Chapter 15: Regulatory mechanisims in animals

Question 1

Hormones

Answer 1

intercellular messengers that modify the activity of specific receptor cells

Question 2

Neurons

Answer 2

excitable cells that conduct impulses along their axon membranes

Question 3

Regulatory pathways

Answer 3

Animals coordinate the activities of their cells, and respond to outside stimuli using both their nervous and endocrine (hormonal) systems. Responses often occur to achieve homeostasis – a stable internal environment. Negative feedback systems are stimulus-response models (STIMULUS—Receptor—-Control Centre—Effector—RESPONSE) that result in the reduction of the effect of the stimulus.

Question 4

Homeostasis

Answer 4

a stable internal environment

Question 5

Negative Feedback

Answer 5

Negative feedback systems are stimulus-response models (STIMULUS—Receptor—-Control Centre—Effector—RESPONSE) that result in the reduction of the effect of the stimulus.

Question 6

Hormonal Pathways

Answer 6

Hormones are produced in one part of an organism, then they travel in the internal transport system to transmit their signal to target cells which have a specific receptor. Hormones are highly specific and are only released when there is a particular stimulus and only target very specific cells. Hormones are generally slower than nervous system response as they travel to their target organs in the bloodstream.

Question 7

Types of Hormones

Answer 7

• Fat based: synthesised from fatty acids which are small and lipid-soluble and can therefore pass through the plasma membrane
. • Protein based: synthesised from amino acids are water-soluble so can’t pass through the plasma membrane.

Question 8

5 Endocrine Glands

Answer 8

Pituitary, Thyroid, Adrenal, Ovaries, Testes. Pituitary gland although small is involved in about half of all hormone activity in mammals.

Question 9

Pituitary

Answer 9

The pituitary gland is a pea-sized structure located at the base of the brain, just below the hypothalamus, to which it is attached via nerve fibres.

• The anterior lobe is mainly involved in development of the body, sexual maturation, and reproduction. Hormones produced by the anterior lobe regulate growth, and stimulate the adrenal and thyroid glands, as well as the ovaries and testes. It also generates prolactin, which enables new mothers to produce milk.
• The intermediate lobe of the pituitary gland releases a hormone that stimulates the melanocytes, cells which control pigmentation — like skin color — through the production of melanin.
• The posterior lobe produces antidiuretic hormone, which reclaims water from the kidneys and conserves it in the bloodstream to prevent dehydration. Oxytocin is also produced by the posterior lobe, aiding in uterine contractions during childbirth and stimulating the production and release of milk.

Question 10

Thyroid

Answer 10

The thyroid gland is a butterfly-shaped organ located in the base of your neck. It releases hormones that control metabolism—the way your body uses energy. The thyroid's hormones regulate vital body functions, including:
•Breathing
•Heart rate
•Central and peripheral nervous systems
•Body weight
•Muscle strength
•Menstrual cycles
- Body temperature
- Cholesterol

Question 11

Adrenal

Answer 11

The adrenal glands are two glands that sit on top of your kidneys that are made up of two distinct parts.
•The adrenal cortex—the outer part of the gland—produces hormones that are vital to life, such as cortisol (which helps regulate metabolism and helps your body respond to stress) and aldosterone (which helps control blood pressure).
•The adrenal medulla—the inner part of the gland—produces nonessential (that is, you don’t need them to live) hormones, such as adrenaline (which helps your body react to stress).

Question 12

Ovaries

Answer 12

The ovaries have two main reproductive functions in the body. They produce oocytes (eggs) for fertilisation and they produce the reproductive hormones, oestrogen and progesterone. The function of the ovaries is controlled by gonadotrophin-releasing hormone released from nerve cells in the hypothalamus which send their messages to the pituitary gland to produce luteinising hormone and follicle stimulating hormone. These are carried in the bloodstream to control the menstrual cycle.

Question 13

Testes

Answer 13

The testes have two functions - to produce sperm and to produce hormones, particularly testosterone.

Question 14

The Nervous System

Answer 14

Nervous system is composed of neurons which send electrical messages to specific effector cells via other neurons. Dendrites collect message, which then passes along axon and is passed on from axon terminals. Axon insulated by myelin sheath. Nervous responses are very quick however they require more energy than hormonal responses.

Question 15

2 Parts of the Nervous System in mammals

Answer 15

• central nervous system (CNS) composed of the brain and spinal cord, and the
• peripheral nervous system (PNS) which encompasses the rest of the neurons in the body.

Question 16

Central Nervous System

Answer 16

CNS: Spinal Cord & Brain (includes parts such as cerebral cortex, hypothalamus, cerebellum & brainstem).

Question 17

Peripheral Nervous System

Answer 17

PNS: sensory neurons, motor neurons which can be somatic (voluntary) or autonomic (involuntary).

Question 18

Autonomic Nervous System

Answer 18

Autonomic nervous system: Unconscious responses. Can be split into the sympathetic division which generally increases energy use, and the parasympathetic division which works to conserve energy. Third part of Autonomic nervous system is the enteric nervous system which controls the functions of the gut.

Question 19

What is a Reflex Response

Answer 19

Reflexes are very quick, unconscious, and automatic responses to stimuli

Question 20

Process of a reflex response

Answer 20

Generally involves a sensory neuron which receives the stimulus, an interneuron which passes the message on to, a motor neuron which generates a response from a muscle. Many reflex actions are very complicated and involve a number of neural pathways to achieve the desired response

Question 21

3 Major Sense organs and their functions

Answer 21

• Vision: Photoreceptors collect light information. -Hearing: Sound waves detected by mechanoreceptors. -Taste and Smell: Chemoreceptors detect the different chemicals in food and the air.

Question 22

What are Neurons

Answer 22

In the body neurons are bundled together to form a nerve.

Question 23

How do Neurons send messages electrically

Answer 23

1. Generate an impulse (action potential) via sensory neurons. Stimulation of sensory neurons causes them to become slightly more negative (depolarised) if this is big enough an action potential is generated.
2. Conduct the impulse along the axon. Na+ and K+ ions flow into and out of the neuron through protein channels in a wave along the axon.
3. Transmit the signal across synapses. When the action potential arrives at the axon terminal it triggers the release of vesicles containing neurotransmitters. These small molecules cross the small space between neurons (synapse) to bind to specific receptors to continue the message.