Chapter 9 - Homeostasis Of Body Temperature And Body Fluids Flashcards Preview

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Flashcards in Chapter 9 - Homeostasis Of Body Temperature And Body Fluids Deck (74):

What are the important aspects of the internal environment that the body needs to regulate?

• core body temperature
• pH and concentration of dissolved substances in the body fluids
• concentration of glucose in the blood
• concentration of oxygen and carbons dioxide in the blood and other body fluids
• blood pressure
• concentration of metabolic wastes


Define Homeostasis.

It is the process of keeping the environment inside he body fairly constant.


Outline the Feedback Loop.

1. Stimulus - a change in the environment.
2. Receptor - the stimulus is detected by sensory cells.
3. Message - sensory cells generate a message in the form of a nerve impulse or hormone.
4. Modulator - a control centre processes the message received from the receptor.
5. Message - a new message is sent out by the modulator.
6. Effector - muscles or glands receive the message from the modulator.
7. Response - the effector organs bring about an appropriate reaction.
8. Feedback - the response changes the original stimulus.


What is a feedback system/loop?

It is a situation in which the response to a stimulus modifies the stimulus.


What is a negative feedback?

It occurs when our body reacts/respond to a negative stimulus such as feeling cold or threatened; thus we respond by avoiding these situations which reduces or eliminates the original stimulus.


Define Dynamic Equilibrium.

Occurs when there is a fluctuation around a normal level. The point around which conditions fluctuate is called the set point. (Eg. 37 degrees)


What is an alternative name for negative feedback?

Steady state control systems.


What happens when a positive feedback occurs?

The response to a stimulus reinforces and intensifies the stimulus. The intensified stimulus results in an even greater response, and so on.


Give an example of positive feedback.

Positive feedback occurs during child brith, a process that must be completed as rapidly as possible to avoid stress and damage to the mother and baby.


Give an example of a situation where positive feedback may be harmful.

High fever. A small rise in body temperature can be beneficial in fighting infection; however, if body temperature rises above 42 degrees, a dangerous positive feedback loop can occur.


Define Thermoregulation.

Maintaining the balance between heat production and heat loss.


Why is the constancy of body Temperature a very important aspect of homeostasis?

This is because the chemical reactions occurring in cells are very heat-sensitive.


What happens when food is oxidized in cells? (Broken down food)

Energy is released; Most of which are released in the form of heat.


Define metabolic rate.

The rate at which energy is released by the breakdown of food.


Which factor affects the metabolic rate the greatest?

Exercise; muscular activity can increase metabolic rate by up to 40 times! So that very large quantities of heat are released.


Why do our metabolic rate increase during stress?

Because of the activities of the autonomic division of the nervous system.


How do our metabolic rate increase during stress?

Stimulation of sympathetic nerves release noradrenaline from the nerve endings; noradrenaline increases the metabolic activity if cells. Strong sympathetic stimulation may cause dramatic increases in the metabolic rate, but usually for only a few minutes.


How does the rising body temperature affect (increase) metabolic activity?

For each 1 degree Celsius rise in temperature, the rate of biochemical reactions increase by about 10%.


What is another word for Temperature receptors?



What is a peripheral thermoreceptor?

They are located in the skin and in some mucous membranes. They provide the hypothalamus with information about the external environment.


There are two types if peripheral thermoreceptors:

• Cold receptors are stimulated by the environmental temperatures lower than normal

• Heat receptors detect temperatures higher than normal.


What happens when the cold and heat receptors are stimulated?

When cold receptors are stimulated, the hypothalamus receives the information and initiates hear conservation and heat production mechanisms. If heat receptors are stimulated, mechanisms operate to reduce best production and increase heat loss.


Which is the body's main temperature-regulating centre?

The Hypothalamus.


How do blood vessels get rid of heat from the body?

•Blood vessels carry heat to the skin from the core of the body.

•Heat can then be lost from the skin by conduction, convection, radiation and evaporation.


What controls the diameter of blood vessels to the skin?

Autonomic nerves, which can act to increase or decrease flow if blood to the surface, thereby increasing or decreasing the rate of heat loss.


What happens when large amounts of body heat must be lost and snub blood vessels are already at maximum dilation?

Sweating must occur.


Explain the process of sweating.

•Sweating is the active secretion of fluid by the sweat glands and the periodic contraction of cells surrounding the ducts to pump the sweat to the skin surface.

•This production and transport of swear to the skin surface is stimulated by sympathetic nerves.


What is Sweat?

Swear is water containing dissolved substances, primarily sodium chloride, along with small amounts of urea, lactic acid and potassium ions.


What is the main purpose if sweating?

•Evaporation of sweat from the skin has a cooling effect; heat is removed from the skin when liquid sweat changes into Vapour.

•Cooling of the skin results in fooling of the blood flowing through the skin.


What is vasoconstriction?

• It is a physiological response which occurs in the skin.


Explain the process of Vasoconstriction.

•Impulses from the hypothalamus stimulate sympathetic nerves that cause blood vessels in the skin to constrict.

•The vasoconstriction decreases the flow of warm blood to the skin from the internal organs, this decreasing the transfer of heat from the internal body organs to the skin.


What is the result of vasoconstriction?

•The skin becomes cooler because there is less warm blood flowing through it.

•Less heat will then be lost from the body surface.

•In this way, vasoconstriction of skin blood vessels helps maintain body temperature in cold conditions.


Explain the stimulation of adrenal medulla by sympathetic nerves.

•This stimulation results in the medulla secreting saddens line and noradrenaline into the blood.

•These hormones bring about an increase in cellular metabolism that leads to an increase in heat production.

•This helps to maintain internal body temperature in conditions where there is rapid heat loss.


Explain the process of Shivering.

•A fall in body temperature will cause the hypothalamus to send stimuli to the parts of the brain that increase skeletal muscle tone.

•This increase in muscle tone leads to oscillating, rhythmic muscle tremors occurring at a rate of around 10 to 20 per second.

•These tremors are known as shivering and can increase body heat production several-fold within minutes.

•As no external work is done, all the energy liberated by the metabolic activity goes towards internal heat. Shivering is under the primary control of the hypothalamus, but conscious input from the cerebral cortex can suppress the urge to shiver.


How does the increase in the production of thyroxine occur?

•The hypothalamus is able to cause the anterior lobe of the pituitary to secrete thyroid stimulating hormone (TSH), which causes the thyroid gland to release thyroxine into the blood.

•The increased levels of thyroxine increase metabolic rate, resulting in an increase in body temperature.

•This response is slower to have an effect, but it is longer -lasting than other responses.

•The small change in metabolic rate that occurs between the warm summer months and cool winter ones is a result of this response.


Give an example of a behavioral response that may occur during the prevention of falling body temperature.

•If we feel cold we can behave in such a way that we reduce heat loss, such as by putting on an extra jumper or sheltering from a cold wind.

•Another behavioral response that helps to reduce heat loss is reducing the surface area of the body from which hear can be lost.

•You may notice that when you are cold in bed you tend to curl up into a ball.


Explain the process of Vasodilation.

•Vasodilation of skin blood vessels increases blood flow brought the skin.

•The skin becomes reddish in colour, surface temperature rises, and there is greater heat loss through radiation and convection.


Can sweating occur anywhere?

No; if both humidity and temperature are high, individuals often suffer considerable discomfort as the sweat remains on the skin or simply drips off. To


In the long term how can our body decrease our metabolic rate?

By reduction in the secretion if thyroxine, a response that occurs in summer when there is much less heat loss than in winter.


Give an example of a behavioral response in the prevention of body temperature rising.

Actions such as turning on a fan or air conditioner, removing external clothing and reducing physical activity can all help to keep temperature constant.


What is a heat stroke?

•When the temperature and relative humidity are high, it is difficult for the body to lose heat by radiation or evaporation.

•In this case body temperature rises and the regulatory mechanisms ceases.


How does Heat Exhaustion occur?

•This occurs as a result of extreme sweating and Vasolidation to lose heat.

•The loss of water in sweating reduces the volume of blood plasma and the Vasolidation reduces resistance to blood flow.

•Blood pressure is this reduced and output f blood from the heart decreases.

•The person may, therefore, collapse.


What is Hyperthermia?

If a person's cite temperature falls below 33 degrees Celsius, the metabolic is so low that heat production is unable to replace the heat lost and body temperature continues to fall.


Approximately how much water do our bodies contain?

~60%, but this proportion varies considerably between individuals and can be as low as 45% or as high as 75%.

Males ~ 65%
Females ~ 55%


State the components and proportion of the body fluid: Intracellular fluid.

• 2/3 of total body water
• Fluid inside the cell - the cytoplasm


State the components and proportion of the body fluid: Extracellular Fluid.

• 1/3 of total body water
• Fluid that is outside the cell.


State the components and proportion of the body fluid: Plasma.

• 1/4 of extracellular fluid
• The fluid part of the blood


State the components and proportion of the body fluid: intercellular fluid.

• 3/4 extracellular fluid
• Lymph, cerebrospinal fluid, synovial fluid in joints, fluids of eyes and ears, fluid in the chest and abdominal cavities and around the heart, fluids of the alimentary canal, kidney filtrate.


Are the different body fluids isolated from one another?

Nope, there is a continuous exchange of materials between them.


What separates the plasma from the intercellular fluid?

•Thin walls of the capillaries, and there is a relatively free exchange of materials between the two.

•However, dissolved materials that are large molecules, such as the proteins of the plasma, tend to remain within the blood vessels as they are too large to move through the capillary walls.


What so metabolic water?

It is water obtained as a by-product of chemical processes occurring within the cells.


Define excretion.

Excretion is the removal from the body of the waste products of metabolism.


How are our lungs involved in the excretion of carbon dioxide?

•CO2 is produced during cellular respiration and it is carried in the blood until it reaches the lungs where it is excreted.

•Some water is also lost from the lungs, in the form of water vapor, as we exhale.


How is the alimentary canal involved in the process of excretion.

•The alimentary canal passed out bike pigments that entered the small intestine with the bile.

•These pigments are the breakdown products of haemoglobin from RBC.

•They leave the body with the faeces. However, the bulk of the faeces is composed of undigested food materials.

•These are not considered to be excretory products as they have not been produced by the cells.


What part of our body is the main excretory organs?

Kidneys- they are responsible for maintaining the constant concentration of materials in the body fluids.

•One of the important wastes removed by the kidneys is urea, and this is produced in the liver during the breakdown of proteins.


Why are our kidneys so important?

•Only water loss from the kidneys can be regulated to achieve a constant concentration of dissolved substances in the body fluids.

•They play a major role in regulating the composition of body fluids.


Explain the location of the kidneys.

•The kidneys are a pair of reddish-brown organs located in the abdomen.

•They are on either side of the vertebral column, at about the level of the lowest ribs, and are attached to the rear wall of the abdominal cavity.

•Each kidney is about 11cm long, and due to the presence of the liver, the right kidney is usually slightly lower than the left.

•The kidneys are embedded in, and held in position by, a mass of fatty tissue.


Explain the structure of the kidneys.

•A tube, the ureter, leaves each kidney and drains into a muscular reservoir, the urinary bladder.

•This empties to the outside through a tube, the urethra.

•Each kidney contains about 1.2 million microscopic units called nephrons.


What is a nephron?

It is the functional unit of the kidney; that is, it is the nephrons that carry out the kidney's role in excretion and water regulation.


List the kidneys and associated organs.

•Renal vein- takes blood away from the kidney.

•Renal artery- takes blood to the kidney.

•Urethra - a tube from the bladder that opens to the outside.

•Ureter - a tube that drains urine away from the kidney.

•Bladder - a muscular bag that holds the urine until it is passed out of the body.


List the steps if the functional unit of the kidney is the nephron.

1. Blood enters the glomerulus under high pressure.

2. Filtration- the high blood pressure forces water and small dissolved molecules out of the blood and into the capsule. Large molecules and blood cels are retained in the blood.

3. The filtrate is collected by the glomerular capsule.

4. Reabsorption
•the filtrate passes through the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and the collections duct.
•water and other useful substances are reabsorbed into the peritubular capillaries.

6. Secretion - some materials that need to be removed from the body are secreted into the kidney tubule from the peritubular capillaries.

7. Urine - the water and dissolved substances that remain make up the urine. Urine is carried by collecting ducts to the ureter and then to the bladder.


What does the volume and compositions of urine produced by the kidneys depend on?

How much water there is in the body fluids.


What is the difference in your urine when you are well hydrated and when you are dehydrated?

•Hydrated - a large volume of dilute urine.

•Dehydrated - a small volume of concentrated urine.


How much water is reabsorbed in the kidneys.

•Approximately 99% of the water filtered through the glomeruli of the kidneys.


Explain the process of Reabsorption.

•This Reabsorption occurs through the walls of the kidney tubules along their entire length.

•However, the reabsorption occurring at the proximal convoluted tubule and loop of Henle is by osmosis, while Reabsorption at the distal convoluted tubule and collecting tubule is active Reabsorption.


What hormones control the active Reabsorption?

Antidiuretic hormone (ADH).

•The permeability of the walls of the distal convoluted tubule and collecting duct is controlled by ADH.


What happens when the concentration of ADH in the blood plasma is high, what happens to the tubules?

The tubules are very permeable to water, and thus water is able to leave the tubule and enter the surrounding capillary network.

-This outward flow of water from the fluid within the tubules reduces its volume and hence increases the concentration of the materials remaining.


What happens when the concentration of ADH in the blood plasma is low, what happens to the tubules?

The tubules are not very permeable to water, and little water is reabsorbed into the plasma of the blood.

-In this situation the fluid within the tubules remains fairly dilute, as its volume is not reduced to any significant extent.


Describe the feedback process of The Action of ADH in Controlling Water Balance.

1. If a decreased amount of water in the blood (eg. Sweat), the water concentration of the blood plasma would decrease. This means the osmotic pressure of the blood is raised.

2. Osmoreceptors in the hypothalamus detect the increased osmotic pressure of the blood.

3. The hypothalamus stimulates the posterior lobe of the pituitary gland to release ADH into the bloodstream.

4. ADH is carried all over the body by the blood but it affects its target organs, which are the nephron tubules and the collecting ducts is increased.

5. More water is then reabsorbed into the blood plasma from the tubules and ducts.

6. The reabsorption of water increases the water concentration in the plasma so that the osmotic pressure of the blood is decreased.

7. The response is decreased osmotic pressure of the blood. This has eliminated or reduced the original stimulus that was increasing osmotic pressure of the plasma. Negative feedback has occurred.


Why does water move from the intercellular fluid into the plasma by osmosis?

As water is lost from the blood, the plasma becomes more concentrated, has a lower water content and hence a higher osmotic pressure.

- Now the intercellular fluid is more concentrated and water diffuses out of the cells so that the cells start to shrink from dehydration.


Describe the events that takes place to bring about intake of water and restoration of the water balance.

1. As water is lost from the various body fluids, there is a reduction in plasma volume and an increase in osmotic concentration of the extracellular fluid.

2. Osmoreceptors in a thirst centre in the hypothalamus detect the rising osmotic concentration of the blood. Other stimuli such as a dry mouth are also involved.

3. Stimulation of the thirst centre makes the person feel thirsty.

4. The conscious feeling of thirst stimulates the person to drink.

5. The fluid consumed is absorbed into the plasma from the alimentary canal.

6. As the blood circulates through the body, it enables the intercellular fluid and intracellular fluid to return to the proper osmotic concentration.

7. After drinking, the thirst centre is no longer stimulated and the desire to take in water ceases. This is another negative feedback loop. In this case it is involved in the regulation of the water content in the body.


Explain the movement of water between the various parts of the body.

Alimentary Canal:
- Water in the fluids that we consume is absorbed into the blood from the alimentary canal.

Blood Stream:
- There is a constant exchange of water between the blood, the extracellular fluid and the intracellular fluid.

Lymph -> Blood Stream:
- Any excess fluid in the extracellular fluid is collected by the lymph system and returned to the blood by lymph vessels that join veins in the upper chest.


When does the symptoms of Dehydration become noticeable?

When a person has lost about 2% of the normal body water. (Sweating, Vomiting, Diarrhoea)


What is water intoxication?

Having too much water. This occurs when body fluid become diluted and cells take in extra water by osmosis.