Transcript The Regulation of Internal Body States

Chapter Ten
The Regulation of Internal Body States
Temperature Regulation
Homeostasis-keeping body variables within a fixed range
Set Point-a single value that the body works to maintain
Homeothermic-mammals and birds use physiological mechanisms
to maintain an almost constant body temperature despite large
variations in the temperature in the environment
Advantages of Consistent Body Temperature
o
Generally, we rest with temperature around 37 C
Advantages
Higher than air temperature so we don’t have to rely on
inefficient methods to cool the body
Body is as warm as it can be without damaging necessary
proteins
Rapid muscle contractions are more possible at this
temperature
Temperature Regulation
Brain Mechanisms
preoptic area is most critical
Behavioral Mechanisms
Seeking a warm place when cold, etc.
Fever
Prostaglandins stimulate a rise in temperature in response to
invading bacteria and viruses
Thirst and Related Processes
When the body needs water=thirst
Related Processes
Vasopressin-hormone released from posterior pituitary
constricts blood vessels
enables kidneys to reabsorb water
Types of Thirst
Osmotic Thirst
When solutes become concentrated outside the cell and water
is extracted from inside cells
OVLT-organum vasculosum laminae terminalis
detects osmotic pressure
sends information to hypothalamus
paraventricular nucleus
supraoptic nucleus
lateral preoptic area
Figure 10.6 The consequence of a difference in osmotic pressure
(a) A solute such as NaCl is more concentrated outside the cell than inside. (b)
Water flows by osmosis out of the cell until the concentrations are equal. Neurons
in certain brain areas detect their own dehydration and trigger thirst.
Figure 10.3 Major subdivisions of the hypothalamus and pituitary
Types of Thirst
Hypovolemic Thirst
thirst resulting from low blood volume
Mechanisms
Baroreceptors-attached to large veins detect pressure of blood
returning to the heart
Renin released by kidneys assists in creating high levels of
angiotensin II which constricts blood vessels and signals
brain to stimulate thirst
Table 10.1
Digestive System
Digestion
Begins with saliva in the mouth
Down esophagus
Stomach tears up food using acids and enzymes
Small Intestine-digested materials absorbed through small
intestine
Large intestine-absorbs water and minerals
Influences on Food Selection
Food Preference
carnivores-meat
herbivores-plants
omnivores-meat and plants
Flavor
Familiarity
Potential conditioned taste aversions-the tendency to form a dislike
to any food that has become associated with illness
Ex: People receiving chemotherapy will develop a dislike for
fluids they consume during therapy
Bodily Influences on Hunger
Mouth
oral sensations
Stomach
Vagus nerve-transmits information on stomach distention
Splanchnic nerve-transmits information on nutrient content of
food being consumed
Intestines
duodenum-once food reaches here, CCK is released and
signals to stop eating
Glucose, Insulin, and Glucagon
Glucose-primary energy source for cells
Insulin-assists glucose entering cells
When high, hunger levels drop
Glucagon-stimulates liver to convert glycogen to glucose
The Hypothalamus and Eating Regulation
Lateral Hypothalamus
Damage to this area = animal refuses food
axons extend to nucleus of the tractus solitarius in the medulla
possibly altering taste sensations
axons extend to forebrain facilitating ingestion and swallowing
activates a circuit that excites dopamine cells initiating
reinforcement of behaviors
sends axons to spinal cord controlling autonomic responses
such as digestive secretions
The Hypothalamus and Eating Regulation
Paraventricular Nucleus
Damage here = eating larger than normal meals
Ventromedial Hypothalamus
Lesions to the VMH lead to finicky eating and sometimes to
overeating
The overeating is due to eating more frequently than normal
Causes
increased stomach motility and secretions
leads to a lasting increase in insulin production
Satiety Signals and Eating Disorders
Hormones
Leptin-produced by fat cells and signal no need to eat
Neuropeptide Y-neuromodulator that inhibits the PVN of the
hypothalamus and results in an increase in meal size
Figure 10.24 Relation among weight, leptin, NPY, and eating
Ordinarily, high levels of body fat produce leptin, which inhibits eating.
Obese mice fail to produce leptin. Obese humans produce leptin but fail to
respond to it.
Genetics, Metabolic Rate, and Body Weight
Genetics-heritability of .4 to .7
Metabolic Rate-the higher the rate the more difficulty someone will
have gaining weight
Ideas for Weight Loss
Increase exercise
Reduce consumption
Eating Disorders
Anorexia
defined-unwilling to eat, significantly underweight
occurs mostly in women during adolescence
Bulimia
defined-alternating between dieting and overeating
May be associated with alterations in PYY, CCK and serotonin