PHYSIOL A Flashcards
what are the targets of homeostatic control?
- conc. of O2 & CO2, nutrients, salts & electrolytes, waste products
- temp
- volume and pressure of extracellular fluid
- pH of internal environment
define homeostasis:
regulation of internal environment so as to maintiain appropriate life sustaining conditions to cells and tissues of the body
what is the concept of positive feedback?
amplifies initial change by amplifying signal indefinitely - ended by a separate mechanism
allows large response to develop from small initial signal
describe blood clotting as a positive feedback mechanism:
- tear in vessel wall
- stimulates platelet aggregation
- platelets release chemicals to attract other platelets
- newly attracted platelets further release chemicals to attract other platelets
- clot formation complete other inhibitory processes prevent further aggregation
simply describe Ferguson reflex:
fetus’ head stretches isthmus - stimulates stretch receptor neurons
- signals to brain relayed to pituitary stimulates release of oxytocin from posterior pituitary …oxytocin stimulates contraction
- fetus’ head pushes against isthmus more => more oxytocin produced and released
what is the homeostatic control of blood pressure?
- haemorrhage reduced BP
- stretch of baroreceptors decreases
- info sent afferent path to brain
- info through efferent to heart and vessels
- response = heart beats faster and blood vessels constrict to raise blood press to normal level (“homeostatic” level)
effects of excessively low blood glucose(Hypoglycaemia)?
<4mmol/L
- CNS dysfunction
- dysfunction/damage to retina, germinal epithelium and RBCs
cells almost exclusively glucose for energy
what do endocrine cells release?
hormones
which can be either paracrine or autocrine
what do nerve cells release in terms of homeostasis regulation?
neurotransmitters - physical connections through synapses
what do chemical signals act on?
receptors at target site, on membrane or within cell
in terms of thermoregulation what happens when the environmental temperature is higher than body temperature?
- vasodilatation, moving blood away from skin surface
- sweating
- hair follicles relax, air flow next to skin increases heat loss by convention
in terms of thermoregulation what happens when body temp is higher than environmental temperature?
- reduced sweating
- piloerection(hairs erect due to pilorum muscles) goose bumps!
- constriction of skin arterioles
- shivering(muscles)
- metabolic changes(brown fat mitochondrion)
describe the blood glucose feedback loop in steps:
- eating increases blood glucose
- this change in blood glucose is detected by beta cells in pancreas
- causes insulin release into blood stream
- insulin acts on target tissues(liver/muscles)
- response of target tissues will result in removal of glucose from circulation - due to the increased uptake by liver & muscle
- blood glucose levels decrease, restoring homeostasis
when blood glucose rises, cells increase their uptake but what do they do with the glucose?
- used for metabolic energy
- fat synthesis (storage)
- glycogen synthesis (storage)
in periods of fasting describe the feedback mechanism that brings blood glucose back to homeostatic levels:
- low blood glucose is recognised by beta cells in pancreas
- pancreas is stimulated to secrete glucagon
- increase of circulating glucagon(but cannot be used yet)
- glycogen broken down in liver
- released into blood stream for use
what goes wrong in type 1 diabetes?
beta cells fail to detect blood glucose, therefore failure to release insulin into blood stream to stimulate uptake of increased blood glucose
what goes wrong in type 2 diabetes?
tissue cells are desensitised to insulin,
what are 5 important roles of calcium in homeostasis?
- neurotransmitter and hormone release mechanism
- muscle contraction
- hardening of teeth and skeleton
- blood clotting
- cell devision and excitability
describe blood calcium regulation:
- decrease in plasma calcium concentration
- decrease detected by CHEMOreceptors in PARATHYROID gland
- this stimulates release of ParaThyroid Hormone(PTH) release into blood stream
- PTH acts on target tissues (bone, kidney, gut)
- response= increase REsorption FROM bone, BY kidney, TO gut(where it is absorbed)
some potential consequences of diabetes mellitus?
- CVD
- retinopathy/neuropathy (think glucose only energy supply)
in terms of feedback mechanisms what is the cause of rickets?
rickets is a disease surround calcium levels in the blood
When one has rickets, low blood causes PTH hormone release and increased resorbtion of Calcium from bone BUT vitamin D3 is needed for this, its not there so, calcium isn’t resorbed meaning it cannot be absorbed in gut
what are the communication types in the endocrine system?
- gap junctions(cell to cell)
- contact-dependent signals(interaction between membrane molecules)
- local communication(paracrine/autocrine)
- long-distance communication(through blood=endocrine)
what are the major endocrine glands(top to bottom)?
- pituitary gland
- thyroid gland
- parathyroid gland
- adrenal glands(on tops of kidneys
roles of endocrine system?
4 x regulation of metabolism
H2O and electrolytes
growth and development
responding to stress
3 x controlling wake-sleep patterns
temperature
repoduction
describe endocrine glands:
ductless
release into surrounding FLUID
describe exocrine glands:
ducts
substances travel along ducts to SURFACE
what 3 things can stimulate hormone release?
- hormonal
- neural
- humoral
describe the action of hormonal stimulation of hormone release?
hypothalamus stimulates anterior pituitary which in turn stimulates thyroid gland, adrenal cortex, gonads which release hormones
describe the action of neural stimulation of hormone release?
this is stimulation from nerve fibres
CNS(spinal cord) acts through SNS fibres on the adrenal medulla which secretes CATECHOLAMINES through blood capillaries
describe the action of humoral stimulation of hormone release?
stimulation by detection of levels of substances in blood eg. ions
eg. low Ca2+ in capillaries stimulates release of PTH from parathyroid gland
define “up-regulation”:
target cells form more receptors in response to the hormone
define “down-regulation”:
target cells lose receptors in response to hormone
define permissiveness:
when a hormone must be present to permit another hormones effect
define synergism:
combination of hormones produces an effect greater than the sum of their separate effects
define antagonism:
a hormone reduces the effectiveness of another hormone
what is a hormones half life?
the length of time taken for the hormone concentration to drop by half
can range from seconds to days
percentage of endo/exocrine glands in the pancreas?
98% exocrine
2% endocrine
where does the release of insulin and glucagon occur?
at the islands of langaham
what are the 2 types of endocrine dysfunction?
hyper + hypo secretion
primary = abnormality within the gland secondary = gland is normal, but too little/much stimulation
what are the 3 main hormone types?
- peptide: derived from chains of AA
- amines: derived from AAs tyrosine and tryptophan
- steriods: derived from cholesterol
what is the most common type of hormone?
peptide!
steps in synthesis and release of peptide hormones?
- synthesised at preprohormone in the RER
- can be modified to prohormone in the golgi apparatus
- released into extracellular space via secretory vesicles
how do pepide hormones influence a cell?
peptide hormones cannot diffuse across cell membranes, so second messenger cascade systems are needed
- cascade leads to signal amplification, rapid effects ..HOW?
receptor-ligand complex activates an amplifier enzyme resulting in a single signal molecule turning into many second messenger molecules
name the Amine hormones and from which AAs they are derived from:
Catecholamines FROM tyrosine
Thyroid hormones FROM tyrosine
Melatonin FROM tryptophan
what is the difference between catecholamines and thyroid hormones?
C = tyrosine derivative TH = iodinated tyrosine derivative C = hydrophilic TH = hydrophobic C = cell surface recept TH = intracellular receptors C = activates 2nd messen TH = activates genes C = few secs half life TH = few days for half life
what are steroid hormones derived from?
cholesterol (lipophilic)
how are steroids transported?
needs to be bound to carrier proteins
where are receptors for steroid hormones?
in the cytoplasm or nucleus
how do steroid hormones effect singular cells?
effects target cell by activating target genes for protein synthesis
why do membrane receptors usually elicit a faster response than intracellular receptors?
because receptors in cytoplasm and nucleus often cause transcription which is a slower process
what tissues make up the 2 sections of the pituitary gland?
anterior = glandular epithelial tissue posterior = nervous tissue
how are neurohormones made?
via neurohypophysis
made and packaged in cell body of neurons in hypothalamus that transport neurohormones in vesicles directly to posterior pituitary where they are stored in hypothalamic neuron terminals
what does the posterior pituitary do? which 2 hormones does it release?
it does NOT synthesise hormones, but stores the hormones formed in hypothalamic neurons
secretes hormones directly into the blood
Releases: AntiDiuretic Hormone, Oxytocin
what stimulates release of AntiDiuretic Hormone from posterior pituitary?
ADH produced by neurosecretory cells in supraoptic and paraventricular nucleus
- increase in osmolarity
- decrease in blood pressure
- increase stressors(adrenergic)
what converts cholesterol into steroid hormone?
enzymes in mitochondria and endoplasmic reticulum of tissues
what is ADH effect on blood and renal vessel?
increase of vasoconstriction
- works to retain fluid
what is ADH effect on CNS?
increase in thirst
what is ADH effect on kidney?
increases H2O reabsorption
what is ADH effect on the anterior pituitary gland?
increases secretion of AdrenoCorticoTrophic Hormone (ACTH)
which LEADS to
-> increase aldosterone secretion and the
-> increase conservation of Na+ and H2O
what stimulates contraction of uterine smooth muscle during childbirth:
- decreased levels of progesterone(at end of pregnancy)
- cervical stretch receptors
this is a positive feedback system
how do hypophysiotrophic hormones get to the ANTERIOR pituitary?
synthesised in neurons in hypothal
uptake into special blood capillaries that go direct to anterior pituitary via Hypothalamic-Hypophyseal portal system
what are the 2 types of hypophysiotrophic hormones?
- releasing hormones (stimulates release of…)
2. inhibiting hormones (suppresses release of…)
what are the endocrine cells of the anterior pituitary controlled by?
hypophysiotrophic hormones
endocrine cells secrete anterior pituitary hormones into systemic blood
**NOTE endocrine cells = anterior pituitary hormones
hypothalamic-hypophyseal portal system = hypophysiotrophic hormones
what type of hormones are hypophysiotrophic hormones?
peptide neurohormones
what do stressors trigger in the endocrine system?
both internal and external stressors trigger the release of cortisol via 2 hormonal intermediates: CRH(from brain to anterior pituitary), ACTH(anterior pituitary to adrenal cortex)
these hormonal intermediates are self regulated via negative feedback
state steps of stress release of hormones:
BRAIN 1. CRH ANTERIOR PITUITARY 2. ACTH ADRENAL CORTEX 3. cortisol TARGET CELL ...=> response!
what are the 5 hormones of the anterior pituitary?
- TSH Thyroid Stimulating Hormone
- ACTH
- Prolactin
- LH & FSH
- Growth Hormone
what does Thyroid Stimulating Hormone TSH do?
it has a positive influence on thyroid gland stimulating release of T3 and T4
-> Metabolic Rate
what does ACTH do?
influences Adrenal Cortex
stimulates release of Cortisol
-> Metabolic rate, stress response
what does Prolactin do?
influences mammary glands
stimulates breast growth and milk secretion
what does LH and FSH do?
both influence the Gonads(MALE = testes FEMALE = ovaries)
LH: sex hormone secretion
FSH: gamete production
what sex hormones are produced in males and females?
females = oestrogen & progesterone males = testosterone
what are gamete?
person creating stuff
female = ova
male = sperm
what does Growth Hormone do?
influences liver(+) stimulates release of somatomedins -> bone & soft tissue = growth
also influences other tissues(both + and -)
what factors influence growth:
- nutrition
- genetics
- free from stress and disease
- growth influencing hormone
what does the growth hormone act via?
somatomedins
- these are produced in the liver and at the target sites of bone and muscle
what is growth hormone regulated by?
antagonistic GHRH and GHIH (somatostatin)
what is the overall effect of growth hormone?
- uses up fat stores
- promotes protein synthesis
are is the different between somatotropin, somatostatin, somatomedins:
somatotropin = growth hormone somatostatin = growth hormone inhibiting hormone somatomedins = insulin-like growth factors (IGF)
what are IGFs?
Insulin like Growth Factors = peptide hormone
produced in the liver
encourage cell division
2 types: IGF-1 - effects most cells, inhibits apoptosis
IGF-2 - growth promotion during gestation
describe the release pattern of growth hormone
it is release in bursts due to the firing pattern of neurons
-> during sleep growth hormone fires more
what increases amplitude of bursts to growth hormone, thus increasing release rate?
- exercise
- stress
- hypoglycemia
- fasting (IGF-1 is low)
- circadian rhythm …anything that requires use of fat stores basically
what effects does the growth hormone have on growth?
- hyperplasia (increase NUMBER of cells)
- hypertrophy (increase SIZE of cells)
- increase protein synthesis
- increase bone growth
what effect does growth hormone have on metabolism?
- increase fat breakdown
- increase glucose output from liver
- decrease insulin sensitivity in muscle => decrease glucose uptake by muscle => instead muscles use free fatty acids resulting in increased blood glucose
what happens with the hypersecretion of growth hormone? give an example of the cause:
eg. tumour of the anterior pituitary
functions of vasopressin:
- produced in hypothalamus
- increases kidney reabsorption of water
- potent arteriolar vasoconstrictor
- released when osmolarity of the plasma increases
what hormone is released from hypothalamus:
CRH
what hormone is primarily regulated by the anterior pituitary?
cortisol
what does the anterior pituitary primarily secrete?
trophic hormones
how does growth hormone exert its effects on bone?
via somatomedin release
excessive growth hormone secretion in adults leads to?
acromegaly
- disproportionate growth resulting in thickened bones and coarse features
what does LH stimulate?
formation of the corpus luteum
T OR F
noradrenaline is released from sympathetic nerve terminals, whereas adrenaline is the most abundant secretory product of adrenal medulla
true
what are Catecholamines important for?
maintenance of blood pressure
what will a student experiencing psychological and emotional stress secrete?
CRH (from hypothal)
ACTH
cortisol
and may experience greater risk of infection due to immune system suppression
what does increased levels of ACTH lead to?
increased plasma cortisol
primary function of ACTH is to?
stimulate cortisol secretion from adrenal cortex
describe layers of adrenal gland from outer most to inner most:
connective tissue capsule glomerulosa fasciculata reticularis medulla
different levels of the adrenal glands produce different things: Glomerulosa: Fasciculata: Reticularis: Medulla:
Glomerulosa = mineralocorticoids Fasciculata = glucocorticoids Reticularis = glucocorticoids and androgens Medulla = catecholamines
how does movement of thyroid hormone from follicular cells into the circulation occur?
through exocytosis
where does T3 come from?
- use percentages
10% = secreted directly from thyroid 90% = obtained from conversion of T4 in tissues(deiodinase enzyme)
what is a goiter?
an enlarged thyroid hormone
may occur with hyper or hypothyroidism
what is associated with hypothyroidism?
- poor resistance to cold
- dry coarse hair
- weight gain
- slow speech, poor memory
what disease is associated with bulging eyes?
Grave’s disease
basic cause of Conn’s disease?
inappropriately high aldosterone
basic cause of Cushing’s disease?
Hyeradrenalism…Excess cortisol
what are 3 hormonal factors that influence Ca2+ metabolism?
parathyroid hormone (PTH)
calcitonin
vit D
what secretes the hormone causing bone resorption?
parathyroid
what secretes the hormone causing calcium deposition?
thyroid
what is the most important hormone in control of calcium metabolism?
PTH
how does vit D increase Ca2+ absorption?
- increasing expression of Ca channels on apical membrane
- increasing expression of calbindin which ferries Ca across cell
- increasing expression of Ca-ATPase pumps on the basolateral membrane
what happens when plasma calcium is low?
- positive stimulus on parathyroid glands
- increase PTH
- increase plasma Ca2+
what happens when plasma calcium is high?
- positive stimulus on thyroid C cells
- increase in calcitonin
- decrease in plasma Ca2+
when you think parathyroid hormone…
CALCIUM regulation
PTH
what can hypothyroidism be due to?
iodine deficiency
what can hyperthyroidism be due to?
Grave’s disease
what hormones do Gonadotropins refer to?
LH
FSH
produced by GONADOTROPHS in the anterior pituitary
what do gonadotrophs do in males?
FSH stimulates sperm production in testes
LH stimulates testosterone secretion by leydig cells
what stimulates gonadotrophic hormone release from anterior pituitary?
GnRH
what do gonadotrophic hormones do in females?
FSH promotes follicular growth, stimulates follicular growth
LH surge stimulates ovulation(when the egg thing bursts out of shell thing) and maintains development of corpus luteum and estrogen + progesterone secretion
function of chondrocytes?
divide in bone to add to LENGTH and produce cartilage
function of osteoblasts?
lay down bone on top of cartilage
briefly describe menstruation phases:
- early to mid-follicular(low estrogen, negative effect on GnRH)
- late follicular and ovulation(high estrogen, increases LH release, FSH suppressed by inhibin)
- early to mid-luteal(Decrease in FSH & LH: high estrogen/progesterone/inhibin = corpus luteum)
- late luteal(Increase FSH(stimulating new follicules) & LH(corpus luteum dies => decrease in estrogen and progesterone)
function of prolactin?
produced by lactotrophs
release determined by hypothalamic hormones (PIH)
stimulates lactation
what causes release of hormones from adrenal cortex?
sympathetic stimulation
- acetylcoline
“fight” or “flight” response
main form, major function and region released of catecholamines:
adrenaline
resist stress - fight or flight
medulla
main form, major function and region released of androgens:
DHEA - DiHydroEpiAndosterone
‘masculizing’ hormone convert to testosterone in the testes
zona reticularis
main form, major function and region released of Glucocorticoids:
cortisol
helps resist stress, role in metabolism of macro
zona fasciculata
main form, major function and region released of mineralo-corticoids:
aldosterone
electrolyte balence and blood pressure
zona glomerulosa
what does zona reticularis release?
sex hormones
what does medulla secrete?
catecholamines - adrenaline
what does zona fasciculata secrete?
glucocorticoids - cortisol
what does zona glomerulosa secrete?
aldosterone -
PNS -> nicotinic receptors -> muscarinic receptors
SNS -> nicotinic -> beta and alpha
what is acute stress response?
- stimulation of SNS
- activation of release of catecholamine
long term stress response?
- cortisol release from zona fasciculata
describe how cortisol release is governed?
secretion of cortisol governed by ACTH which is itself governed by CRH(from hypothalamus)
stress feedback circuit?
- stress picked up by brain
- CRH
- ACTH
- Cortisol - released from adrenal cortex(zona fasciculata)
- effects
primary role of cortisol?
- increase blood glucose at expense of fats and protein
- stimulates liver gluconeogenesis(new glucose made from protein)
- inhibits glucose uptake EXCEPT brain
- inhibits bone formation
- anti-inflammatory and immunosuppressive
how does a cell respond to steroid hormone?
steroid hormone enters cell and binds to hormone-receptor complex, which moves to nucleus and binds to complementary hormone-response element in DNA
=> initiating gene transcription => synthesis of new proteins
what is the only sex hormone produced in adrenal gland?
DHEA
DeHydroEpiAndrosterone
what does ACTH act primarily on?
zona fasciculata and reticularis to simulate release of cortisol and androgens
describe effects of hypersecretion of cortisol:
Cushing’s syndrome
adrenal cortext is over stimulated meaning more cortisol secretion leading to increased circulating glucose(by inhibiting uptake) so body has store it somewhere, redirected to the face
does not inhibit it in the brain
describe the absorptive state:
absorptive state is when you are feed and nutrients are high insulin is released to: - increase glucose oxidation - increase glycogen synthesis - increase protein and fat synthesis
describe the postabsorptive state:
fasted state where nutrients are required to come out storage
glucagon works to:
- increase glycogenolysis(glycogen -> glucose)
- increase gluconeogenesis(proteins -> glucose)
- increase ketogenesis
- increase protein breakdown
where is insulin release?
beta cells in pancreas
reduces blood sugar levels
what do alpha cells in pancreas release?
glucagon
works to increase blood glucose, with primary target cells being in the liver
what do delta cells in the pancreas secrete?
somatostatin
which decreases gastric secretion and inhibits digestion of nutrients
what cells are sensitive to glucose in blood?
beta cells of islets of langerhaus in pancreas
describe how glucose stimulates insulin secretion:
- enters cell through GLUT-2 transporter
- increase in ATP/ADP ratio closes K+ channels(ball on string)
- causing depolarisation, Ca2+ channels respond
- Ca2+ enters causing exocytotic insulin vesicles to be released
(insulin is made in endoplasmic reticulum pre-proinsulin -> proinsulin)
what are the glucose transporters?
GLUT-1,2,3 and 4
only 4 is regulated by insulin
insulin promotes glucose entry into cells…how?
- insulin binds to receptor
- signal transduction cascade
- exocytosis of vesicles with GLUT-4 receptors
- glucose enters cell
in the fed state what is metabolism under the influence of?
insulin
in the fasted state what is metabolism under the influence of?
glucagon
where is glycogen stored?
in hepatocytes in the liver, which stain pink
type 1 diabetes?
destruction of beta cells so no insulin secreted
type 2 diabetes?
gradual development of insulin resistance
thyroid hormone functions?
- acts on almost every cell in the body
- increases basal metabolic rate
- rapid protein synthesis
- enhances effect of growth hormone
- regulates body temp
what cells secrete in thyroid gland?
c cells = calcitonin
follicular cells = thyroid hormone TH
where is TH stored?
within colloid, in the middle of follicular cells(extracellular)
what are the types of TH?
T3 = 3 iodine T4 = 4 iodine
describe the steps involved in creation of thyroid hormone:
- Rough ER: synthesises Thyroglobulin -> exocytosed to lumen
- iodine pumped into cell via I-, Na+ symporter
- iodine is oxidised by ThyroPerOxidase(TPO) on the luminal membr..
- iodine “meets up with” thyroglobulin and is attached to tyrosine = DIT & MIT
- iodinated tyroines couple to form T3 and T4
- thyroglobulin is exocytosed and combined with a lysosome
- enzymes of lysosomes cleave T3 and T4 from thyroglobulin and exit cell moving to peripheral tissues
how does the body obtain iodine?
it must be obtained by the diet
it is reduced from I to I- and absorbed by the small intestine
it is then transported through the blood stream and enters thyroid cells via the I-/Na+ symporter
iodine is then oxidised and attached to tyrosine and coupled to form T3 & T4 thyroid horome
what is the carrier protein of T3 and T4 in blood? and how do they enter target cell?
Thyrosine binding globulin
enter target cell via diffusion
describe the regulation of thyroid hormone release circuit:
Hypothalamus: TRH (Thyrotropin-Releasing Hormone) travels to anterior pituitary
-> triggers release of Thyroid-Stimulating Hormone
-> stimulates Thyroid gland to release T4 and T3
NEGATIVE feedback maintains steady supply of thyroid hormones
how/where is thyroid hormone stored?
stored in thyroglobin form
can have enough stored to supply for months
HOW does TSH stimulate thyroid gland to release T3 & 4?
TSH binds to TSH receptors -> cAMP which stimulates transcription
effects:
- iodine uptake
- iodination and coupling
- thyroglobulin production
- increase T3 & 4 production
what is hypothyroidism due to?
iodine deficiency
which leads to no thyroid hormone to create negative feedback loop
