HOMEOSTASIS (Motivation)
Overview of Topics
Lesson Objectives
Definition & Description
Temperature Regulation
Water Regulation
Food Regulation
Recovery from Aphagia
Learning
Lesson Objectives
- How is homeostasis important in behavioral flexibility?
- Describe the basic processes common to all regulatory systems.
- What are the major characteristics of hypothalamic areas that are similar for all regulatory processes?
- All regulatory systems have multiple sources of input that are important in maintaining a balance. How does this influence recovery from a lesion to the hypothalamus?
- Why do animals stabilize body weight during the static phase of hypothalamic hyperphagia?
- Describe the process of temperature regulation.
- Describe the process of recovery from lateral hypothalamic lesions.
- Explain how ADH operates to maintain water balance.
Definition and Description
Homeostasis: The ability of the body to maintain a balance with regard to food and water intake and excretion is necessary if animals are to become mobile and less dependent on their environment.
With phylogenetic development, some organisms developed the ability to establish within their body conditions which differed drastically from their environment.
To regulate the internal environment, the following is required:
- Some imbalance (deficit or excess occurs)
- Some detector or detectors which sense deviations from stable levels
- Some central processing system -- hypothalamus.
- Effectors capable of remedying the imbalance -- involuntary or reflexive.
- Complex learned behaviors - aid in maintaining a balance.
- Planning external aids to deal with future imbalances.
Temperature Regulation (30-40 degrees C.)
Detectors
- Hot and cold receptors on surface of the skin
- Detectors in anterior hypothalamus. (AH) (preoptic nucleus)
- Warming leads to panting, sweating
- Cooling leads to huddling, shivering
- Preoptic region increases firing rate when heated
- Ice cube to roof of mouth cools AH -- reduces sweating but sharp rise in temperature
- Probably both central and peripheral receptors involved.
- Electrical stimulation of AH leads to same behavior as heating
Effectors
- Thyrotropic hormones released from anterior pituitary
- Epinephrine releases controlled by hypothalamic
Behavior
- Cold-blooded regulate temperature by changing area
- Warm-blooded animals (when cool -- fluff out hair or feathers; when hot -- sweat, pant, or lick body)
- Gross movement
- Rats will press bar to turn on heat in cold environment
- Rats will take shower if hot
Water Regulation
General
- Water continually ingested, excreted and secreted to remove wastes and regulate temperature.
- Animal can maintain water balances within narrow limits (+.22% of body if water available)
- Below .5%, thirst results
Detectors
- Oral-pharyngeal factors -- taste, osmoreceptors, local cooling and muscle feedback.
- Osmotic pressure -- movement of water across membrane to establish equal concentrations of salt solution.
- These detectors may affect firing rate of cells in hypothalamus
- (Na) Sodium-free diet may produce an initial weight loss of 5 lbs. but stabilizes
- Glucose --->NaC1 loss and glucose taken in ------> acute Na loss ------> drinking
- Blood volume -- drop triggers drinking
- Detectors must be near vessels of carotid artery
- Blood loss -- thirst
- Reduced volume and increased osmotic pressure are involved
- Gastric factors -- stomach distention important for termination of drinking
- Central factors -- hypothalamic detectors
- Injection of NaC1 or electrical stimulation of AH drinking (Anderson, 1953).
- Grossman, 1960, 1962 -- Acetylcholine in LH drinking.
- Septal and amygdaloid lesions ---> modify water intake
- Preoptic (AH) lesions fatal ----> eliminate drinking
Effectors
- Supraoptic and paraventricular nuclei -----> synthesize ADH (antidiuretic hormones)
- When cells fire, (ADH) is released into pituitary where it enters system.
- When ADH reaches kidneys it causes water to be reabsorbed into circulatory system.
- This increases urine concentration and conserves water.
- Lesions in supraoptic or paraventricular nuclei produce diabetes insipidus (water is excreted with urine).
- Accompanied by polydipsia
- Olfactory tubercle lesions or olfactory bulb ablations produce polyuria and polydipsia
Behavior
- Termination of eating and drinking probably conditioned.
Food Regulation
Detectors
- Stomach contractions (Cannon & Washburn, 1912)
- Stomach stretch -- important for termination of eating
- Food intake probably regulated by spacing meals rather than eating more at each meal
- Humoral factors
- Blood from satiated rats inhibited other rats' eating.
- Food in stomach dehydrates cells of water; thus osmoreceptors may be involved
- Injecting water in blood during feeding increases amount eaten
- Blood glucose -- very important
- Mayer (1953) -- glucostatic theory -- rate of use of glucose
- Glucogen and epinephrine -- hormones increase level of blood glucose and rate/ use.
- Receptors in ventromedial hypothalamus (VMH) -- glucose injection to VMH leads to increased cell activity
- Glucose injection --> no effect; procaine injection produced eating.
- Temperature theory doesn't hold up after animals adapt to heat
- Probably many different detectors for food regulation.
Effectors
- Frolich (1901) -- tumor in VMH leads to obesity
- Hetherington & Ransom -- hypothalamus
- VMH lesion -----> hypothalamic hyperphagia
- Reynolds vs. Hoebel -- Radio frequency vs. Direct current lesions
- Females used as subjects.
- Stimulation of VMH -- eating stops.
- Static vs. dynamic phase.
Recovery from Aphagia
Aphagia results from lateral hypothalamic lesions
Stages of Recovery
|
Stage I Adipsia Aphagia |
Stage II Adipsia Anorexia |
Stage III Adipsia Aphagia |
Stage IV Recovery Dehydration |
| Eats wet food? |
No |
Yes |
Yes |
Yes |
| Regulates weight on wet food? |
No |
No |
Yes |
Yes |
| Eats dry food? |
No |
No |
Yes |
Yes |
| Drinks water? |
No |
No |
No |
Yes |
Learning
- Epstein & Teitalbaum (1962) -- food regulation with food ingestion through a cannula
- Brain stem -- no cortex -- still eat but not discriminative.
Water transfer mechanism:
- Diffusion -- across membrane permeable to solute (kinetic molecular energy).
- Filtration -- passage due to mechanical force
- Osmosis -- differential permeability-water movement
- Oral-pharyngeal factors -- taste, osmoreceptors, local cooling, muscle feedback.
- Gastric factors -- distention
- Central factors -- hypothalamic detectors
Terms to Know
| Homeostasis |
Aphagia |
Supraoptic nuclei of hypothalamus |
| Anterior hypothalamus (AH) |
Anorexia |
Paraventricular nucleus of hypothalamus (PVN) |
| Convoluted tubule |
Adipsia |
Lateral hypothalamus (LH) |
| Preoptic nuclei |
Epinephrine |
Antidiuretic hormone (ADH) |
| Thyrotropic hormones |
Polydipsia |
Diabetes insipidus |
| Osmoreceptors |
|
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