task 7

Question 1

homeostasis

Answer 1

process by which body’s substances & characteristics are maintained at optimal level
> with help of ingestive behaviour

Question 2

regulatory system

Answer 2

negative feedback system
> system variable / set point / detector / correctional mechanism
> negative feedback

> ingestive behaviour is controlled by satiety mechanisms

Question 3

drinking

Answer 3

body contains 4 major fluid compartments:
> 1 intracellular fluid
> 3 compartments of extracellular fluid:
1. intravascular fluid
2. cerebrospinal fluid
3. interstitial fluid
> interstitial fluid becomes hypertonic when water out of cells; vice versa -> hypotonic
> hypovolemia (low volume of blood) when intravascular fluid not regulated right

Question 4

kinds of thirst

Answer 4

> two receptors; measuring blood volume / cell volume

> two kinds of thirst caused by evaporation:
1. osmometric thirst:
concentration of interstitial fluid decreases -> decrease pulls water out of cell
osmoreceptors’ firing rate affected by level of hydration
- osmoreceptors (OR) found in lamina terminalis, which contains OVLT & SFO (hypothalamus)
- supraoptic nucleus of hypothalamus contains OR -> controls secretion of vasopressin (regulates excretion of water by kidneys)

2. volumetric thirst:
   > loss of blood / salt appetite
   > produced by hypovolemia -> decreased blood flow to kidneys
   - cells produce renin -> angiotensinogen that catalyses to angiotensin (A1->A2)
   - A2 leads to secretion of hormones by pituitary gland and adrenal cortex
   - A2 initiates drinking and salt appetite to reduce hypovolemia

Question 5

neural mechanisms of thirst

Answer 5

> osmoreceptors in OVLT and SFO imitate drinking
lamina terminalis controls osmometric and volumetric signals
volumetric thirst is provided by angiotensin 2
low injected doses of A2 in SFO cause drinking
destruction of SFO or lamina terminalis -> abolished drinking or adipsia (lack of drinking)
median prophetic nucleus situated around decussation of anterior commissure -> plays role in thirst, stimulated by angiotensin

Question 6

eating

Answer 6

two reservoirs:
1. short-term:
> located in cells of liver & muscles & is filled with glycogen
> insulin stimulates cells to convert glucose into glycogen
- some of glucose used as fuel; some stored as glycogen
> decrease of glucose is recognised by pancreas -> stop of secretion of insulin but glucagon (stimulates conversion of glycogen in glucose)

2. long-term:
   > adipose tissue filled with triglycerides, which contain glycerol combined with fatty acids
   > its cells absorb nutrients from blood & convert them to triglycerides for storage
   > fatty acids can directly be metabolised by cells in all of the body except the brain
   - brain is living on glucose that is released by liver
   - glucose easily dissolves in water but not it fats -> glucose transporter with insulin receptors (exception for nervous system)

Question 7

fasting phase:

Answer 7

> nutrients are not available from digestive system

> glucose / amino acids / fatty acids are derived from glycogen / protein / adipose tissue

Question 8

absorptive phase

Answer 8

> nutrients are absorbed by digestive system -> glucose & amino acids constitute principle energy source for cells

> rest is stored

Question 9

mechanisms that cause 1. motivation to eat & 2. restrain food intake once it’s enough

Answer 9

> signals from environment due to ancestors (feast or famine)