hunger & thirst

Homeostasis

The process of actively maintaining internal conditions, particularly with respect to food and water availability and body temperature

Happes when the body is too cold

• Basal metabolic rate increases (calories are burned to generate heat)

• The body shivers ( a way of burning calories to generate heat)

• Peripheral blood vessels conscrit, moving blood to the interior of the body so less heat is lost through the skin

Happens when the body is too hot

• Animals sweat or pant ( breath heavily) because water evaporation has a cooling effect

• Peripheral blood vessels expand; blood moves closer to the skin so body heat can more easily dissipate into the surrounding hair

Cold blooded animals (ectotherm )

Not good at maintaining their body temperature, so their ability to move and function is highly dependent on the ambient temperature

Need state

• we experience this when our body temperature becomes uncomfortable

• They are motivating. They drive us to correct a specific problem

Anticipation of pleasure

Motivates us to perform an action, even in the absence of a corresponding need

Primary causes of water loss

Urination, sweat, breathing

Reasons why we drink water

Osmometric thirst and volumetric thirst

Osmometric thirst

Not enough water inside the cells

Volumetric thirst

Not enough blood ( liquid) in our circulatory system

Osmosis

The movement of water from areas of low tonicity to areas of high tonicity

Isotonic solution

Cells neither gain nor loose water ( same concentration inside and outside the cell)

Hypotonic solution

Cells absorb water and grow in size

Hypertonic solution

Cells loose water and shrink in size

Osmoreceptors

• Neurons whose membrane potential is determined by the size of the cell

Low blood volume ( hypovolemia )

Causes cells in the kidneys to release the enzyme renin, which initiates a cascade of chemical reactions

AV3V region

Feelings of thirst relate to neural activity in this region of the hypothalamus

What food mostly consists of

Sugar, fat, amino acids, nucleotides, salts and vitamins

What urine contains

• Excess water, salt, and sugar

• Urea from the breakdown of proteins

• Unit acid from the breakdown of nucleic acids

What fat is broken into

Water and carbon dioxide

Characteristics of hypothalamus in relation to hunger

• it receives information throughout the forebrain about the external environment

• Monitor hormone levels in the blood

• Indirectly receives information about digestive processes from the 10th cranial nerve

Pancreas

Monitors blood-glucose levels which rise after we eat

Insulin

The pancreas releases this when blood glucose is high

Glucagon

The pancreas releases this when blood- glucose is low

Glycogen

• Represents our short-term storage of glucose

• Its levels build up when insulin is released

• Its levels deplete when glucagon is released

Happens in the absence of insulin

muscle and fat cells stop taking in glucose and switch to using ketones for energy ( made from fat)

Ghrelin

A peptide released when the stomach and intestines are empty

Effect of a swelled stomach

Slightly reduces hunger

CCK and GLP-1

• Hormones that are released by the intestines in the proportion to the number of calories ingested

• They regulate the release of digestive enzymes and insulin

Exogenous administration of CCK

Decreases hunger and meal size, but does not causes weight loss, it used repeatedly

GLP-1 agonists

Proven to be highly effective in reducing hunger and weight in most people

lipoprivation

Dangerously low levels of fat which can trigger immense nurses

Lepton

• An hormone released by fat cells

• Its levels increase as fat cells grow and proliferate

• Its blood levels correlate with the amount of fat on the body

Types of emergency hunger circuits

Gluco privation and lipoprivation

Glucoprivation

• With dangerously low levels of blood-glucose levels, it triggers intense feelings of hunger

• Can result from excessive insulin signaling as well as from drugs that inhibit glucose metabolism

Lipoprivation

Dangerously low levels of body fat

Diabetes

A condition where people either do not release enough insulin or they are insensitive to insulin signaling

Effects of glucoprivation and lipoprivation

• The pancreas stops releasing insulin and starts releasing glucagon

• CCK and glp-1 are ignored

• Energy expenditure slows basal metabolic rate, halting growth and reproductive systems

• A potent feeling of hunger takes hold

• Adrenaline is released as part of the fight or flight response, which increases heart rate, sweating and muscle tremors

Two intermingled cell populations in the accurate nucleus of the hypothalamus that regulate hunger

POMC neurons and AGRP/NPY neurons

AGRP / NPY neurons

• Promote hunger

• Activated by ghrelin and inhibited by leptin and CCK

POMC neurons

• Inhibit hunger

• They are inhibited by hunger and activated by leptin and CCK

PVN

• Where firing rates track leptin levels

• These cells seem to orchestrate the effects of lipodeprivation

Prader-Willi syndrome

• Chromosomal abnormality in which 7 genes are deleted from chromosome 15

• People with this condition feel like they are starving to death

Bariatric surgery

Modifies the stomach, small intestine, or both

Roux-en-y gastric bypass

The second part of the intestine is cut and attached to the top of the stomach. The stomach is also made smaller