chapter 2 - chemical messengers Flashcards
1
Q
what is steady state
A
- body is not always in optimal conditions my cells ensure that correct materials are in / out of cells and energy is balanced, fluctuations may occur
2
Q
what are the two systems involved in homeostasis
A
- endocrine and nervous are the main sensory / controlling systems, operate through feedback systems
- nervous: sends electrical messages to appropriate organs (fast)
- endocrine: secretes chemical messengers / hormones info blood (slower)
- sense changes in external / internal environment and optimise the environment
3
Q
what is a feedback system
A
- circular situation in which the body responds to a change (stimulus), with response altering the original stimulus
- -ve feedback response causes stimulus to change in a direction opposite to original stimulus
- +ve feedback causes an increase in the original stimulus
4
Q
what is homeostasis
A
- maintenance of a constant internal environment, despite fluctuations in the external environment
- important that cells environment is at an optimal level for normal cell / body functioning
- maintains optimum conc. of nutrients, ions, gas and water, stays at constant temp and maintains pressure
5
Q
describe the pathway of a negative feedback system
A
- stimulus (change in environment that causes system to operate)
- receptor (stimulus is detected by sensory cells)
- modulator (control centre responsible for processing message received)
- effector (muscles / glands receive message from modulator)
- response (effector organs bring about appropriate reaction)
- feedback (achieved, original stimulus has been changed)
6
Q
endocrine vs exocrine
A
- endocrine: secrete hormones into the extracellular fluid (ductless), carried into capillaries and into blood (hypothalamus, pineal, thymus, pancreas)
- exocrine: secrete into a duct, carries secretion to the body surface / body cavity (sweat, mucous, salivary glands, those of alimentary canal)
7
Q
hormones vs paracrines
A
- hormones: secreted by endocrine glands / specialised cells only, affect all cells of body (target cells / organs), receptor specific, saturation occurs
- paracrines (local hormones): secreted by all cells, communicates with other cells in same tissue / adjacent cells, not receptor specific, no saturation
8
Q
two types of hormones
A
- protein / amine: water soluble (cannot cross cell membrane), attach to receptor molecule on membrane of target cell
- -> hormone + receptor = secondary messenger substance diffuses into cell, activating enzymes (cascade reaction), activate cell functioning (e.g. insulin + insulin receptor = glucose into cell)
- steroid: lipid soluble, enters target cell, combines with receptor protein (mitochondria / nucleus)
- -> hormone receptor complex = activates genes controlling protein synthesis
9
Q
function of hormones
A
- change functioning of cells by changing the type of activities or quantities of proteins produced (not enzymes), can change activity / conc. of enzymes
- activate certain genes (so that particular enzymes / structural proteins are produced)
- change shape / structure of enzymes (on / off)
- change rate of production of enzymes / structural protein by changing rate of transcription / translation during protein synthesis)
10
Q
what is enzyme amplification / clearance
A
- A:hormone molecule activates 1000’s of enzymes, very small stimulus can create a large effect, hormones trigger cascade of events
- C: once completing job, turned off, molecules are broken down in target cell, liver and kidneys, degraded hormones are excreted in bile / urine
11
Q
what is the control of hormones
A
- hormone secretion must be closely regulated by negative feedback
- over / under secretion will result in abnormal functioning
- hypothalamus secretes releasing or inhibiting factors
12
Q
summary of the hypothalamus
A
- located at base of brain, regulates many body functions (water balance, temp, heart rate), many functions carried out in pituitary gland
- hormones released are sent to pituitary gland via blood vessels (anterior) or nerve fibres / long extensions (posterior)
13
Q
summary of pituitary
A
- hypophysis, located under hypothalamus, infundibulum connects the two, size of a large pea, two lobes
- anterior: at the front, connected to hypothalamus by a complex network of BV, receives releasing / inhibiting factors
- posterior: at the back, connected to hypothalamus via nerve fibres (long extensions run through infundibulum), not a true gland (doesn’t secrete own hormones)
14
Q
function / hormones released in the anterior lobe of pituitary
A
- function: regulate many body activities, hypothalamus regulates these hormones, secreting hormones into extracellular fluid around cells of hypothalamus
- FSH: gonadotropin, targets ovaries (growth of follicle) / testes (maturation of sperm)
- LH: gonadotropin, targets ovaries (ovulation, formation, maturation of corpus luteum) / testes (stimulates secretion of testosterone)
- ACTH: adrenocorticotropin, targets adrenal cortex (secretion and production of hormones)
- TSH: thyrotropin, targets thyroid gland (secretion / production of hormones)
- PRL: lactose mic hormones, targets mammary glands (initiates / maintains milk production)
- GH: somatotropin, targets all cells, growth / protein synthesis (maintains mature organ size, increases AA intake by cells)
15
Q
function / hormones in posterior lobe of the pituitary
A
- function: release oxytocin and ADH (produced in special nerve cells in hypothalamus which pass through infundibulum via long extensions)
- stay in posterior lobe until ready to be released, nerve impulses initiate the release of hormones into BS
- OT: vasopressin, targets uterus (contractions) / mammary glands (release of milk)
- ADH: targets kidneys (reabsorption of water / vasoconstriction of small arteries)
