Regulatory System in

Animal- Internal Environment

- Homeostasis- Negative Feedback

Internal Environment• In an adult, the total amount of water

is approximately 60% of his/her body weight.

• Internal environment of animals = the extracellular fluid environment (the outside of the cells in the body)

How do we maintain the internal

environment?• Diffusion

• Refers to the passive transport of the substance from a higher concentration to a lower concentration (we call this difference concentration gradient)

• However, only small non-polar molecules (i.e. oxygen, carbon dioxide) can pass through our membrane.

• Other substances require extra assistance (i.e. protein channels, carrier proteins) to diffuse across the membrane, and we call this kind of diffusion facilitated diffusion

• Diffusion/Facilitated diffusion do not require any energy.

Osmosis• Osmosis is a special case of

diffusion. It refers to the net movement of free water molecules across the membrane.

• What is the net movement of the water molecules in this case?

• Water molecules are moving from left to right (along its own concentration gradient) OR from a dilute solution to a concentrated solution

• The concentration gradient of WATER is known as osmotic gradient.

• The pressure that cause the water to move along the osmotic gradient is called osmotic pressure

Biological Properties of Diffusion

• Molecules always move down a concentration gradient (from high to low concentration)

• Molecules diffuse along their own concentration gradient, independent of other molecules

• Diffusion rates are higher at higher temperatures

• Diffusion rates are faster when the concentration gradient is greater

• Thicker barriers slow diffusion

Net Movement of Water

• Tonicity: is a measure of the difference between the osmotic pressure across the membrane

• Hypertonic: higher concentration of solute molecules (lower concentration of water molecules)

• Hypotonic: lower concentration of solute molecules (higher concentration of water molecules)

• Isotonic: the concentrations of the solute and water are equal

• Q1. Osmosis is best defined as the movement of•  A) molecules from an area of high concentration to an area of lower concentration.

• B) molecules from an area of low concentration to an area of higher concentration.

• C)water molecules across a membrane from an area of low water to an area of higher concentration.

• D)water molecules across a membrane from an area of high water concentration to an area of lower concentration.

• E)water molecules inside a container.

• Q2. Which of the following pass through a cell membrane the most easily?• A) Small polar molecules

• B) Small non-polar molecules

• C) Large polar molecules

• D) Large non-polar molecules

• Q3. A red blood cell placed in a hypotonic solution will

• A) expand

• B) burst

• C) have no change

• D) shrink

• Q4. A 5% urea solution is hypotonic to a 10% urea solution

• A) true

• B) false

• Q5. If a cell is placed in a isotonic solution, there will be no net movement of the water

• A) true

• B) false

HOMEOSTASIS• Refers to the maintenance of the internal

environment, despite of the external changes, within an organism

• WHY do we need homeostasis?

• Mechanism maintaining homeostasis (stimulus-response mechanism)

Homeostasis can be regulated by the release of hormones from glands into the blood stream

Negative Feedback System

• Regulates secretion of almost every hormone

• Involves nervous and/or hormonal systems

• The response provides feedback that has a negative effect on the stimulus

• Heating systems in your home SET POINT

• The regulations happen within our tolerance range (i.e. Our body temperature fluctuates between 36.0 - 37.9 degrees.).

Hormonal Pathways

• Hormones act as intercellular messengers to regulate cell functions

• Hormones travel along the blood stream to all parts of the body and reach their target cells

• DIRECTLY – passing through cell membrane

• INDIRECTLY – interacting with a receptor outside the cell

• Effective in low concentrations

• They are very SPECIFIC! – Most hormones affect specific organs and often only one type of cell within that organ.

• Hormonal effects are generally slower than nervous responses, longer in duration and often affect cells that are widely distributed throughout the body.

Types of Hormones

• Lipid-soluble/Fatty acid-based hormones: steroid hormones

• Water-soluble/Protein-based hormones: adrenaline

• Which of these act directly to target cells? (Hint: cell membrane structure)

Summary • It is important for the animals to maintain a stable internal

environment within their tolerance range (homeostasis).

• Internal environment of animals = the extracellular fluid environment (the outside of the cells within the body)

• Small molecules travel across cell membranes by diffusion/facilitated diffusion. Water molecules travel across cell membranes by osmosis

• Some biological properties of diffusion

• Tonicity is a measure of the difference between the osmotic pressure across the membrane

• Net water movement in a hypotonic, hypertonic and isotonic solution

• Negative feedback system regulates the secretion of almost every hormone.

• Lipid-soluble hormones can assert their effect by entering the cell membrane directly; while water-soluble hormones need to bind to a receptor outside the cells to regulate cell functions

• The hormonal pathways are very specific, and are generally slower than nervous responses

Endocrine System VS. Nervous System

Endocrine Glands

• Release hormones directly into the circulatory system

The ‘Master Gland’ –Pituitary Gland

• Release more than half of the hormones in mammals

• Involved in the regulation of growth, reproductive state, skin pigmentation, fat tissue, kidney function, and the activities of the thyroid and adrenal glands

Hypothalamus

• Receive information from all parts of body, relating to food and water satiety, smell, pain and emotions

• The information it receives is used to regulate secretion from the pituitary gland

• The hypothalamus contains neurons that control the release of hormones from the pituitary

• The posterior pituitary releases hormones in the blood circulation that are produced in nerve cells in the hypothalamus

Hypothalamus

• The hypothalamus-releasing hormones (TRH) travel in small blood vessels from the hypothalamus to anterior pituitary, where they pass out and trigger the release of anterior pituitary hormones (TSH) into the thyroid gland

• http://www.youtube.com/watch?v=Vae5CcaPN_8

• Simple flow chart (Figure 15.4, p.283)

Nervous System• The nervous system involves more

direct pathways between parts of the body, and the responses are much faster than hormonal responses.

• It performs three basic functions:

1. Receive sensory inputs from internal and external environments

2. Interpret the input

3. Respond to stimuli

• It is often interpreted with the endocrine system to maintain a stable internal environment as well as to respond to the external environment

Functional Units of the Nervous System

• The neuron is the functional unit of the nervous system. Humans have about 100 billions neurons in their brain alone

• They generate electric signals from one part of the body to another

• All neurons have dendrites, cell body and axons

Functioning Neurons• Dendrites receive and carry

impulses to the cell body

• Axons carry the impulses from the cell body to the next neuron

• There is only ONE axon leaving each cell body each time, but there can be many dendrites carrying impulses towards the cell body

• The axons travel along the nerves, axons are often (not all) wrapped around by a fatty acid sheath called myelin

Neurons are excitable cells

• The membrane of the neurons, like all other cells, has unequal distribution of charges between the two sides of the membrane.

• The inside of the cells is negative with respect to the outside of the cell

• In excitable cells, ions can move across the membrane causing a change in the level of polarisation

• There are three basic steps involved in the function of neurons:

• 1. generation of a nerve impulse (action potential) by sensory neurons

• 2. conduction (propagation) of an impulse along axons

• 3. chemical transmission of a signal to another cell across a synapse.

1. Generation of the Action Potential

• An action potential (nerve impulse) is a wave of electrical change that passes rapidly along an axon membrane

• Stimulus need to be strong enough to reach the threshold potential of the cell

• Stimulation of the sensory receptors causes Na+ coming into the cells, initiating action potential

• Once the cell has become positive (briefly), K+ will then leave the cell, bringing the cell back to negative again (down to the original).

• The action potential begins at one spot of the membrane, but spreads to the nearby area of the membrane propagating the length of message along the membrane

• A region that has just generated an action potential cannot produce another action potential for a brief period, which is called the refractory period.

2. Conduction of an Action Potential

• How do we increase the rate of conduction?

• Increased diameters and increased insulation.

• Myelin sheaths increase insulation

• Myelin sheath only present in PNS neurons but not in CNS

3. Synaptic Transmission

• Synapse: a junction between one nerve cell and another cell

• Arrival of the action potential causes some of the vesicles containing neurotransmitter to release their contents into the synaptic cleft

• The neurotransmitter diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane.

• Released neurotransmitters are quickly inactivated by being either broken down or taken back up into the nerve

Central Nervous System

• Central nervous system (CNS) includes the brain and the spinal cord

The cerebral cortex is responsible for motor activity, sensory input, speech, sight and hearing

The hypothalamus receives information relating to the well-being of the body, and functions in maintaining homeostasis

The cerebellum is responsible for coordination of muscular activity, including posture, balance and movement

The brainstem has a role in the control of the heart, blood vessels and lung ventilation

• Peripheral nervous system (PNS) includes all the nerves that are outside the brain and the spinal cord

The peripheral nervous system includes sensory nerves and motor nerves

Somatic Nervous System

• Somatic Nervous System: includes all nerves controlling the muscular system and external sensory receptors.

• Reflex: nerve pathway that produces an unconscious ‘automatic’ response to a stimulus, often very rapid. It is the simplest nervous response in an animals

• In general, a sensory neuron detects a change and sends a signal (sometimes via another neuron) to an effector cell, which produces a response

• The knee-jerk reflex usually involves two neurons, which is known as a monosynaptic reflex. Sometimes reflex response involves one extra interneuron in the central nervous system between the sensory neuron an the motor neuron (in the withdrawal reflex)

Autonomic Nervous System

• The autonomic nervous system is the part in PNS including the motor neurons that control the internal organs

• It is consisted of two major subdivisions: sympathetic division and parasympathetic division

• Sympathetic division increases energy use and prepares the body for action in emergencies by increasing the heart and metabolic rate (fight responses)

• Parasympathetic division enhances activities that conserve energy, such as digestion and slowing the heart rate (relaxation responses)

Major Sensory Organs

Five Senses (Sense Organs)

Sensory Receptors

Vision (Eyes) Photoreceptors (light-senistive cells)

Hearing (Ears) Mechanoreceptors (vibration-sensitive cells)

Taste (Tongue) Chemoreceptors (chemical-sensitive cells)

Smell (Nose) Chemoreceptors (chemical-sensitive cells)

Touch (Skin) Mechanoreceptors (detect external pressure)Sensory neurons (detect internal stimuli such as muscle tension)Thermoreceptors (detect temperature changes)

Summary• Endocrine glands release hormones directly into the

circulatory system (i.e. thyroid glands, anterior pituitary gland)

• Pituitary gland is involved in the regulation of growth, reproductive state, skin pigmentation, fat tissue, kidney function, and the activities of the thyroid and adrenal glands.

• The hypothalamus receives information from all parts of body, which is used to regulate the release of hormones from the pituitary gland.

• The nervous system involves more direct pathways between parts of the body, and the responses are much faster than hormonal responses.

• The neuron is the functional unit of the nervous system

Is the room temperature close to our body

temperature ?

Case Study: Blood Glucose Regulation

Set points and optimum conditions are maintained

through negative feedback.

Negative feedback is extremely important in homeostasis as the response is always to restore the internal environment back to a constant set of conditions.

Blood Glucose Level

Blood Glucose Level

• Stimulus

• Receptors

• Control Center

• Effector

• Response

Diabetes Mellitus• Diabetes mellitus is a condition in which the body is unable to

regulate blood glucose levels, resulting in too much sugar in the blood.

• Type 1 Diabetes – problem in the insulin signalling pathway –insulin not produced. About 5 -10% of diabetics are type 1 or insulin dependent and require regular injections of insulin

• Type 2 Diabetes - cells of the muscles and liver not responding adequately to insulin – a breakdown in the signal transduction pathway of the target cells. About 90 – 95% of diabetics are type 2 and is genetic or linked to weight and life-style. These people may still produce insulin in normal quantities but their cells can not produce the correct response. Insulin injections may be useless, but regulation of diet and exercise may control blood glucose levels.

Diabetes Mellitus

• Hyperglycaemia – higher than normal blood glucose levels – may lead to coma and death. Requires insulin injection

• Hypoglycaemia – lower than normal blood glucose levels. Requires ingestion of glucose eg jelly-beans.

• Over time high blood glucose levels may cause complications of damage to the eyes, nerves and kidneys and damage to blood vessels leading to an increase in the risk of heart attack, stroke, impotence, and foot damage leading to amputation. This damage can occur before the person knows they have diabetes.

Summary• Blood glucose level is regulated by negative feedback system

• Pancreas is the receptor AS WELL AS the effector

• Two types of cells in pancreas: alpha cells (produce glucagon); beta cells (produce insulin)

• Blood glucose too high insulin > glucagon cells take up glucose

• Blood glucose too low insulin < glucagon glycogen converted to glucose

• Type 1 diabetics are not able to produce insulin, they need insulin injection

• Type 2 diabetics can produce insulin, but cells do NOT respond to it, they need to control their sugar intake

• Hypoglycemia: glucose level lower than normal, need to increase sugar intake from diet

• Hyperglycemia: glucose level higher than normal, need insulin injection. Long-term hyperglycemia can lead to damages to other organs