Module 5: Endocrinology

Question 1

what are the different types of chemical signalling?

Answer 1

> endocrine signalling
- secreted molecules (hormones) diffuse into the blood stream, circulate, and trigger responses in target cells anywhere in the body.
synaptic signalling
- secreted molecules (neurotransmitters) diffuse across a synapse, triggering response in target cell tissue
neuroendocrine signalling
- secreted molecules (neurohormones) diffuse into the blood stream, circulate, and trigger responses in target cells anywhere in the body.
paracrine signalling
- secreted molecules (local regulators) diffuse locally through the ECF, triggering a response in neighbouring cells
autocrine signalling
- secreted molecules (local regulators) diffuse locally, triggering a response in the cell which secreted them.

Question 2

describe regulators and conformers

Answer 2

> regulators
- regulate their internal environment despite external fluctuation
conformers
- allow internal condition to conform to the external environment

Question 3

what are types of hormones and give an example

Answer 3

WATER-SOLUBLE:
> Polypeptides
- insulin
> amines
- adrenaline
LIPID-SOLUBLE
> steroids
- cortisol
> amines
- thyroxine

Question 4

how does reception location vary with hormone type?

Answer 4

> water soluble hormones
- bind to signal receptor proteins on the surface of target cell.
- this interaction triggers events that lead to either a change in cytoplasmic function, or change in gene transcription in the nucleus.
Lipid-soluble hormones
- penetrates the target cell’s plasma membrane and binds to an intracellular signal receptor, either in the cytoplasm or in the nucleus
- the hormone receptor complex acts as a transcription factor, typically activating gene expression.

Question 5

what is the signal pathway for adrenaline (water -soluble) ?

Answer 5

> water-soluble, so surface receptor
g-protein coupled receptor
binding of adrenaline triggers cascade of events that produce cAMP as a second messenger
PKA inhibits glycogen synthesis and promotes glycogen breakdown
liver releases glucose into bloodstream.

Question 6

what is the signal transduction pathway of oestradiol (lipid-soluble) ?

Answer 6

> lipid-soluble, intracellular receptor
oestradiol passes through plasma membrane
binds to oestradiol receptor
forms hormone-receptor complex
travels into nucleus and binds to DNA
interacts with specific DNA-binding protein or response elements to alter transcription
response

Question 7

how can one hormone have multiple responses?

Answer 7

> By having different receptors or different intracellular proteins (different cell types)
KNOW DIAGRAM

Question 8

how do the nervous and endocrine systems interact?

Answer 8

> both long distance regulators
signals from nervous system initiate and regulate endocrine signals
- hormone regulation of insect development
- hypothalamus and pituitary gland in vertebrates.

Question 9

describe a hormone cascade pathway

Answer 9

> stimulus - cold
sensory neuron
hypothalamus - secretes thyrotropin-releasing hormone
neurosecretory cell
hormone is transported by blood vessel
anterior pituitary - secretes TSH
goes into blood vessels
reaches endocrine cell - thyroid gland - secretes thyroid hormone
blood vessel
target cells - body tissues
response - increased cellular metabolism

Question 10

describe a negative feedback loop

Answer 10

> in the case of the thyrotropin-releasing hormone pathway
thyroid hormone itself carries out negative feedback.
thyroid blocks TSH and TRH release
negative feedback loop prevents overproduction of thyroid
the hormone cascade pathway brings about a self-limiting response to the original target cells.

Question 11

describe a positive feedback loop

Answer 11

> KNOW DIAGRAM
sensory neurons respond to stimulus
send impulse to hypothalamus/posterior pituitary
neurosecretory cell releases neurohormone
travels in blood stream to its target cells
produces response
response increases the stimulus, thus amplifying the signal pathway
example - suckling and milk production

Question 12

describe homeostasis in relation to antagonistic pairs of hormones

Answer 12

> KNOW DIAGRAM
when blood glucose rises above the normal range, release of insulin triggers uptake of glucose from the blood into body cells, decreasing the blood glucose concentration.
when blood glucose drops below the normal level, the release of glucagon promotes the release of glucose into the blood from energy stores, such as liver glycogen, increasing the blood glucose concentration.
insulin and glucagon have opposing effects.

Question 13

what is diabetes mellitus?

Answer 13

> type I diabetes mellitus (insulin-dependent)
- an autoimmune disorder in which the immune system destroys pancreatic beta cells - i.e., no insulin
type II diabetes mellitus (non-insulin- dependent)
- involves insulin deficiency or reduced response of target cells due to change in insulin receptors

Question 14

describe blood pressure homeostasis by RAAS

Answer 14

1) low blood pressure in afferent arteries in kidney causes juxtaglomeruler apparatus (JGA) to release renin
2) renin cleaves angiotensinogen released by the liver to form angiotensin I
3) angiotensin I is cleaved by Angiotensin-converting enzyme (ACE) released from the lungs, to form angiotensin II.
4) angiotensin II acts on the adrenal gland to produce aldosterone.
5) angiotensin II also constricts arterioles, increasing blood pressure.
6) aldosterone acts on the nephrons’ distal tubules and collecting duct, making them re-absorb more Na+ and water, thus increasing blood volume and pressure.

Question 15

what are the major endocrine glands?

Answer 15

>hypothalamus
> pineal gland
> pituitary gland
> thyroid gland
> parathyroid glands (behind thyroid)
> adrenal glands (atop kidneys)
> pancreas
> ovaries
> testes

Question 16

what are the organs that contain endocrine cells?

Answer 16

> thymus
> heart
> liver
> stomach
> kidneys
> small intestine

Question 17

describe the posterior pituitary and its hormones

Answer 17

> extension of they hypothalamus
hypothalamic axons that reach into the posterior pituitary secrete neurohormones synthesised in the hypothalamus.
oxytocin and ADH
these hormones travel to the post. pit to be stored in pituitary cells.
hormones released in response to nerve impulses transmitted by the hypothalamus.
oxytocin - targets mammary glands and uterine muscles
ADH - targets kidney tubules.

Question 18

how does ADH impact on fluid retention?

Answer 18

1) stimulus - increase in blood osmolarity from sweating or something
2) osmoreceptors in hypothalamus trigger release of ADH from posterior pituitary
3) ADH stimulates thirst - brings blood osmolarity back down to normal
4) ADH also acts on the collecting duct of the kidney to increase water reabsorption to further increase blood osmolarity
5) reach homeostasis again

Question 19

how does AHD affect the collecting ducts of kidneys?

Answer 19

1) ADH binds to membrane receptor
2) receptor activates cAMP second messenger system
3) PKA is catalysed
4) PKA acts on vesicles with aquaporin water channels and inserts them into the membrane lining lumen of the collecting duct.
5) aquaporin channels enhance reabsorption of water from collecting duct into interstitial fluid

Question 20

what is diabetes insipidus?

Answer 20

> mutations that prevent ADH production or inactivate ADH receptor gene, cause diabetes insipidus
similarly, mutation in aquaporin gene can also cause it
consequences: severe dehydration, solute imbalances due to increased (dilute) urine volume
not always associated with genetic changes - alcohol can inhibit ADH release, excess urine and dehydration.

Question 21

describe the anterior pituitary

Answer 21

> endocrine gland that synthesises and secretes hormones in response to signals from the hypothalamus
every anterior pituitary hormone is controlled by at least one releasing hormone from the hypothalamus
some have both inhibiting and releasing hormones controlling them.
the hypothalamic hormones are secreted near capillaries at the base of the hypothalamus.
the capillaries drain into short blood vessels, called portal vessels, which subdivide into a second capillary bed within the anterior pituitary.
the releasing and inhibiting hormones have direct access to the gland they control.

Question 22

what are the hormones secreted by the anterior pituitary?

Answer 22

TROPIC HORMONES:
> FSH and LH
- testes and ovaries
> TSH
- thyroid
> ACTH
- adrenal cortex
NONTROPIC:
> prolactin
- mammary glands
> MSH
- melanocytes
- melanin production
TROPIC AND NONTROPIC
> GH
- liver
- bones
- other tissues
- exerts diverse metabolic effects to raise blood glucose(nontropic)
- acts on liver to release insulin-like growth factors, which circulate in blood and directly stimulate bone and cartilage growth.

Question 23

what are tropic hormones?

Answer 23

> regulate the function of endocrine cells or glands with a new set of hormones

Question 24

What are nontropic hormones?

Answer 24

> hormones that target nonendocrine tissues

Question 25

describe the adrenal cortex

Answer 25

> supra-renal organs
true endocrine cells
release corticosteriods (steroid hormones)
- glucocorticoids (e.g cortisol) - raise blood glucose level - stimulated by ACTH
- mineralocorticoids (e.g aldosterone) - promote reabsorption of Na+ and excretion of K+ in kidneys - stimulated by angiotensin II

Question 26

describe the adrenal medulla

Answer 26

> cells derived from neural tissue during embryonic development
releases catecholamines (amine hormones) - stimulated by nervous system.
- adrenaline and noradrenaline - raise blood glucose level; increase metabolic activities; constrict certain blood vessels

Question 27

describe the short term response to stress in the adrenal medula + draw diagram

Answer 27

1) stressful stimuli cause the hypothalamus to activate the adrenal medulla via nerve impulses
2) adrenal medulla secretes adrenaline and noradrenaline
- act on alpha-adrenoceptors and beta- adrenoceptors in target tissues
3) effects:
- glycogen broken down to glucose; increased blood glucose
- increased blood pressure
- increased breathing rate
- increased metabolic rate
- change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity

Question 28

describe the long-term response to stress and the adrenal cortex

Answer 28

1) stressful stimuli cause the hypothalamus to activate the adrenal cortex via hormonal signals.
2) adrenal cortex secretes mineralocorticoids and glucocorticoids
3) effects of mineralocorticoids:
- retention of sodium ions and water by kidneys
- increased blood volume and blood pressure
4) effects of glucorticoids
- proteins and fats broken down and converted to glucose, leading to increased blood glucose
- partial suppression of immune system