Chapter 5.1 - HOMEOSTASIS

Question 1

Define Homeostasis

Answer 1

Homeostasis is the MAINTENANCE of a relatively CONSTANT INTERNAL ENVIRONMENT, DESPITE FLUCTUATIONS in the EXTERNAL ENVIRONMENT.

• THE PROCESS OF KEEPING THE ENVIRONMENT INSIDE THE BODY FAIRLY CONSTANT.

Question 2

Why is Homeostasis Important?

Answer 2

1. Cells of the Body, work best in particular conditions. Maintaining optimal conditions ensures optimal enzyme action throughout the body, as well as all cell functions.
   - body’s cells are surrounded by fluid, the composition, and temperature of which must be maintained within very narrow limits.
2. Helps us to be INDEPENDENT of our EXTERNAL ENVIRONMENT, therefore organs and cells will function normally when there is a change in the external environment.

Question 3

The important aspects of the internal environment that the body needs to regulate include:

Answer 3

1. core body temp
2. pH and Cont. of dissolved subst. in body fluids
3. Cont. of glucose in the blood
4. Cont. of O2 and CO2 in blood and other body fluids
5. Blood pressure
6. Cont. of Metabolic wastes

Question 4

Define Steady State:

Answer 4

same as homeostasis

Question 5

How is this steady state maintained?

Answer 5

• does not mean nothing changes
• there is DYNAMIC EQUILIBRIUM in which INPUT and OUTPUT of MATERIALS AND ENERGY ARE BALANCED.
• All body systems contribute to homeostasis via supplying for cells’ needs and maintain a constant cellular environment
• to maintain homeostasis, the body must SENSE CHANGES in the internal and external environment and COMPENSTATE for those changes.
  Via ENDOCRINE AND NERVOUS SYSTEM which are the main body sensory and body control systems.

Question 6

Define Feedback Systems:

Answer 6

A circular situation where the response to a stimulus changes the original stimulus.

Two types
- positive and negative

Question 7

Define Stimulus:

Answer 7

Any change, internal or external that causes a response

Question 8

Define Steady State control system:

Answer 8

A negative feedback system that maintains homeostasis.

Question 9

Define Set point:

Answer 9

In a feedback system, the level at which a variable is to be maintained

Question 10

Define Positive Feedback System:

Answer 10

Feedback that REINFORCES the original stimulus.

• they usually do not occur to result in homeostasis, but in a few situations, it does occur where it is important in controlling processes that must be completed quickly

Question 11

Define Negative feedback system:

Answer 11

Feedback that REDUCES the effect of, or ELIMINATES, the original stimulus.

Question 12

What is a Model?

Answer 12

A simplified representation of an idea or a process: eg. diagram, flow chart, a simplified description of a complex situation or physical model.

examples: the model of a cell, lock-and-key model for enzyme action, stimulus-response-feedback

Question 13

What is a Modulator?

Answer 13

A control center responsible for processing information received from a receptor and for sending information to the effector.

Question 14

What are the Common Features of FEEDBACK SYSTEMS?

Answer 14

1. STIMULUS - change in the environment that cause the system to operate
2. RECEPTOR - sensory cells DETECT the stimulus
3. MODULATOR - control centre responsible for processing information received from the receptor and for sending information to the effector.
   (message received before, and message sent after)
4. EFFECTOR - Muscles or glands receive the message from the modulator, CARRIES OUT A RESPONSE COUNTERACTING or ENHANCING the effect of the stimulus.
5. FEEDBACK - the response changes the original stimulus

Question 15

What is Dynamic Equilibrium

Answer 15

A state reached when the rates of forward and reverse changes are equal: a stable, balanced or unchanging system results.

Question 16

Define Tolerance Limit

Answer 16

The limit of factors such as the body temperature and fluid balance beyond which the body malfunctions.

Question 17

Examples of negative feedback systems in the body

Answer 17

1. Exercise
   Muscles use glucose to release the energy required for muscle contraction.
   Muscles absorb glucose from the blood and, consequently, the blood glucose level tends to fall.
   - STIMULUS
   The liver responds by releasing more glucose into the blood.
   Thus the response has caused the blood glucose level to go up, which is the OPPOSITE of the fall in glucose that initiated the response.
   This way the blood glucose level is maintained within a range that is acceptable for efficient cellular functioning.
2. Getting Cold
   and putting a jumper on

Question 18

How are homeostatic mechanisms controlled in the body?

Answer 18

Nervous and Endocrine system.

• both detect when the body is beginning to deviate from its normal balanced state
• nervous system sends electrical messages to the appropriate organs so that the change is counteracted
• the glands of the endocrine system secrete chemical messengers, or hormones into the blood (works more slowly than nerve impulses when coordinating homeostasis.)

Question 19

Examples of positive feedback systems in the body - CHILDBIRTH

Answer 19

CHILDBIRTH - needs to be completed rapidly to avoid stress and injury to the mother and baby

1. labor is initiated by the secretion of the oxytocin hormone from the posterior lobe of pit. gland.
   Oxytocin causes contractions of the uterus, which push the baby’s head against the mother’s cervix. (Stimulus)
2. the simulation of the cervix causes it to send nerve impulses to the brain, which responds by instructing the pit. gland to secret more oxytocin.
3. the increased oxytocin makes the uterus contract more strongly which pushes the baby’s head more forcibly against the cervix, which sends more impulses to the brain, thus uterine contractions are increasingly intensified.
4. ONCE BABY IS DELIVERED THE CERVIX IS NO LONGER STRETCHED: IT CEASES SENDING NERVE IMPULSES TO THE BRAIN AND THE POSITIVE FEEDBACK CYCLE STOPS

Question 20

Examples of positive feedback systems in the body - BLOOD CLOTTING

Answer 20

BLOOD CLOTTING - completed quickly to minimise blood loss

Question 21

Examples of positive feedback systems in the body - FEVER - dangerous

Answer 21

Can be harmful.

High fever

• small rise in body temp can be beneficial in fighting infection: however, if body temp causes a higher metabolic rate that produces more heat, which raises the temp still further.
• this increases the metabolic rate and so the temp spirals upwards.

unless medical treatment is given death will result when the body reaches about 45 degrees Celcius.