Ch. 40 – animal form and function

Overview

Animals inhabit almost every part of the biosphere (earth, water, and air – basically the planet)

All animals face a similar set of problems (food, shelter, water, space)

When you look at and study animals, you can see that form and function are closely related, which is what helps them address their problems (food, shelter, water, space)

Physical laws and the environment constrain animal size and shape Physical laws and the need

to exchange materials with the environment place limits on the range of animal forms (like size)

The ability to perform certain actions depends on an animal’s shape and size

Evolutionary convergence reflects different species’ adaptations to a similar environmental challenge (for example, most animals that live in water all have certain features in common)

Exchange with the environment An animal’s size and shape directly

affect how it exchanges energy and materials with its surroundings

Exchange occurs as substances dissolved are transported across the cells’ plasma membranes

EXAMPLES: A single-celled protist living in water

has a sufficient surface area of plasma membrane to service its entire volume of cytoplasm

Multicellular organisms with a sac body plan (like the hydra or jellyfish) have body walls that are only two cells thick, facilitating diffusion of materials

A tapeworm is very thin, so as it sits in the intestinal juices of it’s host it can easily diffuse nutrients

More complex organisms have highly folded internal surfaces for exchanging materials (like the intestines).

*This is an important tie-in to past concepts, like respiration, surface area, and the cell membrane

Diffusion

Mouth

Diffusion

Two cell layersSingle cell

Diffusion

Gastrovascularcavity

Digestivesystem

Circulatorysystem

Excretorysystem

Interstitialfluid

Cells

Nutrients

Heart

Animalbody

Respiratorysystem

Bloo

d

CO2FoodMouth

External environment

O2

50 µ

m

A microscopic view of the lung reveals that it is much more spongelike than balloonlike. This construction provides an expansive wet surface for gas exchange with the environment (SEM).

10 µm

Inside a kidney is a mass of microscopic tubules that exchange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM).

The lining of the small intestine, a digestive organ, is elaborated with fingerlike projections that expand the surface area for nutrient absorption (cross-section, SEM).

Unabsorbedmatter (feces)

Metabolic wasteproducts (urine)

Anus

0.5 cm

Animal Form and the Levels of Organization The levels of organization

are: Cell-tissue-organ-organ

system-organism Most animals are

composed of specialized cells (eukaryotic) organized into tissues

Different tissues have different structures that are suited to their functions

Tissues are classified into four main categories: epithelial, connective, muscle, and nervous

Tissues Epithelial tissue covers the outside of

the body and lines the organs and cavities within the body (first line of defense against foreign invaders)

Connective tissue mainly binds and supports other tissues (Ligaments are an example)

Muscle tissue consists of long cells called muscle fibers, which contract in response to nerve signals. It is divided in the vertebrate body into three types: Skeletal (voluntary actions,

striated, attached to bone), Cardiac (found in the walls of the

heart) smooth (found in hollow organ

cavities like the stomach , bladder, and uterus; involuntary actions)

Nervous tissue senses stimuli and transmits signals throughout the animal Brain, spinal cord

Organ Systems

These are groups of organs working together to perform a specific function

Organ systems carry out the major body functions of most animals

11 organ systems are found in the human body

How many organ systems and their functions can you name?

Organ Systems

• Digestive System: mouth … anus

• Circulatory System: heart, blood vessels, blood

• Respiratory System: lungs, trachea, other breathing tubes

• Immune and Lymphatic System: marrow, lymph nodes, spleen, WBC

• Excretory System: kidneys, ureters, bladder, urethra

• Endocrine System: hormone-secreting glands

• Reproductive System: ovaries, testes, etc.

• Nervous System: brain, spinal cord, nerves

• Integumentary System: skin and its derivatives

• Skeletal System: bones, tendons, ligaments, cartilage

• Muscular System: skeletal muscles

Using Energy in Food

All organisms require chemical energy for growth, repair, physiological processes, regulation, and reproduction (you are what you eat)

Bioenergetics (the flow of energy through an animal – how living things make use of free energy), limits behavior, growth, and reproduction

It determines how much food an animal needs

Studying bioenergetics tells us about an animal’s adaptations

Bioenergetics cont.

We are constantly burning ATP (free-energy), and if we don’t do that, we die

Remember the laws of thermodynamics? (1st – law of conservation of energy; we can convert energy, but not destroy it. 2nd – with each reaction, we release some heat, which increases entropy)

Energy sources and allocation (how to get it) Animals harvest chemical

energy from food (heterotrophs)

Energy-containing molecules from food are usually used to make ATP, which powers cellular work (through cellular respiration)

After the needs of staying alive are met, remaining food molecules can be used in biosynthesis (creating chemical compounds in a living organism – basically making more cells)

Metabolism Metabolism is how

quickly an organism consumes energy

Metabolic rates are affected by many factors, including whether an animal is an endotherm (create their own heat) or ectotherm (use heat from their surroundings), size, and activity levels

Relationship between metabolism and size larger organisms have low

metabolisms compared to a smaller organism

Basically the smaller organism has a harder time maintaining homeostasis because it loses a lot of heat

*we’ll talk about ectotherms and endotherms later in these notes (during thermoregulation)

Use of energy is partitioned to activity, homeostasis, growth, and reproduction

Homeostasis

The internal environment of vertebrates is called the interstitial fluid and is very different from the external environment

Homeostasis is a balance between external changes and the animal’s internal control mechanisms that oppose the changes

This is our ability to maintain a stable internal environment regardless of outside conditions

Homeostasis – positive and negative feedback loops Humans use feedback loops to

maintain homeostasis (in our house we use a thermostat)

All loops have a receptor (the thermostat, or what receives the signal), and effectors (what’s affected by a change in a stimulus – the thermostat will turn off or on, depending on the temp.)

Overview – positive and negative feedback loops in homeostasis A negative feedback

loop brings you closer to a set target point (temperature regulation is an example)

A positive feedback loop amplifies or moves you away from a set target point (fruit ripening is an example)

Alterations are mistakes in the feedback loops (diabetes is an example – problems sensing insulin)

4 Important Homeostatic Mechanisms (that use feedback loops) Thermoregulate (Maintain

temp)– controlled by hypothalamus

Blood glucose (gives us the fuel for our cells) – controlled by the pancreas

Blood calcium (used for our nerves, muscles) – controlled by thyroid and parathyroid

Osmolarity (concentration of the blood – remember hypotonic and hypertonic?) – controlled by hypothalamus and pituitary

We’ll talk about the first two feedback loops in the next several slides, as well as a couple of others that are on your standards

Feedback loops – positive feedback Positive feedback: this is when you

overshoot your target – produce too much of something

Used when we want something to happen quickly – it usually doesn’t go on for a long period of time.

Examples:

If you wanted fruit on a tree to ripen (and they do this to attract animals that will spread the seeds), the plants communicate by releasing ethylene (remember your plant hormones?), which causes the fruit to ripen at the same time. This causes amplification, so as the fruit ripens, more and more fruit ripens

Childbirth – the pressure of the babies head on the cervix causes contractions, which puts more pressure on the cervix, which causes more contractions (until the baby is born)

Feedback Loops cont. – blood glucose (when things go wrong) Examples of negative

feedback – glucose levels and diabetes

Your pancreas helps put digestive enzymes into your small intestine to help break down food, but they also help regulate glucose levels.

They have two types of cells – beta and alpha – whose major jobs are to sense the glucose level in your blood.

Feedback Loops cont. – blood glucose (when things go wrong) If we have a lot of blood glucose, the

beta cells sense that and it causes our body to release some calcium and insulin (so when the blood glucose is high, insulin is released from the pancreas, spreads through the body, and it tells our cells to absorb the glucose. (It also tells our liver to store it as glycogen).

This causes our blood glucose to go down.

When those levels go down, the body stops producing insulin, and the alpha cells tell the body to start producing glucagon, which increases the blood glucose level.

When you increase glucose, there is an increase in insulin – when glucose levels fall, insulin levels fall

Feedback Loops cont. – blood glucose (when things go wrong) In a diabetic (type I) the beta

cells don’t work. That means when the blood glucose goes up, there’s nothing there to tell the body to secrete insulin, so the glucose continues to go up. This increases blood pressure, nausea, blindness, and death.

Type II diabetics (consume too much glucose in your life, not enough exercise) – your body stops recognizing insulin and therefore stops taking it in. They have to take insulin shots throughout the day (usually around mealtimes)

Thermoregulation – aiding in homeostasis Thermoregulation

is the process by which animals maintain an internal temperature within a tolerable range

Thermoregulation - overview There are a few basic ways to

transfer heat: Conduction- (direct contact

(you actually touch a flame Convection – movement of

heat through air and fluids (heater)

Radiation – transfer of heat through empty space (sun to the earth)

Respiration – though metabolism we can generate heat

(the book also mentions evaporation, which is the removal of heat from the surface of a liquid that’s turning to gas – like when you sweat)

Thermoregulation cont. Life has evolved a couple of different

strategies to interact with heat:

1. Ectotherm (heat from outside) – they derive their temp from their surroundings.

Advantages – don’t need to burn up energy to create energy

Disadvantage – if it’s really cold, your body processes slow down too

*tend to have a lower metabolism

In general, ectotherms tolerate greater variation in internal temperature than endotherms

2. Endotherms – generate heat inside of them (metabolism)

Advantages – internal temp. is always the same

Disadvantage – constantly need to eat to maintain temp.

*tend to have a higher metabolism

Balancing Heat Loss and Gain In thermoregulation,

physiological and behavioral adjustments balance heat loss and gain

Five general adaptations help animals thermoregulate: Insulation Circulatory adaptations Cooling by evaporative

heat loss Behavioral responses Adjusting metabolic

heat production

thermoregulation cont. -(negative feedback )

Humans (and all endotherms) use a negative feedback loop to maintain a constant body temp (approx. 98 degrees F)

If you get too hot, your hypothalamus (in your brain) senses the change, and causes you to sweat , and blood is carried to the surface of your skin through vasodilatation, which cools your blood through convection. You also sweat, which cools through evaporation

If you get too cold, then you start to get goose bumps (which causes hair to stand up and contracts your skin), blood gets pulled closer into your body, called vasoconstriction (decreasing convection), and you can shiver to create heat.

Insulation

Insulation is a major thermoregulatory adaptation in mammals and birds

It reduces heat flow between an animal and its environment

Examples are skin, feathers, fur, and blubber

In mammals, the integumentary system acts as insulating material

Circulatory Adaptations

Many endotherms and some ectotherms can alter the amount of blood flowing between the body core and the skin

In vasodilatation, blood flow in the skin increases, facilitating heat loss

In vasoconstriction, blood flow in the skin decreases, lowering heat loss

Circulatory Adaptations cont Many marine mammals and birds have an arrangement of blood vessels called a countercurrent heat exchanger

Countercurrent heat exchangers are important for reducing heat loss

Arterial blood leaves the bird’s core at a warm body temperature, while venous (returning) blood in the bird’s foot is quite cool.

As cold blood runs up the leg from the foot and passes by the arteries, it picks up most of the heat from the arteries via conductance.

As it travels, the blood flowing down is cooled, and the blood flowing up is warmed.

Thus, by the time arterial blood reaches the foot, it is cool and does not lose too much heat in the cold water, and venous blood reaching the core has already been warmed, helping maintain core heat.

Cooling by Evaporative Heat Loss Many types of

animals lose heat through evaporation of water in sweat

Panting augments the cooling effect in birds and many mammals

Bathing moistens the skin, helping to cool an animal down

Behavioral Responses

Both endotherms and ectotherms use behavioral responses to control body temperature

Some terrestrial invertebrates have postures that minimize or maximize (or minimize) absorption of solar heat

Acclimatization

In acclimatization, many animals adjust to a new range of environmental temperatures over a period of days or weeks

Acclimatization may involve cellular adjustments or (as in birds and mammals) adjustments of insulation and metabolic heat production

Torpor and Energy Conservation Torpor is a physiological

state in which activity is low and metabolism decreases

Torpor enables animals to save energy while avoiding difficult and dangerous conditions

Hibernation is long-term torpor that is an adaptation to winter cold and food scarcity

Estivation, or summer torpor, enables animals to survive long periods of high temperatures and scarce water supplies

Daily torpor is exhibited by many small mammals and birds and seems adapted to feeding patterns