DIGESTION AND ABSORPTION IN SMALL INTESTINES

 

INTRODUCTION: The secretion of the epithelium of the intestinal glands is stimulated by the presence of food in the duodenum. The intestinal enzymes are the peptidases and sucrase, maltase, and lactase. Peptidases complete the digestion of protein by breaking down short polypeptide chains to amino acids. Sucrase, maltase, and lactase, respectively, digest the disaccharides sucrose, maltose, and lactose to constituent monosaccharides. The enteroendocrine cells of the intestinal glands secrete the hormones of the small intestine. Secretion is stimulated by food entering the duodenum.

ABSORPTION OF DIGESTIVE PRODUCTS: Most absorption of the end products of digestion takes place in the small intestine, although the stomach does absorb water and alcohol. The process of absorption requires a large surface area, which is provided by several structural modifications of the small intestine; Plica circulares, or circular folds, are macroscopic folds of the mucosa and submucosa, somewhat like accordion pleats. The mucosa is further folded into projections called villi, which give the inner surface of the intestine a velvetlike appearance. Each columnar cell with exception of the mucus-secreting goblet cells, of the villi also has microvilli on its free surface. Microvilli are microscopic folds of the cell membrane, and are collectively called the brush border. All of these folds greatly increase the surface area of the intestinal lining. The absorption of nutrients takes place from the lumen of the intestine into the vessels within the villi. Water-soluble nutrients are absorbed into the blood in the capillary networks.

MECHANISM OF ABSORPTION: Monosaccharides, amino acids, positive ions, and the water-soluble vitamins that is, vitamin C and the B vitamins, are absorbed by active transport. Negative ions may be absorbed by either passive or active transport mechanisms. Water is absorbed by osmosis following the absorption of minerals, especially sodium. Certain nutrients have additional special requirements for their absorption: For example, vitamin B12 requires the intrinsic factor produced by the parietal cells of the gastric mucosa, and the efficient absorption of calcium ions requires parathyroid hormone and vitamin D.

Fat-soluble nutrients are absorbed into the lymph in the lacteals of the villi. Bile salts are necessary for the efficient absorption of fatty acids and the fat-soluble vitamins (A, D, E, and K). Once absorbed, fatty acids are recombined with glycerol to form triglycerides. These triglycerides then form globules that include cholesterol and protein; these lipid–protein complexes are called chylomicrons. In the form of chylomicrons, most absorbed fat is transported by the lymph and eventually enters the blood in the left subclavian vein. Blood from the capillary networks in the villi does not return directly to the heart but first travels through the portal vein to the liver. This pathway enables the liver to regulate the blood levels of glucose and amino acids, store certain vitamins, and remove potential poisons from the blood.

RELATED;

1.  DIGESTIVE FUNCTIONS OF PANCREATIC JUICE

2.  PHASES OF METABOLISM

3.  ANATOMY AND PHYSIOLOGY

REFERENCES

CARDIAC OUTPUT

 

INTRODUCTION: Cardiac output is the amount of blood pumped by a ventricle in 1 minute. A certain level of cardiac output is needed at all times to transport oxygen to tissues and to remove waste products. During exercise, cardiac output must increase to meet the body’s need for more oxygen. To calculate cardiac output, we must know the pulse rate and how much blood is pumped per beat.

STROKE VOLUME: Stroke volume is the term for the amount of blood pumped by a ventricle per beat; an average resting stroke volume is 60 to 80 ml per beat. A simple formula then enables us to determine cardiac output:

Cardiac output = stroke volume X pulse (heart rate)

Let us put into this formula an average resting stroke volume, 70 ml, and an average resting pulse, 70 beats per minute (bpm):

Cardiac output= 70 ml X 70 bpm

Cardiac output= 4900 ml per minute, which is approximately 5 liters.

VARIATION OF CARDIAC: Naturally, cardiac output varies with the size of the person, but the average resting cardiac output is 5 to 6 liters per minute. Notice that this amount is just about the same as a person’s average volume of blood. At rest, the heart pumps all of the blood in the body within about a minute. Changes are possible, depending on circumstances and extent of physical activity. If we now reconsider the athlete, you will be able to see precisely why the athlete has a low resting pulse. In our formula, we will use an average resting cardiac output of about 5 liters, and an athlete’s pulse rate of 50:

Cardiac output = stroke volume X pulse

5000 ml = stroke volume X 50 bpm

5000/50 = stroke volume = 100 ml stroke volume

Notice that the athlete’s resting stroke volume is significantly higher than the average. The athlete’s more efficient heart pumps more blood with each beat and so can maintain a normal resting cardiac output with fewer beats. 

CARDIAC OUTPUT DURING EXERCISE: Now let us see how the heart responds to exercise. Heart rate (pulse) increases during exercise, and so does stroke volume. The increase in stroke volume is the result of Starling’s law of the heart, which states that the more the cardiac muscle fibers are stretched, the more forcefully they contract. During exercise, more blood returns to the heart; this is called venous return. Increased venous return stretches the myocardium of the ventricles, which contract more forcefully and pump more blood, thereby increasing stroke volume. Therefore, during exercise, our formula might be the following:

Cardiac output = stroke volume X pulse

Cardiac output = 100 ml X 100 bpm

Cardiac output = 10,000 ml (10 liters)

This exercise cardiac output is twice the resting cardiac output we first calculated, which should not be considered unusual. The cardiac output of a healthy young person may increase up to four times the resting level during strenuous exercise. This difference is the cardiac reserve, the extra volume the heart can pump when necessary. If resting cardiac output is 5 liters and exercise cardiac output is 20 liters, the cardiac reserve is 15 liters. The marathon runner’s cardiac output may increase six times or more compared to the resting level, and cardiac reserve is even greater than for the average young person; this is the result of the marathoner’s extremely efficient heart. Because of Starling’s law, it is almost impossible to overwork a healthy heart. No matter how much the volume of venous return increases, the ventricles simply pump more forcefully and increase the stroke volume and cardiac output.

THE EJECTION FRACTION: Also related to cardiac output, and another measure of the health of the heart, is the ejection fraction. This is the percent of the blood in a ventricle that is pumped during systole. A ventricle does not empty completely when it contracts, but should pump out 60% to 70% of the blood within it. A lower percentage would indicate that the ventricle is weakening.

RELATED;

1. CHAMBERS AND CIRCULATION THROUGH THE HEART

2. CARDIAC FUNCTIONING AND THE HEART SOUNDS

3. HEART MURMURS

REFERENCES

OXYTOCIN

 

INTRODUCTION: Oxytocin stimulates contraction of the uterus at the end of pregnancy and stimulates release of milk from the mammary glands. As labor begins, the cervix of the uterus is stretched, which generates sensory impulses to the hypothalamus, which in turn stimulates the posterior pituitary to release oxytocin. Oxytocin then causes strong contractions of the smooth muscle also known as ,myometrium, of the uterus to bring about delivery of the baby and the placenta.

SECRETION OF OXYTOCIN: The secretion of oxytocin is one of the few positive feedback mechanisms within the body, and the external brake or shutoff of the feedback cycle is delivery of the baby and the placenta. It has been discovered that the placenta itself secretes oxytocin at the end of gestation and in an amount far higher than that from the posterior pituitary gland. Research is continuing to determine the exact mechanism and precise role of the placenta in labor.

When a baby is breast-fed, the sucking of the baby stimulates sensory impulses from the mother’s nipple to the hypothalamus. Nerve impulses from the hypothalamus to the posterior pituitary cause the release of oxytocin, which stimulates contraction of the smooth muscle cells around the mammary ducts. This release of milk is sometimes called the “milk let-down” reflex.

HUMAN LIFE AND THE ROLE OF PITUITARY GLAND: Both ADH and oxytocin are peptide hormones with similar structure, having nine amino acids each. And both have been found to influence aspects of behavior such as nurturing and trustfulness. Certain brain cells have receptors for vasopressin, and they seem to be involved in creating the bonds that sustain family life. Trust is part of many social encounters such as friendship, school, sports and games, and buying and selling, as well as family life. These two small hormones seem to have some influence on us mentally as well as physically.

RELATED;

1. FETAL DIAGNOSIS

2. STAGES OF LABOR

3. NORMAL LABOR AND VARGINAL DELIVERY

4.  PARTURITION AND LABOR

5.  PHARMACOLOGY AND THERAPEUTICS

REFERENCES

THROMBOCYTOPENIA

 

INTRODUCTION: Thrombocytopenia which is a condition of low platelet count, is the most common cause of abnormal bleeding.

PATHOPHYSIOLOGY: Thrombocytopenia can result from decreased production of platelets within the bone marrow or from increased destruction or consumption of platelets.

CAUSES: Causes include failure of production as a result of hematologic malignancies, myelodysplastic syndromes, metastatic involvement of bone marrow from solid tumors, certain anemias, toxins, medications, infections, alcohol, and chemotherapy; increased destruction as a result of idiopathic thrombocytopenia purpura, lupus erythematosus, malignant lymphoma, chronic lymphocytic leukemia, medications, infections, and sequestration; and increased utilization, such as results from disseminated intravascular coagulopathy (DIC).

CLINICAL MANIFESTATIONS: With platelet count below 50,000/mm³ : bleeding and petechiae. With platelet count below 20,000/mm³ : petechiae, along with nasal and gingival bleeding, excessive menstrual bleeding, and excessive bleeding after surgery or dental extractions. With platelet count below 5,000/mm³: spontaneous, potentially fatal central nervous system hemorrhage or gastrointestinal hemorrhage.

ASSESSMENT AND DIAGNOSTIC FINDINGS: Bone marrow aspiration and biopsy, if platelet deficiency is secondary to decreased production. Increased megakaryocytes (the cells from which platelets originate) and normal or even increased platelet production in bone marrow, when platelet destruction is the cause.

MEDICAL MANAGEMENT: The management of secondary thrombocytopenia is usually treatment of the underlying disease. Platelet transfusions are used to raise platelet count and stop bleeding or prevent spontaneous hemorrhage if platelet production is impaired; if excessive platelet destruction is the cause, the patient is treated as indicated for idiopathic thrombocytopenia purpura.

For some patients a splenectomy can be therapeutic, although it may not be an option for other patients for example, patients in whom the enlarged spleen is due to portal hypertension related to cirrhosis.

RELATED;

1. BLOOD PLATELETS

2. THE COAGULATION CASCADE

3. BLEEDING DISORDERS

4.  MEDICAL CONDITIONS

REFERENCES

HEART MURMUR

 

INTRODUCTION: A heart murmur is an abnormal or extra heart sound caused by a malfunctioning heart valve. The function of heart valves is to prevent backflow of blood, and when a valve does not close properly, blood will regurgitate or in simple terms, go backward, creating turbulence that may be heard with a stethoscope. Medicalinstruments

RHEUMATIC HEART DISEASE AND HEART MURMURS: Rheumatic heart disease is a now uncommon complication of a streptococcal infection. In rheumatic fever, the heart valves are damaged by an abnormal response by the immune system. Erosion of the valves makes them “leaky” and inefficient, and a murmur of backflowing blood will be heard. Mitral valve regurgitation, for example, will be heard as a systolic murmur, because this valve is meant to close and prevent backflow during ventricular systole.

HEART MURMURS AS CONGENITAL DEFECTS: Some valve defects involve a narrowing also known as stenosis, and are congenital; that is, the child is born with an abnormally narrow valve. In aortic stenosis, for example, blood cannot easily pass from the left ventricle to the aorta. The ventricle must then work harder to pump blood through the narrow valve to the arteries, and the turbulence created is also heard as a systolic murmur. Children sometimes have heart murmurs that are called functional because no structural cause can be found. These murmurs usually disappear with no adverse effects on the child however.

RELATED;

1. HEART SOUNDS

2. PHYSIOLOGY OF THE HUMAN HEART

3. BLOOD PRESSURE AND HYPERTENSION

REFERENCES

MEASLES

 

INTRODUCTION: Measles is a highly contagious, acute, febrile illness. In the developing countries it has the highest morbidity and mortality among all vaccine preventable illnesses. Measles is one of the most ubiquitous and persistent of human viruses. Its distribution is worldwide and it causes disease in any climate and under any conditions, provided enough susceptible human beings are brought together to enable it to spread.

CLINICAL FEATURES: Measles is one of the most important childhood infections. After an incubation period of 10-12 days, the disease manifests with prodromal symptoms of fever and upper respiratory tract infection marked with coryza, cough and conjunctivitis. Early diagnosis can be made by detecting Koplik’s spots, which are red macules or ulcers with a bluish white centre, seen on the mucous membrane of the inside of cheek. Rashes appear on different parts of the body starting from head followed by chest, trunk and then limbs. After a few days they start fading and then recovery is rapid and complete. Measles can cause severe and multiple complications in a large number of patients (10-20%). Encephalomyelitis has an incidence of less than one out of 1000, but carries a mortality of 15%. It also has sequelae of epilepsy and personality changes.

PATHOGENESIS: Measles, like mumps, is a typical systemic viral infection. Virus gains entry through respiratory tract, multiplies in the epithelial lining and then spreads to lymph nodes where another phase of replication occurs. Further spread to organs takes place and skin, brain and lungs get involved. Lesions produced are characterised by the presence of multinucleated giant cells with well defined intranuclear and intracytoplasmic inclusions. It is now well established that the maculopapular rash of measles is mediated by immunopathological mechanism. Such rashes do not appear in immunologically compromised patients who develop pneumonia and in case of adults, the disease proves fatal.

IMMUNE RESPONSE: High titres of IgG, IgM as well as secretory IgA are seen after primary infection with measles virus. IgM and IgA disappear after sometime but IgG persist lifelong making the individual immune to reinfection. Though a strong immune response is mounted by the body on getting infected with measles virus, the disease has got an immunosuppressive action.

LABORATORY DIAGNOSIS: Clinical Samples: Diagnosis of a typical case of measles can be made based upon clinical symptoms. However, demonstration of the virus or seroconversion against the virus is necessary to confirm the diagnosis. Best results for isolation of virus are obtained when specimens are taken during the first few days of illness.

RELATED;

1.  MUMPS

2.  HEPATITIS

3.  MEDICAL CONDITIONS

REFERENCES

PSEUDOMONAS AERUGINOSA

 

OCCURRENCE AND SIGNIFICANCE: All pseudomonads are widespread in nature. They are regularly found in soils, surface water, including the ocean, on plants and, in small numbers, in human and animal intestines. They can proliferate in a moist milieu containing only traces of nutrient substances. The most important species in this group from a medical point of view is P. aeruginosa, which causes infections in person with immune defects.

MORPHOLOGY AND CULTURE: P. aeruginosa are plump, 2–4 µm long rods with one to several polar flagella. Some strains can produce a viscous extracellular slime layer. These mucoid strains are frequently isolated in material from cystic fibrosis patients. P. aeruginosa possesses an outer membrane as part of its cell wall. The architecture of this membrane is responsible for the natural resistance of this bacterium to many antibiotics. Antimicrobialdrug resistance

P. aeruginosa can only be grown in culture mediums containing free O2 as a terminal electron acceptor. In nutrient broth, the organism therefore grows at the surface to form a so-called pellicle. Colonies on nutrient agar often have a metallic sheen. Given suitable conditions, P. aeruginosa can produce two pigments, that is to say, both yellow-green fluorescein and blue-green pyocyanin.

PATHOGENESIS AND CLINICAL PICTURES: The pathomechanisms involved are highly complex. P. aeruginosa usually enters body tissues through injuries. It attaches to tissue cells using specific attachment fimbriae. The most important virulence factor is exotoxin A also called ADP ribosyl transferase, which blocks translation in protein synthesis by inactivating the elongation factor eEF2. Virulence factors of microorganisms

There is also an exoenzyme S which is also an ADP ribosyl transferase, that inactivates cytoskeletal proteins and GTP-binding proteins in eukaryotic cells. The so-called cytotoxin damages cells by creating transmembrane pores. Various different metalloproteases hydrolyze elastin, collagen, or laminin. Collagen

Two type C phospholipases show membrane activity. Despite these pathogenic determinants, infections are rare in immunocompetent individuals. Defective nonspecific and specific immune defenses are preconditions for clinically manifest infections. Patients suffering from a neutropenia are at high risk. The main infections are pneumonias in cystic fibrosis or in patients on respiratory equipment, infections of burn wounds, postoperative wound infections, chronic pyelonephritis, endocarditis in drug addicts, sepsis, and malignant otitis externa. P. aeruginosa frequently causes nosocomial infections.

DIAGNOSIS: Laboratory diagnosis includes isolation of the pathogen from relevant materials and its identification based on a specific pattern of metabolic properties.

THERAPY: The antibiotics that can be used to treat P. aeruginosa infections are aminoglycosides, acylureidopenicillins, carboxylpenicillins, group 3b cephalosporins, and carbapenems. Combination of an aminoglycoside with a betalactam is indicated in severe infections. Beta lactam antibiotics  Susceptibility tests are necessary due to frequent resistance.

RELATED;

1.  CLOSTRIDIUM  

2.  ANTIBIOTICS

3.  BACTERIA AND DISEASE

REFERENCES

GASTRIC JUICE AND IT'S FUNCTIONS

 

MECHANISM OF HCl SECRETION: The gastric mucosa has different types of cells:

(a) The mucous secreting surface epithelial cells,

(b) The oxyntic or parietal cells which secrete acid, and

(c) The chief cells or peptic cells that secrete enzymes.

The HCl secreted by the parietal cells is of high concentration about 0.15 M with a pH as low as 0.8. Acids,Bases and the pH,

THE K⁺/H⁺ATPase: The parietal cells transport protons against a concentration gradient at the extracellular fluid pH of 7.4. It is an energy-requiring process. The K⁺ activated ATPase is necessary for the production of HCl. It is located on the luminal side of the plasma membrane. The H⁺ ions are generated within the cell by ionization of carbonic acid. The carbonic anhydrase is active in the parietal cells. Proton pump inhibitors  One molecule of ATP is hydrolyzed for every molecule of H⁺ secreted. The hydrolysis of ATP is coupled with an exchange of K⁺ for H⁺. The hydrogen ions are then secreted into gastric lumen. Side by side with the H⁺ to K⁺ exchange, a bicarbonate to chloride exchange is also taking place. When the bicarbonate level within the cell increases which is formed from Carbonic acid (H2CO3), it is reabsorbed into bloodstream, in exchange for Cl^– . The chloride is then secreted into the lumen to form HCl. This would account for the alkaline tide of plasma and urine, following hydrochloric acid secretion, immediately after meals.

REGULATION OF ACID SECRETION: Gastrin, the gastrointestinal peptide hormone secreted by G cells, stimulates secretion of HCl. The secretion of gastrin is cut off by acidic pH by a feedback regulatory control. The most potent stimulus for acid secretion is histamine, which acts through specific H2 receptors on the gastric mucosa. ANTIHISTAMINES

OTHER CONSTITUENTS OF GASTRIC SECRETIONS: The major enzyme present in gastric juice is pepsin, which is responsible for digestion of proteins. One of the functions of HCl is to activate the zymogen pepsinogen to pepsin by partial proteolysis. In addition, the HCl helps in the absorption of iron and calcium. The gastric juice also contains a glycoprotein required for the absorption of B12, the Castle's intrinsic factor.

RELATED;

1. PEPTIC ULCER DISEASE

2.  NAUSEA AND VOMITING

3.  ANATOMY AND PHYSIOLOGY

REFERENCES

DIGESTIVE FUNCTIONS OF PANCREATIC JUICE

 

INTRODUCTION: The secretion of pancreatic juice aids digestion in several ways. The large amount of bicarbonate in the juice helps to neutralize the acidic chyme from the stomach so that the pancreatic enzymes can function optimally in a neutral pH range. Each enzyme also has an important digestive function.

CARBOHYDRATE DIGESTION: In digesting carbohydrates, pancreatic amylase splits straight-chain glucose polysaccharides also known as amyloses in starch, into smaller α-limit dextrins: maltose and maltotriose. Brush border enzymes in the small intestine complete the hydrolysis of these smaller sugars into glucose, which is transported across the intestinal epithelium by Na⁺-coupled transport.

FAT METABOLISM: Pancreatic lipase contributes to fat metabolism by hydrolyzing triglycerides into fatty acids and a monoglyceride; this activity is most efficient in the presence of bile acids, which serve to emulsify the triglycerides. Phospholipase A2 splits a fatty acid off from lecithin to form lysolecithin.

NUCLEIC ACID METABOLISM: Ribonuclease and deoxyribonuclease attack the nucleic acids.  The remaining enzymes help digest proteins. Trypsin, chymotrypsin, and elastase are endopeptidases that is to say, they cleave peptide bonds in the middle of polypeptide chains. Carboxypeptidase is an exopeptidase that is, it splits peptide bonds adjacent to the carboxyl terminals of peptide chains. Together, these proteases break down proteins into oligopeptides and free amino acids.

RELATED;

1.  THE ENDOCRINE PANCREAS

2.  INFLAMMATION OF THE PANCREAS

3.  ANATOMY AND PHYSIOLOGY

REFERENCES

HEMOGLOBIN AND RED BLOOD CELLS

 

INTRODUCTION: Red blood cells (RBC) are biconcave discs, with a diameter of about 7 microns. RBCs live for about 120 days in peripheral circulation, and 100 ml blood contains about 14.5 g of Hb. Mature RBC is non-nucleated; have no mitochondria and does not contain TCA cycle enzymes. However, the glycolytic pathway is active which provides energy and 2,3-bisphosphoglycerate (2,3-BPG).  The HMP shunt pathway provides the NADPH.

PRODUCTION OF RED BLOOD CELLS: Human erythropoietin, a glycoprotein with molecular weight of 34 kD, is the major stimulator of erythropoiesis. It is synthesized in kidney and is released in response to hypoxia. RBC formation in the bone marrow requires amino acids, iron, copper, folic acid, vitamin B12, vitamin C, pyridoxal phosphate and pantothenic acid; they are used as hematinics in clinical practice.

FUNCTION OF HEME: Hemoglobin is a conjugated protein having heme as the prosthetic group and the protein, the globin. It is a tetrameric protein with 4 subunits, each subunit having a prosthetic heme group and the globin polypeptide. The polypeptide chains are usually two alpha and two beta chains. Hemoglobin has a molecular weight of about 67,000 Daltons. Each gram of Hb contains 3.4 mg of iron.

Heme is present in;  1) Hemoglobin  2) Myoglobin  3) Cytochromes  4) Peroxidase  5) Catalase  6) Tryptophan pyrrolase  7) Nitricoxide synthase

PRODUCTION OF HEME: Heme is produced by the combination of iron with a porphyrin ring. Chlorophyll, the photosynthetic green pigment in plants is magnesium porphyrin complex. Heme can be synthesized by almost all the tissues in the body. Heme is synthesized in the normoblasts, but not in the matured erythrocytes. The pathway is partly cytoplasmic and partly mitochondrial.

RELATED;

1. THE HUMAN RED BLOOD CELLS  

2. STRUCTURE AND FUNCTION OF HEMOGLOBIN  

3. OXYGEN  

4. THE GASEOUS EXCHANGE PROCESS

5.  ANATOMY AND PHYSIOLOGY

REFERENCES

METABOLISM AND HOMEOSTASIS

 

INTRODUCTION: Metabolism is all of the chemical reactions and physical processes that take place within the body. Metabolism includes growing, repairing, reacting, and reproducing all the characteristics of life. The pumping of the heart, the digestion of food in the stomach, the diffusion of gases in the lungs and tissues, and the production of energy in each cell of the body are just a few of the thousands of aspects of metabolism. Cardiaccycle and the heart sounds: Gaseous exchange.

METABOLIC RATE: A related concept, metabolic rate, is most often used to mean the speed at which the body produces energy and heat, or, put another way, energy production per unit of time, such as 24 hours. Metabolic rate, therefore, is one aspect of metabolism. A person who is in good health may be said to be in a state of homeostasis.

HOMEOSTASIS: Homeostasis reflects the ability of the body to maintain a relatively stable metabolism and to function normally despite many constant changes. The changes that are part of normal metabolism may be internal or external, and the body must respond appropriately. Eating breakfast, for example, brings about an internal change. Suddenly there is food in the stomach, and something must be done with it. The food is digested or broken down into simple chemicals that the body can use. An example of an external change is a rise in environmental temperature. On a hot day, the body temperature would also tend to rise. However, body temperature must be kept within its normal range of about 36⁰ to 37.6⁰C in order to support normal functioning. One of the body’s responses to the external temperature rise is to increase sweating so that excess body heat can be lost by the evaporation of sweat on the surface of the skin. This response, however, may bring about an undesirable internal change, dehydration. 

As body water decreases, we feel the sensation of thirst and drink fluids to replace the water lost in sweating. Notice that when certain body responses occur, they reverse the event that triggered them. In the preceding example a rising body temperature stimulates increased sweating, which lowers body temperature, which in turn decreases sweating. Unnecessary sweating that would be wasteful of water is prevented.

RELATED;

1. METABOLISM AND METABOLIC DISORDER

2. METABOLIC PROFILE OF ORGANS

REFERENCES

5 WONDERS OF THE HUMAN LIFE

WONDERS OF THE HUMAN LIFE:  The human life is one of it's kind and it has several wonders that we hardly think about.  The human body is seen as wholly and a single entity that may seem to have no divisions but unlike bacteria, and other microbes, our bodies are complex and made up of organs and systems.  From head to toe, the human body is seen as a whole entity almost made up of no special components and functioning is far from reach to a naked eye.  From birth to adulthood, and including the very many processes going on in the human body, including in-utero, this article is going to be looking at the most incredible circumstances that every mankind should think about.  These are physiological processes, anatomical formations or just abnormal changes and deviations in the human body.

1.  THE CARDIOVASCULAR SYSTEM: Our very first wonder is located in the cardiovascular system and specifically the heart.  The human heart is formed in the 4th week of the embryonic life in the uterus and by the fifth week, it has started pumping although there are no developed blood vessels and blood or chambers at a time.  This body's vital organ the size of your fist in an average adult individual, continues to pump unstoppably throughout life and it will only stop at the point of death.  With it's ability to pump blood through more than 75Kg of an average individual, this backbone of life can make the approximate 5.5-7 liters of blood for an average individual circulate the entire body in only about 75 seconds.

It is also astonishing to know that the human heart is capable of generating nerve impulses on it's own irrespective of the input from the central nervous system and can remain pumping for more than 9 minutes outside the human body as long as it is immersed in a solution containing glucose.  There is too much I have discussed about the human heart and to read more about the human heart, click here.

2.  THE PARALLEL CONNECTION OF BLOOD SUPPLY:  It is astonishing to know that all organs of the human body supplied blood via a parallel connection.  This means that every organ receives it's own branch of blood vessel from the main blood vessel, the aorta.  There are only two known instances where a series connection is available and in that sense, blood from one organ will pass through another organ and we call the blood vessel in that case, a portal vein.  This is between the hypothalamus and pituitary in the first instance, and in that case we have the hypothalamic portal vein, then between the liver and the intestines, in which case we have the hepatic portal vein.  I have recently discussed about the hepatic circulation and you can read more about it here.

3.  THE CONTINUOUS DEMAND FOR INTAKE OF FOOD:  The other most unnotably wonderful fact about the human body is the endless demand to eat.  Our bodies start the continuous input of food in our mother's wombs when we are feeding via the umbrical cord and it continues to breast milk feeding after birth linking the same body that natured us, and then food is introduced at advancing age and the eating habit continues.  This unstoppable and continuous process of the human body continues throughout life and it is the only way the body get nourished with nutrients.  It is therefore our role and responsibility to feed our bodies.

4.  THE MATERNAL-FETAL CIRCULATION:  Our fourth wonder of the human body lies between the blood supply of a pregnant mother and her fetus.  It is known by very few that the maternal blood does not mix with that of the fetus during pregnancy and both the mother and the growing fetus both rely on independent circulatory systems.  It could be proved wrong or misunderstood but to clearly state the evidence, we look at the maternal blood group versus the fetal blood group which may be totally different and this would trigger death from blood incompatibilities if both blood systems were communicating directly.

During embryonic development, there develops an organ known as the placenta on the inner walls of the uterus and this is where exchange of material happens.  Now depending on the nature of the substance, some will diffuse from the mother to the fetal side and vice versa.

5.  THE GIT TRANSIT TIME:  The human gastrointestinal tract is about 9 meters long from the mouth to the anal canal.  This system is the only one responsible for nourishing the body with ions and nutrient, following input and digestion of food.  The wonders of this multi-organ system of varying tissues and diameters is that food will stay in it for about 36 hours on average following ingestion.  But of course this time will depend on the type of food eaten and the extent of exercise carried out by the individual plus some other factors such as disease state.   It is this time that all the possible nutrients will be absorbed. The deviation from that, will be of two extents; either increased transit time in which food will overstay in it, or reduced transit time in which food will harry leaving the system.  The two extremes have two consequences as we can see; in case of increased time, the fecal matter will be compacted and become super solid leading to a condition known as constipation.  In case or reduced transit time, food will harry leaving the system and with it, goes the precious nutrients and water leading to a condition known as diarrhea.

RELATED;

1.  CHAMBERS OF THE HEART AND ASSOCIATED STRUCTURE

2.  THE HEPATIC PORTAL CIRCULATION

3.  CONSTIPATION

4.  DIARRHEA

NEUROTRANSMITTER SYSTEMS

 

INTRODUCTION: There are several systems of neurotransmitters that are found at various synapses in the nervous system. These groups refer to the chemicals that are the neurotransmitters, and within the groups are specific systems. The first group, which is a neurotransmitter system of its own, is the cholinergic system. It is the system based on acetylcholine. This includes the NeuroMascular Junction (NMJ) as an example of a cholinergic synapse, but cholinergic synapses are found in other parts of the nervous system. They are in the autonomic nervous system, as well as distributed throughout the brain.

THE CHOLINERGIC SYSTEM: The cholinergic system has two types of receptors, the nicotinic receptor is found in the NMJ as well as other synapses. There is also an acetylcholine receptor known as the muscarinic receptor. Both of these receptors are named for drugs that interact with the receptor in addition to acetylcholine. Nicotine will bind to the nicotinic receptor and activate it similar to acetylcholine. Nicotine

Muscarine, a product of certain mushrooms, will bind to the muscarinic receptor. However, nicotine will not bind to the muscarinic receptor and muscarine will not bind to the nicotinic receptor.

AMINO ACIDS AS NEUROTRANSMITTERS: Another group of neurotransmitters are amino acids. This includes glutamate (Glu), GABA (gamma-aminobutyric acid, a derivative of glutamate), and glycine (Gly). These amino acids have an amino group and a carboxyl group in their chemical structures. Glutamate is one of the 20 amino acids that are used to make proteins. Each amino acid neurotransmitter would be part of its own system, namely the glutamatergic, GABAergic, and glycinergic systems. They each have their own receptors and do not interact with each other.

Amino acid neurotransmitters are eliminated from the synapse by reuptake. A pump in the cell membrane of the presynaptic element, or sometimes a neighboring glial cell, will clear the amino acid from the synaptic cleft so that it can be recycled, repackaged in vesicles, and released again.

BIOGENIC AMINES AS NEUROTRANSMITTERS: Another class of neurotransmitter is the biogenic amine, a group of neurotransmitters that are enzymatically made from amino acids. They have amino groups in them, but no longer have carboxyl groups and are therefore no longer classified as amino acids. Serotonin is made from tryptophan. It is the basis of the serotonergic system, which has its own specific receptors. Serotonin is transported back into the presynaptic cell for repackaging. Other biogenic amines are made from tyrosine, and include dopamine, norepinephrine, and epinephrine. Dopamine

Dopamine is part of its own system, the dopaminergic system, which has dopamine receptors. Dopamine is removed from the synapse by transport proteins in the presynaptic cell membrane. Norepinephrine and epinephrine belong to the adrenergic neurotransmitter system. The two molecules are very similar and bind to the same receptors, which are referred to as alpha and beta receptors. Norepinephrine and epinephrine are also transported back into the presynaptic cell. The chemical epinephrine is also known as adrenaline, and norepinephrine is sometimes referred to as noradrenaline.

EFFECTS OF NEUROTRANSMITTERS ON THE POSTSYNAPTIC MEMBRANES: The effect of a neurotransmitter on the postsynaptic element is entirely dependent on the receptor protein. First, if there is no receptor protein in the membrane of the postsynaptic element, then the neurotransmitter has no effect. The depolarizing or hyperpolarizing effect is also dependent on the receptor. When acetylcholine binds to the nicotinic receptor, the postsynaptic cell is depolarized. This is because the receptor is a cation channel and positively charged Na⁺ will rush into the cell. However, when acetylcholine binds to the muscarinic receptor, of which there are several variants, it might cause depolarization or hyperpolarization of the target cell. The amino acid neurotransmitters, glutamate, glycine, and GABA, are almost exclusively associated with just one effect. Glutamate is considered an excitatory amino acid, but only because Glu receptors in the adult cause depolarization of the postsynaptic cell. Glycine and GABA are considered inhibitory amino acids, again because their receptors cause hyperpolarization. The biogenic amines have mixed effects. For example, the dopamine receptors that are classified as D1 receptors are excitatory whereas D2-type receptors are inhibitory. Biogenic amine receptors and neuropeptide receptors can have even more complex effects because some may not directly affect the membrane potential, but rather have an effect on gene transcription or other metabolic processes in the neuron.

RELATED;

1. GENERATION OF AN ACTION POTENTIAL  

2. PARTS OF THE NERVOUS SYSTEM  

3. THE ENTERIC NERVOUS SYSTEM

4.  ANATOMY AND PHYSIOLOGY

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