The cell is a fundamental component of all the living creatures. It carries nucleic acids, which determine the genome. More cells that have the same structure and function compose a tissue. There are four types of tissues in our body – muscular, connective, nerve and epithelial. Several types of tissue connect into an organ. More organs make an organ system. There are twelve systems in a human body – nervous, digestive, cardiovascular, muscular, skeletal, endocrine, urinary, immune, integumentary, respiratory, excretory and reproductive.

b. cells, tissues, organs, organ systems

After a meal, the glucose is absorbed from the intestine which cause its blood level to rise. That is a stimulus for the endocrine pancreas to secrete insulin. This hormone facilitates the transport of glucose into the cells. Inside the cell, glucose molecules are phosphorylated and can be instantly used to generate energy or it is being stored as glycogen. Liver and muscle cells have a major role in the process of glycogenesis, and in maintaining the concentration of glucose in a normal range after a meal. If our body needs glucose for generating energy, the liver releases it in the circulation in the process of glycogenolysis.

c. 2, 4, 1, 3

A homeostasis is the ability of an organism to preserve the ideal conditions in its internal environment. Our cells are the most effective if the internal environment is constant, which means that the concentration of different molecules, body temperature or pH is regulated in a small range. If these conditions change widely or sudden, the cells will perform in a different way in order to survive which can cause loss of normal functions of the tissues and organs.

There are four types of tissues in our body – muscular, connective, nerve and epithelial. We can make voluntary movements thanks to the nerve and muscular tissue. To be more precise, precentral gyrus of the brain cortex and skeletal muscles are included in performing voluntary movements.

When the food is ingested, it passes from the oral cavity through the esophagus to the stomach, small and than large intestine. The process of digestion starts in the mouth where the food is mechanically and chemically digested. We use our teeth to smash food into smaller parts, while saliva contains enzymes that can dissolve carbs.

b. the mouth

The blood is filtered in the kidneys and the waste products along with the excess water goes as urine from each kidney through its ureter to the bladder, where the urine is stored. When the process of miction begins, the urine is excreted through the urethra.

a. kidney

The components of blood are plasma and the blood cells – erythrocytes, leukocytes, and thrombocytes. Typically, about 55% of the blood volume is made up of plasma, while the other 45% is made of formed elements. The plasma is a liquid where are found three proteins- albumins, globulins (alpha, beta, and gamma) and fibrinogen. Erythrocytes have a major role in oxygen and carbon dioxide transport from the lungs to the tissues and vice verca. Leukocytes are included in the immune response, while thrombocytes are the part of the coagulation process.

The main muscle in the respiratory system is the diaphragm. The diaphragm contracts in order to widen the thorax which decreases the pressure in the airway. We inhale air when the intrapulmonary pressure is lower than the atmospheric, so the inspiration is active while expirationg is a passive process.

The main muscle in the respiratory system is the diaphragm. The diaphragm contracts in order to widen the thorax which decreases the pressure in the airway. We inhale air when the intrapulmonary pressure is lower than the atmospheric, so the inspiration is active while expiration is a passive process.

Alveoli are small sacs in the lungs that are connected to the bronchioli. Gas exchange between the erythrocytes and inhaled air happens within these tiny structures. Through the alveoles epithelium, our vessels in the lungs take oxygen molecules from the inhaled air and they eliminate carbon dioxide which we than exhale. The process of gas exchange occurs fast because of the immense lung surface, the structure of the alveolar-capillary membrane and because gasses diffuse passively from high to low concentration area.

The lymphatic system contains a large web of vessels and the lymph organs (spleen and lymph nodes). It has a role in collecting the interstitial fluid from the tissues and transport it to the large vein vessels where this fluid enters the circulation. The other role is in the immune response.

The chemical digestion of starch begins in the mouth when salivary amylase breaks it down into poly- and disaccharides. In the small intestine, pancreatic amylase continues to dissolve polysaccharides into disaccharides – maltose, which consists of two glucose molecules. The enzyme which is also present in the small intestine, maltase, breaks down maltose into glucose molecules which can now be absorbed. The chemical digestion of sugar (sucrose and lactose) is done in the small intestine by sucrase and lactase enzymes. Sucrose is dissolved into a molecule of glucose and a molecule of fructose, while lactose is dissolved into a molecule of glucose and a molecule of galactose.

The digestion of proteins in the peach begins in the stomach where pepsin dissolves them into large peptides. In the small intestine, enzyme trypsin continues to dissolve proteins while peptidase breaks down dipeptides into amino acids.

Heart muscle is controlled by the autonomic nervous system but it has its own electrical conduction mechanism. The parasympathetic nervous system affects the SA node and decreases the heart rate, while the sympathetic nervous system increases the heart frequency.

b. autonomic

There are different types of muscle cells – skeletal, smooth and cardiac muscle. Skeletal muscle tissue is found in the skeletal muscles of the human body. The control over them is completely voluntary. Smooth muscle cells are found in the walls of internal organs and blood vessels, they are controlled by the autonomic nervous system. Cardiac tissue is present in the heart muscle. It is also controlled by the autonomic nervous system but it has its own electrical conduction mechanism. Therefore, only cardiac muscle cells can contract without stimuli from the nervous system.

d. cardiac only

Besides the protection of the internal organs and providing support for our body, the skeletal system has a few other functions. It has a great role in the movement of the human body along with the nervous and skeletal systems. The bones are also depo of the calcium and other ions. When the calcium blood level is low, the parathyroid gland secretes PTH which activates osteoclasts to dissolve bone tissue. That brings the calcium level back to normal. The blood cells are produced in the bone marrow in a process called hematopoiesis.

The skin has a major role in non-specific defenses against infections and injuries because it represents a mechanical barrier. Sebaceous glands produce acid secrete that makes the skin an unsuitable medium for the growth of bacteria. Sweat glands are included in the regulation of body temperature, but they also remove waste products of our body. The skin also contains the dendrites of the afferent nerves, which provide sensory information to the central nervous system.

Hormones are regulated by feedback inhibition. An example is a regulation of cortisol. When its level in the blood is low, that affect pituitary gland to secrete more ACTH, which stimulates cells of the adrenal cortex to produce more cortisol. The high blood level inhibits the secretion of ACTH, which eventually lowers the concentration of the cortisol. This represents an example of feedback inhibition, where one stimulus, high or low, lead to a series of changes that can bring its values to a normal range.

Organs of the male reproductive system are testes, epididymis, the duct system, penis, and accessory glands (prostate, seminal, and bulbourethral). A female reproductive system consists of ovaries, uterine tubes, uterus, vagina and external genitalia.

There are three types of non-specific protection – the skin and mucous membranes with its glands, inflammatory response and the fever. The skin and mucous membranes provide mechanical protection and only if their continuity is interrupted, bacteria and viruses can pass. Mucous, tears, and saliva contain an enzyme that is called lysozyme, which dissolves the wall of bacteria.

b. mucus, sweat, and tears

People who have allergies have a modified immune response. Their immune system overproduces IgE antibodies in the presence of certain allergens. That causes secretion of a large amount of mucus and contraction of the smooth muscles of the bronchi which are known as the asthma attack.

b . Particular antigens trigger muscle contractions that make it difficult to breathe

There are three types of non-specific protection – the skin and mucous membranes with its glands, inflammatory response and the fever. After infection or injury, our body attempts to localize the tissue damage and cause an inflammatory response, which is defined with local pain, swelling, redness, higher temperature and loss of function.

c . inflammatory response

Our immune system has a non-specific and specific response. Non-specific response implies a generalized reaction of our immune system against infectious agents, while the specific response is highly explicit against one particular pathogen. The skin and mucosal membranes, leukocytes, the complement system, and cells and particles that are included in the inflammatory response belong to the non-specific immune system. The specific or adaptive immune system includes the activity of lymphocytes.

The vaccine contains a weak or inactive form of pathogens, or even their toxins, that are given in process of vaccination with a cause of acquiring immunity from specific antigens. When we receive antigens through the vaccine, our body begins a weaker immune reaction which leads to the production of memory cells. Memory cells have a major role in a prompt and effective response if they get in touch with the same antigen again. Which practically means that when we get in contact with bacteria or virus, from which we are vaccinated, there are much lower chances that we would get sick.

An antigen is a large molecule that is located on the cell surface. By his chemical structure, it can be protein, glycolipid, polysaccharide or nucleic acid. Our immune system recognizes all the cells of our body as their own, while it reacts on the foreign cells or organisms that are expressing unknown antigens. Therefore, a foreign antigen induces an immune response.

The HIV is a human immunodeficiency virus that can lead to the acquired immune deficiency syndrome or shortly AIDS. The HIV is transmitted through the blood and bodily fluids. The initial symptoms are flu-like, after which starts the latent period. This disorder leads to the reduction of the T helper cells which affects the immune response and causes the vulnerability of the body towards the infections. When their number goes below 200 cells per µL, or when the patient has some illnesses that can be related to the HIV infection, the AIDS can be diagnosed.

This image represents the process of phagocytosis. This is a cell-mediated immune response. A macrophage ingests a virus, which is being dissolved by its lysosomal enzymes. The viral particles are now presented on the surface of a macrophage, where these antigens are bonded with MHC-II molecules. In this way, an antigen presenting cells expose foreign antigens to the lymphocytes.

The cell is a fundamental component of all the living creatures. It carries nucleic acids, which determine the genome. More cells that have the same structure and function compose a tissue. There are four types of tissues in our body – muscular, connective, nerve and epithelial. Several types of tissue connect into an organ. More organs make an organ system. The blood is a fluid with cells and molecules in it. It has numerous functions, in tissue oxygenation, immune response, coagulation etc. It also connects other organs and systems. The blood is formed from the mesoderm like the tissues. Therefore, we can conclude that it is the most similar by its characteristics to the connective tissue.

A small intestine has three parts – duodenum, jejunum, and ileum. It has a major role in the absorption of nutrients. If we presume that the whole small intestine must be removed, it would mean that all the nutrients that we need in order to survive have to be given directly into to blood. Living in these conditions would be impossible. Luckily in the majority of cases, only a certain part of the small intestine has to be removed, while the other part is capable of absorbing nutrients.

The blood comes from the arterioles through the capillary network to the veins. However, some amount of plasma transfers through the capillary membrane to the tissues, which is now called the interstitial fluid. When it enters the lymphatic vessels it is called the lymph. The lymph has more leukocytes and more fat molecules, which are absorbed from the intestine. The lymph travels to the large vein vessels and enters back to the circulation, in this way our body don’t lose fluids. The lymphatic vessels have one-way valves which allow the fluid to move only in one direction. The action of the muscles and organs cause the flow of the lymph.

The lymph nodes are organs in which lymphocytes come in touch with antigen presenting cells. When they recognize an antigen as a foreign particle, they induce a specific immune response. If a person doesn’t have lymph nodes, besides swelling, he or she would also have a compromised immune response. The lymphocytes would take much more time to discover antigens, during which, pathogens could continue to invade cells and tissues.

Schwann cells produce myelin coverage for axons of peripheral neurons and insulate them. The impulse travels saltatory, from one Ranvier node to another, like the ripples over the water surface. That provides a faster impulse transmission.

The cartilage has an important role in joint movements because it provides perfect sliding between the articular surfaces. If the cartilage tissue was absent, the bones that make a joint would become damaged very fast because of the friction. The cartilage tissue is flexible and elastic. It also has a role in connecting some bone structures, such as the ribs with the sternum.

Smoking tobacco affects the immune system. The substances that tobacco smoke contains can alter the respiratory mucosa. These substances affect neutrophils, NK cells, T lymphocytes and macrophages of the lung tissue. The phagocytosis and chemotaxis of neutrophils are damaged. The activity of the NK cells decreases. The rate of T helpers and suppressor cells is changed. The macrophages function is impaired as well as the production of surfactant. These conditions favor the development of bacteria and other pathogens. When the respiratory mucosa is damaged and the innate immune response altered, we can conclude that the prevalence of respiratory diseases is higher in smokers than non-smokers.

The blood flow in skeletal muscles is 18% but during exercise, it rises to 75%. When we are active, our skeletal muscles need more energy and the production of metabolic waste, such as lactic acid, increases. Therefore, their blood flow rises in order to supply the muscular tissue with enough oxygen and nutrients, but also to efficiently remove waste products.

The blood flow in the lungs is 100%. It corresponds to the fact that all blood from the right ventricle goes to the pulmonary artery and enters the pulmonary circulation where it is being oxygenized. As oxygenized, blood goes into the left heart from where it is distributed to the tissues and organs. For example, the blood flow in the kidneys is 22% while in the heart only 5%.

The blood flow through the heart is only 5% when resting, but the oxygen consumption by the mass is the highest in the body. The heart muscle gets an almost entire amount of oxygen during the diastolic phase. During the systolic phase, the coronary arteries are constricted, therefore, the blood flow is almost absent.

The fetus continuously develops in the womb. All the organs and organs system mature, and therefore change. In that way, the fetus is being prepared for the outer environment. However, the environment in the uterus is quite stable in order to provide fetus the best conditions for the growth.

In the city model, the road would represent the blood vessels while vehicles would be blood cells. The telephone wires correspond with the nerve cells that conduct impulses. The sewage system of the city has the function of the kidneys in the body, to remove the liquid waste.

The impulse speed depends on the axon diameter and the existence of a myelin sheath. Axons with the larger diameter have lower resistance to the ion flow (more ion canals on a large membrane surface), so they conduct the impulse faster than the small diameter axons. The myelin sheats significantly speed up the conduction of nerve impulses. In a myelinated nerve, the impulse travels saltatory from one node of Ranvier to another.

time = 16,7 s

As we can see on the graph, at the beginning the level of glucose was about 85 mg/dL. The glucose level has risen after the meal up to 160 mg/dL. After 3 hours, the blood concentration of glucose was back to its homeostatic value.

The range of glucose blood concentration in a healthy adult is 70 to 100 mg/mL when fasting. About 90 minutes after a meal, it rises to 140 mg/mL. We can conclude that a glucose concentration of a healthy person is represented with the blue stripe. In type two diabetes, the cells can’t use enough glucose for their metabolic processes because of the insulin resistance. Therefore, the glucose blood level is higher than normal, from 70 to 126 mg/dL before, and under 153 mg/dL for 90 minutes after a meal. To diagnose diabetes, the blood level of glucose when fasting is over 126 mg/dL, and over 200 mg/dL when it is measured 2 hours after a meal. Since the level of glucose is over 150 mg/dL before, and over 350 mg/dL two hours after a meal, we can conclude that the person represented with the red stripe has a type two diabetes.

The process of food digesting begins in the mouth. Teeth mechanically digest while enzyme known as salivary amylase starts to divide the bun (carbohydrates). Chewed food passes through the esophagus and enters the stomach where meat proteins are chemically divided by pepsin. After 30 to 90 minutes, food enters the small intestine. Pancreatic enzymes, trypsin, lipase, and amylase continue the process of chemical digestion of hamburger and the bun. The nutrients are absorbed in the small intestine, while the water is absorbed in the large intestine.

When a person is talking with a phone, the nervous system sends signals to the muscles in the body so he could maintain the posture and hold the telephone. The person receives and process sound information, so the nervous system can send signals to the muscles included in the speech production. The respiratory system has a major role in the production of speech because it contains larynx, the voice box.

From the left ventricle arises aorta which branches into smaller arteries and arterioles. All organs, besides lungs, are supplied with oxygen and nutrients by arterial blood vessels. Arterioles bring blood through the capillary network where gas exchange happens between the erythrocytes and the tissue. Unoxygenated blood goes into the venules and veins. All veins in our organism merge into superior and inferior vena cava. These large vessels transport blood to the right atrium. From that point, blood goes to the right ventricle, pulmonary artery and lungs. In this organ, blood gets oxygenized and through the pulmonary veins goes into the left atrium and left ventricle.