the stomach until ready for digestion. Model of a molecule. Atom, Biology, Molecular Structure, Science, Science and Technology. Homepage 2010 arts and entertainment, history and society BRITANNICA QUIZ What Lies Beneath the Skin: A Human Anatomy Quiz The human body is made up of many different systems working together to create an amazing machine. Do you know what your body is made of? Take our human anatomy quiz and find out. Know the cause of feeling full and heartburn after eating a big meal Know the cause of feeling full and heartburn after eating a big mealSee all videos for this article The stomach has the ability to expand or contract depending upon the amount of food contained within it. When contracted, the interior walls form numerous folds (rugae), which disappear when the walls are distended. The thick mucous-membrane lining of the walls is densely packed with small gastric glands; these secrete a mixture of enzymes and hydrochloric acid that partly digest proteins and fats. The stomach muscles are rarely inactive. Upon entry of food, they relax briefly, then begin to contract. Periodic contractions churn and knead food into a semifluid mixture called chyme; rhythmical pumping (peristaltic) waves move food toward the pylorus and small intestine. Peristaltic contractions persist after the stomach empties and, increasing with time, may become painful. Such hunger pangs may also be related to the amount of sugar in the blood. If the level of sugar decreases significantly, hunger can be experienced without the stomach’s intervention. The absorption of food, water, and electrolytes by the stomach is practically negligible, but iron and highly fat-soluble substances such as alcohol and some drugs are absorbed directly. Secretions and movements of the stomach are controlled by the vagus nerve and the sympathetic nervous system; emotional stress can alter normal stomach functions. Common stomach disorders include peptic ulcer, cancer, and gastritis. Other animals The stomachs of some other animals differ considerably from that of humans; many have multiple-chambered organs or special adaptations. The stomachs of cows and most cud-chewing (ruminant) animals are divided into four separate parts. Food is received first in the rumen, where mucus is added and cellulose is broken down. Next, it goes back to the mouth to be thoroughly rechewed. When swallowed again, it is passed to the second and third chambers, the reticulum and omasum, where water is extracted and absorbed. The food then goes to a final chamber, the abomasum, to receive the digestive enzymes. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now Birds have a three-chambered stomach: the first chamber, the crop, receives the food initially and either stores or begins to moisten and soften (macerate) it; the true stomach area adds digestive juices; and the gizzard, with its stones, or toothlike structures, grinds the food. Rodents have only one stomach area, and many must eat their food twice before absorption takes place. Food is eaten and passed through the lower digestive tract, where it is coated with metabolites to help break it down. The fecal material is then re-eaten and mixed with additional food. Enzymes and water are removed from the once-passed material by the stomach and used to help digest new nutritional substances. Dry fecal pellets are finally excreted. The starfish can turn its stomach inside out and extrude it partly from the body to eat the soft contents of shelled animals such as clams. Camels and llamas can regurgitate their stomach contents and spit this material at approaching enemies. Crayfish produce stones of calcium salts in their stomach. These are stored until the animal sheds its external shell, when the stones are reabsorbed by the stomach and used in forming a new shell. The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Adam Augustyn. Joy Delivery SPONSORED BY JOY DELIVERY [Photos] At 91, This Is The Car Clint Eastwood Drives READ MORE USA Remote Jobs Ads SPONSORED BY USA REMOTE JOBS ADS Working Remotely Is Now More Common Than You Might Think These Online Jobs In The USA Are Making Indians a Fortune LEARN MORE artificial organ Introduction Fast Facts Related Content More Contributors Article History Home Health & Medicine Anatomy & Physiology artificial organ By The Editors of Encyclopaedia Britannica Edit History Key People: John Jacob Abel Related Topics: artificial heart cochlear implant pacemaker bionic eye ventilator artificial organ, any machine, device, or other material that is used to replace the functions of a faulty or missing organ or other part of the human body. Artificial organs include the artificial heart and pacemaker (qq.v.), the use of dialysis (q.v.) to perform kidney functions, and the use of artificial substitutes for missing limbs (see prosthesis). brain Introduction & Top Questions Fast Facts brain summary Top Questions Facts & Related Content Quizzes Media Videos Images More More Articles On This Topic Additional Reading Contributors Article History Home Health & Medicine Anatomy & Physiology brain anatomy Alternate titles: encephalon By The Editors of Encyclopaedia Britannica Edit History right cerebral hemisphere of the human brain right cerebral hemisphere of the human brain See all media Key People: Ben Carson William Williams Keen Harvey Williams Cushing Ernst von Bergmann Fred H. Gage Related Topics: neuroplasticity midbrain cross-modal plasticity meninges cerebrum Top Questions What is a brain? Is the Internet affecting human brains and "making us stupid"? Summary Read a brief summary of this topic brain, the mass of nerve tissue in the anterior end of an organism. The brain integrates sensory information and directs motor responses; in higher vertebrates it is also the centre of learning. The human brain weighs approximately 1.4 kg (3 pounds) and is made up of billions of cells called neurons. Junctions between neurons, known as synapses, enable electrical and chemical messages to be transmitted from one neuron to the next in the brain, a process that underlies basic sensory functions and that is critical to learning, memory and thought formation, and other cognitive activities. In lower vertebrates the brain is tubular and resembles an early developmental stage of the brain in higher vertebrates. It consists of three distinct regions: the hindbrain, the midbrain, and the forebrain. Although the brain of higher vertebrates undergoes considerable modification during embryonic development, these three regions are still discernible. Muscles of forearm (posterior view), human anatomy, (Netter replacement project - CMM). Forelimb, upper limb, appendage, human forearm, human arm, triceps, biceps, human hand, body part. BRITANNICA QUIZ The Human Body: Fact or Fiction? Can people choose to be left or right-handed? From nerves and genes to muscles and organs, see how ambidextrous you are by choosing between right --and wrong-- in this quiz. human brain; magnetic resonance imaging (MRI) human brain; magnetic resonance imaging (MRI) The hindbrain is composed of the medulla oblongata and the pons. The medulla transmits signals between the spinal cord and the higher parts of the brain; it also controls such autonomic functions as heartbeat and respiration. The pons is partly made up of tracts connecting the spinal cord with higher brain levels, and it also contains cell groups that transfer information from the cerebrum to the cerebellum. The midbrain, the upper portion of which evolved from the optic lobes, is the main centre of sensory integration in fish and amphibians. It also is involved with integration in reptiles and birds. In mammals the midbrain is greatly reduced, serving primarily as a connecting link between the hindbrain and the forebrain. Connected to the medulla, pons, and midbrain by large bundles of fibres is the cerebellum. Relatively large in humans, this “little brain” controls balance and coordination by producing smooth, coordinated movements of muscle groups. The forebrain includes the cerebral hemispheres and, under these, the brainstem, which contains the thalamus and hypothalamus. The thalamus is the main relay centre between the medulla and the cerebrum; the hypothalamus is an important control centre for sex drive, pleasure, pain, hunger, thirst, blood pressure, body temperature, and other visceral functions. The hypothalamus produces hormones that control the secretions of the anterior pituitary gland, and it also produces oxytocin and antidiuretic hormone, which are stored in and released by the posterior pituitary gland. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now The cerebrum, originally functioning as part of the olfactory lobes, is involved with the more complex functions of the human brain. In humans and other advanced vertebrates, the cerebrum has grown over the rest of the brain, forming a convoluted (wrinkled) layer of gray matter. The degree of convolution is partly dependent on the size of the body. Small mammals (e.g., lesser anteater, marmoset) generally have smooth brains, and large mammals (e.g., whale, elephant, dolphin) generally have highly convoluted ones. left cerebral hemisphere of the human brain left cerebral hemisphere of the human brain The cerebral hemispheres are separated by a deep groove, the longitudinal cerebral fissure. At the base of this fissure lies a thick bundle of nerve fibres, called the corpus callosum, which provides a communication link between the hemispheres. The left hemisphere controls the right half of the body, and vice versa, because of a crossing of the nerve fibres in the medulla or, less commonly, in the spinal cord. Although the right and left hemispheres are mirror images of one another in many ways, there are important functional distinctions. In most people, for example, the areas that control speech are located in the left hemisphere, while areas that control spatial perceptions are located in the right hemisphere. Uncover the science behind the split-brain syndrome Uncover the science behind the split-brain syndromeSee all videos for this article Two major furrows—the central sulcus and the lateral sulcus—divide each cerebral hemisphere into four sections: the frontal, parietal, temporal, and occipital lobes. The central sulcus, also known as the fissure of Rolando, also separates the cortical motor area (which is anterior to the fissure) from the cortical sensory area (which is posterior to the fissure). Starting from the top of the hemisphere, the upper regions of the motor and sensory areas control the lower parts of the body, and the lower regions of the motor and sensory areas control the upper parts of the body. Other functional areas of the cerebral hemispheres have been identified, including the visual cortex in the occipital lobe and the auditory cortex in the temporal lobe. A large amount of the primate cortex, however, is devoted to no specific motor or sensory function; this so-called association cortex is apparently involved in higher mental activities. (For more information about the human brain, see nervous system, human.) The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Kara Rogers. Speedfindr SPONSORED BY SPEEDFINDR Search Short Mba Programs Online Top Online Suggestions. Discover More About It LEARN MORE esophagus Introduction Fast Facts Facts & Related Content Quizzes Media Images More More Articles On This Topic Contributors Article History Home Health & Medicine Anatomy & Physiology esophagus anatomy Alternate titles: gullet, oesophagus By The Editors of Encyclopaedia Britannica Last Updated: Sep 28, 2022 Edit History esophagus esophagus See all media Key People: Theodor Billroth Related Topics: cricopharyngeus muscle esophageal sphincter crop lower esophageal sphincter honey stomach human digestive system human digestive system esophagus, also spelled oesophagus, relatively straight muscular tube through which food passes from the pharynx to the stomach. The esophagus can contract or expand to allow for the passage of food. Anatomically, it lies behind the trachea and heart and in front of the spinal column; it passes through the muscular diaphragm before entering the stomach. Both ends of the esophagus are closed off by muscular constrictions known as sphincters; at the anterior, or upper, end is the upper esophageal sphincter, and at the distal, or lower, end is the lower esophageal sphincter. The upper esophageal sphincter is composed of circular muscle tissue and remains closed most of the time. Food entering the pharynx relaxes this sphincter and passes through it into the esophagus; the sphincter immediately closes to prevent food from backing up. Contractions of the muscles in the esophageal wall (peristalsis) move the food down the esophageal tube. The food is pushed ahead of the peristaltic wave until it reaches the lower esophageal sphincter, which opens, allowing food to pass into the stomach, and then closes to prevent the stomach’s gastric juices and contents from entering the esophagus. 3d illustration human heart. Adult Anatomy Aorta Black Blood Vessel Cardiovascular System Coronary Artery Coronary Sinus Front View Glowing Human Artery Human Heart Human Internal Organ Medical X-ray Myocardium BRITANNICA QUIZ Human Organs How much of the human body’s energy does the brain use? On average, how many times does the human heart beat per minute? Energize your brain and quicken your pulse rate by taking this quiz. Disorders of the esophagus include ulceration and bleeding; heartburn, caused by gastric juices in the esophagus; achalasia, an inability to swallow or to pass food from the esophagus to the stomach, caused by destruction of the nerve endings in the walls of the esophagus; scleroderma, a collagen disease; and spasms of the esophageal muscles. In some vertebrates the esophagus is not merely a tubular connection between the pharynx and the stomach but rather may serve as a storage reservoir or an ancillary digestive organ. In many birds, for example, an expanded region of the esophagus anterior to the stomach forms a thin-walled crop, which is the bird’s principal organ for the temporary storage of food. Some birds use the crop to carry food to their young. Ruminant mammals, such as the cow, are often said to have four “stomachs.” Actually, the first three of these chambers (rumen, reticulum, and omasum) are thought to be derived from the esophagus. Vast numbers of bacteria and protozoans live in the rumen and reticulum. When food enters these chambers, the microbes begin to digest and ferment it, breaking down not only protein, starch, and fats but cellulose as well. The larger, coarser material is periodically regurgitated as the cud, and after further chewing the cud is reswallowed. Slowly the products of microbial action, and some of the microbes themselves, move into the cow’s true stomach and intestine, where further digestion and absorption take place. Since the cow, like other mammals, has no cellulose-digesting enzymes of its own, it relies upon the digestive activity of these symbiotic microbes in its digestive tract. Much of the cellulose in the cow’s herbivorous diet, which otherwise would have no nutritive value, is thereby made available to the cow. This article was most recently revised and updated by Amy Tikkanen. USA Remote Jobs Ads SPONSORED BY USA REMOTE JOBS ADS Working Remotely Is Now More Common Than You Might Think These Online Jobs In The USA Are Making Indians a Fortune LEARN MORE pylorus Introduction Fast Facts Related Content Quizzes More More Articles On This Topic Contributors Article History Home Health & Medicine Anatomy & Physiology pylorus anatomy By The Editors of Encyclopaedia Britannica Edit History Key People: Theodor Billroth Related Topics: stomach pyloric sphincter pylorus, cone-shaped constriction in the gastrointestinal tract that demarcates the end of the stomach and the beginning of the small intestine. The main functions of the pylorus are to prevent intestinal contents from reentering the stomach when the small intestine contracts and to limit the passage of large food particles or undigested material into the intestine. The internal surface of the pylorus is covered with a mucous-membrane lining that secretes gastric juices. Beneath the lining, circular muscle tissue allows the pyloric sphincter to open or close, permitting food to pass or be retained. The sphincter remains in an open or relaxed state two-thirds of the time, permitting small quantities of food to pass into the duodenum, the upper portion of the small intestine. When the duodenum begins to fill, pressure increases and causes the pyloric sphincter to contract and close. Muscular contractions (peristaltic waves) in the duodenum then push food deeper into the intestine. Because the pyloric sphincter is relatively narrow, only small amounts of well-emulsified food can pass through it even while it is open. Surgical removal of the valve does not significantly affect the gastric emptying of the stomach. The term pylorus is used to refer to the pyloric sphincter and can also be applied to that portion of the stomach immediately above the pyloric sphincter. Superficial arteries and veins of face and scalp, cardiovascular system, human anatomy, (Netter replacement project - SSC) BRITANNICA QUIZ The Human Body You may know that the human brain is composed of two halves, but what fraction of the human body is made up of blood? Learn this fact and much more as you test both halves of your mind in this human anatomy quiz. USA Remote Jobs Ads SPONSORED BY USA REMOTE JOBS ADS These Online Jobs In The USA Are Making Indians A Fortune Working remotely in India for US companies is more common than you think LEARN MORE mucous membrane Introduction Fast Facts Facts & Related Content Media Images More More Articles On This Topic Contributors Article History Home Health & Medicine Anatomy & Physiology mucous membrane anatomy Alternate titles: mucosa By The Editors of Encyclopaedia Britannica Edit History Epithelial mucous surface cells (A) extend into the gastric pits (B) of the mucosal lining in the lumen of the stomach (C, gastric glands; D, muscularis mucosa of the stomach). mucous membrane See all media Related Topics: mucus mucin goblet cell mucoid cell conjunctiva mucous membrane, membrane lining body cavities and canals that lead to the outside, chiefly the respiratory, digestive, and urogenital tracts. Mucous membranes line many tracts and structures of the body, including the mouth, nose, eyelids, trachea (windpipe) and lungs, stomach and intestines, and the ureters, urethra, and urinary bladder. mucus mucus Mucous membranes vary in structure, but they all have a surface layer of epithelial cells over a deeper layer of connective tissue. Usually, the epithelial layer of the membrane consists of either stratified squamous epithelium (multiple layers of epithelial cells, the top layer being flattened) or simple columnar epithelium (a layer of column-shaped epithelial cells, the cells being significantly greater in height than width). These types of epithelium are notably tough—able to endure abrasion and other forms of wear that are associated with exposure to external factors (e.g., food particles). They also typically contain cells specially adapted for absorption and secretion. The term mucous membrane comes from the fact that the major substance secreted from the membranes is mucus; the principal constituent of mucus is a
