5. Homeostasis: Active Regulation of the Internal Environment Flashcards
Homeostasis
The active processes that take place in the body to balance internal environment
Sometimes includes behaviors that you do to maintain a normal state
Thermoregulation
The active processes of closely regulating body temperature around a set value
Endotherms
Generate most of their own heat through internal processes
Pros of endotherms
- independence from environmental conditions
- improved oxygen use capacity sustains greater muscular activity
Cons of endotherms
Uses a lot of food energy to produce heat
Homeostatic mechanisms that regulate temperature, body fluids, and metabolism are primarily ___________ feedback systems
negative
Set point
most ideal point
Set zone
Range of tolerance in a system
You’re okay if you’re in this zone
Allows for flexibility so you’re not turning on regulating systems all the time
Thermoregulation in mammals
Receptors detect temperature all around the body: skin, body core, hypothalamus
They receive info → send info to spinal cord, brain stem, and hypothalamus
Thermoregulation in humans
The body has multiple physiological systems for the generation of heat; preoptic area of the hypothalamus is an important area
- Restricting blood vessels to warm you up
- Dilating blood vessels to cool you down
- Breaking down brown fat
- Shivering
- Increased thyroid activity
- Sweating
Ectotherms
Get most of their heat from the environment
Thermoregulation: endotherms AND ectotherms
Behavioral regulation of temperature
3 strategies for behavioral regulation of temperature
Change exposure of the body surface
Ex: huddle to cover your limbs when you’re cold
Changing external insulation
Ex: building a nest, putting on layers
Changing surroundings
Ex: going underground, going into a warm room
Behavioral thermoregulation in bacteria-challenged lizards
Iguanas will regulate their body temperature using a heat lamp
If exposed to bacteria, it will create a “fever” by moving toward a heat source
–> Behavioral fever
Ectotherms have to manually bring their core temperature up to kill off virus
Fluid regulation
We are constantly using and replenishing water and salts (urination, breathing, etc.), so we have both physiological and behavioral mechanisms to replace them
The brain itself is almost 80% water, so a careful balance of fluids and dissolved salts is required so it can function
Water is balanced between two body compartments
Intracellular compartment
Extracellular compartment
Intracellular compartment
Fluid contained within our cells where most water resides
Extracellular compartment
Fluid outside of our cells
Interstitial fluid: fluid in between cells
Blood plasma: protein-rich fluid that carries red and white blood cells
Aquaporins
Water moves in and out of cells through aquaporins via osmosis
Osmosis
The passive movement of a solvent (the liquid) to move through a membrane in order to equalize the concentration of solute
(molecules of a substance)
Osmotic pressure
The physical force that pushes or pulls water across the membrane due to differences in concentrations of salts
Osmolality
Number of solute particles per unit volume of solvent
Isotonic salt solution
Mixture of salt and water
About 0.9% sodium chloride
A ____ solution has more salt than an isotonic solution, while a ____ solution has less salt
Hypertonic, hypotonic
How does salt impact cells?
If cells are surrounded by saltier solutions (that is, a hypertonic solution), they will lose water
If they are surrounded by less salty solutions (a hypotonic solution), water will push into the cells
If excessive, this movement can damage or even kill cells
Two kinds of thirst
Osmotic thirst
Hypovolemic thirst
Osmotic thirst
If the outside of your cells have more salt, water leaves the cells
This is usually why we feel thirsty: obligatory water loss by normal physiological processes like respiration, perspiration, and urination, or eating a salty meal
Hypovolemic thirst
Loss of volume of extracellular fluid
______ in the hypothalamus respond to changes in osmotic pressure as water is drawn out of cells by osmosis
Osmosensory neurons
Important brain regions in osmotic thirst
areas in the hypothalamus (POA, supraoptic nucleus, anterior hypothalamus) and the circumventricular organs
Circumventriuclar organs
Lie in the walls of the ventricles
Thinning in the blood-brain barrier at these locations so they can better detect concentration of solute particles
Baroreceptors
Located in major blood vessels and the heart
Detect drop in blood pressure
Remedy to osmotic thirst
Water
Remedy to hypovolemic thirst
Water and salts
Hypovolemia causes release of _____, or antidiuretic hormone (ADH)
Causes release of vasopressin
From the posterior pituitary gland
Induces blood vessel constriction and reduces water flow to the bladder
Renin
Kidneys release enzyme called renin to conserve water from hypovolemia
Triggers other hormones, resulting in circulation of angiotensin II
Angiotensin II
Conserves water by constricting blood vessels, increasing blood pressure, and releasing vasopressin and aldosterone
Angiotensin II also acts at the circumventricular organs to stimulate drinking
Glucose
Principal sugar used for energy
Glycogen
Complex carbohydrate made by combining a bunch of glucose molecules and then storing it for a short time in the liver and muscles
Glycogensis
The process of converting glucose to glycogen, regulated by the pancreatic hormone insulin, released by beta cells in the pancreas
Glucagon
Another pancreatic hormone released by alpha cells in the pancreas
Mediates glycogenolysis– conversion of glycogen back into glucose when blood glucose levels drop
Lipids
(or fats) for longer-term storage
Deposited in adipose tissue
Under periods of longer food deprivation
gluconeogenesis kicks in to convert fat and proteins into glucose and ketones
Insulin is required for:
getting glucose into cells to be used by the body
Insulin is NOT required for:
glucose to be used by brain cells; and not required to make use of ready energy from fatty acids
Why does the body need insulin?
To help glucose transporters import glucose from the blood into most cells
And to help monitor appetite
Diabetes mellitus
Caused by the failure of insulin to induce glucose absorption
Type 1 (juvenile-onset)
A failure of the pancreas to produce insulin
Type 2 (adult-onset)
Primarily a consequence of reduced sensitivity to insulin
Ventromedial hypothalamus (VMH)
Satiety center
Lateral hypothalamus (LH)
Hunger center
The _____ of the hypothalamus is key in integrating peptide hormone signals from the body
arcuate nucleus
2 hormones in appetite control
Ghrelin
PYY3-36
Ghrelin
Synthesized and released by endocrine cells of the stomach
Appetite stimulant
PYY3-36
Released by intestinal cells; reaches high levels after you eat
Appetite-suppressant
2 sets of neurons in appetite control
POMC neurons: inhibiting appetite and increasing metabolism
NPY neurons: hunger neurons; stimulating appetite and reducing metabolism
Ghrelin and PYY3-36 act on NPY hunger neurons in opposition
Ghrelin stimulates them and increases appetite
PYY3-36 inhibits them and reduces appetite
Nucleus of the solitary tract (NST)
Where appetite signals converge
Common pathway for feeding behavior
Cholecystokinin (CCK)
peptide released by the gut after feeding and acts on the vagus nerve to inhibit appetite
Leptin
Fat cells release leptin into the bloodstream to provide information to the brain about long-term energy reserves
Activates POMC neurons but inhibits NPY neurons, so leptin works to suppress hunger
Defects in leptin
Cause overeating and obesity
