Discuss negative and positive feedback regulation of endocrine secretion.

Discuss negative and positive feedback regulation of endocrine secretion.


  1. Discuss negative and positive feedback regulation of endocrine secretion.

Endocrinesystem in a living organism is a control center that is controlled bypositive and negative feedback mechanisms. Negative feedbackmechanisms are aimed at bringing the condition of the body or part ofthe body to the balance or normal state. The mechanism can becompared to a thermostat which regulates temperatures in electronics.A rise in temperature is considered to be a deviation from the normalstate, which initiates mechanical mechanism such as air conditioningto restore the condition. In the human body, there are numerousexamples of negative feedback mechanisms. A typical example is theregulation of calcium levels in the blood. Concentration of calciumis regulated by parathyroid hormone secreted by the parathyroidglands. A decrease in concentration of calcium in the blood resultinto increased secretion of the hormone. This increases the amount ofcalcium released from the bones into the blood stream. A reverse ofthe process occurs if there is high concentration of calcium in theblood. Another example of negative feedback mechanism is in thecontrol of glucose level in the blood by insulin. High concentrationof glucose triggers the production of insulin and vice versa.Positive feedback mechanisms are events in the body that are selfperpetuating. This means that the body reacts to a stimulus bypromoting it rather that negating. Positive feedbacks are lesscommon. They play a critical role in child birth. For example, duringchild birth, the pressure receptors in the uterus send a message tothe brain which increases the production of oxytocin which increaseslabor contractions. Another example is production of milk duringlactation (Marieb &amp Hoehn, 2015).

  1. Discuss the hormones that have a direct effect on blood sugar levels and describe how they achieve this control.

Thereare two main hormones that are responsible for regulation of bloodsugar, insulin and glucagon. They are secreted by the pancreas andare responsible to regulation of blood sugar in the opposite fashion.The secretion of insulin is stimulated by higher concentration ofblood sugar. This condition is referred to as hyperglycemia. Anincrease in blood sugar can be as a result of several factors whichinclude ingestion of food, trauma, stress hormones or drugs. Adecrease in the concentration of sugar results into reduction in thesecretion of insulin. The increased secretion of insulin triggers theconversion of blood sugar (glucose) into glycogen through a processknown as glycogensis. Glycogen is then stored in the body cells,mainly in the muscle tissues. This results into a reduction in thelevel of blood sugar. A decrease in the blood sugar concentrationtriggers the secretion of glucagon by the pancreas. This condition isreferred to as hypoglycemia. Increased levels of glucagon initiatesthe conversion of glycogen stored in body cell to glucose (bloodsugar). This process is referred to as gycogenolysis. The glucoseproduced in the liver enters the bloodstream resulting into increasedconcentration of blood sugar. However, there are some hormones whichare indirectly involved in the control of blood sugar which includesomatostatin, epinephrine, cortisol, ACTH and growth hormones (Marieb&amp Hoehn, 2015).

3. Describe the life cycle of the red blood cells.

Humanerythrocytes or red blood cells are produced from stem cells througha complex process referred to as erythropoiesis. Erythropoiesisprocess is stumilated by a decrease in oxygen concentration in thebody circulatory system. The decrease is detected by specializedreceptos in the kidney which results into secretion of a hormonecalled erythropoietin. This leads to proliferation anddifferentiation of the stem cells, red blood cells precursors. Thisstimulates erythropoiesis process in the hemopoietic tissuesresulting into increased production of blood cell. In birds andmammals, which include humans, the hemopoietic tissues are located inthe bone marrow. However, in the early stages of fetus development,hemopoietic takes place in the yolk sac in the mesodermal tissues andin the liver in the later stages of development. Mature red bloodcells live in the blood stream for three and half to four months.They are eliminated from circulation after they become senescent.Erythropoiesis is complicated process that takes seven stages ofdevelopment and differentiation. However, a mature healthy human canproduce up to two million red blood cells per second. Senescent redblood cells undergo self programmed death where they undergo changesin the plasma membrane which increases their susceptibility tomacrophages. This initiates the process of phagocytosis in thespleen, liver and the bone marrow. This process occurs at the samerate as the production of new red blood cells. The by products of thered blood cells mainly hemoglobin is reduced to iron III ions andalbumin, which is stored in the liver or removed from the body asplasma protein (Marieb&amp Hoehn, 2015).

4. Describe the factors that influence the transport of Oxygen andcarbon dioxide in the blood.

Theability of hemoglobin to carry oxygen determines the amounts ofoxygen reaching the body tissues. There are several factors thataffected the oxygen carrying capacity of hemoglobin. This includesenvironmental factors as well as body related factors. Additionally,these factors affect the ability of blood to transport carbonmonoxide. One major factor that influences the ability of blood tocarry oxygen is the concentration of carbon dioxide in the blood.Carbon dioxide is transported in the blood in the form ofbicarbonate. The bicarbonate is formed when carbon dioxide dissolvesin water to form a weak acid. The reduced PH of the blood plasmaresult into reduced affinity of the red blood cells for oxygen. Alower PH, more oxygen is required to reach the same oxygen saturationlevel in the blood as at higher PH. A blood temperature can resultinto reduced affinity of hemoglobin for oxygen. Another factor thataffects the ability amount of blood transported by blood is diseasessuch as thalassemia and sickle cell anemia. In individuals withsickle cell anemia, the red blood cells are crescent shaped, whichreduces their ability to deriver oxygen or pass through capillaries.Thalassemia on the other hand reduces the number of red blood cellsin the blood (Marieb&amp Hoehn, 2015).

5. Describe the interactions between the immunocytes which produces theimmune system response.

Thereare two ways through which immunocytes, a class of white blood cells,produces an immune system response in the body. Cell medicated immuneresponse activation of a cytotoxic immunocytes or T cells that arespecific to the antigen resulting into production of cytokines. Thisimmune response does not involve the production of antibodies.Although this type of immunocytes interactions is more common in nonphagocytic cells, it is critical in removing infected cells, generalimmunity and it’s the major process that is involved in transplantrejection. Humoral immunity response on the other hand involves theproduction of mediating macromolecules by the immunocytes. The mainmediating macromolecules are antibodies. Immunocytes involved in thisimmune response are the B cells which are triggered by the presenceof antigen to produce an antigen. The B cells engulf and digest theantigen. The fragments of the antigen trigger the production ofmatching T cells (helper cells) against the antigen. The cytokinesproduced by the T cells results into increased of antibody producingB cells (Marieb &amp Hoehn, 2015).


Marieb,Elaine. &amp Hoehn, Katja. N. (2015). HumanAnatomy &amp Physiology,Pearson Education, ISBN 0133995194.