Physiological Psychology 413 Ingestive Behavior DRINKING Adriano Alpajora

Physiological Psychology 413 Ingestive Behavior: DRINKING Adriano, Alpajora, Cruz, De Lara, Rodriguez

Physiological Psychology 413 Ingestive Behavior: Drinking “The constancy of the internal milieu is a necessary condition for a free life” – Claude Bernard

Physiological Psychology 413 Ingestive Behavior: Drinking Homeostasis It is the maintenance of equilibrium within a living organism'. This basically means the body's methods of keeping its functions within the range where it can continue functioning.

Physiological Psychology 413 Ingestive Behavior: Drinking Physiological Regulatory Mechanisms - It is the maintenance of equilibrium within a living organism. - It is body’s methods of keeping its functions within a range where it can continue functioning.

Physiological Psychology 413 Ingestive Behavior:

Physiological Psychology 413 Ingestive Behavior: Drinking 4 Essential Features of Regulatory Mechanisms o System Variable A variable that is controlled by a regulatory mechanism. o Set Point The optimal value of the system variable in a regulatory mechanism.

Physiological Psychology 413 Ingestive Behavior: Drinking 4 Essential Features of Regulatory Mechanisms o Detector A mechanism that signals when the system variable deviates from its set point. o. Correctional Mechanism The mechanism that is capable of changing the value of the system variable.

Physiological Psychology 413 Ingestive Behavior: Drinking The body contains four major fluid compartments; one compartment of intracellular fluid and three compartments of extracellular fluid.

Physiological Psychology 413 Ingestive Behavior:

Physiological Psychology 413 Ingestive Behavior: Drinking Intracellular Fluid • It is the fluid portion of cytoplasm. • It includes: o. Intravascular fluid (blood plasma) o. Cerebrospinal fluid o. Interstitial Fluid

Physiological Psychology 413 Ingestive Behavior: Drinking Two of the fluid compartments of the body must be kept within precise limits: the intracellular fluid and the intravascular fluid. The intracellular fluid is controlled by the concentration of solutes in the interstitial fluid. Normally, the interstitial fluid is “isotonic” with the intracellular fluid.

Physiological Psychology 413 Ingestive Behavior: Drinking That is, the concentration of solutes in the cells and in the interstitial fluid that bathes them in balance, so that water does not tend to move into or out of the cells. If the interstitial fluid loses water (hypertonic) water will move into the cells. Either condition endangers cells.

Physiological Psychology 413 Ingestive Behavior: Drinking The volume of the blood plasma must be closely regulated because of the mechanics of the operation of the heart. If the blood volume falls too low, the heart can no longer pump the blood effectively; if the volume is not restored, heart failure will result. This condition is called “hypovelemia”

Physiological Psychology 413 Ingestive Behavior: Drinking 2 Important Characteristics of the Body Fluids that are monitored by 2 different set of receptors: o. The solute concentration of the Intracellular fluid o The volume of the blood

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Osmometric Thirst It occurs when the tonicity (solute concentration) of the interstitial fluid increases. The increase draws water out of the cells, and they shrink in volume.

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Osmometric Thirst The term “osmometric” refers to the fact that the detectors are actually responding to (metering) changes in the concentration of the interstitial fluid that surrounds them.

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Osmometric Thirst Osmoreceptor , suggested by Verney (1947) are neurons whose firing rate was affected by the level of hydration. If the interstitial fluid surrounding them because more concentrated, they would cause them to alter their firing rate, which would send signals to other parts of the brain.

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Osmometric Thirst When we eat a salty meal, from the digestive system into the blood plasma: hence, the blood plasma becomes hypertonic. This condition draws water from the interstitial fluid, which makes this compartment become hypertonic too and thus causes water to leave the cells.

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Osmometric Thirst As the blood plasma increases in volume, the kidneys begin excreting large amounts of both sodium and water. Eventually, the excess sodium is excreted, along with the water that was taken from the interstitial and intracellular fluid. The result is loss of water from the cells.

Physiological Psychology 413 Ingestive Behavior:

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Volumetric Thirst It occurs when the volume of the blood plasma decrease. When we lose water through evaporation, we lose it from all three fluid compartments: Intracellular, Interstitial & Intravascular

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Volumetric Thirst Evaporation produces both volumetric and osmometric thirst. The loss of blood, vomiting and diarrhea all cause loss of blood volume w/o depleting the intracellular fluid.

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Volumetric Thirst Two sets of receptors are responsible for initiating volumetric thirst and salt appetite: One set in the kidneys One set in the heart and large blood vessels

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Volumetric Thirst Role of Angiotensin The kidneys contain cells that are able to detect decreases in the flow of blood to the kidneys. The usual cause of a reduced flow of blood is a loss of blood volume; thus these cells detect the presence of

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Volumetric Thirst Role of Angiotensin When the flow of blood to the kidneys decreases these cells secrete an enzyme called renin. Renin enters the blood where it catalyzes the conversion of a protein called angiotensinogen into a hormone called angiotensin.

Physiological Psychology 413 Ingestive Behavior:

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Volumetric Thirst Atrial Baroreceptors It is the second set of receptors for volumetric thirst lies within the heart. The atria of the heart contain sensory neurons that detect stretch. The atria are passively filled with blood being returned from the body by the veins

Physiological Psychology 413 Ingestive Behavior: Drinking Two types of Thirst o. Volumetric Thirst Atrial Baroreceptors The more blood in the veins, the fuller the atria become just before the contraction of the heart. Thus, when the volume of the blood plasma falls, the atria become less full and the stretch receptors within them will detect this change.

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst The osmoreceptors that initiated drinking are located in the brain tissue around the AV 3 V. The entire region around the anterior third ventricledorsal as well as ventralseems to be the part of the brain where osmometric and volumetric signals are integrated to control drinking.

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst The region around the AV 3 V also appears to receive information that can stimulate volumetric thirst. Sensory information from the baroreceptors located in the atria of the heart is sent to a nucleus in the medulla: the nucleus of the solitary tract.

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst This nucleus sends efferent axons to many parts of the brain, including the region around the AV 3 V (Johnson and Edward, 1990).

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst The second signal for volumetric thirst is provided by angiotensin II. Because this peptide does not cross the blood brain barrier, it cannot directly affect neurons in the brain except for those located in one of the circumventricular organs.

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst In fact, research indicates that one of these organs, the subfornical organ (SFO), is the site at which blood angiotensin acts to produce thirst. This structure gets its name from its location, just below the commissure of the ventral fornix.

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism ofand Thirst Simpson, Epstein, Camardo (1978) found that very low doses of angiotensin injected directly into the SFO caused drinking and that destruction of the SFO or injection of a drug that blocks angiotensin receptors abolished the drinking that normally occurs when angiotensin is injected into the

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst Philips and Felix (1976) found that injections of minute quantities of angiotensin into the SFO increased the firing rate of single neurons located there: evidently, these neurons contain angiotensin receptors.

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst In fact, research indicates that one of these organs, the subfornical organ (SFO), is the site at which blood angiotensin acts to produce thirst. This structure gets its name from its location, just below the commissure of the ventral fornix.

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst Neurons in the subfornical organ send their axons to the median preoptic nucleus, a small nucleus wrapped around the front of the anterior commissure, a fiber bundle that connects the amygdale and anterior temporal lobe.

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst The nucleus receives information from the region around the AV 3 V and from the nucleus of the solitary tract. The median preoptic nucleus integrates the information it receives and through its efferent connections with other parts of the brain, controls drinking.

Physiological Psychology 413 Ingestive Behavior: Drinking Neural Mechanism of Thirst The region of AV 3 V seems to play a critical role in fluid regulation in humans as well. Lack of drinking (adipsia) is a brain damage that causes the patient to feel no sensation of thirst even after they are given an injection of hypertonic saline.

Physiological Psychology 413 Ingestive Behavior: