Hunger/ Thirst

What is homeostasis?

The maintenance of a stable, balanced internal environment

What is the main homeostatic mechanism?

NEGATIVE FEEDBACK SYTEMS.

If you deviate from ______, compensatory action begins.

SET POINT, you body will try to compensate to keep things balanced

Motivation is...

Factors that initiate, sustain, or direct behavior

What drives physiological motivation?

Homeostatic systems

What are the 2 systems involved in thermoregulation?

1. Preoptic Area:

• part of the hypothalamus

• lesions here result in impaired physiological response, NOT behavioral response.

• Physiological responses: sweating, constriction/dilation of blood vessels, respiration

2. Lateral Hypothalamus:

• Lesions here result in the loss of behavioral regulation of temperature. (shivering and heat-seeking/avoiding behaviors)

What is hypovolemic thirst?

Hypovolemic thirst is thirst caused by LOW OR LOSS OF EXTRACELLULAR/INTRAVASCULAR (WATER) VOLUME.

outside cells have less water = low blood pressure.

Baroreceptors detect.

Arteries constrict to raise BP.

NOTE: CONCENTRATION is not changed

Vasopressin and Renin are released due to hypovolemic thirst. What are their functions, respectively?

Vasopressin (ADH) – Released from posterior pituitary, blood vessel constriction, less blood flow to bladder, more water retention
Renin – Released from the kidneys when blood volume decreases, plays a major role in the Angiotensin cascade

What is the angiotensin cascade, in order?

Which of your organs helps resolve hypovolemic thirst?

SUBFORNICAL ORGAN; Angiotensin II acts here to signal to other brain sites (such as the POA) to initiate drinking

What is osmotic thirst?

Osmotic thirst is thirst stimulated by HIGH EXTRACELLULAR SOLUTE CONCENTRATION.

Water can leave the cell, but salt cannot. When water leaves the cell, the cell shrinks

What neurons respond to a rise in blood osmotic pressure? Where are they found?

OSMOSENSORY NEURONS, which are found in the anterior hypothalamus (OVLT).

Response: increasing osmotic pressure by causing the posterior pituitary to release ADH/Vasopressin

Which of your organs helps resolve osmotic thirst?

OVLT

What is the principal energy source, which is also used by your brain?

GLUCOSE. Your body even uses a process called glycogenesis to convert glucose to glycogen for storage

If absolutely necessary, what other form of energy will your brain be willing to use?

FAT- but only if your brain is starving and there is no other glucose left. Lipids and fat tissue are generally for longer-term storage of energy.

What is glycogen, and how is it made?

Your body makes glycogen through a process called glycogenesis to convert glucose into glycogen for short-term storage in the liver. Glycogenesis involves the use of insulin.

Increased insulin levels lead to _______, whereas increased glucagon levels lead to _______

Increased insulin levels = glycogen production, less glucose.

increased glucagon levels = more glucose production, less glycogen

What is Leptin?

Leptin is produced by adipocytes (fat cells) and is secreted into the bloodstream.

deficit in leptin production = low report of body fat, causing animals to overeat.

What would weight loss do to leptin levels?

Decrease leptin levels, hypothalamus will signal your body to increase food intake and use less energy.

What would weight gain do to leptin levels?

Increase leptin levels, food intake will go down, and use more energy.

What is Ghrelin?

GHRELIN is released by STOMACH endocrine cells.

an appetite stimulant that RISES DURING FASTING and DROPS AFTER EATING.

When you are full after eating food, do you have high or low ghrelin and leptin levels?

Low Ghrelin levels, high Leptin levels

What disorder do some obese people have with a problem with peripheral signals?

PRADER-WILLI SYNDROME: when people have abnormally elevated ghrelin levels, and eat as if they were starving.

Where in the brain would lesions cause overeating?

lesions in the VENTROMEDIAL HYPOTHALAMUS, which cause obesity.

In an experiment, VMH lesioned rats overeat until they become obese.

• a new SET POINT was made at the heavier weight.

• rats will remain at the new overweight set point when force feeding stops instead of at the healthy set point

Lesions in what part of your brain would cause refusal to eat?

LATERAL HYPOTHALAMUS.

• LH lesioned animals stop eating, and stabilize their weight at a new lower level because of a new, lower set point.

• Perhaps anorexics have a lower set point

NPY/AgRP neurons produce neuropeptide Y and agouti-related peptide. What do these do?

They STIMULATE appetite and LOWER metabolism. Weight gain
Leptin inhibits NPY neurons and stimulates POMC neurons

What do POMC neurons do?

• POMC/CART neurons produce pro-opiomelanocortin (POMC) and CART, which INHIBIT appetite and RAISE metabolism

VMH lesions destroy the ____

Anorexigenic Paraventricular Nucleus (PVN)

LH lesions destroy the __

Orexigenic Lateral Hypothalamus (LH)

High calorie diets cause __________ and ___________

Hypothalamic scarring and microglial activation

Overeating leads to hypothalamic inflammation, which:

Inhibits neurogenesis, resets your set point

Izzy was obese and died of heart failure. How did he get up to 757 pounds?

Izzy might have had leptin deficiency or VMH lesion. We don’t exactly know, but it is certain he had a high set point from weight gain that made it hard to diet.

Why do diets fail for most people?

because your BASAL METABOLIC RATE (energy required to fuel brain/body and maintain temperature) falls to PREVENT losing weight. Your body is working against your diet because it is scared you will die!

What are effective treatments for obesity?

• Eat less and exercise 

• having a cannabinoid receptor antagonist. (but blocking cannaboids can cause suicidal thoughts)

• for obesity REDUCING D2 receptors and DECREASING IN PREFRONTAL METABOLISM may be effective.

• GASTRIC BYPASS SURGERY is the best. GHRELIN IS REDUCED and PYY AND GLP-1 IS INCREASED, reducing hunger. 25% average weight loss in patients is long lasting, reduces mortality, and has many health benefits

(True or False): Increasing Leptin and decreasing Ghrelin levels are an effective method for treating obesity

FALSE

What is anorexia nervosa? What are some symptoms?

ANOREXIA NERVOSA is not maintaining body weight due to a fear of weight gain and body image issues,

It can be a restricting or a binge-eating/purging type. It is 10x more common in woman than in men

What is bulimia? What are some symptoms?

BULIMIA is binge eating with recurrent inappropriate, compensatory behavior.

often goes on for at least 2x/week for 3 months.

Symptoms include thinning of bones, brittle hair and nails, drop in body temperature, low blood pressure, slow breathing, etc.

Teenage girls with anorexia have (larger/smaller) Insula and (larger/smaller) Orbitofrontal Cortex (OFC)

Larger, larger

What are some treatments for anorexia or bulimia?

For anorexia or bulimia, SEROTONIN is LOW. Treating this as a mood disorder might be successful. Antidepressants and anti-schizophrenic drugs (like Olazapine) produces some benefit. Dopamine might be involved as well.

George is a sleep deprived graduate professor – he is able to sleep only from 5AM to 1PM. What does George have?

Delayed Sleep Phase Syndrome

Why should you sleep?

It helps with learning consolidation, gives the body time to rest, and is a safety precaution in animals. Sleep lets us LEARN

What type of rhythm do Humans have? What type do owls have?

Diurnal – active in the day. 

Owls are nocturnal – active at night.

How long are Circadian rhythms? What are they generated by?

24 hours. They are generated by endogenous (internal) clocks in the Suprachiasmatic Nucleus (SCN)