physiological homeostasis

7/28/2019 Physiological Homeostasis

1/16

Alford Academy

Higher Biology

Unit 3: Control and Regulation

Physiological HomeostasisChapter 33

1

Name: ________________ Teacher: ________________


2/16

Physiological Homeostasis

Homeostasis literally means staying the same. Physiological homeostasis is

the maintenance of the bodys internal environment within certain tolerable

limits. The community of cells and the tissue fluid that surrounds them are

collectively known as the internal environment.

The following are examples of factors which are controlled by homeostatic

mechanisms:-

Water concentration (Osmoregulation)

Blood sugar levels (Glucose concentration)

Temperature (Thermoregulation)

1) Why does the core body temperature need to be precisely controlled?

2) Why does the water concentration of the blood need to be precisely

controlled?

3) Why does the sugar level of the blood need to be precisely

controlled?

Negative feedback control

The maintenance of homeostasis is by the method of negative feedback. This

means that a change from the norm/set point in one direction automatically

brings about a change in the opposite direction. In order to bring this about

receptors and effectors are needed.

2


3/16

Receptors detect a change from the Norm or Set-Point of the bodys internal

environment. These receptors send nervous or hormonal messages, which arereceived by effectors. The effectors respond which counteracts the original

change, returning the system to the set-point.

Osmoregulation

The water content of the blood is detected by osmoreceptors in the

hypothalamus. If the water content of the blood is low the hypothalamus

triggers the release of Antidiuretic Hormone (ADH) by the pituitary gland.

ADH stimulates the kidney tubules to become more permeable and increases

the volume of water reabsorbed into the blood.

3


4/16

The Kidney

Urinary system Nephron

1. In which part of the nephron does filtration

take place?

2. In which part of the nephron does reabsorption takes place?

3. If you drink a lot of water what happens to the volume and concentration of

the urine you produce afterwards?

4. If you are short of water, perhaps from sweating a lot, what happens to the

volume and concentration of the urine you produce?

4


5/16

Read Torrance page 279 (old), page 307 (new).

Use the following words to complete the exercise: Hypothalamus, less,

pituitary gland, more, sweating, collecting ducts,

When the water concentration of the blood falls, due to for

example, osmoreceptors in the of the brain are

stimulated.

These osmoreceptors stimulate the to release ADH (anti-

diuretic hormone) into the blood. When ADH reaches the kidney it acts on the

5


6/16

tubules and , making them permeable to water.

Due to this, water which would normally have passed along the collecting duct to

become urine is instead reabsorbed into the blood, increasing the water

concentration of the blood to the normal level.

This return to the set point is detected by the osmoreceptors and ADH

production is reduced. This in turn reduces the permeability of the kidney tubules

so that water is reabsorbed into the blood; instead it will pass

through the collecting duct and become urine.

TYK page 280 (old) or page 308 (new)

1a) What is meant by the term physiological homeostasis?

bi) Outline the principle of negative feedback control.

bii) Why is such control of advantage to an organism?

2ai) Where in the human body are the osmoreceptors found that respond to a

decrease in water concentration of the blood?

ii) Which part of the body releases an increased concentration of ADH under

these circumstances?

b) By what means does ADH bring about its effect so that water is conserved

by the body?

6


7/16

3. Compare the relative volume and concentration of urine produced when the

water concentration of the blood is

(i) above the set point

(ii) below the set point

Control of Blood Sugar Level

All respiring cells require a supply of glucose. The nervous system is sensitive to

any reduction in the normal glucose level. A rise in blood glucose level can also be

dangerous.

The supply of glucose varies in mammals because they do not eat continuously and

the quantity of carbohydrate intake changes from meal to meal. There may be

long periods when no glucose is absorbed from the gut into the blood.

Cells require a constant supply of glucose for respiration. A system which

maintains a steady glucose level in the blood despite intermittent supplies from

the gut is required.

If blood sugar levels rise above the set-point, cells in the Pancreas called Islets

of Langerhans detect this change. These cells respond by producing Insulin. This

hormone is transported to the liver in the bloodstream where it activates an

enzyme which catalyses the reaction Glucose Glycogen, this brings the bloodsugar level back to normal.

If blood sugar level drops, different cells in the Islets of Langerhans release

Glucagon. Again this hormone is transported to the liver where it activates a

different enzyme which catalyses the reaction, Glycogen Glucose, bringing theblood sugar level back to normal.

7


8/16

Glucose is stored in the liver as Glycogen. This store can be removed from or

added to.

Diabetes Mellitus

This is a condition in which some or all of the Insulin secreting cells are non-

functional. This causes a rise in blood sugar level causing sugar to be excreted in

the urine, as there is too much to be reabsorbed. This can cause weight loss and

wasting of tissues, however, it can be controlled by Insulin injections and

controlled diet.

Adrenaline

In an emergency, the body may need additional supplies of glucose to provide

energy for fight or flight. Adrenal Glands, which are positioned above the

kidney, release Adrenaline. Adrenaline then overrides normal homeostatic control

of blood sugar level. Insulin is inhibited and Glycogen Glucose is promoted.Once the emergency is over, secretion of adrenaline is reduced and blood sugar

level returns to normal.

Homeostatic control of blood sugar

8


9/16

Complete the following diagram using information from the previous pages and

your Torrance textbook.

TYK page 283 (old) or page 311(new)

1. Hormones are chemical messengers released directly into the bloodstream

by endocrine glands.

Complete the table on the next page using one or more answers from

the list below it

Hormone Endocrine gland that Effect of hormone

9

Normal glucose concentration in

blood

in blood glucoseafter eating food.

Detected by receptor cells

in the

Pancreas produces ____

insulin and glucagon

Excess glucose stored as

glycogen in the

in bloodglucose after exercise.

Glycogen converted into

__________in the liver

Pancreas produces

insulin and glucagon

Detected by receptor

cells in the


10/16

secretes it

Adrenaline

Insulin

ADH

Glucagon

List

A promotes conversion of excess glucose to glycogen

B increases permeability of kidney collecting ducts

C promotes conversion of glycogen to glucoseD decreases blood sugar level

E prepares the body to cope with an emergency

2a) With reference to concentration of sugar in the bloodstream, state the

circumstances that lead to:

(i) glycogen being converted to glucose

(ii) glucose being converted to glycogen

(3) (i) In the homeostatic control of blood sugar level, which organ is the

receptor and which is the effector?

(ii)Suggest why such a corrective mechanism is described as a form of

negative feedback control.

Now answer AYK Question 2 page 289 (old), page 318(new).

Control of body temperature

10


11/16

Ectotherms

These are animals that are unable to regulate their body temperature. This means

that their body temperature varies directly with that of the external

environment. Includes all invertebrates, fish, amphibians and reptiles.

Endotherms

These animals are able to maintain their body temperature despite changes in the

external temperature. All birds and mammals are endotherms. They have a high

metabolic rate, which generates heat energy. Regulation of their body

temperature is brought about by homeostatic control.

Homeostatic control in endotherms

The hypothalamus acts as a receptor in regulation, by detecting fluctuations in

temperature. These receptors are better known as thermoreceptors. The skin

also possesses thermoreceptors,

which can detect the temperature of the external environment. This information

is relayed to the hypothalamus.

The hypothalamus transmits nervous impulses to the skin which acts as an

effector. The hypothalamus also sends messages to other effectors which can

alter the metabolic rate.

Thermoregulation

11


12/16

12


13/16

Role of skin

Correction of overheating

Vasodilation- dilation of arterioles under skin allow more heat to be lost by

radiation.

Increased sweating- brings body temperature down as body heat is used to

evaporate the sweat.

Correction of overcooling

Vasoconstriction-constriction of arterioles under skin means less heat is

lost by radiation.

Decreased sweating-means more body heat is conserved

13

Capillaries receive large volume of

overheated blood

Arterioles become dilated

Nerve impulses from

hypothalamusArteriole Venule

Much heat lost by radiation

Arteriole Venule

Capillaries receive small volume

of blood

Arteriole becomes constricted

Nerve impulses from

hypothalamus

Very little heat lost by radiation


14/16

Contraction of hair erector muscles-hairs rise allowing a layer of air to be

trapped between the skin and external environment. Air is a poor conductor

of heat and acts as a good insulator.

Other corrective mechanisms

Include increase in shivering and metabolic rate when the temperature drops. And

a decrease in metabolic rate when the temperature rises.

Extreme conditions

If exposure is prolonged for example to freezing temperatures, negative

feedback breaks down and can result in death.

Now answer TYK questions 1-4 Page 288 (old), page 317 (new)

Now answer AYK question 5 page 289 (old), page 318 (new).

Control of heat by an ectotherm

14


15/16

1. Describe the changes in the lizard body temperature and in the

environment temperatures as shown by the graph.

2. Explain how posture (A) helps the iguana to warm up.

3. Explain why the iguana takes up the elevated posture (B) when it is warm

enough.

4. Suggest what the iguana could do if its body temperature rose too high.

5.The graph below shows a graph of oxygen consumption and air temperature of an

endotherm and exotherm. Decide which is for the ectotherm and which is

for the endotherm (X or Y) and give reasons for you choice.

X=________________Y = _________________

Explanation: _______________________________________

Physiological Homeostasis

15


16/16

Activity I can find

this in my

notes

I can

do

this

State the meaning of the term "Homeostasis"

State why each of these must be maintained within

particular levels: glucose content of blood; water content

of blood & cell chemicals; temperature

State what is meant by the term "Negative Feedback"

Briefly describe the mechanism of negative feedback in

general terms using points: changes in body's conditions;

receptor sites; messages sent; effectors; initiation of

correcting mechanism; final outcome

Describe how the negative feedback process operates toreturn the water content of blood to normal when the

body has: a) too much water b) too little water

Describe how the negative feedback process operates to

return the blood sugar levels to normal if the body has: a)

too much glucose b) too little glucose

State when the body must release extra adrenaline

Describe the role of adrenaline in glucose metabolism

Describe how the negative feedback process operates to

return the body temperature to normal when:a) the body

is too hot b) the body is too cold

Define the terms "endotherm" and "ectotherm" and give

examples of each

physiological homeostasis

Documents