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Higher Biology

Homeostasis in humans- part 1

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Human Homeostasis

By the end of this lesson you should be able to:

Know the principle of negative feedback Know how the water concentration of the blood is

maintained. Explain the role of ADH in osmoregulation Know how the blood sugar concentration is maintained. Explain the role of insulin, glucagon and adrenaline in

controlling blood sugar levels.

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Physiological Homeostasis

Physiological homeostasis- body’s ability to maintain relatively stable internal conditions even though the outside world changes continuously.dynamic vs. steady state is

constant (example- water bath temperature control)

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Physiological Homeostasis

What do we mean by internal environment?

The millions of cells that make up our body and the tissue fluid that bathes them is the internal environment.

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Physiological Homeostasis

We will look at how the body regulates:

1. Water concentration of the blood2. Blood glucose levels3. Internal body temperature.

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Physiological Homeostasis

Why do we need to regulate1. Water concentration of the blood?

Otherwise many physiological and biochemical functions would be impaired.

e.g. nervous co-ordination and membrane permeability.

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Physiological Homeostasis

Why do we need to regulate:2. Blood glucose levels?

To provide the energy needed by cells to perform energy demanding jobs.

e.g. synthesis of protein, active transport, muscle contraction.

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Physiological Homeostasis

Why do we need to regulate:3. Internal body temperature?

To provide the optimum conditions for enzyme-catalysed reactions to be carried out.

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Water Bath

Temperature set on thermostatToo cool? Heater kicks on and temperature goes upToo warm? Heater stays off until bath cools down

Constant checking and turning on and off

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Control of homeostasis through feedback

Feedback system- cycle of events in which the status of a body condition is continually monitored, evaluated, changed, re-monitored, re-evaluated, etc.

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1) receptor sensor that responds to changes

(stimuli) 2) control centre

sets range of values, evaluates input and sends output

3) effector receives output from control centre and

produces a response

3 basic components of a feedback system

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Osmoregulation

This is where the body maintains its concentration of water, salts and ions at the correct level.

The receptors are in the hypothalamus- called osmoreceptors.

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Osmoregulation

The control centre is the pituitary gland.

It responds by producing ADH (Anti-Diuretic Hormone).

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Osmoregulation

ADH travels in the blood to the kidney.

The effector is the tubules in the kidney.

They responds by changing their permeability to water.

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Osmoregulation-increase in water concentration of the blood.

The water concentration of the blood can increase due to: Drinking lots of dilute liquids.

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Osmoregulation-increase in water concentration of the blood.

1. Detected by osmoreceptors in the hypothalamus.

2. Causes pituitary gland to release less ADH.3. ADH travels in blood.4. Kidney tubules become less permeable to

water.5. Less water reabsorbed by osmosis into the

blood.6. Large volume of dilute urine produced.7. Water concentration of the blood falls back

to normal.

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Osmoregulation-decrease in water concentration of the blood.

The water concentration of the blood can decrease due to: Sweating. Eating salty food Lack of drinking water

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Osmoregulation-decrease in water concentration of the blood.

1. Detected by osmoreceptors in the hypothalamus.

2. Causes pituitary gland to release more ADH.3. ADH travels in blood.4. Kidney tubules become more permeable to

water.5. More water reabsorbed by osmosis into the

blood.6. Small volume of concentrated urine

produced.7. Water concentration of the blood rises back

to normal.

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Osmoregulation

1. Insert and complete the “Control of Blood Water Concentration” diagram

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Control of Blood sugar

All cells need a continuous supply of energy- glucose is therefore constantly being used up by cells.

Glucose is only supplied to the body during eating.

Stored glucose can be broken down as required to meet the cells demands.

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Stored glucose

Glucose is stored as glycogen in the liver.

Two hormones are involved:

INSULIN Activates the enzyme

for this reaction:

Glucose glycogen

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Stored glucose

Two hormones are involved:

GLUCAGON Activates the enzyme for this

reaction:

Glycogen glucose

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Control of Blood Glucose Levels

The receptors are in the Islets of Langerhans in the pancreas.

They produce insulin or glucagon

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Control of Blood Glucose Levels

The target organ for these hormones is the liver.

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Increase in glucose concentration of the blood.

The blood glucose levels (BGL) can increase due to: Eating a meal

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Increase in BGL

1. Detected by receptors in the Islets of Langerhans.

2. These receptors cells produce insulin.3. Insulin travels in the blood to the liver4. At the liver an enzyme stores excess

glucose as glycogen.5. BGL falls back to normal.

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Decrease in glucose concentration of the blood.

The blood glucose levels (BGL) can decrease due to: Between meals During the night

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Decrease in BGL

1. Detected by receptors in the Islets of Langerhans.

2. These receptors cells produce glucagon.3. Glucagon travels in the blood to the liver4. At the liver an enzyme stores breaks down

glycogen to glucose.5. BGL increases back to normal.

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What about Adrenaline?

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Practice Questions

Torrance1. TYK page 277 Q1-4

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Human Homeostasis

Can you do it?

Know how the water concentration of the blood ismaintained.

Explain the role of ADH in osmoregulation Know how the blood sugar concentration is maintained. Explain the role of insulin, glucagon and adrenaline in

controlling blood sugar levels.