homeostasis 2011

Pn. Anwarul Hidayah ZulkifliFB 1020

Founder of Homeostasis concept Claude Bernard (mid 1800’s): stability of

various physiological functions, i.e. body temperature, heart rate and blood pressure La fixite du milieu interieur (the constancy of

the internal environment) Walter Cannon (1929): created the word

“homeostasis” to describe the regulation of internal environment. Homeo: same/similar (internal environment is

maintained within a range of values rather than at exact fixed value.

Stasis: condition

Cannon’s proposed variables that are under homeostatic control Environmental factors that affect

cells --~osmolarity, temperature and pH

Materials for cell needs (nutrients, water, sodium, calcium,

inorganic ions, oxygen and internal secretions having general and continuous affects)

IF A BODY FAILS TO MAINTAIN HOMEOSTASIS OF THE VARIABLES, THEN NORMAL FUNCTION IS DISRUPTED AND A

DISEASE STATE/PATHOLOTICAL CONDITION RESULTED.

Homeostasis Steady state The process of keeping the internal body environment

in a steady state (maintaining constancy of the internal environment), when the external environment is changed.

Is a process of maintaining constant physical and chemical factors within an internal body environment.

Internal environment: the environment surrounding the cells (tissue fluids that fills the spaces between the cells).

Physical factors: temperature, blood pressure, osmotic pressure.

Chemical factors: pH value, concentration of sugar and salt

BASIC FEATURES OF HOMEOSTASIS

Questions asked relating to homeostasis Referring to “Adaptive Significance” Why does a certain function help an

animal survive in a particular situation? What structures and mechanisms evolved

in our anatomy and physiology that enable us to survive in hostile environment?

E.g. humans are large, mobile, terrestrial animals whose bodies maintain relatively constant water content living in dry, highly variable external environment.

Problems faced: Most body cells are not that tolerant of

changes in their surroundings Thus, they are similar to early organisms

that lived in tropical seas: salinity, oxygen content and pH vary a little; light and temperature cycle.

As organisms evolved and migrated from the ancient seas estuaries freshwater environments land (need to encounter highly variable external environments)

Rains dilute salty water + habituated organisms must cope with the influx of water into their body fluids.

Terrestrial organisms constantly lose internal water to the dry air around them need to keep internal environment relatively stable

BENEFITS OF HOMEOSTATIC CONTROL1. Life of the organism becomes less dependent on

the external environment.

2. Organism can live in a wider range of habitats, and the species can live in areas with variable conditions.

3. Organism can increase or decrease the metabolic rate of its body according to its requirements.

4. Enables more efficient and economical metabolic reactions because the total substrate used and the products formed, as well as the respective rates of reaction, are accurately coordinated.

PATHOLOGICAL CONDITIONS

Internal causes External causes Abnormal growth of cells

(cancer/benign tumor) Production of antibodies

by the body against its own tissues (autoimmune diseases)

Premature death of cells/failure of cell processes.

Inherited/genetic disorders

Toxic chemicals Physical trauma Foreign invaders such

as viruses and bacteria

Importance of ECF in homeostasis Watery internal environment of

multicellular animals extracellular fluid (ECF)

ECF serves as transition between an organism’s external environment and intracellular fluid inside cells.

ECF serves as a buffer zone between external part of the body and most cells of the body

When ECF composition varies outside its normal range of values, compensatory mechanisms activate and return the fluid to normal state

E.g. when a person drink a large volume of water, dilution of ECF triggers a mechanism that causes kidneys to remove excess water and protect cells from dilution.

Homeostasis Internal conditions vary, but always

within relatively narrow limits. Hormone-controlled homeostatic

mechanism, there is significant time-lag before corrective mechanism can be activated. It takes times for protein synthesis to

commence, the hormone to diffuse into the blood stream and for it to circulate around the body and take effect.

Law of mass balance

Amount of substance in the body is to remain constant, any gain = loss

Total amount (load) of substance x in the body = intake + production – excretion – metabolism

Maintain mass balance via: Excrete material (elimination of material

from the body via urine, feces, lungs, or skin)

Metabolize substance to different substance

Sensor

(receptor)

Effector

Control centre

Internal environme

ntExternal

environmental

Input feedback

Output

Figure: Homeostatic circuit

Detect changes

Execute changes

Defines changes and

triggers action

Negative Feedback Positive Feedback

maintain a constant value (set point).

Fluctuation from set level/set point in motion changes return to original value.

internal factors are controlled by antagonistic effectors

Have “push-pull” action-Increasing activity of one

effector is accompanied by decrease in the other

Involves: change in internal factor level detection by receptors activation of effectors restoring factors to its set point

a change in some variable causes a reaction which increases that change.

Steady state sets off a series of changes that intensify the changes

steady state causes changes that intensify (rather than reverse) the changes

Negative feedback

Fig. 38-5, p.381 (Solomon)

Positive feedback: Hemorrhage

Positive feedback: Contraction during childbirth

REGULATION OF BODY TEMPERATURE

PHYSICAL FACTORS

thermoregulation Antagonistic effectors involved Process of maintaining body temperature

within certain limits despite changes in surrounding temperature

Temperature change detected by hypothalamus in brain

Animals have different structural, behavioral, and physiological strategies

Animals that Maintain a fairly constant body temperature

(birds and mammals): Homeotherm Have a variable body temperature: Poikilotherm

Balancing Heat Loss and Gain Radiation: emission of electromagnetic waves by

all objects warmer than absolute zero.

Evaporation: removal of heat from the surface of a liquid that is losing some of its molecules as gas.

Convection: transfer of heat by movement of air or liquid past a surface

Conduction: direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other

Insulation reduces the flow of heat between an

animal and its environment sources of insulation include hair, feathers

and layers of fat formed by adipose tissue. •Raising fur or feathers in reaction to coldness. This action traps a thicker layer of air, thereby increasing the insulating power of the fur or feather layer.•To repel water that would reduce insulating capacity of feathers or fur•Secreting oily substances, such as the oils that birds apply to their feathers during preening/grooming.•Humans rely on fat for insulation.•Goose bumps (vestige of hair raising) formation in human in reaction to coldness or scared•Blubber (very thick layer of insulating fat) in marine mammals such as walruses and whales to maintain body core temperatures of about 36-38°C without requiring much more food energy.

Countercurrent Heat Exchange Flow of adjacent fluids in opposing directions

that maximizes transfer rates of heat or solutes. Heat transfer involves an antiparallel

arrangement of blood vessels. It occurs among many birds, mammals, certain

sharks, bony fishes, and insects. As warm blood passes through arteries, it

transfers heat to the colder blood returning from the extremities in the veins.

Due to countercurrent blood flow in arteries and veins, heat transfer occurs along the entire length of the exchanger.

In the flippers of a dolphin, each artery is surrounded by several veins in a countercurrent arrangement, allowing efficient heat exchange between arterialand venous blood.

Canada

goose

Artery Vein

35°C

Blood flow

Vein

Artery

30º

20º

10º

33°

27º

18º

9º

Pacific

bottlenose

dolphin

2

1

3

2

3

Arteries carrying warm blood down the legs of a goose or the flippers of a dolphin are in close contact with veins conveying cool blood in the opposite direction, back toward the trunk of the body. This arrangement facilitates heat transfer from arteries to veins (black arrows) along the entire length of the blood vessels.

1

Near the end of the leg or flipper, where arterial blood has been cooled to far below the animal’s core temperature, the artery can still transfer heat to the even colder blood of an adjacent vein. The venous blood continues to absorb heat as it passes warmer and warmer arterial blood traveling in the opposite direction.

2

Thermoregulation When body temperature rises,

Erector muscles relax hairs lie flat against the skin, no longer trapping air, allowing

more heat to be lost by radiation (radiation: heat transfer from body to air)

Dermal blood vessels dilate Sweat glands are stimulated into vigorous secretory activity. Evaporation of sweat from skin surface dissipates body heat Body cools down thus preventing overheating.

When the external environment is cold, Erector muscle attached to your hair follicles contract,

which made your hairs stand, trapping air. Dermal blood vessels constricted. This causes the warm

blood to bypass the skin temporarily and allows skin temperature to drop to that of the external environment.

Shivering: involuntary shuddering contractions of the skeletal muscles, effective in increasing body temperature, muscle activity produces large amounts of heat.

Enhance thyroxine (thyroid gland) and adrenaline (adrenal gland) release increases the metabolic rate.

THERMONEUTRAL ZONE

Range of external (environmental) temperatures in which a naked man can survive without losing or producing heat.

27-31°C 27°C: lowest/critical temperature Body temperature changes are

compensated for, mainly by adjustment in blood flow (e.g. vasoconstriction and vasodilation)

Heat can be acquired by: Basal metabolic processes produce approximately

100 kcal of heat per hour or 1 kcal/kg/h body temperature raised by 1.1°C/h if the heat dissipating mechanisms are nonfunctional.

Strenuous physical activity can increase heat production more than 10-fold to levels exceeding 1000 kcal/h.

Fever, shivering, tremors, convulsions, thyrotoxicosis, sepsis, sympathomimetic drugs, and many other conditions

heat dissipation, including conduction, convection, and radiation.

Vasodilation of cutaneous blood vessels Blood flow in the skin increases, facilitating heat

loss.

Vasoconstriction of cutaneous blood vessels Blood flow in the skin decreases, lowering heat

loss. Blood is restricted to deep body areas and largely

bypasses the skin. The skin is separated from deeper organs by a

layer of insulating subcutaneous (fatty) tissue, heat loss reduced.

Vasodilation and vasoconstriction

Restriction blood flow to the skin for a brief period is not a problem , but if prolonged exposure to very cold weather, skin cells deprived of oxygen and nutrients begin to die. This extremely serious condition is called frostbite.

In humans, the hypothalamus

(the ventral/ underside part of the vertebrate forebrain), Contains a group of nerve

cells that function as a thermostat

Thermostat inhypothalamusactivates coolingmechanisms.

Sweat glands secrete sweat that evaporates, cooling the body.

Blood vessels

in skin dilate:capillaries fillwith warm blood;heat radiates fromskin surface.

Body temperaturedecreases;thermostat

shuts off coolingmechanisms.

Increased body temperature (such as when exercising

or in hot surroundings)

Homeostasis:Internal body temperature

36–38CBody temperature

increases;thermostat

shuts off warmingmechanisms.

Decreased bodytemperature

(coldsurroundings)

Blood vessels in skin

constrict, diverting bloodfrom skin to deeper tissues and reducing heat lossfrom skin surface.

Skeletal muscles rapidlycontract, causing shivering,which generates heat.

Thermostat inhypothalamusactivateswarmingmechanisms.

Figure 40.21: The thermostat function of the hypothalamus in human thermoregulation

Pg 839 ,Campbell textbook

*

*

38

Homeostasis: body temperature regulation

CONSEQUENCES: FAILURE TO THERMAL ADJUSTMENT Heat stress : body can no longer cope

with excessively high temperature. Feel dizzy or suffer from heat collapse. Dehydration may result due to heat

exhaustion. Heat stroke and characterized by

breakdown of temperature regulation mechanism body core temperature 42°C or higher may result to irreversible damage to cells and proteins coma

Robert S Helman (2010). Heatstroke. eMedecine

Heat illness/heat stroke Minor heat related illnesses: heat edema, heat rash (ie,

prickly heat), heat cramps, and tetany, as well as heat syncope and heat exhaustion.

Heatstroke is the most severe form of the heat-related illnesses and is defined as a body temperature higher than 41.1°C (106°F) associated with neurologic dysfunction. Exertional heatstroke (EHS) : occurs in young

individuals who engage in strenuous physical activity for a prolonged period of time in a hot environment.

Classic nonexertional heatstroke (NEHS) more commonly affects sedentary elderly individuals, persons who are chronically ill, and very young persons.

Cases of heatstroke In the United States, Centers for Disease

Control and Prevention reported: 8,015 deaths were attributed to excessive heat

exposure (summer) from 1979-2003 average of approximately 334 deaths per year. 1700 deaths were attributed to heat (1980)

Heatstroke is uncommon in subtropical climates and commonly affects people who undertake a pilgrimage to Mecca, especially when the pilgrims arrive from a cold environment.

In India (1998): more than 2600 deaths in 10 weeks.

COLD STRESS

Cold stress: body can no longer cope with the effect of cold.

Cause severely reduced blood circulation which deprives the tissue s of nutrients and normal metabolic reactions fail.

Chilblains (perniosis) may develop due to exposure to cold and humidity.

Tissues may freeze (destructive effects of the formation of extracellular ice crystals) need to be gently warmed.

exposure damages capillary beds in the skin, which in turn can cause redness, itching, blisters, and inflammation.

Chilblain

Frostbite

temperature of the skin or extremities dips below freezing, the water and liquids inside and between cells begin to crystallize.

As the water freezes, the microscopic ice crystals rupture and kill cells, causing irreversible tissue damage.

ECTOTHERMS ENDOTHERMS

body temperature depends on temperature of environment

Use behavioral strategies to adjust body temperatures

Benefits of ectothermy very little energy used to

maintain the metabolic rate ectotherms can survive on

less food

Disadvantage of ectothermy activity limited by daily and

seasonal temperature

Include most invertebrates, fishes, amphibians, and reptiles

Have homeostatic mechanisms regulate body

temperature within a narrow range

37oC or 98.6oF Benefits of endothermy

high metabolic rate constant body

temperature allows higher rate of enzyme activity

active even in low winter temperatures

Disadvantage of endothermy high energy

Include birds and mammals

BLOOD GLUCOSE REGULATION

CHEMICAL FACTORS

Blood Glucose regulation

Figure 41.3

STIMULUS:Blood glucose

level risesafter eating.

Homeostasis:Blood glucose level

90 mg/100 mL

STIMULUS:Blood glucose

level dropsbelow set

point.

1 When blood glucose level rises, the pancreas secretes insulin, a hormone, into the blood.

Glucagon promotesthe breakdown of

glycogen in theliver and the

release of glucoseinto the blood,

increasing bloodglucose level.

4

When blood glucose level drops, the pancreas secretes the hormone glucagon into the blood.

3

Insulin enhances the uptake of glucose in body cells and stimulates the liver and muscle cells to store glucose as glycogen. As a result, blood glucose level drops.

2

Hyperglycemic

Hypoglycemic

-cells

-cells

Pancreas

Blood glucose concentration is controlled by the pancreas

Pancreas has Glucose receptor cells, which monitor

the concentration of glucose in the blood Endocrine cells (called the Islets of

Langerhans), which secrete hormones. -cells: secrete the hormone, glucagon -cells: secrete the hormone, insulin

Type I diabetes

Insulin-dependent diabetes or early onset diabetes

Due to an autoimmune disorder, killing off the -cells

Treatment: Insulin injection

Appears during childhood, disability to produce insulin

Type II diabetes

Non insulin-dependent diabetes or late-onset diabetes

Most type II diabetics produce insulin, but the amount is inadequate or

The insulin receptors are unable to respond to insulin, a phenomenon called “insulin resistance”

Cause: excess body weight, high sugar diet, lack of exercise

Treatment: Drug therapy, careful diet.

Mostly occurs after age of 40 years

Symptoms of diabetes: Excessive thirst

Due to osmosis of water from cells to the blood, which has a low water potential

Copious urine Huge urine output due to excess water in blood

Poor vision Due to osmotic loss of water from the eye lens

Tiredness Due to loss of glucose in urine and poor uptakes of

glucose by liver and muscle cells Ketosis

Abnormal condition of excess ketone bodies (fatty acid metabolites) production, break down of lipids to supply energy

Muscle wasting Due to gluconeogenesis caused by increase glucagon

BLOOD CHOLESTEROL

CHEMICAL FACTORS

REGULATION OF CHOLESTEROLCHOLESTEROL IN THE BODY CHOLESTEROL IN THE

BLOOD

Made by liver cells Important as

component of membranes: bile salts (fat digestion), steroid hormones synthesis (estrogen and testosterone), acetylcholine synthesis

Insoluble in water Carried by

lipoproteins (LDL)

Why regulate cholesterol? Cholesterol needed by all cells need to

be circulated in reasonable concentrations in the blood

High cholesterol concentrations deposited in the linings of the artery walls Narrows the artery and resulted to heart

attack or stroke Patients with an inherited inability to

regulate blood cholesterol would not survive beyond childhood without treatment.

Liver cells are able to regulate cholesterol concentrations in their own cytoplasm

Cholesterol inhibits one of the enzymes involved in its own synthesis (negative feedback).

Cholesterol regulation by the liver

CHOLESTEROL AT NORMAL LEVEL IN BLOOD

BLOOD PH

CHEMICAL FACTORS

Regulation of Blood pH

maintaining the acid/base balance of your blood

Rely on buffers, the lungs and the kidneys.

Buffers pH is a measurement of the concentration of

hydrogen H+ ions Buffers are molecules which take in or release

ions in order to maintain the H+ ion concentration at a certain level. 

Haemoglobin (Hb), certain proteins (Prot) and phosphates

Excessive H+ions in the blood , blood becomes acidic buffers remove the excess H + ions

Lack of H+ ions in the blood , blood becoming too basic, and so the buffers release H+ ions.

 H-Hb↔Hb- + H+

Prot-H↔Prot- + H+

H2PO4-↔HPO4

2- + H+

Lungs control of blood pH HCO3

- + H+↔ H2CO3↔ CO2 + H2O

Breathing quickly will allow more CO2 to pass from the bloodstream into the air lower the level of CO2 in the blood. 

If the CO2 is removed through breathing, it can't react and turn back into HCO3

- + H+. H+ is removed from the blood by reacting

with the buffer, but can't be remade because the CO2 required to do so has left the body. 

raise your blood pH by hyperventilatinglower your blood pH by hypoventilatingfall below normal pH caused by hypoventilation is known as a respiratory acidosisrise in pH due to hyperventilation is known as a respiratory alkalosis

Kidney control of blood pH

Hydrogencarbonate mechanism

• In the cells lining the PCT and DCT, carbon dioxide reacts with water to form carbonic acid, which then dissociates into hydrogencarbonate ions and hydrogen ions.

CO2 + water Carbonic acid, H2CO3 HCO3+ + H+

• The hydrogencarbonate ions are reabsorbed into the blood whose pH is increased consequently. This is accompanied by the pumping of unwanted hydrogen ions into the lumen of the tubule.

In the lumen, the hydrogen ions combine with hydrogenphosphate ions to form dihydrogenphosphate ions, which is excreted in the urine.

At the same time, sodium ions are reabsorbed in exchange for the hydrogen ions. In the bloodstream, sodium ions maintain electrical neutrality with the hydrogencarbonate ions.

Ammonium mechanism The epithelial cells of DCT contain an enzyme,

which catalyses the formation of ammonia from the amino acid glutamine. (Amino acid glutamine ammonia)

In the lumen of the DCT, excess hydrogen ions combine with ammonia to form ammonium ions, which are excreted in the urine. (H+ + NH3+ NH4+)

The blood and tissue fluid normally have a pH of about 7.4.

The kidneys can decrease the hydrogen ion concentration either by hydrogencarbonate mechanism or by ammonium mechanism.

BLOOD SALT

CHEMICAL FACTORS

Rozaini Othman, GC Biologi

Regulation of Menstrual Cycle High oestrogen levels in the blood

around the time of ovulation have two effects: Inhibit the further release of GnRF and

hence of FSH by negative feedback. Cause anterior pituitary to release

increasing amounts of luteinising hormone (LH) positive feedback.

POSITIVE FEEDBACK: LH

LH stimulates ovulation, in which the ovarian follicle ruptures to release the secondary oocyte into the ovarian (fallopian) funnel.

It also stimulates the remains of the follicle in the ovary to develop into the corpus luteum (yellow body) secrete the hormone progesterone as well as oestrogen.

Oestrogen and progesterone maintain and develop the uterine wall further.

Negative Feedback: If fertilisation does not occur, the increasing

levels of these hormones eventually inhibit the further release of LH by negative feedback.

Without the maintaining effect of LH, the corpus luteum degenerates

Concentrations of oestrogen and progesterone fall and their maintaining action on the uterine wall is lost.

Uterine wall breaks down, resulting in the menstrual flow of cells and blood out through the vagina.

ALTERATIONS IN HOMEOSTASIS

Regulated changes

set points and normal ranges for homeostasis can change under various circumstances

associated with a particular stage in life, such as radical shift in hormone balance that occurs during puberty.

cyclic, such as the variation in hormone levels responsible for women’s menstrual cycle.

Acclimatization animal adjusts to changes in its

external environment acclimatization, a temporary change

during animal’s lifetime adaptation, a process of change in a

population brought about by natural selection acting over many generations.

For example, when a mammal moves from sea level to a much higher elevation, changes that occur several days facilitate activity at lowered oxygen concentrations such as:•Increased blood flow in the lungs•Increased production of red blood cells that carry oxygen

Thank you for your

attention.

The end….

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