Homeostasis & Excretion

LPK TB Chapter 12 & 11

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HOW ARE HOMEOSTASIS AND EXCRETION RELATED?

Homeostasis is … Excretion is …

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In the case of these fishes…• Homeostasis is somewhat like how Salty Sail

maintains the water potential of his cells. • Drinking a lot of water and Excreting salt is the

way he achieves it.

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Definition

Excretion is the process by which metabolic waste products and toxic materials are removed from the body of an organism.

Homeostasis is the maintenance of a constant internal environment. e.g. Body temperature, blood glucose concentration & blood water potential

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Receptor

Normal/Ideal condition

Stimulus

Corrective Mechanism

Principle of Homeostasis

Response/Changes

Not normal/ideal

when it becomes

Sends a

to

Activates

Which causes

Which allows condition to go back to

e.g. Excretion

e.g. negative feedback

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What is homeostasis?

•Control and maintenance of a constant internal

environment around the cells in the body

What is negative feedback?

•A feedback mechanism is called negative if the resulting

action opposes the condition that triggers it.

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Excretory organs Lungs

Skin

Liver Kidney

What are the organs involved in maintaining homeostasis in our body?

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Excretory organ

Type of waste excreted

Lungs Carbon dioxide

Kidneys Urea, excess water, mineral salts

Liver Urea

Skin Heat, excess water, mineral salts and urea

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THE SKIN

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Learning Objectives for ‘Skin’

• Identify and label parts of the skin

• Describe the functions of parts of the skin

• Describe the maintenance of a constant body temperature in humans

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4) Hair follicle

6) Sense receptors

7) Blood vessels 8) Hair

9) Sebaceous gland

1) Epidermis

2) Dermis

3) Subcutaneous fat

10) Erector muscle

5) Sweat pore

11) Sweat gland

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Structure of the Mammalian Skin

Skin

What are the 4 general functions of the mammalian skin?

• Excretory organ

• Temperature regulation

• Protective covering

ÞRemoves excess salts, water and urea in the form of sweat

Prevents entry of bacteria, protects from mechanical damage and excessive loss of water by evaporation

• Sense organÞDetect pain, pressure changes and temperature

Þto maintain a constant body temperature

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Structure of Epidermis – Protective Layer

• Outer cornified layer

outer cornified layer

consists of flat, dead cells that continually wear off

prevent bacteria from gaining entry into body

prevent mechanical injury to cells deeper inside skin

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Þcontains living cells which is gradually pushed up to

replace the worn-out cells in the cornified layer

• Granular layer

outer cornified layer

granular layer

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Þcontains actively dividing cells to produce new epidermis

Þcontains melanin pigments that gives skin its colour and

absorbs ultraviolet radiation

• Malpighian layer

outer cornified layer

granular layer

Malpighian layer

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Why do some people have freckles?

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• Due to uneven melanin production.

• More obvious in fair-skinned people.

• Freckles become more prominent when exposed to sunlight because the skin produces extra melanin in sunny conditions.

Why doesn’t bleeding occur when we lightly scratch ourselves sometimes?

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• No blood vessels in epidermis

Structure of dermis:

• Connective tissue with many collagen fibres and elastic

fibres

• Hair follicle and hair

• Sebaceous gland secrete sebum to lubricate skin

ÞDetect pain, changes in temperature and pressure on skin

• Nerve endings

• Erector muscles Controls the erection of hair

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Structure of dermis:

• Sweat gland

• Blood vessels

ÞAbsorbs salts and water from blood capillaries to produce

sweat for temperature regulation and excretion

ÞRegulate temperature by vascular constriction or dilation

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Why do we get pimples?

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• Dead skin cells block hair follicles • sebum builds up in clogged pores • Sebaceous glands continue to produce

sebum but it has no where to go • Sebum becomes infected with bacteria.

Causes clogged pores to become inflamed and swollen. Zits!!!

Why do we get wrinkles and fine lines?

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Fine lines and wrinkles arise because of irregular thickening of the dermis and because of a decrease in the amount of water held by the epidermis. This is mainly caused by sun damage and exposure to environmental toxins such as tobacco smoke.

Why are tattoos permanent?

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What you see when you look at a tattoo is the ink that's left in the skin after the tattooing. The ink is not in the epidermis, which is the layer of skin that we see and the skin that gets replaced constantly, but instead intermingles with cells in the dermis and shows through the epidermis. The cells of the dermis are remarkably stable, so the tattoo's ink will last, with minor fading and dispersion, for your entire life!

Why is the mammalian skin considered as an excretory organ?

The skin produces sweat, which may contain a small amount of metabolic waste product, i.e. urea.

Sweat contains:• water• dissolved sodium chloride• urea

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Sweat is secreted by the sweat gland. It travels through the sweat duct and out onto the skin via the sweat pore.

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Test YourselfWhich part of the skin regulates the following functions?

Sweat glandsBody odour

EpidermisVitamin D synthesis

Subcutaneous fatCalorie reserve

Sebaceous glands Lubrication

Nerve endings Sensation

Subcutaneous fatInsulation

Blood vessels & sweat glands Temperature regulation

Subcutaneous fat Shock absorber

EpidermisProtection from harmful agents of external environment: biological germs, UV light & chemicals

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Which part of the skin contributes to thermal homeostasis?

Body odour

EpidermisVitamin D synthesis

Subcutaneous fatCalorie reserve

Sebaceous glands Lubrication

Nerve endings Sensation

Subcutaneous fatInsulation

Blood vessels & sweat glands Temperature regulation

Subcutaneous fat Shock absorber

EpidermisProtection from harmful agents of external environment: biological germs, UV light & chemicals

Sweat glands

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Q. What do we call animals which keep their body temperature at a roughly constant level, regardless of the environment’s temperature?

Warm-bloodedness generally refers to three separate aspects of thermoregulation.1. Endothermy (control via internal means strictly -

metabolism) 2. Homeothermy (thermoregulation within

regardless of external influence; opposite = poikilothermy)

3. Tachymetabolism (high resting metabolism rate)

Animals

“Warm blooded”/

Homoiothermic

“Cold blooded”/

Poikilothermic

Reptile

Amphibian Invertebrates

Mammals Fish

Birds

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Mechanisms in warm-blooded creatures To generate heat/Keep warm To prevent overheating“Warm-blooded creatrues” • have a larger number of

mitochondria per cell. • need more food needed to

sustain their higher metabolism.

• hibernates/Adjusts body temperature

• Have insulation e.g fur, feathers, fats & blood vessels in lower legs.

• Vasoconstriction in skin

• Panting (water evaporation)• Sweat• Radiators e.g. Elephants flapping their ears to increase the airflow over them• Vasodilation/Flushing

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Arterioles in skin dilate

More blood and more heat send to skin

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Sweat gland active

As sweat evaporates, latent heat lost

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Erector muscle

Erector muscles relax Hair lie flat, close to skin

4 Metabolic rate slows down

Less heat is produced

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Arterioles

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Arterioles in skin constrict Less blood and less heat send to skin

Arterioles

1 2

Sweat gland inactive

Shivering occurs 3

5 Metabolic rate speeds up More heat is produced

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Erector muscles

Erector muscles contract

Hairs trap a layer of air close to skin.

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Hypothalamus

Normal temperature

Stimulus

Principle of Homeostasis

Too Hotwhen it becomes

Heat receptors on skin sends

to

causes

Which leads to

Which allows condition to go back to

Too Cold

Reduced heat loss

Increased heat loss

Which allows condition to go back to

Arterioles constrict

Arterioles dilate

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Summary for ‘Skin’• Parts of the skin consists of the epidermis; dermis; subcutaneous layer Corn|Granular|Malphigian; connective tissues

containing HENSBS• Function of parts of the skin for 1. Maintenance of a constant body temperature

in humans2. Excretion of waste products3. Sense4. Protection

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Recap - What is excretion?

Excretion is the process by which metabolic waste products and toxic materials are removed from the body of an organism.

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Q1. What is metabolism?• Chemical activities of the cells which keep the

organism alive

Anabolic

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Excretion is the process by which metabolic waste products and toxic materials are removed from the body of an organism.

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Anabolic MetabolicCatabolic + =

Metabolic Waste Products• substances left over from excretory processes• cannot be used (surplus/lethal effect)• must be excreted. E.g.Nitrogen compounds, water, CO2,

phosphates, sulfates, medicals, food additives

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Q2. Why must living organisms excrete metabolic waste products?

• Accumulation of these substances – Can interfere with proper functioning of cells– Change the concentration of tissue fluid around

cells

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Q2.1 What is the difference between excretion and egestion?

Excretion ≠ Egestion

(metabolic waste) (undigested waste)

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