How does a negative feedback system work?
Sensor monitors the variablecontrol center compares magnitude of variable to the setpoint value, integrates the information, and controls the response of the effector system(s), which control the magnitude of the variable, bringing it back to set point
what are the two primary types of controls of effectors in multicellular animals, and what do they do?
nerve cells that produce electrical impulses (that usually transmit information via neurotransmitters)hormones that provide chemical signals
What do chemical messages such as hormones do?
they produce and coordinate anatomical, physiological, developmental and behavioral changes
Where do hormones come from?
they are secreted by endocrine cells (often in endocrine glands)
What is the difference between hormones and nerve impulse transmission?
Hormones work much more slowly than nerve impulse transmission and are not useful for controlling rapid actionshormones coordinate longer-term developmental processes such as reproductive cycles
cells or glands that do not have ducts leading to the outside of the body; they secrete their products directly into the extracellular fluid
have ducts that release their secretions into the gut, etc.
Are all endocrine cells part or a gland?
No, some endocrine cells are single cells within a tissuedigestive hormones, for example are secreted by isolated endocrine cells in the wall of the stomach and small intestine
Some endocrine cells aggregate into secretory organs called endocrine glands
In vertebrates, nine major endocrine glands make up the endocrine system
hormone secreting cells
cells receiving the hormonal messages, they must have appropriate receptorsthe binding of the receptor activates a response
what characteristic determines hormone groups?
The distance over which teh signal operates distinguishes hormone groupssome act close to the release site, others at distant body locations
most hormones diffuse into the blood, which distributes them throughout the bodywhen the hormone message encounters a cell with the proper receptor, it binds and triggers a response
What does the position on/in a cell of a receptor tell you about the hormone?
It can tell you if it is water or lipid soluble and if it can diffuse across the cell membrane
act locallytwo types: autocrine, paracrine
act on the secreting cell itself
stimulate growth and differentiation of cells, are a major class fo paracrine hormonesalso act as autocrine hormones: some of the hormone influences the cell that secreted it, preventing the cell from secreting too much hormone
What are some major types of local hormones
growth factorsneurons may also be considered to be paracrine cells because they use chemicals called neurotransmitters to send messages to another cell
act on cells near the site of releasereleased in tiny amounts or inactivated rapidly by enzymes, or are taken up efficiently by local cellsthey never get into the circulatory system
What are the three main groups of hormones based on structure?
peptides or protienssteroid hormonesamine hormones
peptide or protein hormones
water solubletransported by vesicles out of the cell that made themtheir receptors are on the outside of the cell membrane of the target cell (they can't get into the cells)
lipid-solublecan diffuse out of the cells that made themin the blood they must be bound to carrier proteinsbc they can diffuse through the cell membrane their receptors are usually in the cytoplasm of the target cells
derivatives of the amino acid tyrosinemost are water-soluble, but some are lipid-soluble
the receptors for lipid-soluble hormones are inside cells, either in the cytoplasm or in the nucleusthe action of lipid-soluble hormones is mediated by intracellular hormone receptors that usually alter gene expression
water solublble hormone receptors
large glycoproteins on the cell surface with three domains
What are the three domains of water-soluble hormone receptors?
binding domain: projecting outside the plasma membranetransmembrane domain: anchors the receptor in the membranecytoplasmic domain: extends into the cytoplasm of the cell
How does the cytoplasmic domain initiate the target cells respone?
It activates protein kinases or protein phosphotases (signal transduction cascades)
What determines how a cell responds to a hormone?
responses to hormones depend on their receptors and target cellsthe same hormone can cause different responses in different types of cells
How does epinephrine act on different cells in the body?
in the heart, it stimulates faster (increases HR) and stronger (increases stroke volume) heartbeat (increase cardiac output)blood vessels in some areas (gut, skin, etc.) constrict to send more blood to skeletal musclesin the liver, glycogen is broken down to glucose to provide quick energyin fat tissues, fats are mobilized as another energy source, fatty acids
When in evolution did hormones arise and how do we know?
hormonal comunication arose early in evolutionall multicellular animals have chemical communication between cells, even spongesplants also have hormones, mainly to control growty and development
why must insects molt?
because insects have rigid exoskeletons, they have episodic growth patterns and must molt periodically
the growth stage between each molt
How is molting regulated in insects
two hormones, brain hormone and ecdysone (molting hormone) work together to regulate molting
pair of structures attached to the insect brain that store brain hormone
endocrine gland in the thorax of insects which receives brain hormone and releases ecdysone which stimulates molting
the rear part of the insect headproduces juvenile hormone
prevents molting to the adult stageif it is present the insect molts into another juvenile instar
a link between the nervous system and many endocrine glands and plays a crucial role in the endocrine systemthe pituitary gland sits in a depression at the bottom of the skull and is attached to the hypothalamusmade of two parts: anterior and posterior
Posterior pituitary (neurohypophysis)
an extension of the hypothalamus and therefor neural tissuereleases 2 hormones: ADH, oxytocin
Where are the hormones from the posterior pituitary made and how do they get into the gland?
they are made by neurons in the hypothalamus (and therefore are neurohormones) an are packaged in vesiclesthe vesicles are transported down the axons of the neurons that made them and are stored in the posterior pituitarythis movement of vesicles is achieved by kinesin proteins, powered by ATP, that "walk" down the microtubules of the axon
anterior pituitary (adenohypophysis)
forms from an inpocketing of the roof of the mouth (Rathke's pouch)releases four tropic hormones which control (stimulate) activities of other endocrine glandsthey are peptide and protein hormoneseach is produced by a different type of pituitary cellother peptide and protein anterior pituitary hormones influence tissues that are not endocrine glands
Antidiuretic hormone (vasopressin)
the major function is to increase water conservation by the kidneyIf there is a high level of ADH secretion, the kidneys reabsorb water, decreasing urine outputADH stimulates increased aquaporins in the collecting ductsif there is a low level of ADH secretion, the kidneys release water in dilute, high volume urineADH release by the posterior pituitary increases if blood pressure falls or blood becomes too saltyADH also causes peripheral blood vessel constriction
a major function of oxytocin is to stimulate uterine smooth muscle contraction for the birth process (Pitocin)it also stimulates milk flow (stimulates smooth muscle for ejection of milk) in the mother's breasts
What are the four types of tropic hormones?
thyrotropinadrenocorticotropingonadotropinslutenizing hormone and follicle stimulating hormone
What nontropic hormones are produced by the anterior pituitary?
growth hormoneprolactinmelanocyte-stimulating hormoneendogenous opiodes endorphines and enkephalins
acts on many tissues to promote growthstimulates cells to take up amino acidsstimulates the liver to produce chemical messages (insulin-like growth factors) that stimulate bone and cartilage growth
the result of overproduction of GH in children
caused by the underproduction of GH GH can now be produced by genetically engineered bacteria
stimulates the production and, to a lesser extent, secretion of milk in female mammalsit is also important in pregnancy and, in males, has a role in controlling the endocrine functions of the testes
endorphins and enkephalins
the body's natural opiatesin the brain, these molecules act as neurotransmitters to reduce pain in pain pathways
What controls the anterior pituitary and how?
the anterior pituitary is controlled by neurohormones from the hypothalamusthe hypothalamus obtains data about body conditions and the external environment through both neuronal and hormonal signalsthe hypothalamus and the anterior pituitary are connected by portal blood vesselssecretions from the hypothalamic nerves are transported by these blood vessels to the anterior pituitary
Thyrotropin-releasing hormone (TRH)
from the hypothalamuscuases anterior pituitary cells to release thyrotropin, which in turn stimulates the thyroid gland
gonadotropin-releasing hormone (GnRH)
causes the anterior pituitary to release tropic hormones that control gonad activity (follicle stimulating hormone and luteinizing hormone)
What type of feedback system controls anterior pituitary cells and the hypothalamus?
They are under negative feedback control by the hormones of the glands they stimulate
Cortisol feedback system
cortisol is produced by the adrenal gland in response to adrenocorticotropin. It returns to the pituitary in the blood, and inhibits further release of adrenocorticotropinCortisol also exerts negative feedback control on the hypothalamu, inhibiting release of adrenocorticotropin-releasing hormonehowever, higher brain input to the hypothalamus also controls circulating anterior pituitary hormone levels
located near the tracheaanother example of an endochrineproduces the hormone thyroxine in specialized structures called follicles
two active forms T3 and T4 are made from tyrosineT3: 3 IT4: 4 Imore T4 is produced, but its can be converted to T3 by an enzyme in the bloodT3 is the more active form of the hormone
Roles of thyroxine in metabolism
it stimulates the transcription of many genes in nearly all cells in the body. Theses include genes for enzymes of energy pathways, transport proteins, and structural proteinsit elevates metabolic rates in most cells and tissues (important in thermoregualtion)it raises blood glucose and promotes the use of carbohydrates over fats for fuel
Irreversible neural damage and retardation caused by insufficient thyroxine after the 4th month of human fetal life which results in inadequate formation of the myelin sheath around the axons of neurons
Controls of thyroxine
Thyrotropin (or TSH) from the anterior pituitary activates thyroid gland cells to produce thyroxineThyrotropin-releasing hormone (TRH) from the hypothalamus activates TSH-producing cells in the anterior pituitaryIn a negative feedback loop, thyroxine inhibits the response of pituitary cells to TRH. Therefore, less TSH is released when levels are high, and more is released when levels are lowThyroxin also feeds back to reduce TRH from the hypothalamus
an enlarged thyroid gland associated with eigher very low (hypothyroidism) or very high (hyperthyroidism) levels of thyroxine
What is the structure of a thyroid follicle?
a thyroid follicle is a layer of epithelial cells surrounding a mass of glycoprotein called thyroglobulin
contains iodinated tyrosines and is digested by the epithelial cells of the follicle to make thyroxine
What happens if there is inadequate iodine present when thryoglobulin is made?
the released molecules will be neither T3 nor T4 and will not bind to appropriate receptors (including those in the hypothalamus and anterior pituitary)Goiter occurs when thyroglobulin production is above normal and the follicles are enlarged
results when there is insufficient thyroxine to turn off TSH productionthe most common cause is a deficiency of dietary iodinewith high TSH levels, the thyroid gland continues to produce nonfunctional thyroxine and becomes very largethe body symptoms of this condition are low metabolic rate, cold intolerance, and physical and mental sluggishness
results when the negative feedback mechanism fails even though blood levels of thyroxine are hight. A common cause is an autoimmune disease in which an antibody to the TSH receptor is produced. Common symptom is high metabolic rate.
What three hormones control blood calcium
calcitonin, parathyroid hormone and vitamine D
Blood calcium regulation processes (3)
Deposition and absorption of bone exceretion of calcium by hte kidneys Absorption of calcium from the digestive tract
released by the thryroid gland acts to lower calcium levels in the bloodCalcitonin decreases osteoclast activity and stimulates the osteoblasts to take up calcium from the blood for bone growth
Osteoclasts break down bone and release calcium to the bloodOsteoblasts secrete the protein matrix and use circulating calcium to build new bone. As bone is laid down the osteoblasts are surrounded and develop into osteocytes.
embedded in the posterior surface of the thyroid gladreleases parathyroid hormone when blood Ca is low
parathyroid hormone (PTH)
causes the osteoclases to dissolve bone and release calciumpromotes calcium resorption by the kidney to prevent loss in the urinepromoting vitamin D activation which stimulates the gut to absorb calcium from foodActs on the kidneys to increase the elimination of phosphate to reduce the possibility of calcium phosphate salt precipitation (kidney stones)
not actually a vitamin, produced by the bodyactivates to form (1,25) dihydroxyvitamin D, stimulated by PTHThe active form binds to cyctoplasmic receptors and forms transcription factors. in the digestive tract the transcription factors act to increase synthesis fo calcium pumps, calcium channels and calcium binding proteins, promoting uptake of calciumIn the kidneys and bone acts like PTHNegative feedback to inhibit PTH
bone stored in egg laying female birds to store calcium , under the control of PTH
insulin and glucagon are produced in the pancrease in cell clusters called islets of Langerhans
required for glucose uptake by most cells but not nerve cellsinhibits lipase (lipid breakdown) in adipose tissue, and stimualtes amino acid uptake by cells
type 1 - lack of the protein hormone insulintype 2 - lack of insulin receptors on target cellscauses excessive urine production
hyposecreation of ADH (makes you pee more)
stimulates liver to convert glycogen to glucose when glucose levels are low
paracrine functions that inhibit both insulin and glucagonslows the gut activitesinhibits release of GH and thyrotropin
made up of adrenal medulla and the adrenal cortex two seperate endocrine organs
produces epinephrine and norepinephrinedevelopes from the nervous system and is under the control of the nervous system
under hormonal control mainly by adrenocorticotropin (ACTH) from the anterior pituitary
prevent epi from binding to the beta-adrenergic recptors on target cellsused to reduce fight-or-flight response for heart patients leaves alpha sites open for regulatory function
prodcues by the adrenal cortex using cholesterolacts by stimulating transcription of certain genesglucocorticoidsmineralocorticoidsSEX steroids
raise blood glucose concentrations and other aspects of fuel molecule metabolism
infulence extracellular ionic (mainly Na and K) balance
stimualte SEXUAL developement and reproductive activity. Under normal conditions theses are secreated in only minimal amounts by the adrenal cortex
the main mineralocoritcoid stimulates the kidney to conserve sodium and excrete potassiumrelease is stimulated by angiotensin-II
release is stimulated by lo blood Na and or lo blood pressure
the main glucocorticoid helps control blood levels of glucose and other energery sources and to mediate the body's response to stressraises blood glucose by stimulating gluconeogenesis by the liver and inhibiting peripheral use of glucose (saving for neural tissue) mobilizes fatty acids from adipose tissue and increases blood (amino acid) from muscle for uptake and use in gluconeogenesisstress response ensures that muscles have enough glucose for immediate response and brain has enough glucose to functionalso blocks the immune system reactions which temporarily are less critical, can be used to reduce inflammation and allergy
from the hypothalamus to stimulate the release of ACTH which controls cortisol levels
stimulates secretion of HCl and pepsin, increases motility of stomach
slows the movement of the stomach
releases bicarbonate solution from pancrease to neutralize HCl before it enters the intestines
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH)
controls the SEX steroids released by the anterior pituitary
Gonadotropin-releasing hormone (GnRH)
released by the hypothamalus to stimulate the release of gonadotropins (LH and FSH)
How/why does puberty start
Starts when the hypothalamus becomes less sensitive to negative feedback by the SEX steroids
remaining follices left over in the ovary during ovulation that function as an endocrine gland and produces estrogen and progesterone for about two weeks
the state of sexual receptivity around the time of ovulation
human chorionic gonadatropic (hCG)
similar to funcion in LH but only produced by cells covering the blastocystdetected by pregnancy tests
produced by the pineal gland, released in dark