Unit 11 - Hypothalamus

Question 1

hypothalamic nuclei

Answer 1

part of diencephalon

under corpus callosum

Question 2

role of hypothalamus

Answer 2

integrates autonomic responses and endocrine function with behaviour

• controls BP and electrolyte composition - drinking, salt, appetite, blood osmolality, vasomotor tone
• regulates temp - metabolic thermogenesis, behaviour
• controls energy/metabolism - feeding, digestion, metabolic rate
• behavioural expression - reproduction, emotional expression, circadian rhythm
• controls stress response - vasomotor tone, secretion of stress hormones

compares sensory info with biological set points

Question 3

thermoregulation

how does our temp change

Answer 3

heat production - heat loss

temp set point

37°C - circadian rhythm 0.5-0.7°C change

Question 4

how does temp measurement differ in various parts of the body

Answer 4

rectal > head > trunk > hand > feet

exercise increases temp up to 40°C

Question 5

where are thermoreceptors found

Answer 5

skin

deep tissues

spinal cord

extrahypothalamic regions

hypothalamus (20%)

Question 6

types of thermoreceptors

Answer 6

Aδ and C fibres

separate warm and cold receptors (TPRV, Transient Potential voltage, receptors)

cold (Aδ) > warm (C)

activated at temperatures that are not necessarily painful

>42°C or <17°C is painful

lower threshold

Question 7

cold fibres

Answer 7

Aδ

Question 8

warm fibres

Answer 8

C

Question 9

peripheral thermoreceptors

Answer 9

anterolateral system to somatosensory cortex - SPINOTHALAMIC TRACT

also projections to thermoregulatory centre in hypothalamus

Question 10

where are central thermoreceptors located on

Answer 10

GABA neurons

Question 11

anterolateral system =

Answer 11

spinothalamic tract

Question 12

increased heat production causes activation of

what does this cause

Answer 12

preoptic area in anterior hypothalamus

promotes heat loss

vasodilation, sweating, increased respiration

anorexia

apathy

Question 13

lesion of preoptic area in anterior hypothalamus

Answer 13

chronic hypERthermia - inability to lose heat

Question 14

increased heat loss activates

Answer 14

neurons in posterior hypothalamus

promotes heat generation

shivering, hunger, voluntary activity, vasoconstriction (goose bumps), curling

Question 15

lesion of posterior hypothalamus

Answer 15

no effects at room temp

in cold, no ability to conserve heat

Question 16

overview of hypothalamic control of temperature

Answer 16

Under normal circumstances the anterior hypothalamus inhibits posterior hypothalamus

Inhibition prevented with lowering in body temp

Question 17

thermoregulation

Answer 17

Question 18

decrease in temp

Answer 18

Question 19

increase in temp

Answer 19

Question 20

temp regulation in an infant

Answer 20

neonate has very narrow temp zone

very little capacity for heat conservation

brown fat has a high rate of metabolism, thermogenic function - High thermogenic value so produces a lot of heat but can also get used up

BY 3 MONTHS

metabolic rate increases

rise in ratio of mass to SA

increase in body fat

maturation of shiver response

3 month old has less capacity to dissipate heat than neonate

head - 40% of heat production, 85% of heat loss

if head is covered or overwrapped, CNS temp can increase dangerously

resp affected - SIDS

Question 21

fever and temp

Answer 21

pyrogens/toxins → cytokines → OVLT → preoptic area

IL-1B, IL-6, IFNβ, IFNγ, TNFα: receptors in OVLT

causes local release of PGs in preoptic area which alter set point

heat production mechanisms ⇒ fever

beneficial in certain instances e.g. leprosy, viral infections

antipyretic effect of COX2 inhibitors (COX makes PGs) e.g. aspirin

Question 22

Answer 22

C

Question 23

factors that stimulate thirst

Answer 23

dryness of pharyngeal mucus membrane

gastric/oropharyngeal signals

psychological and social factors

hyperosmolality

reduced blood volume

Question 24

hypothalamic mechanisms involved in thirst

Answer 24

organum vasculosum of the lamina terminalis (OVLT)/medial preoptic hypothalamus

plasma osmolality, ECF volume

Question 25

Medial preoptic nucleus of hypothalamus and OVLT

Answer 25

Close anatomically Often grouped together GABAergic and glutaminergic neurons - increases or decreases thirst response

Question 26

plasma osmolality - receptors where do they project to what do they do

Answer 26

osmoreceptors in OVLT detect change \<1% Na2+ conc (monitoring blood flow over them) projections to supra-optic and paraventricular nuclei to ***_produce_*** ADH released by pituitary increases thirst response and promotes fluid intake also, increases water permeability in DCT of kidney - AQP-2, which allow water to be reabsorbed ⇒ reduction in osmolality

Question 27

reduced or absent secretion of ADH

Answer 27

diabetes insipidus

Question 28

where is ADH produced

Answer 28

supra optic and paraventricular nuclei

Question 29

what does ADH also act as

Answer 29

NT - emotional response to thirst - prefrontal cortex

Question 30

thirst and fluid balance (ECF vol) - where and how is pressure monitored

Answer 30

BARORECEPTORS aortic arch and carotid sinus decrease ECF vol (\>10%) → low BP ADH release Mechanoreceptor - sense stretch depending on EC fluid vol - if we lose fluid, we decrease stretch and neural signal sent to hypothalamus - goes to OVLT and PV nucleus to produce ADH

Question 31

RAA system

Answer 31

Renin produced in response to decrease in EC fluid vol angiotensin II receptors in subfornical (SFO) organ and OVLT signal sent to preoptic, supra-optic and PV nuclei ADH release

Question 32

overview of thirst and fluid balance

Answer 32

reduction must be greater than 10%

Question 33

Answer 33

C

Question 34

lateral nuclei of hypothalamus = destruction/stimulation rate of activity

Answer 34

feeding centre chronically active - if there is not inhibitory control, we would never be hungry destruction ⇒ lack of desire for food, emaciation stimulation ⇒ increased appetite

Question 35

ventromedial nuclei = function destruction/stimulation

Answer 35

sense of fullness inhibits feeding centre (LN of hypo.) destruction ⇒ obesity due to inability to depress feeding behaviour stimulation ⇒ reduced appetite, aphagia

Question 36

apart from VM nuclei and lateral nuclei of hypothalamus, what other nuclei play a part in hunger and feeding

Answer 36

Paraventricular dorsomedial arcuate

Question 37

injection of substances to PV nuclei

Answer 37

leads to selective food intake NA - CHO e.g. chocolate Galanin - fat opiates - protein

Question 38

NA ⇒

Answer 38

CHO

Question 39

galanin ⇒

Answer 39

fat

Question 40

opiates ⇒

Answer 40

protein

Question 41

overview of hypothalamic control of feeding

Answer 41

Question 42

short term control of food intake - 4 methods

Answer 42

1. GI distension 2. GI hormonal factors 3. Ghrelin - GI hormone 4. Insulin

Question 43

GI distension

Answer 43

stretch inhibitory receptors activated and inhibit feeding centres + stimulate satiety centre

Question 44

GI hormonal factors

Answer 44

CCK - release due to fat entering duodenum and inhibits feeding centre - travel In blood - directly inhibit feeding centre and activate satiety centre Peptide YY - released by G tract 1-2hrs post feeding, inhibits feeding centre - longer effect - not hungry straight after a meal Glucagon Like Peptide and Insulin - appetite suppressant

Question 45

ghrelin

Answer 45

mainly released by stomach, levels rise in fasting and decrease after eating - stimulate feeding behaviour most GI hormones inhibit feeding centre

Question 46

overview of influences on hunger/feeding

Answer 46

Question 47

long term control of food intake what is produced what is its effect

Answer 47

adipose tissue produces leptin - decreases food intake, increases energy use SUPPRESSES APPETITE release appetite-suppressing neuropeptides α-melanocyte stimulating hormone (α-MSH) cocaine and amphetamine related transcript (CART) INHIBITS STIMULATION OF FOOD INTAKE inhibits release of appetite-stimulating neuropeptides neuropeptide Y Agouti-related peptide

Question 48

other effects of leptin

Answer 48

increased CRH (decreases food intake) increases SNS (neural projections from hypothalamus to vasomotor areas - increase in metabolic rate and energy expenditure) decreased insulin secretion by pancreatic β cells, which decreases energy stores overall acts to signal that enough energy stored and intake of food is no longer required

Question 49

leptin deficiency

Answer 49

obesity and hyperphagia - observed in humans with mutations in genes encoding leptin relative deficiency of leptin may predict future weight gain

Question 50

Answer 50

D