Mrs. Jackie

Homeostasis and excretion

Homeostasis includeMaintaining a constant interval

environment despite possible fluctuations in the external environmentInclude blood pHCarbon dioxide and glucose concentrationBlood glucoseBody temperatureWater balance

An example of homeostasis in a non biological system

Temperature rises

Desired temperat

ure of bath water

Temperature falls

Temperature falls

Temperature rises

Detected by thermostat

Heater switched on

Heater switched off

Detected by thermostat

Examples of homeostasisOxygen and carbon dioxide concentrations

Maintain in balance due to chemodetectorsBlood glucoseBody temperatureWater balanceBlood PH

Main within narrow limits around 7.4Contain buffers to minimize fluctuations in

pH

Homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms

Negative feedbackThe control of a process by the result or

effect of the process in such a way that an increase in the results or effects is always reversed.

RequiresSensors – require to pass the information to a center

which knows the desire value and compares the current situation to the norm. If the values are not the same the center activates a mechanisms to bring the current value to normal levels

The center will turn off the mechanisms once it reaches the norm

Nervous and endocrine systems are both involved in homeostasisThermoregulation is done via nervesBlood glucose levels are maintain via

hormones

Nervous system consists of the central nervous system and peripheral nerves composed of neurons

Central nervous system (CNS)BrainSpinal chord

Peripheral nervesEverything elseMade of neurons

Transport messages in the form of electrical impulses to specific sites

Control of body temperature Thermoregulation

Body of mammals/birds has thermo-receptors in the skin and in the heat center in the brain for monitoring temperature changes in the environment as well as changes in the blood temperature

IF the organisms is to hotVasodilatation- blood vessels in the skin become wider which

increases the flow of blood to the skin. Skin becomes warmer which increases heat loss to the environment.

Sweating- evaporation of fluid from the skin; change of phase(liquid to gas) , requires energy which is taken from the body.

Decreased metabolism- any reaction produces heat as a by product

Behavior adaptations: birds-bating, desert rodent- retreat into humid burrows, dogs- dig holes and allow cool earth to absorb heat from belly

Vasodilation

Vasoconstriction

Control of body temperatureIf the organism is too cold

Vasoconstriction- blood vessels in the skin contract which decreases the flow of blood to the skin; as a result the skin becomes colder reducing the heat loss to the environment.

Shivering- any reaction will produce heat as a by product. Muscular contraction produce a lot of heat

Increased metabolism: increase production of heatFluffing of hair or feathers: increases the thickness

of the insulating layer of air.Thick layer of brown fat or of blubber: this is a good

insulator and reduces radiation and convection and generates heat

Special structure hair: (polar bears) which absorbs UV light

Endocrine systemConsist of glands which

release hormones that are transported in the blood

Endocrine glands are ductless- they do not release their product into a duct but to the bloodAs the hormones passes

cells, only those with special receptors will react to the presence of the hormone- TARGET CELLS

Control of glucose concentration in bloodPancreas is both an exocrine

and endocrine glandExocrine cells in the pancreas

produce digestive enzymes which are released into the small intestine via the pancreatic duct.

Endocrine cells are clustered together in groups called the Islets of LangerhansProduce hormones which help

in regulating the blood glucose levels.

Control of blood glucoseIslet of Langerhans cells in the pancreas have

chemoreceptors which are sensitive to levels of glucose

Levels of glucose can go up after a meal and down after exercise

IF glucose levels are to low (see figure 1 page 138)The alpha cells in the islets in the pancreas secrete

glucagonGlucagon- protein hormone whose main target is the

liverHepatocytes- cells of the liver will respond to the

presence of glucagon by converting glycogen to glucose and releasing it to the blood. Amino acids and glycerol are also converted to glucose

Control of blood glucoseIf blood glucose levels are to high

Beta cells in the islets of langerhans in the pancreas secrete insulin

Insulin is a protein hormone travel to all parts of the body. Its presence will make the muscle cells absorbs more glucose

The muscle cells and hepatocytes converte glucose into glycogen

In adipose tissue glucose is converted into fat in the presence of the hormone insulin.

See diagram on figure 2 page 139

Excretion

ExcretionRemoval from an organism of the toxic

waste products of metabolism

Role of the kidneyMain functions

Maintenance of the water balance in the body and the removal of nitrogenous metabolic waste via excretion.

Two basic processUltrafiltration- some components of the blood flowing

through the kidney are pushed out of the blood vessels into kidney tubules. Only plasma and small particles can be filtered. Large proteins and cells stay in the blood

Reabsoption- substances useful for the body such as glucose and amino acids are reabsorbed and send back to the blood. The amount of water and salts reabsorbed is regulated to maintain homeostasis.

Unwanted substances become urine and is excreted