web viewliterally means _____ - refers to the process of . keeping the internal body environment in...

Homeostasis

Literally means _____________________________ - refers to the process of

keeping the internal body environment in a steady state.

Very important - a great deal of the ____________________ system and autonomic

____________________ system is dedicated to homeostasis.

Negative FeedbackAll homeostatic mechanisms use _________________ __________________ to

maintain a constant value (called the _______ _________).

Negative feedback means that whenever a change occurs in a system, the change

automatically causes a ______________ ________________ to start, which

reverses the original change and brings the system back to normal.

The bigger the change the ______________ the corrective mechanism.

Applies to electronic circuits and central heating systems as well as to biological

systems.

So, in a system controlled by negative feedback the level is never maintained perfectly,

but constantly _________________ about the set point.

An efficient homeostatic system ____________________the size of the oscillations.

Regulation of Body TemperatureAnimals that maintain a fairly constant body temperature (

__________ and _______________) are called

__________________ (or endotherms)

Animals with variable body temperature (all others) are called __________________

(or ectotherms).

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Homeostasis

Homeotherms maintain their body temperatures at around

________i.e. warm-blooded, but poikilothermic animals can also have very warm blood

during the day by basking in the sun.

In humans temperature is controlled by the _______________________ centre in

the __________________________.

This receives input from two sets of _________________: receptors in the

hypothalamus itself monitor the temperature of the blood as it passes through the

_____________ (the core temperature), and receptors in the ___________ monitor

the external temperature.

Both pieces of information are needed so that the body can make appropriate adjustments. The thermoregulatory centre sends impulses to several different effectors to adjust body temperature:


Homeostasis

The thermoregulatory centre is part of the ________________ nervous system, so

the various responses are all ________________.

Some responses to low temperature actually generate heat (________________),

while others ________________ heat.

Some of the responses to heat ____________ cool the body down, while others just

reduce heat production or ________________ heat to the surface.

The body thus has a range of responses available, depending on the internal and

external temperatures.

What mechanisms are being used to control temperature here? Behavioural or physiological? What effectors are involved? Heating up or cooling down?

The thermoregulatory centre normally maintains a set point of 37.5 ± 0.5 °C in most


Homeostasis

mammals. However the set point can be altered is special circumstances:

Fever - chemicals called ____________ released by

_____________blood cells raise the set point of the

thermoregulatory centre causing the whole body temperature to

increase by ____________. This helps to kill ______________ and

explains why you shiver even though you are hot.

Hibernation - some mammals release _______________ that reduce their set point

to around 5°C while they hibernate. This drastically reduces their

_________________ __________ and so conserves their food reserves.

Torpor - bats and hummingbirds _____________

their set point every day while they are

_____________. They have a high surface

area:volume ratio, so this reduces heat loss.

Control of Blood Glucose LevelsGlucose is the transport carbohydrate in animals, and its concentration in the blood affects every cell in the body. Its concentration is therefore strictly controlled - range 80-100 mg 100cm-3

Very low levels (__________________) or very high levels (___________________)

are both serious and can lead to death.

Blood glucose concentration is controlled by the ________________.

The pancreas has __________ ____________ cells, which monitor the concentration

of glucose in the _____________, and it also has _____________ cells (called the

islets of Langerhans), which secrete __________________.


Homeostasis

The cells secrete the hormone ___________, while cells secrete ____________.

These hormones are _______________, and have opposite effects on blood glucose:

Insulin stimulates the _____________ of glucose by cells for ______________, and

in the _________ it stimulates the conversion of glucose to_______________

(glycogenesis). It therefore ______________ blood glucose.

Glucagon stimulates the _________________ of glycogen to glucose in the

__________ (glycogenolysis), and in extreme cases it can also stimulate the synthesis

of glucose from ____________. It therefore _____________ blood glucose.

Diabetes is a disease caused by a failure of glucose homeostasis.

Insulin-dependent diabetes (__________ _ or early onset diabetes) - is a severe insulin deficiency due to autoimmune killing of b cells (possibly due to a virus)

Non insulin-dependent diabetes (type 2 or _________-_________diabetes) - insulin is produced, but the insulin receptors in the target cells don’t work, so insulin has no effect.


Homeostasis

In both cases there is a very high blood glucose concentration after a meal, so the

____________ __________________ pumps in the proximal convoluted tubule of

the kidney can’t reabsorb it all from the kidney ____________, so much of the

glucose is excreted in ____________.

Symptoms of diabetes:

Symptom Cause

Diabetes can be treated by __________ with insulin or by careful ________.

It can be monitored using _________ or blood/urine __________.


Homeostasis

Water Regulation in the KidneyThe water potential of the blood must be regulated to prevent loss or gain of water from cells.

Controlled by the _____________ - contains ___________________ cells, which

can detect changes in the _____________ _____________ of the blood passing

through the brain.

In response, the hypothalamus controls the sensation of _________, and it also

secretes the hormone ADH (___________________ ________________).

ADH is stored in the _____________ gland, and its target cells are the endothelial

cells of the ___________ ducts of the kidney ____________.

These cells are unusual in that water molecules can only cross their membranes via

water channels called _____________, rather than through the lipid bilayer. ADH

causes these water channels to open.


Homeostasis

The _________________ limb of the loop of Henle is ____________ to water.

The ascending limb is __________________.

Na+ and Cl- ions are _____________ transported out of the ascending limb and

______________ move into the descending limb.

This creates a _______________ gradient across the medulla.

There is a _________ ion concentration gradient at the top of the ascending limb and

a much ___________ ion concentration gradient at the bottom.

The water potential of the tissue fluid in the medulla is always _______ negative than

that of the filtrate in the ________________ duct.

Whether the water actually leaves the collecting duct (by ____________ ) is

determined by the hormone ADH (anti-diuretic hormone)

_______________ in the hypothalamus detect the low levels of water, so the

___________________ sends an impulse to the pituitary gland which releases ADH

into the bloodstream. ADH makes the wall of the collecting duct _________

permeable to water. Therefore, when ADH is present more water is ______________

and less is excreted.


Homeostasis

Excretory Organ What is excreted

Excretion and Homeostasis

This section is mainly concerned with the excretion of ___________________ waste

as __________. The body cannot store protein in the way it can store carbohydrate

and fat, so it cannot keep excess amino acids. The “__________ ___________” of

the amino acids can be used in respiration, but the nitrogenous amino group must be

_______________.

Amino acid metabolism takes place in the _________ and consists of three stages:

Transamination - in this reaction an amino group is transferred from an amino acid to a

keto acid, to form a different amino acid.


Homeostasis

A A 1 + Keto acid 2 ↔ Keto acid 1 + A A 2

In this way __________ amino acids can be made from _______________ones.

In adult humans only 11 of the 20 amino acids can be made by transamination. The

others are called _______________ amino acids, and they must be supplied in the

diet.

Deamination - in this reaction an __________ __________ is removed from an amino

acid to form ____________ and a keto acid.

The most common example is glutamate deamination: This reaction is

catalysed by the enzyme glutamate dehydrogenase.

Most other amino acids

are first

transaminated to form glutamate, which is then

deaminated.

The NADH produced is used in the respiratory chain; the a-ketoglutarate enters the

Krebs cycle; and the ammonia is converted to urea in the urea cycle.

Urea synthesis - in this reaction ________________ is converted to urea, ready for

excretion by the ______________. Ammonia is highly ___________, due to the

reversal of the _________________ _____________________ reaction that would

use up all the a-ketoglutarate and so stop the Krebs cycle.

Urea is less toxic than ammonia, so it is safer to have in the bloodstream.


Homeostasis

The disadvantage is that it “costs” 3 ATP molecules to make one urea molecule.

This is not in fact a single reaction, but is a summary of another cyclic pathway, called

the urea cycle (or orthnthine cycle). It was the first cyclic pathway discovered.


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