Appetite Flashcards
What are the 3 factors control thirst
Body fluid osmolality
Blood volume is reduced
Blood pressure is reduced
What is the most potent stimulus in controlling thirst
Plasma osmolality
What % change in plasma osmolality is needed to induce a desire to drink?
2-3
What % change in blood vol or arterial pressure is needed to induce a desire to drink?
10-15
What is the other name for ADH?
Vasopressin
What does ADH act on?
Collecting duct in kidney
What happens to urine volume when ADH is low? What is this called
Vol of urine excreted is large
This is called water diuresis
What happens to urine volume when ADH is high? What is this called
Vol of urine excreted is small
This is called anti diuresis
What type of receptor are osmoreceptors?
Sensory
Where are osmoreceptors found?
In the hypothalamus in the organum vasculosum and subfornical organ
How do osmoreceptors cause ADH release?
When plasma is more concentrated cells shrink
Proportion of cation channels increases (membrane depolarises)
This sends signals to the ADH producing cells to increase ADH
This causes fluid retention and involves drinking
Where are receptors involved in short term relief of thirst found?
Mouth
Pharynx
Oesophagus
When is thirst completely satisfied?
Once plasma osmolality is decreased or blood volume or arterial pressure corrected
What cells in the renin angiotensin system detect a fall in BP?
Juxtoglomerular cells
Where are juxtoglomerular cells found?
Renal afferent arterioles
What does fall in BP stimulate from juxtoglomerular cells?
Angiotensin release
What is angiotensin also known as?
Renin
What is angiotensin converted to in the liver and how?
Angiotensin I via angiotensinogen
What is angiotensin I converted to in the lungs and how?
Angiotensin II via ACE
What are the conversion steps to go from angiotensin to angiotensin II (include enzymes and locations)
In the liver angiotensin is converted to angiotensin I via angiotensinogen
In the lungs angiotensin I is converted to angiotensin II via ACE
What are the effects of angiotensin II?
Vasoconstriction via increased sympathetic activity
Thirst
Aldosterone release from the zona glomerulosa of the adrenal cortex
Aldosterone causes water retention via sodium and chloride absorption and potassium secretion
ADH secretion
What happens in an overfed or weight augmented state?
Increased sympathetic nervous system activity
Increased energy expenditure
Reduced hunger/good intake
What happens in an underfed or weight reduced state?
Decreased sympathetic nervous system activity
Decreased energy expenditure
Increased hunger/good intake
Reduced thyroid function
What substances are appetite stimulants?
Orexigenic
What structure in the brain is important for appetite regulation?
Hypothalamus
What substances are appetite suppressants?
Anorectic
What is the arcuate nucleus and what is its role?
Brain area involved in the regulation of food intake
It has an incomplete blood brain barrier, allows access to peripheral hormones.
Integrates peripheral and central feeding signals
What does the stimulatory neuronal population involve?
NPY/Agrp
What does the inhibitory neuronal population involve?
POMC
If feeding needs to be increased what in the arcuate nucleus is involved?
NPY/Agrp neurons
If feeding needs to be decreased what in the arcuate nucleus is involved?
POMC
Where do NPY/Agrp and POMC act?
On the paraventricular nucleus
What are melanocortins a product of?
The POMC chain
What receptors in the hypothalamus when stimulated lead to reduction in appetite?
Melanocortin 4 receptors
What can POMC and MC4-R deficiency cause?
Morbid obesity
Are mutations responsible for the prevalence of obesity?
No they just help explain signalling
How does the vagus nerve feedback in terms of appetite?
It feedsback to the brainstem which then can go hypothalamus
What is adipostat?
This is a circulating hormone produced by fat
What may misregulation of the adipostat mechanism lead to?
Obesity
How does adipostat affect food intake?
Hypothalamus senses the concentration of hormone
and then alters neuropeptides to increase or decrease food intake
What makes leptin?
Adipocytes in white adipose tissue
What is leptin and what does it do?
A hormone that decreases appetite
What happens to leptin level as body weight rises?
It also rises
What are the ways by which the mechanism of action of leptin can be disrupted?
Insufficient production
Defect in receptor signalling
Decreased sensitivity to leptin
How effective is leptin as weight control drug?
Not effective
What 2 main hormones secreted by enteroendocrine cells regulate appetite?
Ghrelin and peptide YY
What 2 main hormones are involved with short term regulation of appetite?
Ghrelin and peptide YY
Where are ghrelin and peptide YY produced?
Enteroendocrine cells in the stomach, pancreas & SB
When are ghrelin levels highest? Why?
Before a meal as it helps prepare for food intake by increasing gastric motility and acid secretion
What does ghrelin stimulate and inhibit?
Stimulates NPY/Agrp neurons
Inhibits POMC neurons
What does ghrelin do to appetite?
Increases it
When and where is PYY released?
Released in the terminal ileum (TI) and colon in response to feeding (when food arrives in those areas)
What does PYY do to appetite?
Reduced it
What does PYY stimulate and inhibit?
Stimulates POMC neurons
Inhibits NPY/Agrp neurons
Define polydipsia
Excessive thirst or excess drinking
Define adipsia
Inappropriate lack of thirst with consequent failure to drink in order to correct hyperosmolality
Define anorexia
Lack or loss of appetite for food
What is the difference between anorexia and anorexia nervosa?
Anorexia nervosa is the psychological condition
Anorexia is just a loss of appetite for food, it can be a result of other physiological conditions
What are the 2 classes of thirst disorders?
Polydipsic
Adipsic
What are the types of polydipsia or adipsia?
Primary or secondary
What are some causes of secondary polydipsia
Chronic conditions (eg diabetes, kidney failure, Conn’s, Addison’s, sickle cell)
Medications (diuretics, laxatives, antidepressants)
Dehydration (acute ilnness, sweating, fevers, vomitting, diarrhoea)
What is the difference between diabetes insipidus and mellitus?
Mellitus= problems with insulin and blood glucose Insipidus= problems with ADH and water regulation
What are the main conditions that can cause polydipsia asides from diabetes?
Acute kidney failure
Conn’s syndrome (primary aldosteronism)
Addison’s disease (hypoadrenocorticism)
What are some causes of primary polydipsia?
Mental illness (psychogenic, schizophrenia, mood disorders, anorexia, drug use)
Brain injury
Organic brain damage
How many types of adipsia are there? Which is most common?
There are 4 types (A, B, C and D) and A is the most common
Define the term eating disorders
Mental disorders defined by abnormal eating habits
What disorders do eating disorders encompass?
Binge eating disorder Anorexia nervosa Bulimia nervosa Pica Rumination syndrome Avoidant/restrictive food intake disorder
What is pica?
People eat non food items of no nutritional value eg hair, paint chips
What is rumination syndrome and how is it different to bullimia nervosa?
It is a condition where people regurgitate food that is undigested and not acidic, in bullimia nervosa food is digested and acidic and regurgitation involves cycles of binging and purging
What are some signs of eating disorders?
Low BMI Continuous weight loss Amenorrhea Halitosis Mood swings Dry hair, skin & hair thinning
What is the BMI range for mild anorexia?
over 17
What is the BMI range for moderate anorexia?
16-16.99
What is the BMI range for severe anorexia?
15-15.99
What is the BMI range for extreme anorexia?
less than 15
Out of diet and exercise, what is most effective for weight reduction in obesity?
Diet more than exercise but a combination of both is best
What happens to ghrelin, GLP1, GLP2 and PYY after bariatric surgery?
Ghrelin reduces
GLP1, GLP2 and PYY increase
What commonly presents with gingival bleeding?
Scurvy
