Neuroendocrine Regulation and Homeostasis: Mechanisms and Impact
Neuroendocrine Regulation and Homeostasis
Pituitary and Hypothalamus
The pituitary is the main endocrine gland and is involved in regulating the hydrosaline balance, among other functions. The hypothalamus is a structure of the nervous system that controls the functioning of the pituitary.
Formation of Hypertonic and Hypotonic Urine
Glomerular filtration changes in its composition as it progresses through the various passages that form the renal tubule. Harmful substances are removed from the blood, but reabsorbable amounts of water and solutes enter the peritubular capillaries, which contributes to the formation of more dilute (hypotonic) or more concentrated (hypertonic) urine.
Hypotonic urine formation: The formation of dilute urine is produced by an increased reabsorption of solutes, and a decrease in the secretion of ADH (antidiuretic hormone) that determines that the cells of the collecting tube wall prevent water from leaving by osmosis.
Homeostasis and Neuroendocrine Regulation
This equilibrium is under the control of the nervous and endocrine systems. In our body, blood pressure, body temperature, and blood glucose are maintained within normal ranges. Control circuits are similar to that seen for equilibrium. Hydrosaline feedback circuits record information from the internal or external environment, governing the operation of the body’s systems, and are classified as positive (+) or negative (-). Negative feedback reduces or reverses differences detected by the system. Positive feedback magnifies the differences found. In most organisms, negative feedback is more common. When a disturbance occurs in the internal environment, negative feedback for homeostasis increases. In some cases, it inhibits the process it performs.
Regulation of Glycemia
Several hormones are involved in regulating the concentration of blood glucose (glycemia). Two of these, insulin and glucagon, are produced by specific cells in the pancreas. Insulin is secreted in response to an increased concentration of blood sugar because it facilitates the entry of glucose and stimulates its utilization. Additionally, it stimulates the storage of glucose as glycogen in both muscle cells and the liver. When the concentration of blood glucose is low, the pancreas releases the hormone glucagon, which stimulates the degradation of glucose from glycogen stored in muscles and in the liver. The effects of this hormone are opposite to those exerted by insulin.
Blood Pressure Regulation
Glucose and blood pressure are regulated by different mechanisms, some quite complex. The schemes presented below show some processes and structures involved in regulating blood pressure.
Homeostasis and Stress
The nervous and endocrine systems are involved in the homeostasis of organic variables such as blood pressure, blood pH, and hydrosaline balance, in response to a stressor agent that may affect homeostasis. What is stress? Specialists studying stress define it as an innate behavior to a threat. It consists of a defensive or adaptive response that aims to control the conduct of the person against a stimulus that produces stress (stressor). How does your body react against stress? When you are scared, the force with which your heart contracts and the number of times it beats each minute increases. This response is rapid, due to the action of the sympathetic nervous system that releases the neurotransmitter epinephrine. This same molecule is released by the adrenal glands into the blood, allowing it to complement the action of the nervous system and keep the body on alert if the stress situation is maintained for longer.
Stressors Agents
The agent that produces stress is called a stressor or stressor agent. It typically is derived from the natural environment and the people around us, for example, pollution, tobacco, drugs, violence, trafficking, and robbery. In this case, the agent is exogenous. The stressor may also be endogenous, born inside each individual. The environment resulting from the action of the stressor is the most common and universal threat, due to its potential to endanger the physical and mental integrity of persons. To deal with the stressor, the body requires increasing the amount of blood to the brain and muscles. It must also increase the supply of O2 and glucose transported by the blood to these organs. Adrenaline (which can act as a neurotransmitter and hormone) and cortisol are examples of chemicals that allow these functions. They generate a stress response, determining that the body receives more oxygen and glucose. This explains why heart rate and breathing increase.
Types of Stress
- Acute stress: This is when a dangerous situation might endanger our lives. Then, the innate response against the stressor agent is conduct that assures survival.
- Chronic stress: This occurs when the stress situation is sustained over time. It is crippling, as if one feels pressured constantly for work or poor living conditions.
Neuroendocrine Response Against Stress
Both the nervous and the endocrine systems release specific chemicals to combat stress. The first releases neurotransmitters at the synapse level, and the second releases hormones into the blood. Which exerts its effects more quickly? Which generates a more sustained effect over time? Facing a situation of stress, the nervous system activates the sympathetic centers that send information to different parts of the body, that is, towards the adrenal medulla for epinephrine and norepinephrine. These synthesized hormones cause increased heart rate, constriction of the blood vessels of the viscera, synthesis of glucose, decreased digestive activity, and dilation of the airways.
1) Stressor agent -> stress -> hypothalamus (+) -> sympathetic nervous system -> adrenaline -> increases heart rate -> waking state -> increased brain and muscle irrigation -> decreased skin and kidney irrigation (+) endocrine system -> adrenal glands -> adrenaline and cortisol -> increased glycemia -> reduces inflammation -> inhibits allergic reactions.
2) Increased blood pressure is taken by baroreceptors. The carotid and aortic bodies send information to the medulla oblongata, where the cardiac center is located. This determines the activity of the parasympathetic system, causing a reduced heart rate, which determines the decrease in cardiac output. The vasomotor center determines the decrease in the activity of the sympathetic system, which causes vasodilation, decreased blood vessel resistance, and a decrease in blood pressure.
Hypertonic Urine Formation
- Kidney: Participates in the elimination of metabolic wastes and the regulation of salt concentration, amount of water, and blood pH.
- Ureter: Carries urine from the kidney to the bladder.
- Urinary Bladder: Stores urine until urination occurs.
- Urethra: Allows urination or evacuation of urine from the bladder to the outside.
- Renal Cortex: The kidney’s outer region extends from the renal capsule to the base of the renal pyramids.
- Renal Pyramid: A conical structure whose base is oriented toward the cortex and its apex toward the center of the kidney; it contains part of the nephron tubular system.
Urine Formation
It consists of 3 stages: filtration, tubular reabsorption, and tubular secretion. Blood enters the glomerulus through the afferent arteriole and is pressed. This implies that small solutes dissolved in the plasma can pass through the capillaries (permeable) and enter Bowman’s capsule. Part of the liquid plasma component also passes into Bowman’s capsule; this is called glomerular filtration. The glomerulus acts as a sort of strainer that filters metabolic wastes (mainly urea) and small nutrients such as glucose and amino acids. In this way, the liquid is incorporated into the capsule and contains waste substances and molecules useful for the organism. The filtered liquid, called glomerular filtrate, scrolls through the renal tubules, where useful molecules are reabsorbed into the blood. This is called tubular reabsorption. Tubular secretion is the last stage of cleaning, in which certain substances that were not filtered (potassium, hydrogen, urea) are removed from the blood capillaries (peritubular) into the renal tubule.
Along the renal tubule, waste substances are transported from the capillary tube into the tubular lumen. Tubular secretion is similar to absorption, which occurs only in the reverse direction, from the blood into the urine. Like absorption, secretion can be achieved through active or passive transport. In this process, toxic substances that have not been eliminated and are harmful are added to the urine in formation. The substances that can be eliminated in the urine come from the filtered fluid.
Change in Concentration of Urine
In dehydration, urine is more concentrated because the kidney tubules absorb more water. The urine produced after water intake is more diluted because less water is reabsorbed in the glomerulus. Variation of volume, salt, and water homeostasis to maintain the nervous and endocrine systems is involved in the formation of a concentrated or dilute urine of lesser or greater volume, according to the need to maintain the body’s homeostasis. The pituitary gland is the main endocrine gland and participates in the regulation of the hydrosaline balance that regulates the concentration and volume of urine. The hypothalamus is a structure of the nervous system that controls the operation of the pituitary.
Formation of Hypotonic and Hypertonic Urine
Glomerular filtration rate changes in composition as it moves through different ducts that are in the renal tubule. Harmful substances are removed from the blood but are reabsorbed into the peritubular capillaries in varying amounts of water and solutes, which contributes to the formation of hypotonic or diluted urine and hypertonic or concentrated urine. The formation of dilute urine is produced by more solute reabsorption, decreasing the secretion of antidiuretic hormone or ADH. This determines that the cells of the collecting tube wall prevent water from leaving by osmosis, that is, it inhibits the optional reabsorption of water. A decrease in secreted ADH results in dilute urine.
Urine Formation Stages
Urine is formed from the blood supply to the nephrons, and its formation occurs in 3 stages: filtration, tubular reabsorption, and tubular secretion. The blood enters the glomerulus through the afferent arteriole and is pressed. This implies that small solutes dissolved in the plasma can pass through the capillaries (permeable) and enter Bowman’s capsule. Part of the liquid plasma component also passes into Bowman’s capsule; this is called glomerular filtration. The glomerulus acts as a sort of strainer that filters metabolic wastes (mainly urea) and small nutrients such as glucose and amino acids. In this way, the liquid is incorporated into the capsule and contains waste substances and molecules useful for the organism. The filtered liquid is called glomerular filtrate and scrolls through the renal tubules, where useful molecules are reabsorbed into the blood. This is called tubular reabsorption. The liquid is altered to form urine. Not all filtered substances are reabsorbed into the blood; useful substances are reabsorbed, and waste is eliminated through urine. Tubular reabsorption occurs differentially along the entire renal tubule. Every minute, about 125 ml of filtered plasma and solutes dissolved in it enter the uriniferous space. 180 liters of filtrate occur daily. This is not related to daily urine output, as approximately 124 ml will be reabsorbed so that only 1 ml of urine is formed. Through a selective uptake process, water, glucose, and other nutrients are reabsorbed. The cells of the tubes capture, by an active or passive transport mechanism, the useful substances to the space and back into the blood. The solutes are specified by membrane transporters located in the tubule cells, proximal convoluted tubules (PCT). Water reabsorption occurs in the early portion of the renal tubules by osmosis (compulsory resorption), and the rest is reabsorbed in more remote regions (optional reabsorption). Optional reabsorption is regulated by the action of antidiuretic hormone and its mechanism of action.
Solvent: Medium in which the solute is dissolved (e.g., salts).
Solute: Substrate that interacts with the solvent.
63% intracellular fluid, 37% interstitial fluid, plasma, transcellular fluid, lymph. Tissues and cells; external environment.
Internal environment: Constant amount of solute (salt); change the concentration of solvent (by volume).
External environment: Solvent concentration varied; solute concentration varied.
Osmosis: Movement of water through the membrane from a medium with at least the concentration of solute to half the higher concentration of solute.
Isotonic: Same concentration of salts in relation to the solvent.
Hypotonic: Lower concentration of salts in relation to the solvent.
Hypertonic: Higher concentration of salts in relation to the solvent. Water rises in the middle of a hypertonic product due to osmosis.
Only the solvent moves, not the solute.
Vegetable cell: Hypotonic medium of contact pressure.
Homeostasis: Equilibrium between the internal and external.
Salt and water homeostasis: Maintaining the level of salts, water, temperature, and pH (acidity level).
Fish in a marine environment: Mechanism that will maintain the levels of water in your body to avoid loss of this element. Maintain isotonic levels in the blood and interstitial fluid.
Factors that disadvantage hydrosaline balance: High temperature (water loss through sweat), feed (entry of salts and water), environment (salinity and moisture to the environment), and exercise (water loss).
Kidney system: Controls regulating pH balance of excretion of H+ (protons). Blood pressure control through the secretion of a protein called renin. Controlled concentration of salts and water (liquid).
Kidneys: Excretory organs that make up the renal system and eliminate wastes through the formation of urine. Processes in which water is lost: urine (kidneys lose more water), sweat (skin), lubricating (tears, salivation), and respiration (lungs). Water entry leads to the production of urine. Greater penetration of water leads to increased urine production. Urinary output is the production of urine in an amount of time. The main ion involved in salt and water homeostasis is sodium (Na+), entering as NaCl. By increasing water intake, blood plasma levels and urinary output increase. Sodium levels in the blood or plasma must be maintained at constant levels, as an increase in these levels in the blood plasma requires the kidneys to excrete an increased amount of sodium. In spite of this, sodium excretion levels or urine formation tend to be constant.
Formation of urine: Renal artery -> nephron -> ureter -> bladder -> urethra -> urine leaves.