What would happen to me if I stuck my head in cold water??

Mammalian Dive ReflexHomeostatic Responses During:• Vasoconstriction in extremities to conserve heat• Decrease in heart rate• Blood flow returning to heart is increased• Kidneys release urine in effort to counter high blood

volume in core

WHY ??Optimizes respiration to allow staying underwater for

extended periods of time.

It is exhibited strongly in aquatic mammals (seals, otters, dolphins, etc.), but exists in a weaker version in other mammals, including humans

Homeostatic Responses After:• Vasodilation in extremities (face) to bring heat and

oxygen back• Heart rate increases and re-sets rhythm

What is a homeostatic response??

Homeostasis – process by which a constant internal environment is maintained despite changes in the external environment

Poor old me, trying to get back in shape

• Dynamic Equilibrium – condition that remains stable within fluctuating limits (homeostasis is a dynamic equilibrium)

• All homeostatic control systems have:– Monitors and sensors– Coordinating centre– Regulator and effectors

Hire-wire Artist ModelVariable:position of bodySetpoint: directly over the wireMonitors and Sensors: nerve receptors (eyes, inner ears, muscle stretch receptors, etc.)Regulator: brainEffectors: skeletal muscles

High-wire artist uses negative feedback to maintain relatively constant position on wire.

http://www.youtube.com/watch?v=WvMI9o5zwEI

Heat and cold receptors, rather than detecting specific temperatures as does like a thermostat, are adapted to

signal CHANGES in environmental temperatures

Extension #1: Using this information, explain why you might feel a chill when you step out of a warm shower even though room temperature is comfortable

Extension #2: Using this information, explain why when a frog is placed in a beaker of water above 40°C, the frog will leap out immediately, but when the frog is placed in room-temperature water and the temperature is slowly elevated, the frog does not leap out

Negative Feedback Systems (common)• Bring system back to acceptable range• Prevents small internal adjustments from getting out

of hand• Eg. When body temperature continues to drop, body

begins to shiver to reverse the temperature (bring back to norm)

Blood glucose

Positive Feedback Systems (uncommon)• Amplify a small change, moves away from equilibrium• Allows a discrete event to happen rapidly• Eg. Lactation – suckling baby stimulates production of oxytocin,

in turns causes contraction of milk duct muscles, causing milk flow… and flow of milk increases suckling

A reflex

A specific, involuntary, unpremeditated response to a particular stimulus.

A stimulus being a detectable change in the internal or external environment. The pathway meditating a reflex is called a reflex arc.

We will be examining 3 systems that help maintain homeostasis

The excretory systemThe nervous systemThe endocrine system

Excretory System

Why do we really pee???• Average person consumes more protein than necessary• While most are converted to carbohydrates, the leftover nitrogen

must be eliminated• Process is called deamination which produces urea - N2COH2

Kidneys play a crucial in:• Removing waste• Balancing blood pH• Maintaining water balance

Excretory System

Bladder• Sphincter at base allows storage of urine• When 200 ml is collected, bladder stretches

which sends nerve message to the brain• 600 ml or more – bladder relaxes and you

urinate!• Urine is voided via the urethra

http://cbs.fas.harvard.edu/science/connectome-project/brainbow

Neurons: Cells which can transmit nerve impulses in the form of electrochemical messages

The axon sends a wave of depolarization along its length

The wave of depolarization is primarily the movement of Na+ and K+ ions across the axon’s membrane

The nervous system

Endocrine hormones are produced in glands and are secreted into the bloodstream find target cells

The endocrine system is the system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body.

Endocrine system