Homeostasis

What is homeostasis? (4)

• A state of balance and stability

• The ability to maintain a stable internal environment within an organism, regardless of internal or external stresses or conditions

• Homeostasis is a dynamic equilibrium

• The fluctuations are kept within an acceptable range by the use of feedback systems.

Why must homeostasis be maintained?

• So organs systems can function optimally.

• Allows for responses to constant stresses and stimuli

What are 6 examples of homeostasis?

• Body temperature

• pH

• Water levels

• O₂/CO₂ levels

• Nutrient levels (glucose in blood), vitamins and minerals

• Electrolytes (dissolved ions

What are the 3 essential parts of all homeostatic systems?

1. Monitor/ sensor

2. Coordinating/ integrating centre

3. Regulator/ effector

What is a negative feedback loop?

• Back to equilibrium

• External stimuli are combated by a counterreaction

• A process by which a mechanism is activated to restore the conditions of its original state

• Does the opposite of the stimulus

• Most body functions rely on negative feedback

e.g. body temperature, blood pressure, volume, and pH, glucose in blood

What is a positive feedback loop?

• More, more, more!

• External stimuli are increased

• Acts to increase the strength of stimuli even further away from the equilibrium

• Considered non-homeostatic

• Relatively rare in natural systems

e.g. childbirth, baby’s growth in pregnancy, breastfeeding (all relate to oxytocin)

How is baby growth a positive feedback loop?

• Baby’s growth takes ups all the space in the uterus

• Resulting in stretch receptors activated in uterus

• Brain signals for the release of oxytocin

• Oxytocin cause uterine muscles to contract

• Contraction gets stringer until baby is delivered

What is thermoregulation?

The regulation of body temperature

What region of the brain is thermoregulation controlled by and how?

• Hypothalamus

• Triggers heat loss or heat generating mechanisms

What is a fever result of?

The system’s set point is altered

• A temporary form of positive feedback

What are endotherms?

Animals that can regulate their own body temperature regardless of external conditions

• Able to generate most of their heat

  through metabolism

(e.g. mammals and birds)

What are ectotherms?

Gain heat from external sources

(e.g. invertebrates, most fish, and reptiles)

What are poikilotherm?

Animals whose internal temperature varies

How do animals regulate their temperature?

Behavioural responses

What is Torpor, Esivation, and hibernation?

• Animals sleep for a long duration of time

  • Torpor - 24 hours

  • Estivation - summer

  • Hibernation - winter

• Act of slowing metabolic rate to reduce demand for energy in times where food is less available

What are physiological responses to excessive heating?

• Sensors in the brain detect increase in body

  temperature

• Message is sent to sweat glands to secrete

  sweat (evaporative cooling).

• Another message is sent to blood vessels

  in skin; the skin blood vessels dilate,

  increasing blood flow to skin (promoting

  heat loss).

• Cooler body temperature turns off

  mechanism.

• Example of a negative feedback loop

What are physiological response to excessive cooling?

• Temperature receptors in skin detect drop in temperature → message is sent to brain

• Message is sent to organs and tissues; blood vessels in skin constrict limiting blood

  flow to skin minimizing heat loss.

• Message is sent to skeletal muscles; series

  of rapid contractions (shivering)

  generates heat by increasing metabolism.

• Muscles around hair follicles contract

  causing the hair to stand up (air is

  trapped within the animal’s fur to help

  insulate the body).

  • Note: this occurs in humans as well,

    but since we have no fur it causes

    “goosebumps”.

• Warmer body temperature turns off

  mechanism.

What does a lack of control of body temperature result in?

Heat exhaustion, heat stroke, and hypothermia

What are the symptoms of heat exhaustion?

• Faint or dizzy

• Excessive sweating

• Cool, pale, clammy skin

• Nausea or vomiting

• Rapid, weak pulse

• Muscle cramps

What are the symptoms of heat stroke?

• Throbbing headache

• No sweating

• Body temperature above 103 degrees

  • Red, hot, dry skin

• Nausea or vomiting

• Rapid, strong pulse

• May lose consciousness

What are the symptoms of hypothermia?

• Confusion

• Shivering

• Difficulty speaking

• Sleepiness

• Stiff muscles

How is blood sugar regulated?

• By pancreatic hormones are produced in the islets of langerhans

  • Beta cells produce insulin

  • Alpha cells produce glucagon

What does insulin do?

• Lowers blood sugar

• Released when blood sugar is high

• Allows cells to take in glucose and produce ATP

• Tells the liver to store extra sugar as a substance called glucagon

What does glucagon do?

• Raises blood sugar

• Tells the liver to break down stored glycogen back into glucose

• Releases glucose into blood stream

What is hypoglycemia?

Deficient in glucose/ low blood sugar (3,3 mmol/l)

What are normal levels of glucose in blood?

3,3-5,5-mmol/l

What is hyperglycemia?

A lot of of glucose in blood/ high blood sugar (5,5-8,3 mmol/l)

What are the levels of glucose in diabetes?

8,3-21,1 mmol/l

What occurs in type 1 and type 2 diabetes?

• Type 1

  • Insulin dependent

  • Early degradation of beta cells

  • Cannot produce insulin

• Type 2

  • Non-insulin dependent

  • Decreased insulin or ineffective use

  • Controlled with diet, exercise, oral drugs

• Absence of insulin → little/no glucose in cells → cells metabolize fats and proteins for energy

• Kidney unable to reabsorb all blood glucose → excess glucose in urine

  • High glucose concentration in nephrons draws water out of blood

  • Excessive urination