Chapter 10Physiological adaptations for survival

External & internal environments

External environment refers to the surrounds of an organism- temperature, humidity, wind etc. It can vary widely (even in one day- think about Melbourne weather!)

Internal environment inside organisms need to be maintained within a tolerance range. Eg. Humans internal body temp (36.1-37.8)

Homeostasis: keeping within the tolerance range

Homeostasis refers to the maintenance of a relatively stable internal environment.

When challenges cause a deviation from the normal conditions, the organism has mechanisms that act to restore the normal state. (Eg Shivering, sweating)

Refer to pg 300 table 10.1

Body systems contribute to homeostasis

The two major systems contributing to homeostasis are: The nervous system (nerves) The endocrine system (hormones)

Other cells and systems also contribute to homeostasis.

Structure of the nervous system

The nervous system consists of: Brain (CNS) Spinal cord (CNS) All nerve cells (PNS)

CNS refers to the Central Nervous system

PNS refers to the Peripheral Nervous system

Nerve cells

Nerve cells (AKA neurons) have a large cell body (with the nucleus) and an extension stemming off this called axon- they carry messages to other cells

Also stemming off the cell body are dendrites – they receive messages

See picture pg 302

Nerve cells (cont)

There are three kinds of neuron: Affector (sensory) neurons

‘information detectors’ send messages back to the CNS

Effector (motor) neurons ‘responders’ send messages from the

CNS, cause cells to respond Connecting neurons- link neurons

together

Start from here after temperature regulation

Major sense organs: sensing our environment

Sense organs monitor our external environment and send messages back to the CNS in the form of electrical impulses.

When the message reaches the CNS, the brain stimulates effectors to complete a response (to the external stimulus)

Over to you....

Human Light receptors

Light enters the human eye through the cornea It passes through the lens where it is focussed onto the

retina It contains two kinds of photoreceptors known as rods

and cones Rods and cones contain light sensitive pigments Fibres lead to the optic nerve at the back of the eye

carrying information to the brain Concentrated in the central region of the retina, cones

cells function in high light intensities, detecting colour and detail.

Cones provide us with our central vision Rod cells detect light with low intensity and can detect

movement

Human taste receptors

Taste receptors are located in the taste buds on the tongue.

Each tastebuds contains 50 receptors cells. Receptors transmit encoded information about

taste of food in the mouth. The brain then decodes and interprets the information.

These receptors can detect chemical substances in the saliva of the mouth.

Five basic taste: sour, salt, bitter, sweet and umami (a taste sensation produced by monosodium glutamate [MSG] and other glutamates found in fermented foods.

Human olfactory receptors Olfactory receptors are located on bony outgrowths inside the

nasal cavity. In humans they are nerve cells. The fibres from these form the

olfactory nerve leading to the brain. Olfactory receptors in the nose can detect substances at a

concentration 10,000 times less than that required for detection by taste receptors.

Some people cannot smell scent: e.g. scent of flowers The taste of many foods come form the combination of several

sensory inputs. There are 3 types of stimuli:

Olfactory stimuli- arising from the odour of food before and while it is in the mouth

Tactile stimuli- arising from the texture of food Gustatory stimuli- arising from the taste of dissolved food Temperature stimuli- such as the heat or coldness of food

Touch and other tactile recptors Receptors to detect stimuli that produce

sensations of touch pressure, temperature and pain are distributed over the entire skin surface.

In order to stimulate the receptors an object must make physical contact with the outer body surface

Mammals use their whiskers as extensions of their body, to increase their ability to collect information from their surroundings

Pain is a valuable sensations that tells us that the stimulus is causing tissue damage

Ears and hearing

In mammals, birds, reptiles and amphibians, sound receptors are concentrated in the ear.

There are three regions in the human ear. The outer ear is made of cartilage, this leads to the

ear canal. To the middle ear is an air filled cavity. Sound waves

cause the eardrum to vibrate and this vibration is then conducted across the middle ear to the inner ear.

The inner ear magnifies the sounds. The inner ear consists of small coiled structure called

the cochlea which is filled in the inner ear. Information about the sound is then encoded into nerve impulses and sent to the brain.

Go to chapter review pg 337 Answer Q 3, 4, 5, 6, 7, 9, 10, 12, 13

Detecting temperature change

Core temperature is maintained at about 37 degrees

Changes to external temperature are detected by receptors in the skin: cold and hot receptors

These send a message to the hypothalamus in the brain

The hypothalamus serves as the temperature control centre of the brain

Maintaining core temperature Homeostasis requires a stable internal

body temp.

Conduction= transfer of heat to other ‘objects’

Convection= air currents taking heat away

Ways of gaining heat Ways of losing heat

Basic metabolic processes

Evaporation of sweat

Shivering Panting

Exercise /muscular activity

Convection

Radiation & conducting TO the body

Radiation and conduction FROM the body

Gaining heat & reducing heat loss

Shivering: contraction & relaxation of small muscle groups

Metabolic processes produce heat. The hypothalamus produces TRH which instructs the pituitary to secrete TSH which stimulates the thyroid. The thyroid releases thyroxine which increases metabolic activity

Hypothalamus can instruct blood vessels to constrict (in the skin) to reduce the amount of heat lost via the skins surface

TSH = Thyroid stimulating hormone TRH= Thyrotropin- releasing hormone

Hypothalamus releases

TRH

Pituitary (stimulated

by TRH) releases TSH

Thyroid (stimulated

by TSH) releases thyroxine

Thyroxine increases metabolic

rate

Body becomes warmer

Cooling off

When the core body temperature is set to exceed 37 degrees, the hypothalamus acts to increase heat loss by: Dilation of blood vessels at the skins surface Metabolic activity is reduced (secretion of TRH

is reduced therefore....TSH is reduced, therefore...)

Sweat glands are activated (evaporation of sweat requires heat energy)

Heat source: external or internal

Ectothermic: relies on external heat source eg snake

Poikilothermic: have fluctuating temperatures

Endothermic: have an internal heat source (able to generate their own heat) eg people

Homeothermic: have a constant body temperature

Water balance in living organisms

Kidneys- are responsible for water balance. They eliminate nitrogenous wastes and cause water to be reabsorbed

ADH (antidiuretic hormone) and renin act on the kidneys to absorb more water to be returned to the body (to prevent dehydration)

Complete biochallenge pg 336