PSL300 > 27 > Flashcards

27 Flashcards

(48 cards)

Study These Flashcards
1
Q

Where are the hypothalamus and pituitary located?

A

in the diencephalon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the function of the hypothalamus?

A
  • contains control centres for many biological systems
  • it is crucial to the control of feeding, plasma osmolality, body temperature, and sexual and stress responses
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what does hypothalamic control always involve?

A

negative feedback: processing chemical and neural signals from the body to monitor how well things are working and to detect disturbances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what two impacts can hypothalamic control have?

A
  • some control systems maintain homeostasis
  • other control systems vary things through time (eg circadian rhythms)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

define homeostasis

A

keeping some aspect of the internal environment (eg osmolality) roughly constant despite disturbances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

in what ways does the hypothalamus exert its influence

A

neurally and hormonally

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

describe how the hypothalamus exerts its influence neurally

A

nuclei within the hypothalamus send neural signals to each other and to other parts of the brain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

describe two ways in which the hypothalamus exerts its influence hormonally

A
  1. synthesises hormones which it transports down axons to the posterior lobe of the pituitary, where they are released into the blood
  2. synthesises releasing hormones that travel through capillaries (the hypophyseal portal system) to the anterior pituitary, where they trigger the release into the blood of other hormones, made in the pituitary
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

describe how the anterior pituitary is regulated

A
  • The anterior pituitary is tightly regulated by parvocellular neurosecretory neurons in the hypothalamus, mainly in the arcuate nucleus, paraventricular nucleus (parvocellular part), and preoptic area.
  • These neurons send short axons to the median eminence, where they release hypophysiotropic hormones (releasing/inhibiting hormones) into the primary capillary plexus supplied by the superior hypophyseal artery.
  • Blood from the primary plexus drains into the hypophyseal portal veins, which deliver these hormones directly to the secondary capillary plexus in the anterior pituitary.
  • The secondary plexus is surrounded by anterior pituitary endocrine cells, which respond by releasing their own hormones into systemic circulation.
  • This two-capillary, portal system allows for highly localised control using very small amounts of hypothalamic releasing factors, preventing dilution in the general circulation.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

describe how the posterior pituitary is regulated

A
  • The posterior pituitary is not glandular; it is a direct neural extension of the hypothalamus, composed mainly of axons, terminals, and glial-like cells called pituicytes.
  • It contains the axon terminals of magnocellular neurosecretory neurons from the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus.
  • These axons travel through the infundibulum, forming the hypothalamo-hypophyseal tract, and terminate in a network of capillaries supplied primarily by the inferior hypophyseal artery.
  • Along these axons are Herring bodies—swellings that store neurosecretory vesicles containing oxytocin or vasopressin (ADH).
  • When these hypothalamic neurons fire action potentials, the vesicles in the terminals undergo exocytosis, releasing hormones directly into systemic circulation.
  • This arrangement allows for rapid, direct neural control, making the system fast and efficient.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

how do we know that feeding is tightly controlled for caloric intake?

A

mice fed solutions with different concentrations of nutrients adjust their eating to jeep their caloric intake consistent (eg if the nutrient concentration is halved, they eat twice as much)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

how do we know that the hypothalamus is crucial to feeding control?

A

mice with lesions in the ventromedial hypothalamus (VMH) overeat and become obese; those with lesions in the lateral hypothalamus (LH) get thin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are the VMH and LH controlled by?

A

two groups of neurons in the arcuate nucleus of the hypothalamus: arcuate NPY/AgRP cells drive feeding, while arcuate POMC neurons inhibit feeding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

arcuate nucleus (ARC) - function

A

first order sensor of hunger/satiety signals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

NPY/AgRP neurons - function

A

drives hunger (orexigenic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

POMC neurons - function

A

promotes satiety (anorexigenic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Ventromedial Hypothalamus (VMH) - function

A

satiety center

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

lateral Hypothalamus (LH) - function

A

feeding/motivation centre

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

fasting vs postprandial state

A

fasting state: arcuate NPY neurons encourage feeding
postprandial state: arcuate POMC neurons inhibit feeding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

describe Arcuate-NPY neurons and what they do

Study These Flashcards
A

neurons in the arcuate nucleus of the hypothalamus which release neuropeptide Y (NPY), GABA, and (in the case of some cells) also agouti-related peptide (AgRP)

21
Q

where does Arc-NPY project to?

Study These Flashcards
A
  • signals from Arc-NPY cells inhibit neurons in the PVN of the hypothalamus, a satiety/anorexigenic centre
  • signals from Arc-NPY cells excite neurons in the lateral hypothalamus (LH), a feeding centre
22
Q

what is a later effect of Arc-NPY inhibiting PVN action?

Study These Flashcards
A
  • high activity in the PVN would excite the sympathetic system, but Arc-NPY inhibits PVN, so the sympathetic system receives very little excitation from there
  • thus, Arc-NPY acts via PVN to decrease sympathetic activity
23
Q

what is the result of LH being excited?

Study These Flashcards
A
  • protections from LH release orexin at their synapses, inhibiting PVN and stimulating feeding behaviour
  • the mechanisms by which orexin affects feeding are not understood in any detail
24
Q

what is the result of reduced sympathetic action due to Arc-NPY?

Study These Flashcards
A

high sympathetic activity would inhibit feeding, but Arc-NPY inhibits those sympathetic actions; thus, Arc-NPY disinhibits feeding behaviour

25
describe Arc-POMC neurons and what they do
- a group of neurons in the arcuate nucleus containing pro-opiomelanocortin (POMC) - they cleave POMC to make an α-melanocyte stimulating hormone (α-MSH), which they release at their synapses
26
where do Arc-POMC neurons project to?
α-MSH released from the synapses of POMC cells: - excites neurons in the PVN - excites neurons in the ventromedial hypothalamus (VMH) - inhibits neurons in the dorsomedial hypothalamus (DMH)
27
what is a later effect of Arc-NPY releasing α-MSH?
- PVN and VMH excite the sympathetic nervous system - activity in DMH inhibits the sympathetic system, but Arc-POMC inhibits DMH, so the net result is that sympathetic activity is disinhibited (increased)
28
what is the effect of sympathetic activity on feeding?
sympathetic activity inhibits feeding
29
describe how feeding is controlled
- works based on negative feedback - hypothalamic feeding and anorexigenic centres receive feedback
30
what is Arc-POMC excited/inhibited by? why is this important
excited by sympathetic activity -> positive feedback loop helps to amplify system inhibited by Arc-NPY -> reciprocal inhibition ensures the two systems work in balance
31
how do we know that in feeding, the set point of the feeding system defines a target body weight?
- rats with VMH lesions don't get fatter and fatter for ever, but level off at a new set point above their original weight - rats with LH lesions level off at a new, low set point
32
how does the hypothalamus infer body weight?
from leptin levels
33
define leptin
a protein released into the blood mainly by fat cells
34
how do leptin levels change with fat?
the more fat you have, the more circulating leptin
35
what is the target of leptin?
cells in the body that have membrane receptors for leptin, including especially cells in the feeding and anorexigenic centres of the hypothalamus
36
what is a potential impact of mutations in the genes that produce leptin or the leptin receptor?
cause obesity in mice and humans due to increased feeding behaviour
37
describe the impact of leptin on the Arc-NPY pathway
- directly inhibits Arc-NPY - directly inhibits LH - directly excites PVN - thus, PVN boosts sympathetic activity even more, causing inhibition of feeding
38
describe the impact of leptin on the Arc-POMC pathway
- directly excites Arc-POMC - directly excites PVN - directly excites VMH - directly inhibits DMH - thus, PVN boosts sympathetic activity even more, causing inhibition of feeding
39
does your brain know when to end a meal thanks to leptin?
no, because it is too slow: you don't lay on much new fat during a single meal. the control system needs faster sources of feedback
40
how does your brain know when to end a meal?
- blood glucose: it increases as you eat, and its rising level excites Arc-POMC and inhibits LH, inhibiting further feeding - sensors in the walls of the stomach and intestines that measure nutrients and stretch, and respond by releasing hormones that act on the hypothalamus
41
what is the role of gut hormones in the postprandial state?
inhibit feeding
42
describe the gut hormones released in the postprandial state
- sensors in the wall of the small intestine detect stretch and sugar and protein, leading to the release of cholecystokinin (CKK), peptide YY (PYY), and glucagon-like peptide 1 (GLP-1) - these hormones act via the blood to excited Arc-POMC, PVN, and VMH and to inhibit DMH
43
what is the role of ghrelin in the fasting state?
encourages feeding
44
describe the action of ghrelin
- the hunger hormone - released into the blood by cells in the stomach wall when the stomach is empty; stretching the stomach stops ghrelin release - ghrelin acts directly on Arc-NPY and LH (exciting them) and on PVN (inhibiting it)
45
what is the issue with many drug treatments for obesity?
many drugs suppress appetite, but they are dangerous, eg amphetamines and fenfluramine (an anti-obesity drug withdrawn in 1997 because of cardiovascular side effects)
46
leptin as a drug for anti obesity
rarely helps because fewer than 1% of humans with morbid obesity are leptin-deficient
47
rimonabant
- blocks CB1 endocannabinoid receptors - can lead to moderate weight loss but causes nausea, major depression, and suicide
48
CCK, PYY and GLP-1 agonists
- CCK and PYY agonists have been tested without much success - a GLP-1 agonist called liraglutide may be better
PSL300
flashcards
Decks in class (55)
# Cards
Brainscape helps you reach your goals faster, through stronger study habits.
© 2026 Bold Learning Solutions. Terms and Conditions