ap bio: chapter 32-homeostasis and endocrine signaling
loose connective tissue
holds skin and organs in place
describe the hormone cascade pathway that occurs when thyroid hormone levels fall
1-thyroid hormone levels drop below normal range 2-hypothalamus secretes thyrotropin-releasing hormone (trh) into the blood. portal vessels carry trh into the anterior pituitary 3-trh causes the anterior pathway to secrete thyroid-stimulating hormone (tsh/thyrotropin) into the circulatory system 4-tsh stimulates endocrine cells in the thyroid gland to secrete thyroid hormone (t3 and t4) into the circulatory system 5-thyroid hormone levels increase in blood and body tissues, returning to its normal range/ it acts on target cells throughout the body to control bioenergetics, help keep normal blood pressure, heart rate, and muscle tone, and regulate digestive and reproductive functions 6-thyroid hormone blocks trh release from hypothalamus and tsh release from the anterior pituitary, forming a negative-feedback loop, preventing overproduction of the thyroid hormone
describe an example of how the nervous system conveys information by the pathway taken by the signal
each musical note's frequency activates different neurons connecting the ear to the brain
what drives the diversity in anatomy between animals?
adaptation, natural selection favors variations in a population the increase relative fitness, usually matching form to function anatomy often hints at physiology
negative feedback
a form of regulation where accumulation of an end product of a process slows the process a main mechanism of homeostasis, where a change in a variable triggers a response that counteracts the initial change ex: you are working out, producing heat, increasing body temperature. your nervous system detects this increase and triggers sweating. the evaporation of water from your skin cools your body, helping body temperature return to the set point
bone
a hard connective tissue a hard mineral of calcium, magnesium, and phosphate ions in a matrix of collagen
neurons
a nerve cell, a fundamental unit of the nervous system its structure and properties let it conduct signals by taking advantage of the electrical charge across its plasma membranes it receives nerve impulses from other neurons via its cell body and extensions (dendrites) they transmit impulses to neurons, muscles, or other cells via extensions (axons) that are often bundled together into nerves
response
a physiological activity that helps return the variable to the set point, triggered by a change in the variable
sensor
a receptor that detects a stimulus
set point
a value maintained for a particular variable
explain some circulatory adaptations for thermoregulation
adaptations that regulate the extent of blood flow near the body surface or that trap heat within the body core play large roles in thermoregulation (circulatory adaptations) to respond to changes in the temperature of their surroundings, many animals alter the amount of blood and heat flowing between the body core and skin (vasodilation and vasoconstriction)
describe acclimation in ectotherms
adjustments at the cellular level ex: cells may propagate variants of enzymes that have the same function but different optimal temperatures, proportions of saturated and unsaturated lipids in membranes may change (unsaturated lipids help membranes stay fluid at low temperatures) some ectotherms that endure subzero temperatures produce antifreeze proteins, preventing ice from forming in the cells
adrenal glands
adrenal cortex-secretes glucocorticoids-raise blood glucose level, as well as mineralocorticoids-promote reabsorption of na+ and excretion of k+ in kidneys adrenal medulla-secretes epinephrine and norepinephrine-raise blood glucose level, increase metabolic activities, and constrict certain blood vessels
describe the structure of epithelial tissue
all epithelia are polarized (have 2 different sides) apical surface-faces lumen (cavity) or outside of organ and is exposed to fluid/air basal surface-attached to the basal lamina (a dense mat of extracellular matrix that separates the epithelium from the underlying tissue
conformer
an animal whose internal condition conforms to (changes in accordance with) changes in an environmental factor ex: this fish conforms to temperature of the water it's in
regulator
an animal whose mechanisms of homeostasis moderate changes in a particular variable in the face of external fluctuation of that variable its internal mechanisms control internal changes in response to external fluctuation ex: elk, a regulator for temperature, keeps its body at a temperature that's independent of the temperature of the environment it's in
what does thermoregulation depend on?
an animal's ability to control the exchange of heat with the environment an organism exchanges heat by 4 physical processes, which account for the flow of heat within an organism and between an organism and its external environment heat is always transferred from hotter object to cooler object radiation, evaporation, convection, conduction
connective tissue
animal tissue whose main function is to bind and support other tissues consists of a sparse population of cells scattered through extracellular matrix fibroblasts-cells within the matrix that secrete fiber proteins macrophages-cells within the matrix that engulf foreign particles and cell debris
describe how concurrent exchange functions in human arteries and veins
arteries and veins are adjacent to each other warm blood moves from the body core in arteries, transferring heat to colder blood returning from extremities in veins because the blood flows through arteries and veins in opposite directions, heat is transferred along entire length of exchanger, maximizing the rate of heat exchange 1-arteries carrying warm blood to animal's extremities are close to veins with cool blood carried in the opposite direction, towards the trunk. this facilitates heat transfer from arteries to veins along the entire length of blood vessels 2-near the end of the artery, the blood is much colder then the core. the artery still transfers heat to the colder vein. veinous blood keeps absorbing heat as it passes warmer blood traveling in the opposite direction in the arteries 3-as blood in the veins approaches the center of the body, it's about as warm as the body core, minimizing heat loss that results from supplying blood to body parts in cold water
skeletal muscle
attached to bones by tendons, aka striated muscle, responsible for voluntary movements, arrangement of contractile units along the cell gives them a striped (striated) look
what is an advantage of ectothermy?
because their heat comes mainly from their environment, they usually don't need as much food as endotherms of the same size
what do water-soluble, lipid-insoluble polypeptide hormones do to bring about a cellular change?
because they can't pass through plasma membranes, they bind to cell-surface receptors, triggering events at the plasma membrane that result in a cellular response a series of changes in cellular proteins converts the extracellular signal to a specific intracellular response (signal transduction). one of these pathways usually has several steps, each involving specific molecular interactions
how do animals manage their internal environment when faced with environmental fluctuations?
by either regulating or conforming
how do animals achieve homeostasis?
by maintaining a variable, such as temperature or solute concentration, at or near a set point fluctuations in the variable above or below the set point are the stimulus detected by a sensor when it receives a signal from the sensor, a control center generates an output that triggers a response
epinephrine
catecholamine that, when secreted as a hormone by adrenal medulla, mediates "fight or flight" responses to short-term stresses, released by some neurons as a neurotransmitter, aka adrenaline secreted by adrenal glands atop the kidneys release of epinephrine quickly triggers responses including raising blood glucose levels, increasing blood flow to muscles, and decreasing blood flow to the digestive system
how does an endotherm react to a cold environment? a warm environment?
cold environment-generates heat to keep body warmer than surroundings warm environment-have mechanisms for cooling the body, letting them withstand heat that most ectotherms can't
where are thermoregulation sensors located?
concentrated in brain region, the hypothalamus-ventral part of vertebrate forebrain, functions in maintaining homeostasis, especially in coordinating the endocrine and nervous systems, secretes hormones of posterior pituitary and releasing factors that regulate the anterior pituitary within this region, a group of nerve cells works as a thermostat, responding to body temperatures outside a normal range by activating mechanisms that promotes heat loss or gain
cartilage
connective tissue that provides flexible support in the spine and other places
adipose tissue
connective tissue that stores fat and blood (consists of cells and cell fragments suspended in liquid (plasma))
anterior pituitary
develops from non-neural tissue, consists of endocrine cells that synthesize and secrete several trophic (relating to feeding and nutrition) and non trophic hormones
conduction
direct transfer of thermal motion (heat) between molecules in contact with each other
endocrine glands
ductless glands that empty their hormonal products directly into the blood
how does an ectotherm react to a cold environment? a warm one?
ectotherms don't generate enough heat for thermoregulation, many adjust their body temperature through behavior ex: seeking shade, basking in sun
fever
elevated body temperature, can be due to certain bacterial and viral infections in mammals and birds it reflects an increase in the biological thermometer's set point ex: artificially raising the temperature of the hypothalamus in an infected animal reduces fever in the rest of the body
radiation
emission of electromagnetic waves by all objects warmer than absolute zero
what are the two major systems for coordinating and controlling an animal's response to stimuli?
endocrine and nervous
describe simple endocrine pathways
endocrine cells respond directly to an internal or environmental stimulus by secreting a specific hormone, which travels through the bloodstream to target cells, where it interacts with specific receptors, within target cells, signal transduction triggers a response
pituitary gland
endocrine gland at base of hypothalamus posterior lobe-stores and releases two hormones produced by the hypothalamus anterior lobe-produces and secretes hormones that regulate diverse body functions anterior pituitary-hormones secreted by the hypothalamus regulate the anterior pituitary, either stimulating or inhibiting the release of one or more hormones (follicle-stimulating hormone, luteinizing hormone, thyroid-stimulating hormone, adrenocorticotrophic hormone, prolactin, melanocyte-stimulating hormone, growth hormone) posterior pituitary-secretes oxycotin-simulates contraction of uterus and mammary gland cells, as well as vasopressin (antidiuretic hormone, adu)-promotes retention of water by kidneys, influences social behavior and bonding
testes (in males)
endocrine gland that secretes androgens-support sperm formation, promote development and maintenance of male secondary sex characteristics
ovaries (in females)
endocrine gland that secretes estrogen-stimulates uterine lining growth, promotes development and maintenance of female secondary sex characteristics, as well as progesterone-promotes uterine lining growth
pineal gland
endocrine gland that secretes melatonin-regulates biological rhythms
parathyroid gland
endocrine gland that secretes parathyroid hormone (pth)-raises blood calcium level
thyroid gland
endocrine gland that secretes thyroid hormone (t3 and t4)-stimulates and maintains metabolic processes, as well as calcitonin-lowers blood calcium levels
hypothalamus
endocrine gland whose hormones are released from the posterior pituitary releasing and inhibiting hormones-regulate anterior pituitary
what are the 4 main groups of animal tissues?
epithelial connective muscle nervous
what hormones are present in both genders but only plays a major role in one?
estrogens and progesterone (plays major role in females) androgens (plays major role in males)
describe an example of a simple endocrine pathway
ex: control of ph in the duodenum partially digested food passes to it from the stomach (whose digestive juices are acidic) digestive juices must be neutralized before future steps of digestion contents of the stomach enter the duodenum. low ph acts as a stimulus for certain endocrine cells (s cells) in duodenum lining stimulated s cells secrete the hormone secretin into the bloodstream reaching target cells in the pancreas pancreas target cells respond by releasing bicarbonate into ducts that lead to the duodenum, raising ph in the duodenum, neutralizing stomach acid
negative feedback regulation
ex: release of bicarbonate by the pancreas increases ph in intestine, eliminating the stimulus and shutting off the pathway prevents excessive pathway activity by decreasing or stopping hormone signaling
concurrent exchange
exchange of a substance or heat between 2 fluids flowing in opposite directions ex: blood in the fish gill flows in opposite direction of water passing over gill, maximizing the diffusion of oxygen into and carbon dioxide out of the blood
posterior pituitary
extension of hypothalamus composed of nervous tissue that secretes oxycotin and antidiuretic hormone made in the hypothalamic neurosecretory cells, temporary storage site for these hormones
describe feedback regulation in endocrine pathways
feedback loop linking a response to its initial stimulus is characteristic of endocrine pathways, dampening the stimulus the response pathway can include negative feedback regulation or positive feedback regulation
duodenum
first part of the small intestine
interstitial fluid
fluid surrounding body cells
positive feedback
form of regulation where a process' end product speeds up that process. in physiology, a control mechanism where a change in a variable triggers a response that reinforces or amplifies the change, leading to an even greater response in animals-positive-feedback loops don't play a large role in homeostasis but help drive processes to completion ex-oxycotin pathway-in response to circulating oxycotin, mammary glands secrete milk. milk released in response to oxycotin leads to more suckling and more stimulation, activation of the pathway continues until the baby stops suckling. other oxycotin functions (ex: stimulating uterine contractions during labor) sow positive feedback
what does viewing body organization from cells to organ tissues show? from organ tissues to cells?
from cells to organ systems-emergent properties organ tissues to cells-the multilayered basis of specialization (what happens so the organ system can perform its function)
pancreas
gland with exocrine and endocrine tissues. exocrine portion functions in digestion, secreting enzymes and an alkaline solution into small intestine via duct ductless endocrine portion works in homeostasis, secreting the hormones insulin and glucagon into the blood a gland located behind the stomach endocrine gland that secretes insulin-lowers blood glucose level, as well as glucagon-raises blood glucose level
organ system
group of organs that work together in performing vital body functions
tissues
groups of cells with a similar appearance and a common function
what can and what can't homeostasis do?
homeostasis moderates but doesn't eliminate changes in the internal environment additional fluctuation happens if a variable has a normal range set points and normal ranges for homeostasis are usually stable, but certain regulated changes in the internal environment are needed
describe how the anterior pituitary and hypothalamus work together
hormonal signals from the hypothalamus trigger synthesis and release of hormones from the anterior pituitary, which often regulate other hormone glands
oxycotin
hormone produced by the hypothalamus and released from the posterior pituitary, induces contractions of uterine muscles during labor and causes mammary glands to eject milk during nursing
describe the roles of the hypothalamus and anterior pituitary
hormones produced by the hypothalamus regulate the anterior pituitary hypothalamic hormones are secreted near the capillaries at the base of the hypothalamus, which drain into shorter blood vessels (portal vessels), which connect directly to a second capillary bed in the anterior pituitary hypothalamic hormones travel from the hypothalamus to the gland they regulate without first circulating through other body tissues when they reach the anterior pituitary, each hypothalamic hormones either stimulates or inhibits the release of one or more specific hormones (follicle-stimulating hormone, luteinizing hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, prolactin, melanocyte-stimulating hormone, growth hormone)
stimulus
in feedback regulation, a fluctuation in a variable that triggers a response
hormones
in multicellular organisms, a secreted chemical formed in specialized cells, travel in body fluid, and act on specific target cells in other body parts, changing the target cell's function, important in long-distance signaling different hormones have different effects, only cells with receptors for the specific hormone respond depending on which cells have the receptor, the hormone could affect one or several locations it takes many seconds for hormones to enter the bloodstream and be released from it, but its effects are long lasting
explain how the body utilizes the immediate environment of most cells?
in multicellular organisms, the immediate environment of most cells is the internal body fluid. control systems that regulate the composition of this solution let the animal maintain a pretty stable internal environment, regardless of the external environment's variability
fibrous connective tissue
in tendons and ligaments
describe how epinephrine has so many different effects on the body?
in the liver, epinephrine binds to β-type epinephrine receptor in target cell membrane, which activates enzyme protein kinase a, which regulates the enzymes of glycogen metabolism, causing glucose release into the bloodstream in blood vessels supplying skeletal muscles, the same kinase is activated by the same receptor, inactivating a muscle-specific enzyme, resulting in smooth muscle relaxation, vasodilation, and increased blood flow intestinal blood vessels have α-type epinephrine receptor, which triggers a distinct signaling pathway involving different enzymes (not protein kinase a), which results in smooth muscle contraction, vascoconstriction, and restricted intestinal blood flow
describe an example of a simple neuroendocrine pathway
infant sucking stimulates sensory neurons in the nipple, generating nerve impulses that reach the hypothalamus, nerve impulses from the hypothalamus trigger oxycotin release from the posterior pituitary, stimulating mammary glands to secrete milk
what happens if an animal's body temperature is outside of the normal range?
it can reduce efficiency of enzymatic reactions, alter membrane fluidity, and affect other temperature sensitive biochemical process, with possibly fatal results
what is an advantage of having many cells?
it facilitates specialization
describe the hypothalamus' role in vertebrates
it plays a large role in integrating endocrine and nervous systems it receives information from nerves throughout the body (including the brain) signals from the hypothalamus travel to a gland located at its base, the pituitary gland
smooth muscles
lacks striations of skeletal and cardiac muscle because of the uniform distribution of myosin filaments in the cell, responsible for involuntary movements and body activities found in the walls of many internal organs
immune and lymphatic system
main components-bone marrow, lymph nodes, thymus, spleen, lymph vessels, white blood cells functions-body defense (fighting infections and cancer)
nervous system
main components-brain, spinal chords, sensory organs function-coordination of body activities, detection of stimuli and formulation of responses to them fast acting internal communication system involving sensory receptors, nerve cell networks, and connections to muscles and glands that respond to nerve signals, works with the endocrine system to affect internal regulation and maintain homeostasis neurons transmit signals along routes connecting specific locations in the body
circulatory system
main components-heart, blood vessels, blood functions-internal distribution of materials
excretory system
main components-kidneys, ureters, urinary bladder, urethra functions-disposal of metabolic wastes, regulation of osmotic balance of blood
respiratory system
main components-lungs, trachea, other breathing tubes functions-gas exchange (uptake of oxygen, disposal of carbon dioxide)
digestive system
main components-mouth, pharnyx, esophagus, stomach, intestines, liver, pancreas, anus functions-food processing (ingestion, digestion, absorption, elimination)
reproductive system
main components-ovaries/testes and associated organs functions-reproduction
endocrine system
main components-pituitary, thyroid, pancreas, adrenal, and other hormone-secreting glands functions-coordinates body activities (such as digestion and metabolism) internal system of communication involving hormones, ductless glands that secrete hormones, and molecular receptors on/in target cells that respond to hormones, works with the nervous system to effect internal regulation and maintain homeostasis signaling molecules are released into the bloodstream and carried to all parts of the body
muscular system
main components-skeletal muscles functions-locomotion and other movement
skeletal system
main components-skeleton (bones, tendons, ligaments, cartilage) functions-body support, protection of internal organs, movement
integumentary system
main components-skin and its derivatives (hair, claws, skin glands) function-protection against mechanical injury, infection, dehydration, thermoregulation
what do lipid soluble hormones do to bring about a cellular response?
major receptors for these steroid hormones (ex: sex hormones estradiol and testosterone) are in the cytosol, not the cell surface a steroid hormone binds to cytosolic receptor, a hormone-receptor complex forms and moves into the nucleus, where the receptor portion of the complex alters the transcription of certain genes
explain some adaptations that enhance thermoregulation
mammals and birds-insulation reduces the flow of heat between body and the environment (hair, feathers, fat formed by adipose tissue (ex:whale's blubber)) in response to cold, many land mammals and birds raise their fur/feathers, trapping a thicker layer of air, increasing insulating power of fur/feathers humans rely mostly on fat for insulation. goosebumps-vestige of hair raising
describe how hormones are secreted
many are secreted by ductless organs (endocrine glands) others are secreted by isolated endocrine cells in other organs (thymus, heart, liver, stomach, small intestine, kidneys) where ever they're produced, they reach target cells through the circulatory system
what 4 cell types can receive nerve impulses?
muscle, other neurons, endocrine, and exocrine
vasodilation
nerve signals relax the muscles of vessel walls, causing the widening of superficial (near body surface) blood vessels increases blood flow to skin
glia (glial cells)
nervous system cells that support, regulate, and augment the function of nerves help nourish, insulate, and replenish neurons and in some cases modulate (control) neuron function in many animals, a concentration of nervous tissue forms a brain
describe the method of signaling used by the nervous system
nervous system's signals-nerve impulses travel to specific target cells along communication lines consisting mainly of axons, 4 types of cells can receive these nerve impulses unlike the endocrine system, nervous system conveys information by the pathway taken by the signal communication usually involves more than one type of signal. nerve impulses travel along axons (sometimes over long distances) as changes in voltage passing information from one neuron to another often involves short-range chemical signals transmission in the nervous system is overall very fast, nerve impulses don't last long but travel fast
are endothermy and ectothermy mutually exclusive?
no ex: a bird is mainly endothermic, but can warm itself in the sun
is an animal exclusively a regulator or a conformer?
no, an animal can regulate some internal conditions and conform to the environment for others ex: bass conforms to temperature, but regulates solute concentration in its blood and interstitial fluid
what must all animals do?
obtain oxygen obtain nutrients fight off infection produce offspring
what organisms develop fever?
only endotherms develop fever lizards can be infected with a certain bacteria (dipsosaurus dorsalis) which causes them to seek a warmer environment and maintain a higher body temperature similar observations in fish, amphibians, and cockroaches show that raising body temperature in response to infection is a common feature of many animal species
ectothermic
organisms (ex: amphibians, fish, nonavian reptiles) where external sources provide most heat for temperature regulation
endothermic
organisms (ex: humans, most mammals, birds) that are warmed by heat generated by their own metabolism they usually keep a relatively stable internal body temperature that is higher than the temperature of their external environment they keep a stable body temperature when environmental temperature fluctuates
neuroendocrine pathway
pathway that responds to stimuli from external environment that relies on a nervous system sensor
acclimation
physiological adjustment to environmental changes, contributes to thermoregulation in many animal species ex: birds and mammals-acclimation to seasonal temperature changes often includes adding/losing insulation, helping endotherms keep a constant body temperature year-round
physiology
process and functions of an organism
thermoregulation
process where animals keep an internal temperature within a normal range
vasoconstriction
reduces blood flow and heat transfer by decreasing superficial vessel diameter
evaporation
removal of heat from surface of a liquid that's losing some molecules as gas
follicle-stimulating hormone
secreted by anterior pituitary, target cells are in testes/ovaries
luteinizing hormone
secreted by anterior pituitary, targets cells in the testes/ovaries
thyroid-stimulating hormone
secreted by anterior pituitary, targets cells in the thyroid gland
adrenocorticotropic hormone
secreted by the anterior lobe of the pituitary gland, targets cells in the adrenal cortex
growth hormone
secreted by the anterior lobe of the pituitary gland, targets cells in the liver, ones and other tissues
prolactin
secreted by the anterior lobe of the pituitary gland, targets cells in the mammary glands
melanocyte-stimulating hormone
secreted by the anterior lobe of the pituitary gland, targets cells in the melanocytes
epithelial tissue
sheets of tightly packed cells that line organs and body crevices and external surfaces aka epithelium works as a barrier against mechanical injury, pathogens, and fluid loss. forms active interfaces with the environment
compare and contrast the methods of signaling used by the nervous system and the endocrine system
signal type-endocrine uses hormones, nervous uses nerve impulses transmission-endocrine can bring a response to cells with a receptor for a specific hormone, but spreads the hormone throughout the body as it travels through the bloodstream. the nervous system brings responses to cells that connect to an axon (which transmits an impulse) by specialized junctions, nerve impulses travel to specific target cells speed-the nervous system is generally faster then the endocrine system duration-nerve impulses don't last long, hormones can be long-acting endocrine-adapted for coordinating gradual changes affecting the whole body (ex: growth, development, reproduction, metabolic processes, digestion) nervous system-directs immediate and rapid responses to the environment (ex: fast locomotion, behavior) both systems work together to maintain homeostasis
why are some fluctuations in a variable needed?
some changes are associated with certain stages of life ex: shift in hormone balance during puberty others are cyclic ex: monthly variation in hormone levels needed for the menstrual cycle
organs
specialized center of body function composed of several different tissue types (simplest animals, like sponges, lack organs or even true tissues) many organs contain tissues with distinct physiological roles, which are sometimes different enough that we consider the organ to belong to more than one body system (ex-pancreas produces enzymes needed for the function of the digestive system and regulates blood sugar level as part of the endocrine system)
homeostasis
steady-state physiological condition of the body, maintains internal balance when its achieved, an animal keeps a relatively constant internal environment even when external environment changes a lot. animals show homeostasis for a wide range of physical and chemical properties ex: humans keep a fairly constant body temperature of about 37 degrees celsius, a blood ph within 0.1 ph unit of 7.4, and a blood glucose concentration mainly in the range of 70-110 mg per 100 ml of blood
anatomy
structure of an organism
what accounts for cells emergent properties?
successive levels of structural and functional organization
how can one hormone have many different effects on the body?
target cells can vary in their responses if they differ in their receptor type or in the molecules that produce the response (intracellular proteins)
why does the endocrine system produce hormones?
the hormones regulate growth, development, metabolism, homeostasis, and reproduction
describe the method of signaling used by the endocrine system
the type of pathway is the same regardless of the distance of the signal's ultimate target the endocrine uses hormones as signaling molecules, which pass through the bloodstream and are carried to all locations of the body. only cells with the receptor appropriate for the specific hormone respond. depending on which cells have a receptor, the hormone could affect one or several locations. endocrine signaling is slower than nervous signaling, and is important in long distance signaling. its effects are long lasting
why are circulatory systems important?
they are a major route for heat flow between the interior and exterior of the body
what effect has evolution had on hormones?
through evolution, functions of a given hormone often diverge between species ex-thyroid hormone plays a role in regulating metabolism in many lineages, but in frogs, thyroid hormone thyroxine (t4) stimulates the resorption of tadpoles tail during metamorphosis another vertebrate hormone, prolactin, stimulates mammary gland growth and milk synthesis in mammals, but stimulates fat metabolism and reproduction in birds, and delays metamorphosis in amphibians, regulates salt and water balance in freshwater fish, suggesting prolactin is an old hormone with functions that diversified as vertebrate groups evolved
describe how a thyroid scan is used
thyroid hormone contains iodine (obtained from seafood or ionized salt). because iodine is dedicated to the production of thyroid hormone, doctors use a radioactive isotope of iodine to detect abnormal iodine uptake patterns, which may indicate a thyroid disorder
muscle tissue
tissue consisting of long muscle cells that can contract, either on its own or when stimulated by nerve impulses vertebrates have 3 types, skeletal, smooth, cardiac. all muscle cells consist of filaments containing proteins actin and myosin, which work together to contract muscles
nervous tissue
tissue made up of neurons and supportive cells, works in the receipt, processing, and transmission of information neurons and glia
convection
transfer of heat by movement of air or liquid past a surface ex: blood moves heat from the body core to the extremities
cardiac muscles
type of striated muscle that forms contractile wall of the heart its cells are joined by intercalated discs that relay elastic signals underlying each heartbeat
normal range
upper and lower limit of a variable, not a set point
hormone cascade pathways
usually how sets of hormones from the hypothalamus, anterior pituitary, and target endocrine gland are organized signals to the brain stimulate the hypothalamus to secrete a hormone that regulates the release of an anterior pituitary hormone this anterior pituitary hormone acts on another endocrine organ, which stimulates the secretion of another hormone, affecting specific target tissues because these pathways redirect signals from the hypothalamus to other endocrine glands, the anterior pituitary hormones in these pathways are called trophic hormones or trophins
how does the hypothalamic "thermostat" respond to hot and cold temperature?
warm receptors signal the hypothalamic thermostat when the body temperature increases, cold receptors signal when it decreases at body temperatures below the normal range, the thermostat inhibits heat loss mechanisms and activates mechanisms that either save heat (vasoconstriction of vessels in skin) or generate heat (shivering) at elevated body temperatures, the thermostat shuts down heat retention mechanisms and promotes cooling by vasodilation of vessels in skin, panting, sweating
