Human physiology

The physiology from the Greek physiologia (knowledge of nature) is the science that studies the functions of living beings, that is, their origin, development and evolutionary process. Many of the aspects of human physiology are closely related to animal physiology, where it can be seen that the information available today has been obtained thanks to animal experimentation, but above all thanks to autopsies. Anatomy and physiology are closely related fields of study where the first emphasizes the knowledge of form while the second places interest in the study of the function of each part of the body, both areas of vital importance in medical knowledge. general.

Anatomy is a science that studies the structure of living beings, that is, the shape, topography, location, arrangement, and relationship among themselves of the organs that compose them. In unicellular organisms, all life processes occur in a single cell. As multicellular organisms evolved, various groups of cells took over particular functions. In humans and other vertebrates, specialized cell groups include: digestive system, which digests and absorbs food; the respiratory system, which captures O2 and eliminates CO2; urinary system, which eliminates waste; a cardiovascular system, which distributes food, O2 and the products of metabolism; reproductive system, to perpetuate the species, and endocrine and nervous system, to coordinate and integrate the functions of the other systems.

Cells in multicellular organisms develop and function as an organized whole. Cells are organized into tissues, groups of cells that are similar in structure and function. The different types of tissues, structurally united and coordinated in their activities, form the organs. The organs that work together in an integrated and organized way constitute the organic systems. One of the advantages of multicellularity is the ability to create a controlled internal environment in which the component cells live and function.

Homeostasis

Homeostasis, (from the Greek homoios meaning similar, and stasis, in Greek στάσις, position, stability) is a term used by physiologists to describe and explain the persistence of static or constant conditions in the internal environment. Generally, all organs and tissues in the body carry out functions that help maintain these constant conditions. From the lungs that take in oxygen, to the kidneys that keep the concentrations of ions in the body constant, each organ and cell contributes a function that adds to the total functions of the other systems that support human life. homeostasis is also a process for the regulation of physical exercise.

Structure of a typical animal cell: 1. Nucleus, 2. Nucleus, 3. Ribosome, 4. Movie, 5. Rugged Endoplasmic Reticle, 6. Golgi's appartment, 7. Cytoskeleton (microtubules), 8. Liso Endoplasmic Reticle, 9. Mitochondria, 10. Peroxisoma, 11. Cytoplasm, 12. Lisosoma. 13. Focus.

The true environment in which the cells of the organism are found is the interstitial component of the extracellular fluid. Since normal cell function depends on the constancy of that fluid, it is not surprising that, in multicellular animals, a vast world of regulatory mechanisms have evolved to maintain it. To describe "the various physiological mechanisms that serve to restore the normal state once disturbed", W. B. Cannon coined the term homeostasis. The buffering properties of body fluids, and renal and respiratory adjustments in the presence of excess acids or alkalis, are homeostatic mechanisms.

Regarding the physiological characteristics of cells, that is, normal functions or forms of organized activity, which serve as the basis for defining the living cell. In a multicellular organism, the important specialization of the different cell types means that not all these characteristics are present in all cells. The great development of a function in a certain type of cells generally occurs at the expense of others.

The internal environment

Water is the most abundant molecule in the human body, accounting for around 55% of the total weight of an adult. Approximately 65% of this water is found inside the cells and constitutes the intracellular fluid, the rest is found outside the cells and is the extracellular fluid. Extracellular fluid can be interstitial fluid found between cells and intravascular fluid found in the blood. A small part of the extracellular fluid is the so-called transcellular fluid that accumulates in certain anatomical cavities: pleural fluid in the pleura, cerebrospinal fluid in the central nervous system, synovial fluid in the joints, pericardial fluid in the pericardium, peritoneal fluid in the peritoneum and intraocular fluid inside the eye.

Extracellular fluid is in constant motion within the body. It is rapidly mixed by the blood circulation and by diffusion between the blood and tissue fluids, and contains the ions and nutrients required for cells to maintain their function. Virtually all cells live surrounded by extracellular fluid, which is why this fluid is known as the body's internal environment as the physiologist Claude Bernard called it.

Cell Survival

To carry out their functions, cells need adequate concentrations of oxygen, glucose, ions, various amino acids and other substances that serve as building blocks of nutrition in the internal environment.

Devices and systems

The body is made up of cells, these make up tissues, the tissues make up organs, and the organs in turn make up the apparatus and systems that keep the organism alive.

• Nervous system. It is divided into two parts: central nervous system consisting of the brain and spinal cord, and the peripheral nervous system formed by the peripheral nerves. The brain is the organ of thought, emotions, the processing of sensory information and many other aspects that coordinate the integrated function of the organism. The eyes, ears, tongue, skin, and nose, as well as receptors sheltered in the musculoskeletal system (responsible from the same sense), gather the sensory information from the environment as well as from our own body and send it to the brain for processing. The branches of medicine that study nervous system diseases are neurology and psychiatry. Neurosciences and neurophysiology study their functioning.

• Musculoskeletal system. It is formed by human skeleton and voluntary muscles. It includes bones, ligaments, tendons, cartilages, synovial bags, joints and numerous muscles. This system provides the basic mechanical structure of the body and provides it with movement capacity. In addition to the basic function of bra and movement, long bones contain bone marrow, which functions to form red blood cells (eritropoyesis) and other blood cells. In addition, bones play a fundamental role in the metabolism of calcium, being the largest reservoir of phosphorus and calcium in the body. It is studied by osteology, orthopaedics, traumatology, rheumatology and musculoskeletal physiology.

• Circulatory systemIt consists of the heart and blood vessels (arteries, veins and capillaries). The heart has the function of pumping the blood through the circulatory pathways so that it has the ability to reach each of the tissues of the body, providing the cells with the oxygen and nutritious substances necessary for life. Numerous essential substances are distributed through the circulatory system, including hormones that act as chemical messengers and immunoglobulins that form part of the immune system, and removes waste substances so they can be eliminated through the kidney. Blood is a fluid formed by plasma and blood cells. The circulatory system is studied by cardiology, cardiac physiology and hematology.

• Respiratory system. It is formed by the nose, pharynx, larynx, trachea and lungs. It is responsible for the gaseous exchange to provide the body with the oxygen necessary for the intermediate metabolism, in addition to eliminating the carbon dioxide produced by the latter and controlling the blood pH to keep it at the right level. He studied pneumology and respiratory physiology.

• The gastrointestinal system It consists of the mouth, esophagus, stomach, small intestine, large intestine, and rectum, in addition to the annexed glands that cooperate in the digestion of foods: liver and gallbladder (sales biliares), pancreas (exocrine secretion) and salivary glands. The goal of digestion is to convert food into substances that can be used by the body, in addition to producing the removal of toxic or non-metabolizable wastes by the body. He is studied by gastrointestinal physiology.

• The integumentary system consists of portions covering the body (the skin), including, hair and nails as well as sweat glands and sebaceous glands. The skin provides the structure, support and protection for other organs, but also offers a large area of contact with the external environment and sensitive pathways for the detection of heat, pain or pressure. It is studied by the dermatology and physiology of the skin.

• The urinary system consists of kidneys, ureters, urinary bladder and urethra. It is responsible for filtering the blood to produce urine, which consists of water along with various substances of cell metabolic waste. It is studied by nephrology, urology and renal physiology.

• The reproductive system consists of gonads and external and internal sexual organs. The reproductive system produces gametes (in testicles and ovaries according to man and woman respectively), in addition to producing hormones and providing a necessary environment to maintain in optimal conditions the development of these gametes. In the case of female sex, an environment suitable for the development of embryo (uter). It is studied by gynaecology (women), andrology (men), sexology (behavioural aspects) and reproductive physiology

• The immune system consists of white blood cells, thymus, lymph nodes and lymph ducts, which are also part of the lymphatic system. Other organs involved in the immune system are spleen and bone marrow, where recirculation and production of immune cells are produced respectively. The immune system is responsible for generating a defense response to external organisms that could lead to the development of a disease or possible damage to the tissue level of the organism. Within the defense mechanisms there are two types of response, innate and adaptive, the second one dependent on the first and where there are varied interactions to react in the best way possible according to the pathogen. He's studying immunology.

• The endocrine system It consists of the main endocrine glands: hypophysis, thyroids, adrenal gland, parathyroids, pancreas and gonada, although the secretion of hormones is also performed by various tissues locally, as well as a few hormones produced at the kidney and liver level. Endocrine hormones serve as a mechanism of communication between the various parts of the body, having in general a predominance of cephalic to flow, i.e., the pituitary is the endocrine gland with greater power of action at the human body level, triggering various responses at the level of many white organs. He studied endocrinology.

It should be taken into account that many parts of the body belonging to different systems are interconnected, for example the brain belongs to the nervous system, but it also has a hormonal function and is connected to the endocrine system through the hypothalamus, which is why the systems can be organized according to function, embryological origin or another type of particular characteristic. The pancreas is a gland located in the abdomen that has a hormonal function and produces insulin, which is why it is included in the endocrine system, however it also produces enzymes that are released into the digestive tract and make digestion possible, which is why it also belongs to the digestive system. Neuroendocrinology is the branch of physiology that studies the interaction between the nervous system and the endocrine system.

Control mechanisms

The human body has various control systems. It is these mechanisms that allow life and are of great biomedical importance, since if one of the systems fails, the homeostatic balance is at risk and sometimes the failure may be incompatible with life. The most complex are the genetic control systems within the cell, but there are others that become apparent from the point of view of an organ or system as a whole. Within these control mechanisms, which number hundreds, we have the regulation of oxygen and carbon dioxide concentrations, regulation of blood pressure, regulation of body temperature, hormonal regulation, among others.

Negative feedback

The control systems of the human body operate through a process of negative feedback. If any factor reaches exaggerated or excessive or too low concentrations, a control system initiates a negative feedback that consists of a series of changes that return the aforementioned factor towards a certain mean value, thereby maintaining homeostasis. A good example to illustrate this process is the regulation of the concentration of carbon dioxide in the organism. When there is an increased concentration of CO2 in the extracellular fluid, pulmonary ventilation increases, which at the same time decreases the concentration of the gas in the internal environment, since its expulsion increases with each breath. This is the same as saying that the response is negative with respect to the initial stimulus. On the contrary, if the CO2 decreases excessively, the process of the control system begins so that the levels of the gas increase to an adequate level, since it is of vital importance for the human being.

Positive Feedback

Positive feedback is also known as a vicious circle and is regularly fatal for the organism that suffers from it. A positive feedback, contrary to the negative feedback, does not result in a stability of the system, but in a dangerous instability. An example to illustrate this concept is: when a man suffers a serious hemorrhage of two liters of blood causing the blood volume to be so low that the heart does not have enough to pump effectively. This causes blood pressure to drop and the blood supply from the heart's coronary arteries to the heart muscle to be so low that the organ begins to suffer from lack of oxygen. This weakens the heart and makes the pumping weaker and lessened, which makes the heart weaker, continuing until the system collapses due to the vicious cycle generated.

In many cases the same organism will try to provide negative feedback to break the vicious circle in which the factors are found. If in the hemorrhage example, instead of two liters, the person lost only one liter of blood, normal control mechanisms would provide the negative feedback to control cardiac output, and blood pressure would effectively compensate for the positive feedback. and the person will recover without difficulty.

During childbirth, a beneficial effect of positive feedback with the hormone oxytocin occurs.

Anticipation

^{[citation required]} It is a special control mechanism of the nervous system. It allows adapting to a situation before the variables are altered, and it is always mediated by the same nervous system. When the brain orders to do something, it receives a retrospective signal about what it has done, and if a correction is necessary, it will do so the next time it makes that movement. The cerebellum and basal ganglia are particularly involved, and it is related to motor and coordination learning skills.

Classification

Taking attention to the various types of cells, organs and systems, we can distinguish the following:

• Heart physiology
• Physiology of the muscle cell
• Cellular physiology
• Exercise physiology
• Physiology of the endocrinological system
• Gastrointestinal physiology
• Physiology of taste
• Muscular physiology
• Physiology of neuron
• Physiology of smell
• Renal physiology
• Physiology of reproduction
• Respiratory physiology
• Physiology of blood tissue
• Vascular physiology
• physiology of vision
• Neurophysiology
• It is called physiopathology to science that studies the altered physiological mechanisms that occur in the different diseases.